Transformer fault identification method and system using current sampling value

Abstract

The invention discloses a transformer fault identification method and system using a current sampling value. Converting the current sampling value variation of each side to the same side, and obtaining the converted current of the high-voltage side, the medium-voltage side and the low-voltage side; comparing the amplitude values of the high-voltage side current, the medium-voltage side current and the low-voltage side current of the transformer after conversion at each moment, and selecting a maximum value; a first current sampling value corresponding to the maximum value is determined, and after the maximum value is removed, the sum of the current sampling values on the remaining two sides is determined as a second current sampling value; performing point-by-point integration on the first current sampling value and the second current sampling value to obtain a current sampling integral value; taking the first current sampling integral value and the second current sampling integral value as horizontal and vertical coordinates, establishing a sampling value two-dimensional plane, and when the first current sampling integral value is located in the second quadrant of the two-dimensional plane, judging that the transformer is in an external fault; and when the first current sampling integral value is located in the Ith quadrant of the two-dimensional plane, determining that the internal fault of the transformer occurs. And the sensitivity of the alternating-current protection principle is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of relay protection, and in particular to a transformer fault identification method and system using current sampling values. Background Art

[0002] In recent years, the rapid growth of new energy power generation represented by wind power and photovoltaic power has led to profound changes in the power structure of the power system. Compared with conventional energy sources, the fault characteristics of new energy sources under the control strategy are significantly different, the transient process is complex, and the fault evolution mechanism is still unclear. The sensitivity, rapidity, selectivity and reliability of conventional protection are fully challenged, which seriously affects the accurate identification and rapid isolation of faults. The existing AC protection principle is based on the power frequency phasor, and Fourier transformation is required to extract the amplitude and phase information of the power frequency component. A data window length of 20ms is required, and the fault location and fault type are judged on this basis. The fault response characteristics of new energy sources are affected by the control strategy. Due to the fast response speed of the control strategy (less than 10ms), the power frequency component in the short-circuit current provided by the new energy source is quickly suppressed. The existing AC protection is limited by the fixed data window length, and it is difficult to quickly extract the fault characteristics. The existing AC protection principle is mainly based on industrial frequency electrical quantities. When a high-proportion new energy system fails, it is affected by the new energy control system, and the proportion of industrial frequency quantities in the fault electrical quantities drops significantly. The content of various harmonics is large and the frequency components are rich, resulting in a decrease in the sensitivity of the existing AC protection principle. In severe cases, the protection may even fail.

[0003] The protection principle based on transient quantities currently proposed mainly uses the wave head characteristics of traveling waves or the transient energy of different frequency bands in the frequency domain for fault identification. However, it requires a high sampling rate and the mathematical algorithm for extracting transient components has a large amount of calculation. The protection action performance is restricted by multiple factors such as fault moment and transition resistance. The reliability of protection needs to be further improved. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a transformer fault identification method using current sampling values, comprising:

[0005] Collect the current on each side of the transformer, and calculate the change of the current sampling value on each side according to the current on each side of the transformer;

[0006] Convert the current sampling value changes on each side to the same side to obtain the converted currents on the high voltage side, the medium voltage side and the low voltage side;

[0007] Compare the amplitudes of the currents on the high-voltage side, the medium-voltage side and the low-voltage side of the transformer after conversion at each moment, and select the maximum value; determine the first current sampling value corresponding to the maximum value, and determine the sum of the current sampling values ​​on the remaining two sides after removing the maximum value as the second current sampling value;

[0008] Integrate the first current sampling value and the second current sampling value point by point to obtain a first current sampling integral value and a second current sampling integral value;

[0009] A two-dimensional plane of sampling values ​​is established with the first current sampling integral value as the horizontal coordinate and the second current sampling integral value as the vertical coordinate. When the first current sampling integral value is located in the second quadrant of the two-dimensional plane, it is judged as an external fault of the transformer; when the first current sampling integral value is located in the first quadrant of the two-dimensional plane, it is judged as an internal fault of the transformer.

[0010] Furthermore, the change amount of the current sampling value at each side is calculated according to the current at each side of the transformer, including:

[0011] The calculation formula for the change in the current sampling value of each phase on each side △i(t) is:

[0012]

[0013] In the formula, The high, medium and low pressure sides at the current moment The current sampling value of the phase, High, medium and low voltage sides 20ms ago The current sampling value of each phase, N is the number of sampling points corresponding to 20ms, A, B, C.

