Method and device for judging and protecting mixed ac filter grounding switch from stealing trip

Abstract

The application belongs to the technical field of DC protection of extra-high voltage / high voltage DC transmission system, and particularly relates to a judgment and protection method and device for mixed AC filter grounding switch stealing trip. The application takes the current at the head end and tail end of a passive AC filter and the current at the head end of an active filter as the criterion for the action of mixed AC filter grounding switch stealing trip protection, solves the problem of low reliability caused by the dependence of grounding switch stealing trip protection on circuit breaker auxiliary contact, can timely and effectively detect grounding switch stealing trip faults in the working conditions of active filter maintenance, pre-input and normal exit, avoids breakdown accidents caused by excessive voltage borne by a lightning arrester, and thus ensures the safe and stable operation of a DC transmission system.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of DC protection of extra-high voltage / high voltage direct current transmission systems, and particularly relates to a judgment and protection method and device for sneak tripping of a grounding switch of a hybrid AC filter. BACKGROUND

[0002] A passive AC filter (ACF) is composed of capacitors, reactances and resistors in series and parallel. The basic principle of the AC filter is to make the impedance of a certain harmonic current through it minimum through different combinations of reactors, capacitors and resistors, so as to filter out the characteristic harmonic in the system. In order to solve the problem that the passive filter generates large 5th and 7th harmonics under the condition of large harmonics and poor system harmonic impedance of the power grid, affecting the capacity and safe operation of the filter equipment, a hybrid AC filter (HAPF) is usually used, that is, as shown in Figure 1 , a passive filter (APF) is connected to the AC filter bus through the tail end of the passive AC filter (ACF), that is, the harmonic filtering problem of the converter station and the system background harmonic problem can be solved.

[0003] Figure 1 In the figure, the APF is connected to the tail end of the ACF through the switch Q2, and at the same time, the ACF is grounded through the switch Q1. The switch Q1 serves as a bypass switch of the APF, which ensures that the ACF can operate normally when the APF is out of operation. Figure 1 In the figure, the dashed box is the active filter, and the area outside the dashed box is the passive AC filter. The active AC filter (APF) is designed as a controllable current source, which measures the harmonic current of the converter bus and injects a real-time harmonic compensation current into the bus to offset the harmonic current in the system, thereby achieving the effect of filtering.

[0004] In the process of putting the hybrid AC filter into operation, the normal exit of the active filter and the maintenance of the active filter, there is a working condition of the passive AC filter operating alone. In this working condition, the normal state of the grounding switch Q1 should be closed. However, if the originally closed grounding switch Q1 sneaks tripping, an excessive power frequency voltage will be applied to the surge arrester F3, resulting in thermal breakdown of the surge arrester and damage. Therefore, it is necessary to identify the sneak tripping of the grounding switch Q1 in time to trigger the related protection action. In the existing switch control protection technology, it is usually necessary to rely on the auxiliary contact of the circuit breaker to determine whether the grounding switch sneaks tripping. The reliability is insufficient, which may lead to the failure to determine the sneak tripping of the grounding switch in time or misjudgment, thereby affecting the safety and transmission efficiency of the power transmission system. SUMMARY

[0005] The application aims to provide a method and device for judging and protecting the stealing of a grounding switch of a hybrid AC filter, so as to solve the problem of failure to judge the stealing of the grounding switch or misjudgment caused by the low reliability of the existing technology which relies on the auxiliary contact of a circuit breaker to judge whether the grounding switch is stolen.

[0006] To achieve the above-mentioned purpose, the application provides a method for judging the stealing of a grounding switch of a hybrid AC filter.

[0007] Condition one: any phase of the grounding switch changes from a closed position to an open position.

[0008] Condition two: the passive AC filter is in an operating state.

[0009] Condition three: the active filter is in a maintenance state, or the active filter is not in a maintenance state and the active filter is in an un-input state.

[0010] The grounding switch is a switch for grounding the tail end of the passive AC filter.

[0011] The above-mentioned technical solution has the following beneficial effects: by collecting the current at the head end of the passive AC filter, the current at the tail end of the passive AC filter and the current at the head end of the active filter as the criterion for the protection action of the stealing of the grounding switch of the hybrid AC filter, the problem of low reliability caused by the dependence of the stealing protection of the grounding switch on the auxiliary contact of the circuit breaker is solved, and the stealing fault of the grounding switch of the hybrid AC filter under the working conditions of the maintenance of the active filter, before the input of the active filter and the normal exit of the active filter from the separate operation of the passive AC filter can be detected in time and effectively.

