Transformer core multipoint grounding equivalent circuit and fault processing method

Abstract

The invention provides a transformer core multipoint grounding equivalent circuit and a fault processing method, and relates to the technical field of power transformers. The equivalent circuit comprises a primary side equivalent branch, a secondary side equivalent branch, a fault equivalent branch, a current-limiting resistor and an insulation resistor, one ends of the primary side equivalent branch and the secondary side equivalent branch are connected with the ground, and the other ends are connected with the ground through insulation resistors; one end of the fault equivalent branch is connected with the ground through a current-limiting resistor, and the other end is connected with the ground through an insulation resistor; and the fault equivalent branch is equivalent to a secondary winding and is used for equivalent induction electromotive force generated by multi-point grounding of the iron core. The multi-point grounding condition of the transformer core can be simulated, and the selection accuracy of the resistance value of the current-limiting resistor is improved.

Description

Technical Field

[0001] The present disclosure relates to the technical field of power transformers, and more particularly to a transformer core multi-point grounding equivalent circuit and a fault handling method. Background Art

[0002] With the rapid development of power systems, transformers, as core equipment in these systems, are becoming increasingly important for their reliability and efficiency. When transformer cores are grounded at multiple points, the selection of current-limiting resistors is crucial for ensuring safe operation and improving efficiency. Existing techniques often rely on empirical experience and lack systematic theoretical guidance, resulting in inaccurate resistor values ​​and potentially impacting transformer performance.

[0003] In the existing technology, the selection of current-limiting resistors has the following main shortcomings: lack of accurate theoretical model support, resulting in inaccurate selected resistance values, strong dependence on experience, difficulty in adapting to the needs under different working conditions, and lack of dynamic response analysis under multi-point grounding of the transformer core. Summary of the Invention

[0004] In view of this, the present disclosure provides a transformer core multi-point grounding equivalent circuit and a fault handling method.

[0005] One aspect of the present disclosure provides a transformer core multi-point grounding equivalent circuit, comprising: a primary side equivalent branch, a secondary side equivalent branch, a fault equivalent branch, a current limiting resistor, and an insulation resistor;

[0006] One end of the primary side equivalent branch and the secondary side equivalent branch are both connected to the ground, and the other ends are both connected to the ground through the insulation resistor;

[0007] One end of the fault equivalent branch is connected to the ground through the current limiting resistor, and the other end is connected to the ground through the insulation resistor;

[0008] The fault equivalent branch is equivalent to a secondary winding, and is used to equalize the induced electromotive force generated by multi-point grounding of the iron core.

[0009] According to an embodiment of the present disclosure, the primary-side equivalent branch includes a primary equivalent winding and a first equivalent resistance and capacitance of the primary equivalent winding to the iron core;

[0010] One end of the primary equivalent winding is connected to the ground, and the other end is connected to the insulation resistor through the first equivalent resistance and capacitance;

[0011] The primary equivalent winding is equivalent to the primary winding of the target transformer.

[0012] According to an embodiment of the present disclosure, the first equivalent resistance and capacitance include a first equivalent resistor and a first equivalent capacitor connected in series; the resistance value of the first equivalent resistor and the capacitance value of the first equivalent capacitor are determined by the Schilling bridge method to determine the equivalent capacitance and dielectric loss angle of the primary winding to the iron core, and are calculated using the principle of identical impedance.

[0013] According to an embodiment of the present disclosure, the secondary-side equivalent branch includes a secondary equivalent winding and a second equivalent resistance and capacitance of the secondary equivalent winding to the core;

[0014] One end of the secondary equivalent winding is connected to the ground, and the other end is connected to the insulation resistor via the second equivalent resistance and capacitance;

[0015] The secondary equivalent winding is equivalent to the secondary winding of the target transformer.

[0016] According to an embodiment of the present disclosure, the second equivalent resistance and capacitance include a second equivalent resistor and a second equivalent capacitor connected in series; the resistance value of the second equivalent resistor and the capacitance value of the second equivalent capacitor are determined by the Schilling bridge method to determine the equivalent capacitance and dielectric loss angle of the equivalent winding to the iron core, and are calculated using the principle of identical impedance.

