Oil-filled electrical equipment overheating multipoint fault simulation experiment device and method

Abstract

The invention relates to an oil-filled electrical equipment overheating multipoint fault simulation experiment device and method, and belongs to the field of oil-filled electrical equipment monitoring and fault diagnosis. The heating device at least comprises a sealing cavity and a plurality of heating bodies arranged in the sealing cavity, a sealing cover is arranged at the top of the sealing cavity, a plurality of ceramic sleeves penetrate through the sealing cover and are connected to the heating bodies in the cavity, and the suspension height of the heating bodies in the sealing cavity is adjusted according to the lengths of the ceramic sleeves in the sealing cavity, the heating body at least comprises a resistance wire and a spherical shell, the resistance wire is arranged in the spherical shell, and a powdery insulating heat transfer body is filled between the resistance wire and the spherical shell; the spherical shell is connected with the ceramic sleeve and internally penetrates through the joint, the resistance wire is connected with a power line in the ceramic sleeve, and the power line extends out of the sealed tank body through the ceramic sleeve. According to the invention, overheating faults caused by various factors can be simulated, so that the influence of different factors on pyrolysis and gas production of mineral oil is researched.

Description

Technical Field

[0001] The invention belongs to the field of monitoring and fault diagnosis of oil-filled electrical equipment, and relates to an overheating multi-point fault simulation experimental device and method for oil-filled electrical equipment. Background Art

[0002] Oil-filled electrical equipment is widely used in power systems. Timely detection of potential faults within the equipment for diagnosis and evaluation is particularly important for the safe operation of the power system. Overheating faults are the main cause of insulation failure inside the equipment. It is of great significance to find effective ways and methods to determine the severity of discharge faults and overheating faults.

[0003] The existing transformer thermal fault diagnosis methods are all based on the total amount of dissolved gas, type, generation rate, ratio between gases, and the relationship between them to diagnose transformer faults, and do not consider the mechanism factor that the energy required to produce different gases is different. The existing thermal fault experimental device can only simulate single-point faults, while there may be multiple-point faults inside the transformer at the same time. Traditional diagnosis does not consider multiple-point faults. In the actual process of fault generation and development, different factors such as fault temperature, fault volume size, heat generation power per unit area, and fault location inside the transformer will affect the thermal decomposition of transformer oil, affect the gas production process of the fault, and then affect the diagnosis of transformer fault type and fault severity in practice.

[0004] The existing mineral oil pyrolysis device does not take into account the fault temperature, the size of the fault volume, the heat power per unit area of ​​the fault, the location of the fault inside the transformer, and whether the fault exists in multiple locations. Therefore, it is impossible to accurately simulate the entire pyrolysis process under the existing experimental conditions, and it is difficult to accurately judge the severity of the discharge fault. Summary of the invention

[0005] In view of this, an object of the present invention is to provide an overheating multi-point fault simulation experiment device and method for oil-filled electrical equipment.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] A multi-point overheating fault simulation experiment device for oil-filled electrical equipment, the device at least comprises a sealed cavity and a plurality of heating elements arranged inside the sealed cavity, a sealing cover is arranged on the top of the sealed cavity, a plurality of ceramic sleeves penetrate the sealing cover and are connected to the plurality of heating elements inside the cavity, the heating elements adjust their suspended height in the sealed cavity according to the length of the ceramic sleeve in the sealed cavity, wherein the heating elements at least comprise a resistance wire and a spherical shell, the resistance wire is arranged inside the spherical shell, a powdered insulating heat transfer body is filled between the resistance wire and the spherical shell; the spherical shell is connected to the ceramic sleeve and penetrates inside at the connection, the resistance wire is connected to a power line inside the ceramic sleeve, and the power line extends to the outside of the sealed tank body through the ceramic sleeve.

[0008] Furthermore, the sealing cavity is designed as a cylindrical hollow cavity, the sealing cover adopts a flange structure, is installed by a plurality of fastening screws, and the penetration between the ceramic sleeve and the sealing cover is sealed by an insulating sleeve.

