Method for identifying and locating faults of capacitive elements of ac filter capacitor banks with h-type wiring

Abstract

The application discloses a kind of H-type wiring AC filter capacitor bank capacitor element fault identification and positioning method, it is related to filter capacitor bank fault identification field, comprising: real-time record H-type wiring AC filter capacitor bank parameters, and according to the H-type wiring AC filter capacitor bank parameters calculation capacitor element breakdown threshold;According to the H-type wiring AC filter capacitor bank parameters and the breakdown threshold of the capacitor element, capacitor element breakdown fault identification is carried out;According to capacitor element breakdown fault identification result, the breakdown time of capacitor element is determined using wavelet transform;According to the positive and negative situation of voltage half cycle of the breakdown time of capacitor element and the mutation gradient direction of H-type wiring AC filter capacitor bank parameters, capacitor element breakdown fault positioning is carried out, and H-type wiring AC filter capacitor bank capacitor element fault identification and positioning are completed.The application solves the problem that existing method cannot effectively identify and position capacitor element breakdown fault.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of filter capacitor bank fault identification, in particular to a method for identifying and locating the fault of the capacitor element of an H-type wiring AC filter capacitor bank. BACKGROUND

[0002] The converter station is a key device in the high-voltage direct current transmission system, and its main function is to convert AC power into DC power or vice versa. In the converter station, the AC filter is not only used to filter 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 at the same time increases the complexity of fault identification and location. The capacitor element is an important component of the AC filter capacitor bank, and its breakdown fault will cause the performance of the capacitor bank to decline, and even cause serious safety accidents. Therefore, timely and accurate identification and location of the breakdown fault of the capacitor element is the key to ensuring the reliable operation of the converter station.

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

[0004] There is less research on accurate positioning after the fault of the capacitor bank, and most methods are to increase current transformers at the high-voltage side, but this will increase a lot of cost. In addition, traditional fault location methods are usually based on steady-state values for calculation, but due to the small number of faulty elements, the steady-state value changes very little, and it may not be able to effectively locate the faulty bridge arm. In actual engineering, the positioning and maintenance after the fault of the capacitor is usually manually measured by using a multi-digit oscillating meter to measure the capacitance value of each bridge arm capacitor unit to determine the faulty bridge arm; and then measuring the capacitance value of each bridge arm capacitor unit to check the fault, which is low in efficiency. Since the capacitor has the function of energy storage, if the capacitor is not completely discharged, it may threaten the personal safety of the inspection personnel. Therefore, an accurate and reliable fault location method can effectively improve the fault detection efficiency and ensure the personal safety of the inspection personnel. SUMMARY

[0005] In view of the above problems in the prior art, the H-type wiring AC filter capacitor bank capacitor element fault identification and positioning method provided by the application solves the problem that the prior art cannot effectively identify and position capacitor element breakdown faults.

[0006] To achieve the above-mentioned purposes, the application adopts the technical scheme of an H-type wiring AC filter capacitor bank capacitor element fault identification and positioning method, comprising the following steps:

[0007] S1: Real-time record H-type wiring AC filter capacitor bank parameters, and calculate the breakdown threshold of the capacitor element according to the H-type wiring AC filter capacitor bank parameters;

[0008] S2: Perform capacitor element breakdown fault identification according to the H-type wiring AC filter capacitor bank parameters and the breakdown threshold of the capacitor element;

[0009] S3: According to the capacitor element breakdown fault identification result, determine the capacitor element breakdown time by wavelet transform;

[0010] S4: According to the voltage half-cycle positive and negative situation of the capacitor element breakdown time and the mutation gradient direction of the H-type wiring AC filter capacitor bank parameters, perform capacitor element breakdown fault positioning, and complete H-type wiring AC filter capacitor bank capacitor element fault identification and positioning.

[0011] Further, the H-type wiring AC filter capacitor bank parameters in S1 include three-phase voltage instantaneous value , three-phase current instantaneous value , three-phase unbalanced current instantaneous value , and three-phase low-voltage side current instantaneous value .