[0017] According to an embodiment of the present disclosure, the resistance value of the current-limiting resistor is determined by simulating the multi-point grounding equivalent circuit of the transformer core to generate test parameter values ​​of the transformer core when waveforms corresponding to different grounding currents and different potentials are generated.

[0018] According to an embodiment of the present disclosure, when simulating the transformer core multi-point grounding equivalent circuit, it is necessary to input transformer parameters, winding insulation parameters, the insulation resistance value and the current limiting resistor value;

[0019] The transformer parameters are the nominal parameters of the target transformer; the winding insulation parameters are the insulation equivalent parameters of the winding of the target transformer to the iron core; the resistance value of the insulation resistance is the grounding resistance value of the iron core fault point of the target transformer; and the resistance value of the current limiting resistor is the test parameter value.

[0020] According to an embodiment of the present disclosure, the resistance of the current-limiting resistor is such that the current value of the grounding current of the transformer is less than or equal to a preset current value and the potential value of the iron core of the transformer is less than a preset potential value.

[0021] Another aspect of the present disclosure provides a fault handling method based on a transformer core multi-point grounding equivalent circuit, comprising: measuring an induced electromotive force after a target transformer fault occurs; the induced electromotive force is generated by a hinge magnetic flux of the target transformer core multi-point grounding;

[0022] Adjusting the transformation ratio of the secondary winding equivalent to the fault equivalent branch of the transformer core multi-point grounding equivalent circuit according to the induced electromotive force, to obtain the equivalent circuit of the target transformer after the fault;

[0023] The equivalent circuit of the target transformer after the fault is simulated, and the target resistance value of the current limiting resistor is determined based on the waveforms of the target transformer core corresponding to different grounding currents and different potentials. The current limiting resistor is updated based on the target resistance value to handle multi-point grounding faults of the target transformer.

[0024] According to an embodiment of the present disclosure, the resistance of the current-limiting resistor is such that the current value of the grounding current of the transformer is less than or equal to a preset current value and the potential value of the iron core of the transformer is less than a preset potential value.

[0025] According to the embodiments of the present disclosure, because the fault equivalent branch is equivalent to the secondary winding, the fault equivalent branch can be equivalent to the induced electromotive force generated by multi-point grounding of the iron core. By adjusting the transformation ratio of the secondary winding, a transformer with multi-point grounding faults is simulated, thereby at least partially overcoming the technical problem of lack of theoretical model support in the prior art, thereby achieving the technical effect of improving the accuracy of current limiting resistor selection. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The above and other objects, features and advantages of the present disclosure will become more apparent through the following description of the embodiments of the present disclosure with reference to the accompanying drawings, in which:

[0027] Figure 1A A schematic diagram of a transformer core and a clamp being grounded normally according to an embodiment of the present disclosure is shown;

[0028] Figure 1B A schematic diagram of a transformer core and a clamp multi-point grounding fault according to an embodiment of the present disclosure is shown;

[0029] Figure 2A Schematically shows a schematic diagram of an equivalent circuit of winding-to-core insulation according to an embodiment of the present disclosure;

[0030] Figure 2B Schematically shows a phasor diagram of an equivalent circuit of winding-to-core insulation according to an embodiment of the present disclosure;

[0031] Figure 2C A schematic diagram of a parallel RC circuit after simplifying the winding-to-core insulation equivalent circuit according to an embodiment of the present disclosure is shown;

[0032] Figure 2D A schematic diagram of a simplified series RC circuit of the winding-to-core insulation equivalent circuit according to an embodiment of the present disclosure is shown;

[0033] Figure 3 The following schematically shows a schematic diagram of an equivalent winding circuit model of a single-phase double-winding transformer core multi-point grounding fault according to an embodiment of the present disclosure;

[0034] Figure 4 Schematically shows a schematic diagram of an equivalent circuit model of a transformer core multi-point grounding according to an embodiment of the present disclosure;