[0009] Furthermore, the thickness of the sealed cavity is determined at least according to the internal pressure and the external pressure it bears, wherein:

[0010] 1) When subjected to internal pressure, the thickness S of the sealed cavity i satisfy:

[0011]

[0012] In the formula, P is the limit allowable pressure; D is the cavity diameter of the container; C is the additional thickness, and σ is the allowable stress of the material. The calculation formula is:

[0013]

[0014] In the formula, σ b is the lower limit of the standard tensile strength of the material; σ s is the standard room temperature yield point of the material; n b is the safety factor of tensile strength; n s is the safety factor of the yield point;

[0015] 2) When subjected to external pressure, the thickness S of the sealing cavity o satisfy:

[0016]

[0017] Where P a is the critical external pressure; D is the cavity diameter of the container; E is the elastic modulus of the material used to seal the cavity;

[0018] Finally, the thickness of the sealed cavity is determined comprehensively based on the test temperature, container perforation and the airtightness of the perforation.

[0019] Furthermore, a plurality of oil extraction holes at different heights are arranged on one side of the sealed cavity, and a plurality of temperature sensors at different heights are arranged on the other side. Both the oil extraction holes and the temperature sensors are designed with air cushion sealing and fixed with external screws.

[0020] Furthermore, a movable probe is arranged on the temperature sensor, and an armored thermocouple is used for parallel movement.

[0021] Furthermore, the material used for the sealing cavity is austenitic high alloy steel.

[0022] Furthermore, the material of the resistance wire of the heating element is iron-aluminum alloy; the material of the spherical shell of the heating element is austenitic high-alloy steel; the insulating heat transfer body of the heating element is made of alumina powder, and the alumina powder is compressed and compacted.

[0023] The present invention also proposes a simulation experiment method using the aforementioned oil-filled electrical equipment overheating multi-point fault simulation experiment device, which adjusts the temperature of the heating element through a single-phase contact AC voltage regulator to simulate the temperature of different faults; simulates multi-point faults by adjusting the number of heating elements; simulates different fault positions by adjusting the vertical position of the heating element; and simulates the size of the fault volume by adjusting the volume of the heating element.

[0024] The beneficial effects of the present invention are:

[0025] The device of the present invention can simulate overheating faults caused by different fault temperatures, fault volume sizes, heating power per unit area of ​​the fault, and different positions and numbers of faults inside the transformer, so as to facilitate the study of the influence of the heat source surface temperature, heat source heating time, heat source surface heating power, and the position and number of faults inside the transformer on the pyrolysis and gas production of mineral oil. The device has a simple structure and is easy to operate, can achieve good experimental results, and is conducive to accurately evaluating the status of the oil filling equipment.

[0026] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0028] Figure 1 A cross-sectional view of the oil-filled electrical equipment overheating multi-point fault simulation experimental device of the present invention;

[0029] Figure 2It is a top view of the oil-filled electrical equipment overheating multi-point fault simulation experimental device of the present invention.

[0030] Figure numerals: 1-ceramic sleeve; 2-insulating sleeve; 3-fastening screw; 4-sealing cover; 5-sealing cavity; 6-temperature sensor; 7-oil extraction hole; 8-heating element. DETAILED DESCRIPTION

[0031] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0032] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0033] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0034] See also Figure 1-2 , which is a simulation experimental device and method for overheating multi-point faults of oil-filled electrical equipment.

[0035] Example

[0036] This embodiment provides a multi-point fault simulation experiment device for overheating of oil-filled electrical equipment. Figure 1The cross-sectional view of the overheating multi-point fault simulation experimental device of the oil-filled electrical equipment shown in the figure at least comprises a sealed cavity 5 and a plurality of heating elements 8 placed inside the sealed cavity 5. A sealing cover is arranged on the top of the sealed cavity 5. A plurality of ceramic sleeves 1 penetrate the sealing cover and are connected to the plurality of heating elements 8 inside the cavity. The heating element 8 adjusts its suspended height in the sealed cavity 5 according to the length of the ceramic sleeve 1 in the sealed cavity 5.

[0037] The heating element 8 at least includes a resistance wire and a spherical shell, the resistance wire is placed inside the spherical shell, and a powdered insulating heat transfer body is filled between the resistance wire and the spherical shell; the spherical shell is connected to the ceramic sleeve 1 and penetrates the inside at the connection, the resistance wire is connected to the power line inside the ceramic sleeve 1, and the power line extends to the outside of the sealed tank through the ceramic sleeve 1. The power line is connected to an external power supply to provide power for the resistance wire.

