Device and method for measuring fault current of neutral point on high-voltage side of voltage transformer

Abstract

The invention discloses a voltage transformer high-voltage side neutral point fault current measuring device and method, and belongs to the technical field of power distribution networks. The device comprises a power distribution network voltage transformer fault current test experiment platform, and a power supply module, a simulation bus 0P, a simulation bus 1P, a simulation bus 2P, a simulation impedance Z, a ground capacitor C1, a ground capacitor C2, a ground capacitor C3, a voltage transformer PT and single-phase breakers corresponding to three phases A, B and C in the power distribution network voltage transformer fault current test experiment platform. The size of the capacitors on the circuits and the number of the circuits can be changed by controlling opening and closing of the three-phase circuit breakers, series connection and parallel connection of the capacitors are achieved, faults of any phase can be controlled to occur or stop, and experiments are more flexible. The device is applied to a 6-35KV grade power distribution network, a measurement experiment can be completed under the condition of uninterruptible power supply, and the voltage transformer is protected from being burnt by fault current in the experiment.

Description

Technical Field

[0001] The invention belongs to the technical field of distribution networks, and particularly relates to a device and method for measuring the fault current of the neutral point on the high-voltage side of a voltage transformer. Background Art

[0002] At present, the 6-35 kV distribution network is large in scale and complex in structure. To reduce the impact of shutdown and improve the stability of power supply, the neutral point is generally not directly grounded. When a single-phase grounding fault occurs in the neutral-point non-grounding system and at the moment when the single-phase grounding fault disappears, due to the change of the fault-phase voltage, a large amount of free charge transfer will cause overcurrent inside the system, resulting in faults in the power equipment in the distribution network system and affecting the normal operation of the power grid system.

[0003] Engineering measures such as installing a harmonic suppression device on the open winding of the voltage transformer and installing a resistor between the neutral point of the high-voltage side of the voltage transformer and the ground have been adopted to avoid faults. However, with the continuous development of the distribution network, the proportion of cable lines in the urban distribution network is increasing, and the line-to-ground capacitive current is increasing day by day. The existing suppression measures are gradually not applicable to the current distribution network system. Therefore, an experimental device and method that can simulate the real operation environment of the distribution network, freely control the operating conditions, and detect the overcurrent in the system in real time are of great significance for the safe and economic operation of the distribution network system.

[0004] In the current measurement experiments, once a large fault current appears inside the system, it will trigger protection and cause the experiment to stop. Moreover, when measuring the fault current without installing a surge suppressor, the voltage transformer is easily burned out accidentally. Therefore, there is currently no suitable device and method for measuring the fault current of the neutral point on the high-voltage side of the voltage transformer. Summary of the Invention

[0005] Aiming at the above deficiencies in the prior art, the device and method for measuring the fault current of the neutral point on the high-voltage side of a voltage transformer provided by the invention solve the technical problems that in the existing methods, a large fault current will appear inside the system during measurement, triggering protection, or when measuring the inrush current without installing an inrush current suppressor, the voltage transformer is accidentally burned out, resulting in the inability to carry out the test normally.

[0006] To achieve the above invention purpose, the technical solution adopted by the invention is: a device for measuring the fault current of the neutral point on the high-voltage side of a voltage transformer, including a test experiment platform for the fault current of the distribution network voltage transformer and a power supply module, an analog bus 0P, an analog bus 1P, an analog bus 2P, an analog impedance Z, a ground capacitance C1, a ground capacitance C2, a ground capacitance C3, a voltage transformer PT, and single-phase circuit breakers corresponding to three phases A, B, and C inside the test experiment platform for the fault current of the distribution network voltage transformer;

[0007] Among them, the power supply module is connected to one end of the analog impedance Z through the analog bus 0P, the other end of the analog impedance Z is connected to the analog bus 1P, the analog bus 1P is also respectively connected to the potential transformer PT, the analog bus 2P, the ground capacitance C1, the ground capacitance C2 and the ground capacitance C3, and the analog bus 2P is also connected to three single-phase circuit breakers;

[0008] The power supply module is used to provide power, the single-phase circuit breaker is used to precisely control the single-phase ground fault that occurs, the analog bus 0P is used to connect the power supply module and the analog impedance Z, the analog bus 1P is used to replace the potential transformer to prevent it from being accidentally burned, and the analog bus 2P is used to prevent the single-phase ground fault from having an uncontrollable impact on the inside of the experimental platform.

