Power system secondary circuit fuse failure monitoring method and device

Abstract

The application is suitable for the technical field of power system fault monitoring, and provides a power system secondary circuit fuse fault monitoring method and device. The method comprises the following steps: constructing a temperature field model and a circuit model of a fuse, determining an equivalent resistance of the fuse when the fuse is faulty according to the temperature field model and the circuit model; acquiring real-time current, real-time voltage and heat dissipation power of the fuse, calculating temperature rise power of the fuse according to the real-time current, the real-time voltage and the heat dissipation power, and determining the temperature of the fuse according to the temperature rise power; calculating the theoretical resistance of the fuse according to the temperature of the fuse, and performing fault monitoring on the fuse according to the theoretical resistance and the equivalent resistance. The application can diagnose the early fault state of the fuse when the fuse melts for the first time according to the two resistances, so as to early warn the secondary circuit.

Description

Technical Field

[0001] This application belongs to the field of power system fault monitoring technology, and in particular relates to a method and device for monitoring faults in secondary circuit fuses of power systems. Background Technology

[0002] In power systems, the secondary circuits are used to monitor, control, and protect primary equipment. They play a vital role in ensuring the safe operation of the power system. To determine whether the secondary circuits are operating normally, it is necessary to monitor the working status of the secondary equipment in real time. Therefore, it is especially important to accurately identify secondary equipment faults and issue fault warnings.

[0003] As a short-circuit and overcurrent protector, fuses are widely used in power systems due to their simple construction and ease of use. Connected in series in the secondary circuit of a power system, a fuse heats the fuse element when the current in the circuit increases to a certain value, such as in the event of an overload or short circuit. The fuse element melts before the temperature of the protected equipment reaches a point where it can damage the insulation, thus breaking the circuit and protecting the equipment.

[0004] Traditional circuit breaker fault detection is usually based on the voltage across the fuse. For example, during the operation of the secondary circuit of a power system, the voltage across the fuses of phase A and phase C of the secondary circuit is collected in real time. The two voltages are input into the detection circuit, which outputs a signal. Based on this signal, the state of the fuse can be determined as normal or faulty, thereby enabling corresponding control of the secondary circuit.

[0005] However, by the time this circuit breaker fault detection method detects a fuse failure, the fuse has already blown, making it impossible to diagnose the early fault of the fuse in time so that appropriate measures can be taken to address it promptly. Summary of the Invention

[0006] To overcome the problems existing in related technologies, this application provides a method and device for monitoring the faults of secondary circuit fuses in power systems.

[0007] This application is achieved through the following technical solution: In a first aspect, embodiments of this application provide a method for monitoring faults in secondary circuit fuses of a power system, including: A temperature field model and a circuit model of a fuse are constructed. The temperature field model includes a first boundary condition and a second boundary condition. The first boundary condition is the boundary condition corresponding to the contact between the two ends of the fuse element and the air. The second boundary condition is the boundary condition corresponding to the contact between the fuse element and the quartz sand. Determine the equivalent resistance of the fuse when it fails based on the temperature field model and the circuit model; The real-time current, real-time voltage, and heat dissipation power of the fuse are obtained; the temperature rise power of the fuse is calculated based on the real-time current, the real-time voltage, and the heat dissipation power; and the temperature of the fuse is determined based on the temperature rise power. The theoretical resistance of the fuse is calculated based on its temperature, and the fuse is then monitored for faults based on the theoretical resistance and the equivalent resistance.

[0008] In conjunction with the first aspect, in some embodiments, the process of constructing a temperature field model of the fuse is as follows: Set the fuse element to a length of [length missing]. l For a cylindrical body with a length d, the length of the melt is much greater than the radius of the cross-section, and there is a temperature difference between the melt on both sides and the melt inside in the transverse direction; x The unit melt, in d x The temperature of the unit melt is the same within the length range; According to the principle of energy conservation, the differential equation for the heat conduction of a single melt is: in, For the heat passing through the first end of the unit melt, For the heat passing through the second end of the unit melt, This refers to the heat generated per unit volume of melt per unit time. This represents the voltage corresponding to the unit melt. According to the theory of heat transfer, the formulas for calculating the heat in each part are as follows: Where λ is the thermal conductivity coefficient of the melt. r Where is the radius of the melt cross-section, and T is the unit melt temperature. ρ The density of the melt material, c The specific heat capacity of the molten material. t For time; Therefore, the temperature field model of the melt is obtained as follows: V represents the field under study.

[0009] In conjunction with the first aspect, in some embodiments, the melt satisfies the first boundary condition at both ends and the contact surface. Second boundary conditions A certain end face of the melt is in contact with air, and the temperature of the air that convects with the end face of the melt is known. T 0 and the conversion coefficient αThe heat flux density per unit time at the interface between the two ends of the melt and the air can be obtained, thus yielding the first boundary condition. for , x =0 or x = l 0, t >0, n x Let be the normal vector of an arbitrary element's melt cross section; the melt and the silica sand have a contact surface, and the thermal conductivity of the silica sand is known to be... β The thickness of the quartz sand is d The outer layer temperature is T 0 and the radius of the melt cross section is r The heat flux density at the interface between the melt and the quartz sand can be obtained, thus yielding the second boundary condition. for .

