H-type wiring AC filter capacitor bank capacitor element fault identification and positioning method

Abstract

The invention discloses an H-type wiring AC filter capacitor bank capacitor element fault identification and positioning method, and relates to the field of filter capacitor bank fault identification, and the method comprises the steps: recording the parameters of an H-type wiring AC filter capacitor bank in real time, and calculating the breakdown threshold value of a capacitor element according to the parameters of the H-type wiring AC filter capacitor bank; according to the parameters of the H-type wiring AC filter capacitor bank and the breakdown threshold value of the capacitor element, carrying out breakdown fault identification on the capacitor element; determining the breakdown moment of the capacitor element by using wavelet transform according to the breakdown fault identification result of the capacitor element; and according to the positive and negative conditions of the voltage half cycle at the breakdown moment of the capacitor element and the abrupt change gradient direction of the parameters of the H-type wiring AC filter capacitor bank, capacitor element breakdown fault positioning is carried out, and fault identification and positioning of the capacitor element of the H-type wiring AC filter capacitor bank are completed. The method solves the problem that the breakdown fault of the capacitor element cannot be effectively identified and positioned by the existing method.

Description

Technical Field

[0001] The invention relates to the field of fault identification of filter capacitor groups, and in particular to a method for identifying and locating faults of capacitor elements of an H-type connection AC filter capacitor group. Background Art

[0002] The converter station is a key equipment in the high-voltage direct current transmission system. Its main function is to convert alternating current into direct current or vice versa. In the converter station, the AC filter is not only used to filter out harmonics, but also to compensate for the reactive power consumed by the DC system to ensure the stable operation of the power system. The AC filter capacitor bank usually adopts an H-type wiring structure, which can effectively reduce the impact of harmonics on the power grid, but also increases the complexity of fault identification and location. Capacitor elements are an important part of the AC filter capacitor bank. Their breakdown failure will cause the performance of the capacitor bank to deteriorate and even cause serious safety accidents. Therefore, timely and accurate identification and location of the breakdown failure of capacitor elements is the key to ensuring the reliable operation of the converter station.

[0003] At present, there are three methods for identifying the breakdown fault of the internal components of the capacitor group, mainly based on the change of the unbalanced bridge current: the unbalanced current effective value method, the ratio detection method and the pulse detection method. The unbalanced current effective value method is greatly affected by factors such as the system operation mode and frequency, and it cannot identify the fault in the case of a symmetrical fault, so it is not directly used. The ratio detection method uses the ratio of the unbalanced current to the total current to identify the fault, and the ratio changes little. The pulse detection method identifies the fault based on the change in the ratio of the unbalanced current to the total current. These methods mainly identify faults based on steady-state values. When the number of faulty components is small, the steady-state value changes little, and the fault may not be effectively identified.

[0004] There are few studies on the accurate positioning of capacitor bank faults. Most methods are to add current transformers on the high-voltage side, but this will increase a lot of costs. In addition, traditional fault location methods are usually calculated based on steady-state values, but due to the small number of faulty components and the small change in steady-state values, the faulty bridge arm may not be effectively located. In actual engineering, the positioning and maintenance of capacitor faults is usually done manually using a multi-digital megger to measure the capacitance value of each bridge arm capacitor unit to determine the faulty bridge arm; then measure the capacitance value of each bridge arm capacitor unit to troubleshoot the fault, which is inefficient. Since capacitors have the function of storing energy, if the capacitors are not fully discharged, it may threaten the personal safety of patrol personnel. Therefore, accurate and reliable fault location methods can effectively improve the efficiency of fault detection and ensure the personal safety of patrol personnel. Summary of the invention

[0005] In view of the above-mentioned deficiencies in the prior art, the present invention provides a method for identifying and locating capacitor element faults in an H-type connection AC filter capacitor group, which solves the problem that the prior method cannot effectively identify and locate capacitor element breakdown faults.

