Intelligent line switching identification method based on full compensation device

Abstract

The invention discloses a line switching intelligent identification method based on a full compensation device, and the method specifically comprises the following steps: collecting a system analog signal in real time, and identifying whether a system has a single-phase grounding fault or not; after a single-phase earth fault of the system is identified, outputting current to carry out earth fault full compensation, recording an initial value of the current after the system is stable, and monitoring and recording a change state of the output current in real time; whether the fault line exits correctly or not is judged according to the variable quantity of the output current of the full-compensation device and the neutral point zero sequence voltage, so that the full-compensation device can be immediately used for direct compensation when the fault occurs and automatically exits before the line selection device completes line selection and the fault line is cut off, and the system recovers the initial grounding state. The system is convenient to successfully isolate a fault line, the equipment response time is short, good cooperation of the line selection device and the full compensation device is realized, and safe and stable operation of a power grid and network hanging equipment is effectively guaranteed.

Description

Technical Field

[0001] The invention relates to the technical field of single-phase grounding fault protection for distribution networks, in particular to a method for identifying line switching on and off. Background Art

[0002] The distribution network is the foundation of national economic and industrial development and an indispensable part of the power system. Modern society has put forward higher requirements for the safe, stable and reliable operation of the power grid. At present, more than 80% of the faults in the distribution networks at home and abroad are single-phase grounding faults. In order to limit the fault current and eliminate the fault in a timely and rapid manner, the distribution networks at home and abroad generally adopt the operation modes of neutral point ungrounded, neutral point grounded through arc suppression coils, and neutral point grounded through small resistors. With the continuous increase in the capacity of the distribution network and the commissioning of a large number of non-linear loads and cable lines, the active current component in the ground fault current increases sharply, which is easy to cause arc grounding faults and the grounding arc is difficult to extinguish by itself, thereby causing overvoltage in the power system, expanding the power grid fault, and seriously affecting the safe operation of the power grid and power equipment. Fault current full compensation can effectively compensate for the active and reactive components in the single-phase grounding current of the distribution network, thereby reducing the fault current, destroying the arcing conditions of the ground fault, and reducing the possibility of fault expansion, which is of great significance to improving the reliability of power supply of the power grid.

[0003] The existing full compensation device can realize the effective compensation of the single-phase grounding current of the system. It has a voltage clamping function. After a single-phase grounding fault occurs in the system, the full compensation device will clamp the fault phase voltage to 0V and raise the zero-sequence voltage to the rated value. Then, the line selection device selects the line, selects the fault line, and issues a fault line tripping command. After the fault line exits, if the system can operate normally, the line selection device will no longer be put into operation. If it cannot operate normally, the line selection device will be put into operation again to select the line. However, during the line switching process, since the full compensation device is always in the compensation state and the zero-sequence voltage is maintained at the rated voltage value, the system believes that the fault has not been removed and the single-phase grounding fault state cannot be removed, and an instruction to put the line selection device into operation will be issued; in this case, the full compensation device can only be exited first and then the line can be cut, which is easy to cause coordination errors, prolong the exit time of the fault line, and cannot guarantee the stability of the system operation. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide an intelligent identification method for line switching on and off based on a full compensation device. The full compensation device can automatically switch off before the line selection device completes line selection and the faulty line is cut off, so as to facilitate the system to successfully isolate the faulty line and further ensure the stable operation of the system.

[0005] In order to solve the above technical problems, the technical solutions adopted by the present invention are as follows.

[0006] A line switching intelligent identification method based on a full compensation device, the method specifically comprising the following steps:

[0007] A. The full compensation device collects the system analog signal and identifies whether a single-phase grounding fault occurs in the system;

[0008] B. After a single-phase grounding fault is identified in the system, the output current is fully compensated for the grounding fault. After the system is stable, the initial current value IS0 is recorded, and the output current IS change status is monitored and recorded in real time;

[0009] C. If the output current IS changes, record the change value IS1. If the change value IS1 lasts for △t1, IS1-IS0>△IS set , it is considered that the system is exiting the line, and the full compensation device will automatically exit regardless of whether the exited line is a faulty line;

[0010] D. Within △t2 after the full compensation device exits, the system returns to the initial grounding state and assigns IS1 to IS0;

[0011] E. During △t2, monitor the neutral point zero-sequence voltage U0. If the zero-sequence voltage U0 still exceeds the threshold U set , it is determined that the exit from the faulty line has failed and the grounding fault has not disappeared. The full compensation device immediately starts compensation, the line selection device reselects the line, and steps BE are repeated; otherwise, the exit from the faulty line is successful, and the full compensation device no longer outputs.

[0012] Preferably: the analog signal in step A includes the system bus voltage and the zero-sequence voltage U0.

