Differential protection method and system for preventing abnormal current from entering non-fault phase
By introducing data calculation, start-up discrimination, lock-out discrimination and open discrimination links into the differential protection method, the error lock-out and quickness problems caused by the non-fault phase incoming abnormal currents are solved, and reliable non-fault phase differential protection and rapid phase opening are achieved, which improves the anti-abnormal current capability of differential protection.
Patent Information
- Application Number
- CN202410204362.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-02-23
- Publication Date
- 2025-08-26
AI Technical Summary
The prior art cannot effectively prevent the non-failure abnormal current from intersecting in series with abnormal current, causing false locking of differential protection and affecting protection quickness, especially in the case of high-resistance grounding faults, which may be mistakenly locking or affecting quickness.
A differential protection method that resists the abnormal current in series with non-faults is adopted. Through data calculation, start-up judgment, lock-up judgment and open judgment links, it is possible to reliably lock non-fault phase differential protection when the abnormal current is in series with non-faults, and quickly open the locked fault phase differential protection in the case of converting and developing faults.
It realizes reliable locking of non-fault phase differential protection when the abnormal current is in series with abnormal current, avoids false locking during high-resistance grounding faults, ensures protection quickness, and improves the ability of differential protection to resist abnormal current in series with abnormal current.
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Figure CN120545928A_ABST
Abstract
Description
Technical Field
[0001] The present application belongs to the technical field of power grid relay protection, and particularly to the technical field of differential protection against abnormal current, and specifically to a differential protection method and system for resisting abnormal current entering a non-fault phase. Background Art
[0002] Differential protection, a primary protection mechanism in power systems, is based on Kirchhoff's current law. Due to its simple principle, reliable operation, and excellent selectivity, differential protection is widely used as a primary protection mechanism in power systems. Its research and application have long garnered significant attention from relay protection practitioners.
[0003] The premise for the normal operation of current differential protection is normal current sampling. If the current is abnormal, such as CT saturation in the fault phase or abnormal current flowing into the non-fault phase, there is a risk of incorrect operation of the current differential protection. Current differential protection methods for resisting abnormal currents focus on CT saturation in the fault phase, and the commonly used method is the asynchronous method. However, this method cannot prevent abnormal differential protection caused by abnormal current flowing into the non-fault phase. Existing differential protection methods for resisting abnormal current flowing into the non-fault phase include: fault phase current braking and harmonic blocking. The former may be incorrectly blocked in the event of an out-of-zone to in-zone fault, and the latter may be incorrectly blocked in the event of a high-resistance grounding fault and affect the protection speed. Summary of the Invention
[0004] The purpose of the present application is to provide a differential protection method and system for resisting abnormal currents entering non-fault phases, to solve the problems of possible false locking and affecting the protection speed in the prior art, to achieve reliable locking of the non-fault phase differential protection when abnormal currents enter the non-fault phase, and to quickly open the locked fault phase differential protection in the event of conversion and development faults.
[0005] In order to achieve the above objectives, this application adopts the following technical solutions:
[0006] According to a first aspect of the present application, a differential protection method for resisting abnormal current in a non-fault phase is proposed, comprising a data calculation link, a start-up judgment link, a blocking judgment link, an opening judgment link, and a differential calculation link;
[0007] In the data calculation link, analog data is calculated, and the analog data includes three-phase voltage on each side, three-phase current on each side, differential current, and braking current;
[0008] In the start-up judgment link, it is judged according to the analog data whether the lockout judgment start-up condition is met, and if it is met, the lockout judgment link is entered, and if it is not met, the differential calculation link is entered;
[0009] In the blocking judgment link, it is judged whether the single-phase fault condition is met according to the analog data, and the differential protection of the non-fault phase is blocked if the condition is met, and the differential protection is not blocked if the condition is not met;
[0010] In the opening judgment link, judging whether the blocked phase in the blocking judgment link meets the fault opening condition according to the analog data, opening the phase differential protection if it meets the condition, and continuing to block the phase differential protection if it does not meet the condition;
[0011] In the differential calculation link, when the blocking judgment start condition is met, the non-blocked phase of the blocking judgment link and the open phase of the open judgment link perform differential protection logic operation, and the differential protection of other phases is locked; when the blocking judgment start condition is not met, all phases perform differential protection logic operation.
