Zero-sequence voltage verification-based zero-sequence overcurrent protection method for arc suppression coil grounding system

Abstract

The invention provides an arc suppression coil grounding system zero-sequence overcurrent protection method based on zero-sequence voltage verification. The protection reliability is improved through multi-criterion fusion. The method specifically comprises the following steps: S1, arc suppression coil system fault starting criterion: monitoring a zero sequence voltage in real time, and triggering a protection algorithm when the amplitude of the zero sequence voltage exceeds a preset threshold value; s2, fault time calculation: calculating the duration time of a grounding fault based on the duration characteristic of the zero-sequence voltage; s3, fault position discrimination: in combination with the amplitude characteristics of the zero-sequence current, distinguishing an internal fault from an external fault; and S4, intelligent comprehensive decision making: fusing the transient and steady state characteristic quantities of the zero-sequence voltage and the zero-sequence current, and generating a protection action signal. According to the invention, by dynamically checking the correlation characteristics of the zero-sequence voltage and current, the problems of insufficient sensitivity and high maloperation rate of the traditional zero-sequence overcurrent protection in the arc suppression coil grounding system are effectively solved.

Description

Technical Field

[0001] This invention relates to the field of power distribution automation technology, and in particular to a zero-sequence overcurrent protection method for arc suppression coil grounding systems based on zero-sequence voltage verification. Background Technology

[0002] Arc suppression coil grounding systems are widely used in distribution networks, but their single-phase ground fault detection faces significant challenges: traditional zero-sequence overcurrent protection suffers from insufficient sensitivity due to the attenuation of zero-sequence current amplitude caused by arc suppression coil compensation; ground fault protection based on phase characteristics is susceptible to interference from changes in distribution network operation and is complex to implement; existing high-precision algorithms suffer from high computational load and cost. To address these technical bottlenecks, there is an urgent need to develop a new ground fault protection method that can adapt to the compensation characteristics of arc suppression coils, avoid the effects of unstable phase characteristics, and is computationally simple and easy to implement in engineering. Summary of the Invention

[0003] This invention proposes a zero-sequence overcurrent protection method for arc suppression coil grounding systems based on zero-sequence voltage verification. It can be used in low-current grounding systems, is not affected by arc suppression coil compensation, avoids complex phase calculations while ensuring calculation efficiency, and can achieve reliable grounding protection.

[0004] The technical problem to be solved by this invention is: how to achieve a reliable grounding protection method in an arc suppression coil grounding system that is not affected by arc suppression coil compensation, avoids complex phase calculations, and ensures calculation efficiency.

[0005] The present invention adopts the following technical solution.

[0006] A zero-sequence overcurrent protection method for arc suppression coil grounding system based on zero-sequence voltage verification is proposed. The protection method improves sensitivity and prevents false tripping by dynamically verifying the correlation characteristics between zero-sequence voltage and current. The method includes the following steps: Step S1: Fault start criterion for arc suppression coil system: Real-time monitoring of zero-sequence voltage; when its amplitude exceeds a preset threshold, the protection algorithm is triggered. Step S2: Fault duration calculation: Calculate the duration of the ground fault based on the duration characteristics of the zero-sequence voltage; Step S3: Fault location determination: Based on the amplitude characteristics of the zero-sequence current, distinguish between faults within the fault zone and faults outside the fault zone; Step S4: Intelligent integrated decision-making: Integrate the transient and steady-state characteristics of zero-sequence voltage and zero-sequence current to generate protection action signals.

[0007] In step S1, the arc suppression coil grounding system is a low-current grounding system.

[0008] In step S1, the effective value of the zero-sequence voltage is calculated using the sliding window Fourier algorithm; the zero-sequence voltage mutation is defined as the difference between the effective values ​​of the zero-sequence voltage of two adjacent power frequency cycles obtained by the sliding window Fourier algorithm. The protection algorithm is activated when any of the following conditions are met: The effective value of the zero-sequence voltage exceeds the first preset threshold U0 set1 The first preset threshold is 10%-15% of the system's rated voltage; The zero-sequence voltage mutation exceeds the second preset threshold U0 set2 The second preset threshold is 5% of the system rated voltage.