[0014] Furthermore, the current sampling value changes on each side are converted to the same side to obtain the converted currents on the high voltage side, the medium voltage side and the low voltage side, including:

[0015] The changes in the current sampling values ​​on the medium voltage side and the low voltage side are converted by ratio conversion and △ / Y conversion, and then returned to the high voltage side. The changes in the current sampling values ​​on the high voltage side, the medium voltage side, and the low voltage side after conversion are respectively and

[0016] If the transformation ratio between the medium voltage side and the high voltage side is k M-H , the medium voltage side is star-connected, then

[0017] If the transformation ratio between the low-pressure side and the high-pressure side is k L-H , the low voltage side is a triangle connection, then

[0018] where Δi LA (t) is the change in the current sampling value of phase A on the low voltage side, Δi LB (t) is the change in the current sampling value of phase B on the low voltage side, Δi LC (t) is the change in the sampling value of the C phase current on the low voltage side, Δi L 'A (t) is the converted change of the current sampling value of phase A on the low voltage side, Δi L ' B (t) is the converted change of the low-voltage side B phase current sampling value, Δi′ LC (t) is the converted change in the low-voltage side C phase current sampling value.

[0019] Furthermore, the amplitudes of the currents on the high voltage side, medium voltage side and low voltage side of the transformer after conversion at each moment are compared, and the maximum value is selected, including:

[0020] Compare the transformer sides and phases at each moment The amplitude of

[0021]

[0022] Further, determining a first current sampling value corresponding to the maximum value, and determining the sum of the current sampling values ​​on both sides remaining after removing the maximum value as the second current sampling value, including:

[0023] make is the sum of the current sampling values, The maximum sampling value The corresponding first current sampling value is but for The second current sampling value.

[0024] Further, integrating the first current sampling value and the second current sampling value point by point to obtain a first current sampling integral value and a second current sampling integral value includes:

[0025] right Perform point-by-point integration to obtain the first current sampling integral value and the second current sampling integral value

[0026] The present invention also provides a transformer fault identification system using current sampling values, comprising:

[0027] The variation calculation module is used to collect the current on each side of the transformer and calculate the variation of the current sampling value on each side according to the current on each side of the transformer;

[0028] A conversion module is used to convert the current sampling value changes on each side to the same side to obtain the converted currents on the high-voltage side, the medium-voltage side and the low-voltage side;

[0029] The sampling value determination module is used to compare the amplitudes of the currents on the high-voltage side, the medium-voltage side and the low-voltage side of the transformer after conversion at each moment, and select the maximum value; determine the first current sampling value corresponding to the maximum value, and determine the sum of the current sampling values ​​on the remaining two sides after removing the maximum value as the second current sampling value;

[0030] An integration module, used for integrating the first current sampling value and the second current sampling value point by point to obtain a first current sampling integral value and a second current sampling integral value;

[0031] The fault judgment module is used to establish a two-dimensional plane of sampling values ​​with the first current sampling integral value as the horizontal coordinate and the second current sampling integral value as the vertical coordinate. When the first current sampling integral value is located in the second quadrant of the two-dimensional plane, it is judged as an external fault of the transformer; when the first current sampling integral value is located in the first quadrant of the two-dimensional plane, it is judged as an internal fault of the transformer.

[0032] The present invention provides a transformer fault identification method and system using current sampling values. By collecting current sampling values ​​on each side of the transformer and processing the data, a two-dimensional sampling value plane for identifying transformer faults is established. In the case of internal and external faults, the current sampling values ​​are in different quadrants on the plane. Based on this, internal and external faults of the transformer can be accurately identified. The method makes full use of the fault time domain information in the transient current, overcomes the influence of the distortion and weakening of the power frequency electrical quantity characteristics after the fault caused by the new energy power supply control strategy on the protection performance, and improves the sensitivity of the AC protection principle. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a flow chart of a transformer fault identification method using current sampling values ​​provided by the present invention;

[0034] Figure 2 The present invention relates to a current sampling value plane for identifying internal and external faults of a transformer;

[0035] Figure 3 It is the internal fault track of the transformer involved in the present invention;

[0036] Figure 4 It is the transformer external fault trajectory involved in the present invention;

[0037] Figure 5 The present invention provides a schematic diagram of the structure of a transformer fault identification system using current sampling values. DETAILED DESCRIPTION

[0038] Many specific details are set forth in the following description to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways than those described herein, and those skilled in the art can make similar generalizations without violating the connotation of the present invention, so the present invention is not limited to the specific implementation disclosed below.