[0035] Figure 5 A diagram schematically shows a transformer grounding current variation diagram when the insulation resistance is 5Ω according to an embodiment of the present disclosure;

[0036] Figure 6 A diagram schematically shows a transformer core potential change diagram when the insulation resistance is 5Ω according to an embodiment of the present disclosure;

[0037] Figure 7 Schematically shows a diagram of transformer grounding current variation when the insulation resistance is 1 kΩ according to an embodiment of the present disclosure;

[0038] Figure 8 A diagram schematically shows a transformer core potential change diagram when the insulation resistance is 1 kΩ according to an embodiment of the present disclosure;

[0039] Figure 9 The flowchart of the fault handling method based on the transformer core multi-point grounding equivalent circuit according to the embodiment of the present disclosure is schematically shown. DETAILED DESCRIPTION

[0040] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are merely exemplary and are not intended to limit the scope of the present disclosure. In the detailed description below, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of the embodiments of the present disclosure. However, it is apparent that one or more embodiments may also be implemented without these specific details. In addition, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessary confusion of the concepts of the present disclosure.

[0041] The terms used herein are only for describing specific embodiments and are not intended to limit the present disclosure. The terms "comprise," "include," etc. used herein indicate the presence of the features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0042] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification and should not be interpreted in an idealized or overly rigid manner.

[0043] When expressions such as "at least one of A, B, and C, etc." are used, they should generally be interpreted in accordance with the meaning commonly understood by those skilled in the art (for example, "a system having at least one of A, B, and C" should include but is not limited to a system having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, C, etc.).

[0044] In the embodiments of this disclosure, the collection, updating, analysis, processing, use, transmission, provision, disclosure, and storage of all data involved (including, but not limited to, user personal information) comply with relevant laws and regulations, are used for legitimate purposes, and do not violate public order and good morals. In particular, necessary measures have been taken to prevent unauthorized access to user personal information data and to safeguard the security of user personal information, network security, and national security.

[0045] In the embodiments of the present disclosure, the user's authorization or consent is obtained before obtaining or collecting the user's personal information.

[0046] An embodiment of the present disclosure provides a transformer core multi-point grounding equivalent circuit, comprising: a primary side equivalent branch, a secondary side equivalent branch, a fault equivalent branch, a current limiting resistor, and an insulation resistor.

[0047] One end of the primary side equivalent branch and the secondary side equivalent branch are both connected to the ground, and the other ends are both connected to the ground through the insulation resistor.

[0048] One end of the fault equivalent branch is connected to the ground through the current limiting resistor, and the other end is connected to the ground through the insulation resistor.

[0049] The fault equivalent branch is equivalent to a secondary winding, and is used to equalize the induced electromotive force generated by multi-point grounding of the iron core.

[0050] Specifically, the primary side equivalent branch includes a primary equivalent winding and a first equivalent resistance and capacitance of the primary equivalent winding to the iron core; one end of the primary equivalent winding is connected to the ground, and the other end is connected to the insulation resistor through the first equivalent resistance and capacitance; the primary equivalent winding is equivalent to the primary winding of the target transformer.

[0051] The first equivalent resistance and capacitance include a first equivalent resistor and a first equivalent capacitor connected in series; the resistance value of the first equivalent resistor and the capacitance value of the first equivalent capacitor are determined by the Schilling bridge method to determine the equivalent capacitance and dielectric loss angle of the primary winding to the iron core, and are calculated using the principle of identical impedance.

[0052] The secondary side equivalent branch includes a secondary equivalent winding and a second equivalent resistance and capacitance of the secondary equivalent winding to the iron core; one end of the secondary equivalent winding is connected to the ground, and the other end is connected to the insulation resistor through the second equivalent resistance and capacitance; the secondary equivalent winding is equivalent to the secondary winding of the target transformer.

[0053] The second equivalent resistance and capacitance include a second equivalent resistor and a second equivalent capacitor connected in series; the resistance value of the second equivalent resistor and the capacitance value of the second equivalent capacitor are determined by the Schilling bridge method to determine the equivalent capacitance and dielectric loss angle of the equivalent winding to the iron core, and are calculated using the principle of identical impedance.

