Method and system for judging and protecting hybrid AC filter bypass switch failure

Abstract

The present invention belongs to the technical field of DC protection for ultra-high voltage (UHV) and high-voltage direct current (HVDC) transmission systems, and specifically relates to a method and system for determining and protecting the bypass switch failure of a hybrid AC filter. By collecting the current at the head end of the passive AC filter, the current at the bypass switch, and the current at the head end of the active filter as criteria for the hybrid AC filter bypass switch closing failure protection, the present invention addresses the issue of the bypass switch closing failure protection relying on the reliability of the circuit breaker auxiliary contacts and the low reliability caused by the closing failure input. This significantly improves the reliability of the closing failure protection and ensures the safe and stable operation of high voltage and ultra-high voltage DC transmission systems.

Description

Technical Field

[0001] The present invention belongs to the technical field of DC protection of ultra-high voltage / high voltage DC transmission systems, and particularly relates to a method and system for judging and protecting a hybrid AC filter bypass switch failure. Background Art

[0002] A passive AC filter (ACF) consists of capacitors, reactors, and resistors connected in series and parallel. The basic principle of an AC filter is to minimize the impedance presented by a particular harmonic when it flows through it through different combinations of reactors, capacitors, and resistors, thereby filtering out characteristic subharmonics in the system. An active AC filter (APF), on the other hand, is typically designed as a controllable current source. Its operating principle is to measure the harmonic current of the commutation bus and inject a real-time, anti-phase harmonic compensation current into the bus to offset the harmonic current in the system, achieving a filtering effect.

[0003] For power grids with large background harmonics and poor system harmonic impedance conditions, if a pure passive filter (ACF) solution is used, harmonics will be amplified, generating large 5th and 7th harmonics, affecting the capacity of the filter equipment and operational safety. The solution is to use a hybrid AC filter (HAPF). The active power filter (APF) is connected to the AC filter group busbar by connecting the tail end of the passive AC filter (ACF). This can solve the harmonic filtering problem of the converter station and the system background harmonic problem. Figure 1 As shown in FIG, the hybrid AC filter (HAPF) includes two parts: a passive AC filter (ACF) and an active power filter (APF). The APF is connected to the tail end of the ACF through a connecting switch Q2. At the same time, the APF is provided with a bypass switch Q1, which can bypass the APF from the hybrid AC filter. Figure 1 In the figure, the area inside the dotted box is the active filter, and the area outside the dotted box is the passive AC filter.

[0004] When an APF fault occurs within the area, the connecting switch Q2 is tripped and the bypass switch Q1 is closed, allowing the ACF to operate independently. The control system also normally exits the APF by tripping the connecting switch Q2 and closing the bypass switch Q1, allowing the ACF to operate independently. However, when the hybrid AC filter exits the APF normally or due to a fault, if the connecting switch Q2 trips but the bypass switch Q1 fails to close, the lightning arrester F3 will be subjected to a large power frequency voltage, causing thermal breakdown and damage to the lightning arrester, threatening the safe and stable operation of the high-voltage and ultra-high-voltage direct current transmission system. Existing switch control and protection technology typically relies on circuit breaker auxiliary contacts and closing failure input signals to determine whether the bypass switch closing has failed. This lacks reliability and may result in the inability to promptly determine bypass switch closing failure or misjudgment, affecting the safety and transmission efficiency of the transmission system. Summary of the Invention

[0005] The object of the present invention is to provide a hybrid AC filter bypass switch failure judgment and protection method and system, which is used to solve the problem that the existing method of relying on the circuit breaker auxiliary contacts and the closing failure input signal to judge whether the bypass switch closing has failed is not reliable enough, resulting in the inability to timely judge the bypass switch closing failure or misjudgment.

[0006] To achieve the above objectives, the present invention provides a method for determining a hybrid AC filter bypass switch failure. When the following three conditions are met simultaneously, the hybrid AC filter bypass switch closing failure is determined:

[0007] 1) All phases of the connected switches change from closed position to tripped position;

[0008] 2) The current of any phase at the bypass switch is less than the first no-current threshold;

[0009] 3) The minimum value of the three-phase current at the head end of the passive AC filter is greater than the current threshold;

[0010] The bypass switch is a switch for bypassing the active filter; the connecting switch is a switch for connecting the active filter and the tail end of the passive AC filter.

