Cable terminal with heat-indicating properties

Abstract

The technical solution relates to cable terminals, and more particularly to cable terminals designed to be capable of irreversibly indicating heating above a temperature threshold. A cable terminal capable of indicating heating above a temperature threshold comprises a metallic electrically conductive portion that is fastenable to a conductor(s) (non-insulated end) of a cable by crimping, and a dielectric portion that is connected to said electrically conductive portion. The dielectric portion comprises a base that is securable to a cable and has a dielectric strength of not less than 3 kV / mm and a thermal conductivity of not less than 0.1 W / (m⋅K), wherein the front surface of said base has a heat-sensitive material applied thereto which undergoes an irreversible change in transparency when heated above a threshold temperature, and the minimum distance from the heat-sensitive material to the metallic electrically conductive portion is not greater than 10 mm. The technical solution provides increased fire safety and electrical safety during the use of electrical equipment by providing a reliable contact connection that is capable of irreversibly indicating heating above a temperature threshold to allow timely identification of defects in the contact connection.

Description

[0001] Cable lug with temperature indicator properties Field of technology

[0002] The technical solution relates to cable lugs, namely to cable lugs designed with the ability to irreversibly register the fact of heating above the threshold temperature.

[0003] State of the art

[0004] Thermal monitoring of the condition of contacts and contact connections of electrical installations is an important task during the operation of electrical equipment. Timely detection of contact defects allows preventing emergency situations that can lead to equipment damage, fires and conflagrations. Excessive heating of contacts and contact connections in most cases is associated with an increase in transient contact resistance, which can occur during operation under the influence of various factors:

[0005] • reduction of the contact area of ​​conductors;

[0006] • oxidation of contact surfaces or formation of carbon deposits on them;

[0007] • galvanic incompatibility of metals of the connected conductors;

[0008] • insufficient applied compression force during installation of the connection;

[0009] • reduction of pressure during operation;

[0010] • destruction of the surface of conductors due to aggressive chemical or electrochemical action;

[0011] • mechanical impact followed by loosening of the contact connection and / or partial removal of the wire from the terminal under the influence of the applied force.

[0012] The methods of control and testing of contacts and contact connections of electrical equipment and electrical devices are regulated by normative documents, in particular, GOST 17441-84 "Electrical contact connections. Acceptance rules and testing methods" and GOST 10434-82 "Electrical contact connections. Classification, general technical requirements", which disclose, among other things, the methods of testing detachable contact connections equipped with cable connectors for heating with rated (long-term permissible) current, as well as accelerated testing in cyclic heating mode.There are two approaches to ensuring the general safety of contact connections of electrical equipment: regular thermal diagnostics of contacts and contact connections using a thermal imager or irreversible thermal indicators for the timely detection and elimination of defects; the use of special devices that improve the reliability of the contact connection, such as terminal blocks, special connectors, conductive lubricants or cable lugs.

[0013] A cable lug (or “terminal”, “connector”) is a specially designed product for installation on the end of a wire, including a hollow conductive cylinder of a fixed or variable diameter, on which an insulating element made in the form of a dielectric tube can be fixed.

[0014] The use of cable connectors allows to increase the reliability of the contact connection in use by preventing the growth of the transition contact connection by reducing the external impact on the surface of metals (oxidation, chemical and electrochemical effects, etc.), tight crimping of the wire, increasing the area of ​​the contacting surfaces of the conductors, as well as a number of other reasons.

[0015] However, the use of cable connectors does not completely eliminate the possibility of contact and contact connection defects during operation. Defects and associated fire hazard heating may be caused by violations of the rules for selecting cable tips (for example, the tip size does not match the wire cross-section or conductor material) or violations of installation rules, for example, insufficient wire crimping.

[0016] To detect such defects in a timely manner, it is advisable to carry out regular thermal monitoring of contacts.

[0017] Existing diagnostic methods developed to detect defects in contact connections are based on identifying the facts of exceeding the established maximum permissible temperatures of contact connections. However, in the case of using cable lugs, such methods are not sufficiently effective. One of the methods of thermal control is thermal imaging control. However, using a thermal imager to assess the condition of contact connections made using cable lugs has a number of significant difficulties.

[0018] Firstly, when making contact connections using cable tips, the contact point of the conductors is not accessible for inspection, and the insulating element of the tip, as a rule, does not tightly enough compress the wire and significantly distorts the real heating temperature. Due to this, it is not possible to determine the exact heating temperature using a thermal imager.

[0019] Secondly, cable tips are used only in electrical networks with voltage up to 1000 V, in which the use of a thermal imager as a thermal instrument is ineffective, since temperature measurement is carried out only at the time of inspection. At the same time, maximum heating temperatures of contact connections are achieved at maximum load currents.

[0020] In addition, the use of a thermal imager involves inspection of equipment under voltage and is associated with increased danger to personnel.

[0021] A more effective method of thermal control of contact connections is thermal indicator control. The method is based on the use of irreversible thermal indicators, which are independent compositions (varnishes and paints) or devices that are fixed on the controlled elements and register the facts of exceeding the threshold temperature by changing color. However, when diagnosing contact connections made using cable tips, this method also has a number of features, the main one of which is the need to place the heat-sensitive composition (i.e., the material that changes color) in the maximum proximity to the potential heating point (i.e., the contact point).

[0022] For thermal monitoring of the state of contact connections, thermal indicator stickers are most widely used.

[0023] However, in the case of using cable lugs, the use of thermal indicator stickers is not effective. When a contact connection defect occurs, heating occurs at the point of contact. As it moves away from the point of heating, the temperature of the wire decreases significantly due to heat dissipation. Therefore, placing a thermal indicator on the wire outside the cable lug will be aimed at recording the heating of the wire, not the point of contact, and will not provide reliable information about the heating temperature at the point of contact.

[0024] When installing thermal indicator stickers directly on the insulating part of the cable lug, a significant discrepancy between the temperature registered by the thermal indicator and the actual heating temperature of the contact area is also possible. This is due not only to the significant temperature measurement as it moves away from the contact point, but also to the presence of a large number of thermal insulation layers (wire insulation, material of the insulating part of the cable lug, adhesive layer, thermal indicator base, etc.). In addition, installing a thermal indicator on an already mounted cable lug may lead to deterioration of the contact connection due to the applied mechanical impact.

[0025] In some cases, placing thermal indicator stickers on contact connections is generally not possible due to insufficient contact connection area, small distance between electrical equipment elements, etc.

[0026] The use of other types of temperature indicators also has a number of obvious limitations.

[0027] The heat-sensitive composition used in temperature-indicating products can be of two types: reversible (changing its appearance only when heated and returning it upon cooling) and irreversible (changing its appearance after exceeding a given temperature and maintaining it after cooling).

[0028] The peculiarity of reversible temperature indicators is that they allow informing only about the current overheating, i.e. whether the temperature exceeds the threshold values ​​at the current moment of time, and not about the maximum temperature to which the controlled element of electrical equipment was heated at the moment of maximum load during the entire service life. Unlike reversible indicators, irreversible indicators allow not only to detect, but also to record the fact of exceeding the threshold temperature during the entire service life.

[0029] The importance of using irreversible temperature indicators, especially in energy, is revealed, in particular, in the work of M.Yu. Lvov, A.V. Lesiv, “Thermal indicator control of contacts and contact connections of electrical equipment and power transmission lines”, Moscow, NTF “Energoprogress”, Energetik”, 2023. In the article by M.Yu. Lvov, D.Sc. (Eng.), S.D. Nikitin - JSC “OEK”, Yu.N. Lvov, D.Sc. (Eng.) - “NTC Rosseti FGC UES”, A.V. Lesiv - OOO “TermoElektrika”, “On standardization of requirements for thermal indicator control of the state of contacts and contact connections during operation of electrical installations”, “ENERGY OF THE SINGLE GRID” No. 1 (68) 2023, which provides typical requirements for thermal indicators, principles of their selection and methodology for assessing the state of contacts and contact connections using thermal indicators, developed on the basis of the conducted research and accumulated operating experience.The first and main requirement for thermal indicators is the irreversibility of the thermal indicator: “For the purposes of assessing the condition of contacts and contact connections (controlling the fact of reaching the set temperature during operation of electrical installations), only irreversible melting thermal indicators are used.”

[0030] Irreversible heating indicators can be classified by the operating principle of the heat-sensitive material. There are indicators based on the mechanical destruction of the heat-sensitive element, on the chemical reaction of the components of the thermal composition, or on the phase transition of the heat-sensitive component. The use of thermal indicator compositions based on the mechanical destruction of the heat-sensitive element is limited due to their features associated with a long response time, as well as the impossibility of creating a flexible thermal indicator device that fits tightly to the controlled surface.Physicochemical aspects of the reaction of the components of the thermal composition introduce a number of limitations in the use of thermal indicators based on a chemical reaction, since such thermal indicators do not have sufficient accuracy, have a pronounced dependence of the response time on temperature and the possibility of returning the original color of the triggered indicator after a long exposure at a low temperature due to the reversibility of the color transition reactions.

[0031] A separate disadvantage of indicators based on mechanical or chemical principles is that when the layer of the temperature-sensitive element is deformed, the indicator may be triggered prematurely, and their original implementation in the form of devices with a shape other than flat is not always possible.

[0032] The most accurate are irreversible temperature indicators based on phase transition, namely, on melting of the heat-sensitive component. Since, unlike a chemical reaction, the phase transition temperature does not depend on the time of exposure, such indicators have the highest accuracy and are capable of maintaining the initial state for a long time at a temperature slightly lower than the threshold.

[0033] Some of the known state-of-the-art versions of thermal indicators based on the phase transition of a thermal composition are thermal indicator paints or varnishes that can be applied to a surface of any shape and size without strong mechanical impact on the controlled element. However, they have a number of features that significantly limit their use, including making them ineffective when used for temperature control of contact connections equipped with cable tips:

[0034] - it is impossible to indicate the temperature on the paint. During a visual inspection of the equipment, the operator can only see the fact that the temperature has been exceeded, but cannot determine the numerical value of the exceeded threshold. For this, special notes must be made;

[0035] - flow of indicator paint when the threshold temperature is exceeded. When exposed to elevated temperatures and the heat-sensitive component melts, the paint may flow from the surface and fall on open elements of the electrical installation or moving elements of the mechanisms, which may lead to a short circuit or the creation of an insulating environment between the contacts;

[0036] - the impossibility of applying a uniform and homogeneous layer to surfaces of complex shape. The consequence of this is the impossibility of determining the exact temperature of the controlled element, since the thicker the layer, the higher the difference between the surface temperature and the phase transition (action);

[0037] - low adhesion of varnishes and paints to the surface of controlled elements, difficulty in applying paint to non-adhesive materials (silicone, polyethylene, fluoroplastic). This leads to the composition easily separating from the controlled surface under mechanical influences;

[0038] - dependence of the paint response temperature on the chemical composition of the surface to which it is applied. Since the paint comes into direct contact with the material to which it is applied, various substances, primarily fire retardants and plasticizers, can be extracted into the temperature indicator paint. Such substances can lead to the formation of eutectic mixtures with a hot-melting component or otherwise affect the response temperature.

[0039] Thus, to improve the safety of electrical equipment operation, it is necessary to ensure reliability and the most prompt and reliable detection of defects accompanied by overheating. The solution to this problem can be achieved by using a cable tip that has the properties of a thermal indicator.

[0040] An example of an article combining the function of a cable lug and temperature-indicating properties is the device known from JP2009198201 A, publication date 03.09.2009, which is a heat-sensitive part attached to a housing that ensures close contact with an insulating cap attached to an electrical terminal fitting, and it is disclosed that the device discolors when heated. The housing of the described device can be made in the form of a cylinder with a longitudinal slit or gap, a spring, have fastening elements, a tightening part or other devices that ensure a tight fit to electrical wires. The heat-sensitive part includes a heat-sensitive color-changing body and a transparent part for detecting color. In this case, the heat-sensitive part can have an adhesive layer attached to it, be supplied separately from the housing and be mounted on it by gluing or other methods.The use of a device consisting of two parts, each of which can be used independently, reduces the rate of overheating registration due to the presence of an additional layer of the base of the heat-sensitive part, separating the thermochromic material, which reacts to temperature changes, from the controlled element. In addition, the thermochromic material according to the invention described is reversible, which makes it inapplicable in power engineering, for the reasons described above.

[0041] Another similar device, known from KR102022029B 1, publication date 17.07.2019 and chosen by us as a prototype, is an insulating cap of a crimping tip for wiring, part of which is made of polyvinyl chloride and formed by the inclusion of a thermal coloring pigment, allowing to determine a sharp change in temperature between the wire and the crimping clamp, and the other part is made in the form of a solderless terminal, improving the adhesion force of the tip body and the controlled elements of the electrical wiring, and the parts of the device can overlap each other to improve the adhesion force between them.In this device, a thermal coloring pigment is included in the material from which the first part of the device is made, as a result of which, when heated, this part of the device changes color and retains it upon subsequent cooling to normal operating temperature, and the operator monitoring the electrical wiring elements can determine the fact that these elements are heated above the maximum permissible temperature.

[0042] The document does not disclose the substances used as thermal coloring pigments, as well as the linear dimensions, thickness of the device and its individual parts. The document does not disclose the range of temperatures recorded, as well as the accuracy of their recording and the speed of the device's response. However, due to the uniform distribution of the thermal coloring pigment in the material of a part of the device, when overheating of the controlled elements occurs, in order to change the color, it is necessary to heat up the entire volume of this part of the device, which will not allow recording short-term overheating of the controlled elements, will reduce the accuracy of overheating registration and may lead to false failures of the product.

[0043] Also, the use of a thermal coloring pigment, initially distributed throughout the volume of the polymer material, significantly reduces the processing capabilities of this material, in particular, it limits the use of methods such as casting, baking and other methods associated with an increase in temperature, since this will lead to premature melting of the pigment.