[0054] Furthermore, the resistance of the current-limiting resistor is determined by simulating the multi-point grounding equivalent circuit of the transformer core to generate test parameter values ​​of the transformer core when waveforms corresponding to different grounding currents and different potentials are generated.

[0055] The resistance of the current-limiting resistor is such that the current value of the grounding current of the transformer is less than or equal to a preset current value and the potential value of the iron core of the transformer is less than a preset potential value.

[0056] Among them, when simulating the multi-point grounding equivalent circuit of the transformer core, it is necessary to input transformer parameters, winding insulation parameters, the resistance value of the insulation resistor and the resistance value of the current limiting resistor; the transformer parameters are the nominal parameters of the target transformer; the winding insulation parameters are the insulation equivalent parameters of the winding of the target transformer to the core; the resistance value of the insulation resistor is the grounding resistance value of the core fault point of the target transformer; the resistance value of the current limiting resistor is the test parameter value.

[0057] Figure 1A The following schematically shows the transformer core and clamp grounding in a normal state according to an embodiment of the present disclosure. Figure 1A As shown in the figure, when the transformer is operating normally, in order to prevent electromagnetic induction from generating a floating potential on the iron core and discharging to the grounded shell, the iron core is usually connected to the transformer tank or the lead wire is connected to the upper bushing of the oil tank to achieve reliable grounding, ensuring that the iron core is at a low potential.

[0058] Figure 1B The following schematically shows a transformer core and clamp multi-point grounding fault diagram according to an embodiment of the present disclosure. Figure 1B As shown in the figure, when the iron core is grounded at multiple points due to burrs or welding slag on the internal casing, the induced electromotive force between the two grounding points forms a short-circuit loop through the earth, generating a large grounding current flowing through the iron core, affecting the normal operation of the transformer. Long-term short-circuit state will further lead to a larger transformer accident. Therefore, it is necessary to promptly detect and eliminate the transformer's multi-point grounding fault to maintain power supply stability.

[0059] Figure 2AThe figure schematically shows an equivalent circuit diagram of the winding-to-core insulation according to an embodiment of the present disclosure. Figure 2B The figure schematically shows a phasor diagram of an equivalent circuit of winding to core insulation according to an embodiment of the present disclosure. Figure 2C The figure schematically shows a simplified parallel RC circuit diagram of the winding-to-core insulation equivalent circuit according to an embodiment of the present disclosure. Figure 2D The following schematically shows a simplified series RC circuit diagram of the winding-to-core insulation equivalent circuit according to an embodiment of the present disclosure. Figure 2A As shown, the capacitor branch is used to describe the lossless polarization of the dielectric, which is described by the capacitor C1 and the current i1 flowing through the capacitor C1; the capacitor-resistor series branch and the resistor branch are used to characterize the dielectric loss between the winding and the core, which is mainly composed of conductivity loss and lossy polarization loss. C2 and R2 and the i2 flowing through C2 and R2 describe the lossy polarization of the dielectric, and R3 and the i3 flowing through R3 are used to characterize the conductivity loss of the dielectric. Figure 2B As shown, is the current phasor flowing through resistor R2, is the current phasor flowing through resistor R3, is the current phasor flowing through capacitor C2, is the current phasor flowing through capacitor C2 and resistor R2, is the current phasor flowing through capacitor C1, is the current phasor flowing through capacitor C1, capacitor C2, resistor R2 and resistor R3, U is the voltage, Figure 2B It can be seen that the dielectric loss angle As the current leads the voltage by an angle φ, it can be further equated to a parallel circuit of resistance and capacitance, such as Figure 2C As shown, in Figure 2C In the figure, the current flowing through the capacitor C is i C , the current flowing through the resistor R is i R , or it can be further equivalent to a series circuit of resistance and capacitance, such as Figure 2D As shown, in Figure 2D In the figure, the current flowing through the capacitor C is i C , the current flowing through the resistor R is i R .

