Method for detecting partial discharge of ultra / extra-high voltage transformer

Abstract

The invention belongs to the field of transformer operation and maintenance detection, and relates to an ultra / extra-high voltage transformer partial discharge detection method, which comprises the following steps of: sleeving a high-frequency current transformer at a bushing capacitor end screen and a high-voltage neutral point of a tested transformer, connecting the high-frequency current transformer with an amplitude modulation and phase modulation unit, and connecting the amplitude modulation and phase modulation unit with a partial discharge detection terminal, a square-wave generator is connected in series with a high-voltage terminal of the tested transformer; interference pulses are injected through the square-wave generators on each phase branch, the positions of amplitude modulation and phase modulation knobs corresponding to the high-frequency current transformers are adjusted, so that the discharge capacity indication of the partial discharge detection terminal is minimum, finally, interference pulses are injected through all the square-wave generators at the same time, the positions of the amplitude modulation and phase modulation knobs corresponding to the high-frequency current transformers are adjusted again, and the discharge capacity indication of the partial discharge detection terminal is minimum. The indication of the partial discharge detection terminal is still maintained to be minimum; and completing partial discharge detection of the tested transformer. According to the invention, the signals among the phase terminals are balanced through the amplitude modulation and phase modulation unit, so that the purpose of counteracting external interference signals is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of transformer operation and maintenance detection, and relates to a partial discharge detection method for ultra-high voltage and extra-high voltage transformers that can effectively eliminate external interference signals on site, and is particularly suitable for the partial discharge detection of large-capacity ultra-high voltage and extra-high voltage transformers in on-site operation. Background Art

[0002] With the rapid development of China's economic construction, the requirements for the safety and reliability of power grid operation are also getting higher and higher. As the core equipment of the power grid, the operation state of power transformers will directly affect the safety and reliability of the power grid.

[0003] Research results show that the long-term operation life of ultra-high voltage and extra-high voltage transformers under working voltage is closely related to whether there is partial discharge in their insulation. In order to ensure the safe and reliable operation of such transformers throughout their life cycle, on-line partial discharge detection devices are often installed on ultra-high voltage and extra-high voltage transformers as real-time monitoring means during operation to analyze and judge the internal partial discharge level and change trend of the transformers online. However, due to the very complex partial discharge interference sources in the on-site operation environment of transformers, and in addition, at present, domestic on-line partial discharge detection devices for transformers are produced by different manufacturers, lacking unified communication protocols and manufacturing standards, and the reliability of partial discharge detection devices and the accuracy of detection data are still not convincing. Therefore, how to effectively distinguish the internal partial discharge signals and external interference signals of ultra-high voltage and extra-high voltage transformers in the operating state, so that the partial discharge detection device can play a full role in the transformer equipment condition maintenance work, is the main technical problem that needs to be solved urgently at present. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides a partial discharge detection method for ultra-high voltage and extra-high voltage transformers. The technical solution adopted by the present invention is as follows: A partial discharge detection method for ultra-high voltage and extra-high voltage transformers, which suppresses external interference signals through the adjustment of an amplitude modulation and phase modulation unit, includes the following steps: In the power-off state, high-frequency current transformers are sleeved at the capacitive end screen of the high-voltage side bushing and the high-voltage neutral point of the transformer under test, the high-frequency current transformers are electrically connected to the input end of the amplitude modulation and phase modulation unit, the output end of the amplitude modulation and phase modulation unit is electrically connected to the partial discharge detection terminal, and a square wave generator is connected in series to each high-voltage terminal of the transformer under test; First, fix the amplitude and phase modulation knob corresponding to the high-frequency current transformer corresponding to the high-voltage neutral point to the position where the background noise of the measurement signal of the partial discharge detection terminal is relatively the lowest. Then, inject an interference pulse through the corresponding square wave generator on each phase branch in turn, and adjust the position of the amplitude and phase modulation knob corresponding to the corresponding high-frequency current transformer, that is, adjust the pulse signal conversion coefficient of the high-frequency current transformer, so that the discharge quantity indication of the partial discharge detection terminal is the smallest. Finally, inject interference pulses through all the square wave generators at the same time, and adjust the position of the amplitude and phase modulation knob corresponding to each high-frequency current transformer again, that is, adjust the pulse signal conversion coefficient of the high-frequency current transformer, so that the indication of the partial discharge detection terminal still remains the smallest, thus suppressing the external interference signal; After the test transformer is powered on, the pulse signal measured by the high-frequency current transformer enters the partial discharge detection terminal through the amplitude and phase modulation unit for display, and the partial discharge detection of the test transformer is completed.

