A short-circuit control system and method for a small-current ground fault simulation test

Abstract

The application provides a short-circuit control system and method for a small-current grounding fault simulation test, and belongs to the technical field of power system fault simulation. The system solves the problem that the control precision and cost of the initial phase angle of the existing fault simulation device are difficult to be considered, and the simulation reliability of the transition resistance is low. The system comprises a main circuit and a control circuit. The main circuit is provided with a transition resistance circuit and a bidirectional thyristor in series. The control circuit comprises a synchronous transformer, a zero-crossing detection circuit, a single-chip microcomputer control unit and a thyristor drive circuit which are sequentially connected by signals. The system voltage zero-crossing point is locked by the zero-crossing detection. The bidirectional thyristor is triggered by the single-chip microcomputer according to the preset fault initial phase angle and the transition resistance circuit with multiple fixed resistance parallel connections to realize the grounding fault simulation. The application has the advantages of accurate control, low cost and high reliability, and can be widely applied to the power system fault simulation test and the performance test of the line selection device.

Description

Technical Field

[0001] This application belongs to the field of force system fault simulation technology, specifically relating to a short-circuit control system and method for simulating small current grounding faults. Background Technology

[0002] In my country's 35kV and below medium and low voltage distribution networks, a low-current grounding operation mode with an ungrounded neutral point and grounded via an arc suppression coil is widely adopted. Single-phase grounding faults are the most frequent type of fault in this type of system. The initial phase angle of the fault and the transition resistance are two main factors that determine the transient steady-state characteristics of grounding faults. Accurately simulating single-phase grounding faults under different operating conditions is the foundation for conducting fault characteristic research and verifying the performance of fault location devices.

[0003] In existing technologies, low-current grounding fault simulation devices struggle to simultaneously balance control accuracy, equipment cost, and operational reliability. Some solutions employ RC phase-shifting circuits for trigger angle control, which are simple in structure but lack control accuracy and are susceptible to grid harmonic interference, failing to meet the requirements of high-precision quantitative testing. Other solutions utilize DSP / PLC controllers for precise control, achieving the required accuracy but involving complex hardware and software design and high equipment costs, hindering mass production. Furthermore, existing devices often use adjustable resistors to simulate transition resistance, which is prone to poor contact and resistance drift, leading to distorted test data and insufficient operational reliability.

[0004] Therefore, there is an urgent need to develop a low-current grounding fault simulation short-circuit control system that is simple in structure, precise in control, low in cost, and reliable in operation. Summary of the Invention

[0005] The purpose of this invention is to provide a short-circuit control system and method for simulating small current grounding faults, in order to solve the problems in the prior art.

[0006] In a first aspect, embodiments of this application provide a short-circuit control system for simulating low-current grounding faults, the system comprising: Main circuit and control circuit; The main circuit includes a transition resistor circuit and a bidirectional thyristor connected in series between the fault phase and ground. The control circuit includes a synchronous transformer, a zero-crossing detection circuit, a microcontroller control unit, and a bidirectional thyristor drive circuit. The primary side of the synchronous transformer is connected to the system voltage to be simulated, which is used to transform the system voltage into a low-voltage sinusoidal signal with the same phase. The zero-crossing detection circuit is connected to the secondary side of the synchronous transformer. The zero-crossing detection circuit is used to shape the low-voltage sinusoidal signal into a square wave signal corresponding to the positive zero-crossing point of the system voltage. The input terminal of the microcontroller control unit is connected to the output terminal of the zero-crossing detection circuit. The microcontroller control unit is used to receive the square wave signal, start the internal timer on the falling edge of the square wave signal according to the preset fault initial phase angle, and output the conduction control signal through the bidirectional thyristor drive circuit when the timing time reaches the delay time corresponding to the fault initial phase angle. The input terminal of the bidirectional thyristor drive circuit is connected to the output terminal of the microcontroller control unit, and the output terminal is connected to the gate of the bidirectional thyristor. The bidirectional thyristor drive circuit is used to receive the conduction control signal and trigger the bidirectional thyristor to conduct, so that the faulty phase is grounded through a preset transition resistor circuit, thus completing the simulation of a single-phase grounding fault.

