A method for identifying the breakdown of parallel capacitor banks based on the instantaneous symmetrical component method

Abstract

The present invention discloses a method for identifying the electrical breakdown of a parallel capacitor group based on the instantaneous symmetrical component method, which relates to the technical field of identifying the electrical breakdown of a parallel capacitor group, and comprises the following steps: putting a capacitor group into operation, and extracting the transient current waveform data of one cycle after the capacitor group is put into operation; using the FFT algorithm to extract the high frequency generated when the capacitor group is put into operation according to the transient current waveform data; using the improved instantaneous symmetrical component method to calculate the instantaneous value of the negative sequence component of the transient current waveform data; using the second-order difference to process the instantaneous value of the negative sequence component to detect the flying point; representing the flying point with 1, and the remaining sampling points with 0, connecting all the sampling points in time order to obtain a continuous signal curve; and identifying the electrical breakdown of the parallel capacitor group when it is put into operation according to the continuous signal curve. The present invention solves the problem of low accuracy and slow response of the existing identification method.

Description

Technical Field

[0001] The invention relates to the technical field of electrical breakdown identification of a parallel capacitor group, and in particular to an electrical breakdown identification method of a parallel capacitor group based on an instantaneous symmetrical component method. Background Art

[0002] Shunt capacitor banks are widely used in power systems for reactive power compensation and voltage stabilization. However, when the capacitor bank is put into operation, the capacitor elements may experience electrical breakdown. The occurrence of electrical breakdown will reduce the operational reliability of the power system and even cause more serious failures. The electrical breakdown phenomenon has the following characteristics:

[0003] Short occurrence time: The electrical breakdown phenomenon usually occurs within 1 millisecond (ms) after the capacitor bank is put into operation and lasts for a very short time.

[0004] Three-phase asymmetry: Electrical breakdown usually occurs in one phase first, resulting in three-phase asymmetry in the power system.

[0005] Existing fault detection methods mainly rely on power frequency steady-state signals for identification. However, since the occurrence time of electrical breakdown is extremely short, the power frequency steady-state signal cannot capture this fault phenomenon in a timely and accurate manner. In addition, simple transient signal detection methods are also difficult to effectively distinguish and identify electrical breakdown phenomena because the frequency of electrical breakdown is close to the frequency of capacitor input. Therefore, the use of power frequency steady-state signals and simple transient signal detection methods to identify electrical breakdown faults has the following shortcomings:

[0006] Slow response: The power frequency steady-state signal cannot provide effective fault information at the moment when the electrical breakdown occurs.

[0007] Low accuracy: Since the electrical breakdown phenomenon occurs instantaneously and is short-lived, traditional steady-state signal detection methods and simple transient signal detection methods are difficult to accurately identify. Summary of the invention

[0008] In view of the above-mentioned deficiencies in the prior art, the present invention provides a method for identifying the breakdown of a parallel capacitor group based on an instantaneous symmetrical component method, which solves the problems of low accuracy and slow response of the prior identification methods.

[0009] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention is: a method for identifying the electrical breakdown of a parallel capacitor bank based on the instantaneous symmetrical component method, comprising the following steps:

[0010] S1: Put a capacitor bank into operation and extract transient current waveform data of one cycle after the capacitor bank is put into operation;

[0011] S2: Use FFT algorithm to extract the high frequency generated when the device is put into operation based on the transient current waveform data;

[0012] S3: Calculate the instantaneous value of the negative sequence component of the transient current waveform data using the improved instantaneous symmetrical component method;

[0013] S4: Based on the high frequency and the instantaneous value of the negative sequence component, the instantaneous value of the negative sequence component is processed by the second-order difference to detect the flying point;

[0014] S5: The flying point is represented by 1, and the other sampling points are represented by 0, and all the sampling points are connected in time sequence to obtain a continuous signal curve;

[0015] S6: Identify the electrical breakdown when the parallel capacitor group is put into operation according to the continuous signal curve, and complete the identification of the electrical breakdown when the parallel capacitor group is put into operation based on the instantaneous symmetrical component method.

[0016] The beneficial effects of the above scheme are as follows: the present invention adopts an improved instantaneous symmetrical component method for the transient signal when the capacitor group is put into operation, which can quickly and accurately extract the negative sequence component in the transient signal to reflect the occurrence of the electrical breakdown phenomenon; by performing secondary differential processing on the extracted negative sequence component, the characteristics of the signal are further enhanced, making the identification of the electrical breakdown phenomenon more accurate and reliable. The present invention solves the problem of low accuracy and slow response of the existing identification method.