[0011] The beneficial effect of the above scheme is as follows: by collecting the current at the head end of the passive AC filter, the current at the bypass switch, and the current at the head end of the active filter as the judgment criteria for the hybrid AC filter bypass switch closing failure protection action, the problem of low reliability caused by the bypass switch closing failure protection relying on the reliability of the circuit breaker auxiliary contacts and the closing failure input is solved. The reliability of the closing failure protection can be greatly improved, and the safe and stable operation of the high-voltage and ultra-high-voltage direct current transmission systems is guaranteed.

[0012] Furthermore, a specific method for determining whether the condition that all phases of the connection switch change from the closed position to the tripped position is satisfied is that the three-phase currents at the head end of the active filter are all less than the second no-current threshold, and the sudden change amount of each phase current meets the sudden change condition.

[0013] Furthermore, when the condition that all phases of the connected switches change from the closed position to the tripped position is met, if within the set extension time, the current of any phase at the bypass switch is less than the first no-current threshold and the minimum value of the three-phase current at the head end of the passive AC filter is greater than the current threshold, it is determined that the three conditions are met at the same time.

[0014] Furthermore, the mutation condition is: the phase current satisfies | i ( t )|-| i ( t -2 T )|<-k I e ,ini ( t ) is the fundamental effective value of the phase current at the current moment, i ( t -2 T ) is the effective value of the fundamental current of the phase two cycles ago, k is a coefficient greater than 0, I e is the rated current of the passive AC filter.

[0015] The present invention also provides a hybrid AC filter bypass switch failure determination system, comprising a collector and a processor. The collector is configured to obtain phase current values ​​at the bypass switch and at the head end of the passive AC filter, respectively. The processor is configured to execute program instructions to implement the hybrid AC filter bypass switch failure determination method described above. This determination system can achieve the same beneficial effects as the hybrid AC filter bypass switch failure determination method described above.

[0016] The present invention also provides a hybrid AC filter bypass switch failure protection method. When the following three conditions are met simultaneously, it is determined that the hybrid AC filter bypass switch closing failure has occurred, and the bypass switch closing failure protection action is controlled:

[0017] 1) All phases of the connected switches change from closed position to tripped position;

[0018] 2) The current of any phase at the bypass switch is less than the first no-current threshold;

[0019] 3) The minimum value of the three-phase current at the head end of the passive AC filter is greater than the current threshold;

[0020] The bypass switch is a switch for bypassing the active filter; the connecting switch is a switch for connecting the active filter and the tail end of the passive AC filter.

[0021] The beneficial effect of the above scheme is as follows: by collecting the current at the head end of the passive AC filter, the current at the bypass switch, and the current at the head end of the active filter as the judgment criteria for the hybrid AC filter bypass switch closing failure protection action, the problem of low reliability caused by the bypass switch closing failure protection relying on the reliability of the circuit breaker auxiliary contacts and the closing failure input is solved. The reliability of the closing failure protection can be greatly improved, and the safe and stable operation of the high-voltage and ultra-high-voltage direct current transmission systems is guaranteed.

[0022] Furthermore, a specific method for determining whether the condition that all phases of the connection switch change from the closed position to the tripped position is satisfied is that the three-phase currents at the head end of the active filter are all less than the second no-current threshold, and the sudden change amount of each phase current meets the sudden change condition.

[0023] Furthermore, when the condition that all phases of the connected switches change from the closed position to the tripped position is met, if within the set extension time, the current of any phase at the bypass switch is less than the first no-current threshold and the minimum value of the three-phase current at the head end of the passive AC filter is greater than the current threshold, it is determined that the three conditions are met at the same time.

[0024] Furthermore, the specific method of controlling the bypass switch closing failure protection action is: when it is determined that the hybrid AC filter bypass switch closing failure occurs, the high-voltage switch is tripped after a set delay time; the high-voltage switch is a switch that connects the head end of the passive AC filter to the AC filter group bus.