[0012] According to some embodiments, in the data calculation link, the calculated three-phase voltages on each side are used for the open judgment link; the calculated three-phase currents on each side are used for the start judgment link and the lock judgment link; the calculated differential current is used for the lock judgment link, the open judgment link, and the differential calculation link; and the calculated braking current is used for the lock judgment link and the differential calculation link.
[0013] According to some embodiments, in the start-up judgment link, the lockout judgment start-up condition includes at least one of the following conditions: the maximum phase current on each side is greater than the phase current start-up threshold, the maximum phase current change on each side is greater than the phase current change start-up threshold, the maximum value of the phase current scalar sum is greater than the phase current scalar sum start-up threshold, the maximum value of the phase current scalar sum change is greater than the phase current scalar sum change start-up threshold, wherein the phase current scalar sum is the scalar sum of the phase currents on each side calculated by phase; when the lockout judgment start-up condition includes two or more conditions, if any one condition is met, it is determined that the lockout judgment start-up condition is met.
[0014] According to some embodiments, in the locking judgment link, the single-phase fault condition includes at least one of the following conditions: only one phase current is greater than the sum of the phase current judgment threshold and A1 times the sum of other phase currents, only one phase current scalar sum is greater than the sum of the phase current scalar sum judgment threshold and A2 times the sum of other phase current scalars, only one phase differential current is greater than the differential current judgment threshold and A3 times the sum of other phase differential currents, only one phase braking current is greater than the braking current judgment threshold and A4 times the sum of other phase braking currents, only one phase current change is greater than the phase current change judgment threshold and A5 times the sum of other phase current changes, only one The phase current scalar and variation are greater than the sum of the phase current scalar and variation judgment threshold and A6 times the sum of the other phase current scalars and variations, only one phase differential current variation is greater than the differential current variation judgment threshold and A7 times the sum of the other phase differential current variations, and only one phase braking current variation is greater than the braking current variation judgment threshold and A8 times the sum of the other phase braking current variations; wherein, A1, A2, A3, A4, A5, A6, A7, and A8 are all greater than 0 and less than 1; when the single-phase fault condition includes two or more conditions, it is determined that the single-phase fault condition is met if any one condition is met.
[0015] According to some embodiments, in the locking judgment link, the method of not locking the differential protection when the conditions are not met is specifically: not locking the differential protection when all phases do not meet the single-phase fault conditions or not locking the differential protection when two or more phases meet the single-phase fault conditions.
[0016] According to some embodiments, in the open judgment link, the fault open condition includes at least one of the following conditions: the phase voltage on either side is less than the voltage open threshold, the phase voltage change on either side is greater than the voltage change open threshold, the differential current is greater than the differential current open threshold and the duration exceeds the differential current open delay set value, the differential current change is greater than the differential current change open threshold and the sum of B1 times the differential current change of other phases; wherein B1 is greater than or equal to A7 and less than 1.
[0017] According to another aspect of the present application, a differential protection system for resisting abnormal current entering a non-fault phase is proposed, comprising a data calculation module, a start-up judgment module, a blocking judgment module, an opening judgment module, and a differential calculation module;
[0018] The data calculation module calculates analog data, wherein the analog data includes three-phase voltage on each side, three-phase current on each side, differential current, and braking current;
[0019] The start-up judgment module judges whether the lockout judgment start-up condition is met according to the analog data, and enters the lockout judgment module if the condition is met, and enters the differential calculation module if the condition is not met;
[0020] The blocking judgment module judges whether the single-phase fault condition is met according to the analog data, and blocks the differential protection of the non-fault phase if the condition is met, and does not block the differential protection if the condition is not met;
[0021] The opening determination module determines whether the locked phase in the locking determination module meets the fault opening condition according to the analog data, and opens the phase differential protection if the condition is met, and continues to lock the phase differential protection if the condition is not met;
[0022] In the differential calculation module, when the locking judgment starting conditions are met, the non-locked phase of the locking judgment module and the open phase of the open judgment module perform differential protection logic operations, and the differential protection of other phases is locked; when the locking judgment starting conditions are not met, all phases perform differential protection logic operations.