[0006] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention is: a method for identifying and locating the fault of the capacitor element of an H-type connection AC filter capacitor group, comprising the following steps: S1: recording parameters of an H-type connection AC filter capacitor bank in real time, and calculating a breakdown threshold of a capacitor element according to the parameters of the H-type connection AC filter capacitor bank; S2: Identifying a capacitor breakdown fault according to the parameters of the H-type connection AC filter capacitor bank and the breakdown threshold of the capacitor element; S3: According to the capacitor breakdown fault identification result, the capacitor breakdown moment is determined by wavelet transform; S4: According to the positive and negative conditions of the voltage half cycle at the time of the capacitor breakdown and the sudden change gradient direction of the parameters of the H-type connection AC filter capacitor group, the capacitor breakdown fault is located to complete the capacitor component fault identification and location of the H-type connection AC filter capacitor group.

[0007] Furthermore, the parameters of the H-type AC filter capacitor bank in S1 include the instantaneous values ​​of the three-phase voltages , three-phase current instantaneous value , Instantaneous value of three-phase unbalanced current And the instantaneous value of the three-phase low-voltage side current .

[0008] Furthermore, the breakdown threshold of the capacitor element calculated in S1 according to the parameters of the H-type connection AC filter capacitor bank is:

[0009]

[0010]

[0011]

[0012] in, is the first breakdown threshold of the capacitor element, is the second breakdown threshold of the capacitor element, is the number of capacitor units in each arm of the H-bridge, is the number of parallel modules in the capacitor unit, is the maximum instantaneous value of the three-phase current, express Mutually, Harmony Mutually.

[0013] Furthermore, the capacitor breakdown fault identification is performed in S2, and the specific method is as follows: when and ,but There is a component breakdown fault in the phase, otherwise it is not a component breakdown fault.

[0014] Furthermore, the use of wavelet transform to determine the breakdown moment of the capacitor element in S3 includes the following steps: S31: Using db4 wavelet to calculate the instantaneous value of three-phase unbalanced current Perform wavelet decomposition, the formula is:

[0015]

[0016]

[0017]

[0018] in, and They are respectively the low-frequency coefficient and high-frequency coefficient obtained by performing the first-layer decomposition of the instantaneous value of the three-phase unbalanced current using the db4 wavelet. is the position of the low-frequency coefficients and the high-frequency coefficients, , is the index position, , is the total number of sampling points, is the low-pass filter coefficient, is the high-pass filter coefficient, is the instantaneous value of three-phase unbalanced current; S32: Calculate the absolute value of the high frequency coefficient and find the maximum value. The formula is:

[0019] From the absolute value of the high frequency coefficient Find the position index corresponding to the maximum value in for:

[0020] S33: Determine the breakdown moment of the capacitor element for:

[0021] in, is the sampling time interval.

[0022] Furthermore, the S4 includes the following sub-steps: S41: Find the instantaneous values ​​of the three-phase unbalanced currents respectively , Instantaneous value of three-phase low-voltage side current and exist The time point after the moment becomes 0 , and , the formula is:

[0023] in, For the The time corresponding to each sampling point is For the The time corresponding to each sampling point; S42: Calculate the instantaneous value of three-phase unbalanced current from arrive The integral of the three-phase low-voltage side current instantaneous value from arrive The integral of the three-phase low-voltage side current instantaneous value from arrive The integral of

[0024] in, , , and Respectively , , and The index position corresponding to the moment; S43: Based on the positive and negative voltage half-cycle at the moment of capacitor breakdown and the instantaneous value of the three-phase unbalanced current , Instantaneous value of three-phase low-voltage side current and The positive or negative condition of the integral is used to determine the bridge arm position when the capacitor element breaks down.