[0009] Further: The power supply module includes an alternator U S and a voltage regulating transformer G1. The voltage regulating transformer G1 adopts a Y0 / Y0 / open delta connection method and is used to boost the voltage to the voltage level required for the experiment.

[0010] Further: A circuit breaker is provided between the analog bus 0P and the analog bus 1P, and a circuit breaker is provided between the analog bus 1P and the analog bus 2P.

[0011] A method for measuring the neutral point fault current on the high voltage side of a potential transformer, the method includes the following steps:

[0012] S1. Connect the potential transformer and the ground capacitance to the analog bus, and simulate the state of the potential transformer under normal operation in a 6-35 kV distribution network through the distribution network potential transformer fault current test experimental platform;

[0013] S2. Ground the analog bus 2P through the single-phase circuit breaker that controls the ground fault, connect the analog bus 1P and the analog bus 2P through the three-phase circuit breaker, and close the circuit breaker between any single-phase circuit breaker and the analog bus to simulate the state when a single-phase ground fault occurs in a 6-35 kV distribution network;

[0014] S3. Simulate the state of the 6-35 kV distribution network at the moment when the single-phase ground fault disappears by disconnecting the circuit breaker between the analog buses, and measure the magnitude of the fault current at the moment when the single-phase ground fault disappears without installing a protection device or the magnitude of the fault current at the moment when the single-phase ground fault disappears with a protection device installed through the distribution network potential transformer fault current test experimental platform.

[0015] Further: In the S3, the method for measuring the magnitude of the fault current at the moment when the single-phase ground fault disappears without installing a protection device includes the following sub-steps:

[0016] A1. Separate the voltage transformer from the test platform for measuring the fault current of the distribution network voltage transformer, control the elimination of the single-phase ground fault, and simultaneously ground the simulation bus. Simulate the state at the moment when the single-phase ground fault disappears when the protection device is not installed on the voltage transformer under a 6 - 35 kV distribution network through the test platform for measuring the fault current of the grid voltage transformer;

[0017] A2. Connect the waveform recording analyzer to the simulation bus at the fault location for measuring the target current value.

[0018] Furthermore, in step S3, the method for measuring the magnitude of the fault current at the moment when the single-phase ground fault disappears with the protection device installed includes the following sub-steps:

[0019] B1. Control the elimination of the single-phase ground fault, and simulate the state at the moment when the single-phase ground fault disappears when the protection device is installed on the voltage transformer under a 6 - 35 kV distribution network through the test platform for measuring the fault current of the grid voltage transformer;

[0020] B2. Connect the waveform recording analyzer to the simulation bus at the fault location for measuring the target current value.

[0021] The beneficial effects of the present invention are as follows: The present invention provides a device and method for measuring the fault current at the neutral point of the high voltage side of a voltage transformer. It can change the size of the capacitance and the number of lines on the line by controlling the opening and closing of the three-phase circuit breaker to achieve the series and parallel connection of capacitors, and can also control any phase to have or stop a fault, making the experiment more flexible.

[0022] The present invention is applied to a 6 - 35 kV distribution network, accurately measures the fault current at the neutral point of the high voltage side of the voltage transformer during the occurrence and disappearance of a single-phase ground fault in the system, can complete the measurement experiment without power interruption, and protects the voltage transformer from being burned by the fault current during the experiment. Description of the Drawings

[0023] Figure 1 It is a schematic diagram of a device for measuring the fault current at the neutral point of the high voltage side of a voltage transformer according to the present invention.

[0024] Figure 2 It is a flowchart of a method for measuring the fault current at the neutral point of the high voltage side of a voltage transformer according to the present invention.

[0025] Figure 3 It is an equivalent calculation circuit of a 6 - 35 kV distribution network.

[0026] Figure 4 It is a relationship diagram of current and reactance ratio.