[0010] In conjunction with the first aspect, in some embodiments, the process of constructing the circuit model of the fuse is as follows: Treat the fuse as a resistor with a preset resistance value. R Furthermore, a linear resistor with a uniform resistance distribution can be divided into n unit resistors connected in series, with the resistance of each unit resistor being a preset resistance value divided by 1 / 2. n ; When the fuse is put into operation, it carries load current or short-circuit current for a long time. The fusible element melts faster and becomes thicker. The linear resistance changes from a series configuration to a configuration with multiple resistors in parallel on two branches and multiple single resistors in parallel on multiple branches. The parallel configuration of the two branches with multiple resistors is as follows: x A unit resistor connected in series n - x A single unit resistor is connected in series, and two series branches are connected in parallel; the configuration of multiple branches with single resistors in parallel is as follows: n - x A unit resistor connected in series x Each unit resistor is connected in parallel with a series branch.

[0011] In conjunction with the first aspect, in some embodiments, determining the equivalent resistance of the fuse when it fails based on the temperature field model and the circuit model includes: When the linear resistor changes from a series connection to a parallel connection of two branches with multiple resistors, the resistance of the fuse becomes... R x = R -15 x / n , x < n / 2; When the linear resistor changes from a series configuration to a configuration of multiple branches with single resistors in parallel, the resistance of the fuse becomes Rx = R -20 x / n +R / nx , x < n / 2; When the unit resistance of the linear resistor is sufficiently small and n is sufficiently large, R / nx The resistance of the fuse is approximately 0, therefore the resistance of the fuse at this time becomes... R x = R -20 x / n , x < n / 2; Based on the resistance of the fuse in both states, the equivalent resistance when the fuse fails is located at... R -15 x / n and R -20 x / n between.

[0012] In conjunction with the first aspect, in some embodiments, calculating the temperature rise power of the fuse based on the current, the voltage, and the heat dissipation power, and determining the temperature of the fuse based on the temperature rise power, includes: The power of the melt temperature rise is , for t The power of temperature rise of the melt at any given time for t The voltage across the fuse is constant. for t The resistance value of the fuse at all times. P This refers to heat dissipation power; Set the temperature rise power at the previous moment to be The current temperature rise power is The heat generated by the melt is ; The temperature of the melt at the current moment is , c The specific heat capacity of the melt. for t The heat generated by the melt at all times, for t The temperature of the melt at all times, for The temperature of the melt at any given time.

[0013] In conjunction with the first aspect, in some embodiments, calculating the theoretical resistance of the fuse based on its temperature includes: The theoretical resistance of the melt is , K The temperature coefficient of the melt resistance. R on This is the resistance when the melt is normally conducting.

[0014] In conjunction with the first aspect, in some embodiments, the step of fault monitoring of the fuse based on the theoretical resistance and the equivalent resistance includes: If the temperature of the melt Temperature above the melting point of the melt T max Then the melt is in a broken state at the narrow neck; If the temperature of the melt greater than temperature T 0 and less than or equal to temperature T max If so, the melt is in the initial melting state; If the theoretical resistance Greater than or equal to the maximum resistance of the melt R off If the arc is extinguished, the fuse will be in the open state.

[0015] In conjunction with the first aspect, in some embodiments, the power system secondary circuit fuse fault monitoring method further includes: The real-time temperature waveform of the fusible element when the fuse enters the early fault state is obtained through simulation. If the temperature waveform of the molten metal is detected to be consistent with the real-time temperature waveform, it is determined that the fuse has entered an early fault state.

[0016] Secondly, embodiments of this application provide a power system secondary circuit fuse fault monitoring device, comprising: The model building module is used to build the temperature field model and circuit model of the fuse. The temperature field model includes a first boundary condition and a second boundary condition. The first boundary condition is the boundary condition corresponding to the contact between the two ends of the fuse molten element and the air, and the second boundary condition is the boundary condition corresponding to the contact between the molten element and the quartz sand. The resistance determination module is used to determine the equivalent resistance of a fuse when it fails, based on the temperature field model and the circuit model. The calculation module is used to obtain the real-time current, real-time voltage and heat dissipation power of the fuse, calculate the temperature rise power of the fuse based on the real-time current, the real-time voltage and the heat dissipation power, and determine the temperature of the fuse based on the temperature rise power. The fault monitoring module is used to calculate the theoretical resistance of the fuse based on the temperature of the fuse, and to perform fault monitoring on the fuse based on the theoretical resistance and the equivalent resistance.

[0017] The beneficial effects of the embodiments in this application compared with the prior art are: In this embodiment, a temperature field model and a circuit model of the fuse are first constructed, and the equivalent resistance of the fuse when a fault occurs is determined based on these models. Then, the real-time current, real-time voltage, and heat dissipation power of the fuse are acquired. The temperature rise power of the fuse is calculated based on these data, and the temperature of the fuse is determined based on the temperature rise power. Finally, the theoretical resistance of the fuse is calculated based on its temperature. Fault monitoring of the fuse is performed based on the theoretical resistance and the equivalent resistance. This allows for the diagnosis of early fault states when the fuse element initially melts, enabling early fault warnings for the secondary circuit, rather than detecting specific fault information after the fuse has completely broken.

[0018] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit this specification. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a flowchart illustrating a method for monitoring the faults of secondary circuit fuses in a power system according to an embodiment of this application. Figure 2 This is a schematic diagram of the physical process of fuse element melting according to an embodiment of this application; Figure 3 This is a schematic diagram of the selection of unit melt provided in an embodiment of this application; Figure 4 This is a schematic diagram of the heat of a unit melt provided in an embodiment of this application; Figure 5 This is a schematic diagram of a circuit model of a fuse provided in one embodiment of this application; Figure 6 This is a schematic diagram of two branches with multiple resistors connected in parallel according to an embodiment of this application; Figure 7 This is a schematic diagram of multiple branch single resistors connected in parallel according to an embodiment of this application; Figure 8 This is a schematic diagram of the structure of a power system secondary circuit fuse fault monitoring device provided in one embodiment of this application. Detailed Implementation

[0021] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of this application. However, those skilled in the art will understand that this application may also be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods have been omitted so as not to obscure the description of this application with unnecessary detail.