[0009] In the arc suppression coil grounding system, the neutral point of the three-phase transformer is grounded through the arc suppression coil. The arc suppression coil can limit resonant overvoltage by using parallel or series damping resistors. The system has several outgoing feeders, each equipped with a zero-sequence current transformer to detect the zero-sequence current of the line. The system also includes a zero-sequence voltage transformer at the busbar or utilizes the open delta winding of the busbar PT to obtain the zero-sequence voltage. When a single-phase ground fault occurs on a feeder, the grounding current forms a loop through the fault line's capacitance to ground and the arc suppression coil. The inductive current generated by the arc suppression coil is out of phase with the system's capacitance to ground to achieve current compensation, reducing the fault current but also decreasing the sensitivity of the zero-sequence current protection.

[0010] Furthermore, the zero-sequence voltage is one of the main characteristics of a ground fault in the system, and a continuous zero-sequence voltage exceeding the threshold indicates that a ground fault exists in the system.

[0011] When a grounding fault occurs in the arc suppression coil grounding system, its zero-sequence voltage continues to exceed the threshold, and the fault point current decreases, resulting in a decrease in the sensitivity of the zero-sequence current protection.

[0012] In step S2, the cumulative time T0 during which the zero-sequence voltage parameter continuously exceeds the threshold is recorded as the duration of the ground fault.

[0013] In step S3, the maximum effective value I0 of the zero-sequence current is calculated within the fault duration T0. max : When I0 max Exceeding the third preset threshold I0 _set When this occurs, it is determined to be a fault within the zone; When I0 max It did not exceed the third preset threshold I0 _set At that time, it was determined to be an out-of-area fault.

[0014] The term "in-zone fault" refers to a single-phase ground fault located within the upstream protection range of the monitoring point of the line protection system near the busbar side. The term "out-of-zone fault" refers to a single-phase ground fault located downstream of the monitoring point of the line protection system near the load side, as well as the areas belonging to other feeders and branches.

[0015] In step S4, a protection action signal is generated when the following conditions are met simultaneously: Condition 1: The fault duration T0 exceeds the fourth preset threshold T. set ; Condition 2: Step S3 determines the fault to be within the zone.

[0016] A zero-sequence current transformer is installed at the beginning of each feeder.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1) Traditional zero-sequence overcurrent protection schemes rely on zero-sequence current amplitude criteria and are only applicable to low-resistance grounding systems. They are unable to effectively address the zero-sequence current attenuation problem caused by arc suppression coil compensation in arc suppression coil grounding systems. This invention innovatively introduces dual criteria of zero-sequence voltage duration and zero-sequence current peak value during a fault. By dynamically correlating voltage-current timing characteristics, it significantly reduces the impact of arc suppression coil compensation on protection reliability, making the zero-sequence current protection method practically valuable in arc suppression coil grounding systems.

[0018] 2) Compared with other ground fault protection methods: Existing ground fault protection methods based on phase characteristics (such as transient power method, first half-wave method, etc.) require complex phase calculations and are easily affected by changes in distribution network topology (such as power transfer operations). This invention only uses zero-sequence voltage and current amplitude characteristics to achieve fault identification, and has the following technical benefits: Improved computational efficiency: Eliminating the phase synchronization and angle calculation steps reduces algorithm complexity by more than 60%; Enhanced engineering applicability: Avoids interference with phase characteristics caused by changes in distribution network operation mode, and improves the reliability of protection actions.

[0019] This invention is particularly applicable to user boundary protection in arc suppression coil grounding systems: considering the large number of user boundary switches and high investment costs, as well as the characteristic of zero-sequence current first rising and then decaying when the user side is grounded, this method provides a reliable single-phase ground fault protection solution for user boundary equipment in arc suppression coil grounding systems. Attached Figure Description

[0020] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments: Appendix Figure 1 This is a schematic diagram of the zero-sequence overcurrent protection process of an arc suppression coil grounding system based on zero-sequence voltage verification in an embodiment of the present invention; Appendix Figure 2 This is a schematic diagram of zero-sequence overcurrent protection of an arc suppression coil grounding system based on zero-sequence voltage verification in an embodiment of the present invention; Appendix Figure 3 This is a schematic diagram of a neutral point grounding system via an arc suppression coil in an embodiment of the present invention. Detailed Implementation