[0060] Figure 3 The schematic diagram of the equivalent winding circuit model of a single-phase dual-winding transformer core multi-point grounding fault according to an embodiment of the present disclosure is shown; the present disclosure uses an additional winding to represent the induced electromotive force generated by the core multi-point grounding hinge magnetic flux, and can represent the induced electromotive force difference caused by different grounding point positions by adjusting the transformation ratio of the additional winding. Taking the core multi-point grounding fault of a single-phase dual-winding transformer as an example, the following is established: Figure 3The transformer winding circuit model shown in Figure 2 is a tertiary winding. In addition to the primary winding and the secondary winding, a third winding is used to represent the induced electromotive force between two grounding points when the core is grounded at multiple points. By varying the voltage value of the third winding, the difference in hinge flux caused by different grounding points can be described.

[0061] Figure 4 The schematic diagram of the transformer core multi-point grounding equivalent circuit model according to the embodiment of the present disclosure is shown; the equivalent circuit of the winding-to-core insulation equivalent circuit, the simplified parallel RC circuit of the winding-to-core insulation equivalent circuit, the simplified series RC circuit of the winding-to-core insulation equivalent circuit and the equivalent winding circuit of the single-phase double-winding transformer core multi-point grounding fault is established. Figure 4 The transformer multi-point grounding equivalent circuit model is shown in Figure 1. The resistance and capacitance series branches are used to respectively equalize the insulation impedance of the primary and secondary windings to the core. Figure 4 The third winding voltage represents the magnetic flux size of the hinge between different grounding points of the core. When multiple grounding points occur, the voltage value can be adjusted according to the different grounding points. The core insulation resistance to the box and the current limiting resistance are respectively equivalent to two resistors. Figure 4 In the figure, the primary winding 1 and the secondary winding 2 are the primary winding and the secondary winding of the actual transformer when no multi-point grounding fault occurs. The tertiary winding 3 represents the induced electromotive force between the two grounding points when the core is multi-point grounded. The hinge flux difference caused by different grounding point positions can be described by changing the voltage value of the tertiary winding. The equivalent resistance and capacitance of the grid-side winding to the core is the first equivalent resistance and capacitance, and the equivalent resistance and capacitance of the valve-side winding to the core is the second equivalent resistance and capacitance. The primary winding 1 is the primary equivalent winding, and the secondary winding 2 is the secondary equivalent winding. The equivalent resistance and capacitance of the primary winding 1 and the grid-side winding to the core constitute the primary side equivalent branch, the equivalent resistance and capacitance of the secondary winding 2 and the valve-side winding to the core constitute the secondary side equivalent branch, and the tertiary winding is the fault equivalent branch.

[0062] Figure 5 Schematically shows a diagram showing a transformer grounding current change when the insulation resistance is 5Ω according to an embodiment of the present disclosure; Figure 5 As shown in the figure, under different induced electromotive forces of the third winding (60V, 120V, 240V, 480V, 600V), the series current limiting resistor increases the grounding loop impedance, which increases the capacitive current shunt from the iron core through the short-circuit point to the earth side. However, in the case of a low-impedance grounding fault, the conduction current value in the grounding current is significantly greater than the displacement current value. The current change trend mainly reflects the change law of the conduction current, so the overall current also decreases with the increase of the current limiting resistor.

[0063] Figure 6 Schematically shows the transformer core potential change diagram when the insulation resistance is 5Ω according to an embodiment of the present disclosure; Figure 6As shown in the figure, when a low-impedance ground fault occurs in the core, the core potential decreases as the current-limiting resistor increases. This is primarily because an increase in the current-limiting resistor reduces the overall loop current, which in turn reduces the core potential connected to the ground via the short-circuit impedance. The increase in the tertiary winding voltage indicates that the induced ground loop voltage (60V, 120V, 240V, 480V, and 600V) increases at different grounding points. While the loop impedance remains constant, this increases the induced current and the voltage across the insulation resistance, leading to an increase in the core potential. Combining the short-circuit current and core potential changes under low-impedance conditions shows that a larger current-limiting resistor is more effective in limiting the ground current and reducing the core potential.