[0012] Further, the specific way of judging the condition that any phase of the grounding switch changes from a closed position to an open position is that the phase current of any phase at the tail end of the passive AC filter is less than a first no-flow threshold value, and the mutation amount of the phase current meets a mutation condition.

[0013] Further, when the condition that any phase of the grounding switch changes from a closed position to an open position is met, if the condition two and the condition three are met simultaneously within a set extension time, it is determined that the three conditions are met simultaneously.

[0014] Further, the mutation condition is that the phase current meets |i(t)|-|i(t-2T)|<-kI e , where i(t) is the fundamental effective value of the phase current at the current moment, i(t-2T) is the fundamental effective value of the phase current two periods ago, k is a coefficient greater than 0, and I e is the rated current of the passive AC filter.

[0015] Further, the condition for determining that the passive AC filter is in the operating state is specifically that the three-phase currents at the first end of the passive AC filter are all greater than the flow threshold.

[0016] Further, the condition for determining that the active filter is in the non-put-in state is specifically that the phase currents of the three phases at the first end of the active filter are all less than the second flow threshold.

[0017] The application further provides a judgment device for the ground switch trip of the hybrid AC filter, comprising a processor configured to execute program instructions to realize the judgment method for the ground switch trip of the hybrid AC filter.

[0018] The application further provides a protection method for the ground switch trip of the hybrid AC filter, which controls the ground switch trip protection action when determining the ground switch trip of the hybrid AC filter; the method for determining the ground switch trip of the hybrid AC filter is the judgment method for the ground switch trip of the hybrid AC filter.

[0019] Further, the specific manner for controlling the ground switch trip protection action is to trip the high-voltage switch after setting a delay time when determining the ground switch trip of the hybrid AC filter; the high-voltage switch is a switch connecting the first end of the passive AC filter to the AC filter large-group bus.

[0020] The application further provides a protection device for the ground switch trip of the hybrid AC filter, comprising a processor configured to execute program instructions to realize the protection method for the ground switch trip of the hybrid AC filter. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 A circuit schematic diagram of the hybrid AC filter in the background art of the application;

[0022] Figure 2 A logic diagram between the conditions for determining the ground switch trip in the protection method for the ground switch trip of the hybrid AC filter of the application;

[0023] Figure 3 A flow chart for determining the ground switch trip in the protection method for the ground switch trip of the hybrid AC filter of the application. DETAILED DESCRIPTION

[0024] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0025] Example of a protection method for the grounding switch of a hybrid AC filter to prevent accidental tripping:

[0026] This embodiment provides a protection method for the grounding switch of a hybrid AC filter to trip unexpectedly. The method is characterized by first judging the tripping situation of the grounding switch of the hybrid AC filter, and determining that the grounding switch of the hybrid AC filter has tripped unexpectedly when the following three conditions are met simultaneously.

[0027] Condition 1: Any phase of the grounding switch changes from the closed position to the tripped position;

[0028] Condition 2: The passive AC filter is in operation;

[0029] Condition 3: The active filter is under maintenance; or the active filter is not under maintenance and is not in operation.

[0030] When it is determined that the grounding switch of the hybrid AC filter has tripped, the grounding switch tripping protection is activated. In this embodiment, the specific method of activating the grounding switch tripping protection is as follows: when it is determined that the grounding switch of the hybrid AC filter has tripped, the high-voltage switch is tripped after a set delay time.

[0031] Among them, reference Figure 1 The grounding switch is Q1, which grounds the tail end of the passive AC filter; the high-voltage switch is Q0, which connects the head end of the passive AC filter to the main busbar of the AC filter. The specific method for determining whether any phase of the grounding switch changes from closed to open is as follows: the phase current of any phase at the tail end of the passive AC filter is less than the first no-current threshold, and the sudden change in the phase current satisfies the sudden change condition; this sudden change condition is: the phase current satisfies |i(t)|-|i(t-2T)|<-kI e Where i(t) is the effective value of the fundamental phase current at the current moment, i(t-2T) is the effective value of the fundamental phase current two cycles ago, k is a coefficient greater than 0, and I e This is the rated current of the passive AC filter; in other embodiments, the effective value of the fundamental phase current before other cycles can also be used, as long as it can ensure timely detection of sudden changes in phase current; k is a coefficient greater than 0, I e This is the rated current of the passive AC filter. In this embodiment, the three-phase current at the end of the passive AC filter is measured... Figure 1 The three-phase currents of the current transformer T4 installed at the end of the passive AC filter are obtained accordingly, and the first no-current threshold is taken as 0.04I. n I nThe rated current of the current transformer T4 installed at the end of the passive AC filter is generally a fixed value, I. n The secondary rating of the current transformer is represented by I. For a system with the same hybrid AC filter, the secondary rating of all current transformers is consistent. Therefore, in this embodiment, the rated current of the current transformer is represented by I. n It is indicated that, in other embodiments, the first no-current threshold can also take other values, as long as they can reflect the no-current state of the phase current.

