A control method for a fast switching fault current limiter

Abstract

The present invention discloses a control method for a fast-switching fault current limiter. The fast switch and a current-limiting reactor are connected in parallel to form the fast-switching fault current limiter, which is then connected in series with a power grid circuit breaker. The fast switch is configured with two sets of switch drive units and two sets of switch drive units. The control method is implemented as follows: first, the power grid circuit breaker current, the fast switch current, and the fast switch position are collected. The fast switch then adopts a double-opening and double-closing control strategy, making a comprehensive judgment based on the short-circuit current tolerance and rated current tolerance of the current-limiting reactor. After an overload action, the power grid circuit breaker is controlled to open. The present invention overcomes the shortcoming of the current-limiting reactor in existing technical solutions, which can only operate for a long time, and improves the reliability and cost-effectiveness of the fast-switching fault current limiter.

Description

Technical Field

[0001] The present invention relates to a fast switching type fault current limiter, and in particular to a control method of the fast switching type fault current limiter. Background Art

[0002] With the continued development of power generation, the increasing power load, and the close interconnection of AC and DC power grids across various regions, short-circuit current levels in power systems are increasing, seriously threatening the interrupting capacity of circuit breakers. Excessive short-circuit currents have become a common problem in load-intensive and power-intensive areas, hindering power development and the safe and stable operation of power grids.

[0003] In principle, suppressing short-circuit current primarily involves increasing the equivalent short-circuit impedance at the fault point. Conventional methods include: First, changing the system structure or operating mode, including busbar segmentation, line shutdown, and line disconnection. These measures can significantly alter the grid structure, compromise grid integrity, and negatively impact system operation. Second, installing current-limiting reactors, primarily series reactors and split reactors, can effectively reduce short-circuit current levels. However, these reactors can lead to uneven current distribution, impacting grid efficiency. Furthermore, high-voltage current-limiting reactors require significant floor space and are expensive, making retrofitting difficult and challenging for load center substations due to site constraints. Third, employing fault current limiters (FCLs). Dozens of FCL technology solutions exist. FCLs based on superconducting materials, solid-state devices, and series resonant circuits overcome the shortcomings of traditional series current-limiting reactors and effectively balance system operation with short-circuit current limitation. However, their application in engineering projects is limited by technological maturity and economic feasibility, particularly in high-voltage grids of 220 kV and above.

[0004] A fast-switching fault current limiter, consisting of a fast switch connected in parallel with a current-limiting reactor, is a widely adopted current-limiting method. During normal grid operation, the fast switch is controlled to close, bypassing the current-limiting reactor. Following a short-circuit fault, the fast switch is controlled to open within approximately one cycle, enabling the current-limiting reactor to operate. After the fault is cleared, the fast switch is controlled to reclose, bypassing the reactor again. Current control methods for fast-switching fault current limiters have the following major drawbacks: First, the fast switch typically operates in an open-close-open sequence. This lacks appropriate remedial measures in the event of a failure to open or close the switch, potentially leaving the current-limiting reactor in the grid for extended periods, adversely impacting normal grid operation. Second, current-limiting reactors generally use fixed series reactors, which can withstand the rated current of the power grid for a long time. However, for the special application scenario of fast-switching fault current limiters, the current-limiting reactor only needs to be briefly connected to the power grid to withstand the short-circuit current during the fault. Therefore, the current technical solution has led to long-term high equipment investment, which seriously restricts the promotion of fast-switching fault current limiters. The current control method also lacks support for the short-term tolerance solution of the current-limiting reactor. Summary of the Invention

[0005] Purpose of the invention: The purpose of the present invention is to provide a fast switching type fault current limiter control method and device that can shorten the time it takes for a current limiting reactor to be put into the grid and withstand the short-circuit current during a fault.