[0025] Furthermore, the position of the bridge arm at which the capacitor element is located when the breakdown fault occurs in S43 is specifically: When the capacitor element breaks down during the positive half cycle of voltage: For positive, is positive and is positive, the capacitor element breakdown occurs at Bridge arm; For positive, is negative and is positive, the capacitor element breakdown occurs at Bridge arm; Negative, is positive and is positive, the capacitor element breakdown occurs at Bridge arm; Negative, is negative and is positive, the capacitor element breakdown occurs at Bridge arm; When the capacitor element breaks down during the negative half cycle of voltage: For positive, is negative and is positive, the capacitor element breakdown occurs at Bridge arm; For positive, is negative and is negative, the capacitor element will breakdown. Bridge arm; Negative, is positive and is negative, the capacitor element will breakdown. Bridge arm; Negative, is negative and is negative, the capacitor element will breakdown. Bridge arm; Said Bridge arm and The bridge arm is located at the lower bridge arm close to the ground end, Bridge arm and The bridge arm is located at the upper bridge arm far away from the ground end. The bridge arm represents the capacitor bank on the left side of the bridge arm of the H bridge. The bridge arm represents the capacitor bank on the right side of the bridge arm of the H bridge. The bridge arm represents the capacitor bank on the left side of the lower bridge arm of the H bridge. The bridge arm represents the capacitor bank on the right side of the lower arm of the H-bridge.

[0026] The beneficial effects of the present invention are: (1) Improve the reliability and stability of the system: Existing methods mainly rely on adding a current transformer on the high-voltage side or using steady-state values ​​for fault location, which not only increases the cost, but also cannot effectively and accurately locate the faulty bridge arm when the number of faulty components is small. The present invention only needs to add a current transformer on the low-voltage side to achieve rapid and accurate location of the faulty bridge arm. The present invention can detect and locate the breakdown fault of the capacitor element in a timely and accurate manner, avoiding the degradation of system performance and potential safety issues caused by the failure to detect the fault in time.

[0027] (2) Extending equipment life: Through rapid and accurate fault identification and location, the present invention helps to repair or replace faulty components in a timely manner, thereby extending the service life of the entire capacitor bank.

[0028] (3) Reduce maintenance costs: The low cost and high efficiency of the method of the present invention not only reduce the initial investment in equipment, but also reduce the cost of daily maintenance and inspection, thereby improving the overall economic benefits.

[0029] (4) Improve inspection safety: Currently, the capacitance value of each bridge arm capacitor unit is measured manually using a multi-digital megohmmeter, which is time-consuming and labor-intensive, and there is a safety hazard caused by incomplete discharge. The present invention avoids the need for manual measurement through automatic identification and positioning, and significantly improves inspection efficiency and safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The present invention is a flow chart of the method for identifying and locating capacitor component faults in an H-type connection AC filter capacitor group.

[0031] Figure 2 This is a schematic diagram of the wiring of the H-type filter capacitor group and the internal structure of the capacitor unit. DETAILED DESCRIPTION

[0032] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0033] like Figure 1 As shown, a method for identifying and locating a capacitor component fault in an H-type connection AC filter capacitor bank comprises the following steps: S1: recording parameters of an H-type connection AC filter capacitor bank in real time, and calculating a breakdown threshold of a capacitor element according to the parameters of the H-type connection AC filter capacitor bank; S2: Identifying a capacitor breakdown fault according to the parameters of the H-type connection AC filter capacitor bank and the breakdown threshold of the capacitor element; S3: According to the capacitor breakdown fault identification result, the capacitor breakdown moment is determined by wavelet transform; S4: According to the positive and negative conditions of the voltage half cycle at the time of the capacitor breakdown and the sudden change gradient direction of the parameters of the H-type connection AC filter capacitor group, the capacitor breakdown fault is located to complete the capacitor component fault identification and location of the H-type connection AC filter capacitor group.

[0034] In one embodiment of the present invention, Figure 2 As shown, the H-bridge includes Bridge arm, Bridge arm, Bridge arm and The position of the bridge arm can be determined by the direction of the unbalanced current. Assuming that the unbalanced current flows from left to right in the positive direction, the bridge arm on the left is and , the right arm of the bridge is and In addition, the lower bridge arm is closer to the ground end, and the upper bridge arm is farther away from the ground end. and is the lower bridge arm, and For the upper bridge arm.