[0022] It should be understood that, when used in this application specification and the appended claims, the term "comprising" indicates the presence of the described features, integrals, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or a collection thereof.

[0023] It should also be understood that the term “and / or” as used in this application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0024] As used in this application specification and the appended claims, the term "if" may be interpreted, depending on the context, as "when," "once," "in response to determination," or "in response to detection." Similarly, the phrase "if determined" or "if detected [the described condition or event]" may be interpreted, depending on the context, as meaning "once determined," "in response to determination," "once detected [the described condition or event]," or "in response to detection [the described condition or event]."

[0025] Furthermore, in the description of this application and the appended claims, the terms "first," "second," "third," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0026] References to "one embodiment" or "some embodiments" as described in this specification mean that one or more embodiments of this application include a specific feature, structure, or characteristic described in connection with that embodiment. Therefore, the phrases "in one embodiment," "in some embodiments," "in other embodiments," "in still other embodiments," etc., appearing in different parts of this specification do not necessarily refer to the same embodiment, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized. The terms "comprising," "including," "having," and variations thereof mean "including but not limited to," unless otherwise specifically emphasized.

[0027] Figure 1 This is a flowchart illustrating a power system secondary circuit fuse fault monitoring method according to an embodiment of this application, with reference to... Figure 1The detailed description of the fault monitoring method for secondary circuit fuses in this power system is as follows: Step 101: Construct the temperature field model and circuit model of the fuse.

[0028] For example, the process of constructing a temperature field model for a fuse is as follows: Set the fuse element to a length of [length missing]. l For a cylindrical body with a length d, the length of the melt is much greater than the radius of the cross-section, and there is a temperature difference between the melt on both sides and the melt inside in the transverse direction; x The unit melt, in d x The temperature of the unit melt is the same within the length range; According to the principle of energy conservation, the differential equation for the heat conduction of a single melt is: in, For the heat passing through the first end of the unit melt, For the heat passing through the second end of the unit melt, This refers to the heat generated per unit volume of melt per unit time. This represents the voltage corresponding to the unit melt. According to the theory of heat transfer, the formulas for calculating the heat in each part are as follows: Where λ is the thermal conductivity coefficient of the melt. r Where is the radius of the melt cross-section, and T is the unit melt temperature. ρ The density of the melt material, c The specific heat capacity of the molten material. t For time; Therefore, the temperature field model of the melt is obtained as follows: V represents the field under study.

[0029] The melt satisfies the first boundary condition at both ends and the contact surface. Second boundary conditions A certain end face of the melt is in contact with air, and the temperature of the air that convects with the end face of the melt is known. T 0 and the conversion coefficient α The heat flux density per unit time at the interface between the two ends of the melt and the air can be obtained, thus yielding the first boundary condition. for , x =0 or x = l 0, t >0,n x Let be the normal vector of an arbitrary element's melt cross section; the melt and the silica sand have a contact surface, and the thermal conductivity of the silica sand is known to be... β The thickness of the quartz sand is d and the radius of the melt cross section is r The heat flux density at the interface between the melt and the quartz sand can be obtained, thus yielding the second boundary condition. for .

[0030] See Figure 2 First, we will introduce the physical process of fuse element melting. Figure 2 middle, T 0、 T 熔 and T 沸 These represent the initial ambient temperature, melting point temperature, and boiling point temperature of the fuse element, respectively. t 1 represents the time it takes for the melt to reach its melting point from its initial ambient temperature. t 2 represents the melting time of the melt. t 3 represents the time between complete melting and the boiling point temperature of the melt; t 4 represents the vaporization time of the molten material. The normal fusing process of a fuse may include: If the current through the melt exceeds the rated minimum breaking current, the heat generated by the melt will increase and exceed the heat dissipation, thus causing the temperature to rise. exist t At point 1, the melt reaches its melting point and becomes liquid. The transition from solid to liquid requires the accumulation of latent heat of fusion, so the melt will melt under isothermal conditions. In this state, all the heat generated by the melt's temperature rise is converted into latent heat of fusion. t At step 2, the melt will turn into a liquid state; go through t After step 2, the temperature of the melt will increase at a faster rate. t 3. When the temperature reaches boiling point, the evaporation of the melt also requires the accumulation of latent heat of vaporization. Therefore, the melt will evaporate at a constant temperature. Under these circumstances, the heat generated by the melt will also be converted into latent heat of vaporization. when t 4. After the time is up, all the molten material turns into steam, which forms an electric arc and is extinguished by the arc-quenching agent, thus achieving melting and breaking.

[0031] Typically, the fuse element is a single silver wire, shaped like a cylinder. The fuse element generates heat through Joule heating of the current. However, the heat dissipation methods of the fuse elements at both ends and the inner fuse element differ: the inner fuse element dissipates heat through conduction with the quartz sand contact surface, while the fuse elements at both ends dissipate heat through convection with the air contact surface and conduction with the quartz sand contact surface. Therefore, there can be a temperature difference between the fuse elements at both ends and the inner fuse element.

[0032] Because the melt length is much larger than the interface radius, and there is a temperature difference between the melt on both sides and the internal melt in the transverse direction, the melt cannot be considered as a single entity for analyzing temperature changes. Assume: In the transverse direction, i.e. x The axial direction is selected with a length of d. x Unit melt (set melt length as) l 0); within this length range, the temperature of the unit melt is the same, such as Figure 3 As shown.

[0033] See Figure 4 According to the law of conservation of energy, the differential equation for the heat conduction of a single melt is: in, The heat generated at the first end of the unit melt. The heat generated at the second end of the unit melt. This refers to the heat generated per unit volume of melt per unit time. This represents the voltage corresponding to the unit melt.

