Method for evaluating deformation of transformer winding based on frequency response-impedance-capacitance comprehensive model

Abstract

The invention discloses a method for evaluating deformation of a transformer winding based on a frequency response-impedance-capacitance comprehensive model. Characteristic indexes are obtained through loss testing, direct measurement and a low-voltage impedance method, collaborative diagnosis is conducted through a frequency response method, an impedance method and a capacitance method, a diagnosis model is established, and therefore the specific position and type of a fault are obtained. According to the method, three methods are comprehensively utilized to evaluate the transformer winding, and the problems that an existing transformer winding deformation state evaluation method is single, limited in data and inaccurate in evaluation result are solved.

Description

Technical Field

[0001] The present application relates to the technical field of fault diagnosis of electric power equipment, and in particular to a method for evaluating transformer winding deformation based on a frequency response-impedance-capacitance comprehensive model. Background Art

[0002] Among all types of faults, transformer winding deformation fault is considered to be a more serious one. Usually, the longitudinal compression, axial stretching, winding bulging, twisting and other phenomena that occur after the transformer winding is subjected to electric force impact are collectively referred to as winding deformation. Although slight deformation of the power transformer winding has no obvious effect on its normal operation, serious winding deformation fault is extremely harmful to the transformer. For example, serious winding deformation may damage the internal structure of the transformer, cause the transformer to be forced to shut down, and may cause power outages in a large area, resulting in a large load loss, which will have an adverse impact on the power supply reliability of the power grid and the economic development of the society. Slight deformation of the winding will reduce the winding's ability to resist short circuits. At this time, if the winding is subjected to multiple short-circuit electric force impacts, it will cause serious deformation of the winding, which may damage the pads between the windings and the winding insulation, and cause partial discharge and other faults. Under the combined effect of these factors, the winding will be severely deformed.

[0003] There are three commonly used methods for determining transformer winding deformation faults: frequency response method, short-circuit impedance method, and group capacitance method. The frequency response method is a commonly used method for detecting transformer winding deformation in power systems. It has the advantages of good signal-to-noise ratio and high repeatability. It is also simple to test and easy to use. If the winding is deformed, the corresponding frequency response curve and structural parameters (inductance, capacitance, etc.) will change. If the capacitance value of the transformer winding tested by the capacitance method is significantly different from the value in the database, the winding may be deformed. The present invention combines these three commonly used methods for collaborative diagnosis, overcomes the shortcomings of a single method in determining winding faults, and proposes a method for evaluating transformer winding deformation based on a frequency response-impedance-capacitance comprehensive model. Summary of the invention

[0004] In order to accurately diagnose the deformation of power transformer windings, the present invention provides a method for evaluating the deformation of transformer windings based on a frequency response-impedance-capacitance comprehensive model, comprising the following steps:

[0005] The first step is to obtain the transformer characteristic indicators

[0006] The capacity of the current transformer is obtained through loss testing, the phase voltage of each phase winding is obtained by directly measuring the voltage of the secondary winding of the transformer, the impedance of each phase winding is obtained by the low-voltage impedance method, and the capacity change rate, three-phase imbalance rate and three-phase impedance change rate are calculated. The formula is as follows:

[0007]

[0008] Where j represents the number of historical data during transformer operation, j = 1, 2, ..., m, A j Indicates the capacity change rate, S j is the actual transformer capacity in operation, S is the rated capacity of the transformer, B j Indicates the three-phase unbalance rate, U A , U B , U C are the phase voltages on the three phases of the transformer in actual operation, the max() function returns the maximum value of the input variable, and the min() function returns the minimum value of the input variable. j Indicates the three-phase impedance change rate, Z A1 , Z B1 , Z C1 are the three-phase impedance of the transformer when it leaves the factory, Z A2 , Z B2 , Z C2 They are the impedances of the three phases when the transformer is actually running;

[0009] Construct a characteristic matrix, normalize each element in the characteristic matrix, and obtain a normalized characteristic matrix R. The normalization formula is as follows:

[0010]

[0011] Among them, X is the normalized characteristic index, x is the capacitance change rate A j , three-phase unbalance rate B j And the three-phase impedance change rate C j The actual measured value of a and b is obtained according to the Transformer Operation Regulations and the Preventive Test Regulations for Power Equipment. a and b represent the factory value and the critical threshold of the indicator respectively.