[0039] Example 1

[0040] The present invention proposes a transformer fault identification method using current sampling values. By using the significant difference in current sampling values ​​on each side when the transformer has internal and external faults, a two-dimensional analysis plane of current sampling values ​​for identifying transformer faults is constructed. Through the motion trajectory of the current sampling values ​​on the plane, the internal fault of the transformer can be accurately and quickly identified. The process is as follows: Figure 1 As shown, the following steps are included:

[0041] Step S101 , collecting currents at each side of the transformer, and calculating the variation of current sampling values ​​at each side according to the currents at each side of the transformer.

[0042] The calculation formula for the change in the current sampling value of each phase on each side △i(t) is:

[0043]

[0044] In the formula, The high, medium and low pressure sides at the current moment The current sampling value of the phase, High, medium and low voltage sides 20ms ago The current sampling value of each phase, N is the number of sampling points corresponding to 20ms, A, B, C.

[0045] Step S102, converting the current sampling value changes on each side to the same side, and obtaining the converted currents on the high voltage side, the medium voltage side and the low voltage side.

[0046] The changes in the current sampling values ​​on the medium voltage side and the low voltage side are converted by ratio conversion and △ / Y conversion, and then returned to the high voltage side. The changes in the current sampling values ​​on the high voltage side, the medium voltage side, and the low voltage side after conversion are respectively and

[0047] If the transformation ratio between the medium voltage side and the high voltage side is k M-H , the medium voltage side is star (Y) connection, then

[0048]

[0049] If the transformation ratio between the low-pressure side and the high-pressure side is k L-H , the low voltage side is a triangle (△) connection, then

[0050] Where Δi LA (t) is the change in the current sampling value of phase A on the low voltage side, Δi LB (t) is the change in the current sampling value of phase B on the low voltage side, Δi LC (t) is the change in the sampling value of the C phase current on the low voltage side, Δi L ' A (t) is the converted change of the current sampling value of phase A on the low voltage side, Δi L ' B (t) is the converted change of the low-voltage side B phase current sampling value, Δi′ LC (t) is the converted change in the low-voltage side C phase current sampling value.

[0051] Step S103, compare the amplitudes of the converted high-voltage side, medium-voltage side and low-voltage side currents of the transformer at each moment, and select the maximum value; determine the first current sampling value corresponding to the maximum value, and determine the sum of the current sampling values ​​on the remaining two sides after removing the maximum value as the second current sampling value.

[0052] Compare the transformer sides and phases at each moment The amplitude of

[0053]

[0054] make is the sum of the current sampling values, The maximum sampling value The corresponding first current sampling value is but for The second current sampling value.

[0055] Furthermore, is a negative value, let like is a positive value, let The purpose of reassignment is to allow It is a positive value, which makes it easy to determine the action area in the two-dimensional coordinate plane.

[0056] Step S104 , integrating the first current sampling value and the second current sampling value point by point to obtain a first current sampling integral value and a second current sampling integral value.

[0057] right Perform point-by-point integration to obtain the first current sampling integral value and the second current sampling integral value

[0058] Step S105, establishing a two-dimensional plane of sampling values ​​with the first current sampling integral value as the horizontal coordinate and the second current sampling integral value as the vertical coordinate. When the first current sampling integral value is located in the second quadrant of the two-dimensional plane, it is determined to be an external fault of the transformer; when the first current sampling integral value is located in the first quadrant of the two-dimensional plane, it is determined to be an internal fault of the transformer.

[0059] Respectively As horizontal and vertical coordinates, establish a two-dimensional plane of sampling values. When it is located in the second quadrant of the two-dimensional plane, it is judged to be an external fault of the transformer; when When it is located in the first quadrant of the two-dimensional plane, it is judged to be an internal fault of the transformer.