[0034] According to heat transfer theory, the formulas for calculating the heat in each part are as follows: Where λ is the thermal conductivity coefficient of the melt. r The radius of the melt cross section, T The unit melt temperature, ρ The density of the melt material, c The specific heat capacity of the molten material. t For time.

[0035] Therefore, the temperature field equation for the melt can be obtained as follows: In the formula, V represents the field under study.

[0036] At the initial moment, assuming the melt is in a cold state before the current flows through it, and the initial temperature is the ambient temperature, for example, 22℃, then the initial conditions can be: T =T 0, t =0.

[0037] The melt satisfies the first boundary condition at both ends and the contact surface. Second boundary conditions Since one end face of the melt is in contact with air, the temperature of the air that convects with the melt end face is known. T 0 and the conversion coefficient α The heat flux density per unit time at the interface between the two ends of the melt and the air can be obtained, thus yielding the first boundary condition. for: , x =0 or x = l 0, t >0 n x Let be the normal vector of an arbitrary element cross-section of the melt. According to heat transfer theory, there is a contact surface between the melt and the silica sand. The thermal conductivity of the silica sand is known to be... β The thickness of the quartz sand is d and the radius of the melt cross section is r The heat flux density at the interface between the melt and the quartz sand can be obtained, thus yielding the second boundary condition. for .

[0038] The mathematical model of the melt temperature field further confirms that the arc-precursor process of the fuse melt is directly related to its temperature. However, considering the difficulty of directly measuring the melt temperature and electrical parameters, in engineering, the fuse can be used as a substitute for the melt as the specific research object, such as considering the melt temperature as the fuse temperature.

[0039] For example, the process of constructing a circuit model for a fuse is as follows: Treat the fuse as a resistor with a preset resistance value. R Furthermore, a linear resistor with a uniform resistance distribution can be divided into n unit resistors connected in series, with the resistance of each unit resistor being a preset resistance value divided by 1 / 2. n ; R 6 When a fuse is put into operation, it carries load current or short-circuit current for an extended period. The fusible element melts and thickens rapidly, and the linear resistance changes from a series connection to a parallel connection of multiple resistors in two branches or a parallel connection of single resistors in multiple branches. The parallel connection of multiple resistors in two branches is as follows: x A unit resistor connected in series n - x A single unit resistor is connected in series, and two series branches are connected in parallel; the configuration of multiple branches with single resistors in parallel is as follows: n - x A unit resistor connected in series xEach unit resistor is connected in parallel with a series branch.

[0040] Step 102: Determine the equivalent resistance of the fuse when it fails based on the temperature field model and the circuit model.

[0041] For example, the implementation process of step 102 may include: when the linear resistor changes from a series configuration to a parallel configuration of two branches with multiple resistors, the resistance of the fuse becomes R x = R -15 x / n , x < n / 2; When the linear resistor changes from a series configuration to a configuration of multiple branch single resistors in parallel, the resistance of the fuse becomes R x = R -20 x / n +R / nx , x < n / 2; When the unit resistance of the linear resistor is sufficiently small and n is sufficiently large, R / nx The resistance of the fuse is approximately 0, therefore the resistance of the fuse at this time becomes... R x = R -20 x / n , x < n / 2; Based on the resistance of the fuse in both states, the equivalent resistance of the fuse when it fails is located at... R -15 x / n and R -20 x / n between.

[0042] For example, the secondary circuit voltage transformer is equipped with an RN2 type high-voltage fuse with a resistance of 10MΩ. For ease of calculation and analysis, the RN2 type high-voltage fuse (replacing the fuse element) is considered as a linear resistor with a uniform resistance of 10MΩ. This linear resistor can be divided into n unit resistors connected in series, and the resistance of each unit resistor is (10 / n)MΩ, such as... Figure 5 As shown.

[0043] When a new fuse is put into operation, its total resistance remains essentially unchanged because the fusible element is not easily melted. However, once a load current or short-circuit current flows through the fuse for an extended period, the fusible element melts more rapidly, thickens, and its resistance changes from a series connection to a parallel connection. This process can be divided into two scenarios: (1) It becomes a parallel configuration of two branches with multiple resistors, such as Figure 6 As shown.

[0044] When the original series resistors are changed to two branches connected in parallel, the resistance of the high-voltage fuse becomes R x =10-15 x / n , x < n / 2.

[0045] (2) It becomes a configuration of multiple branches with single resistors connected in parallel, such as Figure 7 As shown.

[0046] When the original series resistors are replaced by multiple single resistors connected in parallel, the resistance of the high-voltage fuse becomes... R x =10-20 x / n +10 / nx , x < n / 2. When the units are small enough and n is large enough, 10 / nx The value of is approximately zero, therefore its resistance is calculated as follows: R x =10-20 x / n , x < n / 2.

[0047] Typically, the melting of a high-voltage fuse element involves a combination of two conditions; therefore, its resistance should fall between the values ​​of both conditions, ideally between 10 and 20 ohms. x / n < R x <10-15 x / n , x < n / 2.

[0048] when x When the value of reaches 10% of n, the fusible element clearly melts, indicating a fault in the high-voltage fuse. The high-voltage fuse needs to be replaced promptly to ensure stable operation of the circuit and prevent further malfunctions. When the fusible element initially melts to... x = n At 10 o'clock, we can get R x The resistance range is 0-3 MΩ. That is, when the resistance of the high-voltage fuse reaches 3 MΩ, it can be determined that the high-voltage fuse in operation has failed.