[0012] The normalized characteristic matrix R is as follows:

[0013]

[0014] The information entropy of the indicator is calculated using the following formula:

[0015] H i =-X ij ln(X ij ) (6)

[0016] Among them, H i is the information entropy calculated, X ij is the corresponding element in the normalized characteristic matrix R, i = 1, 2, 3, j = 1, 2, 3, ..., m;

[0017] The entropy weight of each indicator is calculated using information entropy. The formula is as follows:

[0018]

[0019] Among them, W i is the entropy weight of each indicator, W1 is the capacitance change rate A j Indicator entropy weight, W2 is the three-phase unbalance rate B j Indicator entropy weight, W3 is the three-phase impedance change rate C j Indicator entropy weight;

[0020] The second step is to use characteristic indicators to determine the winding status

[0021] According to the entropy weight calculated in the previous step, the main evaluation index of winding deformation is determined;

[0022] If W1 is the largest, it means the capacity change rate is A. j It is the main evaluation index of the transformer winding deformation. When 0%≤A j ≤10%, indicating that the transformer is in normal working condition; when A j When it is ≥10%, it means that the transformer winding deformation position should be checked;

[0023] If W2 is the largest, it means the three-phase unbalance rate B j It is the main evaluation index of the transformer winding deformation. When 0%≤B j ≤2%, indicating that the transformer is in normal working condition; when B j When it is ≥2%, it means that the transformer winding deformation position should be checked;

[0024] If W3 is the largest, it means the three-phase impedance change rate C j It is the main evaluation index of the transformer winding deformation. When 0%≤C j ≤2%, indicating that the transformer is in normal working condition; when C j When it is ≥2%, it means that the transformer winding deformation position should be checked;

[0025] Step 3: Calculate the frequency response curve deviation and resonance peak change

[0026] According to the normal operation frequency response curve and abnormal operation frequency response curve of the transformer, the frequency response curve offset and resonance peak change are calculated. The specific formula is as follows:

[0027]

[0028] ΔP=P r2 -P r1 (9)

[0029] Among them, Δf represents the parameter of frequency response curve deviation, ΔP represents the parameter of resonance peak change, and f r1 represents the frequency of the rth point when the winding is not deformed, f r2 Indicates the frequency of the rth point after the winding is deformed, P r1 , P r2 They represent the resonance peak value of the rth point when the winding is not deformed and deformed respectively;

[0030] Step 4: Determine the specific location of the fault and the type of winding fault

[0031] Perform a short-circuit impedance test on the three-phase winding of the transformer, compare the measured short-circuit impedance value with the transformer factory data, and determine the specific location of the fault. The formula is as follows:

[0032]

[0033] Where k represents the impedance change rate, Z represents the short-circuit impedance of a certain winding of the transformer in operation, and Z0 represents the short-circuit impedance designed when the transformer leaves the factory;

[0034] When the impedance change rate is less than 1.6%, the phase winding is in a normal state, and when the impedance change rate is greater than 1.6%, the phase winding is in an abnormal state;

[0035] Use the winding capacitance method to measure the winding capacitance at the faulty winding, compare the measured data with the transformer factory data, and determine the type of winding fault by combining the frequency response curve offset and resonance peak change;

[0036] When the winding capacitance increases, Δf>0, ΔP<0, axial compression deformation occurs;

[0037] When the winding capacitance increases, Δf<0, ΔP<0, radial compression deformation occurs;

[0038] When the winding capacitance decreases, Δf>0, ΔP>0, radial expansion deformation occurs;

[0039] When the winding capacitance decreases, Δf<0, ΔP>0, axial tensile deformation occurs. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 is a flow chart of the method of the present invention;

[0041] Figure 2 It is a comprehensive diagnostic model diagram of the method of the present invention. DETAILED DESCRIPTION

[0042] The present invention will be further described in detail below in conjunction with the accompanying drawings.

[0043] The first step is to obtain the transformer characteristic indicators

[0044] The capacity of the current transformer is obtained through loss testing, the phase voltage of each phase winding is obtained by directly measuring the voltage of the secondary winding of the transformer, the impedance of each phase winding is obtained by the low-voltage impedance method, and the capacity change rate, three-phase imbalance rate and three-phase impedance change rate are calculated. The formula is as follows:

[0045]

[0046] Where j represents the number of historical data during transformer operation, j = 1, 2, ..., m, A j Indicates the capacity change rate, S j is the actual transformer capacity in operation, S is the rated capacity of the transformer, B j Indicates the three-phase unbalance rate, U A , U B , U C are the phase voltages on the three phases of the transformer in actual operation, the max() function returns the maximum value of the input variable, and the min() function returns the minimum value of the input variable. j Indicates the three-phase impedance change rate, Z A1 , Z B1 , Z C1 are the three-phase impedance of the transformer when it leaves the factory, Z A2 , Z B2 , Z C2 They are the impedances of the three phases when the transformer is actually running;

[0047] Construct a characteristic matrix, normalize each element in the characteristic matrix, and obtain a normalized characteristic matrix R. The normalization formula is as follows:

[0048]

[0049] Among them, X is the normalized characteristic index, x is the capacitance change rate A j , three-phase unbalance rate B j And the three-phase impedance change rate C j The actual measured value of a and b is obtained according to the Transformer Operation Regulations and the Preventive Test Regulations for Power Equipment. a and b represent the factory value and the critical threshold of the indicator respectively.