[0023] The beneficial effects of the present invention are as follows: compared with the prior art, the present application discloses a differential protection method and system for resisting abnormal currents entering non-fault phases. By starting judgment, when the fault current is small and the risk of abnormal current entering the non-fault phase is low, no locking judgment is performed, thereby avoiding incorrect locking of differential protection when a high-resistance grounding fault occurs; the non-fault phase differential is locked only in the event of a single-phase fault, ensuring that the non-fault phase differential protection is reliably locked when the risk of abnormal current entering the non-fault phase is high; the locked fault phase differential protection is quickly opened in the event of conversion and development faults, which significantly improves the ability of the differential protection to resist abnormal currents entering the non-fault phase without affecting the speed. BRIEF DESCRIPTION OF THE DRAWINGS
[0024] The following detailed description of the specific embodiments of the present application in conjunction with the accompanying drawings will make the technical solutions and other beneficial effects of the present application apparent.
[0025] Figure 1 This is a flow chart of a differential protection method for resisting abnormal current entering a non-fault phase provided in an embodiment of the present application.
[0026] Figure 2 This is a schematic structural diagram of a differential protection system for resisting abnormal current entering a non-fault phase provided in an embodiment of the present application. DETAILED DESCRIPTION
[0027] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the embodiments described are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without making creative efforts are within the scope of protection of this application.
[0028] The applicant has found that the current differential protection methods against abnormal currents are focused on CT saturation of the fault phase, and the commonly used method is the asynchronous method. However, this method cannot prevent the abnormal current from entering the non-fault phase, which causes the differential protection to be abnormal. The existing differential protection methods against abnormal currents entering the non-fault phase include: fault phase current braking and harmonic blocking. The former may be blocked by mistake when an out-of-zone to in-zone fault occurs, and the latter may be blocked by mistake when a high-resistance grounding fault occurs and will affect the protection speed. Therefore, there is a need for a differential protection method against abnormal currents entering the non-fault phase that can reliably block the non-fault phase differential protection when an abnormal current enters the non-fault phase, and quickly open the blocked fault phase differential protection in the event of conversion and development faults.
[0029] In view of this, the embodiment of the present application provides a differential protection method for resisting abnormal current entering the non-fault phase, such as Figure 1 As shown, the method includes a data calculation link, a start judgment link, a lock judgment link, an open judgment link and a differential calculation link;
[0030] In the data calculation link, analog data is calculated, and the analog data includes three-phase voltage on each side, three-phase current on each side, differential current, and braking current; the calculated three-phase voltage on each side is used for the open judgment link, which is the three-phase voltage on this side for the two-end line. and the opposite three-phase voltage For multi-terminal lines, the same applies; the calculated three-phase current on each side is used for the start-up judgment link and the lock-out judgment link. For two-terminal lines, it is the three-phase current on this side. and the opposite three-phase current For multi-terminal lines, the same applies; the calculated differential current includes Used in the lock judgment link, open judgment link, and differential calculation link; the calculated braking current includes Used in the locking judgment link and differential calculation link;
[0031] In the start-up judgment link, according to the three-phase currents on each side in the analog data, it is judged whether the lockout judgment start-up conditions are met. If the conditions are met, the lockout judgment link is entered, and if the conditions are not met, the differential calculation link is entered; the start-up condition is that the phase current scalar and the maximum value are greater than the phase current scalar and the start-up threshold, that is, max((I mA +I nA ),(I mB +I nB ),(I mC +I nC ))>Phase current scalar and starting threshold;