[0025] The present invention also provides a hybrid AC filter bypass switch failure protection system, comprising a collector and a processor. The collector is configured to obtain phase current values ​​at the bypass switch and at the head end of the passive AC filter, respectively. The processor is configured to execute program instructions to implement the hybrid AC filter bypass switch failure protection method described above. This protection system can achieve the same beneficial effects as the hybrid AC filter bypass switch failure protection method described above. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A circuit diagram of a hybrid AC filter in the background technology of the present invention;

[0027] Figure 2 A logic diagram of conditions for determining a bypass switch closing failure in an embodiment of a hybrid AC filter bypass switch failure protection method of the present invention;

[0028] Figure 3 The present invention is a flowchart of determining a bypass switch closing failure in a hybrid AC filter bypass switch failure protection method embodiment of the present invention. DETAILED DESCRIPTION

[0029] 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.

[0030] Example of a protection method for hybrid AC filter bypass switch failure:

[0031] This embodiment provides a method for protecting a hybrid AC filter from bypass switch failure. First, the hybrid AC filter bypass switch closing failure is determined. When the following three conditions are simultaneously met, the hybrid AC filter bypass switch closing failure is determined:

[0032] 1) All phases of the connected switches change from closed position to tripped position;

[0033] 2) The current of any phase at the bypass switch is less than the first no-current threshold;

[0034] 3) The minimum value of the three-phase current at the head end of the passive AC filter is greater than the current threshold;

[0035] It is determined that the hybrid AC filter bypass switch fails to close, and the bypass switch closing failure protection action is controlled; in this embodiment, the specific method of the protection action is: when it is determined that the hybrid AC filter bypass switch fails to close, the high-voltage switch is tripped after a set delay time.

[0036] Among them, reference Figure 1 The bypass switch is switch Q1 that bypasses the active filter; the connecting switch is switch Q2 that connects the active filter to the tail end of the passive AC filter; the high-voltage switch is switch Q0 that connects the head end of the passive AC filter to the AC filter group busbar; the specific method for determining whether the conditions for all phases of the connecting switch to change from the closed position to the tripped position are met: the three-phase currents at the head end of the active filter are all less than the second no-current threshold, and the sudden change amount of each phase current meets the sudden change condition; the sudden change condition is: the phase current meets | i ( t )|-| i ( t -2 T )|<-k I e ,in i ( t ) is the fundamental effective value of the phase current at the current moment, i ( t -2 T ) is the effective value of the phase current fundamental wave two cycles ago. In other embodiments, the effective value of the phase current fundamental wave before other cycles may also be taken, as long as the sudden change of the phase current can be detected in time; k is a coefficient greater than 0, I e is the rated current of the passive AC filter. Since the reactive power of the active AC filter is all used to filter harmonics and does not contribute reactive power to the system, after the active filter is put into operation, the current flowing through the active AC filter is basically the same as the rated current of the passive AC filter.

[0037] In this embodiment, the three-phase current at the head end of the active filter is measured by Figure 1 The three-phase current of the T5 transformer set at the head end of the active filter is obtained, and the second no-current threshold is 0.04I n , I n It is the rated current of the current transformer T5 provided at the connection switch Q2, which is generally a fixed value. In other embodiments, the second no-current threshold value may also take other values ​​as long as it can reflect the no-current state of the phase current.

[0038] When any phase current at the bypass switch is less than the first no-current threshold, the first no-current threshold is 0.04In , I n The rated current of the current transformer T4 provided at the tail end of the passive AC filter (i.e., at the bypass switch Q1) is generally a fixed value. It should be noted that, in this embodiment, I n Indicates the secondary rated value of the current transformer. The secondary rated values ​​of all current transformers in the same hybrid AC filter system are consistent. Therefore, the rated current of the current transformer in this embodiment is expressed as I n In other embodiments, the first no-current threshold may also take other values ​​as long as it can reflect the no-current state of the phase current.

[0039] The minimum value of the three-phase current at the head end of the passive AC filter is greater than the current threshold, and the current threshold is 0.5I e , so condition 3) can be transformed into formula: I hmin >0.5I e , where I hmin I is the minimum value of the fundamental effective value of the three-phase currents A, B, and C of the current transformer T0 set at the head end of the passive AC filter; e is the rated current of the passive AC filter.