[0049] Step 103: Obtain the real-time current, real-time voltage, and heat dissipation power of the fuse; calculate the temperature rise power of the fuse based on the real-time current, the real-time voltage, and the heat dissipation power; and determine the temperature of the fuse based on the temperature rise power.

[0050] For example, the implementation process of step 103 may include: The power of the melt temperature rise is , for t The power of temperature rise of the melt at any given time for t The voltage across the fuse is constant. for t The resistance value of the fuse at all times. P This refers to heat dissipation power; Set the temperature rise power at the previous moment to be The current temperature rise power is The heat generated by the melt is ; The temperature of the melt at the current moment is , c The specific heat capacity of the melt. for t The heat generated by the melt at all times, for t The temperature of the melt at all times, for The temperature of the melt at any given time.

[0051] Step 104: Calculate the theoretical resistance of the fuse based on its temperature, and perform fault monitoring on the fuse based on the theoretical resistance and the equivalent resistance.

[0052] For example, calculating the theoretical resistance of the fuse based on its temperature in step 104 may include: the theoretical resistance of the fusible element is... , K The temperature coefficient of the melt resistance. R on This is the resistance when the melt is normally conducting. T 0 represents the temperature at which the melt conducts normally, which is the same as the temperature of the air that convects at the melt's end face.

[0053] For example, step 104, which involves fault monitoring of the fuse based on the theoretical resistance and the equivalent resistance, may include: if the temperature of the fusible element... Temperature above the melting point of the melt T max If the temperature of the melt is such that the melt is broken at the neck, then the melt is in a broken state at the neck. greater than temperature T0 and less than or equal to temperature T max Then the melt is in the initial melting state; if the theoretical resistance Greater than or equal to the upper limit resistance value R off If the arc is extinguished, the fuse will be in the open state.

[0054] The embodiments of this application are verified using simulation software in the following sections.

[0055] Specifically, by building a simulation model, the differences in voltage and current frequency bands and the changes in fuse temperature during faults are detected in real time. The Cassie arc algorithm is used to determine the working status of the fuse and to provide timely warnings of fault behavior of the high-voltage side fuse of the voltage transformer.

[0056] According to the black box arc model proposed by electromagnetic simulation software, and combined with a large number of experiments, when the current passing through the arc channel changes, the diameter changes simultaneously, but the temperature does not change at this time. The energy dissipation of the plasma mainly considers the changes in airflow and arc column.

[0057] The electric arc calculation model based on the energy balance principle is as follows: In the formula, This represents the change in energy stored per unit length of the arc column. This represents the power input per unit arc length in the electric arc. This represents the power loss per unit arc length in an electric arc.

[0058] Clearly, the calculation model based on Cassie's arc theory is... In the formula, g The electric arc conductivity, τ is the time constant of the telephone, and uc is a constant arc voltage value, which is generally taken as the peak value of TRV (the short-circuit current that the fuse trips when a short circuit occurs) in calculations.

[0059] Based on the Cassie arc model, the corresponding recursive equation can be obtained by similarly solving it, i.e. At this time, the fuse is in the open state.

[0060] By controlling the switching element connected in parallel with the load, the high-voltage side fuse is set to... t =1s to close the switching element, simulating a typical fault in the system at a specified time. Table 1 shows the melt heat conduction parameters.

[0061] Table 1 Thermal conductivity parameters of the melt Convection heat transfer boundary conditions are set on both sides of the melt and the outer surface of the quartz sand with air. Heat is dissipated through conduction at the contact surface between the melt surface and the quartz sand. A zero potential surface is set on one cross section of the melt, and an AC current load is applied to the other end face.

[0062] To provide early warning of fuse failure, a `Fuse_Cassie_Model` module capable of real-time resistance calculation is added to the fuse model. Three output ports are provided: one for real-time acquisition of fuse voltage, one for calculating fuse element temperature, and one for monitoring the fuse element status. The following is the theoretical derivation of the fault identification algorithm. The calculation method is as follows: assuming a step size of... Fuse resistance Specific heat capacity is c The voltage across the terminals is The normal conduction temperature of the melt is denoted as T 0, the temperature at which the melt reaches its melting point is denoted as . T max The heat dissipation power is P, and the melt temperature is The temperature at the last moment was The temperature coefficient of resistance is K, and the power of melt temperature rise is defined as: Assume the power of temperature rise at the previous moment is The current temperature rise power is Therefore, the heat generated by the fuse is: At this time, the fuse temperature is The working state of the melt is diagnosed based on the temperature at this moment, as follows: When the temperature of the melt Temperature less than the normal conducting state of the fuse T At 0, the fuse temperature is forcibly made equal to the conduction temperature; when the temperature of the molten element... Temperature above the melting point of the melt T max At that time, the melt enters the necked section and breaks apart; when the temperature of the melt... greater than temperature T 0 and less than or equal to temperature T max When the fuse is considered to have entered the initial melting state, the resistance of the fuse element at the next moment is: In the formula, K The temperature coefficient of the melt resistance. R onThis is the resistance when the melt is normally conducting.

[0063] According to this mathematical model, if the calculated melt resistance is greater than or equal to the maximum melt resistance... R off If the arc is extinguished, the fuse is considered to be in the open state. Therefore, real-time calculation and judgment of the change in the fusible element resistance can effectively identify the state before the fuse blows. An alarm can be triggered immediately when a fault occurs in the secondary circuit of the power system, and the switching time should not exceed the moment the arc is extinguished.

[0064] Simulation results show that the larger the current flowing through the fuse, the shorter the required fusing time. When the current flowing through the fuse approaches 0.425kA (the rated fusing current is 0.4 kA), the effective value of the impulse voltage is as high as 2 kV, and the fuse begins to melt, which means it enters the early fault state.