[0032] In the blocking judgment link, according to the three-phase currents on each side in the analog data, it is judged whether the single-phase fault condition is met. If it is met, the differential protection of the non-fault phase is blocked, and if it is not met, the differential protection is not blocked. The single-phase fault condition is that only one phase current is greater than the sum of the phase current judgment threshold and A1 times the sum of the other phase currents; wherein A1 is greater than 0 and less than 1; for example, if A1 is 0.1, then when I mA >(phase current discrimination threshold + 0.1*max(I mB ,I mC )), and I mB ≤(phase current discrimination threshold + 0.1*max(I mA ,I mC )), and I mC ≤(phase current discrimination threshold + 0.1*max(I mA ,I mB )), when phase A meets the single-phase fault condition, the differential protection of phase A is opened and the differential protection of phases B and C is locked; when it does not meet the condition, the differential protection is not locked. The method is: when all phases do not meet the single-phase fault condition, the differential protection is not locked; when two or more phases meet the single-phase fault condition, the differential protection is not locked. For example: A1 is 0.1, then when I mA ≤(phase current discrimination threshold + 0.1*max(L mB ,L mC )), and L mB ≤(phase current discrimination threshold + 0.1*max(I mA ,L mC )), and I mC ≤(phase current discrimination threshold + 0.1*max(I mA ,I mB )), the single-phase fault condition is not met and the differential is not locked; when I mA >(phase current discrimination threshold + 0.1*max(I mB ,I mC )), and I mB >(phase current discrimination threshold + 0.1*max(I mA ,I mC )), and I mC ≤(phase current discrimination threshold + 0.1*max(I mA ,I mB )) When the single-phase fault condition is not met, the differential is not locked;
[0033] In the opening judgment link, according to the three-phase voltages on each side in the analog data, it is judged whether the blocked phase in the blocking judgment link meets the fault opening condition. If it meets the condition, the phase differential protection is opened; if it does not meet the condition, the phase differential protection is still blocked; the fault opening condition is that the phase voltage on either side is less than the voltage opening threshold, for example: min(U mB ,UnB )<voltage opening threshold, open B phase differential;
[0034] In the differential calculation link, when the locking judgment starting conditions are met, the non-locked phase of the locking judgment link and the open phase of the open judgment link are subjected to differential protection logic operation, and the differential protection of other phases is locked. For example: if the non-locked phase of the locking judgment link is phase A and the open phase of the open judgment link is phase B, the differential protection logic operation of phases A and B is performed; when the locking judgment starting conditions are not met, all phases are subjected to differential protection logic operation.
[0035] According to some preferred embodiments of the present application, the lockout judgment starting condition includes at least one of the following conditions: the maximum phase current on each side is greater than the phase current starting threshold, the maximum phase current change on each side is greater than the phase current change starting threshold, the maximum value of the phase current scalar sum is greater than the phase current scalar sum starting threshold, the maximum value of the phase current scalar sum change is greater than the phase current scalar sum change starting threshold, wherein the phase current scalar sum is the scalar sum of the phase currents on each side calculated by phase; when the lockout judgment starting condition includes two or more conditions, if any one condition is met, it is determined that the lockout judgment starting condition is met.
[0036] According to some preferred embodiments of the present application, the single-phase fault condition includes at least one of the following conditions: only one phase current is greater than the sum of the phase current judgment threshold and A1 times the sum of the other phase currents; only one phase current scalar sum is greater than the sum of the phase current scalar sum judgment threshold and A2 times the sum of the other phase current scalar sums; only one phase differential current is greater than the differential current judgment threshold and A3 times the sum of the other phase differential currents; only one phase braking current is greater than the braking current judgment threshold and A4 times the sum of the other phase braking currents; only one phase current change is greater than the phase current change judgment threshold and A5 times the sum of the other phase current changes; only one phase current is greater than the phase current change judgment threshold and A5 times the sum of the other phase current changes; The current scalar quantity and change are greater than the sum of the phase current scalar quantity and change judgment threshold and A6 times the sum of the other phase current scalar quantities and changes, only one phase differential current change is greater than the differential current change judgment threshold and A7 times the sum of the other phase differential current changes, only one phase braking current change is greater than the braking current change judgment threshold and A8 times the sum of the other phase braking current changes; among them, A1, A2, A3, A4, A5, A6, A7, and A8 are all greater than 0 and less than 1; when the single-phase fault condition includes two or more conditions, it is determined that the single-phase fault condition is met if any one condition is met.
[0037] According to some preferred embodiments of the present application, the fault opening conditions include at least one of the following conditions: the phase voltage on either side is less than the voltage opening threshold, the phase voltage change on either side is greater than the voltage change opening threshold, the differential current is greater than the differential current opening threshold and the duration exceeds the differential current opening delay set value, the differential current change is greater than the differential current change opening threshold and the sum of B1 times the differential current change of other phases; wherein, B1 is greater than or equal to A7 and less than 1.