[0064] Figure 7 Schematically shows a transformer grounding current change diagram when the insulation resistance is 1 kΩ according to an embodiment of the present disclosure; Figure 7 As shown in the figure, after the core grounding impedance is changed to a high impedance of 1kΩ, the grounding current also decreases with increasing current-limiting resistance under different tertiary winding induced electromotive forces (60V, 120V, 240V, 480V, and 600V). This indicates that the conduction current still dominates the displacement current, but the overall current value is small. By connecting a suitable current-limiting resistor in series, the grounding current can be limited to below 100mA. When the tertiary winding voltage increases, the loop voltage increases, the conduction current increases, and thus the grounding current increases.

[0065] Figure 8 The figure schematically shows the transformer core potential change diagram when the insulation resistance is 1 kΩ according to an embodiment of the present disclosure. Figure 8 As shown in the figure, when a high-impedance ground fault occurs in the core with a ground resistance of 1 kΩ, the core potential increases with the increase of the current-limiting resistor. At this point, the core-to-ground insulation resistance is essentially equivalent to the current-limiting resistor. The increase in current-limiting resistance increases the voltage across the resistor, leading to an increase in the potential on the side connected to the core, and consequently, an increase in the core potential. Simultaneously, as the tertiary winding voltage increases (60 V, 120 V, 240 V, 480 V, and 600 V), the ground current increases, and the voltage across the current-limiting resistor also increases, causing the core potential to rise. The changes in core ground current and core potential indicate that under high impedance conditions, the core ground current can be restored to a relatively low range, but the introduction of a larger current-limiting resistor may cause an increase in the core potential. Based on actual field fault conditions, when the core potential reaches approximately 100 V, partial discharge at the high-impedance point may occur.

[0066] The present disclosure also provides a fault handling method based on a transformer core multi-point grounding equivalent circuit, the fault handling method comprising:

[0067] Step 1: measuring the induced electromotive force after a fault occurs in a target transformer; the induced electromotive force is generated by the multi-point grounding hinge magnetic flux of the core of the target transformer.

[0068] Step 2: According to the induced electromotive force, the transformation ratio of the secondary winding equivalent to the fault equivalent branch of the transformer core multi-point grounding equivalent circuit provided by the present disclosure is adjusted to obtain the equivalent circuit of the target transformer after the fault.

[0069] Step 3: Simulate the equivalent circuit of the target transformer after the fault, determine the target resistance of the current limiting resistor based on the waveforms of the target transformer core corresponding to different grounding currents and different potentials, and update the current limiting resistor based on the target resistance to handle multi-point grounding faults of the target transformer.

[0070] The resistance of the current-limiting resistor is such that the grounding current of the transformer is less than or equal to a preset current value and the potential of the core of the transformer is less than a preset potential value.

[0071] Figure 9 A flowchart schematically illustrates a fault handling method based on a transformer core multi-point grounding equivalent circuit according to an embodiment of the present disclosure. The equivalent circuit component parameters are determined by testing actual single-phase, dual-winding transformer parameters. Based on the differences in inductive voltage caused by hinge flux differences at different grounding points and the different values ​​of the current-limiting resistor, the core grounding current and core potential under low-impedance and high-impedance grounding conditions of the transformer core are simulated. The current-limiting resistor is selected based on the simulation results, providing a theoretical basis for the selection of the current-limiting resistor.

[0072] like Figure 9 As shown, the transformer parameters are the nominal parameters of the actual simulated transformer, including the transformer input and output voltage levels, turns ratio, winding resistance, winding inductance, as well as excitation resistance and excitation inductance. The present invention also innovatively uses an additional winding to simulate the electromotive force induced by the magnetic flux of the hinge of the core multi-point grounding fault loop, and adjusts the difference in the induced electromotive force value caused by the different grounding point positions by changing the ratio; the winding insulation parameters are the insulation equivalent parameters of the winding to the core, and the equivalent capacitance CX and dielectric loss angle of the winding to the core insulation can be obtained by the Schilling bridge method. The tangent value of The impedance-equalizing principle can then be used to determine the resistance and capacitance of the winding relative to the core. The grounding resistance parameter represents the grounding resistance at the core fault point under low-impedance and high-impedance grounding conditions. This value can be estimated based on the core grounding lead current. Under low-impedance grounding conditions, it is generally 5-10Ω, while under high-impedance grounding, it is generally 1kΩ or higher. The current-limiting resistance value is the initial value of the current-limiting resistor. This value can be preset based on engineering experience. In subsequent circuit model calculations, this current-limiting resistance value can be gradually optimized based on the grounding current and core potential limit requirements.