[0021] As shown in the figure, a zero-sequence overcurrent protection method for an arc suppression coil grounding system based on zero-sequence voltage verification is described. The protection method improves sensitivity and prevents false tripping by dynamically verifying the correlation characteristics between zero-sequence voltage and current. The method includes the following steps: Step S1: Fault start criterion for arc suppression coil system: Real-time monitoring of zero-sequence voltage; when its amplitude exceeds a preset threshold, the protection algorithm is triggered. Step S2: Fault duration calculation: Calculate the duration of the ground fault based on the duration characteristics of the zero-sequence voltage; Step S3: Fault location determination: Based on the amplitude characteristics of the zero-sequence current, distinguish between faults within the fault zone and faults outside the fault zone; Step S4: Intelligent integrated decision-making: Integrate the transient and steady-state characteristics of zero-sequence voltage and zero-sequence current to generate protection action signals.

[0022] In step S1, the arc suppression coil grounding system is a low-current grounding system.

[0023] In step S1, the effective value of the zero-sequence voltage is calculated using the sliding window Fourier algorithm; the zero-sequence voltage mutation is defined as the difference between the effective values ​​of the zero-sequence voltage of two adjacent power frequency cycles obtained by the sliding window Fourier algorithm. The protection algorithm is activated when any of the following conditions are met: The effective value of the zero-sequence voltage exceeds the first preset threshold U0 set1 The first preset threshold is 10%-15% of the system's rated voltage; The zero-sequence voltage mutation exceeds the second preset threshold U0 set2 The second preset threshold is 5% of the system rated voltage.

[0024] In the arc suppression coil grounding system, the neutral point of the three-phase transformer is grounded through the arc suppression coil, and the arc suppression coil is connected in parallel or series with damping resistors to limit resonant overvoltage. The arc suppression coil grounding system has several outgoing feeders, each of which is equipped with a zero-sequence current transformer to detect the zero-sequence current of the feeder line; the arc suppression coil grounding system also has a zero-sequence voltage transformer installed at the busbar or uses the open delta winding of the busbar PT to obtain the zero-sequence voltage.

[0025] When a single-phase ground fault occurs on a feeder, the ground current forms a loop through the ground capacitance of the faulted line and the arc suppression coil. The inductive current generated by the arc suppression coil is out of phase with the system ground capacitance current to achieve current compensation, thereby reducing the current at the fault point. When a grounding fault occurs in the arc suppression coil grounding system, its zero-sequence voltage continues to exceed the threshold, and the fault point current decreases, resulting in a decrease in the sensitivity of the zero-sequence current protection.

[0026] In step S2, the cumulative time T0 during which the zero-sequence voltage parameter continuously exceeds the threshold is recorded as the duration of the ground fault.

[0027] In step S3, the maximum effective value I0 of the zero-sequence current is calculated within the fault duration T0. max : When I0 max Exceeding the third preset threshold I0 _set When this occurs, it is determined to be a fault within the zone; When I0 max It did not exceed the third preset threshold I0 _set At that time, it was determined to be an out-of-area fault.

[0028] The term "in-zone fault" refers to a single-phase grounding fault located within the upstream protection range of the monitoring point of this line's protection system, near the busbar side. The term "outside-area fault" refers to a single-phase grounding fault located downstream of the monitoring point of the line protection system near the load side, as well as in the areas belonging to other feeders and branches.

[0029] In step S4, a protection action signal is generated when the following conditions are met simultaneously: Condition 1: The fault duration T0 exceeds the fourth preset threshold T. set ; Condition 2: Step S3 determines the fault to be within the zone.

[0030] A zero-sequence current transformer is installed at the beginning of each feeder.

[0031] In this example, the zero-sequence voltage is one of the main characteristics of a ground fault in the system. A zero-sequence voltage that continuously exceeds the threshold indicates that a ground fault exists in the system.

Claims

1. A method for zero-sequence overcurrent protection of an arc suppression coil grounding system based on zero-sequence voltage verification, characterized in that: The protection method improves sensitivity and prevents false tripping by dynamically verifying the correlation characteristics between zero-sequence voltage and current, and includes the following steps; Step S1: Fault start criterion for arc suppression coil system: Real-time monitoring of zero-sequence voltage; when its amplitude exceeds a preset threshold, the protection algorithm is triggered. Step S2: Fault duration calculation: Calculate the duration of the ground fault based on the duration characteristics of the zero-sequence voltage; Step S3: Fault location determination: Based on the amplitude characteristics of the zero-sequence current, distinguish between faults within the fault zone and faults outside the fault zone; Step S4: Intelligent integrated decision-making: Integrate the transient and steady-state characteristics of zero-sequence voltage and zero-sequence current to generate protection action signals.