[0007] Furthermore, the zero-crossing detection circuit includes a voltage comparator, a Schmitt trigger, and an optocoupler connected in sequence; The voltage comparator is used to convert a low-voltage sinusoidal signal into a rectangular wave; The Schmitt trigger is used to shape rectangular waves to improve edge steepness and anti-interference capability; The optocoupler isolator is used to achieve electrical isolation between field signals and the microcontroller control unit.

[0008] Furthermore, the microcontroller control unit is also equipped with a serial communication interface, through which the microcontroller control unit communicates with the host computer and receives the preset fault initial phase angle sent by the host computer.

[0009] Furthermore, the transition resistor circuit is composed of multiple resistor branches with different resistance values ​​connected in parallel, and each resistor branch includes a fixed resistor connected in series and a switching switch.

[0010] Furthermore, the fixed resistance values ​​of the plurality of resistor branches with different resistance values ​​are distributed according to an exponential law, and the plurality of resistor branches with different resistance values ​​include at least one of 0Ω branch, 5Ω branch, 50Ω branch, 500Ω branch and 5000Ω branch. Among them, the 0Ω branch is used to simulate metallic grounding faults, the 5Ω and 50Ω branches are used to simulate low-resistance grounding faults, the 500Ω branch is used to simulate medium-resistance grounding faults, and the 5000Ω branch is used to simulate high-resistance grounding faults.

[0011] Furthermore, the bidirectional thyristor is a bidirectional thyristor.

[0012] Furthermore, the microcontroller control unit is internally equipped with an angle-to-time conversion module, used to convert time according to the formula... t =( φ (360°)× T Calculate the delay time corresponding to the initial phase angle of the fault, where, φ The preset initial phase angle of the fault.T The system voltage's power frequency period.

[0013] Secondly, embodiments of this application also provide a short-circuit control method for simulating small-current grounding faults, the method comprising the following steps: S1. Acquire the system voltage to be simulated, convert it into a low-voltage sinusoidal signal with the same phase through a synchronous transformer, and then shape the low-voltage sinusoidal signal into a square wave signal corresponding to the positive zero-crossing point of the system voltage through a zero-crossing detection circuit. The falling edge of the square wave signal corresponds to the positive zero-crossing point of the system voltage. S2. The microcontroller control unit obtains the preset target fault initial phase angle and converts it into the corresponding delay time; S3. The microcontroller control unit monitors the square wave signal in real time. When the falling edge of the square wave signal is detected, the internal timer is immediately started to begin timing. S4. When the timer's duration reaches the delay time, the microcontroller control unit outputs a conduction control signal through the bidirectional thyristor drive circuit; S5. After receiving the conduction control signal, the bidirectional thyristor is triggered to conduct, and the faulty phase is grounded through the preset transition resistor circuit to complete the simulation of a single-phase ground fault.

[0014] Furthermore, in step S2, the microcontroller control unit receives the target fault initial phase angle sent by the host computer through the serial communication interface.

[0015] Furthermore, step S5 is preceded by: Based on the target operating conditions, the on / off state of the corresponding resistor branch in the transition resistor circuit is controlled by switching on / off, and the resistance value of the target transition resistor is obtained by combining the switching on / off state.

[0016] As can be seen from the above technical solutions, the present invention has the following advantages: In the short-circuit control system and method for simulating small-current grounding faults in this application, a reference signal that is strictly in phase with the system voltage is obtained through a synchronous transformer. This signal, combined with a zero-crossing detection circuit, precisely locks the positive zero-crossing point of the system voltage. A single-chip microcomputer control unit then performs high-precision timing triggering according to a preset initial phase angle of the fault, achieving precise control of the fault triggering phase angle. Simultaneously, the core control unit uses a general-purpose single-chip microcomputer, eliminating the need for complex software and hardware development, significantly reducing the overall cost of the equipment and enhancing its portability. The system also solves the problem of insufficient reliability in transition resistance simulation. The main circuit uses a bidirectional thyristor as a contactless high-speed on / off switch, combined with a series transition resistance circuit, replacing the traditional easily damaged adjustable resistor. This avoids problems such as poor contact, resistance drift, and burn-out damage, improving the operational stability of the device and the authenticity and reproducibility of the test data. The overall structure of this system is streamlined, allowing for rapid integration with various power distribution network test systems, thus improving the efficiency of conducting grounding fault simulation tests. Attached Figure Description