[0027] Figure 5 It is a circuit diagram of the voltage transformer with a current-sensitive resistor connected to the primary side as a protection device in the experiment of the present invention.

[0028] Figure 6 This is the circuit diagram of the voltage transformer in the experiment of the present invention when a resistor is connected to the auxiliary side as a protection device. Specific embodiments

[0029] The following describes the specific embodiments of the present invention to facilitate those skilled in the art of this technology to understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those of ordinary skill in the art of this technology, as long as various changes are within the spirit and scope of the present invention defined and determined by the appended claims, these changes are obvious, and all inventions and creations using the concept of the present invention are within the scope of protection.

[0030] As Figure 1 shown, in an embodiment of the present invention, a device for measuring the fault current of the neutral point on the high-voltage side of a voltage transformer includes a test experiment platform for the fault current of a distribution network voltage transformer and a power supply module, an analog bus 0P, an analog bus 1P, an analog bus 2P, an analog impedance Z, a ground capacitance C1, a ground capacitance C2, a ground capacitance C3, a voltage transformer PT, and single-phase circuit breakers corresponding to three phases A, B, and C in the test experiment platform for the fault current of the distribution network voltage transformer;

[0031] Among them, the power supply module is connected to one end of the analog impedance Z through the analog bus 0P, the other end of the analog impedance Z is connected to the analog bus 1P, the analog bus 1P is also respectively connected to the voltage transformer PT, the analog bus 2P, the ground capacitance C1, the ground capacitance C2, and the ground capacitance C3, and the analog bus 2P is also connected to the three single-phase circuit breakers;

[0032] The power supply module is used to provide power, and the single-phase circuit breakers are used to precisely control the single-phase ground fault that occurs. In this embodiment, the number of single-phase circuit breakers used is three, corresponding to three phases A, B, and C respectively. By controlling the opening and closing of the single-phase circuit breakers, the occurrence and elimination of the system ground fault and the control of the specific phase are realized. The analog bus 0P is used to connect the power supply module and the analog impedance Z, the analog bus 1P is used to replace the voltage transformer to prevent it from being accidentally burned, and the analog bus 2P is used to prevent the single-phase ground fault from having an uncontrollable impact on the inside of the experiment platform.

[0033] In this embodiment, the voltage transformer PT is connected to the analog bus 1P, so that the fault current that originally leaked to the ground through the neutral point on the primary side of the voltage transformer PT now directly leaks to the ground through the analog bus 1P. The size of the system ground capacitance C is controlled by multiple grounding lines and their series and parallel connections, and a waveform recording and analyzing instrument is used to collect and measure the target current value of the analog bus at the fault location during the experiment.

[0034] The power supply module includes an AC generator US And a voltage regulating transformer G1, which is connected in the Y0 / Y0 / open delta connection mode, is used to boost the voltage to the voltage level required for the experiment.

[0035] A circuit breaker is provided between the analog bus 0P and the analog bus 1P, and a circuit breaker is provided between the analog bus 1P and the analog bus 2P.

[0036] In this embodiment, there is no externally applied voltage and current on the analog bus 1P. One analog bus can be connected to multiple lines, and a waveform recording analyzer is connected to the analog bus at the fault location to collect the target current value on the analog bus. Among them, the waveform recording analyzer has multiple input and output ports for voltage and current, and can simultaneously record the voltage and current of multiple branches, which is helpful for measuring the target current value.

[0037] Such as Figure 2 shown, a method for measuring the neutral point fault current on the high voltage side of a voltage transformer, the method includes the following steps:

[0038] S1. Connect the voltage transformer and the ground capacitance to the analog bus, and simulate the normal working state of the voltage transformer under a 6 - 35KV distribution network through the distribution network voltage transformer fault current test experimental platform;

[0039] S2. Ground the analog bus 2P through the single - phase circuit breaker for controlling the ground fault, and connect the analog bus 1P and the analog bus 2P through the three - phase circuit breaker. Close the circuit breaker between any single - phase circuit breaker and the analog bus to simulate the state when a single - phase ground fault occurs in a 6 - 35KV distribution network;

[0040] S3. Simulate the state of the 6 - 35KV distribution network at the moment when the single - phase ground fault disappears by disconnecting the circuit breaker between the analog buses, and measure the magnitude of the inrush current at the moment when the single - phase ground fault disappears without installing a protection device or the magnitude of the fault current at the moment when the single - phase ground fault disappears with a protection device installed through the distribution network voltage transformer fault current test experimental platform.