[0073] Substitute all parameter values ​​into the circuit model, run the simulation model, adjust the current-limiting resistor value, and calculate the ground current and core potential under different current-resistance conditions. Under low-impedance grounding conditions, the current-limiting resistor primarily limits the current, typically to 0.1A or less. Under high-impedance grounding conditions, the presence of the current-limiting resistor raises the core potential, potentially causing partial discharge at the high-impedance grounding point and affecting the safe operation of the transformer. Generally, the core potential must be kept below a certain threshold, such as 100V.

[0074] According to the grounding current and core potential limitation requirements under low impedance and high impedance conditions after the current limiting resistor is connected, the resistance value of the connected current limiting resistor is optimized, and finally the current limiting resistor or its resistance range that should be connected to the core grounding lead when the transformer core is grounded at multiple points is determined.

[0075] Compared with the actual current limiting device, the transformer core multi-point grounding equivalent circuit provided by the present invention is continuous and non-interrupted in the simulation of the current limiting resistor value. By changing the current limiting resistor value in the model, the numerical value and change of the core grounding current and core potential after the current limiting resistors of various resistance values ​​are inserted in series in the simulation process are simulated. By simulating the fault state of the actual transformer, the appropriate resistance value of the current limiting resistor is selected so that the core grounding current and core potential can be limited to a level that causes less damage to the transformer. The current limiting resistor can be directly put into the transformer with multi-point grounding of the core, and the current limiting resistor of this resistance value can be used for a long time, saving labor costs. In addition, by changing the parameters of the transformer and the current limiting resistor group, the multi-point grounding fault situation of transformers of different specifications and different grounding impedances can be simulated, and it can adapt to the faults of transformers of different specifications and different grounding impedances. The embodiment of the present invention does not require a complex control module, nor does it need to consider the interference problem in the signal transmission process, saving time and effort, and having high efficiency. If various fault conditions are simulated in advance and the core current and core potential values ​​are recorded, the open circuit voltage and ground current can be detected after the fault occurs. By comparing the recorded data, the ground impedance can be estimated and the appropriate current-limiting resistor can be quickly installed.

[0076] In addition, the embodiments of the present disclosure characterize the electromotive force induced by the magnetic flux of the core multi-point grounding hinge and the difference in the induced electromotive force caused by different grounding point positions.

[0077] In the actual current limiting device, when limiting the grounding current by inputting a current limiting resistor, if the resistance value of the current limiting resistor is inappropriate, the grounding current of the transformer core may be too large or the core potential may be too high, causing damage to the transformer.

[0078] The above describes the embodiments of the present disclosure. However, these embodiments are for illustrative purposes only and are not intended to limit the scope of the present disclosure. Although each embodiment has been described separately above, this does not mean that the measures in each embodiment cannot be advantageously used in combination. Without departing from the scope of the present disclosure, those skilled in the art may make various substitutions and modifications, which should all fall within the scope of the present disclosure.

Claims

1. A transformer core multi-point grounding equivalent circuit, characterized in that: The equivalent circuit comprises: a primary side equivalent branch, a secondary side equivalent branch, a fault equivalent branch, a current limiting resistor and an insulation resistor; One end of the primary side equivalent branch and the secondary side equivalent branch are both connected to the ground, and the other ends are both connected to the ground through the insulation resistor; One end of the fault equivalent branch is connected to the ground through the current limiting resistor, and the other end is connected to the ground through the insulation resistor; The fault equivalent branch is equivalent to a secondary winding, and is used to equalize the induced electromotive force generated by multi-point grounding of the iron core.