[0032] The specific condition for determining whether the passive AC filter is in operation is that all three-phase currents at the start-up terminal of the passive AC filter are greater than the current-carrying threshold. In this embodiment, the current-carrying threshold is set to 0.5I. e Therefore, this condition can be transformed into the formula: I ha >0.5I e And I hb >0.5I e And I hc >0.5I e Among them, I ha I hb I hc These are the fundamental RMS values ​​of the three-phase currents A, B, and C of the current transformer T0 at the beginning of the passive AC filter, respectively. e This is the rated current of the passive AC filter.

[0033] In this embodiment, an active power filter (APF) maintenance hard plate is introduced to determine whether the APF is under maintenance. During maintenance, the maintenance hard plate is engaged (set to the open state). Therefore, when determining whether the APF is under maintenance, the information on whether the APF is under maintenance can be directly obtained through the open signal corresponding to the maintenance hard plate.

[0034] The specific condition for determining that the active filter is in an unactivated state is that the phase currents of all three phases at the start-up terminal of the active filter are all less than the second no-current threshold. In this embodiment, the three-phase currents at the start-up terminal of the active filter are measured... Figure 1 The three-phase currents of the current transformer T5 installed at the beginning of the active filter are obtained accordingly, and the second no-current threshold is taken as 0.04I. n I n The rated current of the current transformer T5 set at the first end of the active filter is generally a fixed value; in other embodiments, the second no-current threshold can also be other values, as long as it can reflect the no-current state of the phase current.

[0035] Reference Figure 2In the embodiment, when the condition that any phase of the grounding switch changes from the closed position to the open position is met, if the conditions two and three are met simultaneously within the set extension time, it is determined that the three conditions are met simultaneously. That is, the logical judgment of the condition one is performed first, and the logical result of the judgment is retained for a period of time (i.e., the extension time T1), and the logical judgment of the conditions two and three is performed in this period of time; if the logical judgment results of the three conditions are all met, the final logical judgment result is output: it is determined that the three conditions are met simultaneously; after the logical judgment result is output, a delay of the set delay time T2 is performed, and then the high-voltage switch Q0 is controlled to be opened; during the delay time T2, the judgment of whether the three conditions are met simultaneously is continuously performed, and only when the three conditions are met simultaneously during the delay time, the protection action is controlled, that is, the high-voltage switch Q0 is opened, so that the misjudgment of the false trip of the grounding switch caused by the normal fluctuation of the current and voltage can be avoided. Figure 2 In the embodiment, the box corresponding to "&" represents a logical AND gate; the box corresponding to ">" represents a logical OR gate; the box corresponding to T1 represents an extension element, and the extension time is T1; and the box corresponding to T2 represents a delay element, and the delay time is T2.

[0036] In the embodiment, the delay T2 is set according to the sum of the time of avoiding the differential protection action and the breaking time of the high-voltage switch Q0; and during the delay, it is continuously determined whether the three conditions are met within the delay time. Since only the sudden change condition lasts for a short time during the judgment, the extension time T1 needs to be set for the condition containing the sudden change (i.e., the condition one); the extension time T1 should be set to be greater than the set delay time T2, so that the three conditions (especially the condition one) can be met simultaneously and last for more than the delay setting T2; and the overall flow of the protection method for the false trip of the grounding switch of the hybrid AC filter in the embodiment is as shown in FIG. 6. Figure 3

[0037] Embodiment of the protection device for the false trip of the grounding switch of the hybrid AC filter:

[0038] The embodiment provides a protection device for the false trip of the grounding switch of the hybrid AC filter, which comprises a processor; the processor is used to execute program instructions to realize the protection method in the embodiment of the protection method for the false trip of the grounding switch of the hybrid AC filter.

[0039] Embodiment of the judgment method for the false trip of the grounding switch of the hybrid AC filter:

[0040] ​The embodiment provides a judgment method of mixed AC filter grounding switch stealing, which is used for judging mixed AC filter grounding switch stealing.

[0041] Condition one: any phase of the grounding switch changes from the closed position to the open position;

[0042] Condition two: the passive AC filter is in the running state;

[0043] Condition three: the active filter is in the maintenance state; or the active filter is not in the maintenance state and the active filter is in the non-input state.