[0041] In the above S3, the method for measuring the magnitude of the fault current at the moment when the single - phase ground fault disappears without installing a protection device includes the following sub - steps:

[0042] A1. Separate the voltage transformer from the distribution network voltage transformer inrush current test experimental platform, control the elimination of the single - phase ground fault, and simultaneously ground the analog bus, and simulate the state of the voltage transformer without installing a protection device at the moment when the single - phase ground fault disappears under a 6 - 35KV distribution network through the power grid voltage transformer fault current test experimental platform;

[0043] A2. Connect the waveform recording analyzer to the analog bus at the fault location to measure the target current value.

[0044] In S3, the method for measuring the magnitude of the fault current at the moment when the single-phase ground fault disappears with the protection device installed includes the following sub-steps:

[0045] B1. Control the elimination of the single-phase ground fault, and simulate the state at the moment when the single-phase ground fault disappears with the protection device installed on the voltage transformer under a 6 - 35 kV distribution network through the power grid voltage transformer fault current test experimental platform;

[0046] B2. Connect the waveform recording analyzer to the analog bus at the fault location for measuring the target current value.

[0047] After a single-phase ground fault occurs, the voltage of the non-fault phase rises from the phase voltage to the line voltage, and after the fault is eliminated, it returns from the line voltage to the phase voltage. However, because the single-phase ground fault has been eliminated, a large amount of charge in the system can only be discharged to the ground through the grounding point on the primary side of the voltage transformer, which will cause the voltage transformer to saturate, generate over-current oscillation, and thus burn out the voltage transformer. Through A1 in step S3, that is, using the analog bus to replace the voltage transformer at the moment when the single-phase ground fault is eliminated, and collecting data through the waveform recording analyzer, the acquisition of the fault current data is completed on the premise of preventing the voltage transformer from being burned out.

[0048] In this embodiment, when the power distribution network voltage transformer fault current test experimental platform provided by the present invention simulates the state of a single-phase ground fault in a 6 - 35 kV distribution network in step S2, it should be known that the magnitude of the fault current at this time is closely related to the residual magnetism Φ of the voltage transformer s and the phase angle α of the fault phase at the fault moment.

[0049] Before the occurrence of the single-phase ground fault in the fault phase, the voltage expression of the non-fault phase voltage transformer is:

[0050] u N =U m sin(ωt + α)

[0051] where u N is the instantaneous value of the system non-fault phase voltage, U m is the peak value of the phase voltage, and α is the initial phase angle of the non-fault phase voltage.

[0052] When a single-phase ground fault occurs in the fault phase, the voltage of the non-fault phase voltage transformer to the ground changes from the phase voltage to the line voltage, and the voltage expression is:

[0053]

[0054] The counter electromotive force of the voltage transformer winding is balanced with the voltage, and the balance expression is:

[0055]

[0056] Among them, N1 is the number of turns of the non-faulty phase voltage transformer winding, φ N is the instantaneous value of the magnetic flux of the non-faulty phase voltage transformer, R1 is the resistance of the primary winding of the voltage transformer, and i m is the exciting current on the primary side of the voltage transformer.

[0057] If the iron core of the voltage transformer is not saturated, the magnetic flux and the exciting current are linearly related, and the linear expression is:

[0058]

[0059] Among them, L1 is the equivalent inductance on the primary side of the voltage transformer.