[0006] Technical Solution: In the control method of the present invention, a fast switch and a current-limiting reactor are connected in parallel to form a fast switch-type fault current limiter, which is connected in series with a power grid circuit breaker. The fast switch is equipped with two sets of switch drive units and two groups of switch drive units. The data acquisition unit collects the power grid circuit breaker current, the fast switch current, and the fast switch position. The data processing unit is used for the state judgment and control logic calculation. The output unit is used to control the working state of the fast switch and the power grid circuit breaker. The method is characterized by comprising the following steps:

[0007] S1, the data acquisition unit collects the grid circuit breaker current, the fast switch current, and the fast switch position. If the grid circuit breaker current or the fast switch current is greater than the set current threshold within a limited time, it is determined to be a grid short circuit fault, and step S2 is executed;

[0008] If the grid circuit breaker current or the fast switch current is less than or equal to the set current threshold within a limited time, the data processing unit performs a cyclic detection;

[0009] When the current limiting reactor is overloaded, step S3 is executed; when the current limiting reactor is operating normally, the data processing unit performs cyclic detection;

[0010] S2: After a grid short circuit occurs, the output unit controls the first group of fast switch drive units to operate. If the fast switch does not open within a specified time, it is determined that the fast switch has failed to open. After the fast switch fails to open, the second group of drive units is controlled to operate.

[0011] Then, after the closing delay setting TC, the first combination switch drive unit of the fast switch is controlled to operate. If the fast switch is not in the closing position within the specified time, it is determined that the fast switch closing has failed. After the fast switch closing fails, the second combination switch drive unit is controlled to operate.

[0012] S3: After the current-limiting reactor is overloaded, the output unit controls the grid circuit breaker to open.

[0013] Furthermore, if any of the conditions in J1, J2, and J3 are met, the current limiting reactor is judged to be overloaded:

[0014] J1, the fast switch is in the open position, the fast switch current is less than the set current threshold, and the grid circuit breaker current is greater than the short-circuit current setting value I1 within the short-circuit condition time setting value T1;

[0015] J2, the fast switch is in the open position, the fast switch current is less than the set current threshold, and the grid circuit breaker current is greater than the load condition current value I2 within the load condition time value T2;

[0016] J3, the fast switch is in the open position, the fast switch current is less than the current threshold, and the grid circuit breaker current is greater than the rated operating current value I3 within the rated operating time value T3;

[0017] Among them, T1≤T2≤T3, I1≥I2≥I3.

[0018] Furthermore, the short-circuit operating current constant I1 is not greater than the short-circuit current tolerance capability of the current-limiting reactor, and the short-circuit operating time constant T1 is not greater than the short-circuit current tolerance time of the current-limiting reactor; the rated operating current constant I3 is not greater than the rated current tolerance capability of the current-limiting reactor, and the rated operating time constant T3 is not greater than the rated current tolerance time of the current-limiting reactor.

[0019] Furthermore, the closing delay constant TC is greater than T max , where T max It is the maximum value of the grid reclosing delay and the backup protection action time.

[0020] Furthermore, when the fault current limiter operates normally, the fast switch executes the "open-TC-close-open-TC-close" operation sequence; when the fast switch fails to open, the "open-open-TC-close" operation sequence is executed; when the fast switch fails to close, the "open-TC-close-close" operation sequence is executed; when the fast switch fails to open and close at the same time, the "open-open-TC-close-close" operation sequence is executed.

[0021] Compared with the prior art, the present invention has the following significant effects:

[0022] 1. The present invention adopts a fast-switching double-opening and double-closing control strategy and a segmented overload judgment method for current-limiting reactors. This overcomes the shortcomings of existing technical solutions, such as imperfect failure protection control logic and the long-term operation limit of current-limiting reactors. It reduces the adverse impact of failure of fast-switching fault current limiters on the power grid, avoids the escalation of accidents, and improves the reliability and cost-effectiveness of fast-switching fault current limiters.

[0023] 2. The overload judgment of the current limiting reactor adopts segmented logic and is independent of the opening and closing control of the fast switch, taking into account both the grid fault current limiting function and the protection function of the equipment itself. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a schematic diagram of a control device of the present invention;

[0025] Figure 2 This is a flow chart of the control method of the present invention. DETAILED DESCRIPTION

[0026] The present invention will be described in further detail below with reference to the accompanying drawings and specific implementations.

[0027] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the specific implementation methods of the technical solutions of the present invention will be described in more detail and clearly with reference to the accompanying drawings and examples. However, the specific implementation methods and examples described below are for illustrative purposes only and are not intended to limit the present invention. They only include some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art for various variations of the present invention are within the scope of protection of the present invention.