[0044] Based on the level of technology that we have studied in detail, it follows that, despite the large selection of cable terminals and temperature indicators, which differ both in their mechanism of action and in their design, there is a need for a cable terminal designed with the ability to irreversibly record the fact of heating of the contact connection above the threshold temperature, which will meet the requirements for temperature indicators used in the power industry:

[0045] - high accuracy, reliability and response speed;

[0046] - irreversibility of operation;

[0047] - low flammability and ignitability;

[0048] - high electrical strength and dielectric properties of the base part;

[0049] - simplicity and safety of installation, replacement, dismantling of the thermal indicator and operation of the electrical equipment itself.

[0050] Moreover, a device with such characteristics can be used in any other field of technology.

[0051] Thus, the technical solution is aimed at creating a cable lug designed with the ability to irreversibly record the fact of heating of the contact connection above the threshold temperature with the accuracy, speed and reliability required in this field of technology, allowing for the timely detection of defects in contact connections.

[0052] Terms and definitions

[0053] "Wire" is a cable product containing one or more twisted wires or one or more insulated cores, over which, depending on the installation and operating conditions, there may be a light non-metallic sheath, winding and (or) braiding made of fibrous materials or wire, and not intended, as a rule, for laying in the ground [GOST 15845-80. Cable products. Terms and definitions]. As applied to this technical solution, the concept of "wire" also includes non-insulated metal current-carrying wires (cores), one or more insulated cores twisted together, enclosed in a common sheath (cables).

[0054] In accordance with GOST 14312-79 “Electrical contacts. Terms and definitions”, a “contact connection” is understood to be a contact of an electrical circuit intended only for conducting electric current and not intended for switching an electrical circuit during a given operation of the device; a “contact” is understood to be a part of an electrical circuit intended for switching and conducting electric current.

[0055] “Contact transition resistance (contact connection)” according to GOST 14312-79 means the electrical resistance of the contact zone, determined by the effective contact area and equal to the ratio of the voltage drop across the contact transition to the current through this transition.

[0056] “Compression (crimping, pressing, pressing, crimping) method” is a method of connecting a wire or cable to a ferrule, usually accomplished by means of a hydraulic or manual press (e.g., crimping pliers), in which the bare conductor is inserted into the metal conductive portion of the ferrule, which is then compressed around it to form a permanent connection.

[0057] The term "thermosensitive material" is understood to mean a material that becomes more transparent to at least part of the visible light relative to the initial state when heated above a threshold temperature, and does not return to the initial state after subsequent cooling. The thermosensitive material may consist, for example, of an individual organic compound or a salt of an organic acid that undergoes a phase transition upon reaching a threshold temperature, or of a mixture of substances. In addition, the thermosensitive material may additionally include a binder, represented, for example, by organic resins, for better adhesion of the thermosensitive material to a flexible base, and other additives.

[0058] The term “threshold temperature” or “threshold temperature value” means the numerical value of the temperature at which an irreversible change in the properties of the heat-sensitive material occurs. In the claimed technical solution, the accuracy of recording the excess of the threshold temperature is 5 °C. The term “accuracy of recording the excess of the threshold temperature” means the following:

[0059] 1. Until the device reaches a temperature equal to the threshold temperature of the corresponding heat-sensitive material minus the declared accuracy value, there is no change in the transparency of the corresponding heat-sensitive material or in the appearance of the device.

[0060] 2. At a temperature equal to or greater than the threshold temperature of the corresponding temperature-sensitive material plus the declared accuracy value, the corresponding temperature-sensitive material is transparent and the device takes on an appearance different from the original.

[0061] 3. The exact value of the phase transition temperature of the temperature-sensitive component is within the declared range and is not further established. The accuracy of recording the excess of the threshold temperature determined in this technical solution is 5 °C.

[0062] “Phase transition” is the transition of a substance from one thermodynamic phase to another when external conditions change.

[0063] In this technical solution, the term “triggering” is applied to a heat-sensitive material that has undergone a phase transition with an increase in transparency. A device in which the heat-sensitive material has changed transparency is designated as “triggered”.

[0064] “Defect” is a non-compliance of an object with the requirements established by the documentation for at least one indicator.

[0065] A “cable lug” (or “terminal”) is a specially designed product that includes a hollow metal cylinder of fixed or variable diameter, on which an insulating element in the form of a polymer tube is fixed. The cable lug is designed to be installed on the end of a wire to ensure a reliable and safe contact connection.

[0066] “Fire resistance” refers to the ability of a material to resist combustion when exposed to an ignition source.

[0067] The term “electric strength” or “dielectric strength” defines the ability of a given material or device to withstand an electrical voltage applied to it. In other words, electrical strength is the minimum electric field strength at which the breakdown of the device occurs.

[0068] The term “dielectric” means the property of a given device to withstand an electrical voltage applied to it, while the minimum electric field strength at which the device breaks down exceeds the electrical strength of air.

[0069] The term “elasticity” describes the ability of a solid material to return to its original shape during elastic deformation, i.e. an elastic material is deformed after an external force is applied to it, but regains its original shape and size after the effect of this force ceases.

[0070] The term “elasticity” reveals the ability of a material, when bent around a cylindrical surface, to repeat its shape without losing its functional properties.

[0071] The terms “elastic base” and “elastic protective film” characterize the base material or protective film, which refers to materials that have the ability to change their shape without breaking under external influence.

[0072] "Microstructure" is the spatial arrangement of particles or individual phases of a material, reflecting the shapes and orientation of the particles that make up the material. Unlike the chemical structure or nanoparticles, the microstructure determines only the physical, optical and mechanical properties of the material, but does not affect the chemical properties of the substances that make up the microstructure. In the context of this technical solution, "irreversible change in microstructure" means an irreversible change in the physical, optical or mechanical properties of the material relative to its initial state, accompanied by a change in its microstructure, i.e. the spatial arrangement of particles or individual phases of the material, their size or shape, up to the complete fusion of the particles and the formation of a single phase.

[0073] The term “solid phase” describes a material structure containing solid particles of arbitrary shape, each of which has at least one point, face or edge in contact with an adjacent particle and connected to each other in such a way that each element of the solid phase can be connected to another element by a single broken line, each point of which is located within this phase. Depending on the shape and size of the solid particles, the continuous solid phase can have a cellular, granular, fibrous, crystalline or flaky structure.

[0074] "Composite material" is a multicomponent material made from two or more components with significantly different physical and / or chemical properties, the combination of which results in new characteristics that differ from the characteristics of the individual components. As applied to the present technical solution, the term "composite materials" includes polymer composite materials, at least one component of which is a polymer material, as well as ceramic-based composite materials. The composition and structure of the composite materials used in the present technical solution may vary, and their choice depends on the specific problem being solved.

[0075] “Specific thermal conductivity coefficient” (X) characterizes the ability of materials to conduct heat from hotter areas to cooler ones and is measured in W / (m*K).

[0076] "The heat transfer coefficient" (a) characterizes the intensity of heat exchange between the surface of the material and the environment. The heat transfer coefficient shows what amount of heat is transferred from a unit of the surface of the material to the environment per unit of time with a temperature difference between the surface of the material and the environment of 1 °C. The heat transfer coefficient depends on many factors: the composition of the material, the properties and shape of its surface, the presence or absence of blowing, etc.

[0077] The essence of the technical solution

[0078] This technical solution is designed to improve the safety of electrical equipment operation, namely, to prevent contact connection fires and to organize a reliable contact connection with the ability to detect defects.

[0079] The objective of this technical solution is to create a cable lug that is designed with the ability to irreversibly register the fact of heating above the threshold temperature with the accuracy, speed and reliability required in this area of ​​technology. The technical result of the claimed technical solution consists in increasing fire safety and electrical safety during the operation of electrical equipment by ensuring a reliable contact connection with the ability to irreversibly register the fact of exceeding a specified threshold temperature for the timely detection of defects in the contact connection.

[0080] The technical result is achieved by using a cable lug according to the present technical solution, made with the possibility of irreversibly registering the fact of heating of the contact connection above the threshold temperature, which includes: a metal conductive part made with the possibility of fastening on the core(s) (non-insulated end) of the wire by crimping; a dielectric part connected to the conductive part, wherein the dielectric part includes a base made with the possibility of fixing on the wire, having a dielectric strength of at least 3 kV / mm and a thermal conductivity coefficient of at least 0.1 W / (m*K), on the front surface of which a heat-sensitive material is applied, irreversibly changing transparency when heated above the threshold temperature, and the minimum distance from the heat-sensitive material to the metal conductive part (D1) does not exceed 10 mm.

[0081] When installing a cable lug according to this technical solution on a contact connection, the metal conductive part provides a larger contact area of ​​the electrical equipment terminal with the uninsulated part of the wire (core or cores) due to its compression, which allows increasing the contact area, preventing the growth of transient contact resistance over time and thereby reducing the risk of a defect, failure or fire. Due to the presence of a metal conductive part, the device can also be easily and safely installed on the end of the wire and securely fix it, in particular, in terminals of electrical devices, on detachable contact connections of conductors with socket connections, on spring contact connections and other elements. At the same time, when installing, replacing and dismantling a thermal indicator cable lug, there is no mechanical impact on the mounted contact connection and its loosening.The layered structure of the dielectric part of the cable tip, which includes a base made of a dielectric material and a heat-sensitive material applied to it, allows using various methods for manufacturing the dielectric part. Thus, when manufacturing the base, it is possible to use not only molding, but also casting, sintering and other methods that require heating to high temperatures, which cannot be used when mixing the heat-sensitive material initially into the base. This significantly expands the choice of base materials used, including those that are not adapted for molding, in particular, thermoplastic polymers (for example, PVC), ceramics and composite materials.

[0082] The heat-sensitive materials applied to the base of the dielectric part, in this case, can also be selected from a wide range of compounds, without the limitations imposed by the mixing of the thermal pigment into the base.

[0083] Each layer of the dielectric part performs its own functions, the combination of which cannot be achieved using a thermal pigment evenly distributed in the base material.

[0084] The shape of the dielectric part of the tip allows to reduce or completely eliminate the possibility of touching the uninsulated part of the wire, including the frayed cores of the multi-core wire, when servicing the electrical installation, and also to slow down the oxidation processes that lead to the formation of oxide films on the contact surface. Also, the presence of the dielectric part allows to reduce the probability of overlapping the frayed cores of the wires and the occurrence of a short circuit.

[0085] The necessary and sufficient properties of the base, such as dielectric strength and thermal conductivity coefficient, must ensure fire safety and electrical safety when using the cable lug, as well as rapid heating of the base to ensure the possibility of registering short-term overheating.

[0086] The authors of this technical solution, based on the research conducted, have established that the following values ​​of these parameters are optimal for achieving the stated technical result: dielectric strength of at least 3 kV / mm, thermal conductivity coefficient of at least 0.1 W / (m*K).

[0087] The presence of a heat-sensitive material on the dielectric part of the tip ensures the possibility of timely detection of defects in contact connections accompanied by heating, due to irreversible registration of the fact of exceeding a specified threshold temperature. The use of an irreversible heat-sensitive material, the action of which is based on a change in transparency (namely, on an increase in transparency) when the threshold temperature is exceeded, is associated with the need to determine the fact of excessive heating of the contact connection at the moment of maximum loads, including short-term ones. Reversible heat-sensitive materials or materials other than those specified by the type of response cannot be used within the framework of this solution, since they do not provide the necessary functional properties of the device, including the necessary values ​​of accuracy, speed and reliability of overheating detection.

[0088] In order to achieve the technical result specified by the applicant, as well as to achieve registration of the fact of heating above the threshold temperature with sufficient accuracy (in accordance with current regulatory documents, the accuracy value of the response of temperature indicator materials should not exceed 10 °C), an important characteristic of the tip is the minimum distance from the heat-sensitive material to the metal conductive part, since when a defect in the contact connection occurs, only the contact spot on the uninsulated end of the wire is subject to heating, and as it moves away from the heating point, the heat quickly dissipates.

[0089] The distance over which the temperature of the tip material decreases by 10 °C can be roughly estimated based on the Fourier law of thermal conductivity and the Newton-Richmann law.

[0090] In accordance with the Fourier law of thermal conductivity, the heat flux removed through a unit area per unit time will be proportional to the thermal conductivity coefficient of the material and the temperature gradient: q = - XM / M), (1) where X is the specific thermal conductivity coefficient, and AT is the change in temperature over the length L / . We will assume that the same heat flux is dissipated into the environment in accordance with the Newton-Richmann law in direct proportion to the difference between the temperature of the cable lug material and the ambient air temperature: q = a - (T - Tocr), (2) where a is the heat transfer coefficient between the lug and the environment (air), T is the temperature of the cable lug, T окр - ambient temperature.

[0091] From these relationships, equating the two heat flows, we obtain the following relationship for the length:

[0092] M = XT / [a-(T- T 0K p)\. (3)

[0093] As a typical value of the heat transfer coefficient we take a equal to 3 W / (m 2 *K). We will take the thermal conductivity coefficient for the base material to be 0.2 W / (m*K) (the average value of the thermal conductivity coefficient for polymeric materials, composite materials and ceramics). We will consider the ambient temperature to be 20 °C and the tip temperature to be 70 °C. With these parameters, the temperature gradient equal to AT = 10 °C will correspond to the length L / % 13 mm.

[0094] Based on the averaging of the parameters of cable lugs, their installation locations, environments in which they are used, the range of recorded temperatures, etc., known to the authors based on the conducted research and experience in this field of technology, the authors of this technical solution have experimentally established that the maximum permissible value of the minimum distance from the heat-sensitive material to the metal conductive part (A1) should not exceed 10 mm.

[0095] Thus, the entire set of features characterizing a cable lug with temperature-indicating properties ensures the solution of the task and the achievement of the specified technical result.