2. The transformer core multi-point grounding equivalent circuit according to claim 1 is characterized in that: The primary side equivalent branch includes a primary equivalent winding and a first equivalent resistance and capacitance of the primary equivalent winding to the iron core; One end of the primary equivalent winding is connected to the ground, and the other end is connected to the insulation resistor through the first equivalent resistance and capacitance; The primary equivalent winding is equivalent to the primary winding of the target transformer.

3. The transformer core multi-point grounding equivalent circuit according to claim 2 is characterized in that: The first equivalent resistance and capacitance include a first equivalent resistor and a first equivalent capacitor connected in series; the resistance value of the first equivalent resistor and the capacitance of the first equivalent capacitor are determined by using the Schilling bridge method to determine the equivalent capacitance and dielectric loss angle of the primary winding to the iron core, and are calculated using the principle of identical impedance.

4. The transformer core multi-point grounding equivalent circuit according to claim 1, characterized in that: The secondary side equivalent branch includes a secondary equivalent winding and a second equivalent resistance and capacitance of the secondary equivalent winding to the iron core; One end of the secondary equivalent winding is connected to the ground, and the other end is connected to the insulation resistor through the second equivalent resistance and capacitance; The secondary equivalent winding is equivalent to the secondary winding of the target transformer.

5. The transformer core multi-point grounding equivalent circuit according to claim 4, characterized in that: The second equivalent resistance and capacitance include a second equivalent resistor and a second equivalent capacitor connected in series; the resistance value of the second equivalent resistor and the capacitance value of the second equivalent capacitor are determined by using the Schilling bridge method to determine the equivalent capacitance and dielectric loss angle of the equivalent winding to the iron core, and are calculated using the principle of identical impedance.

6. The transformer core multi-point grounding equivalent circuit according to claim 1, characterized in that: The resistance value of the current-limiting resistor is determined by simulating the multi-point grounding equivalent circuit of the transformer core to generate test parameter values ​​of waveforms corresponding to different grounding currents and different potentials of the transformer core.

7. The transformer core multi-point grounding equivalent circuit according to claim 6, characterized in that: When simulating the transformer core multi-point grounding equivalent circuit, it is necessary to input transformer parameters, winding insulation parameters, the insulation resistance value and the current limiting resistance value; The transformer parameters are the nominal parameters of the target transformer; the winding insulation parameters are the insulation equivalent parameters of the winding of the target transformer to the iron core; the resistance value of the insulation resistance is the grounding resistance value of the iron core fault point of the target transformer; the resistance value of the current limiting resistor is the test parameter value.

8. The transformer core multi-point grounding equivalent circuit according to claim 6, characterized in that: The resistance of the current-limiting resistor makes the current value of the grounding current of the transformer less than or equal to a preset current value and the potential value of the iron core of the transformer less than a preset potential value.

9. A fault handling method based on a transformer core multi-point grounding equivalent circuit, characterized in that: The fault handling method comprises: Measuring the induced electromotive force after a target transformer fails; the induced electromotive force is generated by the multi-point grounding hinge magnetic flux of the core of the target transformer; According to the induced electromotive force, the transformation ratio of the secondary winding equivalent to the fault equivalent branch of the transformer core multi-point grounding equivalent circuit according to any one of claims 1 to 8 is adjusted to obtain the equivalent circuit of the target transformer after the fault; The equivalent circuit of the target transformer after the fault is simulated, and the target resistance value of the current limiting resistor is determined according to the waveforms of the target transformer core corresponding to different grounding currents and different potentials, and the current limiting resistor is updated based on the target resistance value to handle multi-point grounding faults of the target transformer.

10. The fault handling method based on the transformer core multi-point grounding equivalent circuit according to claim 9 is characterized in that: The resistance of the current-limiting resistor makes the current value of the grounding current of the transformer less than or equal to a preset current value and the potential value of the iron core of the transformer less than a preset potential value.

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