[0012] Further, the breakdown threshold of the capacitor element calculated according to the H-type wiring AC filter capacitor bank parameters in S1 is:

[0013]

[0014]

[0015]

[0016]

[0017] wherein, the first breakdown threshold of the capacitor element, the second breakdown threshold of the capacitor element, the number of capacitor units in each bridge arm of the H-bridge, the number of parallel modules in the capacitor unit, is the maximum instantaneous value of the three-phase current, express Mutually, Harmony Mutually.

[0018] Furthermore, the capacitor breakdown fault is identified in S2, specifically by:

[0019] when and ,but There is a component breakdown fault in the phase, otherwise it is not a component breakdown fault.

[0020] Furthermore, the use of wavelet transform to determine the breakdown moment of the capacitor element in S3 includes the following steps:

[0021] S31: Using db4 wavelet to calculate the instantaneous value of three-phase unbalanced current Perform wavelet decomposition, the formula is:

[0022]

[0023]

[0024]

[0025]

[0026] in, and are the low-frequency coefficient and high-frequency coefficient obtained by using db4 wavelet to decompose the instantaneous value of the three-phase unbalanced current in the first layer, is the position of the low-frequency coefficient and the high-frequency coefficient, , 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;

[0027] S32: Calculate the absolute value of the high-frequency coefficient and find the maximum value. The formula is:

[0028]

[0029] From the absolute value of the high frequency coefficient Find the position index corresponding to the maximum value for:

[0030]

[0031] S33: determining the moment of breakdown of the capacitive element is:

[0032]

[0033] wherein, is the sampling time interval.

[0034] Further, the S4 comprises the following sub-steps:

[0035] S41: finding out the instantaneous values of the three-phase unbalanced current, the instantaneous values of the three-phase low-voltage side current, and at the moment after which the time point becomes 0 , and , the formula is:

[0036]

[0037] wherein, is the time corresponding to the th sampling point, is the time corresponding to the th sampling point;

[0038] S42: calculating the integrals of the instantaneous values of the three-phase unbalanced current from to , the instantaneous values of the three-phase low-voltage side current from to , the instantaneous values of the three-phase low-voltage side current from to ;

[0039]

[0040] wherein, , , and respectively represent the index positions corresponding to the moments , , and ;

[0041] S43: determining the positive and negative situations of the voltage half cycle at the moment of breakdown of the capacitive element and the instantaneous values of the three-phase unbalanced current, the instantaneous values of the three-phase low-voltage side current, and The positive and negative of the integral, judge the capacitor element breakdown fault when the bridge arm position.

[0042] Further, the S43 in the judgment capacitor element breakdown fault when the bridge arm position, specifically:

[0043] When the capacitor element breakdown moment in the voltage positive half cycle:

[0044] For positive, For positive and For positive, the capacitor element breakdown fault is located in Bridge arm;

[0045] For positive, For negative and For positive, the capacitor element breakdown fault is located in Bridge arm;

[0046] For negative, For positive and For positive, the capacitor element breakdown fault is located in Bridge arm;

[0047] For negative, For negative and For positive, the capacitor element breakdown fault is located in Bridge arm;

[0048] When the capacitor element breakdown moment in the voltage negative half cycle:

[0049] For positive, For negative and For positive, the capacitor element breakdown fault is located in Bridge arm;

[0050] For positive, For negative and For negative, the capacitor element breakdown fault is located in Bridge arm;

[0051] For negative, For positive and For negative, the capacitor element breakdown fault is located in Bridge arm;

[0052] For negative, For negative and For negative, the capacitor element breakdown fault is located in Bridge arm;

[0053] The The bridge arm is a lower bridge arm close to the ground end, and the The bridge arm is an upper bridge arm away from the ground end, and the The bridge arm represents a capacitor group on the left side of the upper bridge arm of the H-bridge, and the The bridge arm represents a capacitor group on the right side of the upper bridge arm of the H-bridge, and the The bridge arm represents a capacitor group on the left side of the lower bridge arm of the H-bridge, The bridge arm represents a capacitor group on the right side of the lower bridge arm of the H-bridge.