[0096] The cable lug preferably has a variable diameter, tapering in the area of ​​the metal conductive part, to ensure tight contact of the walls of the cable lug and the wire, both in the part with insulation (in the area of ​​the dielectric part) and in the uninsulated part of the wire (in the area of ​​the metal conductive part). The metal part may have a through hole or be soldered on one side (remote from the dielectric part). The ratio of the inner diameter of the base of the dielectric part (D) to the inner diameter of the metal conductive part (d) is preferably from 1.1 to 2, which is related to the thickness of the wire insulation. If the ratio of these diameters is greater than two, a sufficiently tight fit of the base of the dielectric part of the cable lug to the wire will not be ensured, which may negatively affect the accuracy of determining the heating temperature of the contact joint and affect the safety of the operation of electrical equipment.The ratio of the length of the metal conductive part (L1) to the length of the base of the dielectric part (L2) is preferably from 0.5 to 1.5, preferably from 1.0 to 1.5. This is due to the need to isolate the loosened strands of the multi-core wire that did not get into the metal conductive part during installation of the cable lug, in order to increase electrical safety and reduce the risk of a short circuit when touching the strands of opposite phases. It is taken into account that the length of the uninsulated part of the wire and its strands is approximately equal to the length of the metal conductive part. Depending on the cross-section of the controlled elements, the internal diameter of the base of the dielectric part of the cable lug (internal diameter of the through section D) can be in particular cases 1-25 mm. In these cases, the internal diameter d of the metal conductive part can preferably be 0.5-22.7 mm.The length of the base of the dielectric part (L2) of the cable tip, and, as a consequence, the length of the through hole in it, is preferably 3-25 mm and is selected based on the dimensions of the controlled elements, as well as the area and location of the heat-sensitive material on the outer surface of the base of the dielectric part. In these cases, the length of the metal conductive part L1 can preferably be 3-30 mm. Preferably, the device is designed with the possibility of mounting on electric wires with a diameter of 1 to 10 mm, without additional elements, due to its design features, which ensures ease and safety of installation, replacement and dismantling, and additionally increases the accuracy of fixing the heating of the heat-sensitive material.

[0097] In preferred embodiments, for a tight and reliable fit of the cable lug to the wire and simple and safe fastening thereto, the base of the dielectric part is elastic and / or flexible. Also, the dielectric part may have a longitudinal cut, allowing for convenient, quick and safe fixation of the cable lug on the controlled elements due to the elastic properties of the material.

[0098] In preferred embodiments, the area of ​​the front surface of the dielectric base is at least 3 mm 2 , preferably not less than 10 mm 2 , most preferably not less than 100 mm 2and is selected based on the cross-section of the controlled elements, the location of the cable lug, designed with the ability to register the fact of heating above the threshold temperature, and the distance from the inspection point. In special cases, the area of ​​the outer surface of the base of the dielectric part must ensure the placement of a section of heat-sensitive material with an area of ​​at least 10 mm 2 to simplify the visual registration of the threshold temperature being exceeded. Ensuring the visibility and reliability of the detection of local heating of electrical equipment elements can also be achieved using a version of the device with a surface area of ​​the dielectric part base covered with a heat-sensitive material from 3 to 97% of the area of ​​the front surface of the dielectric part base, preferably not less than 30% of the area of ​​the front surface of the dielectric part base.

[0099] In order to increase the speed of visual transition of the heat-sensitive material when the threshold temperature is exceeded, as well as the accuracy of determining the heating temperature, the thickness of the base of the dielectric part in the zone of the heat-sensitive material is no more than 3 mm, preferably no more than 2 mm. Using a base with a greater thickness does not allow for the necessary heat transfer of the conductor during operation of electrical installations (air cooling). In this case, the base of the dielectric part can have both the same thickness and a smaller thickness in the zone of the heat-sensitive material, in particular, a recess can be made in the base of the dielectric part to fill it with a heat-sensitive material.The location of the heat-sensitive material in the recess allows to reduce the thickness of the dielectric part base in the heat-sensitive material zone in some cases to 1 mm or less, without losing the strength characteristics of the device itself, which increases the heating rate and, as a consequence, the response of the heat-sensitive material when overheated. Also, the location of the heat-sensitive material in the recess protects it from abrasion during installation and prevents the melted heat-sensitive material from flowing down during the phase transition to the contact zone with subsequent ignition.

[0100] In preferred embodiments, the heat-sensitive material is designed to change transparency when heated to a temperature exceeding the threshold, for no more than 5 seconds, preferably no more than 2 seconds. This is due to the fact that the thickness of the heat-sensitive material layer and its structure in combination with the thickness of the base of the dielectric part are selected in such a way as to allow heating the heat-sensitive material when short-term overheating occurs during the peak load period and completely converting it into a melt with an "opaque-transparent" color transition for no more than 5 seconds, preferably no more than 2 seconds.

[0101] In preferred embodiments, the heat-sensitive material irreversibly changes transparency when heated in a range not exceeding 5 °C, preferably not exceeding 2 °C, relative to the threshold temperature indicated on the device. In this case, the minimum distance from the heat-sensitive material to the metal conductive part is also calculated using the above formula (3), taking into account the required response accuracy.

[0102] In preferred embodiments, the dielectric part comprises polymeric materials, preferably halogen-containing polymers, preferably containing the structural unit -CH2CHCI-, preferably polyvinyl chloride, most preferably cast polyvinyl chloride, or ceramic materials, preferably porcelain, or composite materials, preferably textolite.

[0103] In the case of the dielectric part base being made of polymers, the base material is preferably selected in such a way as to ensure the simultaneous fulfillment of the following criteria:

[0104] - elasticity, flexibility and resilience required for tight fit of the device to the surfaces of controlled elements of electrical equipment, which often have complex geometry, while maintaining the ability to register overheating with the stated accuracy; - ensuring the necessary pressing and fixation of the device for its reliable fixation while maintaining a tight fit, including during vibration, under the influence of various environmental factors, mechanical impact, thermal expansion of the material of the controlled element of electrical equipment;

[0105] - ensuring the necessary adhesion between the protective film and the heat-sensitive material;

[0106] - resistance to ignition and self-extinguishing ability in case of exposure to open flame. Ignition of the device, in turn, can lead to a fire in the electrical installation or the occurrence of an electric arc;

[0107] - thermal conductivity sufficient to ensure rapid heating of the device and the heat-sensitive layer to the threshold temperature for reliable and accurate recording of short-term overheating, as well as heat removal from heating wires and contact connections;

[0108] - low electrical conductivity, allowing the device to be installed not only on electrical equipment elements covered with insulating materials, but also on contact connections without insulation. High electrical strength and dielectric properties of the device as a whole are necessary to ensure safe use in electrical installations, engines or various electrical mechanisms. The absence of conductivity and high breakdown voltage prevent electrical circuit failure, short circuit or ignition of an electric arc when the thermal indicator comes into contact with exposed conductive elements;

[0109] - maintaining the original shape when heated, i.e. the materials of the polymer dielectric part of the base and the protective film should not melt to the current state when heated to high temperatures, in order to avoid separation of the thermal indicator from the wire, flowing of the softened material and its contact with the elements of electrical equipment;

[0110] - ensuring stable attachment to the controlled element in a wide temperature range (decomposition temperature is preferably above 150 °C). The most suitable polymeric materials for this purpose are halogen-containing polymers, primarily polyvinyl chloride. Polymer materials in the structure of which halogen atoms are present have some of the highest flexibility and elasticity indices among known polymers. The introduction of halogen atoms into the monomers used as the starting material for polymerization disrupts their symmetry and creates many chiral centers in the polymer. Polymerization or polycondensation of such monomers both with each other and with other halogen-containing or halogen-free monomers leads to the formation of polymer chains with a large number of stereocenters.Regular polymers obtained from non-halogenated monomers without chiral centers tend to form crystalline structures, which reduces their elasticity, while a large number of diastereomers arising during halogenation of monomers impart stereochemical disorder to halogen-containing polymers, which prevents crystallization. Thus, halogen-containing polymeric materials have high elasticity and flexibility due to the features of the chemical structure caused by the presence of halogen atoms in the polymer structure. In addition, halogen-containing materials have good adhesion and low flammability, which serves as an additional guarantee of operational safety of the declared device and electrical equipment on which it is located.

[0111] Based on this, in preferred embodiments, the dielectric portion of the cable lug is elastic and flexible and includes halogen-containing polymers, predominantly containing the structural unit -CH2CHCI-, predominantly polyvinyl chloride, most predominantly cast polyvinyl chloride.

[0112] The use of ceramic materials for the base of the dielectric part provides the cable tip with increased strength and durability, and also increases the service life of the device, due to the high degree of resistance of ceramics to mechanical impacts, chemical effects and moisture. In addition, ceramic products are not subject to corrosion, do not burn and do not emit substances of a high hazard class, which also has a positive effect on the safety of the operation of cable tips with a ceramic base of the dielectric part. The use of composite materials as the base material of the dielectric part allows for high rigidity of the cable tip, which may be necessary in cases requiring reliable and accurate fixation of the wire direction.Composite materials also have high stability when used in extreme conditions and have high strength characteristics, which allows increasing the service life of the device. In addition, composite materials have a low specific gravity.

[0113] The heat-sensitive material may be covered with an elastic protective film that is transparent to at least part of the visible light, which additionally protects the heat-sensitive material and the cable tip itself from external environmental influences, humidity, UV radiation and mechanical damage, increases the service life of the device and prevents the heat-sensitive material from flowing during the phase transition.

[0114] The elastic protective film may be attached to the device by fusion (welding), glue or other methods known from the prior art. The protective film is preferably made of polyvinyl chloride, most preferably cast polyvinyl chloride, taking into account the properties of these materials described above.

[0115] The metal conductive part can be made of aluminum, copper or their alloys and in some cases have a tinned coating to protect against the formation of an oxide film. The choice of materials for the conductive part is due to their high electrical and thermal conductivity, high relative corrosion resistance, as well as resistance to external influences such as temperature, ultraviolet radiation, and chemical action. In addition, the metal of the conductive part must be soft to ensure the possibility of fastening to wires using the crimping method, but at the same time plastic to avoid cracking and breaking during installation.

[0116] In specific embodiments, the dielectric part of the cable lug may be used to mark electrical equipment elements or have a numerical designation. For example, the dielectric part may have a color that complies with the established rules for marking electrical equipment elements. Also, the front surface of the dielectric part may contain digital, color or other marking, in particular, an inscription containing color, letter, digital or alphanumeric marking information. In one case, the inscription may reflect the value of the registered threshold temperature, and also contain information about the end date of the device's service life.

[0117] The above-listed features serve to impart to the cable lug, designed with the ability to register the fact of heating above the threshold temperature, the properties of the elements of electrical equipment marking, which also additionally ensures the safety of operation of the equipment on which such devices are placed, due to the following. In the case of contact connections, wires or units of electrical equipment, we are talking about small surfaces that, on the one hand, require marking, and on the other hand, temperature control. However, the use of two types of devices at once: devices for marking and devices for registering excess temperature separately, is often not possible, due to insufficient space on the controlled surface, as well as the need to take into account the decrease in heating temperature as it moves away from the control point.Using only a cable lug designed to register the fact of heating above the threshold temperature without marking may lead to incorrect identification of the defective unit. Thus, using a cable lug that combines the properties of a marking device and the properties of temperature indicators will have a positive effect on the safety of electrical equipment operation.

[0118] In order to increase the visibility of both the cable lug itself and the fact of its operation, on equipment elements, including those difficult to inspect due to the large size of the installations, the location of the installations outdoors or due to the inspection in bad weather conditions and in conditions of insufficient visibility, at night using a flashlight, as well as for inspecting equipment without artificial lighting and windows, and, as a consequence, to further increase the safety of equipment operation, the dielectric part may have reflective properties or be painted using a substance with luminescent properties. In special cases, the dielectric part may be painted using a substance made with the ability to irreversibly change color when heated.

[0119] The use of substances in the painting of the dielectric part that are capable of irreversibly changing color when heated to a temperature lower than the threshold temperature of the main heat-sensitive material, for example, by 10-30 °C, allows informing personnel about the risk of an emergency defect occurring in the future, and thus ensures the possibility of preventing it, with due response from the personnel responsible for this equipment. Thus, the operation of such a substance, in the absence of the operation of the main heat-sensitive material, indicates the presence of overheating of the equipment that has not reached the maximum permissible values ​​corresponding to the threshold temperature of the main heat-sensitive material, and the need to inspect it in order to identify and eliminate malfunctions that could subsequently lead to the development of an emergency defect.Thus, the presence of a substance capable of irreversibly changing color when heated to a temperature below the threshold temperature of the main heat-sensitive material, in particular by 10-30 °C, additionally increases the safety of operation of both the declared device and the equipment as a whole.

[0120] The dielectric part of the cable lug can be fully or partially painted using dyes designed to reversibly change color when heated. For example, a layer of heat-sensitive paint with the above-mentioned properties can be applied to the front surface of the base.

[0121] The use of dyes capable of reversibly changing color when heated allows informing personnel of overheating at the time of inspection. Heating of the tip at the time of inspection indicates that the equipment is in emergency mode at the CURRENT moment and may be a source of increased danger. At the same time, the main heat-sensitive material, which irreversibly changes transparency when the threshold temperature is exceeded, informs personnel of overheating events that occurred BEFORE the inspection. Thus, the presence of a substance capable of reversibly changing color when heated additionally increases the safety of operation of both the declared cable tip and the equipment as a whole.

[0122] In preferred embodiments, the principle of operation of the heat-sensitive material, which irreversibly changes transparency when heated above the threshold temperature, consists in melting the heat-sensitive component. Preferably, the heat-sensitive material in the initial state is opaque for at least part of the visible light, for example, it is white, and when heated above the threshold temperature, an irreversible increase in transparency occurs with the manifestation of the color of the dielectric part of the base. In special cases, the dielectric part under the heat-sensitive material can be painted black, which, when using a heat-sensitive material that is white in the initial state, provides a color transition with maximum “white-black” contrast, which additionally increases the visibility of the triggered cable tip and, as a result, will increase the safety of operation of the controlled elements of electrical equipment.