[0050] The normalized characteristic matrix R is as follows:

[0051]

[0052] The information entropy of the indicator is calculated using the following formula:

[0053] H i =-Xij ln(X ij ) (6)

[0054] Among them, H i is the information entropy calculated, X ij is the corresponding element in the normalized characteristic matrix R, i = 1, 2, 3, j = 1, 2, 3, ..., m;

[0055] The entropy weight of each indicator is calculated using information entropy. The formula is as follows:

[0056]

[0057] Among them, W i is the entropy weight of each indicator, W1 is the capacitance change rate A j Indicator entropy weight, W2 is the three-phase unbalance rate B j Indicator entropy weight, W3 is the three-phase impedance change rate C j Indicator entropy weight;

[0058] The second step is to use characteristic indicators to determine the winding status

[0059] According to the entropy weight calculated in the previous step, the main evaluation index of winding deformation is determined;

[0060] If W1 is the largest, it means the capacity change rate is A. j It is the main evaluation index of the transformer winding deformation. When 0%≤A j ≤10%, indicating that the transformer is in normal working condition; when A j When it is ≥10%, it means that the transformer winding deformation position should be checked;

[0061] If W2 is the largest, it means the three-phase unbalance rate B j It is the main evaluation index of the transformer winding deformation. When 0%≤B j ≤2%, indicating that the transformer is in normal working condition; when B j When it is ≥2%, it means that the transformer winding deformation position should be checked;

[0062] If W3 is the largest, it means the three-phase impedance change rate C j It is the main evaluation index of the transformer winding deformation. When 0%≤C j ≤2%, indicating that the transformer is in normal working condition; when C j When it is ≥2%, it means that the transformer winding deformation position should be checked;

[0063] Step 3: Calculate the frequency response curve deviation and resonance peak change

[0064] According to the normal operation frequency response curve and abnormal operation frequency response curve of the transformer, the frequency response curve offset and resonance peak change are calculated. The specific formula is as follows:

[0065]

[0066] ΔP=P r2 -P r1 (9)

[0067] Among them, Δf represents the parameter of frequency response curve deviation, ΔP represents the parameter of resonance peak change, and f r1 represents the frequency of the rth point when the winding is not deformed, f r2 Indicates the frequency of the rth point after the winding is deformed, P r1 , P r2 They represent the resonance peak value of the rth point when the winding is not deformed and deformed respectively;

[0068] Step 4: Determine the specific location of the fault and the type of winding fault

[0069] Perform a short-circuit impedance test on the three-phase winding of the transformer, compare the measured short-circuit impedance value with the transformer factory data, and determine the specific location of the fault. The formula is as follows:

[0070]

[0071] Where k represents the impedance change rate, Z represents the short-circuit impedance of a certain winding of the transformer in operation, and Z0 represents the short-circuit impedance designed when the transformer leaves the factory;

[0072] When the impedance change rate is less than 1.6%, the phase winding is in a normal state, and when the impedance change rate is greater than 1.6%, the phase winding is in an abnormal state;

[0073] Use the winding capacitance method to measure the winding capacitance at the faulty winding, compare the measured data with the transformer factory data, and determine the type of winding fault by combining the frequency response curve offset and resonance peak change;

[0074] When the winding capacitance increases, Δf>0, ΔP<0, axial compression deformation occurs;

[0075] When the winding capacitance increases, Δf<0, ΔP<0, radial compression deformation occurs;

[0076] When the winding capacitance decreases, Δf>0, ΔP>0, radial expansion deformation occurs;

[0077] When the winding capacitance decreases, Δf<0, ΔP>0, axial tensile deformation occurs.