[0038] Since most faults are local single-point faults and are relatively concentrated, the fault location can be abstracted into a relatively negligible particle relative to the bulky transformer as a whole. Therefore, in the design, the present invention uses a symmetrical solid structure to simulate the shape of the fault. Considering the simple structure of winding the resistance wire, it is directly immersed in the transformer oil. It has been found through experiments that this approach has the following disadvantages: ① The exposed resistance wire is very easy to break during the heating process; ② The windings are difficult to isolate, and short circuits are caused by mutual contact; ③ After long-term heating, the resistance wire is very easy to oxidize, and an oxide film is formed on the surface, which affects the heat transfer performance. Therefore, a stainless steel shell can be applied to the outside of the resistance wire to standardize the fault shape. Alumina powder can be selected as an insulating heat transfer body between the spherical shell and the resistance wire. Alumina powder has good insulation performance and can withstand high temperatures up to 2000°C. It has good thermal conductivity and a thermal conductivity coefficient of 36K / [W / (m·K)], and its heat transfer performance is second only to metal. In order to prevent short circuits between the iron-aluminum resistance wires and the expansion of the gas inside during heating to cause a small explosion, the internal alumina powder needs to be compressed to ensure good insulation between the resistance wires and no gas filling. Due to process limitations, the shell shape uses a more symmetrical spherical structure.

[0039] The resistance wire of this embodiment selects iron-iron aluminum alloy as the heat source. In conventional transformers, the hot spot temperature is concentrated at 120°C. When it is higher than 120°C, the transformer will be damaged. When there is a fault in the transformer, the temperature of the fault point can reach up to 750°C. Among various materials, only metals can reach such a high temperature and have a strong ability to withstand stress and are not easy to break. In addition, metal materials have a high heat transfer coefficient. The heat transfer coefficient of stainless steel is 460K / [W / (m·K)], which can dissipate heat outward faster to achieve the purpose of fault simulation. Therefore, it was finally determined that the heat source material was iron-iron aluminum alloy. The resistivity of iron-iron aluminum alloy is ρ=1.4×10-6Ω·m, and the best temperature resistance can reach 1400°C. It has the advantages of large heating power and high melting point, which can meet the requirements of fault simulation.

[0040] Preferably, the sealed cavity 5 is designed as a cylindrical hollow cavity. The shape of the sealed cavity 5 is determined by considering that the transformer volume is relatively large in actual situations, while the fault volume is relatively small relative to the overall volume, which is equivalent to the fault being filled with transformer oil around the fault and being infinitely and symmetrically distributed outward. In order to simulate a more common and typical thermal fault, a more symmetrical structure is selected to be closer to the actual situation. Considering the pressure bearing performance, we choose the commonly used cylindrical shape.

[0041] Preferably, the thickness of the sealed cavity 5 is determined based on the internal pressure and external pressure it bears. The thickness of the sealed cavity 5 is a most critical parameter. During the fault simulation process, the transformer oil will decompose and produce a certain amount of gas, causing the pressure in the sealed cavity 5 to increase. Therefore, the thickness of the sealed cavity 5 must be sufficient to withstand the stress under the maximum pressure to reduce the danger of the experiment. The calculation of the cylinder thickness is as follows:

[0042] 1) When subjected to internal pressure, the wall thickness of the experimental device is:

[0043]

[0044] In the formula, S i is the calculated value of the cavity wall thickness when subjected to internal pressure; P is the limit allowable pressure; D is the cavity diameter of the container; C is the additional thickness. σ is the allowable stress of the material, and its calculation formula is:

[0045]

[0046] In the formula, σ b is the lower limit of the standard tensile strength of the material; σ s is the standard room temperature yield point of the material; n b is the safety factor of tensile strength; n s is the safety factor at the yield point.

[0047] my country's JB4732 standard stipulates that the design stress intensity is the application value of the overall primary membrane stress. It is obtained by dividing the short-term tensile properties of the mature material by the corresponding safety factor. The allowable stress is shown in Table 1.

[0048] Table 1

[0049]

[0050] In Table 1, It is the yield point of steel at a set temperature. ① It is used for containers with slight permanent deformation. 2) When subjected to external pressure, the wall thickness S of the experimental device o satisfy:

[0051]

[0052] Where P a is the critical external pressure; D is the cavity diameter of the container; E is the elastic modulus of the material used.