[0060] By combining the above equations, the instantaneous value of the magnetic flux of the non-faulty phase voltage transformer can be obtained as the superposition of two components, namely the steady-state magnetic flux and the transient magnetic flux, and the superposition expression is:

[0061]

[0062] Considering R1 = ωL1, the magnetic flux expression can be obtained:

[0063]

[0064] Among them, Φ m is the peak value of the magnetic flux during normal operation, and

[0065] Then the instantaneous value of the magnetic flux of the non-faulty phase voltage transformer is:

[0066]

[0067] Considering the existence of the residual magnetic flux Φ s the instantaneous value of the magnetic flux of the non-faulty phase voltage transformer is:

[0068]

[0069] When the number of turns of the voltage transformer coil and the terminal voltage are determined, Φ m is a definite value; when the equivalent inductance and equivalent resistance of the voltage transformer are determined, its decay time constant is also determined. Therefore, for a certain voltage transformer, the steady-state magnetic flux amplitude and the decay time constant are determined. The parameters that affect the magnitude of the instantaneous magnetic flux in the iron core are mainly the phase voltage phase angle α at the time of the fault and the residual magnetic flux Φ sWhen a single-phase grounding fault occurs in a power grid with an ungrounded neutral point, for a non-faulty-phase voltage transformer, the terminal voltage suddenly changes to the line voltage, the core of the voltage transformer enters the saturation region, and magnetizing inrush current is generated in the winding. The magnitude of the inrush current can reach dozens or even hundreds of times the steady-state current, and its heat generation may cause damage to the voltage transformer due to overheating. The factors that have a greater impact on the magnitude of the magnetizing inrush current in the voltage transformer winding, that is, on the magnitude of the magnetic flux in the core, are the phase angle α of the voltage of this phase at the time of the fault and the residual magnetic flux Φ in the core. s 。

[0070] Residual magnetic flux Φ s The magnitude of the residual magnetic flux Φ is directly related to whether the voltage transformer is saturated. When measuring the magnitude of the inrush current at the moment when the single-phase grounding fault disappears with the protection device installed in step S3, if the voltage transformer is saturated, it will cause the inrush current to increase again, affecting the measurement result. Figure 3 is the equivalent calculation circuit of a 6 - 35 kV distribution network, E S is the equivalent power source of the upper-level power grid of 6 - 35 kV, X S is the equivalent reactance of the upper-level power grid of 6 - 35 kV, X C is the equivalent capacitive reactance of the 6 - 35 kV power grid, X PT is the equivalent reactance value of the 6 - 35 kV voltage transformer. i S is the total current of 6 - 35 kV, i C is the current flowing through the equivalent capacitive reactance of the 6 - 35 kV power grid, i PT The current flowing through the 6 - 35 kV voltage transformer. U C is the terminal voltage of the equivalent capacitive reactance of the 6 - 35 kV power grid, U PT is the terminal voltage of the 6 - 35 kV voltage transformer. Since the two are in a parallel relationship, so there is U C =U PT 。

[0071] In actual operation, during normal operation, the reactance value of the 6 - 35 kV voltage transformer is as high as several megohms, which is much larger than the capacitive reactance value of the capacitor. Therefore, there is X PT >>X C , since the two are in a parallel relationship, X PT can be ignored during steady-state calculation. Since the equivalent system reactance is very small, define the reactance ratio

[0072]

[0073] In the formula, I is the loop current in the equivalent circuit of the 6 - 35 kV distribution network, X L is the equivalent inductive reactance of the 6 - 35 kV power grid;

[0074] Figure 4It is a graph showing the relationship between current and reactance ratio. The current rises non-linearly as the reactance ratio increases. K X is close to 1, and the current tends to infinity. This is theoretical. However, due to the existence of the voltage transformer, when K X increases, the current also increases accordingly, resulting in an increase in the terminal voltage of the capacitor and the terminal voltage of the voltage transformer. The voltage transformer enters the saturation region for operation, and the reactance decreases somewhat, which also limits the rise of the voltage, restricting the magnitude of the inrush current within a certain range, making it easy to be collected by the waveform recording analyzer. At the same time, it proves that the method provided by the present invention can be achieved regardless of whether the voltage transformer is saturated.