[0017] Furthermore, in S2, the FFT algorithm is used to calculate different frequency signals according to the transient current waveform data, and each frequency signal is sorted by amplitude to obtain the high frequency f0. The calculation formula of the different frequency signals is:

[0018]

[0019]

[0020]

[0021]

[0022] Among them, f k is the frequency corresponding to frequency k, k = 0, 1, ..., N-1, N is the number of sampling points, f s is the sampling frequency, I a [k], I b [k] and I c [k] are the complex values ​​corresponding to the kth frequency of the signal in the frequency domain, |I a [k], |I b [k] and |I c [k]| is the amplitude of the signal corresponding to the kth frequency in the frequency domain, j is an imaginary unit, θ k is the phase corresponding to frequency k.

[0023] The beneficial effect of the above further scheme is that when the high frequency at the time of input is obtained according to the current waveform data using the FFT algorithm, the basic principle is to decompose the signal into a linear combination of sine and cosine waves of different frequencies. According to the above formula, signals of different frequencies are obtained, and the high frequency signal is obtained by sorting the various frequency signals according to the amplitude.

[0024] Furthermore, the improved instantaneous symmetrical component method in S3 obtains the instantaneous value of the negative sequence component of the transient current waveform data by constructing a rotating phasor, and the rotating phasor calculation formula is:

[0025]

[0026]

[0027]

[0028] Among them, I a (·),I b (·) and I c (·) is the rotating phasor, ω is the angular frequency of the steady-state component of the three-phase current power frequency, t is the time, Δt is the sampling interval, i a (·),i b (·) and i c (·) is the instantaneous value of three-phase current;

[0029] Based on the constructed rotating phasor, the instantaneous value of the negative sequence component of the three-phase current I2(t) is obtained, and the formula is:

[0030]

[0031] Here, Im{·} represents taking the imaginary part of a complex number, and a is a complex operator in the symmetric component method.

[0032] The beneficial effect of the above further scheme is that the present invention adopts an improved instantaneous symmetrical component calculation method, that is, the instantaneous value of the negative sequence component of the three-phase current is obtained in real time by constructing a rotating phasor.

[0033] Furthermore, in S4, the instantaneous value of the negative sequence component is processed by using the second-order difference to detect the flying point, and the flying point satisfies the following formula:

[0034] |I2(t+Δt)-2I2(t)-I2(t-Δt)|≥ε

[0035] ε=3Α(2πf0Δt) 2

[0036] Among them, ε is the set threshold, and A is the maximum value of the instantaneous value of the negative sequence component.

[0037] The beneficial effect of the above further solution is that the flying spot detection can be realized through the above formula.

[0038] Furthermore, the electrical breakdown identification when the parallel capacitor bank is put into operation is performed according to the continuous signal curve in S6, including the following situations:

[0039] (1) When the number of square waves within 1 / 4 cycle after the capacitor bank is put into use is greater than 1, the capacitor bank has component breakdown;

[0040] (2) When the number of square waves within 1 / 4 cycle after the capacitor bank is put into operation is ≤1, there is no component breakdown in the capacitor bank.

[0041] The beneficial effect of the above further solution is that through the above technical solution, it can be judged whether the capacitor bank has a breakdown phenomenon according to the number of square waves within 1 / 4 cycle after the capacitor bank is put into use. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 The present invention is a flow chart of the method for identifying electrical breakdown of a parallel capacitor bank.

[0043] Figure 2 This is a schematic diagram of a 10kV simple distribution network system of the present invention.

[0044] Figure 3 This is a structural diagram of the parallel capacitor group of the present invention. DETAILED DESCRIPTION

[0045] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0046] like Figure 1 As shown, a method for identifying the breakdown of a parallel capacitor bank based on the instantaneous symmetrical component method comprises the following steps:

[0047] S1: Put a capacitor bank into operation and extract transient current waveform data of one cycle after the capacitor bank is put into operation;

[0048] S2: Use FFT algorithm to extract the high frequency generated when the device is put into operation based on the transient current waveform data;

[0049] S3: Calculate the instantaneous value of the negative sequence component of the transient current waveform data using the improved instantaneous symmetrical component method;

[0050] S4: Based on the high frequency and the instantaneous value of the negative sequence component, the instantaneous value of the negative sequence component is processed by the second-order difference to detect the flying point;

[0051] S5: The flying point is represented by 1, and the other sampling points are represented by 0, and all the sampling points are connected in time sequence to obtain a continuous signal curve;

[0052] S6: Identify the electrical breakdown when the parallel capacitor group is put into operation according to the continuous signal curve, and complete the identification of the electrical breakdown when the parallel capacitor group is put into operation based on the instantaneous symmetrical component method.