[0123] The use of a heat-sensitive material based on melting, accompanied by an irreversible increase in transparency relative to the initial state when heated to a threshold temperature, additionally ensures and enhances such properties as: irreversibility of the visual effect of operation; high speed of operation of the device; preservation of the initial state at a temperature slightly lower than the threshold; the required accuracy of determining the operation temperature, regardless of the time of exposure to temperature.

[0124] The threshold temperature can be selected from the range of 50-210 °C, preferably 50 °C, 55 °C, 60 °C, 70 °C, 80 °C, 90 °C, 100 °C, 110 °C, 120 °C, 130 °C, 140 °C, 150 °C. The applied heat-sensitive material is selected based on the threshold temperature value selected for registration, which, in turn, is regulated by standard instructions and is also determined by the type of materials of the contact surfaces in the contact connection, the voltage class of the electrical equipment, as well as the insulation class and other parameters.In particular cases, the heat-sensitive material in its initial state has a microstructure that includes a solid phase and voids that form a continuous gas phase, the volume fraction of which is at least 10%, and is designed with the ability to irreversibly change its appearance upon reaching the specified threshold temperature due to the destruction of the microstructure of the heat-sensitive material, accompanied by the fusion of particles of solid organic matter, a decrease in the volume fraction of voids and an increase in its transparency with the manifestation of the color of the base.

[0125] The use of a heat-sensitive material with voids allows to increase the service life, further increase the reliability of overheating detection due to the impossibility of aggregation of solid particles through the gas phase and eliminate the possibility of returning the material to its original state after operation due to an irreversible change in the microstructure, which also has a positive effect on the safety of operation of both the cable tip and the equipment itself. When melting a heat-sensitive material containing voids, an irreversible change in the original microstructure of the material occurs with a decrease in the proportion of voids in it, associated with the fusion of particles of solid organic matter and with a decrease in the area of ​​​​the solid-gas phase boundaries due to the irreversible release of gas contained in the voids to the surface and stratification of the gas and non-gaseous environments.As a result, upon further cooling, the solid organic substance crystallizes without voids, thereby irreversibly changing the transparency (increasing relative to the initial state) of the material for at least part of the visible light, creating a visual effect of changing the appearance of the device with high contrast, which ensures high reliability of recording the excess of temperature above the specified value. Preferably, the proportion of voids in the heat-sensitive material after heating above the threshold temperature value decreases by at least 2 times relative to the initial state, which additionally increases the contrast of the color transition of the cable tip when the threshold temperature value is exceeded.

[0126] The solid phase of the heat-sensitive material may include an organic substance containing a structural fragment C nH(2n+i), where n > 5 and preferably selected from the group: fatty aliphatic acids containing structural fragments C n H(2n+i) with n > 12; salts of fatty aliphatic acids containing structural fragments C n H(2n+i) with n > 5; alkanes containing at least 20 carbon atoms; dialkylphosphinic acids containing structural fragments C n H(2n+i) with n > 5; fatty acid amides containing structural fragments C n H(2n+i) with n > 5; fatty acid anhydrides containing structural fragments C n H(2n+i) with n > 10; fatty aliphatic alcohols containing structural fragments C n H(2n+i) with n > 14; fatty aliphatic amines containing structural fragments C n H(2n+i) with n > 17; nitriles of fatty aliphatic acids containing structural fragments C n H(2n+i) with n > 19.

[0127] The use of organic compounds containing one or more aliphatic hydrocarbon chains C as the organic substance of the solid phase of the heat-sensitive material n H(2n+i) with n > 5, promotes the formation of a crystalline packing in which the elongated structural fragments of linear hydrocarbons are oriented parallel to each other (A.I. Kitaygorodsky, Molecular Crystals, Moscow: Nauka, 1971). Due to the fact that the particles of solid organic matter are formed in the form of fibers, scales or flat or elongated crystals, i.e. have a two-dimensional structure, the heat-sensitive material forms a special microstructure capable of bending and stretching without deformation and loss of functional properties.

[0128] Also, the use of solid organic compounds, which include non-polar aliphatic fragments, additionally contributes to an increase in the electrical strength values ​​of the cable lug as a whole, since such fatty aliphatic derivatives have good dielectric properties.

[0129] In particular cases, the organic substance of the solid phase of the heat-sensitive material is selected from the group: palmitic acid, stearic acid, behenic acid, tetracosane, erucamide, stearic alcohol, cetyl alcohol, polyethylene, wax, paraffin, salts of saturated fatty carboxylic acids of rare earth metals, in particular lanthanum, yttrium, ytterbium, scandium. In particular cases, the microstructure of the heat-sensitive material additionally contains a polymer binder transparent at least for part of the visible light, the phase transition temperature of which is higher than the phase transition temperature of the solid organic substance.In this case, the heat-sensitive material contains the boundaries of the phase separation “solid-transparent solid-gas”, and during melting, an irreversible change in the microstructure of the material also occurs, as a result of which the number of voids decreases relative to the initial state due to the release of the gas contained in them onto the surface of the material and stratification of the gas and non-gaseous environments occurs, as a result of which a decrease in the contact area of ​​the solid phase and voids is observed, i.e. a decrease in the area of ​​the phase separation boundaries.

[0130] Preferably, the volume content of the solid phase in the heat-sensitive material is no more than 90 vol.%. In other words, the heat-sensitive material contains no less than 10 vol.% of voids filled with a gas phase (air).

[0131] In preferred embodiments, the polymer binder is present in the heat-sensitive material in an amount of 1-30 vol.%. In particular cases, the polymer binder covers each individual structural particle of the solid organic substance, ensuring its “glazing”. The binder is selected in such a way as to ensure wettability, but not dissolution, of the particles of the solid organic substance in the polymer binder. Due to this, when “glazing” grains, crystals, fibers, flakes or conglomerates of the said particles, additional gas capture occurs, in the medium of which the heat-sensitive material is formed, and its distribution between the particles of the solid organic substance “glazed” by the binder.

[0132] In preferred embodiments, the heat-sensitive material, including due to its microstructure, is designed with the ability to register local overheating of the surface by changing the transparency of only that part of the heat-sensitive material that was heated above the threshold temperature and maintaining the original color of the heat-sensitive material that was not heated above the threshold temperature, during uneven heating.

[0133] Brief description of the drawings The technical solution will be more understandable from the description, which is not limiting in nature and is given with references to the attached drawings, which show:

[0134] Fig. 1 - Three-dimensional model (1a, c) and front view (16) of a cable lug, designed with the possibility of registering the fact of heating above a threshold temperature, which includes a metal conductive part (1a, c with an open hole, 16 with a sealed hole) and a dielectric part of variable diameter (1a, b without a cut, 1c with a longitudinal cut), on a part of the front surface of the base of which a heat-sensitive material is applied (1a along the entire circumference, in the form of a ring, 16, 1c in the form of a rectangular section) with the shown linear dimensions (length) of the metal conductive and dielectric parts, as well as the minimum distance from the heat-sensitive material to the metal conductive part (A1) (16).

[0135] Fig. 2 - A sectional view of a cable lug designed to register the fact of heating above a threshold temperature, which includes a metal conductive part (2a with an open hole, 26, 2c with a sealed hole) and a dielectric part (2a, b without a cut, 2c with a longitudinal cut), on a part of the front surface of the base of which a heat-sensitive material is applied (2a along the entire circumference, in the form of a ring, 26, c in the form of a rectangular section in a recess made in the material of the dielectric part), with the base of the dielectric part painted with black paint in the area of ​​the heat-sensitive material and a protective layer, with the shown internal diameters of the metal conductive and dielectric parts (2c).

[0136] Fig. 3 - View of a cable tip designed to register the fact of heating above a threshold temperature, with a wire with an uninsulated end placed thereon.

[0137] Fig. 4 - A detachable contact connection of a conductor terminated with a cable tip designed with the possibility of registering the fact of heating above the threshold temperature, in a socket terminal.

[0138] Fig. 5 - A cable lug with an open opening, designed with the possibility of registering the fact of heating above a threshold temperature, the base of the dielectric part of which has light-reflecting and / or luminescent properties, with the base painted with black paint in the area of ​​the heat-sensitive material, and indicating the value of the threshold temperature in this area: (a) - the initial appearance of the cable lug, (b) - a cable lug with a triggered heat-sensitive material after heating the controlled surface above the threshold temperature value, (c) - view of the cable lug after cooling.

[0139] Fig. 6 - A cable lug with a sealed opening, designed with the possibility of registering the fact of heating above a threshold temperature, with the base painted with black paint in the area of ​​the heat-sensitive material, and indicating the value of the threshold temperature in the area free of the heat-sensitive material, as well as with a reversible heat-sensitive material applied to the surface of the base of the dielectric part free of the irreversible heat-sensitive material: (a) - the initial view of the cable lug, (b) - a cable lug with triggered heat-sensitive materials after heating the controlled surface above the threshold values ​​of the temperature of the heat-sensitive materials, (c) - view of the cable lug after cooling below the threshold temperature of the reversible heat-sensitive material.

[0140] Fig. 7 - A cable lug designed with the possibility of registering the fact of heating above a threshold temperature, the base of the dielectric part of which in the zone of the heat-sensitive material is painted black: (a) - the original appearance of the cable lug, (b) - a cable lug with a partially activated heat-sensitive material after point heating of the controlled surface above the threshold temperature value with a change in the transparency of only that area of ​​the heat-sensitive material that was subjected to heating above the threshold temperature, while maintaining an opaque area of ​​this material in its remaining zone that was not subjected to heating.

[0141] Fig. 8 - Microstructure of a heat-sensitive material with particles of organic matter in the form of scales and their conglomerates, a binder and voids forming a continuous gas phase, before activation (a) and after activation (b).

[0142] Detailed description of the drawings

[0143] Fig. 1 shows a three-dimensional model (1a, c) and a front view (16) of a cable lug configured to register the fact of heating above a threshold temperature, which includes a metal conductive part 6 with a circular cross-section (Fig. 1a, c with an open hole, Fig. 16 with a sealed hole) and a dielectric part 1', the base 1 of which has a circular cross-section of variable diameter (Fig. 1a, 16 without a cut, Fig. 1b with a longitudinal cut 15), and on a part of the front surface of the base 1 of which a heat-sensitive material 2 is applied (Fig. 1a along the entire circumference, in the form of a ring, Fig. 16, 1b in the form of a rectangular section), with the linear dimensions (length) of the metal conductive and dielectric parts shown, as well as the distance from the heat-sensitive material to the metal conductive part (16).

[0144] Fig. 2 shows a sectional view of a cable lug configured to register the fact of heating above a threshold temperature, which includes a metal conductive part 6 (Fig. 2a with an open hole, Fig. 26, 2c with a sealed hole) and a dielectric part (Fig. 2a, 26 without a cut, Fig. 2c with a longitudinal cut 15), on a part of the front surface of the base 1 of which a heat-sensitive material 2 is applied (Fig. 2a along the entire circumference, in the form of a ring, Fig. 26, 2c in the form of a rectangular section in a recess made in the material of the base 1 of the dielectric part), with the base 1 of the dielectric part painted with black paint 3 in the area of ​​the heat-sensitive material 2 and a protective layer 5 (Fig. 2a, 2c), with the shown internal diameters of the metal conductive and dielectric parts (2c).

[0145] Fig. 3 shows a view of a cable tip designed to register the fact of heating above a threshold temperature, which includes a metal conductive part 6 and a dielectric part, on part of the front surface of the base 1 of which a heat-sensitive material 2 is applied, with a wire placed thereon, wherein an insulated part of a wire 12 is placed in the base 1 of the dielectric part, and an uninsulated end of a wire (core) 11 is placed in the metal conductive part.

[0146] Fig. 4 shows a detachable contact connection of a conductor 12 terminated with a cable tip designed with the possibility of registering the fact of heating above a threshold temperature, which includes a metal conductive part 6 and a dielectric part, on part of the front surface of the base 1 of which a heat-sensitive material 2 is applied, in a socket terminal 13 equipped with a screw 14.

[0147] Fig. 5 shows a cable lug, designed with the possibility of registering the fact of heating above the threshold temperature, with an open end of the metal conductive part 6, the base 1 of the dielectric part of which has light-reflecting and / or luminescent properties, with the base 1 painted with black paint 3 in the area of ​​the heat-sensitive material 2, and an indication of the value of the threshold temperature 4 in this area, demonstrating the irreversibility of the heat-sensitive material: (a) - the initial appearance of the cable lug, (b) - the cable lug with the triggered heat-indicating material after heating the controlled surface above the threshold temperature value, (c) - the view of the cable lug after cooling.

[0148] Fig. 6 shows a cable lug configured to register the fact of heating above a threshold temperature, with an open end of a metal conductive part 6, the base 1 of the dielectric part of which is coated with a reversible heat-sensitive composition in the area free of heat-sensitive material 2, with the base 1 being painted with black paint 3 in the area of ​​heat-sensitive material 2, and an indication of the value of the threshold temperature 4 in the area free of heat-sensitive material 2, with a demonstration of the irreversibility of the heat-sensitive material and the reversibility of the color change of the reversible heat-sensitive composition (green-red-green): (a) - the initial appearance of the cable lug, (b) - a cable lug with a triggered heat-indicating material after the controlled surface has been heated above the threshold temperature values ​​of the irreversible heat-sensitive material and the reversible heat-sensitive composition,(c) - the appearance of the cable lug after cooling below the threshold temperature of the reversible heat-sensitive material, with the return of the original color of the reversible heat-sensitive composition.