[0075] A method for measuring the fault current at the neutral point of the high-voltage side of a voltage transformer provided by the present invention can, for various different protection methods, measure the magnitude of the fault current in the distribution network system while testing the suppression effect of different protection methods on the fault current. The existing protection methods for the 6 - 35KV distribution network fault current mainly include connecting an arc suppression coil at the system neutral point to suppress the impact current of the voltage transformer when a short circuit occurs, connecting a current-sensitive resistor on the primary side to suppress the inrush current of the voltage transformer when a ground fault occurs and is eliminated, and connecting an adjustable resistor on the auxiliary side to suppress the overcurrent in the system:

[0076] (1) Connect an arc suppression coil at the system neutral point, measure the phase voltage value of the 0P bus and the phase voltage value of the 1P bus. When a short circuit occurs during the operation of any line, substitute into the following formula for calculation:

[0077] I a = 3ωCU

[0078] where C is the line capacitance and U is the phase voltage, to obtain the over-compensation condition, as shown in the following formula:

[0079]

[0080] L is the inductance value of the arc suppression coil. Under the over-compensation condition, when a single-phase ground fault occurs, over-compensation can well suppress the impact current and reduce the effective value of the current of the three-phase voltage transformer after the short circuit fault. Under the under-compensation condition, whether a single-phase fault occurs or at the moment when the short circuit fault disappears, the three-phase of the voltage transformer may generate impact current and oscillating current, but it has a certain occasionality, which is related to the phase of the circuit where the short circuit occurs and disappears, and the magnitudes of the impact current and oscillating current increase with the increase of the compensation inductance.

[0081] (2) Connect a current-sensitive resistor on the primary side, such as Figure 5As shown, when inrush current of the voltage transformer appears, it can be adjusted to an appropriate resistance value to achieve a damping effect, and it has no impact on the system or the transformer during normal operation, that is, the resistance value of the current-limiting resistor is zero during normal operation; when inrush current occurs, the suppression device switches to a high-resistance state and will not be affected by overvoltage and decrease, thus playing a damping role.

[0082] (3) Connect an adjustable resistor on the auxiliary side, such as Figure 6 As shown, the key lies in the accuracy of resonance detection and the rapidity of input. The common principle is to collect the amplitude of the zero-sequence voltage of the system. When it is detected that the zero-sequence voltage exceeds the setting value, it is considered that resonance has occurred in the system. Then, the open delta of the voltage transformer is short-circuited through a resistor for a short time. The smaller the access value of the adjustable resistor, the more effective it is in suppressing overcurrent. Since the adjustable resistor is connected in the zero-sequence circuit of the system, it has no impact on the normal working current.

[0083] In summary, the present invention proposes a method for measuring the fault current at the neutral point of the high-voltage side of a voltage transformer by replacing the voltage transformer with an analog bus, which can freely control the operation environment of the distribution network (including the time of fault occurrence and elimination, the size of the system's capacitance to the ground, the installation of different types of protection devices, etc.), and can be equipped with protection devices to detect their protection effects and is not affected by the fault current measurement method of the system's trip protection.

[0084] The beneficial effects of the present invention are as follows: The present invention provides a device and method for measuring the fault current at the neutral point of the high-voltage side of a voltage transformer, which can change the size of the capacitance on the line and the number of lines by controlling the opening and closing of the three-phase circuit breaker to achieve the series and parallel connection of capacitors, and can also control any phase to have or stop a fault, making the experiment more flexible.

[0085] The present invention is applied to a 6-35 KV-class distribution network, and can accurately measure the fault current at the neutral point of the high-voltage side of the voltage transformer at the moment when a single-phase ground fault occurs and the fault disappears in the system. The measurement experiment can be completed without power interruption, and the voltage transformer can be protected from being burned by the fault current during the experiment.

[0086] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "thickness", "upper", "lower", "horizontal", "top", "bottom", "inner", "outer", "radial", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention. In addition, the terms "first", "second", "third" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of technical features. Therefore, the features defined by "first", "second", "third" may explicitly or implicitly include one or more of such features.