[0053] Since the input signal is the instantaneous value of the three-phase current of one cycle after the capacitor is put into use, it is assumed that the instantaneous values ​​of the three-phase current are i a (t), i b (t), i c (t), where t represents time, f s represents the sampling rate, N represents the number of sampling points, is the sampling interval.

[0054] When the input signal is i a (t), the representation in the frequency domain can be calculated by the following formula:

[0055]

[0056]

[0057] Signals of different frequencies are obtained according to the formula, and the frequency signals are sorted according to their amplitudes, among which the two frequency signals with the highest amplitudes (including the 50 Hz industrial frequency signal and the high-frequency signal with a frequency of f0) are selected to obtain the high-frequency signal f0.

[0058] In S2, the FFT algorithm is used to calculate different frequency signals according to the transient current waveform data, and each frequency signal is sorted according to the amplitude to obtain the high frequency f0. The calculation formula of the different frequency signals is:

[0059]

[0060]

[0061]

[0062]

[0063] Among them, f k is the frequency corresponding to frequency k, k = 0, 1, ..., N-1, N is the number of sampling points, f s is the sampling frequency, I a [k], I b [k] and I c [k] are the complex values ​​corresponding to the kth frequency of the signal in the frequency domain, |I a [k], |I b [k] and |I c [k]| is the amplitude of the signal corresponding to the kth frequency in the frequency domain, j is an imaginary unit, θk is the phase corresponding to frequency k.

[0064] The improved instantaneous symmetrical component method in S3 obtains the instantaneous value of the negative sequence component of the transient current waveform data by constructing a rotating phasor. The rotating phasor calculation formula is:

[0065]

[0066]

[0067]

[0068] Among them, I a (·),I b (·) and I c (·) is the rotating phasor, ω is the angular frequency of the steady-state component of the three-phase current power frequency, t is time, Δt is the sampling interval, i a (·),i b (·) and i c (·) is the instantaneous value of three-phase current;

[0069] Based on the constructed rotating phasor, the instantaneous value of the negative sequence component of the three-phase current I2(t) is obtained, and the formula is:

[0070]

[0071] Among them, Im{·} represents taking the imaginary part of a complex number, a is the complex operator in the symmetric component method,

[0072] The essence of detecting "flying points" based on second-order differences is to detect "flying points" through second-order differences (the difference between the left and right differences is actually the second-order difference). If the second-order differences of three consecutive points are greater than the threshold, the middle point is judged as an abnormal point. The signal that satisfies the following formula is a "flying point".

[0073] In S4, the instantaneous value of the negative sequence component is processed by using the second-order difference to detect the flying point, and the flying point satisfies the following formula:

[0074] |I2(t+Δt)-2I2(t)-I2(t-Δt)|≥ε

[0075] ε=3Α(2πf0Δt) 2

[0076] Among them, ε is the set threshold, and A is the maximum value of the instantaneous value of the negative sequence component.

[0077] In S6, the electrical breakdown identification when the parallel capacitor bank is put into operation is performed according to the continuous signal curve, including the following situations:

[0078] (1) When the number of square waves within 1 / 4 cycle after the capacitor bank is put into operation is greater than 1, there is a component breakdown phenomenon in the capacitor bank;

[0079] (2) When the number of square waves within 1 / 4 cycle after the capacitor bank is put into operation is ≤1, there is no component breakdown in the capacitor bank.

[0080] In one embodiment of the present invention, Figure 2 As shown, this is a schematic diagram of a 10kV simple distribution network system. Figure 3 This is a structural diagram of a parallel capacitor bank. If the capacitor bank experiences electrical breakdown when the capacitor is put into operation, this method can be used to identify it.

[0081] Compared with the prior art, the present invention has the following significant advantages:

[0082] 1. Improve data security. The present invention extracts negative sequence components through an improved instantaneous symmetrical component method, which reduces the need for a large amount of processing of the original data. Only characteristic signals need to be transmitted and processed, reducing the risk in the data transmission process. In addition, the use of secondary differential processing further simplifies the data structure, making sensitive information more difficult to be maliciously obtained and cracked, thereby significantly improving data security.

[0083] 2. Save network resources. The existing technology usually needs to transmit a large amount of original signal data for analysis and processing, resulting in a large consumption of network bandwidth. The present invention extracts and simplifies the characteristics of the transient signal of the three-phase current, and only needs to transmit the characteristic signal data, which greatly reduces the amount of data and saves network bandwidth resources.