[0149] Fig. 7 shows a cable lug, designed with the possibility of registering the fact of heating above the threshold temperature, the base 1 of the dielectric part of which in the zone of the heat-sensitive material 2 is painted black 3: (a) - the initial appearance of the cable lug, (b) - a cable lug with a partially activated heat-sensitive material after point heating of the controlled surface above the threshold temperature value with a change in the transparency of only that area 9 of the heat-sensitive material that was subjected to heating above the threshold temperature, while maintaining an opaque area of ​​this material in its remaining zone, which was not subjected to heating.

[0150] Fig. 8 shows the microstructure of the heat-sensitive material 2 with particles of organic matter 7 made in the form of scales and their conglomerates, binder 10 and voids 8 forming a continuous gas phase, before heating (a) and the microstructure of the heat-sensitive material 2 with a reduced proportion of voids 8 and with an increased apparent density, after the gas phase has reached the surface, and with particles 7 that have undergone fusion and lost their original shape, after heating above the threshold temperature value (b).

[0151] Implementation of a technical solution

[0152] General technology of manufacturing the device.

[0153] The cable lug includes a conductive metal fragment 6, made, in particular, of copper, aluminum or their alloys, for reliable and tight fastening of the cable lug on the uninsulated end of the wire 11 by crimping, as well as for ensuring high thermal and electrical conductivity. In some cases, the conductive metal fragment may have a tinned or other coating to protect against the formation of an oxide film. The conductive metal fragment 6 may have a through hole or be soldered on one side (remote from the dielectric polymer part). Preferably, the conductive metal fragment has a circular cross-section, but is not limited to it.

[0154] Polymeric materials, mainly halogen-containing polymeric materials, in particular chlorine-containing polymers, for example, vinyl chloride copolymers, namely: copolymer C-15 (copolymer of vinyl chloride and vinyl acetate), copolymer VHVD-40 (copolymer of vinyl chloride and vinylidene chloride), polyvinyl chloride (PVC), cast PVC, as well as polyvinylidene fluoride PVDF, fluoroplastic M-40, as well as polyesters with additives of 6.5% hexabromocyclododecane or polyesters modified with 15% trichloroisopropyl phosphate, can be used as the base 1 of the dielectric part 1' of the claimed device. In addition, ceramic materials, mainly porcelain, can be used. Also, in a number of embodiments, other types of ceramic materials or glass can be used. Composite materials, mainly textolite, can be used. In special cases, fiberglass, carbon fiber, cermets and other composite materials can be used.The specified materials have the required strength, make the device fire-resistant and have a dielectric strength of at least 3 kV / mm and a thermal conductivity coefficient of at least 0.1 W / (m*K). In the case of using polymeric materials, the device also acquires its characteristic elasticity, resilience and flexibility. Also, for the convenience of attaching the cable tip to the wire, the dielectric part can have a longitudinal cut.

[0155] Table 1 provides some characteristics of the dielectric base 1'. The choice of a specific value is based, in particular, on the type, size and location of the equipment being inspected, as well as its distance from the inspection point.

[0156] Table 1. Characteristics of the dielectric part.

[0157] The base of the dielectric part preferably has a circular cross-section, but is not limited to it. In order to reduce the thickness of the base of the dielectric part in the area of ​​the heat-sensitive material, as well as to ensure the safety of this material, the base of the dielectric part may contain a recess (Fig. 26, c), in which the irreversible heat-sensitive material 2 is placed.

[0158] In some embodiments, the base 1 of the dielectric part 1' may have reflective properties or may be painted using a substance with luminescent properties to increase the visibility of both the device itself and the fact of its operation, which serves to further increase the safety of equipment operation. Also, in special cases, the dielectric part may be painted to enable the use of the declared thermal indicator for color marking of electrical equipment phases (cables, installation wires, harnesses and other elements of electrical equipment), and the color of the dielectric part 1' is selected in accordance with GOST 28763-90, which establishes, in particular, color marking in the field of electrical engineering. The color does not affect the visual registration of exceeding the threshold temperatures of the equipment surface, but provides for the marking of the device, which is necessary to increase the overall safety of equipment operation.

[0159] In special cases, the base 1 of the dielectric part 1' can be painted using a substance made with the ability to irreversibly change color when heated. The presence of an additional substance made with the ability to irreversibly change color when heated to a temperature below the threshold temperature of the main heat-sensitive material, in particular, by 10-30 °C, allows detecting overheating of equipment that has not reached the maximum permissible values, and, as a result, ensuring the prevention of an emergency defect.

[0160] Also, the base 1 of the dielectric part 1' can be painted using a substance made with the ability to reversibly change color when heated (Fig. 6). For example, a layer of heat-sensitive paint with the above-mentioned properties can be applied to the front surface. The presence of a substance made with the ability to reversibly change color when heated allows informing personnel not only about exceeding the threshold temperature in the past, but also about overheating at the time of inspection.

[0161] In special cases, the area of ​​the base 1 of the dielectric part 1' under the heat-sensitive material can be painted black 3, which, when using a heat-sensitive material that is white in its original state, ensures a color transition with maximum “white-black” contrast.

[0162] The conductive metal part 6 and the dielectric part 1' are connected to form a single structure at the manufacturing plant.

[0163] The dielectric part 1' and, first of all, the heat-sensitive material 2 can be covered with a protective polymer film 5. Polymer materials, mainly halogen-containing polymers, in particular PVC films, or polyurethane films modified with 15% trichloroisopropyl phosphate can also be used as a protective film. However, it must be taken into account that in the case of using them for a protective film, they must be transparent to at least part of the visible light.

[0164] Preparation of heat-sensitive material.

[0165] Preferably, the solid phase of the heat-sensitive material 2 comprises an organic substance containing a structural fragment C n H(2n+i), where n > 5: fatty aliphatic acids containing structural fragments C пH(2n+1) with n > 12; salts of fatty aliphatic acids containing structural fragments C n H(2n+i) with n > 5; alkanes containing at least 20 carbon atoms; dialkylphosphinic acids containing structural fragments C n H(2n+i) with n>5; fatty acid amides containing structural fragments C n H(2n+i) with n > 5; fatty acid anhydrides containing structural fragments C n H(2n+i) with n > 10; fatty aliphatic alcohols containing structural fragments C n H(2n+i) with n > 14; fatty aliphatic amines containing structural fragments C n H(2n+i) with n > 17; nitriles of fatty aliphatic acids containing structural fragments C nH(2n+i) with n > 19, for example, palmitic acid, stearic acid, behenic acid, tetracosane, erucamide, stearyl alcohol, cetyl alcohol, polyethylene, wax, paraffin, salts of saturated fatty carboxylic acids of rare earth metals, in particular lanthanum, yttrium, ytterbium, scandium, or a mixture thereof with a melting point differing from the threshold temperature by no more than 5 °C.

[0166] In preferred embodiments, the volume content of the solid phase in the heat-sensitive material, including organic matter, is no more than 90 vol.%, most preferably no more than 50 vol.%.

[0167] The organic substance is selected in such a way that, upon reaching a threshold temperature in the range of no more than 5 °C, preferably no more than 2 °C, it melts with a visual transition from opaque to transparent within no more than 5 seconds, preferably no more than 2 seconds.

[0168] In various embodiments, the organic substance of the solid phase of the heat-sensitive material is selected in such a way that the threshold temperature can be selected from a range of 50 °C to 210 °C, in particular cases, the temperature threshold is selected from the group: 50 °C, 55 °C, 60 °C, 70 °C, 80 °C, 90 °C, 100 °C, 110 °C, 120 °C, 130 °C, 140 °C, 150 °C.

[0169] To produce a heat-sensitive material, the solid phase, including the organic substance, is ground in a ball mill to a size of 2-3 μm, the liquid phase, represented by water or an organic solvent with a boiling point of less than 180 °C, is successively added, and the resulting suspension is stirred, while preferably, during this period, periodic dispersion of the mixture with air access is ensured until a constant density of the mixture is obtained. The liquid phase is preferably water or an organic solvent, the solubility of the solid phase of the heat-sensitive material in which does not exceed 10 g / kg.

[0170] In preferred embodiments of the invention, the liquid phase is added in an amount of from 50 vol.% to 90 vol.%.

[0171] The difference in density between the liquid phase and the solid phase is preferably less than 0.2 g / cm 3. For this purpose, the liquid phase can be selected from the group: isopropanol, water, methanol, 1-propanol, isobutanol, ethylene glycol monomethyl ether, 1-butanol, acetonitrile, acetic acid, hexane, heptane, 1,1,1-trifluoroethanol, 1,1,1,1,3,3,3-hexafluoroisopropanol, dimethyl formamide, ethanol, butyl acetate, water, acetone, toluene or mixtures thereof, but are not limited to them.

[0172] With this method of production, the obtained heat-sensitive material 2 is preferably represented by two continuous phases: solid 7 and gas 8. In this case, the solid phase 7 is represented by particles predominantly oriented parallel to the surface of the base 1.

[0173] In this case, the obtained heat-sensitive material 2 in the initial state is opaque for at least part of the visible light and in the initial state includes a solid phase 7 and voids 8 filled with a gas phase, the volume fraction of which in the initial state is at least 10 vol.%, and when heated above the corresponding threshold temperature value, an irreversible change in the microstructure of the heat-sensitive material 2 occurs, accompanied by the fusion of particles of solid organic matter, a decrease in the proportion of voids, preferably by 2 or more times (Fig. 8), and an increase in its transparency with the manifestation of the color of the base, and upon subsequent cooling to 20 °C and holding at this temperature for at least one month, preferably one year or more, the transparency of the heat-sensitive material does not return to its original values.

[0174] Depending on the nature of the solid phase 7 and the organic substance included in its composition, the type of the resulting particles of the solid phase 7 may be grains, crystals, fibers, flakes or conglomerates of the said particles.

[0175] In particular cases, the heat-sensitive material 2 additionally contains a polymer binder 10, transparent at least for part of the visible light, the phase transition temperature of which is higher than the phase transition temperature of the organic substance of the solid phase 7. In this case, the crushed solid phase is suspended in a solution of a binder transparent at least for part of the visible light in the liquid phase. In preferred embodiments of the technical solution, the binder is present in the resulting heat-sensitive material in an amount of 1-30 mass %, to ensure the effect of glazing the particles of the solid organic substance.

[0176] In particular cases, the transparent polymer binder is selected from phenol-formaldehyde resin, butyl methacrylic resin, melamine-formaldehyde resin, polyvinyl butyral, polybutyl methacrylate, polyisobutyl methacrylate, polybutyl acrylate, phenoxy resin, polystyrene-acrylic emulsion, polyolefin, polystyrene, polyacrylate, polyethersulfone, polyethylene, polypropylene, polystyrene, polyvinylidene fluoride, polytetrafluoroethylene, polyethersulfone, polyisoprene, polypropylene, polybutadiene, polyisobutylene, polyvinyl acetate, polymethacrylate, ethyl cellulose, polyvinyl chloride, polyvinylidene chloride, polycarbonate, polycaprolactone, polyethylene terephthalate resin, polybutylene terephthalate resin, polyamide resin, polyvinylidene fluoride, polyester, polyester resins, hydroxyethyl cellulose, methyl cellulose, ethyl cellulose, nitrocellulose, carboxymethyl cellulose, gelatin, agar-agar, casein, gum arabic, polyvinyl alcohol, polyethylene oxide or mixtures thereof.

[0177] In some cases, an inscription 4 with information on the threshold temperature was applied to the front surface of the dielectric part 1' of the cable lug. In special cases, in addition to the threshold temperature, information on the end of service life was also applied. In one of the design options, a drawing intended for marking phases or units of electrical equipment containing graphic, numerical or textual information can be applied to the surface of the cable lug, including the dielectric part.

[0178] In general, the process of applying the heat-sensitive material 2 includes the stages of applying one or more layers of a suspension of solid phase particles in a liquid phase to individual sections of the opaque base 1 of the dielectric part 1', removing the liquid phase from the applied layers of the suspension, and also covering the front surface of the workpiece with a transparent protective layer 5. In order to obtain a microstructure of the applied heat-sensitive material 2, including a solid phase 7 and voids 8 filled with a gas phase, the volume fraction of which in the initial state is at least 10%, and ensuring an irreversible change in appearance upon reaching the threshold temperature, which is accompanied by melting of the solid phase particles, a decrease in the proportion of voids and an increase in its transparency with the manifestation of the color of the base 1 of the dielectric part 1', it is possible to use, in particular, the following techniques at the previously disclosed stages of the method:

[0179] - at least one of the above-mentioned stages of the method (applying a suspension of particles of a solid organic substance in the liquid phase, removing the liquid phase from the applied layers of the suspension, covering the front surface of the workpiece with a transparent protective layer) is carried out at a pressure below atmospheric.

[0180] - at least 3 cycles of applying layers of a suspension of solid phase particles in a liquid phase and removing the liquid phase from the applied layers of this suspension are carried out, while the application of the suspension of solid phase particles in the liquid phase is carried out by a method selected from the group: screen printing, flexographic printing, pad printing, silk-screen printing, with the production of a microstructure of a heat-sensitive material, the particles of the solid phase in which are oriented predominantly parallel to the plane of the base surface.

[0181] The removal of the liquid phase from the applied layers of suspension of solid phase particles in the liquid phase or from each layer separately can be carried out either at a pressure below atmospheric pressure or at atmospheric pressure, depending on the selected method of manufacturing the device.

[0182] Subatmospheric pressure, in particular cases of obtaining the device, can be used both immediately after the application of each individual layer of the suspension of solid organic matter in the liquid phase, and at the stage of drying (i.e., removing the liquid phase) of the required number of applied layers of the suspension of solid organic matter in the liquid phase. In this case, spontaneous release of the liquid phase from the volume of the material (sequentially from each layer or from the entire volume of the material) occurs with the formation of a larger number of unstructured voids.