[0044] Wherein, referring to Figure 1 , the grounding switch is a switch Q1 connecting the tail end of the passive AC filter to the ground; and the high-voltage switch is a switch Q0 connecting the head end of the passive AC filter to the AC filter group bus. Since the specific principle and process of the judgment method have been described in detail in the above-mentioned protection method embodiment of mixed AC filter grounding switch stealing, the description will not be repeated here.

[0045] The embodiment provides a judgment device of mixed AC filter grounding switch stealing.

[0046] The embodiment provides a judgment device of mixed AC filter grounding switch stealing, which comprises a processor; the processor is used for executing program instructions to realize the judgment method in the above-mentioned judgment method embodiment of mixed AC filter grounding switch stealing. Since the specific principle and process of the judgment method have been described in detail in the above-mentioned protection method embodiment of mixed AC filter grounding switch stealing, the description will not be repeated here.

[0047] The application has the following characteristics: by collecting the current at the head end of the passive AC filter, the current at the tail end of the passive AC filter and the current at the head end of the active filter as the criterion of the protection action of mixed AC filter grounding switch stealing, the problem of low reliability caused by the dependence of the grounding switch stealing protection on the auxiliary contact of the circuit breaker is solved, the mixed AC filter grounding switch stealing fault under the working condition of active filter maintenance, active filter input and active filter normal exit passive AC filter single operation can be detected in time and effectively, after the grounding switch stealing fault is judged, the high-voltage switch is tripped, the lightning arrester breakdown accident caused by the lightning arrester bearing voltage higher than the design voltage is avoided, and the safe and stable operation of the high-voltage and extra-high-voltage DC power transmission system is ensured.

[0048] It should be understood that the foregoing detailed description of the application, rather than limiting the application, is intended to explain and describe the current implementation of the application. Therefore, any modification, equivalent replacement or improvement made without departing from the spirit and scope of the application should be included in the protection scope of the application. In addition, the appended claims of the application are intended to cover all changes and modifications falling within the scope and boundary of the appended claims, or the equivalent form of such scope and boundary.

Claims

1. A method for determining the unauthorized tripping of a grounding switch in a hybrid AC filter, characterized in that, When the following three conditions are met simultaneously, it is determined that the mixed AC filter grounding switch is tripped; Condition one: the phase current of any phase at the tail end of the passive AC filter is less than a first no-flow threshold, and the mutation of the phase current meets a mutation condition, indicating that the grounding switch of any phase is changed from a closed position to an open position; Condition two: the passive AC filter is in an operating state; the condition for determining that the passive AC filter is in an operating state is that the three-phase current at the head end of the passive AC filter is greater than a flow threshold; Condition three: the active filter is in a maintenance state; or the active filter is not in a maintenance state and the active filter is in an uncommissioned state; the condition for determining that the active filter is in an uncommissioned state is that the phase current of the three phases at the head end of the active filter is less than a second no-flow threshold; The grounding switch is a switch that grounds the passive AC filter.

2. The method of claim 1, wherein the hybrid AC filter ground switch trip is determined based on a comparison of the first and second voltage signals. When the condition that the grounding switch of any phase is changed from a closed position to an open position is met, if conditions two and three are met simultaneously within a set broadening time, it is determined that the three conditions are met simultaneously.

3. The method of claim 1, wherein the hybrid AC filter ground switch trip is determined based on a comparison of the first and second voltage signals. The mutation condition is: phase current satisfies |i(t)|-|i(t-2T)|<-kI e Wherein i(t) is the current time phase current fundamental effective value, i(t-2T) is the two period before phase current fundamental effective value, k is the coefficient greater than 0, I e The rated current of passive ac filter.

4. A device for determining a mixed AC filter ground switch trip, comprising: A processor for executing program instructions to implement the mixed AC filter grounding switch tripping judgment method of any one of claims 1-3.

5. A method of protecting a hybrid AC filter grounding switch from a crowbar, characterized by, When it is determined that the mixed AC filter grounding switch is tripped, control the grounding switch tripping protection action; the method for determining that the mixed AC filter grounding switch is tripped is the mixed AC filter grounding switch tripping judgment method of any one of claims 1-3.

6. The method of hybrid AC filter ground switch trip protection of claim 5, wherein, The specific way of controlling the grounding switch tripping protection action is: when it is determined that the mixed AC filter grounding switch is tripped, the high-voltage switch is opened after a delay of a 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.

7. A protection device for a hybrid AC filter ground switch trip, comprising: A processor for executing program instructions to implement the mixed AC filter grounding switch tripping protection method of claim 5 or 6.

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