Calibration method of square wave calibration circuit for partial discharge test of transformer with oil and gas casing structure

Abstract

The invention belongs to the technical field of electrical equipment testing, and specifically relates to a calibration method for a square wave calibration circuit of a transformer partial discharge test of an oil and gas bushing structure; the scheme adopted is: comprising a transformer, a high-voltage bushing, a GIS air chamber, a control unit, a calibration pulse generator and a grounding connecting piece, the GIS air chamber is connected to the transformer through the high-voltage bushing, a high-voltage bushing end screen is installed on the high-voltage bushing, the high-voltage bushing end screen is connected in series with one end of a measuring impedance, and the other end of the measuring impedance is connected to a partial discharge analyzer through a coaxial cable; the invention solves the problems of GIS sealing component air chamber damage caused by partial discharge test square wave calibration and GIS air chamber poor sealing and moisture caused in a guide rod reinstallation process, thereby improving the test efficiency; the control unit eliminates the influence of GIS conductor on square wave calibration and subsequent tests, thereby ensuring the test accuracy.

Description

Technical Field

[0001] The invention belongs to the technical field of electrical equipment testing, and in particular relates to a calibration method for a square wave calibration circuit of a transformer partial discharge test of an oil and gas bushing structure. Background Art

[0002] For substations and power plants with limited renovation and expansion space and special environmental requirements, the transformer is directly connected to the gas insulated switchgear (GIS) through an oil and gas bushing. This type of transformer has outstanding advantages such as small footprint, small operation and maintenance workload, and high reliability, and is widely used in power systems.

[0003] Under the action of the electric field, only part of the insulation system discharges and has not yet broken down. This is called partial discharge. According to statistics, 50% of large transformer damage accidents are caused by partial discharge. Through the transformer partial discharge test, it is possible to timely find out whether there are partial discharge defects inside the equipment insulation, thereby effectively preventing the occurrence of failures. Partial discharge measurement methods include radio interference measurement method, ultrasonic method and pulse current method, but currently only the pulse current method is relatively mature and can be quantitatively measured.

[0004] The pulse current method uses the high-voltage bushing as a coupling capacitor to transmit the pulse signal to the partial discharge instrument. However, the partial discharge instrument can only display the amplitude or attenuation decibel of the discharge pulse obtained by the detection impedance. In order to obtain the apparent discharge amount on the partial discharge instrument, after the test circuit is connected, it is necessary to perform square wave calibration on the test circuit through the high-voltage bushing. The square wave calibration circuit is as follows: Figure 1 As shown, the bushing end screen capacitor is equivalent to C1 and C2. One end of the detection impedance Zm is connected to the bushing end screen, and the other end is connected to the partial discharge instrument. The calibration pulse generator generates a pulse current in the transformer, bushing end screen capacitor and measurement impedance loop through the high-voltage bushing. The pulse current generates a pulse voltage through the measurement impedance Zm. The pulse voltage signal is collected and amplified by the partial discharge analyzer and displayed in the form of apparent discharge.

[0005] The high-voltage bushing of the transformer with oil-gas bushing structure is directly connected to the gas-insulated switchgear (GIS). The square wave calibration requires opening the GIS air chamber and its internal conductive connecting rod, and testing through the contacts on the bushing side of the conductive connecting rod. After the test, the air chamber is restored. The whole process not only affects the work efficiency, but also causes the GIS air chamber to be poorly sealed or the micro-water exceeds the standard during the guide rod reinstallation process. In addition, other handover tests and preventive tests involving the high-voltage side of the transformer are difficult to carry out, which brings inconvenience to the operation and maintenance of the transformer with oil-gas bushing structure. Summary of the invention

[0006] The invention overcomes the shortcomings of the prior art and provides a calibration method for a square wave calibration circuit of a transformer partial discharge test of an oil and gas casing structure.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0008] In order to minimize the number of times the gas chamber is disassembled, the present invention uses the isolation knife switch and the grounding knife switch directly connected to the oil and gas casing inside the gas-insulated switchgear to perform square wave calibration of the test circuit. This method does not need to open the conductive connecting rod inside the GIS gas chamber, which greatly reduces the test workload and solves the problems of poor sealing of the GIS gas chamber and moisture in the FS6 gas caused by the reinstallation of the conductive connecting rod, thereby ensuring the stable operation of the equipment. Due to the influence of stray capacitance of some equipment such as the isolation knife switch and the grounding knife switch in the test circuit, calibration errors are easily caused, thereby affecting the judgment of the transformer discharge condition. In order to ensure calibration Accuracy: In the infrastructure stage, the present invention obtains the charge calibration factor according to the known charge directly injected by the calibration pulse generator at the casing and the amplitude of the discharge pulse of the partial discharge measuring instrument. After the calibration factor is determined, the known charge is injected again at the isolation switch and the grounding switch directly connected to the oil and gas casing through the calibration pulse generator. The difference between the discharge amount displayed by the partial discharge analyzer and the injected charge is the influence of the isolation switch and the grounding switch on the test; in the test stage, the square wave calibration of the test loop is completed through the grounding connector, and the interference of some equipment such as the GIS isolation switch and the grounding switch is eliminated.

