A method and system for identifying double busbar protection mode

Abstract

The present invention belongs to the technical field of relay protection of power systems, and specifically relates to a method and system for identifying a dual busbar protection mode. The method is specifically as follows: when the three-phase differential currents of the busbar all meet the large differential balance and the small differentials of the two sections of the busbar are unbalanced, all operating branches have knife switch positions, and the busbar has current or the busbar is in a jump position, it is preliminarily determined that the branch knife switch is wrong; when there is only one non-busbar branch current that is equal to the small differential current of the busbar where it is located, try to correct the knife switch position of this branch, and after the correction is successful, identify the operating mode with the corrected knife switch position, otherwise force the busbars to be interconnected. This method improves the reliability and selectivity of the busbar protection after the correction is successful, effectively avoids the problem of incorrect behavior of the fault differential protection action in the busbar area caused by the wrong knife switch position, and even if the correction is unsuccessful, it can effectively improve the reliability and rapidity of the fault differential protection action in the busbar area caused by the wrong knife switch position or the wrong busbar CT connection.

Description

Technical Field

[0001] The present invention belongs to the technical field of power system relay protection, and in particular relates to a double-busbar protection mode identification method and system. Background Art

[0002] In dual-busbar systems (including dual-busbar single-break and dual-busbar dual-break), branches connected to the busbars may switch between the two busbars. This requires the busbar protection to automatically track the switching operations of the primary system. The protection device operates based on the position of the branch switch, automatically identifying the busbar operating mode within the software. This serves as the basis for differential current calculation and output tripping. If the switch position is inconsistent with the primary system, the busbar protection will not operate correctly.

[0003] Existing switch position correction schemes use the current vector and conservation principles to correct the position of current-carrying, non-positioned branches, improving the selectivity and reliability of busbar protection. However, they cannot address the issue of incorrect differential protection behavior for busbar faults caused by incorrect switch position or incorrect bus-tie CT wiring.

[0004] Taking a dual busbar as an example, assume branch m actually operates on busbar I. Due to a secondary wiring error, the busbar protection device detects a 2G switch (busbar II). Consequently, the current in branch m will not be included in the differential current on busbar I, but will be included in the differential current on busbar II. In this case, ignoring the effects of transmission errors, sampling errors, and calculation errors, during normal system operation, there is no large differential current. The small differential currents on the two busbar sections are equal in magnitude (equal to the current in branch m) and opposite in direction. Since there is no large differential current, the busbar protection will not operate. However, in the event of an intra-busbar fault, such as a busbar I fault, busbar I may fail to operate because the fault current provided by branch m is not included in the differential current on busbar I. However, busbar II may malfunction because the current on branch m is calculated. Therefore, when switch misposition occurs, the busbar differential protection may not operate correctly for intra-busbar faults, affecting system stability. Summary of the Invention

[0005] The purpose of the present invention is to provide a dual bus protection mode identification method and system to solve the problem of incorrect differential protection action behavior in the bus area caused by incorrect knife switch position or incorrect bus CT wiring.

[0006] To solve the above technical problems, the present invention provides a method for identifying a double busbar protection mode, comprising the following steps:

[0007] 1) Obtaining data information of the dual busbars; the data information includes: the switch position of the operating branch and the bus tie circuit breaker position, the operating branch current, and the bus tie branch current;

[0008] 2) Calculate the large differential current and the small differential current of each bus section based on the acquired data information; the small differential current of each bus section is: small differential current of bus I and small differential current of bus II; and determine whether the double bus switch position error condition is met; the double bus switch position error condition includes:

[0009] a) The three-phase differential current of the busbar satisfies the large differential current balance, small differential current unbalance, and equal small differential current amplitudes; when the large differential current amplitude is less than the large differential current balance threshold, the small differential current amplitude of bus I and bus II are both greater than the small differential current balance threshold, and the absolute value of the difference between the small differential current amplitude of bus I and bus II is less than the error threshold, the large differential current balance, small differential current unbalance, and equal small differential current amplitudes are satisfied;

[0010] b) All operating branches have knife switches in position;

[0011] c) The bus tie branch current is greater than the set current threshold or the bus tie circuit breaker is in the trip position;

[0012] 3) If both busbar switch position error conditions are met, it is determined that there is a branch switch position error;

[0013] 4) When there is a branch switch position error and only one non-bus tie branch current is equal to the small differential current of the bus where the branch is located, the switch position of the branch is corrected;

[0014] 5) If the knife switch is corrected successfully, the corrected knife switch position will be used for mode identification; if the knife switch is not corrected successfully, the busbars will be forced to be interconnected.