[0084] 3. Improve recognition accuracy. The present invention uses an improved instantaneous symmetrical component method to accurately extract negative sequence components, and combines it with secondary differential processing to significantly improve the recognition accuracy of electrical breakdown phenomena. In the prior art, the power frequency steady-state signal detection method is slow to respond and it is difficult to accurately identify instantaneous electrical breakdown phenomena. The solution of the present invention can accurately identify in a very short time (within 1 millisecond), significantly improving the detection effect.

[0085] 4. Enhance system stability. By quickly and accurately identifying electrical breakdown, the present invention can promptly activate alarms and protection devices to prevent faults from expanding and enhance the stability and safety of the power system. The prior art often fails to control faults in a timely manner due to delayed identification, while the present invention effectively avoids such problems through rapid identification and response.

[0086] 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 the breakdown of a parallel capacitor bank based on the instantaneous symmetrical component method, characterized in that: The following steps are involved: S1: Put a capacitor bank into operation and extract transient current waveform data of one cycle after the capacitor bank is put into operation; S2: Use FFT algorithm to extract the high frequency generated when the device is put into operation based on the transient current waveform data; S3: Calculate the instantaneous value of the negative sequence component of the transient current waveform data using the improved instantaneous symmetrical component method; S4: Based on the high frequency and the instantaneous value of the negative sequence component, the instantaneous value of the negative sequence component is processed by the second-order difference to detect the flying point; S5: The flying point is represented by 1, and the other sampling points are represented by 0, and all the sampling points are connected in time sequence to obtain a continuous signal curve; S6: Identify the electrical breakdown when the parallel capacitor group is put into operation according to the continuous signal curve, and complete the identification of the electrical breakdown when the parallel capacitor group is put into operation based on the instantaneous symmetrical component method.

2. The method for identifying the breakdown of a parallel capacitor bank based on the instantaneous symmetrical component method according to claim 1 is characterized in that: In S2, the FFT algorithm is used to calculate different frequency signals according to the transient current waveform data, and each frequency signal is sorted according to the amplitude to obtain the high frequency f0. The calculation formula of the different frequency signals is: Among them, f k is the frequency corresponding to frequency k, k = 0, 1, ..., N-1, N is the number of sampling points, f s is the sampling frequency, I a [k], I b [k] and I c [k] are the complex values ​​corresponding to the kth frequency of the signal in the frequency domain, |I a [k], |I b [k] and |I c [k]| is the amplitude of the signal corresponding to the kth frequency in the frequency domain, j is an imaginary unit, θ k is the phase corresponding to frequency k.

3. The method for identifying breakdown of a parallel capacitor bank based on the instantaneous symmetrical component method according to claim 2, characterized in that: The improved instantaneous symmetrical component method in S3 obtains the instantaneous value of the negative sequence component of the transient current waveform data by constructing a rotating phasor. The rotating phasor calculation formula is: Among them, I a (·),I b (·) and I c (·) is the rotating phasor, ω is the angular frequency of the steady-state component of the three-phase current power frequency, t is the time, Δt is the sampling interval, i a (·),i b (·) and i c (·) is the instantaneous value of three-phase current; Based on the constructed rotating phasor, the instantaneous value of the negative sequence component of the three-phase current I2(t) is obtained, and the formula is: Here, Im{·} represents taking the imaginary part of a complex number, and a is a complex operator in the symmetric component method.

4. The method for identifying breakdown of a parallel capacitor bank based on the instantaneous symmetrical component method according to claim 3 is characterized in that: In S4, the instantaneous value of the negative sequence component is processed by using the second-order difference to detect the flying point, and the flying point satisfies the following formula: |I2(t+Δt)-2I2(t)-I2(t-Δt)|≥ε ε=3A(2πf0Δt) 2 Among them, ε is the set threshold, and A is the maximum value of the instantaneous value of the negative sequence component.

5. The method for identifying breakdown of a parallel capacitor bank based on the instantaneous symmetrical component method according to claim 1, characterized in that: In S6, the electrical breakdown identification when the parallel capacitor bank is put into operation is performed according to the continuous signal curve, including the following situations: (1) When the number of square waves within 1 / 4 cycle after the capacitor bank is put into use is greater than 1, the capacitor bank has component breakdown; (2) When the number of square waves within 1 / 4 cycle after the capacitor bank is put into operation is ≤1, there is no component breakdown in the capacitor bank.

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