Claims

1. A method for evaluating transformer winding deformation based on a frequency response-impedance-capacitance comprehensive model, characterized in that: The steps include: The first step is to obtain the transformer characteristic index; The capacity of the current transformer is obtained through loss testing, the phase voltage of each phase winding is obtained by directly measuring the voltage of the secondary winding of the transformer, the impedance of each phase winding is obtained by the low-voltage impedance method, and the capacity change rate, three-phase imbalance rate and three-phase impedance change rate are calculated. The formula is as follows: Where j represents the number of historical data during transformer operation, j = 1, 2, ..., m, A j Indicates the capacity change rate, S j is the actual transformer capacity in operation, S is the rated capacity of the transformer, B j Indicates the three-phase unbalance rate, U A , U B , U C are the phase voltages on the three phases of the transformer in actual operation, the max() function returns the maximum value of the input variable, and the min() function returns the minimum value of the input variable. j Indicates the three-phase impedance change rate, Z A1 , Z B1 , Z C1 are the three-phase impedance of the transformer when it leaves the factory, Z A2 , Z B2 , Z C2 They are the impedances of the three phases when the transformer is actually running; Construct a characteristic matrix, normalize each element in the characteristic matrix, and obtain a normalized characteristic matrix R. The normalization formula is as follows: Among them, X is the normalized characteristic index, x is the capacitance change rate A j , three-phase unbalance rate B j And the three-phase impedance change rate C j The actual measured value of a and b is obtained according to the Transformer Operation Regulations and the Preventive Test Regulations for Power Equipment. a and b represent the factory value and the critical threshold of the indicator respectively. The normalized characteristic matrix R is as follows: The information entropy of the indicator is calculated using the following formula: H i =-X ij ln(X ij ) (6) Among them, H i is the information entropy calculated, X ij is the corresponding element in the normalized characteristic matrix R, i = 1, 2, 3, j = 1, 2, 3, ..., m; The entropy weight of each indicator is calculated using information entropy. The formula is as follows: Among them, W i is the entropy weight of each indicator, W1 is the capacitance change rate A j Indicator entropy weight, W2 is the three-phase unbalance rate B j Indicator entropy weight, W3 is the three-phase impedance change rate C j Indicator entropy weight; The second step is to use characteristic indicators to determine the winding status; According to the entropy weight calculated in the previous step, the main evaluation index of winding deformation is determined; If W1 is the largest, it means the capacity change rate is A. j It is the main evaluation index of the transformer winding deformation. When 0%≤A j ≤10%, indicating that the transformer is in normal working condition; when A j When it is ≥10%, it means that the transformer winding deformation position should be checked; If W2 is the largest, it means the three-phase unbalance rate B j It is the main evaluation index of the transformer winding deformation. When 0%≤B j ≤2%, indicating that the transformer is in normal working condition; when B j When it is ≥2%, it means that the transformer winding deformation position should be checked; If W3 is the largest, it means the three-phase impedance change rate C j It is the main evaluation index of the transformer winding deformation. When 0%≤C j ≤2%, indicating that the transformer is in normal working condition; when C j When it is ≥2%, it means that the transformer winding deformation position should be checked; The third step is to calculate the frequency response curve offset and the resonance peak change; According to the normal operation frequency response curve and abnormal operation frequency response curve of the transformer, the frequency response curve offset and resonance peak change are calculated. The specific formula is as follows: ΔP=P r2 -P r1 (9) Among them, Δf represents the parameter of frequency response curve deviation, ΔP represents the parameter of resonance peak change, and f r1 represents the frequency of the rth point when the winding is not deformed, f r2 Indicates the frequency of the rth point after the winding is deformed, P r1 , P r2 They represent the resonance peak value of the rth point when the winding is not deformed and deformed respectively; The fourth step is to determine the specific fault location and the type of winding fault; Perform a short-circuit impedance test on the three-phase winding of the transformer, compare the measured short-circuit impedance value with the transformer factory data, and determine the specific location of the fault. The formula is as follows: Where k represents the impedance change rate, Z represents the short-circuit impedance of a certain winding of the transformer in operation, and Z0 represents the short-circuit impedance designed when the transformer leaves the factory; When the impedance change rate is less than 1.6%, the phase winding is in a normal state, and when the impedance change rate is greater than 1.6%, the phase winding is in an abnormal state; Use the winding capacitance method to measure the winding capacitance at the faulty winding, compare the measured data with the transformer factory data, and determine the type of winding fault by combining the frequency response curve offset and resonance peak change; When the winding capacitance increases, Δf>0, ΔP<0, axial compression deformation occurs; When the winding capacitance increases, Δf<0, ΔP<0, radial compression deformation occurs; When the winding capacitance decreases, Δf>0, ΔP>0, radial expansion deformation occurs; When the winding capacitance decreases, Δf<0, ΔP>0, axial tensile deformation occurs.

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