[0065] In addition, the above method may also include: obtaining the real-time temperature waveform of the fuse element when the fuse enters the early fault state through simulation. If the temperature waveform of the fuse element is detected to be consistent with this real-time temperature waveform in practical applications, it can be determined that the fuse has entered the early fault state.

[0066] Simulation results show that when a single-phase arcing ground fault occurs in the secondary circuit, the temperature of the fuse element rises rapidly from 453℃, reaches its melting point and melts after 0.06s, and when the temperature of the fuse element reaches 961℃, an arcing phenomenon begins to appear at the fuse element break, at which point the temperature of the fuse reaches 960℃; after 0.025s, the arc is extinguished, the temperature of the fuse element reaches 964℃, and the fuse is completely disconnected, at which point the temperature of the fuse reaches 965℃.

[0067] In multiple simulation experiments, the predicted melt temperature was almost identical to the actual value of the fuse, indicating that the accuracy of the fault prediction reached the expected level.

[0068] Considering the actual maintenance scheme of the traction substation, after the initial melting fault of the fuse, the switching of the voltage transformer requires a certain amount of time. Therefore, the Cassie arc algorithm is used to calculate the resistance value of the fuse element at the next moment to monitor the operating status of the fuse element. When the resistance value of the fuse element reaches the upper limit, a final fault warning is issued. Table 2 shows the resistance values ​​of the fuse element at the next moment at different temperatures.

[0069] Table 2. Resistance values ​​of the melt at different temperatures at the next moment. Table 2 shows that when the fuse temperature reaches 450℃~960℃ and the double-ended voltage exceeds 2kV, the early warning condition is met. At this time, the fuse element melts and an arcing phenomenon occurs at the neck. When the fuse temperature reaches 965℃ and the double-ended voltage exceeds 17kV, the critical condition for early warning failure is reached. That is, the fuse at the next sampling time will completely melt, and a power outage fault will occur in the secondary circuit of the corresponding traction side bus.

[0070] The aforementioned method for monitoring fuse faults in the secondary circuit of a power system first constructs a temperature field model and a circuit model of the fuse, and then determines the equivalent resistance of the fuse when a fault occurs based on these models. Next, it acquires the real-time current, real-time voltage, and heat dissipation power of the fuse, calculates the temperature rise power based on these data, and determines the fuse temperature based on the temperature rise power. Finally, it calculates the theoretical resistance of the fuse based on its temperature, and performs fault monitoring on the fuse using both the theoretical and equivalent resistances. This method can diagnose the early fault state when the fuse element initially melts based on these two resistances, thus enabling early fault warnings for the secondary circuit, rather than detecting specific fault information after the fuse has completely broken.

[0071] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0072] The following are device embodiments of the present invention. For details not described in detail, please refer to the corresponding method embodiments described above.

[0073] Figure 8 A schematic diagram of the power system secondary circuit fuse fault monitoring device provided in an embodiment of the present invention is shown. For ease of explanation, only the parts related to the embodiment of the present invention are shown, and are described in detail below: See Figure 8 The power system secondary circuit fuse fault monitoring device 200 includes a model building module 201, a resistance determination module 202, a calculation module 203, and a fault monitoring module 204.

[0074] The model building module 201 is used to build a temperature field model and a circuit model of the fuse. The temperature field model includes a first boundary condition and a second boundary condition. The first boundary condition is the boundary condition corresponding to the contact between the two ends of the fuse molten body and the air, and the second boundary condition is the boundary condition corresponding to the contact between the molten body and the quartz sand.

[0075] The resistance determination module 202 is used to determine the equivalent resistance of a fuse when it fails, based on the temperature field model and the circuit model.

[0076] The calculation module 203 is used to obtain the real-time current, real-time voltage and heat dissipation power of the fuse, calculate the temperature rise power of the fuse based on the real-time current, the real-time voltage and the heat dissipation power, and determine the temperature of the fuse based on the temperature rise power.

[0077] The fault monitoring module 204 is used to calculate the theoretical resistance of the fuse based on the temperature of the fuse, and to perform fault monitoring on the fuse based on the theoretical resistance and the equivalent resistance.

[0078] In one possible implementation, the process by which the model building module 201 builds the temperature field model of the fuse is as follows: Set the fuse element to a length of [length missing]. l For a cylindrical body with a length d, the length of the melt is much greater than the radius of the cross-section, and there is a temperature difference between the melt on both sides and the melt inside in the transverse direction; x The unit melt, in d x The temperature of the unit melt is the same within the length range; According to the principle of energy conservation, the differential equation for the heat conduction of a single melt is: in, The heat generated at the first end of the unit melt. The heat generated at the second end of the unit melt. This refers to the heat generated per unit volume of melt per unit time. This represents the voltage corresponding to the unit melt. According to the theory of heat transfer, the formulas for calculating the heat in each part are as follows: Where λ is the thermal conductivity coefficient of the melt. r Where is the radius of the melt cross-section, and T is the unit melt temperature. ρ The density of the melt material, c The specific heat capacity of the molten material. t For time; Therefore, the temperature field model of the melt is obtained as follows: V represents the field under study.

[0079] In one possible implementation, the melt satisfies the first boundary condition at both ends and the contact surface. Second boundary conditions A certain end face of the melt is in contact with air, and the temperature of the air that convects with the end face of the melt is known. T0 and the conversion coefficient α The heat flux density per unit time at the interface between the two ends of the melt and the air can be obtained, thus yielding the first boundary condition. for , x =0 or x = l 0, t >0, n x Let be the normal vector of an arbitrary element's melt cross section; the melt and the silica sand have a contact surface, and the thermal conductivity of the silica sand is known to be... β The thickness of the quartz sand is d and the radius of the melt cross section is r The heat flux density at the interface between the melt and the quartz sand can be obtained, thus yielding the second boundary condition. for .