[0060] like Figure 2 As shown, further, (1) Transformer external fault

[0061] The current sampling values ​​on each side of the transformer are The current mutation sampling values ​​on each side are divided into two groups When the transformer has an external fault, the fault current is a through current, and the sum of the sampling values ​​of the current mutation on each side of the transformer is and It can be seen that the amplitudes of the two sets of current mutation sampling values ​​are equal and their signs are opposite. lie in Quadrant II of the two-dimensional plane.

[0062] (2) Transformer internal fault

[0063] After an internal fault, the current on each side of the transformer flows to the fault point. The current mutation sampling values ​​on each side are divided into two groups and The polarity is the same. And lie in Quadrant I of the two-dimensional plane.

[0064] Example 2

[0065] For transformer internal and external faults, the current mutation sampling value can be used to construct protection criteria for accurate identification. If the transformer is a three-winding transformer, in terms of data processing:

[0066] (1) First, the currents on the medium voltage side and the low voltage side are converted by transformation ratio and △ / Y conversion, and then converted to the high voltage side. The converted currents on the high voltage side, medium voltage side, and low voltage side are respectively

[0067] (2) For each sampling point, The currents on the three sides are grouped and the one with the largest amplitude is Recorded as The remaining current is recorded as

[0068]

[0069] If the transformer is a two-side transformer, are the current mutation sampling values ​​after transformation ratio conversion and △ / Y conversion on the high voltage side and the low voltage side respectively, and the one with the larger amplitude is The smaller value is

[0071] Figure 3 and Figure 4 This is the change track of the sampling value of the sudden change current when the transformer is faulty and the transformer is empty. It can be seen that the internal fault of the transformer can be accurately identified by using the present invention.

[0072] Example 3

[0073] Based on the same inventive concept, the present invention also provides a transformer fault identification system using current sampling values, such as Figure 5 As shown, including:

[0074] The variation calculation module 510 is used to collect the current on each side of the transformer and calculate the variation of the current sampling value on each side according to the current on each side of the transformer;

[0075] The conversion module 520 is used to convert the current sampling value changes of each side to the same side, and obtain the converted currents of the high voltage side, the medium voltage side and the low voltage side;

[0076] The sampling value determination module 530 is used to compare the amplitudes of the currents on the high-voltage side, the medium-voltage side and the low-voltage side after conversion at each moment of the transformer, and select the maximum value; determine the first current sampling value corresponding to the maximum value, and determine the sum of the current sampling values ​​on the remaining two sides after removing the maximum value as the second current sampling value;

[0077] An integration module 540 is used to integrate the first current sampling value and the second current sampling value point by point to obtain a first current sampling integral value and a second current sampling integral value;

[0078] The fault judgment module 550 is used to establish a two-dimensional plane of sampling values ​​with the first current sampling integral value as the horizontal coordinate and the second current sampling integral value as the vertical coordinate. When the first current sampling integral value is located in the second quadrant of the two-dimensional plane, it is judged as an external fault of the transformer; when the first current sampling integral value is located in the first quadrant of the two-dimensional plane, it is judged as an internal fault of the transformer.

[0079] The present invention provides a transformer fault identification method and system using current sampling values. By collecting current sampling values ​​on each side of the transformer and processing the data, a two-dimensional sampling value plane for identifying transformer faults is established. In the case of internal and external faults, the current sampling values ​​are in different quadrants on the plane. Based on this, internal and external faults of the transformer can be accurately identified. The method makes full use of the fault time domain information in the transient current, overcomes the influence of the distortion and weakening of the power frequency electrical quantity characteristics after the fault caused by the new energy power supply control strategy on the protection performance, and improves the sensitivity of the AC protection principle.