[0009] The square wave calibration circuit of transformer partial discharge test with oil and gas casing structure comprises: a transformer, a high-voltage bushing, a GIS air chamber, a control unit, a calibration pulse generator and a grounding connecting piece, wherein the GIS air chamber is connected to the transformer through the high-voltage bushing, a high-voltage bushing end screen is installed on the high-voltage bushing, the high-voltage bushing end screen is connected in series with one end of the measuring impedance, and the other end of the measuring impedance is connected to the partial discharge analyzer through a coaxial cable; the GIS air chamber comprises: a conductive connecting rod, an isolating knife switch, a grounding knife switch and a circuit breaker, one end of the isolating knife switch is connected to the conductive connecting rod through a first terminal. One end of the control unit is connected with the calibration pulse generator, the other end of the control unit is connected with the third terminal through a wire; the other end of the conductive connecting rod is connected with the high-voltage bushing through a second terminal; one end of the grounding switch is connected with the connection point between the isolation switch and the circuit breaker, the other end of the grounding switch is connected with one end of the grounding connecting piece through a third terminal, and the other end of the grounding connecting piece is connected with the grounding terminal through a fourth terminal; one end of the control unit is connected with the calibration pulse generator in series, and the other end of the control unit is connected with the third terminal through a wire; the grounding connecting piece is connected with the grounding terminal through a fourth terminal.

[0010] The calibration method of the square wave calibration circuit of the transformer partial discharge test of the oil and gas casing structure comprises the following steps:

[0011] Step 1: During the infrastructure construction stage of the transformer, the GIS air chamber where the conductive connecting rod is located is not closed. One end of the conductive connecting rod is connected to the high-voltage bushing through the second terminal, and the other end of the conductive connecting rod is connected to the isolating knife switch through the first terminal. The conductive connecting rod is in a disconnected state. One end of the measuring impedance is connected in series with the end screen of the high-voltage bushing, and the other end is connected to the partial discharge analyzer through a coaxial cable. When partial discharge occurs in the transformer, the transformer will generate an instantaneous voltage change △u. The pulse current generated by △u generates a pulse voltage on the measuring impedance. The pulse voltage is transmitted to the partial discharge analyzer through the coaxial cable. The partial discharge analyzer collects the signal, amplifies and displays it. The test circuit is built and the square wave calibration of the test circuit is started. The calibration pulse generator injects the standard charge through the second terminal and sets the standard charge to P (P is in pC). The pulse voltage signal at both ends of the measuring impedance is transmitted to the partial discharge analyzer. The partial discharge analyzer obtains the charge scale factor based on the injected known charge P and the amplitude of the discharge pulse of the partial discharge analyzer.

[0012] Step 2: Close the conductive connecting rod, seal the GIS air chamber where the conductive connecting rod is located, close the isolation knife switch and the grounding knife switch, open the grounding connecting piece, and set the third and fourth terminals on both sides of the grounding connecting piece respectively. Connect the calibration pulse generator to the third terminal, and inject the standard charge P (P is in pC) again. The partial discharge analyzer obtains the apparent discharge amount P1 according to the charge amount scale factor in the first step; make a difference between the standard charge amount P and the apparent discharge amount P1, △P=P1-P, △P is the influence of the stray capacitance of the GIS isolation knife switch and the grounding knife switch on the apparent discharge amount in the square wave calibration loop;

[0013] Step 3: When the transformer is working normally after being put into operation, the conductive connecting rod is in the GIS air chamber and is in a closed state, the isolating knife is closed, the grounding knife is disconnected, and the circuit breaker is closed. When the transformer needs a partial discharge test, the circuit breaker is disconnected and the transformer is powered off;

[0014] Step 4: The grounding knife switch is closed, and the grounding connecting piece is opened. The grounding connecting piece is connected to the grounding terminal through the fourth terminal for discharge;

[0015] Step 5: After the test circuit is built, perform square wave calibration on the test circuit. The calibration pulse generator is connected to the third terminal through the control unit. The control unit has no partial discharge and has no effect on the test circuit. Turn on the calibration pulse generator and inject the standard charge P2.