[0005] Preferably, the input end of the amplitude and phase modulation unit is electrically connected to the high-frequency current transformer through a coaxial signal cable, and the output end of the amplitude and phase modulation unit is electrically connected to the partial discharge detection terminal through a coaxial signal cable.

[0006] Preferably, the maximum measured current of the high-frequency current transformer is 300000A, and the maximum measured frequency is 13MHz.

[0007] Advantages of the present invention: The present invention utilizes the operating voltage of the power grid, without using other high-voltage equipment, and balances the signals between each phase terminal through the amplitude and phase modulation unit, so as to achieve the purpose of canceling the external interference signal and accurately detecting the internal partial discharge of ultra-high voltage and extra-high voltage transformers. Description of the drawings

[0008] The drawings are used to provide a further understanding of the present invention, and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention, and do not constitute a limitation to the present invention. In the drawings: Figure 1 It is a schematic diagram of the principle of adjusting and suppressing interference signals through the amplitude and phase modulation unit in the embodiment of the present invention. Detailed implementation manners

[0009] Next, the technical solutions of the present invention will be described clearly and completely in conjunction with the drawings. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments.

[0010] Ultra-high and extra-high voltage transformer partial discharge detection method. Taking a three-phase ultra-high and extra-high voltage transformer as an example, in order to avoid magnetic saturation caused by strong power frequency current, a large-capacity high-frequency current transformer is used as the measuring device. The large-capacity high-frequency current transformer can adapt to large currents without saturation. The highest measuring current of the high-frequency current transformer is 300,000 A, and the highest measuring frequency is 13 MHz. The high-frequency current transformer is sleeved and installed at the bushing capacitance end screen and the high-voltage neutral point of the ultra-high and extra-high voltage transformer. The input end of the amplitude modulation and phase modulation unit is electrically connected to the high-frequency current transformer through a coaxial signal cable, and the output end of the amplitude modulation and phase modulation unit is electrically connected to the partial discharge detection terminal through a coaxial signal cable. The pulse signals measured at each high-frequency current transformer measurement point enter the partial discharge detection terminal through the amplitude modulation and phase modulation unit. The amplitude modulation and phase modulation unit is a signal processing unit in the existing partial discharge measurement technology. The partial discharge detection terminal can adopt a partial discharge measuring instrument with the model of TWPD-2E.

[0011] The principle of suppressing interference signals through the adjustment of the amplitude modulation and phase modulation unit is as Figure 1 shown, Figure 1 in which, CT is an actual electronic component, and CT0, CT1, CT2, and CT3 are high-frequency current transformers corresponding to the high-voltage neutral point and the high-voltage three-phase terminals respectively; E0 represents the partial discharge inside the test transformer, and E0 is the partial discharge potential of the test transformer; E1, E2, and E3 represent the external interference signals entering the three-phase terminals of the transformer, and E1, E2, and E3 are the interference potentials corresponding to the three-phase terminals of the test transformer respectively; Z1, Z2, and Z3 are the equivalent impedances of the propagation paths of the external interference signals entering between the three-phase terminals of the test transformer respectively; 0 is the high-voltage neutral point of the test transformer; 1, 2, and 3 are the high-voltage A, B, and C three-phase terminals of the test transformer; K0, K1, K2, and K3 are the pulse signal transformation coefficients of the high-frequency current transformers CT0, CT1, CT2, and CT3 respectively.

[0012] When there is partial discharge inside the test transformer and external interference signals exist, the sum value of the output signals of the four high-frequency current transformers is: I = K0I 00 + K1I 01 + K2I 02 + K3I 03 + Y1(U 11 + U 12 + U 13 ) + Y2(U 21 + U 22 + U 23 ) + Y3(U 31 + U 32 + U 33 ) In the formula: I00 、I 01 、I 02 、I 03 are the current components of E0, E1, E2, and E3 at the high-voltage neutral point, respectively; U 11 、U 12 、U 13 are the voltages of E1, E2, and E3 at terminal 1, respectively; U 21 、U 22 、U 23 are the voltages of E1, E2, and E3 at terminal 2, respectively; U 31 、U 32 、U 33 are the voltages of E1, E2, and E3 at terminal 3, respectively; Y1, Y2, and Y3 are the admittances depending on the internal impedance of the transformer under test and the transformation coefficient of the high-frequency current transformer.