[0054] The beneficial effects of the present application are:

[0055] (1) Improve the reliability and stability of the system: the existing method mainly relies on increasing the current transformer on the high-voltage side or using steady-state values for fault positioning, which not only increases the cost, but also cannot effectively locate the fault bridge arm when the number of fault elements is small. The present application only needs to add a current transformer on the low-voltage side to quickly and accurately locate the fault bridge arm. The present application can timely and accurately detect and locate the breakdown fault of the capacitor element, avoiding the decline in system performance and potential safety problems caused by the failure to discover the fault in time.

[0056] (2) Prolong the service life of the equipment: through rapid and accurate fault identification and positioning, the present application helps to repair or replace the faulty elements in time, thereby prolonging the service life of the entire capacitor group.

[0057] (3) Reduce maintenance costs: the low cost and high efficiency of the present application method not only reduces the initial investment of the equipment, but also reduces the cost of daily maintenance and inspection, and improves the overall economic efficiency.

[0058] (4) Improve inspection safety: Currently, manual use of multi-digital oscillation table is used to measure the capacitance value of each bridge arm capacitor unit, which is time-consuming and labor-intensive and has safety hazards caused by incomplete discharge. The present application avoids the need for manual measurement and significantly improves the efficiency and safety of inspection. BRIEF DESCRIPTION OF DRAWINGS

[0059] Figure 1 The present application is an H-type wiring AC filter capacitor group capacitor element fault identification and positioning method flow chart.

[0060] Figure 2 The present application is an H-type filter capacitor group wiring and capacitor unit internal structure diagram. DETAILED DESCRIPTION

[0061] The present application will be further described below in conjunction with the drawings and specific embodiments. ​​

[0062] As Figure 1 shown, a H-type wiring AC filter capacitor bank capacitor element fault identification and positioning method, comprising the following steps:

[0063] S1: Real-time record H-type wiring AC filter capacitor bank parameters, and calculate the breakdown threshold of the capacitor element according to the H-type wiring AC filter capacitor bank parameters;

[0064] S2: According to the H-type wiring AC filter capacitor bank parameters and the breakdown threshold of the capacitor element, the capacitor element breakdown fault identification is carried out;

[0065] S3: According to the capacitor element breakdown fault identification result, the wavelet transform is used to determine the capacitor element breakdown time;

[0066] S4: According to the voltage half cycle positive and negative situation of the capacitor element breakdown time and the mutation gradient direction of the H-type wiring AC filter capacitor bank parameters, the capacitor element breakdown fault positioning is carried out, and the H-type wiring AC filter capacitor bank capacitor element fault identification and positioning are completed.

[0067] In an embodiment of the present application, as Figure 2 shown, the H bridge includes bridge arm, bridge arm, bridge arm and bridge arm, the position of the bridge arm can be determined by the direction of the unbalanced current. Assuming that the unbalanced current flowing from left to right is the positive direction, then the left bridge arm is and , and the right bridge arm is and . In addition, the lower bridge arm is close to the ground end, and the upper bridge arm is far away from the ground end, so and are the lower bridge arms, and are the upper bridge arms.

[0068] Assuming that each bridge arm of the H bridge is composed of capacitor units in series, there are only elements in the unit, first only elements are connected in parallel to form a parallel module, and then parallel modules are connected in series.

[0069] The H-type wiring AC filter capacitor bank parameters in the S1 include three-phase voltage instantaneous value , three-phase current instantaneous value , three-phase unbalanced current instantaneous value and three-phase low-voltage side current instantaneous value .

[0070] The breakdown threshold of the capacitance element in the S1 is calculated according to the parameters of the H-type wiring AC filter capacitor bank:

[0071]

[0072]

[0073]

[0074]

[0075] wherein, is the first breakdown threshold of the capacitance element, is the second breakdown threshold of the capacitance element, is the number of capacitor units in each bridge arm of the H-bridge, is the number of parallel modules in the capacitor unit, is the maximum value of the three-phase current instantaneous value, represents phase, phase, and phase.

[0076] In the S2, the breakdown fault of the capacitance element is identified, and the specific method is as follows:

[0077] When and , then the phase exists element breakdown fault, otherwise it is not element breakdown fault.