[0183] Layer-by-layer application of a solid phase suspension in a liquid phase can also ensure the production of the claimed device. In this case, after application of the heat-sensitive material, the device is dried by selecting the mode of removing the liquid phase from the applied layers of the suspension, preferably at a temperature of (20±2) °C for 10 minutes in an air atmosphere, then the layer-by-layer application procedure is repeated until the required coating thickness is obtained. The formation of a microstructure including solid phase particles and a large proportion of voids filled with a gas phase occurs layer by layer.The desired microstructure can also be achieved by using a dilute suspension of solid phase particles in the liquid phase (dilution of more than 50%), since the flakes will be oriented in the desired manner and settle in an ordered form in a large volume (the principle of “closed blinds”, which, if observed, will allow a thin layer of flakes to cover the color of the base), in contrast to the use of more concentrated suspensions. Another factor affecting the rate and nature of sedimentation of solid phase particles is the relative difference in the densities of the solvent and solid phase particles. In the presence of a large difference in densities (more than 0.2 g / cm. 3 ) solid phase particles will settle out of the suspension too quickly according to the principle of open blinds, not providing sufficient hiding power. At comparable densities or at a density difference of less than 0.2 g / cm 3a slow settling of solid phase particles will be observed, with the formation of the necessary ordered microstructure of the material and compliance with the principle of closed blinds.

[0184] Thus, adherence to the principle of closed blinds when forming the microstructure of a heat-sensitive material makes it possible to obtain a material whose microstructure in the initial state has a preferential orientation of solid phase particles parallel to the surface of the polymer dielectric part of the base and the protective coating.

[0185] When applying a suspension of solid phase particles in a liquid phase, the area of ​​the front surface of the base 1 of the dielectric part 1' of the device, onto which the heat-sensitive material 2 should not get, is sealed with polyethylene film. A layer of the suspension of solid phase particles in a liquid phase is uniformly applied to the uncovered area of ​​the base 1 of the dielectric part 1' using one of the above-described techniques or other methods that ensure the formation of the described microstructure.

[0186] In preferred embodiments, the thickness of the heat-sensitive material layer is no more than 800 μm, preferably no more than 450 μm, most preferably no more than 150 μm. The use of the specified thickness of the heat-sensitive material layer facilitates its response at a speed of less than 5 seconds, preferably less than 2 seconds, when heated above the threshold temperature. This is due to the fact that such a thickness of the material layer in combination with the thickness of the base of the dielectric part allows heating the heat-sensitive material when short-term overheating occurs during the peak load period and completely converting it into a melt with an "opaque-transparent" color transition in less than 5 seconds, and also ensures the necessary heat transfer during air cooling of the operating devices.

[0187] The surface area of ​​the base 1 of the dielectric part 1' of the cable tip, covered with the heat-sensitive material 2, preferably comprises from 3 to 97% of the area of ​​the front surface of the base 1 of the dielectric part 1', preferably not less than 30% of the area of ​​the front surface of the base 1 of the dielectric part 1', which makes it possible to detect triggered devices from a long distance, and also makes it possible to detect point heating 9 of a large surface of the installations.

[0188] It should be noted that the claimed technical solution is not limited to the use of only one heat-sensitive material, and if necessary, the cable tip, designed with the ability to register the fact of heating above the threshold temperature, can be supplemented with various heat-sensitive materials to determine the excess of several threshold temperatures.

[0189] At the final stage of preparation, the heat-sensitive material can be covered with an elastic protective film 5, transparent at least for part of the visible light, which protects the material and the device itself from external environmental influences, humidity, UV radiation and mechanical damage, increases the service life of the device and does not allow the heat-sensitive material to flow during the phase transition. Thus, the device is designed with the possibility of registering the excess of the threshold temperature of the conductive elements in the open air.

[0190] In some versions of the technical solution, a gap may be made between the protective film 5 and the dielectric part 1', or micro-holes may be made in the transparent protective film 5, allowing the gas phase to escape beyond the device after exceeding the registered temperature. Preferably, the transparent protective film 5 is selected from transparent elastic polymers.

[0191] In preferred embodiments, the heat-sensitive material 2 is designed with the ability to register local overheating of the surface by changing the color of only that part of the heat-sensitive material 9 that was heated above the threshold temperature and maintaining the original color of the heat-sensitive material that was not heated above the threshold temperature, during uneven heating.

[0192] The principle of operation of the device.

[0193] A cable tip designed with the possibility of registering the fact of heating above a threshold temperature, which includes a metal conductive part 6 designed with the possibility of being attached to the non-insulated end of a wire 11 by crimping; a dielectric part 1' with a through hole, onto the front surface of the base 1 of which a heat-sensitive material 2 is applied, irreversibly changing transparency when heated above a threshold temperature, so that the minimum distance from the heat-sensitive material to the metal conductive part A / does not exceed 10 mm.The said tip is installed on the surface of the electric wire 12, ensuring a tight fit of the device due to the compression of the conductive metal part 6 and the properties of the base material 1 of the dielectric part 1', preferably without additional fasteners, and is fixed in the terminals of electrical devices, on detachable contact connections of conductors with socket connections, on spring contact connections and other elements of electrical equipment. Such fastening of the cable tip ensures increased safety of operation of electrical equipment due to ensuring a reliable contact connection of the elements, with the possibility of irreversible registration of the fact of exceeding a specified threshold temperature and, as a consequence, timely detection of defects in the contact connection.

[0194] Regardless of the design of the cable terminal, made with the possibility of registering the fact of heating above the threshold temperature, as well as the type of the controlled element and the attachment to it, the operating principle of the device does not change significantly. The cable terminal, made with the possibility of registering the excess of the threshold temperature, with the applied heat-sensitive material 2, operates as follows. The applied heat-sensitive material 2 in the initial state and before the moment of heating to the threshold temperature is opaque for at least part of the visible light and, in the preferred versions of the technical solution, is white.Until the entire surface of the cable lug or its individual sections located under the heat-sensitive material 2 is heated to the threshold temperature value, the heat-sensitive material 2 remains opaque for at least part of the visible light, thereby preserving the original appearance of the cable lug. When the surface is heated above the threshold temperature of the heat-sensitive material 2, irreversible destruction of the microstructure of the heat-sensitive material 2 occurs on the entire surface of the heat-sensitive material 2 or predominantly on the heated section 9 of the heat-sensitive material 2, respectively, accompanied by fusion of particles of the solid phase 7, a decrease in the proportion of voids 8 and, as a consequence, an increase in transparency. In this case, an increase in the apparent density of the material occurs.The heat-sensitive material 2 with the modified microstructure is transparent and reveals the color of the base 1 of the dielectric part 1' under this material or the color of the paint 3 applied to it in the area of ​​the heat-sensitive material. Upon subsequent cooling of the controlled surface, the heat-sensitive material 2 or its part 9 remains transparent and the appearance of the cable tip does not return to its original state. This ensures the possibility of visually registering the excess of temperature above the threshold temperature value, both at the moment of overheating and after a long period of time.

[0195] During point heating of the controlled surface, a transparent zone 9 is formed only in that area of ​​the heat-sensitive material 2 that was subjected to heating above the threshold temperature, while maintaining an opaque area of ​​this material in its remaining area that was not subjected to heating.

[0196] The numerical value of the threshold temperature 4 can be applied to the front side of the dielectric part 1', in particular cases the value of the threshold temperature can be applied in the zone free from the heat-sensitive material 2, but next to it (Fig. 6), or to the base 1 of the dielectric part 1' under the heat-sensitive material 2 (Fig. 5), in the latter case, when the temperature exceeds the threshold value, after an irreversible change in the microstructure of the heat-sensitive material 2, the color of the base 1 of the dielectric part 1' and the numerical value of the threshold temperature 4 appear. In particular embodiments, the dielectric part can be black, and the heat-sensitive material in its original opaque state can be white.In this case, after the temperature exceeds the threshold value, a change in the appearance of the thermal indicator with a maximum contrast of “white-black” is observed, which additionally ensures the visibility of the triggered thermal indicator and facilitates its visual detection. A similar purpose is served by the implementation of a cable tip, in which the base of the dielectric part has a color other than black, and in the area under the heat-sensitive material 2, which is white in the initial state, black paint 3 is applied. In this case, also when the heat-sensitive material is triggered, a “white-black” color transition is observed.

[0197] In the case of a cable lug hermetically covered with an elastic transparent protective layer 5 at atmospheric pressure, at the moment of operation, as a result of the destruction of the microstructure of the heat-sensitive material 2 and the stratification of the gas and non-gaseous environments, a bubble will form on the surface of the protective layer 5, which decreases when the device cools. When using a temperature indicator with a hermetically sealed protective layer 5 and a pressure inside the voids 8 of the heat-sensitive material 2 below atmospheric, no bubble will be formed on the surface of the protective layer 5 when the threshold temperature is exceeded, due to the fact that the pressure of the gas phase inside the voids 8, created at the stage of obtaining the heat indicator blank when applying the protective layer 5, is initially below atmospheric and compensates for the thermal expansion of the gas released when the microstructure of the heat-sensitive material 2 is destroyed.In other embodiments of the cable lug, in order to prevent the formation of a bubble when the threshold temperature is exceeded, a gap can be made between the transparent protective layer and the base, or micro-holes can be made in the protective layer, providing the possibility of the release of gas released during operation. The embodiments of the cable lug, in which the composition of the heat-sensitive material 2 includes particles of the solid phase 7, voids 8 and a binder 10, have a similar operating principle. When the temperature exceeds the threshold value, the particles 7, “glazed” with the binder 10, fuse with the release of the gas phase and the separation of the gas and non-gaseous environments, as a result of which irreversible destruction of the microstructure of the heat-sensitive material 2 also occurs, accompanied by a decrease in the proportion of voids 8 and, as a consequence, an increase in the transparency of the material.

[0198] Thus, all versions of the cable lug have a principle of operation based on the irreversible destruction of the microstructure of the heat-sensitive material 2, accompanied by the fusion of solid phase particles 7, a decrease in the proportion of voids 8 and, as a consequence, an increase in the transparency of the material and an irreversible change in the appearance of the temperature indicator. Moreover, when the cable lug and heat-sensitive material are cooled, the appearance does not return to its original state, mainly a decrease in the transparency of the heat-sensitive material to its original values ​​does not occur when cooling to 20 °C and maintaining at this temperature for at least one month, preferably one year or more.

[0199] Thus, during a visual inspection of the cable lug, the fact that the temperature of the entire surface or its local area has exceeded the threshold value can be reliably and with high accuracy (in the range of + / - 10 °C, preferably + / - 5 °C, most preferably + / - 2 °C, relative to the threshold temperature indicated on the cable lug) and speed (no more than 5 seconds, preferably no more than 2 seconds), which helps to identify defects in the contact connection.

[0200] Below are presented preferred embodiments of the claimed technical solution, which are illustrative and in no way limit the scope of the requested legal protection.

[0201] Example 1. General technology of manufacturing the device

[0202] Preparation of heat-sensitive material: 100 g of a substance with a melting point corresponding to the threshold registration temperature in the range of 5 °C were ground to a size of 2-3 microns, 300 g of water, methanol, ethanol, isopropanol, ethylene glycol, ethylene glycol monomethyl ether, acetonitrile or their mixtures or a 3-33% solution of a binder in water, methanol, ethanol, isopropanol, ethylene glycol, ethylene glycol monomethyl ether, acetonitrile or their mixtures were successively added and stirred until a homogeneous mass. The suspension was immediately used for applying the composition.

[0203] The metal conductive element of the cable lug was preferably made of copper, aluminum or combinations thereof in the form of a tube with a through hole or a hole sealed at one end inside. The base of the dielectric part was preferably made of polymeric materials, preferably halogen-containing polymers, as well as ceramic or composite materials that are resistant to combustion, have an electric strength of at least 3 kV / mm and a thermal conductivity coefficient of at least 0.1 W / (m*K). The base of the dielectric part was made in the form of a hollow tube with a thickness of preferably no more than 2 mm with a through hole of preferably 3-25 mm in length and a diameter of preferably 1-25 mm for fastening on wires, preferably with a diameter of 1 to 10 mm, without additional fastening elements. In this case, the diameter of the through hole can be either constant or variable.In some cases, the ratio of the diameter of the through hole of the base of the dielectric part to the diameter of the through hole of the metal conductive part is from 1.1 to 2. In this case, the ratio of the length of the metal conductive part to the length of the dielectric part, in particular cases, is from 0.5 to 1.5.

[0204] The conductive part is attached to the dielectric part to form a single structure at the manufacturing plant. In the case of a base made of polymeric materials, the dielectric part is also elastic and / or has a longitudinal cut.

[0205] If necessary, information elements are applied to the base of the dielectric part using solvent dyes, for example, containing the value of the threshold response temperature in degrees Celsius.

[0206] The area of ​​the dielectric part, which should not be exposed to the heat-sensitive material, was sealed with polyethylene film. The heat-sensitive material was applied to the area free of the film using silk-screen printing in 5-7 layers. In this case, the distance from the heat-sensitive material to the metal conductive part does not exceed the parameter A / , calculated using formula (3) taking into account the thermal conductivity coefficient of the materials used for the base of the dielectric part and the threshold temperature of the selected heat-sensitive material. Between applications, the composition was dried in a vacuum chamber or in a thermostat at a temperature not exceeding the response temperature of the composition. After the heat-sensitive material had completely dried, the film was removed. In its initial state, the heat-sensitive material is white.

[0207] Example 2.

[0208] The substance for preparing the heat-sensitive material according to Example 1 was n-docosylamine with a phase transition temperature of 65 °C, and methanol was used as a solvent. The suspension was applied by silk-screen printing onto a base with a constant internal through-hole diameter of 15 mm and a length of 25 mm made of black PVC Oramask 831 with a thickness of 2 mm, according to the method described in Example 1. The distance from the heat-sensitive material to the metal conductive part was 5 mm. The conductive part was made of copper, had a diameter of 10 mm, a length of 15 mm and an open hole. The number of layers of the heat-sensitive material was 7, and between applications the composition was dried in a vacuum chamber at 100 mm Hg and 20 °C for one hour. The thickness of the layer of the heat-sensitive material was 0.6 mm, and its area was 30% of the area of ​​the front surface of the dielectric part of the device base.