[0017] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the description will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a connection diagram of the short-circuit control system for the low-current grounding fault simulation test of this application. Figure 2 This is a schematic diagram of the zero-crossing detection circuit of this application. Figure 3 This is a schematic diagram showing the correspondence between phase angle and time point in this application; Figure 4 This is a schematic diagram of the circuit principle of the thyristor drive circuit of this application; Figure 5 This is a schematic diagram illustrating the implementation principle of different transition resistors in this application; Figure 6 This is a flowchart of the main program of the microcontroller in this application; Figure 7 This is a flowchart illustrating the microcontroller interrupt service routine of this application; Figure 8 This is a flowchart illustrating the serial port communication program of this application; Figure 9 A schematic diagram of the A-phase voltage and zero-mode current waveforms collected when the initial phase angle of the fault is set to 90° and the transition resistance is zero for this application. Figure 10 This is a flowchart illustrating the short-circuit control method for the low-current grounding fault simulation test of this application. Detailed Implementation

[0019] Various embodiments of the invention will be described more fully in the short-circuit control system and method for simulating small-current grounding faults, which will be described in detail below. The invention may have various embodiments, and adjustments and modifications may be made therein. However, it should be understood that there is no intention to limit the various embodiments of the invention to the specific embodiments disclosed herein, but rather the invention should be understood to cover all modifications, equivalents, and / or alternatives falling within the spirit and scope of the various embodiments of the invention.

[0020] It should be understood that, when used in this specification, the term "comprising" indicates the presence of the described feature, integral, step, operation, element, and / or component, but does not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components, and / or collections thereof. The terms "comprising," "including," "having," and variations thereof all mean "including but not limited to," unless otherwise specifically emphasized.

[0021] The terms "one embodiment" or "some embodiments" used in this application mean that one or more embodiments of this application include the specific features, structures, or characteristics described in 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 application do not necessarily refer to the same embodiment, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized.

[0022] To make the objectives, features, and advantages of this invention more apparent and understandable, specific embodiments and accompanying drawings will be used to clearly and completely describe the technical solutions protected by this invention. Obviously, the embodiments described below are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0023] Please see Figure 1 The figure shows a short-circuit control system for a low-current ground fault simulation test. The system includes: Main circuit and control circuit; The main circuit includes a transition resistor circuit and a bidirectional thyristor connected in series between the fault phase and ground. The control circuit includes a synchronous transformer, a zero-crossing detection circuit, a microcontroller control unit, and a bidirectional thyristor drive circuit. The primary side of the synchronous transformer is connected to the system voltage to be simulated, which is used to transform the system voltage into a low-voltage sinusoidal signal with the same phase. The zero-crossing detection circuit is connected to the secondary side of the synchronous transformer. The zero-crossing detection circuit is used to shape the low-voltage sinusoidal signal into a square wave signal corresponding to the positive zero-crossing point of the system voltage. The input terminal of the microcontroller control unit is connected to the output terminal of the zero-crossing detection circuit. The microcontroller control unit is used to receive the square wave signal, start the internal timer on the falling edge of the square wave signal according to the preset fault initial phase angle, and output the conduction control signal through the bidirectional thyristor drive circuit when the timing time reaches the delay time corresponding to the fault initial phase angle. The input terminal of the bidirectional thyristor drive circuit is connected to the output terminal of the microcontroller control unit, and the output terminal is connected to the gate of the bidirectional thyristor. The bidirectional thyristor drive circuit is used to receive the conduction control signal and trigger the bidirectional thyristor to conduct, so that the faulty phase is grounded through a preset transition resistor circuit, thus completing the simulation of a single-phase grounding fault.