[0015] Its beneficial effects are as follows: the present invention attempts to correct the branch switch position error based on the differential current characteristics, branch current and its position information. If the correction is successful, the reliability and selectivity of the busbar protection can be improved, and the problem of incorrect differential protection action behavior for faults in the busbar area caused by the switch position error can be effectively avoided. Even if the correction is unsuccessful, the reliability and rapidity of the differential protection action for faults in the busbar area caused by the switch position error or the busbar CT wiring error can be effectively improved, thereby improving the stability of the system.

[0016] Furthermore, in step 4), the switch of the branch is corrected by correcting the switch position of the branch to the switch position of another busbar.

[0017] Because the wrong switch position will cause the fault differential protection in the bus area to behave incorrectly, after determining that the switch position is wrong, the wrong switch position is corrected, which can effectively avoid the problem of incorrect protection behavior. The present invention corrects the switch position of the branch to the switch position of another bus, that is, if the acquired switch position is 1G switch (I mother switch), the switch position is corrected to 2G switch (II mother switch); if the acquired switch position is 2G switch (II mother switch), the switch position is corrected to 1G switch (I mother switch), thereby achieving the correction of the switch position, and performing mode identification based on the corrected switch position, avoiding the problem of incorrect protection behavior.

[0018] Furthermore, if the position of the branch switch is corrected, the small differential flow is recalculated. If the small differential flow is balanced, the switch correction is successful, otherwise the switch correction is unsuccessful.

[0019] If the calculated small differential currents are balanced after correction, the correction is considered successful and the corrected switch position is enforced. Otherwise, the busbar CT wiring is considered incorrect or the branch switch position wiring is incorrect and cannot be corrected. To ensure the reliability and rapidity of fault protection within the busbar area, forced busbar interconnection can improve the reliability and rapidity of fault protection within the busbar area, thereby improving system stability.

[0020] Furthermore, in step 4), when the amplitude of the phase difference between only one non-bus-coupled branch current and the small differential current of the bus where the branch is located is less than the error threshold, it is determined that the branch current is equal to the small differential current of the bus where the branch is located.

[0021] Furthermore, in step 3), the large difference balance threshold I mk1 For: I mk1 =min[0.9 times the CT break setting, 0.2I n ]; Small difference balance threshold I mk2 For: I mk2 =min[max(2 times the difference flow, 0.08I n ), 0.2I n ]; Error threshold I mk3 For: I mk3 =0.02I n ; Among them I n is the secondary rated value of the current transformer.

[0022] To solve the above technical problems, the present invention further provides a dual bus protection mode identification system, comprising a controller, wherein the controller is configured to execute instructions to implement the following steps:

[0023] 1) Obtaining data information of the dual busbars; the data information includes: the switch position of the operating branch and the bus tie circuit breaker position, the operating branch current, and the bus tie branch current;

[0024] 2) Calculate the large differential current and the small differential current of each bus section based on the acquired data information; the small differential current of each bus section is: small differential current of bus I and small differential current of bus II; and determine whether the double bus switch position error condition is met; the double bus switch position error condition includes:

[0025] a) The three-phase differential current of the busbar satisfies the large differential current balance, small differential current unbalance, and equal small differential current amplitudes; when the large differential current amplitude is less than the large differential current balance threshold, the small differential current amplitude of bus I and bus II are both greater than the small differential current balance threshold, and the absolute value of the difference between the small differential current amplitude of bus I and bus II is less than the error threshold, the large differential current balance, small differential current unbalance, and equal small differential current amplitudes are satisfied;

[0026] b) All operating branches have knife switches in position;

[0027] c) The bus tie branch current is greater than the set current threshold or the bus tie circuit breaker is in the trip position;

[0028] 3) If both busbar switch position error conditions are met, it is determined that there is a branch switch position error;

[0029] 4) When there is a branch switch position error and only one non-bus tie branch current is equal to the small differential current of the bus where the branch is located, the switch position of the branch is corrected;

[0030] 5) If the knife switch is corrected successfully, the corrected knife switch position will be used for mode identification; if the knife switch is not corrected successfully, the busbars will be forced to be interconnected.