[0016] Step 6: In order to avoid the influence of stray capacitance of GIS isolation switch and grounding switch on the apparent discharge in the square wave calibration loop, the control unit makes a difference between P2 and △P to obtain the corrected apparent discharge P3, P3=P2-△P. At this time, the partial discharge analyzer obtains the corresponding calibration factor according to the corrected apparent discharge P3;

[0017] Step 7: Remove the calibration pulse generator, keep other conditions of the test circuit unchanged, and start the partial discharge test. If partial discharge occurs in the transformer, the discharge pulse signal of the partial discharge measuring instrument is multiplied by the corresponding scale factor in step 6, which is the apparent charge of the transformer. The discharge condition of the transformer is determined based on the charge size and phase.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The present invention does not need to remove the conductive connecting rod in the GIS air chamber, but uses the isolation switch and the grounding switch in the combined electrical system to complete the square wave calibration of the transformer partial discharge test circuit, thereby solving the problems of the GIS sealing component air chamber damage caused by the square wave calibration of the partial discharge test and the GIS air chamber being poorly sealed and affected by moisture during the guide rod reinstallation process, thereby improving the test efficiency. In addition, the control unit eliminates the influence of the GIS conductor on the square wave calibration and subsequent tests, thereby ensuring the test accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention will be further described below in conjunction with the accompanying drawings.

[0021] Figure 1 This is the schematic diagram of the frequency response analysis method;

[0022] Figure 2 The square wave calibration circuit in the first step of the calibration method of the present invention;

[0023] Figure 3 The square wave calibration circuit in the second step of the calibration method of the present invention;

[0024] Figure 4 The square wave calibration circuit for partial discharge test of transformer of oil and gas bushing structure of the present invention;

[0025] In the figure: 1 is a transformer, 2 is a high-voltage bushing, 3 is a GIS air chamber, 31 is a conductive connecting rod, 32 is an isolating switch, 33 is a grounding switch, 34 is a circuit breaker, 4 is a control unit, 5 is a calibration pulse sounder, 6 is a grounding connector, 7 is a high-voltage bushing end screen, 8 is a measuring impedance, 9 is a coaxial cable, 10 is a partial discharge analyzer, 11 is a first terminal, 12 is a second terminal, 13 is a third terminal, and 14 is a fourth terminal. DETAILED DESCRIPTION

[0026] As shown in the figure, the square wave calibration circuit of the transformer partial discharge test of the oil and gas casing structure includes: a transformer 1, a high-voltage bushing 2, a GIS air chamber 3, a control unit 4, a calibration pulse generator 5 and a grounding connector 6. The GIS air chamber 3 is connected to the transformer 1 through the high-voltage bushing 2. A high-voltage bushing end screen 7 is installed on the high-voltage bushing 2. The high-voltage bushing end screen 7 is connected in series with one end of the measuring impedance 8, and the other end of the measuring impedance 8 is connected to the partial discharge analyzer 10 through a coaxial cable 9; the GIS air chamber 3 includes: a conductive connecting rod 31, an isolating knife switch 32, a grounding knife switch 33 and a circuit breaker 34. One end of the isolating knife switch 32 is connected to the conductive connecting rod 31 through a first terminal 11. One end of the control unit 4 is connected to the calibration pulse generator 5, and the other end of the control unit 4 is connected to the third terminal 13 through a wire; the grounding terminal 6 is connected to the grounding terminal through the fourth terminal 14.

[0027] The calibration method of the square wave calibration circuit of the transformer partial discharge test of the oil and gas casing structure comprises the following steps:

[0028] Step 1: If Figure 2 As shown, during the infrastructure stage of the transformer 1, the GIS air chamber 3 where the conductive connecting rod 31 is located is not closed, one end of the conductive connecting rod 31 is connected to the high-voltage bushing 2 through the second terminal 12, and the other end of the conductive connecting rod 31 is connected to the isolation switch 32 through the first terminal 11. The conductive connecting rod 31 is in a disconnected state, one end of the measuring impedance 8 is connected in series with the high-voltage bushing end screen 7, and the other end is connected to the partial discharge analyzer 10 through the coaxial cable 9; when partial discharge occurs in the transformer 1, the transformer 1 will generate an instantaneous voltage change △u, and the pulse current generated by △u is measured. A pulse voltage is generated on the impedance 8, and the pulse voltage is transmitted to the partial discharge analyzer 10 via the coaxial cable 9. The partial discharge analyzer 10 collects, amplifies and displays the signal. The test circuit is built, and the square wave calibration of the test circuit is started. The calibration pulse generator 5 injects a standard charge through the second terminal 12, and the standard charge is set to P. The pulse voltage signal at both ends of the measuring impedance 8 is transmitted to the partial discharge analyzer 10. The partial discharge analyzer 10 obtains the charge calibration factor according to the injected known charge P and the amplitude of the discharge pulse of the partial discharge analyzer 10.

[0029] Step 2: If Figure 3As shown, the conductive connecting rod 31 is closed, the GIS air chamber where the conductive connecting rod 31 is located is closed, the isolation knife switch 32 and the grounding knife switch 33 are closed, the grounding connecting piece 6 is opened, and the third terminal 13 and the fourth terminal 14 are respectively provided on both sides of the grounding connecting piece 6. The calibration pulse generator 5 is connected to the third terminal 13, and the standard charge P is injected again. The partial discharge analyzer 10 obtains the apparent discharge amount P1 according to the charge amount scale factor in the first step; the standard charge P is subtracted from the apparent discharge amount P1, △P=P1-P, △P is the influence of the stray capacitance of the isolation knife switch 32 and the grounding knife switch 33 on the apparent discharge amount in the square wave calibration loop;

[0030] Step 3: If Figure 4 As shown, when the transformer 1 is put into operation and works normally, the conductive connecting rod 31 is in the GIS air chamber 3 and is in a closed state, the isolating knife switch 32 is closed, the grounding knife switch 33 is disconnected, and the circuit breaker 34 is closed. When the transformer needs a partial discharge test, the circuit breaker 34 is disconnected and the transformer 1 is powered off;

[0031] Step 4: the grounding switch 33 is closed, the grounding connecting piece 6 is opened, and the grounding connecting piece 6 is connected to the grounding terminal through the fourth terminal 14 for discharge;

[0032] Step 5: After the test circuit is built, square wave calibration is performed on the test circuit. The calibration pulse generator 5 is connected to the third terminal 13 through the control unit 4. The control unit 4 has no partial discharge and has no effect on the test circuit. The calibration pulse generator 5 is turned on and a standard charge P2 is injected.

[0033] Step 6: In order to avoid the influence of the stray capacitance of the isolation switch 32 and the grounding switch 33 on the apparent discharge in the square wave calibration loop, the control unit 4 makes a difference between P2 and △P to obtain a corrected apparent discharge P3, P3=P2-△P. At this time, the partial discharge analyzer 10 obtains the corresponding calibration factor according to the corrected apparent discharge P3;

[0034] Step 7: Remove the correction pulse generator 5, keep other conditions of the test circuit unchanged, and start the partial discharge test. If partial discharge occurs in the transformer 1, the discharge pulse signal of the partial discharge measuring instrument 10 is multiplied by the corresponding scale factor in the sixth step, which is the apparent charge of the transformer 1. The discharge condition of the transformer is determined based on the charge size and phase.