Claims

1. A device for measuring the fault current of the neutral point on the high-voltage side of a voltage transformer, characterized in that, It includes a test experiment platform for the fault current of a distribution network voltage transformer, as well as a power supply module, a simulated bus 0P, a simulated bus 1P, a simulated bus 2P, a simulated impedance Z, a ground capacitance C1, a ground capacitance C2, a ground capacitance C3, a voltage transformer PT, and single-phase circuit breakers corresponding to three phases A, B, and C within the test experiment platform for the fault current of the distribution network voltage transformer; Among them, the power supply module is connected to one end of the simulated impedance Z through the simulated bus 0P, the other end of the simulated impedance Z is connected to the simulated bus 1P, the simulated bus 1P is also respectively connected to the voltage transformer PT, the simulated bus 2P, the ground capacitance C1, the ground capacitance C2, and the ground capacitance C3, and the simulated bus 2P is also connected to three single-phase circuit breakers; The power supply module is used to provide power, the single-phase circuit breaker is used to precisely control the single-phase ground fault that occurs, the simulated bus 0P is used to connect the power supply module and the simulated impedance Z, the simulated bus 1P is used to replace the voltage transformer to prevent it from being accidentally burned, and the simulated bus 2P is used to prevent the single-phase ground fault from having an uncontrollable impact on the interior of the test experiment platform.

2. The measuring device for the neutral point fault current on the high voltage side of the voltage transformer according to claim 1, wherein The power supply module includes an alternator U S and a voltage regulating transformer G1. The voltage regulating transformer G1 is connected in the Y0 / Y0 / open delta connection mode and is used to boost the voltage to the voltage level required for the experiment.

3. The high-voltage side neutral point fault current measuring device for a voltage transformer according to claim 1, wherein A circuit breaker is provided between the simulated bus 0P and the simulated bus 1P, and a circuit breaker is provided between the simulated bus 1P and the simulated bus 2P.

4. A method for measuring the neutral point fault current on the high voltage side of a voltage transformer, which is applied to the device for measuring the neutral point fault current on the high voltage side of the voltage transformer according to any one of claims 1 to 3, characterized in that, The method includes the following steps: S1. Connect the voltage transformer and the ground capacitance to the simulated bus, and simulate the state when the voltage transformer is operating normally under a 6 - 35 kV distribution network through the test experiment platform for the fault current of the distribution network voltage transformer; S2. Ground the simulated bus 2P by controlling the single-phase circuit breaker of the ground fault, connect the simulated bus 1P and the simulated bus 2P through the three-phase circuit breaker, and close the circuit breaker between any single-phase circuit breaker and the simulated bus to simulate the state when a single-phase ground fault occurs in a 6 - 35 kV distribution network; S3. Simulate the state of the 6 - 35 kV distribution network at the moment when the single-phase ground fault disappears by disconnecting the circuit breaker between the simulated buses, and measure the magnitude of the fault current at the moment when the single-phase ground fault disappears without the protection device installed or the magnitude of the fault current at the moment when the single-phase ground fault disappears with the protection device installed through the test experiment platform for the fault current of the distribution network voltage transformer.

5. The method for measuring the neutral point fault current on the high voltage side of a voltage transformer according to claim 4, wherein In the said S3, the method for measuring the magnitude of the fault current at the moment when the single-phase ground fault disappears without the protection device installed includes the following sub-steps: A1. Separate the voltage transformer from the test experiment platform for the fault current of the distribution network voltage transformer, control the elimination of the single-phase ground fault, and simultaneously ground the simulated bus, and simulate the state at the moment when the single-phase ground fault disappears without the protection device installed under a 6 - 35 kV distribution network through the test experiment platform for the fault current of the grid voltage transformer; A2. Connect the waveform recording analyzer to the simulated bus at the fault location and measure the target current value.

6. The method for measuring the neutral point fault current on the high voltage side of a voltage transformer according to claim 4, characterized in that, In the said S3, the method for measuring the magnitude of the fault current at the moment when the single-phase ground fault disappears with the protection device installed includes the following sub-steps: B1. Control the elimination of the single-phase ground fault, and simulate the state at the moment when the single-phase ground fault disappears with the protection device installed under a 6 - 35 kV distribution network through the test experiment platform for the fault current of the grid voltage transformer; B2. Connect the waveform recording analyzer to the analog bus at the fault location for measuring the target current value.

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