[0035] Assume that each arm of the H bridge consists of The capacitor units are connected in series, and there are Only components, first by Only components are connected in parallel to form a parallel module, and then The parallel modules are connected in series.

[0036] The parameters of the H-type AC filter capacitor bank in S1 include the instantaneous values ​​of the three-phase voltage , three-phase current instantaneous value , Instantaneous value of three-phase unbalanced current And the instantaneous value of the three-phase low-voltage side current .

[0037] In S1, the breakdown threshold of the capacitor element is calculated according to the parameters of the H-type connection AC filter capacitor group:

[0038]

[0039]

[0040]

[0041] in, is the first breakdown threshold of the capacitor element, is the second breakdown threshold of the capacitor element, is the number of capacitor units in each arm of the H-bridge, is the number of parallel modules in the capacitor unit, is the maximum instantaneous value of the three-phase current, express Mutually, Harmony Mutually.

[0042] The capacitor breakdown fault is identified in S2, and the specific method is as follows: when and ,but There is a component breakdown fault in the phase, otherwise it is not a component breakdown fault.

[0043] Determining the breakdown moment of the capacitor element by wavelet transform in S3 includes the following steps: S31: Using db4 wavelet to calculate the instantaneous value of three-phase unbalanced current Perform wavelet decomposition, the formula is:

[0044]

[0045]

[0046]

[0047] in, and They are respectively the low-frequency coefficient and high-frequency coefficient obtained by performing the first-layer decomposition of the instantaneous value of the three-phase unbalanced current using the db4 wavelet. is the position of the low-frequency coefficient and the high-frequency coefficient. Due to the downsampling operation, the total number of low-frequency and high-frequency coefficients is ,therefore The value range is , is the index position, , is the total number of sampling points, is the low-pass filter coefficient, is the high-pass filter coefficient, is the instantaneous value of three-phase unbalanced current; S32: Calculate the absolute value of the high frequency coefficient and find the maximum value. The formula is:

[0048] From the absolute value of the high frequency coefficient Find the position index corresponding to the maximum value in for:

[0049] S33: Determine the breakdown moment of the capacitor element for: because Index With the original signal Index There is a downsampling relationship between them, that is, ,therefore The corresponding index in the original signal is Therefore, the breakdown moment It can be expressed as:

[0050] in, is the sampling time interval.

[0051] The S4 includes the following sub-steps: S41: Find the instantaneous values ​​of the three-phase unbalanced currents respectively , Instantaneous value of three-phase low-voltage side current and exist The time point after the moment becomes 0 , and , the formula is:

[0052] in, For the The time corresponding to each sampling point is For the The time corresponding to each sampling point; from Start from the moment and check point by point The sign change of two adjacent current values ​​is calculated using the linear interpolation formula , calculated in the same way and ; S42: Calculate the instantaneous value of three-phase unbalanced current from arrive The integral of the three-phase low-voltage side current instantaneous value from arrive The integral of the three-phase low-voltage side current instantaneous value from arrive The integral of

[0053] in, , , and Respectively , , and The index position corresponding to the moment; S43: Based on the positive and negative voltage half-cycle at the moment of capacitor breakdown and the instantaneous value of the three-phase unbalanced current , Instantaneous value of three-phase low-voltage side current and The positive or negative condition of the integral is used to determine the bridge arm position when the capacitor element breaks down.