[0078] In the S3, the wavelet transform is used to determine the breakdown time of the capacitance element, including the following steps:

[0079] S31: using db4 wavelet to perform wavelet decomposition on the three-phase unbalanced current instantaneous value , the formula is:

[0080]

[0081]

[0082]

[0083]

[0084] wherein, and are the low-frequency coefficients and high-frequency coefficients obtained by using db4 wavelet to perform first-layer decomposition on the three-phase unbalanced current instantaneous value, is the position of the low-frequency coefficient and the high-frequency coefficient, and due to the downsampling operation, the total number of low-frequency and high-frequency coefficients is Therefore is in the range of , 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 three-phase unbalanced current instantaneous value;

[0085] S32: Calculate the absolute value of the high-frequency coefficient and find the maximum value, the formula is:

[0086]

[0087] From the absolute value of the high-frequency coefficient Find the position index corresponding to the maximum value :

[0088]

[0089] S33: Determine the breakdown moment of the capacitive element :

[0090] Since the index and the index of the original signal there is a downsampling relationship, that is Therefore the index in the corresponding original signal is . Therefore, the breakdown moment can be expressed as:

[0091]

[0092] where, is the sampling time interval.

[0093] The S4 includes the following sub-steps:

[0094] S41: Find the three-phase unbalanced current instantaneous value , the three-phase low-voltage side current instantaneous value and the time point , and become 0 after the moment , the formula is:

[0095]

[0096] where, is the The time corresponding to each sampling point, For the The time corresponding to each sampling point;

[0097] from Start at 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 ;

[0098] 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 's points;

[0099]

[0100] in, 、 、 and Respectively 、 、 and The index position corresponding to the moment;

[0101] 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 , three-phase low-voltage side current instantaneous value and The positive or negative condition of the integral is used to determine the bridge arm position when the capacitor element breaks down.

[0102] The bridge arm position where the capacitor element is located when the breakdown fault occurs in S43 is determined as follows:

[0103] When the capacitor element breaks down during the positive half cycle of voltage:

[0104] For positive, is positive and If it is positive, the capacitor element will break down. bridge arm;

[0105] For positive, is negative and If positive, the breakdown fault of the capacitor element is located in the bridge arm;

[0106] If negative, If positive and If positive, the breakdown fault of the capacitor element is located in the bridge arm;

[0107] If negative, If negative and If positive, the breakdown fault of the capacitor element is located in the bridge arm;

[0108] When the breakdown moment of the capacitor element is in the negative half cycle of the voltage:

[0109] If positive, If negative and If positive, the breakdown fault of the capacitor element is located in the bridge arm;

[0110] If positive, If negative and If negative, the breakdown fault of the capacitor element is located in the bridge arm;

[0111] If negative, If positive and If negative, the breakdown fault of the capacitor element is located in the bridge arm;

[0112] If negative, If negative and If negative, the breakdown fault of the capacitor element is located in the bridge arm;

[0113] The bridge arm and bridge arm is the lower bridge arm close to the ground end, the bridge arm and bridge arm is the upper bridge arm away from the ground end, the bridge arm represents the capacitor group on the left side of the upper bridge arm of the H-bridge, the bridge arm represents the capacitor group on the right side of the upper bridge arm of the H-bridge, the bridge arm represents the capacitor group on the left side of the lower bridge arm of the H-bridge, bridge arm represents the capacitor group on the right side of the lower bridge arm of the H-bridge.

[0114] The application positions the fault bridge arm according to the positive and negative situation of the voltage half cycle, the unbalanced current and the mutation gradient direction of the low voltage side at the moment of the element breakdown fault, and further, the application realizes the rapid and accurate positioning of the fault bridge arm by using the positive and negative situation of the voltage half cycle, the unbalanced current and the mutation gradient direction of the low voltage side at the moment of the fault. This method combines various characteristic parameters, improves the accuracy and speed of fault positioning, and ensures that measures can be taken quickly after the fault occurs.