[0040] Reference Figure 2 In this embodiment, when the conditions are met that all phases of the connected switches change from the closed position to the tripped position, if within the set extension time, the current of any phase at the bypass switch is less than the first no-current threshold and the minimum value of the three-phase current at the head end of the passive AC filter is greater than the current threshold, it is determined that the above three conditions are met at the same time. That is, a logical judgment is first made on "whether the condition that all phases of the connected switches change from closed position to tripped position is met", and the judged logical result is retained for a period of time (i.e., the expansion time). During this period, a logical judgment is made on "whether the condition that any phase current at the bypass switch is less than the first no-current threshold is met" and "whether the condition that the minimum value of the three-phase current at the head end of the passive AC filter is greater than the current threshold is met"; if the judgment results of the three groups are all met, the final logical judgment result is output: it is determined that the above three conditions are met at the same time; after the logical judgment result is output, a delay of the set delay time is performed, and then the high-voltage switch Q0 is controlled to be tripped; during the delay time, the judgment on whether the above three conditions are met at the same time is continuously made. Only when the above three conditions are always met within the delay time, the protection action is controlled, that is, the high-voltage switch Q0 is tripped, thereby avoiding the misjudgment of the grounding switch tripping caused by normal current and voltage fluctuations. Figure 2 In the figure, the box corresponding to “&” represents the logic AND gate; the box corresponding to T1 represents the widening element, and the widening time is T1; the box corresponding to T2 represents the delay element, and the delay time is T2; the judgment process corresponding to the above judgment method is as follows Figure 3 shown.

[0041] In the event of a CT disconnection at the tail end of the passive AC filter, the current characteristics also meet the aforementioned three conditions. This fault triggers the passive AC filter's differential protection to trip the high-voltage switch Q0. Therefore, in this embodiment, the delay T2 is set based on the sum of the time it takes to bypass differential protection and the time it takes the high-voltage switch Q0 to trip. During the delay process, the system continuously determines whether the three conditions are met within the delay period. Because only the sudden change condition lasts for a short time during this determination, a corresponding extension time T1 is required for the condition containing the sudden change (i.e., whether the current at any phase of the bypass switch is less than the first no-current threshold). Extension time T1 should be set to be greater than the set delay time T2 to ensure that all three conditions (especially the sudden change condition) are met simultaneously and their duration exceeds the delay value T2.

[0042] Example of a protection system for hybrid AC filter bypass switch failure:

[0043] This embodiment provides a hybrid AC filter bypass switch failure protection system, comprising a data collector and a processor. The data collector is configured to obtain phase current values ​​at the bypass switch, the passive AC filter headend, and the active filter headend, respectively, while the processor is configured to execute program instructions to implement the protection method described in the aforementioned embodiment of the hybrid AC filter bypass switch failure protection method. The specific principles and procedures of this protection method have been described in detail in the aforementioned embodiment of the hybrid AC filter bypass switch failure protection method and will not be further elaborated here.

[0044] Example of a method for determining a hybrid AC filter bypass switch failure:

[0045] This embodiment provides a method for determining a hybrid AC filter bypass switch failure, which is used to determine a hybrid AC filter bypass switch closing failure. When the following three conditions are simultaneously met, the hybrid AC filter bypass switch closing failure is determined to be a hybrid AC filter bypass switch failure:

[0046] 1) All phases of the connected switches change from closed position to tripped position;

[0047] 2) The current of any phase at the bypass switch is less than the first no-current threshold;

[0048] 3) The minimum value of the three-phase current at the head end of the passive AC filter is greater than the current threshold;

[0049] The bypass switch here is a switch that bypasses the active filter, and the connecting switch is a switch that connects the active filter to the tail end of the passive AC filter. The specific principles and process of this determination method have been detailed in the aforementioned embodiment of the hybrid AC filter bypass switch failure protection method, and will not be repeated here.

[0050] Example of a hybrid AC filter bypass switch failure judgment system:

[0051] This embodiment provides a hybrid AC filter bypass switch failure determination system, comprising a data collector and a processor. The data collector is configured to obtain phase current values ​​at the bypass switch, the passive AC filter headend, and the active filter headend, respectively, while the processor is configured to execute program instructions to implement the determination method described in the aforementioned embodiment of the hybrid AC filter bypass switch failure determination method. The specific principles and procedures of this determination method have been described in detail in the aforementioned embodiment of the hybrid AC filter bypass switch failure protection method and will not be further elaborated here.

[0052] The present invention has the following characteristics: by collecting the current at the ACF head end, the current at the bypass switch, and the current at the APF head end as the criterion for the hybrid AC filter bypass switch closing failure protection action, the problem of low reliability caused by the bypass switch failure protection relying on the reliability of the circuit breaker auxiliary contacts and the closing failure input is solved, the reliability of the closing failure protection can be greatly improved, and the safe and stable operation of the high-voltage and ultra-high-voltage direct current transmission systems is guaranteed.