[0080] In one possible implementation, the process by which the model building module 201 builds the circuit model of the fuse is as follows: Treat the fuse as a resistor with a preset resistance value. R Furthermore, a linear resistor with a uniform resistance distribution can be divided into n unit resistors connected in series, with the resistance of each unit resistor being a preset resistance value divided by 1 / 2. n ; When the fuse is put into operation, it carries load current or short-circuit current for a long time. The fusible element melts faster and becomes thicker. The linear resistance changes from a series configuration to a configuration with multiple resistors in parallel on two branches and multiple single resistors in parallel on multiple branches. The parallel configuration of the two branches with multiple resistors is as follows: x A unit resistor connected in series n - x A single unit resistor is connected in series, and two series branches are connected in parallel; the configuration of multiple branches with single resistors in parallel is as follows: n - x A unit resistor connected in series x Each unit resistor is connected in parallel with a series branch.

[0081] In one possible implementation, the resistance determination module 202 is specifically used for: When the linear resistor changes from a series connection to a parallel connection of two branches with multiple resistors, the resistance of the fuse becomes... R x = R -15 x / n , x < n / 2; When the linear resistor changes from a series configuration to a configuration of multiple branches with single resistors in parallel, the resistance of the fuse becomes R x =R -20 x / n +R / nx , x < n / 2; When the unit resistance of the linear resistor is sufficiently small and n is sufficiently large, R / nx The resistance of the fuse is approximately 0, therefore the resistance of the fuse at this time becomes... R x = R -20 x / n , x < n / 2; Based on the resistance of the fuse in both states, the equivalent resistance when the fuse fails is located at... R -15 x / n and R -20 x / n between.

[0082] In one possible implementation, the computing module 203 is specifically used for: The power of the melt temperature rise is , for t The power of temperature rise of the melt at any given time for t The voltage across the fuse is constant. for t The resistance value of the fuse at all times. P This refers to heat dissipation power; Set the temperature rise power at the previous moment to be The current temperature rise power is The heat generated by the melt is ; The temperature of the melt at the current moment is , c The specific heat capacity of the melt. for t The heat generated by the melt at all times, for t The temperature of the melt at all times, for The temperature of the melt at any given time.

[0083] In one possible implementation, the computing module 203 is specifically used for: The theoretical resistance of the melt is , K The temperature coefficient of the melt resistance. R on This is the resistance when the melt is normally conducting. T0 represents the temperature at which the melt conducts normally, which is the same as the temperature of the air that convects at the melt's end face.

[0084] In one possible implementation, the fault monitoring module 204 is specifically used for: If the temperature of the melt Temperature above the melting point of the melt T max Then the melt is in a broken state at the narrow neck; If the temperature of the melt greater than temperature T 0 and less than or equal to temperature T max If so, the melt is in the initial melting state; If the theoretical resistance Greater than or equal to the upper limit resistance value R off If the arc is extinguished, the fuse will be in the open state.

[0085] In one possible implementation, the power system secondary circuit fuse fault monitoring device 200 may further include an early fault determination module. The early fault determination module is used to obtain the real-time temperature waveform of the fuse element when the fuse enters an early fault state through simulation. If the detected temperature waveform of the fuse element is consistent with the real-time temperature waveform, it is determined that the fuse has entered an early fault state.

[0086] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0087] Those skilled in the art will recognize that the templates, units, and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0088] If the module / unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the above embodiments of the present invention can also be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the above embodiments of the power system secondary circuit fuse fault monitoring method. The computer program includes computer program code, which can be in the form of source code, object code, executable file, or some intermediate form. The computer-readable medium can include: any entity or device capable of carrying the computer program code, a recording medium, a USB flash drive, a portable hard drive, a magnetic disk, an optical disk, a computer memory, a read-only memory, a random access memory, an electrical carrier signal, a telecommunication signal, and a software distribution medium, etc.

[0089] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A method for monitoring faults in secondary circuit fuses of a power system, characterized in that, include: A temperature field model and a circuit model of a fuse are constructed. The temperature field model includes a first boundary condition and a second boundary condition. The first boundary condition is the boundary condition corresponding to the contact between the two ends of the fuse element and the air. The second boundary condition is the boundary condition corresponding to the contact between the fuse element and the quartz sand. Determine the equivalent resistance of the fuse when it fails based on the temperature field model and the circuit model; The real-time current, real-time voltage, and heat dissipation power of the fuse are obtained; the temperature rise power of the fuse is calculated based on the real-time current, the real-time voltage, and the heat dissipation power; and the temperature of the fuse is determined based on the temperature rise power. The theoretical resistance of the fuse is calculated based on the temperature of the fuse, and the fuse is then monitored for faults based on the theoretical resistance and the equivalent resistance. The melt satisfies the first boundary condition at both ends and the contact surface. Second boundary conditions A certain end face of the melt is in contact with air, and the temperature of the air that convects with the end face of the melt is known. T 0 and converter coefficient α The heat flux density per unit time at the interface between the two ends of the melt and the air can be obtained, thus yielding the first boundary condition. for , x =0 or x = l 0, t >0, n x Let λ be the normal vector of an arbitrary element melt cross section; λ be the thermal conductivity of the melt; T be the element melt temperature; the melt and the silica sand have a contact surface, and the thermal conductivity of the silica sand is known to be... β The thickness of the quartz sand is d and the radius of the melt cross section is r The heat flux density at the interface between the melt and the quartz sand can be obtained, thus yielding the second boundary condition. for ; The process of constructing the circuit model of the fuse is as follows: Treat the fuse as a resistor with a preset resistance value. R Furthermore, a linear resistor with a uniform resistance distribution can be divided into n unit resistors connected in series, with the resistance of each unit resistor being a preset resistance value divided by 1 / 2. n ; When the fuse is put into operation, it carries load current or short-circuit current for a long time. The fusible element melts faster and becomes thicker. The linear resistance changes from a series configuration to a configuration with multiple resistors in parallel on two branches and multiple single resistors in parallel on multiple branches. The parallel configuration of the two branches with multiple resistors is as follows: x A unit resistor connected in series n - x A single unit resistor is connected in series, and two series branches are connected in parallel; the configuration of multiple branches with single resistors in parallel is as follows: n - x A unit resistor connected in series x Each unit resistor is connected in parallel with a series branch; The step of determining the equivalent resistance of a fuse when it fails based on the temperature field model and the circuit model includes: When the linear resistor changes from a series connection to a parallel connection of two branches with multiple resistors, the resistance of the fuse becomes R x = R -15 x / n , x < n / 2; When the linear resistor changes from a series configuration to a configuration of multiple branches with single resistors in parallel, the resistance of the fuse becomes R x = R -20 x / n +R / nx , x < n / 2; When the unit resistance of the linear resistor is sufficiently small and n is sufficiently large, R / nx The resistance of the fuse is approximately 0, therefore the resistance of the fuse at this time becomes R x = R -20 x / n , x < n / 2; Based on the resistance of the fuse in both states, the equivalent resistance when the fuse fails is located at... R -15 x / n and R -20 x / n between.