[0080] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents, and any modifications or equivalents that do not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A transformer fault identification method using current sampling values, characterized in that: include: Collect the current on each side of the transformer, and calculate the change of the current sampling value on each side according to the current on each side of the transformer; Convert the current sampling value changes on each side to the same side to obtain the converted currents on the high voltage side, the medium voltage side and the low voltage side; Compare the amplitudes of the currents on the high-voltage side, the medium-voltage side and the low-voltage side of the transformer after conversion at each moment, and select the maximum value; determine the first current sampling value corresponding to the maximum value, and determine the sum of the current sampling values ​​on the remaining two sides after removing the maximum value as the second current sampling value; Integrate the first current sampling value and the second current sampling value point by point to obtain a first current sampling integral value and a second current sampling integral value; A two-dimensional plane of sampling values ​​is established with the first current sampling integral value as the horizontal coordinate and the second current sampling integral value as the vertical coordinate. When the first current sampling integral value is located in the second quadrant of the two-dimensional plane, it is judged as an external fault of the transformer; when the first current sampling integral value is located in the first quadrant of the two-dimensional plane, it is judged as an internal fault of the transformer.

2. The method according to claim 1, characterized in that: The change of the current sampling value on each side is calculated according to the current on each side of the transformer, including: The calculation formula for the change in the current sampling value of each phase on each side △i(t) is: In the formula, The high, medium and low pressure sides at the current moment The current sampling value of the phase, High, medium and low voltage sides 20ms ago The current sampling value of each phase, N is the number of sampling points corresponding to 20ms, A, B, C.

3. The method according to claim 1, characterized in that Convert the current sampling value changes on each side to the same side to obtain the converted currents on the high voltage side, medium voltage side, and low voltage side, including: The changes in the current sampling values ​​on the medium voltage side and the low voltage side are converted by ratio conversion and △ / Y conversion, and then returned to the high voltage side. The changes in the current sampling values ​​on the high voltage side, the medium voltage side, and the low voltage side after conversion are respectively and If the transformation ratio between the medium voltage side and the high voltage side is k M-H , the medium voltage side is star-connected, then If the transformation ratio between the low-pressure side and the high-pressure side is k L-H , the low voltage side is a triangle connection, then where Δi LA (t) is the change in the current sampling value of phase A on the low voltage side, Δi LB (t) is the change in the current sampling value of phase B on the low voltage side, Δi LC (t) is the change in the sampling value of the C phase current on the low voltage side, Δi′ LA (t) is the converted change of the current sampling value of phase A on the low voltage side, Δi′ LB (t) is the converted change of the low-voltage side B phase current sampling value, Δi′ LC (t) is the converted change in the low-voltage side C phase current sampling value.

4. The method according to claim 1, characterized in that Compare the current amplitudes of the high-voltage side, medium-voltage side, and low-voltage side of the transformer at each moment, and select the maximum value, including: Compare the transformer sides and phases at each moment The amplitude of 5. The method according to claim 1, characterized in that Determining a first current sampling value corresponding to the maximum value, and determining the sum of the current sampling values ​​on both sides remaining after removing the maximum value as a second current sampling value, including: make is the sum of the current sampling values, The maximum sampling value The corresponding first current sampling value is but for The second current sampling value.

6. The method according to claim 1, characterized in that Integrating the first current sampling value and the second current sampling value point by point to obtain a first current sampling integral value and a second current sampling integral value, including: right Perform point-by-point integration to obtain the first current sampling integral value and the second current sampling integral value 7. A transformer fault identification system using current sampling values, characterized in that: include: The variation calculation module is used to collect the current on each side of the transformer and calculate the variation of the current sampling value on each side according to the current on each side of the transformer; A conversion module is used to convert the current sampling value changes on each side to the same side to obtain the converted currents on the high-voltage side, the medium-voltage side and the low-voltage side; The sampling value determination module is used to compare the amplitudes of the currents on the high-voltage side, the medium-voltage side and the low-voltage side of the transformer after conversion at each moment, and select the maximum value; determine the first current sampling value corresponding to the maximum value, and determine the sum of the current sampling values ​​on the remaining two sides after removing the maximum value as the second current sampling value; An integration module, used for integrating the first current sampling value and the second current sampling value point by point to obtain a first current sampling integral value and a second current sampling integral value; The fault judgment module is used to establish a two-dimensional plane of sampling values ​​with the first current sampling integral value as the horizontal coordinate and the second current sampling integral value as the vertical coordinate. When the first current sampling integral value is located in the second quadrant of the two-dimensional plane, it is judged as an external fault of the transformer; when the first current sampling integral value is located in the first quadrant of the two-dimensional plane, it is judged as an internal fault of the transformer.

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