[0024] As a refinement and extension of the specific implementation of the above embodiments, in order to fully illustrate the specific implementation process of this embodiment, another short-circuit control system for simulating small current ground faults is provided. This system includes: Main circuit and control circuit; The main circuit includes a transition resistor circuit and a bidirectional thyristor connected in series between the fault phase and ground. The control circuit includes a synchronous transformer, a zero-crossing detection circuit, a microcontroller control unit, and a bidirectional thyristor drive circuit. The primary side of the synchronous transformer is connected to the system voltage to be simulated, which is used to transform the system voltage into a low-voltage sinusoidal signal with the same phase. The zero-crossing detection circuit is connected to the secondary side of the synchronous transformer. The zero-crossing detection circuit is used to shape the low-voltage sinusoidal signal into a square wave signal corresponding to the positive zero-crossing point of the system voltage. The input terminal of the microcontroller control unit is connected to the output terminal of the zero-crossing detection circuit. The microcontroller control unit is used to receive the square wave signal, start the internal timer on the falling edge of the square wave signal according to the preset fault initial phase angle, and output the conduction control signal through the bidirectional thyristor drive circuit when the timing time reaches the delay time corresponding to the fault initial phase angle. The input terminal of the bidirectional thyristor drive circuit is connected to the output terminal of the microcontroller control unit, and the output terminal is connected to the gate of the bidirectional thyristor. The bidirectional thyristor drive circuit is used to receive the conduction control signal and trigger the bidirectional thyristor to conduct, so that the faulty phase is grounded through a preset transition resistor circuit, thus completing the simulation of a single-phase grounding fault.

[0025] In some embodiments, the zero-crossing detection circuit includes a voltage comparator, a Schmitt trigger, and an optocoupler connected in sequence; The voltage comparator is used to convert a low-voltage sinusoidal signal into a rectangular wave; The Schmitt trigger is used to shape rectangular waves to improve edge steepness and anti-interference capability; The optocoupler isolator is used to achieve electrical isolation between field signals and the microcontroller control unit.

[0026] In some embodiments, the microcontroller control unit is further configured with a serial communication interface, through which the microcontroller control unit communicates with the host computer and receives a preset fault initial phase angle sent by the host computer.

[0027] In some embodiments, the transition resistor circuit is composed of multiple resistor branches with different resistance values ​​connected in parallel, and each resistor branch includes a fixed resistor connected in series and a switching switch.

[0028] In some embodiments, the fixed resistance values ​​of the plurality of resistor branches with different resistance values ​​are distributed according to an exponential law, and the plurality of resistor branches with different resistance values ​​include at least one of 0Ω branch, 5Ω branch, 50Ω branch, 500Ω branch and 5000Ω branch. Among them, the 0Ω branch is used to simulate metallic grounding faults, the 5Ω and 50Ω branches are used to simulate low-resistance grounding faults, the 500Ω branch is used to simulate medium-resistance grounding faults, and the 5000Ω branch is used to simulate high-resistance grounding faults.

[0029] In some embodiments, the bidirectional thyristor is a bidirectional thyristor.

[0030] In some embodiments, the microcontroller control unit is internally configured with an angle-to-time conversion module, used to convert time according to the formula... t =( φ (360°)× T Calculate the delay time corresponding to the initial phase angle of the fault, where, φ The preset initial phase angle of the fault. T The system voltage's power frequency period.

[0031] For example, a complete and implementable short-circuit control system for simulating small current grounding faults is applied to a 10kV distribution network active static simulation test system. The primary system line voltage is 100V, the power frequency is 50Hz, the period is T=20ms, and the system neutral point is ungrounded.

[0032] The system is divided into two parts: a control loop and a main loop. The control loop realizes system voltage synchronization, zero-crossing detection, fault initial phase angle timing and trigger control; the main loop realizes fault phase short circuit to ground and transition resistance simulation.

[0033] The control circuit consists of four parts connected in sequence: a synchronous transformer, a zero-crossing detection circuit, a microcontroller control unit, and a bidirectional thyristor drive circuit.

[0034] The synchronous transformer uses a precision voltage transformer with a turns ratio of 220V / 5V and an accuracy class of 0.2. The primary side is connected to the line voltage of the system to be simulated, and the secondary side outputs a 5V low-voltage sinusoidal signal that is in phase with the system voltage and has no phase offset, providing a precise phase synchronization reference for the entire system and ensuring that there is no phase error in the zero-crossing detection.