[0013] Preferably: in steps A and D, the full compensation device uses a fast fault identification algorithm to monitor zero-sequence voltage changes and identify the occurrence of a fault; when a single-phase grounding fault is identified, the single-phase grounding fault is identified through the collected system bus voltage and zero-sequence voltage, and compensation is started immediately.

[0014] Due to the adoption of the above technical scheme, the technical progress achieved by the present invention is as follows.

[0015] The present invention determines whether the faulty line is correctly exited based on the dual criteria of the change in the output current △IS of the full compensation device and the neutral point zero-sequence voltage U0, so that the full compensation device can immediately start direct compensation when a fault occurs, and automatically exit before the line selection device completes line selection and the faulty line is removed, so that the system is restored to an initial grounding state, which is convenient for the system to successfully isolate the faulty line. The equipment has a short response time, realizes good coordination between the line selection device and the full compensation device, and effectively ensures the safe and stable operation of the power grid and the network-connected equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1It is a system principle diagram of the present invention. DETAILED DESCRIPTION

[0017] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0018] A line switching intelligent identification method based on a full compensation device, the method is based on a system having a full compensation device, such as Figure 1 As shown, it is used to fully compensate the system when a ground fault occurs in the system.

[0019] The above-mentioned line investment and withdrawal intelligent identification method specifically includes the following steps.

[0020] A. The full compensation device collects the system analog signals in real time and records the analog data when the system is operating normally; it uses a fast fault identification algorithm to monitor the zero-sequence voltage changes and identify whether a single-phase grounding fault occurs in the system.

[0021] In this step, the analog signal includes the system bus voltage and the zero-sequence voltage U0.

[0022] B. After the full compensation device identifies a single-phase grounding fault in the system, it identifies the single-phase grounding fault through the collected system bus voltage and zero-sequence voltage, and then outputs current to perform full compensation for the grounding fault. In the full compensation state, after the system stabilizes, the full compensation device records the initial current value IS0, and monitors and records the output current IS change state in real time.

[0023] C. If the output current IS changes, record the change value IS1. If the change value IS1 lasts for △t1, IS1-IS0>△IS set , it is considered that the system is exiting the line. Regardless of whether the exited line is a faulty line or not, the full compensation device will actively exit.

[0024] △IS set It is set according to the system outgoing line capacitance current value, and is generally configured according to the capacitance current value of the line with the minimum capacitance current.

[0025] D. Within △t2 time after the full compensation device exits, the system returns to the initial grounding state and assigns IS1 to IS0.

[0026] When the full compensation device outputs compensation, the bus voltage is embedded by the full compensation device, and the current value is relatively stable. The smaller the values ​​of △t1 and △t2 are, the faster the response speed is. The larger the values ​​are, the stronger the anti-interference ability is, and the slower the response speed is. In the present invention, the minimum values ​​of △t1 and △t2 are set to 20ms.

[0027] During △t2, the full compensation device monitors the neutral point zero-sequence voltage U0. If the zero-sequence voltage U0 still exceeds the threshold U set, it is determined that the exit from the faulty line has failed and the grounding fault has not disappeared. The full compensation device immediately starts compensation, the line selection device reselects the line, and steps BE are repeated; otherwise, the exit from the faulty line is successful, and the full compensation device no longer outputs.

Claims

1. A line switching intelligent identification method based on a full compensation device, characterized in that: The method specifically comprises the following steps: A. The full compensation device collects the system analog signal and identifies whether a single-phase grounding fault occurs in the system; B. After a single-phase grounding fault is identified in the system, the output current is fully compensated for the grounding fault. After the system is stable, the initial current value IS0 is recorded, and the output current IS change status is monitored and recorded in real time; C. If the output current IS changes, record the change value IS1. If the change value IS1 lasts for △t1, IS1-IS0>△IS set , it is considered that the system is exiting the line, and the full compensation device will automatically exit regardless of whether the exited line is a faulty line; D. Within △t2 after the full compensation device exits, the system returns to the initial grounding state and assigns IS1 to IS0; E. During △t2, monitor the neutral point zero-sequence voltage U0. If the zero-sequence voltage U0 still exceeds the threshold U set , it is determined that the exit from the faulty line has failed and the grounding fault has not disappeared. The full compensation device immediately starts compensation, the line selection device reselects the line, and steps BE are repeated; otherwise, the exit from the faulty line is successful, and the full compensation device no longer outputs.

2. According to claim 1, a line switching intelligent identification method based on a full compensation device is characterized in that: The analog signal in step A includes the system bus voltage and the zero-sequence voltage U0.

3. According to claim 2, a line switching intelligent identification method based on a full compensation device is characterized in that: In steps A and D, the full compensation device uses a fast fault identification algorithm to monitor the zero-sequence voltage change and identify the occurrence of a fault; when a single-phase grounding fault is identified, the single-phase grounding fault is identified through the collected system bus voltage and zero-sequence voltage, and compensation is started immediately.

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