2. The power system secondary circuit fuse fault monitoring method as described in claim 1, characterized in that, The process of constructing a temperature field model for a fuse is as follows: Set the fuse element to a length of [length missing]. l For a cylindrical body with a length d, the length of the melt is much greater than the cross-sectional radius, and there is a temperature difference between the melt on both sides and the melt inside in the transverse direction; x The unit melt, in d x The temperature of the unit melt is the same within the length range; According to the principle of energy conservation, the differential equation for the heat conduction of a single melt is: in, The heat generated at the first end of the unit melt. The heat generated at the second end of the unit melt. This refers to the heat generated per unit volume of melt per unit time. This represents the voltage corresponding to the unit melt. According to the theory of heat transfer, the formulas for calculating the heat in each part are as follows: Where λ is the thermal conductivity coefficient of the melt. r Where is the radius of the melt cross-section, and T is the unit melt temperature. ρ The density of the melt material, c The specific heat capacity of the molten material. t For time; Therefore, the temperature field model of the melt is obtained as follows: V represents the field under study.

3. The power system secondary circuit fuse fault monitoring method as described in claim 1, characterized in that, The step of calculating the temperature rise power of the fuse based on the current, the voltage, and the heat dissipation power, and determining the temperature of the fuse based on the temperature rise power, includes: The power of the melt temperature rise is , for t The power of temperature rise of the melt at any given time for t The voltage across the fuse is constant. for t The resistance value of the fuse at all times. P This refers to heat dissipation power; Set the temperature rise power at the previous moment to be The current temperature rise power is The heat generated by the melt is ; The temperature of the melt at the current moment is , c The specific heat capacity of the melt. for t The heat generated by the melt at all times, for t The temperature of the melt at all times, for The temperature of the melt at any given time.

4. The power system secondary circuit fuse fault monitoring method as described in claim 3, characterized in that, The calculation of the theoretical resistance of the fuse based on its temperature includes: The theoretical resistance of the melt is , K The temperature coefficient of the melt resistance. R on This is the resistance when the melt is normally conducting. T 0 represents the temperature at which the melt conducts normally, which is the same as the temperature of the air that convects at the melt's end face.

5. The power system secondary circuit fuse fault monitoring method as described in claim 4, characterized in that, The step of fault monitoring of the fuse based on the theoretical resistance and the equivalent resistance includes: If the temperature of the melt Temperature above the melting point of the melt T max Then the melt is in a broken state at the narrow neck; If the temperature of the melt greater than temperature T 0 and less than or equal to temperature T max If so, the melt is in the initial melting state; If the theoretical resistance Greater than or equal to the upper limit resistance value R off If the arc is extinguished, the fuse will be in the open state.

6. The power system secondary circuit fuse fault monitoring method as described in claim 5, characterized in that, The power system secondary circuit fuse fault monitoring method also includes: The real-time temperature waveform of the molten element when the fuse enters the early fault state is obtained through simulation. If the temperature waveform of the molten metal is detected to be consistent with the real-time temperature waveform, it is determined that the fuse has entered an early fault state.

7. A power system secondary circuit fuse fault monitoring device for performing the power system secondary circuit fuse fault monitoring method according to any one of claims 1 to 6, characterized in that, include: The model building module is used to build the temperature field model and circuit model of the fuse. The temperature field model includes a first boundary condition and a second boundary condition. The first boundary condition is the boundary condition corresponding to the contact between the two ends of the fuse molten element and the air, and the second boundary condition is the boundary condition corresponding to the contact between the molten element and the quartz sand. The resistance determination module is used to determine the equivalent resistance of a fuse when it fails, based on the temperature field model and the circuit model. The calculation module is used to obtain the real-time current, real-time voltage and heat dissipation power of the fuse, calculate the temperature rise power of the fuse based on the real-time current, the real-time voltage and the heat dissipation power, and determine the temperature of the fuse based on the temperature rise power. The fault monitoring module is used to calculate the theoretical resistance of the fuse based on the temperature of the fuse, and to perform fault monitoring on the fuse based on the theoretical resistance and the equivalent resistance.

Images