[0035] The circuit schematic of the zero-crossing detection circuit is as follows: Figure 2As shown, it consists of three parts connected in sequence: a voltage comparator, a Schmitt trigger, and an optocoupler isolator. The voltage comparator uses the low-power, high-precision LM393 comparator. Its non-inverting input is connected to the low-voltage sinusoidal signal output from the synchronous transformer, and its inverting input is grounded (0 potential reference point). When the sinusoidal signal is in the positive half-cycle, the comparator outputs a high level, and in the negative half-cycle, it outputs a low level, converting the sine wave into a rectangular wave with the corresponding zero crossing point. The Schmitt trigger uses an inverted Schmitt trigger 40106BD with a 100mV hysteresis voltage to shape the square wave, significantly improving the signal edge steepness while suppressing interference from power grid harmonics and avoiding false triggering. After shaping by the inverted Schmitt trigger, the falling edge of the output square wave signal is completely synchronized with the positive zero-crossing point of the system voltage, and the rising edge is completely synchronized with the negative zero-crossing point of the system voltage. The optocoupler uses a TLP521-1 linear optocoupler to achieve electrical isolation between the field high-voltage side signal and the microcontroller control unit, blocking high-voltage interference from entering the control circuit and improving the system's anti-interference capability and operational safety.

[0036] The microcontroller control unit uses the STC89C52 51 series microcontroller with a crystal oscillator frequency of 11.0592MHz and a machine cycle of approximately 1.09μs. The timer operates in mode 1 (16-bit timer mode), which can achieve high-precision timing at the microsecond level and fully meet the control accuracy requirements of the fault initial phase angle.

[0037] The microcontroller's P3.2 pin (external interrupt 0 pin) is connected to the square wave signal output by the zero-crossing detection circuit. The external interrupt is set to be triggered by the falling edge. When the falling edge of the square wave is detected, the external interrupt is triggered immediately to confirm that the system voltage has reached the positive zero-crossing point. The microcontroller is equipped with a UART serial communication interface, which uses the MAX232 chip to convert TTL level to RS232 level, enabling bidirectional serial communication with the host computer (PC). The serial port baud rate is set to 9600, with 8 data bits, 1 stop bit, and no parity bit. It can receive any fault initial phase angle within the range of 0° to 180° from the host computer and send the parameters back to the host computer for confirmation. The microcontroller has an internally built-in angle-to-time conversion module. Figure 3 This diagram illustrates the correspondence between phase angle and time point, which can be derived from the formula. t =( φ (360°)× T Automatically calculate the delay time, where φ The fault initial phase angle set for the host computer, T =20ms (50Hz power frequency cycle); and calculate the initial value of the timer based on the delay time. The calculation formula is: Initial value of timer N=65536-(t / 1.09μs).

[0038] For example, when setting the initial phase angle of the fault φ When the angle is 90°, the calculated delay time is: t =(90° / 360°)×20ms=5ms, timer initial value N =65536-(5000μs / 1.09μs)=65536-4587=60949, which is 0xEE15 in hexadecimal.

[0039] The circuit schematic of the bidirectional thyristor drive circuit is as follows: Figure 4 As shown, an MOC3021 opto-isolated bidirectional thyristor driver is used to achieve secondary electrical isolation between the control circuit and the main circuit; the P1.0 pin of the microcontroller is connected to pin 2 of the MOC3021, and the output of the MOC3021 is connected to the gate of the high-power bidirectional thyristor in the main circuit.

[0040] When the timer reaches the preset delay time, the microcontroller sets the P1.0 pin to a low level, the internal LED of the MOC3021 turns on, triggering the internal photosensitive bidirectional thyristor to turn on, thereby providing trigger current for the external high-power bidirectional thyristor and realizing the conduction of the bidirectional thyristor in the main circuit.

[0041] The main circuit includes a bidirectional thyristor and a transition resistor circuit, which are connected in series between the faulty phase bus and the ground.

[0042] (1) Bidirectional thyristor The bidirectional thyristor uses the BTA41-600B high-power bidirectional thyristor with a rated on-state current of 40A, a reverse withstand voltage of 600V, and a response speed in the microsecond range. It has no contacts and no mechanical wear, can meet the requirements of frequent on / off tests, and has a service life far exceeding that of mechanical switches.

[0043] (2) Transition resistance circuit The topology diagram of the transition resistor circuit is as follows: Figure 5 As shown, it consists of 5 parallel resistor branches with different resistance values. Each branch includes a fixed resistor connected in series and a switching switch. The switching switch uses a DZ47 series miniature circuit breaker, which supports manual fast switching and can also be expanded into a relay automatic switching.