[0053] For a cylinder with a diameter of d = 15 cm and a height of h = 40 cm, the transformer oil density inside it is ρ = 825.4 Kg / m 3 , room temperature T = 20 ° C, the maximum internal pressure P = ρgh + P0 ≈ 0.1MPa, [σ] = 26.7MPa, considering the test conditions C = 0.5-1mm, calculated S i ≈2mm. According to the experimental conditions P a =0.1MPa, E=172-200GPa. S O =1.8mm. Considering the test temperature, the perforation of the container, the airtightness of the perforation, and the pressure bearing capacity, the wall thickness of the sealing cavity 5 can be 10mm.

[0054] The material of the sealed cavity 5 of this embodiment is austenitic high alloy steel. Considering the structure of the box of oil-filled electrical equipment such as actual transformers, it must first have good mechanical properties to withstand the stress of the operation process. Secondly, the transformer must also have good thermal conductivity to facilitate timely heat dissipation. Some acid will be produced during the decomposition process of transformer oil, so it must also have good high temperature resistance and corrosion resistance. Considering the possibility of gas measurement and temperature measurement and the cost of materials, stainless steel is the most ideal choice.

[0055] Preferably, if Figure 2As shown, the sealing cover of the sealing cavity 5 adopts a flange structure, which is installed by a number of fastening screws 4, and the penetration of the ceramic sleeve 1 and the sealing cover is sealed by an insulating sleeve 2. In order to improve the accuracy of the detection of dissolved gas in oil, during the experiment, the sealing cavity 5 adopts an absolutely sealed design. Therefore, the design of the sealing cover adopts a flange structure, and an insulating sleeve 2 is installed, which is fixed with screws around. This sealing structure can withstand the stress of 5 atmospheres, which well ensures the sealing of the device and the safety of the experiment. The contact between the ceramic sleeve 1 and the sealing cover is sealed with a special high-temperature solid glue. When the oil is not taken, the sealing cavity 5 is completely sealed.

[0056] Preferably, a plurality of oil extraction holes 7 of different heights are arranged on one side of the sealed cavity 5, and a plurality of temperature sensors 6 of different heights are arranged on the other side, and both the oil extraction holes 7 and the temperature sensors 6 are designed with air cushion sealing and fixed with external screws. This design can effectively ensure that during the experiment, when the temperature sensor 6 probe moves horizontally at will, mineral oil will not leak out from the oil extraction holes 7 or the temperature sensor 6 installation holes.

[0057] This embodiment also proposes a simulation experiment method based on the aforementioned oil-filled electrical equipment overheating multi-point fault simulation experiment device, which adjusts the temperature of the heating element through a single-phase contact AC voltage regulator to simulate the temperature of different faults; simulates multi-point faults by adjusting the number of heating elements; simulates different fault positions by adjusting the vertical position of the heating element; and simulates the size of the fault volume by adjusting the volume of the heating element.

[0058] For temperature control, a single-phase contact AC voltage regulator STG-500W is used for voltage regulation and temperature control. The voltage output range is between 0-300V, and the maximum output power can reach 500W, which meets the power supply requirements of the heat source. Connecting a voltage regulator at the power supply can accurately control the voltage value. When the resistance value is constant, controlling the voltage is equivalent to controlling the power of the heating element. In a stable state, the heat dissipation power of the heating element to the surrounding is relatively fixed. When the heat generation power and heat dissipation power of the heat source are stable, its temperature can be stabilized at a certain value. As the voltage value increases, the stable temperature of the heat source continues to increase, so that overheating faults at different temperatures can be simulated.

[0059] The device is provided with three heating elements 8, and can simulate multiple fault points inside the transformer by changing the number of heating elements; simulate faults at different positions inside the transformer by vertically moving the positions of the heating elements; and simulate the size of the fault volume by changing the volume of the heating elements.

[0060] The oil-filled electrical equipment overheating multi-point fault simulation experimental device of the present invention can simulate overheating fault tests caused by factors such as the temperature of different faults, the size of the fault volume, and the different positions and numbers of faults inside the transformer, thereby facilitating the study of the influence of the heat source surface temperature, the heat source heating time, the heat source surface heating power, and the position and number of faults inside the transformer on the pyrolysis and gas production of mineral oil, and then accurately judging the severity of the discharge fault.