[0031] Its beneficial effects are as follows: the present invention attempts to correct the branch switch position error based on the differential current characteristics, branch current and its position information. If the correction is successful, the reliability and selectivity of the busbar protection can be improved, and the problem of incorrect differential protection action behavior for faults in the busbar area caused by the switch position error can be avoided. Even if the correction is unsuccessful, the reliability and rapidity of the differential protection action for faults in the busbar area caused by the switch position error or the busbar CT wiring error can be effectively improved, thereby improving the stability of the system.

[0032] Furthermore, in step 4), the switch of the branch is corrected by correcting the switch position of the branch to the switch position of another busbar.

[0033] Because the wrong switch position will cause the fault differential protection in the bus area to behave incorrectly, after determining that the switch position is wrong, the wrong switch position is corrected, which can effectively avoid the problem of incorrect protection behavior. The present invention corrects the switch position of the branch to the switch position of another bus, that is, if the acquired switch position is 1G switch (I mother switch), the switch position is corrected to 2G switch (II mother switch); if the acquired switch position is 2G switch (II mother switch), the switch position is corrected to 1G switch (I mother switch), thereby achieving the correction of the switch position, and performing mode identification based on the corrected switch position, avoiding the problem of incorrect protection behavior.

[0034] Furthermore, if the position of the branch switch is corrected, the small differential flow is recalculated. If the small differential flow is balanced, the switch correction is successful, otherwise the switch correction is unsuccessful.

[0035] If the calculated small differential currents are balanced after correction, the correction is considered successful and the corrected switch position is enforced. Otherwise, the busbar CT wiring is considered incorrect or the branch switch position wiring is incorrect and cannot be corrected. To ensure the reliability and rapidity of fault protection within the busbar area, forced busbar interconnection can improve the reliability and rapidity of fault protection within the busbar area, thereby improving system stability.

[0036] Furthermore, in step 4), when the amplitude of the phase difference between the branch current and the small differential current of the bus where the branch is located is less than the error threshold, it is determined that the branch current is equal to the small differential current of the bus where the branch is located.

[0037] Furthermore, in step 3), the large difference balance threshold I mk1 For: I mk1 =min[0.9 times the CT break setting, 0.2I n ]; Small difference balance threshold I mk2 For: I mk2 =min[max(2 times the difference flow, 0.08I n ), 0.2I n ]; Error threshold I mk3 For: I mk3 =0.02I n ; Among them I n is the secondary rated value of the current transformer. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a flow chart of the double busbar protection mode identification method of the present invention;

[0039] Figure 2 It is a double busbar main wiring diagram. DETAILED DESCRIPTION

[0040] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0041] Example of a method for identifying a double busbar protection mode:

[0042] The dual bus protection mode identification method of the present embodiment is a method for identifying a mode of correcting the branch knife switch position error based on the differential current characteristics, branch current and its position information. The method is specifically as follows: when the three-phase differential current of the bus satisfies the large difference balance and the small difference of the two bus sections is unbalanced, it is determined whether all the running branches have knife switch positions. If all the running branches have knife switch positions, it is then determined whether the bus coupling connecting the two bus sections has current. If the bus coupling has current, it is preliminarily determined that the branch knife switch is wrong; when there is only one non-bus coupling branch current that is equal to the small differential current of the bus where it is located, an attempt is made to correct the knife switch position of this branch. If after correction, all bus differential currents are balanced, then this branch is forced to use the corrected position, otherwise the buses are forced to be interconnected. If the correction is successful, it can effectively avoid the incorrect operation of the bus protection due to the wrong knife switch position. Forced interconnection can improve the rapidity and reliability of protection action during faults within the bus area.

[0043] The specific process of the double bus protection mode identification method in this embodiment is as follows: Figure 1 As shown:

[0044] 1) Calculate the busbar large differential current and each section's small differential current based on the collected branch current and position information. When the busbar large differential current and each section's small differential current satisfy the following formula, the large differential current is balanced, the two busbar sections' small differential currents are unbalanced, and the small differential current amplitudes are equal.

[0045] I d <I mk1 ;

[0046] I d1 >I mk2 ;

[0047] I d2 >I mk2 ;

[0048] |I d1 -I d2 |<I mk3 ;

[0049] Among them, I d is the large differential current amplitude, I d1 is the amplitude of the differential current of the mother I, I d2 is the amplitude of the small differential current of the mother II; I mk1 is the large difference balance threshold, which is set to I mk1=min[0.9 times the CT break setting, 0.2I n ]; I mk2 is the small difference balance threshold, which is set to I mk2 =min[max(2 times the difference flow, 0.08I n ), 0.2I n ]; I mk3 is the error threshold, which is 0.02I n (i.e. I mk3 =0.02I n ), I n The selection of the balance threshold (i.e., the large difference balance threshold and the small difference balance threshold) is mainly based on avoiding the maximum unbalanced current of the system during normal operation.