[0038] Figure 2 The exemplary embodiment of the present application provides a differential protection system for resisting abnormal current flowing into a non-fault phase, including a data calculation module, a start-up judgment module, a blocking judgment module, an opening judgment module, and a differential calculation module;
[0039] The data calculation module calculates analog data, which includes three-phase voltage on each side, three-phase current on each side, differential current, and braking current; the calculated three-phase voltage on each side is used for the open judgment link; the calculated three-phase current on each side is used for the start judgment link and the lock judgment link; the calculated differential current is used for the lock judgment link, the open judgment link, and the differential calculation link; the calculated braking current is used for the lock judgment link and the differential calculation link.
[0040] The start-up judgment module judges whether the lockout judgment start-up condition is met according to the analog data, and enters the lockout judgment module if the condition is met, and enters the differential calculation module if the condition is not met; the start-up condition is that the sum of the phase current scalar and the maximum value is greater than the phase current scalar and the start-up threshold;
[0041] The locking judgment module judges whether the single-phase fault condition is met according to the analog data, and locks the differential protection of the non-fault phase if the condition is met, and does not lock the differential protection if the condition is not met; the single-phase fault condition is that only one phase current is greater than the sum of the phase current judgment threshold and A1 times the other phase currents; wherein A1 is greater than 0 and less than 1; the method of not locking the differential protection if the condition is not met is: not locking the differential protection if all phases do not meet the single-phase fault condition, and not locking the differential protection if two or more phases meet the single-phase fault condition;
[0042] The opening judgment module judges whether the blocked phase in the blocking judgment module meets the fault opening condition based on the analog data, and opens the phase differential protection if it meets the condition, and continues to block the phase differential protection if it does not meet the condition; the fault opening condition is that the phase voltage on either side is less than the voltage opening threshold;
[0043] In the differential calculation module, when the locking judgment starting conditions are met, the non-locked phase of the locking judgment module and the open phase of the open judgment module perform differential protection logic operations, and the differential protection of other phases is locked; when the locking judgment starting conditions are not met, all phases perform differential protection logic operations.
[0044] The above is a detailed introduction to a differential protection method and system for resisting abnormal current entering a non-fault phase provided in an embodiment of the present application, and specific examples are used to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the technical solution and core idea of the present application; ordinary technicians in this field should understand that: they can still modify the technical solutions recorded in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein; and these modifications or replacements do not cause the essence of the corresponding technical solution to deviate from the scope of the technical solution of the embodiments of the present application.
Claims
1. A differential protection method for resisting abnormal current flowing into a non-fault phase, characterized in that: It includes data calculation link, start judgment link, lock judgment link, open judgment link and differential calculation link; In the data calculation link, analog data is calculated, and the analog data includes three-phase voltage on each side, three-phase current on each side, differential current, and braking current; In the start-up judgment link, it is judged according to the analog data whether the lockout judgment start-up condition is met, and if it is met, the lockout judgment link is entered, and if it is not met, the differential calculation link is entered; In the blocking judgment link, it is judged whether the single-phase fault condition is met according to the analog data, and the differential protection of the non-fault phase is blocked if the condition is met, and the differential protection is not blocked if the condition is not met; In the opening judgment link, judging whether the blocked phase in the blocking judgment link meets the fault opening condition according to the analog data, opening the phase differential protection if it meets the condition, and continuing to block the phase differential protection if it does not meet the condition; In the differential calculation link, when the blocking judgment start condition is met, the non-blocked phase of the blocking judgment link and the open phase of the open judgment link are subjected to differential protection logic operation, and the differential protection of other phases is locked; When the blocking judgment start conditions are not met, all phases perform differential protection logic operations.
2. The differential protection method for resisting abnormal current entering a non-fault phase according to claim 1, characterized in that: In the data calculation link, the calculated three-phase voltages on each side are used in the open judgment link; the calculated three-phase currents on each side are used in the start judgment link and the lock judgment link; the calculated differential current is used in the lock judgment link, the open judgment link, and the differential calculation link; the calculated braking current is used in the lock judgment link and the differential calculation link.