2. The zero-sequence overcurrent protection method for arc suppression coil grounding system based on zero-sequence voltage verification according to claim 1, characterized in that: In step S1, the arc suppression coil grounding system is a low-current grounding system.

3. The zero-sequence overcurrent protection method for arc suppression coil grounding system based on zero-sequence voltage verification according to claim 2, characterized in that: In step S1, the effective value of the zero-sequence voltage is calculated using the sliding window Fourier algorithm; the zero-sequence voltage mutation is defined as the difference between the effective values ​​of the zero-sequence voltage of two adjacent power frequency cycles obtained by the sliding window Fourier algorithm. The protection algorithm is activated when any of the following conditions are met: The effective value of the zero-sequence voltage exceeds the first preset threshold U0 set1 The first preset threshold is 10%-15% of the system's rated voltage; The zero-sequence voltage mutation exceeds the second preset threshold U0 set2 .

4. The zero-sequence overcurrent protection method for arc suppression coil grounding system based on zero-sequence voltage verification according to claim 1, characterized in that: In the arc suppression coil grounding system, the neutral point of the three-phase transformer is grounded through the arc suppression coil, and the arc suppression coil is connected in parallel or series with damping resistors to limit resonant overvoltage. The arc suppression coil grounding system has several outgoing feeders, each of which is equipped with a zero-sequence current transformer to detect the zero-sequence current of the feeder line; the arc suppression coil grounding system also has a zero-sequence voltage transformer installed at the busbar or uses the open delta winding of the busbar PT to obtain the zero-sequence voltage.

5. The zero-sequence overcurrent protection method for arc suppression coil grounding system based on zero-sequence voltage verification according to claim 4, characterized in that: When a single-phase ground fault occurs on a feeder, the ground current forms a loop through the ground capacitance of the faulted line and the arc suppression coil. The inductive current generated by the arc suppression coil is out of phase with the system ground capacitance current to achieve current compensation, thereby reducing the current at the fault point. When a grounding fault occurs in the arc suppression coil grounding system, its zero-sequence voltage continues to exceed the threshold, and the fault point current decreases, resulting in a decrease in the sensitivity of the zero-sequence current protection.

6. The zero-sequence overcurrent protection method for arc suppression coil grounding system based on zero-sequence voltage verification according to claim 4, characterized in that: In step S2, the cumulative time T0 during which the zero-sequence voltage parameter continuously exceeds the threshold is recorded as the duration of the ground fault.

7. The zero-sequence overcurrent protection method for arc suppression coil grounding system based on zero-sequence voltage verification according to claim 4, characterized in that: In step S3, the maximum effective value I0 of the zero-sequence current is calculated within the fault duration T0. max : When I0 max Exceeding the third preset threshold I0 _set When this occurs, it is determined to be a fault within the zone; When I0 max It did not exceed the third preset threshold I0 _set At that time, it was determined to be an out-of-area fault.

8. The method for zero-sequence overcurrent protection of an arc suppression coil grounding system based on zero-sequence voltage verification according to claim 7, characterized in that: The term "in-zone fault" refers to a single-phase grounding fault located within the upstream protection range of the monitoring point of this line's protection system, near the busbar side. The term "outside-area fault" refers to a single-phase grounding fault located downstream of the monitoring point of the line protection system near the load side, as well as in the areas belonging to other feeders and branches.

9. The method for zero-sequence overcurrent protection of an arc suppression coil grounding system based on zero-sequence voltage verification according to claim 7, characterized in that: In step S4, a protection action signal is generated when the following conditions are met simultaneously: Condition 1: The fault duration T0 exceeds the fourth preset threshold T. set ; Condition 2: Step S3 determines the fault to be within the zone.

10. The method for zero-sequence overcurrent protection of an arc suppression coil grounding system based on zero-sequence voltage verification according to claim 4, characterized in that: A zero-sequence current transformer is installed at the beginning of each feeder.

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