[0050] The differential circuit consists of a busbar differential and a busbar differential for each busbar segment. The differential is comprised of all branches on the busbar except the busbar coupler (or segment), while the differential for each busbar segment is comprised of all branches on that busbar segment (including the busbar coupler segment). The differential is used to identify faults within and outside the busbar zone, while the differential is used to select the faulty busbar.

[0051] 2) If the large difference balance and small difference imbalance judgment conditions are met, determine whether all operating branches have knife switches in position;

[0052] 3) If all the running branches have knife switch positions, determine whether there is flow in the bus tie branch or the bus tie circuit breaker position is tripped, and the flow threshold is 0.04I n (i.e. the busbar current is greater than the current threshold 0.04I n When , it is determined that there is flow in the main coupling branch);

[0053] 4) If there is current in the bus tie branch or the bus tie circuit breaker is in the tripped position, it is preliminarily determined that the branch switch position is incorrect;

[0054] 5) If the initial identification is that the branch switch position is wrong, a vector comparison is performed on all running branch currents and the small differential current of the bus where they are located. When there is only one non-bus coupling (segmented) branch m whose current is equal to the small differential current of the bus where it is located, an attempt is made to correct the switch of this branch, otherwise the busbars are forced to be interconnected.

[0055] Among them, when the following formula is satisfied, the current in branch m is considered to be equal to the small difference current.

[0056] in, is the current in branch m, The small differential current of the busbar where the branch m is located is determined based on the collected switch position; I mk3 is the error threshold, which is 0.02I n .

[0057] 6) If there is only one non-bus tie branch m in the running branch whose current is equal to the small differential current of the bus, try to correct the knife switch of this branch. The specific method is: Figure 2 In the diagram shown, if the acquired switch position is 1G switch (I mother switch), correct this switch position to 2G switch (II mother switch) and recalculate the small differential current. If the acquired switch position is 2G switch (II mother switch), correct this switch position to 1G switch (I mother switch) and recalculate the small differential current.

[0058] 7) If the calculated small differential currents are balanced after correction, the correction is considered successful and the corrected switch position is enforced. Otherwise, it is considered that the busbar CT wiring is incorrect or the branch switch position wiring is incorrect and cannot be corrected. To ensure the reliability and rapidity of fault protection action within the busbar area, the busbars are forced to be interconnected.

[0059] The method of this embodiment attempts to correct branch switch position errors based on differential current characteristics, branch current, and branch position information. If the correction is successful, it can improve the reliability and selectivity of busbar protection and avoid the problem of incorrect differential protection operation for busbar faults caused by switch position errors. If the correction is unsuccessful, the busbars are forced to be interconnected, which can improve the reliability and speed of protection operation for busbar faults, thereby improving system stability.

[0060] Double bus protection mode identification system embodiment:

[0061] The dual-bus protection mode identification system in this embodiment includes a controller, which is used to execute instructions to implement the process of the dual-bus protection mode identification method. The specific process of implementing the dual-bus protection mode identification method has been described in detail in the dual-bus protection mode identification method embodiment and will not be repeated here.

[0062] While specific implementations have been described above, the present invention is not limited to the implementations described above. The basic concept of the present invention lies in the above-described basic scheme. For those skilled in the art, designing various modified models, formulas, and parameters based on the teachings of the present invention does not require creative effort. Changes, modifications, substitutions, and variations to the implementations without departing from the principles and spirit of the present invention remain within the scope of protection of the present invention.