3. The differential protection method for resisting abnormal current entering a non-fault phase according to claim 1, characterized in that: In the start-up judgment link, the lockout judgment start-up condition includes at least one of the following conditions: the maximum phase current on each side is greater than the phase current start-up threshold, the maximum phase current change on each side is greater than the phase current change start-up threshold, the maximum value of the phase current scalar sum is greater than the phase current scalar sum start-up threshold, and the maximum value of the phase current scalar sum change is greater than the phase current scalar sum change start-up threshold, wherein the phase current scalar sum is the scalar sum of the phase currents on each side calculated by phase; when the lockout judgment start-up condition includes two or more conditions, if any one condition is met, it is determined that the lockout judgment start-up condition is met.
4. The differential protection method for resisting abnormal current entering a non-fault phase according to claim 1, characterized in that: In the locking judgment link, the single-phase fault condition includes at least one of the following conditions: only one phase current is greater than the sum of the phase current judgment threshold and A1 times the sum of other phase currents, only one phase current scalar sum is greater than the sum of the phase current scalar and judgment threshold and A2 times the sum of other phase current scalars, only one phase differential current is greater than the differential current judgment threshold and A3 times the sum of other phase differential currents, only one phase braking current is greater than the braking current judgment threshold and A4 times the sum of other phase braking currents, only one phase current change is greater than the phase current change judgment threshold and A5 times the sum of other phase current changes, only one phase current scalar sum is greater than the phase current scalar sum and the judgment threshold and A2 times the sum of other phase current scalars, The sum of the phase current scalar and change is greater than the phase current scalar and change judgment threshold and A6 times the sum of the other phase current scalars and changes, only one phase differential current change is greater than the differential current change judgment threshold and A7 times the sum of the other phase differential current changes, only one phase braking current change is greater than the braking current change judgment threshold and A8 times the sum of the other phase braking current changes; wherein, A1, A2, A3, A4, A5, A6, A7, and A8 are all greater than 0 and less than 1; when the single-phase fault condition includes two or more conditions, it is determined that the single-phase fault condition is met if any one condition is met.
5. The differential protection method for resisting abnormal current entering a non-fault phase according to claim 1, characterized in that: In the locking judgment link, the method of not locking the differential protection when the conditions are not met is specifically: not locking the differential protection when all phases do not meet the single-phase fault conditions or not locking the differential protection when two or more phases meet the single-phase fault conditions.
6. The differential protection method for resisting abnormal current flowing into a non-fault phase according to claim 4, characterized in that: In the open judgment link, the fault open condition includes at least one of the following conditions: the phase voltage on either side is less than the voltage open threshold, the phase voltage change on either side is greater than the voltage change open threshold, the differential current is greater than the differential current open threshold and the duration exceeds the differential current open delay set value, the differential current change is greater than the differential current change open threshold and B1 times the sum of the differential current changes of other phases; among which, B1 is greater than or equal to A7 and less than 1.
7. A differential protection system for resisting abnormal current flowing into a non-fault phase, characterized in that: It includes a data calculation module, a start judgment module, a lock judgment module, an open judgment module and a differential calculation module; The data calculation module calculates analog data, wherein the analog data includes three-phase voltage on each side, three-phase current on each side, differential current, and braking current; The start-up judgment module judges whether the lockout judgment start-up condition is met according to the analog data, and enters the lockout judgment module if the condition is met, and enters the differential calculation module if the condition is not met; The blocking judgment module judges whether the single-phase fault condition is met according to the analog data, and blocks the differential protection of the non-fault phase if the condition is met, and does not block the differential protection if the condition is not met; The opening determination module determines whether the locked phase in the locking determination module meets the fault opening condition according to the analog data, and opens the phase differential protection if the condition is met, and continues to lock the phase differential protection if the condition is not met; The differential calculation module, when the blocking judgment start condition is met, performs differential protection logic operation on the unblocked phase of the blocking judgment module and the open phase of the open judgment module, and the differential protection of other phases is locked; When the blocking judgment start conditions are not met, all phases perform differential protection logic operations.