[0053] It should be understood that the above-described specific embodiments of the present invention are merely illustrative or illustrative of the principles of the present invention and do not constitute limitations of the present invention. Therefore, any modifications, equivalent substitutions, improvements, etc. made without departing from the spirit and scope of the present invention should be included within the scope of protection of the present invention. In addition, the appended claims are intended to cover all variations and modifications that fall within the scope and metes and bounds of the appended claims, or equivalents thereof.

Claims

1. A method for determining a hybrid AC filter bypass switch failure, characterized in that: When the following three conditions are met at the same time, it is determined that the hybrid AC filter bypass switch closing failure: 1) The three-phase currents at the head end of the active filter are all less than the second no-current threshold, and the sudden change of each phase current meets the sudden change condition, indicating that each phase of the connected switch has changed from the closed position to the tripped position; 2) The current of any phase at the bypass switch is less than the first no-current threshold; 3) The minimum value of the three-phase current at the head end of the passive AC filter is greater than the current threshold; The bypass switch is a switch for bypassing the active filter; the connecting switch is a switch for connecting the active filter and the tail end of the passive AC filter.

2. The method for determining a hybrid AC filter bypass switch failure according to claim 1, wherein: When the conditions are met that all phases of the connected switches change from the closed position to the tripped position, if within the set extension time, the current of any phase at the bypass switch is less than the first no-current threshold and the minimum value of the three-phase current at the head end of the passive AC filter is greater than the current threshold, it is determined that the above three conditions are met at the same time.

3. The method for determining a hybrid AC filter bypass switch failure according to claim 1, wherein: The mutation condition is: the phase current satisfies | i ( t )|-| i ( t -2 T )|<-k I e ,in i ( t ) is the fundamental effective value of the phase current at the current moment, i ( t -2 T ) is the effective value of the fundamental current of the phase two cycles ago, k is a coefficient greater than 0, I e is the rated current of the passive AC filter.

4. A hybrid AC filter bypass switch failure judgment system, characterized in that: The method comprises a collector and a processor, wherein the collector is used to respectively obtain the current values ​​of each phase at the bypass switch and the head end of the passive AC filter, and the processor is used to execute program instructions to implement the method for determining the failure of the hybrid AC filter bypass switch as described in any one of claims 1 to 3.

5. A method for protecting a hybrid AC filter from bypass switch failure, characterized in that: When the following three conditions are met at the same time, it is determined that the hybrid AC filter bypass switch closing failure occurs, and the bypass switch closing failure protection is activated: 1) The three-phase currents at the head end of the active filter are all less than the second no-current threshold, and the sudden change of each phase current meets the sudden change condition, indicating that each phase of the connected switch has changed from the closed position to the tripped position; 2) The current of any phase at the bypass switch is less than the first no-current threshold; 3) The minimum value of the three-phase current at the head end of the passive AC filter is greater than the current threshold; The bypass switch is a switch for bypassing the active filter; the connecting switch is a switch for connecting the active filter and the tail end of the passive AC filter.

6. The method for protecting a hybrid AC filter from bypass switch failure according to claim 5, characterized in that: When the conditions are met that all phases of the connected switches change from the closed position to the tripped position, if within the set extension time, the current of any phase at the bypass switch is less than the first no-current threshold and the minimum value of the three-phase current at the head end of the passive AC filter is greater than the current threshold, it is determined that the above three conditions are met at the same time.

7. The method for protecting a hybrid AC filter from bypass switch failure according to claim 5, characterized in that: The specific method of controlling the bypass switch closing failure protection action is: when it is determined that the hybrid AC filter bypass switch closing failure occurs, the high-voltage switch is tripped after a set delay time; the high-voltage switch is the switch that connects the head end of the passive AC filter to the AC filter group bus.

8. A hybrid AC filter bypass switch failure protection system, characterized in that: The invention comprises a collector and a processor, wherein the collector is used to respectively obtain the current values ​​of each phase at the bypass switch and the head end of the passive AC filter, and the processor is used to execute program instructions to implement the protection method for hybrid AC filter bypass switch failure as described in any one of claims 5 to 7 above.

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