[0044] The fixed resistor values ​​for the five branches are distributed exponentially, namely 0Ω (straight-through branch), 5Ω, 50Ω, 500Ω, and 5000Ω. All resistors are high-power metal film resistors, with power ratings calculated based on the maximum fault current to ensure long-term operational stability. 0Ω branch: Simulates a metallic ground fault; 5Ω / 50Ω branch: Simulates a low-resistance grounding fault; 500Ω branch: Simulates a medium-resistance ground fault; 5000Ω branch: Simulates a high-resistance grounding fault.

[0045] By controlling the on / off state of different branch switching switches, a single branch can be switched on or multiple branches can be connected in parallel to obtain any target resistance value, covering the full range of transition resistance simulation requirements from 0Ω to 5000Ω.

[0046] The software is written based on the Keil C51 development environment and includes four parts: main program, external interrupt service routine, timer interrupt service routine, and serial communication interrupt service routine.

[0047] (1) Main program The main program flow is as follows Figure 6 As shown, after the system is powered on, it first completes the initialization operation, including setting external interrupt 0 to fall-edge trigger, enabling global interrupt, configuring the timer working mode, initializing serial communication parameters, and initializing I / O port status. After initialization, the program enters a loop standby state, waiting for interrupt trigger.

[0048] (2) External interrupt service routine External interrupt service routine flow is as follows Figure 7 As shown, when the falling edge of the square wave signal (the positive zero-crossing point of the system voltage) is detected, external interrupt 0 is immediately triggered. The interrupt service routine only performs the timer start operation, and the timer starts counting immediately. The program execution time is extremely short, with no additional delay, ensuring that the timing start point is completely synchronized with the zero-crossing point.

[0049] (3) Timer interrupt service routine The timer interrupt service routine is the core control program. When the timer overflows (i.e., the preset delay time is reached), it immediately triggers a timer interrupt. The interrupt service routine performs the following operations: Set the microcontroller's P1.0 pin to low level to output a conduction control signal, triggering the bidirectional thyristor to conduct; Start the short-circuit duration timer. In this embodiment, the short-circuit duration is set to 100ms (5 power frequency cycles) to simulate a transient ground fault. After the short circuit duration is reached, the P1.0 pin is set to a high level, the trigger signal is removed, and the bidirectional thyristor is naturally turned off when the AC current crosses zero, thus ending this fault simulation.

[0050] (4) Serial communication interrupt service routine The serial communication interrupt service routine flow is as follows: Figure 8As shown, when the microcontroller receives the fault initial phase angle data sent by the host computer, it triggers a serial port interrupt; the interrupt service routine performs the following operations: Read the fault initial phase angle data in the serial port receive buffer and send the data back to the host computer for confirmation; Call the angle-to-time conversion function to convert the received angle value into the initial value of the timer and store it in the specified register; When the next zero crossing point arrives, the timer automatically uses the updated initial value to keep time, enabling online, code-free modification of the faulty initial phase angle.

[0051] The system of this embodiment was connected to a 10kV distribution network active static simulation test system to conduct multi-condition test verification. The test results are as follows: Figure 9 The measured waveforms of the fault phase voltage and zero-mode current were collected when the initial phase angle of the fault was set to φ=90° and the transition resistance was R=0Ω (metallic grounding). It can be seen that the maximum amplitude of the transient zero-mode current is about 5.5A.

[0052] Table 1 shows the maximum amplitude of transient zero-mode current (transition resistance) under different fault initial phase angles. R =0Ω); Table 2 shows the maximum amplitude of transient zero-mode current (fault initial phase angle) under different transition resistances. φ =90°) Table 1. Maximum amplitude of transient zero-mode current under different fault initial phase angles (transition resistance) R =0Ω)

[0053] Table 2 Maximum amplitude of transient zero-mode current under different transition resistances (fault initial phase angle) φ =90°)

[0054] The experimental results show that the closer the initial phase angle of the fault is to 90°, the larger the amplitude of the transient zero-mode current; the larger the transition resistance, the smaller the amplitude of the transient zero-mode current, which is in complete agreement with the theoretical analysis. This verifies that the system can accurately control the fault conditions and effectively simulate the transient process of single-phase grounding faults under different operating conditions.