[0209] Example 3.

[0210] The substance used to prepare the heat-sensitive material according to Example 1 was docosanitrile with a phase transition temperature of 55 °C, polyvinyl butyral was used as a binder, and a mixture of methanol with ethylene glycol methyl ether (50 / 50 vol.%) was used as a solvent. The suspension was applied by silk-screen printing to a base with a constant internal through-hole diameter of 1 mm and a length of 3 mm, made of red M-40 fluoroplastic with a thickness of 0.2 mm, according to the method described in Example 1. The distance from the heat-sensitive material to the metal conductive part was 1 mm. The conductive part is made of copper, has a diameter of 1 mm, a length of 3 mm and an open hole. The number of layers of heat-sensitive material was 7, between applications the composition was dried in a thermostat at a temperature of 40 °C for three hours.The thickness of the layer of heat-sensitive material was 0.8 mm, and its area was 97% of the area of ​​the front surface of the dielectric part of the device base. The device was covered with a transparent protective film made of PVC, 0.15 mm thick.

[0211] Example 4.

[0212] The substance used to prepare the heat-sensitive material according to Example 1 was 1-tetradecanol with a phase transition temperature of 40 °C, the binder was melamine-formaldehyde resin, and the solvent was a mixture of methanol and isobutanol (90 / 10 vol.%). The suspension was applied by silk-screen printing to a base with a variable internal diameter of the through hole from 5 to 10 mm and a length of 25 mm, made of a red vinyl chloride and vinyl acetate copolymer with a thickness of 0.2 mm, according to the method described in Example 1, wherein a numerical value of the threshold temperature, as well as black paint, were applied in the area of ​​the heat-sensitive material before its application. The distance from the heat-sensitive material to the metal conductive part was 7 mm. The conductive part is made of aluminum, has a diameter of 5 mm, a length of 25 mm and a closed opening.The number of layers of heat-sensitive material was 5, between applications the composition was dried for 24 hours at room temperature. The thickness of the layer of heat-sensitive material was 0.2 mm, and its area was 70% of the area of ​​the front surface of the dielectric part of the base of the device. The device was covered with a transparent protective film made of polyurethane modified with 15% trichloroisopropyl phosphate, 0.15 mm thick.

[0213] Example 5.

[0214] Erucamide with a phase transition temperature of 80 °C was used as a substance for preparing the heat-sensitive material according to Example 1, polyvinyl butyral was used as a binder, and ethanol was used as a solvent. The suspension was applied by silk-screen printing onto a base with a constant internal through-hole diameter of 10 mm and a length of 25 mm, made of a green vinyl chloride and vinylidene chloride copolymer with light-reflecting properties, having a thickness of 0.35 mm, according to the method described in Example 1, wherein in the zone of the heat-sensitive material before its application, a numerical value of the threshold temperature was applied, as well as black paint, and in the zone free of the heat-sensitive material, information on the service life was applied. The distance from the heat-sensitive material to the metal conductive part was 10 mm. The conductive part is made of copper, has a diameter of 5 mm, a length of 30 mm and a closed opening.The number of layers of heat-sensitive material was 5, between applications the composition was dried in a vacuum chamber at 100 mm Hg and 20 °C for one hour. The thickness of the layer of heat-sensitive material was 0.4 mm, and its area was 3% of the area of ​​the front surface of the dielectric part of the device base.

[0215] Example 6.

[0216] Palmitic acid anhydride with a phase transition temperature of 60 °C was used as a substance for preparing the heat-sensitive material according to Example 1, polybutyl methacrylate was used as a binder, and ethanol was used as a solvent. The suspension was applied by silk-screen printing to a base with a constant internal diameter of a through hole of 2 mm and a length of 10 mm, made of polyvinylidene fluoride, painted with orange paint with luminescent properties, having a thickness of 0.15 mm, according to the method described in Example 1, wherein black paint was applied in the zone of the heat-sensitive material before its application, and a numerical value of the threshold temperature was applied in the zone free of the heat-sensitive material. The distance from the heat-sensitive material to the metal conductive part was 5 mm. The conductive part is made of copper, has a diameter of 1 mm, a length of 5 mm and an open hole.The number of layers of heat-sensitive material was 5, between applications the composition was dried in a thermostat at a temperature of 70 °C for three hours. The thickness of the layer of heat-sensitive material was 0.2 mm, and its area was 30% of the area of ​​the front surface of the dielectric part of the base of the device. The device was covered with a transparent protective film made of PVC, 0.05 mm thick.

[0217] Example 7.

[0218] The substance used to prepare the heat-sensitive material according to Example 1 was n-hexadecyl-n-pentylhydrogenphosphate with a phase transition temperature of 40 °C, gelatin was used as a binder, and isopropanol was used as a solvent. The suspension was applied by silk-screen printing to a base with a constant internal diameter of a through hole of 5 mm and a length of 20 mm, made of polyester modified with 6.5% hexabromocyclododecane, yellow in color, having a thickness of 0.3 mm, according to the method described in Example 1, wherein in the area of ​​the heat-sensitive material before its application, a numerical value of the threshold temperature was applied, as well as black paint. The distance from the heat-sensitive material to the metal conductive part was 10 mm. The conductive part is made of copper, has a diameter of 5 mm, a length of 20 mm and an open hole. The number of layers of heat-sensitive material was 6, and between applications the composition was dried for 24 hours at room temperature.The thickness of the layer of heat-sensitive material was 0.5 mm, and its area was 30% of the area of ​​the front surface of the dielectric part of the device base. The device was covered with a transparent protective film made of PVC, 0.05 mm thick.

[0219] Example 8.

[0220] Yttrium caproate with a phase transition temperature of 55 °C was used as a substance for preparing the heat-sensitive material according to Example 1, phenoxy resin was used as a binder, and ethylene glycol was used as a solvent. The suspension was applied by silk-screen printing to a base with a constant internal through-hole diameter of 15 mm and a length of 30 mm, made of black PVC Oramask 831 with a thickness of 5 mm, according to the method described in Example 1, and in the zone free from the heat-sensitive material, a numerical value of the threshold temperature was applied. The distance from the heat-sensitive material to the metal conductive part was 9 mm. The conductive part is made of duralumin, has a diameter of 10 mm, a length of 10 mm and an open hole. The number of layers of heat-sensitive material was 6, between applications the composition was dried in a vacuum chamber at 100 mm Hg and 20 °C for one hour.The thickness of the layer of heat-sensitive material was 0.5 mm, and its area was 70% of the area of ​​the front surface of the dielectric part of the device base.

[0221] Example 9.

[0222] Lithium stearate with a phase transition temperature of 210 °C was used as a substance for preparing the heat-sensitive material according to Example 1, polyethylene was used as a binder, and ethanol was used as a solvent. The suspension was applied by silk-screen printing to a base with a constant internal through-hole diameter of 5 mm and a length of 25 mm, made of black PVC Oramask 831 with a thickness of 0.5 mm, according to the method described in Example 1, and in the zone free from the heat-sensitive material, a numerical value of the threshold temperature was applied. The distance from the heat-sensitive material to the metal conductive part was 2 mm. The conductive part is made of steel, has a diameter of 2 mm, a length of 10 mm and an open hole. The number of layers of heat-sensitive material was 5, between applications the composition was dried in a thermostat at a temperature of 60 °C for three hours.The thickness of the layer of heat-sensitive material was 0.35 mm, and its area was 70% of the area of ​​the front surface of the dielectric part of the device base. The device was covered with a transparent protective film made of PVC, 0.15 mm thick.

[0223] Example 10.

[0224] Zinc caproate with a phase transition temperature of 150 °C was used as a substance for preparing the heat-sensitive material according to Example 1, polycarbonate was used as a binder, and ethanol was used as a solvent. The suspension was applied by silk-screen printing to a base with a constant internal diameter of a through hole of 5 mm and a length of 25 mm, made of brown textolite, having a thickness in the area of ​​the heat-sensitive material of 0.45 mm, according to the method described in Example 1, and in the zone free from the heat-sensitive material, a numerical value of the threshold temperature was applied. The distance from the heat-sensitive material to the metal conductive part was 4 mm. The conductive part is made of copper, has a diameter of 5 mm, a length of 15 mm and an open hole. The number of layers of the heat-sensitive material was 5, between applications the composition was dried for 24 hours at room temperature.The thickness of the layer of heat-sensitive material was 0.4 mm, and its area was 70% of the area of ​​the front surface of the dielectric part of the device base. The device was covered with a transparent protective film made of PVC, 0.02 mm thick.

[0225] Example 11. Zinc palmitate with a phase transition temperature of 140 °C was used as a substance for preparing the heat-sensitive material according to Example 1, nitrocellulose was used as a binder, and ethanol was used as a solvent. The suspension was applied by silk-screen printing to a base with a constant internal through-hole diameter of 5 mm and a length of 25 mm, made of black PVC Oramask 831 with a thickness of 0.4 mm, according to the method described in Example 1, wherein the numerical value of the threshold temperature was applied in the zone free from the heat-sensitive material. The distance from the heat-sensitive material to the metal conductive part was 3 mm. The conductive part is made of copper, has a diameter of 3 mm, a length of 10 mm and an open hole. The number of layers of heat-sensitive material was 6, between applications the composition was dried in a vacuum chamber at 100 mm Hg and 20 °C for one hour.The thickness of the heat-sensitive material layer was 0.45 mm, and its area was 70% of the area of ​​the front surface of the dielectric part of the device base. The device was covered with a transparent protective film made of PVC, 0.03 mm thick.

[0226] Example 12.

[0227] Zinc nonadecanoate with a phase transition temperature of 130 °C was used as a substance for preparing the heat-sensitive material according to Example 1, polyvinylidene fluoride was used as a binder, and ethanol was used as a solvent. The suspension was applied by silk-screen printing to a base with a constant internal through-hole diameter of 5 mm and a length of 30 mm, made of white porcelain with a thickness of 0.5 mm, according to the method described in Example 1, wherein in the zone free from the heat-sensitive material, a numerical value of the threshold temperature was applied, and the zone under the heat-sensitive material was covered with black paint. The distance from the heat-sensitive material to the metal conductive part was 5 mm. The conductive part is made of copper, has a diameter of 2 mm, a length of 20 mm and an open hole. The number of layers of the heat-sensitive material was 5, between applications the composition was dried in a thermostat at a temperature of 60 °C for three hours.The thickness of the heat-sensitive material layer was 0.3 mm, and its area was 70% of the area of ​​the front surface of the dielectric part of the device base. The device was covered with a transparent protective film made of PVC, 0.15 mm thick.

[0228] Example 13.

[0229] Lanthanum capronate with a phase transition temperature of 120 °C was used as a substance for preparing the heat-sensitive material according to Example 1, polybutyl acrylate was used as a binder, and ethanol was used as a solvent. The suspension was applied by silk-screen printing to a base with a constant internal through-hole diameter of 1 mm and a length of 3 mm, made of black PVC Oramask 831, having a thickness of 0.8 mm and having a longitudinal cut, according to the method described in Example 1, and in the zone free from the heat-sensitive material, a numerical value of the threshold temperature was applied. The distance from the heat-sensitive material to the metal conductive part was 0.5 mm. The conductive part is made of copper, has a diameter of 1 mm, a length of 3 mm and an open hole. The number of layers of the heat-sensitive material was 5, between applications the composition was dried for 24 hours at room temperature.The thickness of the layer of heat-sensitive material was 0.4 mm, and its area was 70% of the area of ​​the front surface of the dielectric part of the device base. The device was covered with a transparent protective film made of PVC, 0.1 mm thick.

[0230] Example 14.

[0231] Lanthanum nonadecinate with a phase transition temperature of 110 °C was used as a substance for preparing the heat-sensitive material according to Example 1, polyethersulfone was used as a binder, and ethanol was used as a solvent. The suspension was applied by silk-screen printing to a base with a constant internal through-hole diameter of 5 mm and a length of 25 mm, made of black PVC Oramask 831 with a thickness of 1.0 mm, according to the method described in Example 1, and in the zone free from the heat-sensitive material, a numerical value of the threshold temperature was applied. The distance from the heat-sensitive material to the metal conductive part was 5 mm. The conductive part is made of copper, has a diameter of 2 mm, a length of 15 mm and an open hole. The number of layers of heat-sensitive material was 5, between applications the composition was dried in a vacuum chamber at 100 mm Hg and 20 °C for one hour.The thickness of the layer of heat-sensitive material was 0.25 mm, and its area was 70% of the area of ​​the front surface of the dielectric part of the device base. The device was covered with a transparent protective film made of PVC, 0.15 mm thick.

[0232] Example 15.

[0233] Lanthanum palmitate with a phase transition temperature of 100 °C was used as a substance for preparing the heat-sensitive material according to Example 1, ethyl cellulose was used as a binder, and ethanol was used as a solvent. The suspension was applied by silk-screen printing to a base with a constant internal through-hole diameter of 10 mm and a length of 25 mm, made of black PVC Oramask 831 with a thickness of 0.75 mm, according to the method described in Example 1, and in the zone free from the heat-sensitive material, a numerical value of the threshold temperature was applied. The distance from the heat-sensitive material to the metal conductive part was 6 mm. The conductive part is made of copper, has a diameter of 8 mm, a length of 25 mm and an open hole. The number of layers of heat-sensitive material was 5, between applications the composition was dried in a vacuum chamber at 100 mm Hg and 20 °C for one hour.The thickness of the heat-sensitive material layer was 0.3 mm, and its area was 50% of the area of ​​the front surface of the dielectric part of the device base. The device was covered with a transparent protective film made of PVC, 0.15 mm thick.

[0234] Example 16.