Claims

1. A method for identifying a double busbar protection mode, characterized in that: The steps include: 1) Obtaining data information of the dual busbars; the data information includes: the switch position of the operating branch and the bus tie circuit breaker position, the operating branch current, and the bus tie branch current; 2) Calculate the large differential current and the small differential current of each bus section based on the acquired data information; the small differential current of each bus section is: small differential current of bus I and small differential current of bus II; and determine whether the double bus switch position error condition is met; the double bus switch position error condition includes: a) The three-phase differential current of the busbar satisfies the large differential current balance, small differential current unbalance, and equal small differential current amplitudes; when the large differential current amplitude is less than the large differential current balance threshold, the small differential current amplitude of bus I and bus II are both greater than the small differential current balance threshold, and the absolute value of the difference between the small differential current amplitude of bus I and bus II is less than the error threshold, the large differential current balance, small differential current unbalance, and equal small differential current amplitudes are satisfied; b) All operating branches have knife switches in position; c) The bus tie branch current is greater than the set current threshold or the bus tie circuit breaker is in the trip position; 3) If both busbar switch position error conditions are met, it is determined that there is a branch switch position error; 4) When there is a branch switch position error, and only one non-bus tie branch current is equal to the small differential current of the bus where the branch is located, the switch position of the branch is corrected to the switch position of the other bus of the branch; 5) If the knife switch is corrected successfully, the corrected knife switch position will be used for mode identification; if the knife switch is not corrected successfully, the busbars will be forced to be interconnected.

2. The double busbar protection mode identification method according to claim 1, characterized in that: If the position of the branch switch is corrected, the small differential flow is recalculated. If the small differential flow is balanced, the switch correction is successful, otherwise the switch correction is unsuccessful.

3. The double busbar protection mode identification method according to claim 1, characterized in that: In step 4), when the amplitude of the phase difference between only one non-bus-coupling branch current and the small differential current of the bus where the branch is located is less than the error threshold, it is determined that the branch current is equal to the small differential current of the bus where it is located.

4. The double busbar protection mode identification method according to claim 3 is characterized in that: In step 3), the large difference balance threshold I mk1 For: I mk1 =min[0.9 times the CT break setting, 0.2I n ]; Small difference balance threshold I mk2 For: I mk2 =min[max(2 times the difference flow, 0.08I n ), 0.2I n ]; Error threshold I mk3 For: I mk3 =0.02I n ; Among them I n is the secondary rated value of the current transformer.

5. A double busbar protection mode identification system, characterized in that: The device includes a controller configured to execute instructions to implement the following steps: 1) Obtaining data information of the dual busbars; the data information includes: the switch position of the operating branch and the bus tie circuit breaker position, the operating branch current, and the bus tie branch current; 2) Calculate the large differential current and the small differential current of each bus section based on the acquired data information; the small differential current of each bus section is: small differential current of bus I and small differential current of bus II; and determine whether the double bus switch position error condition is met; the double bus switch position error condition includes: a) The three-phase differential current of the busbar satisfies the large differential current balance, small differential current unbalance, and equal small differential current amplitudes; when the large differential current amplitude is less than the large differential current balance threshold, the small differential current amplitude of bus I and bus II are both greater than the small differential current balance threshold, and the absolute value of the difference between the small differential current amplitude of bus I and bus II is less than the error threshold, the large differential current balance, small differential current unbalance, and equal small differential current amplitudes are satisfied; b) All operating branches have knife switches in position; c) The bus tie branch current is greater than the current threshold or the bus tie circuit breaker is in the trip position; 3) If both busbar switch position error conditions are met, it is determined that there is a branch switch position error; 4) When there is a branch switch position error, and only one non-bus tie branch current is equal to the small differential current of the bus where the branch is located, the switch position of the branch is corrected to the switch position of the other bus of the branch; 5) If the knife switch is corrected successfully, the corrected knife switch position will be used for mode identification; if the knife switch is not corrected successfully, the busbars will be forced to be interconnected.

6. The double busbar protection mode identification system according to claim 5, characterized in that: If the position of the branch switch is corrected, the small differential flow is recalculated. If the small differential flow is balanced, the switch correction is successful, otherwise the switch correction is unsuccessful.

7. The double busbar protection mode identification system according to claim 5, characterized in that: In step 4), when the amplitude of the phase difference between only one non-bus-coupling branch current and the small differential current of the bus where the branch is located is less than the error threshold, it is determined that the branch current is equal to the small differential current of the bus where it is located.

8. The double busbar protection mode identification system according to claim 7, characterized in that: In step 3), the large difference balance threshold I mk1 For: I mk1 =min[0.9 times the CT break setting, 0.2I n ]; Small difference balance threshold I mk2 For: I mk2 =min[max(2 times the difference flow, 0.08I n ), 0.2I n ]; Error threshold I mk3 For: I mk3 =0.02I n ; Among them I n is the secondary rated value of the current transformer.

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