[0035] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Those familiar with the technology may modify or improve the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by those with ordinary knowledge in the technical field without departing from the spirit and technical ideas disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. Calibration method of square wave calibration circuit for partial discharge test of transformer with oil and gas casing structure, the calibration circuit includes: A transformer (1), a high-voltage bushing (2), a GIS air chamber (3), a control unit (4), a calibration pulse generator (5) and a grounding connector (6); the GIS air chamber (3) is connected to the transformer (1) via the high-voltage bushing (2); a high-voltage bushing end screen (7) is installed on the high-voltage bushing (2); the high-voltage bushing end screen (7) is connected in series with one end of a measuring impedance (8); the other end of the measuring impedance (8) is connected to a partial discharge analyzer (10); the GIS air chamber (3) comprises: a conductive connecting rod (31), an isolating knife switch (32), a grounding knife switch (33) and a circuit breaker (34); one end of the isolating knife switch (32) is connected via a first terminal (11) The isolating knife switch (32) is connected to one end of the conductive connecting rod (31), the other end of the isolating knife switch (32) is connected in series with the circuit breaker (34), the other end of the conductive connecting rod (31) is connected to the high-voltage bushing (2) through the second terminal (12), one end of the grounding knife switch (33) is connected to the connection point between the isolating knife switch (32) and the circuit breaker (34), the other end of the grounding knife switch (33) is connected to one end of the grounding connecting piece (6) through the third terminal (13), and the other end of the grounding connecting piece (6) is grounded; one end of the control unit (4) is connected in series with the calibration pulse generator (5), and the other end of the control unit (4) is connected to the third terminal (13) through a wire; It is characterized by comprising the following steps: Step 1: During the construction phase of the transformer (1), the GIS air chamber (3) where the conductive connecting rod (31) is located is not closed, one end of the conductive connecting rod (31) is connected to the high-voltage bushing (2) via the second terminal (12), and the other end of the conductive connecting rod (31) is connected to the isolating knife switch (32) via the first terminal (11). The conductive connecting rod (31) is in a disconnected state, one end of the measuring impedance (8) is connected in series with the high-voltage bushing end screen (7), and the other end is connected to the partial discharge analyzer (10) via a coaxial cable (9); when partial discharge occurs in the transformer (1), the transformer (1) generates an instantaneous voltage change △u, and the voltage generated by △u is The pulse current generates a pulse voltage on the measuring impedance (8), and the pulse voltage is transmitted to the partial discharge analyzer (10) via the coaxial cable (9). The partial discharge analyzer (10) collects, amplifies and displays the signal. After the test circuit is built, the square wave calibration of the test circuit begins. The calibration pulse generator (5) injects a standard charge through the second terminal (12), and the standard charge is set to P. The pulse voltage signal at both ends of the measuring impedance (8) is transmitted to the partial discharge analyzer (10). The partial discharge analyzer (10) obtains the charge calibration factor according to the injected known charge P and the amplitude of the discharge pulse of the partial discharge analyzer (10); Step 2: close the conductive connecting rod (31), seal the GIS air chamber where the conductive connecting rod (31) is located, close the isolation knife switch (32) and the grounding knife switch (33), open the grounding connecting piece (6), and respectively provide a third terminal (13) and a fourth terminal (14) on both sides of the grounding connecting piece (6). Connect the calibration pulse generator (5) to the third terminal (13), inject the standard charge P again, and the partial discharge analyzer (10) obtains the apparent discharge amount P1 according to the charge amount scale factor in the first step; make a difference between the standard charge P and the apparent discharge amount P1, △P=P1-P, △P is the influence of the stray capacitance of the isolation knife switch (32) and the grounding knife switch (33) on the apparent discharge amount in the square wave calibration loop; Step 3: When the transformer (1) is operating normally after being put into operation, the conductive connecting rod (31) is in the GIS air chamber (3) and is in a closed state, the isolating knife switch (32) is closed, the grounding knife switch (33) is disconnected, and the circuit breaker (34) is closed. When the transformer needs a partial discharge test, the circuit breaker (34) is disconnected and the transformer (1) is powered off; Step 4: the grounding knife switch (33) is closed, the grounding connecting piece (6) is opened, and the grounding connecting piece (6) is connected to the grounding terminal via the fourth terminal (14); Step 5: After the test circuit is built, square wave calibration is performed on the test circuit. The calibration pulse generator (5) is connected to the third terminal (13) through the control unit (4). The control unit (4) has no partial discharge and has no effect on the test circuit. The calibration pulse generator (5) is turned on and a standard charge P2 is injected. Step 6: In order to avoid the influence of the stray capacitance of the isolation switch (32) and the grounding switch (33) on the apparent discharge in the square wave calibration loop, the control unit (4) makes a difference between P2 and ΔP to obtain a corrected apparent discharge P3, where P3=P2-ΔP. At this time, the partial discharge analyzer (10) obtains a corresponding calibration factor according to the corrected apparent discharge P3; Step 7: Remove the calibration pulse generator (5), keep other conditions of the test circuit unchanged, and start the partial discharge test. If partial discharge occurs in the transformer (1), the discharge pulse signal of the partial discharge measuring instrument (10) is multiplied by the corresponding scale factor in step 6, which is the apparent charge of the transformer (1). The discharge condition of the transformer is determined based on the charge size and phase.

2. The calibration method of the square wave calibration circuit for partial discharge test of a transformer with an oil and gas casing structure according to claim 1 is characterized in that: The measuring impedance (8) is connected in series with the partial discharge analyzer (10) via a coaxial cable (9).

3. The calibration method of the square wave calibration circuit for partial discharge test of a transformer with an oil and gas casing structure according to claim 1 is characterized in that: The grounding connecting piece (6) is connected to the grounding terminal via a fourth connecting post (14).

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