[0055] It should be noted that, during the experiment, the system in this embodiment achieved precise and flexible control of the initial phase angle and transition resistance of the fault. It is easy to operate, stable and reliable in operation, and the collected test data accurately reflects the influence of different fault conditions on the transient characteristics of small current grounding faults, verifying the practicality and effectiveness of the system. At the same time, the system has low manufacturing cost, is easy to interface with the test system, and can quickly complete multiple sets of tests, greatly improving the test efficiency.

[0056] Please see Figure 10 The diagram shows a flow chart of a short-circuit control method for simulating a low-current grounding fault. The method includes: S1. Acquire the system voltage to be simulated, convert it into a low-voltage sinusoidal signal with the same phase through a synchronous transformer, and then shape the low-voltage sinusoidal signal into a square wave signal corresponding to the positive zero-crossing point of the system voltage through a zero-crossing detection circuit. The falling edge of the square wave signal corresponds to the positive zero-crossing point of the system voltage. S2. The microcontroller control unit obtains the preset target fault initial phase angle and converts it into the corresponding delay time; S3. The microcontroller control unit monitors the square wave signal in real time. When the falling edge of the square wave signal is detected, the internal timer is immediately started to begin timing. S4. When the timer's duration reaches the delay time, the microcontroller control unit outputs a conduction control signal through the bidirectional thyristor drive circuit; S5. After receiving the conduction control signal, the bidirectional thyristor is triggered to conduct, and the faulty phase is grounded through the preset transition resistor circuit to complete the simulation of a single-phase ground fault.

[0057] As a refinement and extension of the specific implementation of the above embodiments, in order to fully illustrate the specific implementation process of this embodiment, another short-circuit control method for simulating small current ground faults is provided, which includes the following steps: S1. Acquire the system voltage to be simulated, convert it into a low-voltage sinusoidal signal with the same phase through a synchronous transformer, and then shape the low-voltage sinusoidal signal into a square wave signal corresponding to the positive zero-crossing point of the system voltage through a zero-crossing detection circuit. The falling edge of the square wave signal corresponds to the positive zero-crossing point of the system voltage. S2. The microcontroller control unit obtains the preset target fault initial phase angle and converts it into the corresponding delay time; in step S2, the microcontroller control unit receives the target fault initial phase angle sent by the host computer through the serial communication interface.

[0058] S3. The microcontroller control unit monitors the square wave signal in real time. When the falling edge of the square wave signal is detected, the internal timer is immediately started to begin timing. S4. When the timer's duration reaches the delay time, the microcontroller control unit outputs a conduction control signal through the bidirectional thyristor drive circuit; Step S5 includes the following: Based on the target operating conditions, the on / off state of the corresponding resistor branch in the transition resistor circuit is controlled by switching on / off, and the resistance value of the target transition resistor is obtained by combining the switching on / off state.

[0059] S5. After receiving the conduction control signal, the bidirectional thyristor is triggered to conduct, and the faulty phase is grounded through the preset transition resistor circuit to complete the simulation of a single-phase ground fault.

[0060] It should be noted that in step S5, after the bidirectional thyristor is turned on, the microcontroller control unit presets the short-circuit fault duration through an internal timer. After the fault duration is reached, the turn-on control signal is removed, and the bidirectional thyristor is naturally turned off when the AC current crosses zero, thus ending the fault simulation process.

[0061] 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 the present invention.

[0062] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A short-circuit control system for simulating small-current grounding faults, characterized in that, The system is used to control the ground fault disconnection of the faulty phase in the test main circuit, and the system includes: Main circuit and control circuit; The main circuit includes a transition resistor circuit and a bidirectional thyristor connected in series between the fault phase and ground. The control circuit includes a synchronous transformer, a zero-crossing detection circuit, a microcontroller control unit, and a bidirectional thyristor drive circuit. The primary side of the synchronous transformer is connected to the system voltage to be simulated, which is used to transform the system voltage into a low-voltage sinusoidal signal with the same phase. The zero-crossing detection circuit is connected to the secondary side of the synchronous transformer. The zero-crossing detection circuit is used to shape the low-voltage sinusoidal signal into a square wave signal corresponding to the positive zero-crossing point of the system voltage. The input terminal of the microcontroller control unit is connected to the output terminal of the zero-crossing detection circuit. The microcontroller control unit is used to receive the square wave signal, start the internal timer on the falling edge of the square wave signal according to the preset fault initial phase angle, and output the conduction control signal through the bidirectional thyristor drive circuit when the timing time reaches the delay time corresponding to the fault initial phase angle. The input terminal of the bidirectional thyristor drive circuit is connected to the output terminal of the microcontroller control unit, and the output terminal is connected to the gate of the bidirectional thyristor. The bidirectional thyristor drive circuit is used to receive the conduction control signal and trigger the bidirectional thyristor to conduct, so that the faulty phase is grounded through a preset transition resistor circuit, thus completing the simulation of a single-phase grounding fault.