[0054] The bridge arm position at which the capacitor element is located when the breakdown fault occurs in S43 is determined as follows: When the capacitor element breaks down during the positive half cycle of voltage: For positive, is positive and is positive, the capacitor element breakdown occurs at Bridge arm; For positive, is negative and is positive, the capacitor element breakdown occurs at Bridge arm; Negative, is positive and is positive, the capacitor element breakdown occurs at Bridge arm; Negative, is negative and is positive, the capacitor element breakdown occurs at Bridge arm; When the capacitor element breaks down during the negative half cycle of voltage: For positive, is negative and is positive, the capacitor element breakdown occurs at Bridge arm; For positive, is negative and is negative, the capacitor element will breakdown. Bridge arm; Negative, is positive and is negative, the capacitor element will breakdown. Bridge arm; Negative, is negative and is negative, the capacitor element will breakdown. Bridge arm; Said Bridge arm and The bridge arm is located at the lower bridge arm close to the ground end, Bridge arm and The bridge arm is located at the upper bridge arm far away from the ground end. The bridge arm represents the capacitor bank on the left side of the bridge arm of the H bridge. The bridge arm represents the capacitor bank on the right side of the bridge arm of the H bridge. The bridge arm represents the capacitor bank on the left side of the lower bridge arm of the H bridge. The bridge arm represents the capacitor bank on the right side of the lower arm of the H-bridge.

[0055] The present invention locates the faulty bridge arm according to the positive and negative conditions of the voltage half cycle at the moment of component breakdown fault, the unbalanced current and the sudden gradient direction of the low-voltage side. Furthermore, the present invention uses the positive and negative conditions of the voltage half cycle at the moment of fault, the unbalanced current and the sudden gradient direction of the low-voltage side to realize rapid and accurate positioning of the faulty bridge arm. This method combines multiple characteristic parameters, improves the accuracy and speed of fault positioning, and ensures that measures can be taken quickly after the fault occurs.

[0056] The core of the present invention is to use the time domain mutation characteristics of unbalanced current to identify the breakdown fault of capacitor elements, and accurately locate the fault phase by analyzing the mutation characteristics. When a capacitor element breaks down, it will cause an instantaneous mutation of the current. This mutation characteristic is very significant in the time domain. By monitoring and comparing this characteristic, rapid identification and location of the fault can be achieved. This method can also effectively detect when the number of faulty components is small, improving the accuracy and reliability of fault identification.

[0057] Those skilled in the art will appreciate that the embodiments described herein are intended to help readers understand the principles of the present invention, and should be understood that the protection scope of the present invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific variations and combinations that do not deviate from the essence of the present invention based on the technical revelations disclosed by the present invention, and these variations and combinations are still within the protection scope of the invention.

Claims

1. A method for identifying and locating capacitor component faults in an H-type AC filter capacitor bank, characterized in that: The following steps are involved: S1: recording parameters of an H-type connection AC filter capacitor bank in real time, and calculating a breakdown threshold of a capacitor element according to the parameters of the H-type connection AC filter capacitor bank; S2: Identifying a capacitor breakdown fault according to the parameters of the H-type connection AC filter capacitor bank and the breakdown threshold of the capacitor element; S3: According to the capacitor breakdown fault identification result, the capacitor breakdown time is determined by wavelet transform; S4: According to the positive and negative conditions of the voltage half cycle at the time of the capacitor breakdown and the sudden change gradient direction of the parameters of the H-type connection AC filter capacitor group, the capacitor breakdown fault is located to complete the identification and location of the capacitor fault of the H-type connection AC filter capacitor group.

2. The method for identifying and locating capacitor component faults of an H-type connection AC filter capacitor bank according to claim 1, characterized in that: The parameters of the H-type AC filter capacitor bank in S1 include the instantaneous values ​​of the three-phase voltage , three-phase current instantaneous value , Instantaneous value of three-phase unbalanced current And the instantaneous value of the three-phase low-voltage side current .

3. The method for identifying and locating capacitor component faults of an H-type connection AC filter capacitor bank according to claim 2, characterized in that: In S1, the breakdown threshold of the capacitor element is calculated according to the parameters of the H-type connection AC filter capacitor group: in, is the first breakdown threshold of the capacitor element, is the second breakdown threshold of the capacitor element, is the number of capacitor units in each arm of the H-bridge, is the number of parallel modules in the capacitor unit, is the maximum instantaneous value of the three-phase current, express Mutually, Harmony Mutually.