[0061] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. An oil-filled electrical equipment overheating multi-point fault simulation experimental device, characterized in that: The device comprises at least a sealed cavity and a plurality of heating elements (8) disposed inside the sealed cavity (5); a sealing cover (4) is disposed on the top of the sealed cavity (5); a plurality of ceramic sleeves (1) penetrate the sealing cover (4) and are connected to the plurality of heating elements (8) inside the cavity; the heating elements (8) adjust their suspended height inside the sealed cavity (5) according to the length of the ceramic sleeves (1) inside the sealed cavity (5); wherein: The heating element (8) comprises at least a resistance wire and a spherical shell, wherein the resistance wire is placed inside the spherical shell, and a powdered insulating heat transfer body is filled between the resistance wire and the spherical shell; the spherical shell is connected to a ceramic sleeve (1) and penetrates the inside at the connection, the resistance wire is connected to a power line inside the ceramic sleeve (1), and the power line extends to the outside of the sealed tank through the ceramic sleeve (1).

2. The oil-filled electrical equipment overheating multi-point fault simulation experimental device according to claim 1 is characterized by: The sealing cavity (5) is designed as a cylindrical hollow cavity, the sealing cover (4) adopts a flange structure and is installed by means of a plurality of fastening screws (3), and the penetration point between the ceramic sleeve (1) and the sealing cover (4) is sealed by means of an insulating sleeve (2).

3. The overheating multi-point fault simulation experimental device for oil-filled electrical equipment according to claim 2 is characterized in that: The thickness of the sealed cavity (5) is determined at least in accordance with the internal pressure and the external pressure it bears, wherein: 1) When subjected to internal pressure, the thickness S of the sealing cavity (5) is i satisfy: In the formula, S i The minimum wall thickness under the internal pressure, P is the limit allowable pressure; D is the cavity diameter of the container; C is the additional thickness, σ is the allowable stress of the material, and the calculation formula is: In the formula, σ b is the lower limit of the standard tensile strength of the material; σ s is the standard room temperature yield point of the material; n b is the safety factor of tensile strength; n s is the safety factor of the yield point; 2) When subjected to external pressure, the thickness S of the sealing cavity (5) is o satisfy: In the formula, S o The minimum wall thickness under the internal pressure, P a is the critical external pressure; D is the cavity diameter of the container; E is the elastic modulus of the material used for the sealing cavity (5); Finally, the thickness of the sealed cavity (5) is determined comprehensively based on the test temperature, the perforation of the container and the airtightness of the perforation.

4. The overheating multi-point fault simulation experimental device for oil-filled electrical equipment according to claim 1 is characterized in that: A plurality of oil extraction holes (7) with different heights are arranged on one side of the sealed cavity (5), and a plurality of temperature sensors (6) with different heights are arranged on the other side. The oil extraction holes (7) and the temperature sensors (6) are both designed with air cushion sealing and fixed with external screws.

5. The overheating multi-point fault simulation experimental device for oil-filled electrical equipment according to claim 1 is characterized in that: A movable probe is arranged on the temperature sensor (6), which adopts an armored thermocouple and moves in the horizontal direction.

6. The overheating multi-point fault simulation experimental device for oil-filled electrical equipment according to claim 1 is characterized by: The material used for the sealing cavity (5) is austenitic high alloy steel.

7. The overheating multi-point fault simulation experimental device for oil-filled electrical equipment according to claim 1 is characterized by: The material of the resistance wire of the heating element (8) is iron-iron aluminum alloy; the material of the spherical shell of the heating element (8) is austenitic high-alloy steel; the insulating heat transfer body of the heating element (8) is made of aluminum oxide powder, and the aluminum oxide powder is compressed and compacted.

8. A simulation experiment method using the oil-filled electrical equipment overheating multi-point fault simulation experiment device according to any one of claims 1 to 7, characterized in that: The temperature of the heating element is adjusted by a single-phase contact AC voltage regulator to simulate the temperature of different faults; multi-point faults are simulated by adjusting the number of heating elements; different fault locations are simulated by adjusting the vertical position of the heating element; and the size of the fault volume is simulated by adjusting the volume of the heating element.

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