[0235] Yttrium behenate with a phase transition temperature of 90 °C was used as a substance for preparing the heat-sensitive material according to Example 1, polymethacrylate was used as a binder, and ethanol was used as a solvent. The suspension was applied by silk-screen printing to a base with a constant internal through-hole diameter of 20 mm and a length of 20 mm, made of black PVC Oramask 831 with a thickness of 0.85 mm, according to the method described in Example 1, and in the zone free from the heat-sensitive material, a numerical value of the threshold temperature was applied. The distance from the heat-sensitive material to the metal conductive part was 7 mm. The conductive part is made of copper, has a diameter of 15 mm, a length of 20 mm and an open hole. The number of layers of heat-sensitive material was 6, between applications the composition was dried in a thermostat at a temperature of 40 °C for three hours.The thickness of the heat-sensitive material layer was 0.55 mm, and its area was 50% of the area of ​​the front surface of the dielectric part of the device base. The device was covered with a transparent protective film made of PVC, 0.02 mm thick.

[0236] Example 17.

[0237] Dioctylphosphinic acid with a phase transition temperature of 80°C was used as a substance for preparing the heat-sensitive material according to Example 1, polycarbonate was used as a binder, and ethanol was used as a solvent. The suspension was applied by silk-screen printing to a base with a constant internal through-hole diameter of 5 mm and a length of 20 mm, made of black PVC Oramask 831 with a thickness of 0.65 mm, according to the method described in Example 1, and in the zone free from the heat-sensitive material, a numerical value of the threshold temperature was applied. The distance from the heat-sensitive material to the metal conductive part was 9 mm. The conductive part is made of copper, has a diameter of 3 mm, a length of 15 mm and an open hole. The number of layers of heat-sensitive material was 7, between applications the composition was dried for 24 hours at room temperature.The thickness of the heat-sensitive material layer was 0.75 mm, and its area was 50% of the area of ​​the front surface of the dielectric part of the device base. The device was covered with a transparent protective film made of PVC, 0.03 mm thick.

[0238] Example 17.

[0239] Eicosanoic acid with a phase transition temperature of 70 °C was used as a substance for preparing the heat-sensitive material according to Example 1, polybutyl acrylate was used as a binder, and ethanol was used as a solvent. The suspension was applied by silk-screen printing to a base with a constant internal through-hole diameter of 5 mm and a length of 20 mm, made of black PVC Oramask 831 with a thickness of 0.1 mm, according to the method described in Example 1, and in the zone free from the heat-sensitive material, a numerical value of the threshold temperature was applied. The distance from the heat-sensitive material to the metal conductive part was 3 mm. The conductive part is made of copper, has a diameter of 5 mm, a length of 20 mm and an open hole. The number of layers of heat-sensitive material was 5, between applications the composition was dried in a vacuum chamber at 100 mm Hg and 20 °C for one hour.The thickness of the heat-sensitive material layer was 0.15 mm, and its area was 70% of the area of ​​the front surface of the dielectric part of the device base. The device was covered with a transparent protective film made of PVC, 0.05 mm thick.

[0240] Example 18.

[0241] Ytterbium caprylate with a phase transition temperature of 60 °C was used as a substance for preparing the heat-sensitive material according to Example 1, polybutyl methacrylate was used as a binder, and ethanol was used as a solvent. The suspension was applied by silk-screen printing to a base with a constant internal through-hole diameter of 1 mm and a length of 3 mm, made of black Oramask 831 PVC with a recess in the area of ​​the heat-sensitive material, having a thickness of 1.5 mm and a thickness in the recess of 1.0 mm, according to the method described in Example 1, and in the zone free of the heat-sensitive material, a numerical value of the threshold temperature was applied. The distance from the heat-sensitive material to the metal conductive part was 0.5 mm. The conductive part is made of copper, has a diameter of 1 mm, a length of 5 mm and an open hole.The number of layers of heat-sensitive material was 5, between applications the composition was dried for 24 hours at room temperature. The thickness of the layer of heat-sensitive material was 0.25 mm, and its area was 70% of the area of ​​the front surface of the dielectric part of the device base. The device was covered with a transparent protective film made of PVC, 0.15 mm thick.

[0242] Example 19.

[0243] Tetracosane with a phase transition temperature of 50 °C was used as a substance for preparing the heat-sensitive material according to Example 1, polyvinyl butyral was used as a binder, and ethanol was used as a solvent. The suspension was applied by silk-screen printing to a base with a constant internal through-hole diameter of 5 mm and a length of 20 mm, made of black OraJet 3106SG PVC with a recess in the area of ​​the heat-sensitive material, having a thickness of 0.55 mm and a thickness in the recess of 0.25 mm, according to the method described in Example 1, wherein the numerical value of the threshold temperature was applied in the zone free of the heat-sensitive material. The distance from the heat-sensitive material to the metal conductive part was 2 mm. The conductive part is made of copper, has a diameter of 5 mm, a length of 10 mm and an open hole. The number of layers of heat-sensitive material was 7, between applications the composition was dried in a vacuum chamber at 100 mm Hg.st and 20 °C for one hour. The thickness of the layer of heat-sensitive material was 0.75 mm, and its area was 90% of the area of ​​the front surface of the dielectric part of the base of the device. The device was covered with a transparent protective film made of PVC, 0.05 mm thick.

[0244] Example 20.

[0245] The area of ​​the base with a constant internal diameter of the through hole of 10 mm and a length of 20 mm, made of black PVC OraJet 3951, onto which the heat-sensitive material will be applied, was sealed with a protective polyethylene film, the free area was covered with pigmented yellow Tempilaq thermal paint with a reversible color change temperature of 113 °C. After the paint dried, the protective polyethylene film was removed and a numerical value of the threshold temperature was applied to the surface of the base containing the thermal paint using solvent dyes. The thickness of the base containing the thermal paint was 0.45 mm. Then the protective polyethylene film was glued to the area that should not be exposed to the heat-sensitive material, the thermal composition was applied using the silk-screen printing method in 7 layers. After the layer completely dried, the protective film was removed.Zinc caproate with a phase transition temperature of 150 °C was used as a substance for preparing the heat-sensitive material according to Example 1, butyl methacrylic resin was used as a binder, and ethanol was used as a solvent. The distance from the heat-sensitive material to the metal conductive part was 3 mm. The conductive part was made of copper, had a diameter of 5 mm, a length of 20 mm, and an open hole. The number of layers of the heat-sensitive material was 6, between applications the composition was dried in a thermostat at a temperature of 40 °C for three hours. The thickness of the layer of the heat-sensitive material was 0.6 mm, and its area was 70% of the area of ​​the front surface of the dielectric part of the device base. The device was covered with a transparent elastic protective film made of PVC, 0.05 mm thick. Example 21.

[0246] The area of ​​the base with a constant internal diameter of the through hole of 10 mm and a length of 25 mm, made of red PVC Oramask 831, onto which the heat-sensitive material will be applied, was sealed with a protective polyethylene film, the free area was covered with pigmented yellow Hallcrest SC thermal paint with an irreversible color change temperature of 80 °C. After the paint dried, the protective polyethylene film was removed and a numerical value of the threshold temperature was applied to the surface of the base containing the thermal paint using solvent dyes. The thickness of the base containing the thermal paint was 0.55 mm. Then the protective polyethylene film was glued to the area that should not be exposed to the heat-sensitive material, this area was covered with solvent black dye and the thermal composition was applied using silk-screen printing in 6 layers. After the layer completely dried, the protective film was removed.Lanthanum caproate with a phase transition temperature of 120 °C was used as a substance for preparing the heat-sensitive material according to Example 1, phenol-formaldehyde resin was used as a binder, and ethanol was used as a solvent. The distance from the heat-sensitive material to the metal conductive part was 10 mm. The conductive part was made of copper, had a diameter of 8 mm, a length of 30 mm and an open hole. The number of layers of the heat-sensitive material was 6, between applications the composition was dried in a vacuum chamber at 100 mm Hg and 20 °C for one hour. The thickness of the layer of the heat-sensitive material was 0.45 mm, and its area was 30% of the area of ​​the front surface of the dielectric part of the device base. The device was covered with a transparent elastic protective film made of PVC, 0.15 mm thick.

[0247] The examples provided do not limit the claimed technical solution, however, they clearly disclose particular cases of the implementation of the claimed technical solution, and also confirm the achievement of the technical result associated with ensuring increased fire safety and electrical safety during the operation of electrical equipment by ensuring a reliable contact connection with the possibility of irreversible registration of the fact of exceeding a specified threshold temperature for the timely detection of defects in the contact connection, by irreversible registration of the fact of exceeding a specified threshold temperature by an element of electrical equipment with a device that is convenient and reliable to mount on wires and other elements of electrical equipment.

[0248] The technical solution has been disclosed above with reference to a specific embodiment of its implementation. Other embodiments of the technical solution may be obvious to specialists, which do not change its essence, as it is disclosed in this description. Accordingly, the technical solution should be considered not limited in scope by the description and examples provided.

Claims

Formula 1. A cable lug capable of registering the fact of heating above a threshold temperature, which includes: a metal conductive part capable of being secured to the core(s) of a wire by crimping; a dielectric part connected to the conductive part, wherein the dielectric part includes a base capable of being fixed to the wire, having a dielectric strength of at least 3 kV / mm and a thermal conductivity coefficient of at least 0.1 W / (m*K), on the front surface of which a heat-sensitive material is applied that irreversibly changes transparency when heated above the threshold temperature, and the minimum distance from the heat-sensitive material to the metal conductive part does not exceed 10 mm.

2. A cable lug according to claim 1, wherein the dielectric part comprises polymeric materials, predominantly halogen-containing polymers, predominantly containing the structural unit -CH2CHCI-, predominantly polyvinyl chloride, most predominantly cast polyvinyl chloride, or ceramic materials, predominantly porcelain, or composite materials, predominantly textolite.

3. A cable lug according to claim 1, wherein the dielectric part is elastic and / or has a longitudinal cut.

4. A cable lug according to item 1, in which the area of the front surface of the base of the dielectric part is at least 3 mm 2 , preferably not less than 10 mm 2 .

5. A cable lug according to claim 1, wherein the ratio of the inner diameter of the base of the dielectric part to the inner diameter of the metal conductive part is from 1.1 to 2, and the ratio of the length of the metal conductive part to the length of the base of the dielectric part is from 0.5 to 1.

5.

6. A cable lug according to item 1, wherein the base of the dielectric part has a through hole with an internal diameter of 1-25 mm and a length of 3-25 mm.

7. A cable lug according to item 1, wherein the thickness of the base of the dielectric part is no more than 2 mm.

8. A cable lug according to item 1, characterized in that the heat-sensitive material is located in a recess made in the material from which the base of the dielectric part is made, and the thickness of the base of the dielectric part in the recess area does not exceed 1 mm.

9. A cable lug according to claim 1, wherein the metal conductive part is made of aluminum, copper or their alloys.

10. A cable lug according to item 1, characterized in that the dielectric part can be used for marking elements of electrical equipment and (or) contains digital, color or other marking, including one indicating the value of the recorded threshold temperature.

11. A cable lug according to claim 1, wherein the dielectric part has light-reflecting properties or is colored using a substance having luminescent properties.

12. A cable lug according to claim 1, wherein the dielectric portion is at least partially colored using a substance capable of reversibly changing color upon heating.

13. A cable lug according to claim 1, wherein the heat-sensitive material is covered with an elastic protective film that is transparent to at least part of the visible light, preferably made of polyvinyl chloride, most preferably cast polyvinyl chloride.

14. A cable lug according to claim 1, wherein the heat-sensitive material is initially colored white, and when the transparency of the heat-sensitive material increases, a visual color transition from white to black occurs.

15. A cable lug according to claim 1, wherein the heat-sensitive material in its initial state has a microstructure including a solid phase and voids forming a continuous gas phase, the volume fraction of which in the heat-sensitive material is at least 10 vol.%, and is designed with the ability to irreversibly change its appearance upon reaching a threshold temperature due to the destruction of the microstructure of the heat-sensitive material, accompanied by the fusion of particles of the solid phase, a decrease in the volume fraction of voids and an increase in its transparency with the manifestation of the color of the dielectric part.

16. A cable lug according to claim 15, wherein the solid phase of the heat-sensitive material comprises an organic substance containing a structural fragment Cn H(2n+i), where n > 5 and preferably selected from the group: fatty aliphatic acids containing structural fragments C n H(2n+i) with n > 12; salts of fatty aliphatic acids containing structural fragments C n H(2n+i) with n > 5; alkanes containing at least 20 carbon atoms; dialkylphosphinic acids containing structural fragments C n H(2n+i) with n > 5; fatty acid amides containing structural fragments C n H(2n+i) with n > 5; fatty acid anhydrides containing structural fragments C n H(2n+i) with n > 10; fatty aliphatic alcohols containing structural fragments C n H(2n+i) with n > 14; fatty aliphatic amines containing structural fragments C n H(2n+i) with n > 17; nitriles of fatty aliphatic acids containing structural fragments C nH(2n+i) with n>19 is preferably selected from the group: palmitic acid, stearic acid, behenic acid, tetracosane, erucamide, stearyl alcohol, cetyl alcohol, polyethylene, wax, paraffin, salts of saturated fatty carboxylic acids of rare earth metals, in particular lanthanum, yttrium, ytterbium, scandium.

17. A cable lug according to item 15, in which the volume content of the solid phase in the heat-sensitive material is no more than 90 vol.%.

18. A cable lug according to claim 1, wherein the heat-sensitive material contains a polymer binder that is transparent to at least part of the visible light in an amount of 1-30 vol.%.

19. A cable lug according to claim 1, wherein the heat-sensitive material is designed to change transparency when heated to a temperature exceeding the threshold, preferably in a range not exceeding 5 °C, preferably not exceeding 2 °C relative to the threshold temperature, and for no more than 5 seconds, preferably no more than 2 seconds.

20. A cable lug according to claim 1, characterized in that, with uneven heating, a change in transparency occurs only in that area of the heat-sensitive material that was heated above the threshold temperature.

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