4. The method for identifying and locating capacitor element faults of an H-type connection AC filter capacitor bank according to claim 3, characterized in that: The capacitor breakdown fault is identified in S2, and the specific method is as follows: when and ,but There is a component breakdown fault in the phase, otherwise it is not a component breakdown fault.

5. The method for identifying and locating capacitor component faults of an H-type connection AC filter capacitor bank according to claim 4, characterized in that: Determining the breakdown moment of the capacitor element by wavelet transform in S3 includes the following steps: S31: Using db4 wavelet to calculate the instantaneous value of three-phase unbalanced current Perform wavelet decomposition, the formula is: in, and They are respectively the low-frequency coefficient and high-frequency coefficient obtained by performing the first-layer decomposition of the instantaneous value of the three-phase unbalanced current using the db4 wavelet. is the position of the low-frequency coefficients and the high-frequency coefficients, , is the index position, , is the total number of sampling points, is the low-pass filter coefficient, is the high-pass filter coefficient, is the instantaneous value of three-phase unbalanced current; S32: Calculate the absolute value of the high frequency coefficient and find the maximum value. The formula is: From the absolute value of the high frequency coefficient Find the position index corresponding to the maximum value in for: S33: Determine the breakdown moment of the capacitor element for: in, is the sampling time interval.

6. A method for identifying and locating capacitor element faults in an H-type connection AC filter capacitor bank according to claim 5, characterized in that: The S4 includes the following sub-steps: S41: Find the instantaneous values ​​of the three-phase unbalanced currents respectively , Instantaneous value of three-phase low-voltage side current and exist The time point that becomes 0 after the moment , and , the formula is: in, For the The time corresponding to each sampling point is For the The time corresponding to each sampling point; S42: Calculate the instantaneous value of three-phase unbalanced current from arrive The integral of the three-phase low-voltage side current instantaneous value from arrive The integral of the three-phase low-voltage side current instantaneous value from arrive The integral of in, , , and Respectively , , and The index position corresponding to the moment; S43: Based on the positive and negative voltage half-cycle at the moment of capacitor breakdown and the instantaneous value of the three-phase unbalanced current , Instantaneous value of three-phase low-voltage side current and The positive or negative condition of the integral is used to determine the bridge arm position when the capacitor element breaks down.

7. A method for identifying and locating capacitor element faults in an H-type connection AC filter capacitor bank according to claim 6, characterized in that: The bridge arm position at which the capacitor element is located when the breakdown fault occurs in S43 is determined as follows: When the capacitor element breaks down during the positive half cycle of voltage: For positive, is positive and is positive, the capacitor element breakdown occurs at Bridge arm; For positive, is negative and is positive, the capacitor element breakdown occurs at Bridge arm; Negative, is positive and is positive, the capacitor element breakdown occurs at Bridge arm; Negative, is negative and is positive, the capacitor element breakdown occurs at Bridge arm; When the capacitor element breaks down during the negative half cycle of voltage: For positive, is negative and is positive, the capacitor element breakdown occurs at Bridge arm; For positive, is negative and is negative, the capacitor element will breakdown. Bridge arm; Negative, is positive and is negative, the capacitor element will breakdown. Bridge arm; Negative, is negative and is negative, the capacitor element will breakdown. Bridge arm; Said Bridge arm and The bridge arm is located at the lower bridge arm close to the ground end, Bridge arm and The bridge arm is located at the upper bridge arm far away from the ground end. The bridge arm represents the capacitor bank on the left side of the bridge arm of the H bridge. The bridge arm represents the capacitor bank on the right side of the bridge arm of the H bridge. The bridge arm represents the capacitor bank on the left side of the lower bridge arm of the H bridge. The bridge arm represents the capacitor bank on the right side of the lower arm of the H-bridge.

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