2. The short-circuit control system for simulating small-current grounding faults according to claim 1, characterized in that, The zero-crossing detection circuit includes a voltage comparator, a Schmitt trigger, and an optocoupler connected in sequence. The voltage comparator is used to convert a low-voltage sinusoidal signal into a rectangular wave; The Schmitt trigger is used to shape rectangular waves to improve edge steepness and anti-interference capability; The optocoupler isolator is used to achieve electrical isolation between field signals and the microcontroller control unit.

3. The short-circuit control system for simulating small-current grounding faults according to claim 1, characterized in that, The microcontroller control unit is also equipped with a serial communication interface. The microcontroller control unit communicates with the host computer through the serial communication interface and receives the preset fault initial phase angle sent by the host computer.

4. The short-circuit control system for simulating small-current grounding faults according to claim 1, characterized in that, The transition resistor circuit is composed of multiple resistor branches with different resistance values ​​connected in parallel. Each resistor branch includes a fixed resistor connected in series and a switching switch.

5. The short-circuit control system for simulating small-current grounding faults according to claim 4, characterized in that, The fixed resistance values ​​of the plurality of resistor branches with different resistance values ​​are distributed according to an exponential law, and the plurality of resistor branches with different resistance values ​​include at least one of 0Ω branch, 5Ω branch, 50Ω branch, 500Ω branch and 5000Ω branch. Among them, the 0Ω branch is used to simulate metallic grounding faults, the 5Ω and 50Ω branches are used to simulate low-resistance grounding faults, the 500Ω branch is used to simulate medium-resistance grounding faults, and the 5000Ω branch is used to simulate high-resistance grounding faults.

6. The short-circuit control system for simulating small-current grounding faults according to claim 1, characterized in that, The bidirectional thyristor is a bidirectional thyristor.

7. The short-circuit control system for simulating small-current grounding faults according to claim 1, characterized in that, The microcontroller control unit is equipped with an angle-to-time conversion module, used to convert time according to the formula... t =( φ (360°)× T Calculate the delay time corresponding to the initial phase angle of the fault, where, φ The preset initial phase angle of the fault. T The system voltage's power frequency period.

8. A short-circuit control method for simulating low-current grounding faults, characterized in that, The method is based on the system according to any one of claims 1-7, and the method includes the following steps: S1. Acquire the system voltage to be simulated, convert it into a low-voltage sinusoidal signal with the same phase through a synchronous transformer, and then shape the low-voltage sinusoidal signal into a square wave signal corresponding to the positive zero-crossing point of the system voltage through a zero-crossing detection circuit. The falling edge of the square wave signal corresponds to the positive zero-crossing point of the system voltage. S2. The microcontroller control unit obtains the preset target fault initial phase angle and converts it into the corresponding delay time; S3. The microcontroller control unit monitors the square wave signal in real time. When the falling edge of the square wave signal is detected, the internal timer is immediately started to begin timing. S4. When the timer's duration reaches the delay time, the microcontroller control unit outputs a conduction control signal through the bidirectional thyristor drive circuit; S5. After receiving the conduction control signal, the bidirectional thyristor is triggered to conduct, and the faulty phase is grounded through the preset transition resistor circuit to complete the simulation of a single-phase ground fault.

9. The short-circuit control method for simulating small-current grounding faults according to claim 8, characterized in that, In step S2, the microcontroller control unit receives the target fault initial phase angle sent by the host computer through the serial communication interface.

10. The short-circuit control method for simulating small-current grounding faults according to claim 8, characterized in that, Step S5 includes the following: Based on the target operating conditions, the on / off state of the corresponding resistor branch in the transition resistor circuit is controlled by switching on / off, and the resistance value of the target transition resistor is obtained by combining the switching on / off state.

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