[0028] Figure 1This is a schematic diagram of the control device of the present invention, wherein the fast switch and the current limiting reactor are connected in parallel to form a fault current limiter, and the grid circuit breaker is connected in series with the fault current limiter. The fast switch is configured with two sets of switch drive units and two sets of switch drive unit controls, and the current transformer is used to collect the fast switch current and the grid circuit breaker current. The control device includes a data acquisition unit, a data processing unit and an output unit connected in series. The data acquisition unit is used to sample the grid circuit breaker current, the fast switch current and the fast switch position. The data processing unit is used to calculate the control method. The output unit is used to control the opening and closing of the fast switch and the grid circuit breaker.

[0029] Figure 2 The control method flow chart of the present invention includes the following steps:

[0030] First, the grid breaker current, fast switch current, and fast switch position are acquired.

[0031] Then, status judgment and control are performed, and the process is as follows:

[0032] Determine whether the power grid has a short-circuit fault. If the fast switch current or the power grid circuit breaker current is greater than the set current threshold within a limited time, it is determined to be a power grid short-circuit fault; otherwise, the data processing unit performs a cyclic detection; after the power grid short-circuit fault, the output unit controls the first group of fast switch switch drive units to operate. If the fast switch is not in the open position within the limited time, it is determined that the fast switch has failed to open. After the fast switch fails to open, the second group of fast switch drive units is controlled to operate; then, after the closing delay setting TC, the first combination of fast switch drive units is controlled to operate. If the fast switch is not in the closed position within the limited time, it is determined that the fast switch has failed to close. After the fast switch fails to close, the second combination of fast switch drive units is controlled to operate; wherein, the maximum value of the power grid reclosing delay and the backup protection action time is taken, recorded as T max , the closing delay setting TC is greater than T max ;

[0033] Determine whether the current-limiting reactor is overloaded. If the fast switch is in the open position, the fast switch current is less than the set current threshold, and the grid circuit breaker current is greater than the current set value I1 within the time set value T1, then the current-limiting reactor overload judgment condition 1 is met; if the fast switch is in the open position, the fast switch current is less than the set current threshold, and the grid circuit breaker current is greater than the current set value I2 within the time set value T2, then the current-limiting reactor overload judgment condition 2 is met; if the fast switch is in the open position, the fast switch current is less than the set current threshold, and the grid circuit breaker current is greater than the current set value I3 within the time set value T3, then the current-limiting reactor overload judgment condition 3 is met; if any of the three conditions is met, it is judged that the current-limiting reactor is overloaded; otherwise, the detection is cyclic.

[0034] Finally, when the current limiting reactor is overloaded, the output unit controls the grid circuit breaker to open.

[0035] In the above process, the time constants T1, T2 and T3 satisfy the relationship: T1≤T2≤T3, and the current constants I1, I2 and I3 satisfy the relationship: I1≥I2≥I3. The time constant T1 and the current constant I1 are parameters reflecting the short-circuit working condition of the current-limiting reactor, the current constant I1 is not greater than the short-circuit current tolerance capability of the current-limiting reactor, and the time constant T1 is not greater than the short-circuit current tolerance time of the current-limiting reactor; the time constant T2 and the current constant I2 are parameters reflecting the overload working condition of the current-limiting reactor, the current constant I2 is not greater than the overload current tolerance capability of the current-limiting reactor, and the time constant T2 is not greater than the overload current tolerance time of the current-limiting reactor; the time constant T3 and the current constant I3 are parameters reflecting the rated working condition of the current-limiting reactor, the current constant I3 is not greater than the rated current tolerance capability of the current-limiting reactor, and the time constant T3 is not greater than the rated current tolerance time of the current-limiting reactor.

[0036] In the control flow described above, when the fault current limiter operates normally, the fast switch executes the "open-TC-close-open-TC-close" sequence to ensure the fast switch's secondary current limiting function after the fault. If the fast switch fails to open, the "open-open-TC-close" sequence is executed. If the fast switch fails to close, the "open-TC-close-close" sequence is executed. If the fast switch fails to open and close simultaneously, the "open-open-TC-close-close" sequence is executed. The overload determination of the current-limiting reactor uses segmented logic and is independent of the fast switch's opening and closing control, balancing the grid fault current limiting function with the device's own protection.