[0115] The core of the application is to identify the breakdown fault of the capacitor element by using the time domain mutation characteristics of the unbalanced current, and to accurately position the fault phase by analyzing the mutation characteristics. When the capacitor element breaks down, it will cause instantaneous mutation of the current, and this mutation characteristic is very significant in the time domain. By monitoring and comparing this characteristic, the rapid identification and positioning of the fault can be realized. This method can effectively detect in the case of fewer fault elements, and improves the accuracy and reliability of fault identification.

[0116] Those skilled in the art will realize that the embodiments described herein are for the purpose of helping the reader understand the principles of the application, and should be understood as not limiting the scope of protection of the application to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations according to the technical inspiration disclosed in the application without departing from the essence of the application, and these modifications and combinations are still within the scope of protection of the application.

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 AC filter capacitor bank in real time, and calculating a breakdown threshold of a capacitor element according to the parameters of the H-type AC filter capacitor bank; S2: Identifying a capacitor breakdown fault based on the parameters of the H-type AC filter capacitor bank and the breakdown threshold of the capacitor element; S3: Based on the capacitor breakdown fault identification result, the capacitor breakdown moment is determined using wavelet transform; S4: Based on the positive and negative conditions of the voltage half-cycle at the moment of breakdown of the capacitor element and the positive and negative conditions of the instantaneous value and integral of the parameters of the H-type connection AC filter capacitor bank, the capacitor element breakdown fault is located, and the capacitor element fault identification and location of the H-type connection AC filter capacitor bank are completed; The S4 includes the following sub-steps: S41: Find the instantaneous value of the three-phase unbalanced current respectively , the instantaneous value of the three-phase low-voltage side current of one bridge arm And the instantaneous value of the three-phase low-voltage side current of the other bridge arm exist The time point that becomes 0 after the moment 、 and , the formula is: in, For the The time corresponding to each sampling point, For the The time corresponding to each sampling point, is the instantaneous value of three-phase current; S42: Calculate the instantaneous value of three-phase unbalanced current from arrive The integral of the three-phase low-voltage side current instantaneous value of a bridge arm from arrive The integral of the three-phase low-voltage side current instantaneous value of the other bridge arm is from arrive 's points; 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 , the instantaneous value of the three-phase low-voltage side current of one bridge arm And the instantaneous value of the three-phase low-voltage side current of the other bridge arm The positive or negative condition of the integral is used to determine the bridge arm position when the capacitor element breaks down.

2. The method for identifying and locating capacitor component faults in an H-type 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 voltages , three-phase current instantaneous value , Instantaneous value of three-phase unbalanced current The instantaneous value of the three-phase low-voltage side current of one bridge arm .

3. The method for identifying and locating capacitor component faults in an H-type AC filter capacitor bank according to claim 2, characterized in that: The breakdown threshold of the capacitor element is calculated in S1 according to the parameters of the H-type connection AC filter capacitor bank: 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 component faults in an H-type 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 in an H-type AC filter capacitor bank according to claim 4, characterized in that: Determining the breakdown moment of the capacitor element by using 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 are the low-frequency coefficient and high-frequency coefficient obtained by using db4 wavelet to decompose the instantaneous value of the three-phase unbalanced current in the first layer, is the position of the low-frequency coefficient and the high-frequency coefficient, , 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 for: S33: Determine the breakdown moment of the capacitor element for: in, is the sampling time interval.

6. The method for identifying and locating capacitor component faults in an H-type AC filter capacitor bank according to claim 5, characterized in that: The bridge arm position where 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 If it is positive, the capacitor element will break down. bridge arm; For positive, is negative and If it is positive, the capacitor element will break down. bridge arm; Negative, is positive and If it is positive, the capacitor element will break down. bridge arm; Negative, is negative and If it is positive, the capacitor element will break down. bridge arm; When the capacitor element breaks down during the negative half cycle of voltage: For positive, is negative and If it is positive, the capacitor element will break down. bridge arm; For positive, is negative and If it is negative, the capacitor element will break down. bridge arm; Negative, is positive and If it is negative, the capacitor element will break down. bridge arm; Negative, is negative and If it is negative, the capacitor element will break down. bridge arm; described 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 upper arm of the H bridge. The bridge arm represents the capacitor bank on the right side of the upper arm of the H bridge. The bridge arm represents the capacitor bank on the left side of the lower 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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