[0037] It should be noted that the various embodiments described above with reference to the accompanying drawings are intended only to illustrate the present invention and are not intended to limit the scope of the present invention. Those skilled in the art should understand that any modifications or equivalent substitutions to the present invention that do not depart from the spirit and scope of the present invention are intended to be encompassed within the scope of the present invention. Furthermore, unless the context otherwise requires, words appearing in the singular include the plural form, and vice versa. Furthermore, unless otherwise specified, all or part of any embodiment may be used in combination with all or part of any other embodiment.

Claims

1. A control method for a fast-switch type fault current limiter, wherein a fast switch and a current-limiting reactor are connected in parallel to form a fast-switch type fault current limiter, and the fast-switch type fault current limiter is connected in series with a power grid circuit breaker; the fast switch is equipped with two sets of switch drive units and two sets of switch drive units; a data acquisition unit collects power grid circuit breaker current, fast switch current, and fast switch position; a data processing unit is used for state judgment and control logic calculation; and an output unit is used to control the working state of the fast switch and the power grid circuit breaker; characterized in that: The steps are as follows: S1, the data acquisition unit collects the grid circuit breaker current, the fast switch current, and the fast switch position. If the grid circuit breaker current or the fast switch current is greater than the set current threshold within a limited time, it is determined to be a grid short circuit fault, and step S2 is executed; If the grid circuit breaker current or the fast switch current is less than or equal to the set current threshold within a limited time, the data processing unit performs a cyclic detection; When the current limiting reactor is overloaded, execute step S3; When the current limiting reactor operates normally, the data processing unit performs cyclic detection; S2: After a grid short circuit occurs, the output unit controls the first group of fast switch drive units to operate. If the fast switch does not open within a specified time, it is determined that the fast switch has failed to open. After the fast switch fails to open, the second group of drive units is controlled to operate. Then, after the closing delay setting TC, the first combination switch drive unit of the fast switch is controlled to operate. If the fast switch is not in the closing position within the specified time, it is determined that the fast switch closing has failed. After the fast switch closing fails, the second combination switch drive unit is controlled to operate. S3, after the current limiting reactor is overloaded, the output unit controls the grid circuit breaker to open; If any of the conditions J1, J2, and J3 are met, the current-limiting reactor is judged to be overloaded: J1, the fast switch is in the open position, the fast switch current is less than the set current threshold, and the grid circuit breaker current is greater than the short-circuit current setting value I1 within the short-circuit condition time setting value T1; J2, the fast switch is in the open position, the fast switch current is less than the set current threshold, and the grid circuit breaker current is greater than the load condition current value I2 within the load condition time value T2; J3, the fast switch is in the open position, the fast switch current is less than the current threshold, and the grid circuit breaker current is greater than the rated operating current value I3 within the rated operating time value T3; Among them, T1≤T2≤T3, I1≥I2≥I3.

2. The control method of the fast switching type fault current limiter according to claim 1, characterized in that: The short-circuit operating current constant I1 is not greater than the short-circuit current tolerance capability of the current-limiting reactor, and the short-circuit operating time constant T1 is not greater than the short-circuit current tolerance time of the current-limiting reactor; the rated operating current constant I3 is not greater than the rated current tolerance capability of the current-limiting reactor, and the rated operating time constant T3 is not greater than the rated current tolerance time of the current-limiting reactor.

3. The control method of the fast switching type fault current limiter according to claim 1, characterized in that: The closing delay setting TC is greater than T max , where T max It is the maximum value of the grid reclosing delay and the backup protection action time.

4. The control method of the fast switching type fault current limiter according to claim 1, characterized in that: When the fault current limiter operates normally, the fast switch executes the "open-TC-close-open-TC-close" operation sequence; when the fast switch fails to open, the "open-open-TC-close" operation sequence is executed; when the fast switch fails to close, the "open-TC-close-close" operation sequence is executed; when the fast switch fails to open and close simultaneously, the "open-open-TC-close-close" operation sequence is executed.

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