[0013] The key to suppressing external interference signals is to make Y1, Y2, Y3 = 0, that is, to make I = K0I 00 +K1I 01 +K2I 02 +K3I 03 , at this time, the total current signal I only reflects the partial discharge inside the transformer under test and does not reflect external interference signals. The physical meaning of the calculation formula of I refers to the sum of the currents measured by four high-frequency current transformers, where K0I 00 +K1I 01 +K2I 02 +K3I 03 is the current measured by CT0 on the high-voltage neutral point side, and Y1(U 11 +U 12 +U 13 ) is the current measured by CT1, Y2(U 21 +U 22 +U 23 ) is the current measured by CT2, and Y3(U 31 +U 32 +U 33) is the current measured by CT3. During actual testing, the external interference potentials E1, E2, and E3 always exist, and the currents generated by them also always exist. They are mainly reflected in the current measured by CT0 on the neutral point side. However, on the high-voltage terminal side CT1, CT2, and CT3, they are suppressed through the previous adjustment and thus not reflected. So during actual measurement, it is only necessary to detect the pulse signals of CT1, CT2, and CT3 on the high-voltage terminal side. If there is no pulse signal, there is no partial discharge inside the transformer under test. If there is a pulse signal, it must be internal partial discharge. The CT0 signal on the neutral point side only exists as an auxiliary detection channel to confirm the existence of external interference signals from the side.

[0014] To make Y1, Y2, and Y3 = 0, it can be achieved by adjusting the values of K0, K1, K2, and K3. The specific adjustment method is as follows: When the transformer under test is in the power-off state, configure high-frequency current transformers on the transformer under test according to the above method, and connect a square wave generator in series on each of the high-voltage A, B, and C phase terminals of the transformer under test to simulate external discharge signals. First, fix the amplitude modulation and phase modulation knob corresponding to the high-frequency current transformer CT0 corresponding to the neutral point 0 at a certain position (this position is based on the relatively lowest background noise of the measurement signal of the partial discharge detection terminal). Then, inject an interference pulse through the corresponding square wave generator on each three-phase terminal in turn, and adjust the position of the amplitude modulation and phase modulation knob of the high-frequency current transformer corresponding to the corresponding three-phase terminal respectively to make the discharge amount indication of the partial discharge detection terminal the smallest (close to zero). Because the amplitude modulation and phase modulation unit is an integrated device with multiple measurement output channels, the outputs of CT0, CT1, CT2, and CT3 are respectively connected to the measurement output channels of the amplitude modulation and phase modulation unit, and K0, K1, K2, and K3 are the adjustment transformation coefficients of each channel respectively. K0 needs to be simply adjusted to make the background noise of the measurement signal of the CT0 channel displayed on the partial discharge detection terminal the relatively lowest. Finally, use three square wave generators to inject interference pulses simultaneously on the three three-phase terminals, and then appropriately adjust the position of the amplitude modulation and phase modulation knob corresponding to each high-frequency current transformer to make the indication of the partial discharge detection terminal still maintain the minimum. In this way, the partial discharge detection terminal has anti-interference performance, and at this time, it can be considered that the external interference signal has been suppressed. The K value is mainly adjusted through the amplitude modulation and phase modulation knob of the amplitude modulation and phase modulation unit, and finally makes the amplitude displayed on the partial discharge detection terminal maintain the minimum. This amplitude modulation and phase modulation unit belongs to the existing application technology of signal adjustment.

[0015] After the transformer under test is powered on, the pulse signals measured by CT0, CT1, CT2, and CT3 enter the partial discharge detection terminal through the amplitude modulation and phase modulation unit for display, and the partial discharge detection of the transformer under test is carried out. At this time, the interference of external signals is excluded.

[0016] In the embodiments of the present invention, the technical features not described in detail are all prior art or conventional technical means, and will not be elaborated herein.

[0017] Finally, it should be noted that the above embodiments are only specific implementation manners of the present invention, used to illustrate the technical solutions of the present invention, rather than limiting it. The protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any person skilled in the art within the technical scope disclosed by the present invention can modify the technical solutions recorded in the foregoing embodiments, or can easily think of changes, or perform equivalent replacements on some of the technical features; and these modifications, changes or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be covered within the protection scope of the present invention.

Claims

1. A method for detecting partial discharge in ultra-high voltage and extra-high voltage transformers, which suppresses external interference signals through the adjustment of an amplitude and phase modulation unit, is characterized in that The steps include: In a power-off state, high-frequency current transformers are sleeved at the capacitance end screen of the high-voltage side bushing and the high-voltage neutral point of the transformer under test. The high-frequency current transformers are electrically connected to the input end of the amplitude modulation and phase modulation unit, the output end of the amplitude modulation and phase modulation unit is electrically connected to the partial discharge detection terminal, and a square wave generator is connected in series to each high-voltage terminal of the transformer under test. First, fix the amplitude modulation and phase modulation knob corresponding to the high-frequency current transformer corresponding to the high-voltage neutral point at the position where the measured signal background noise of the partial discharge detection terminal is relatively the lowest. Then, inject an interference pulse through the corresponding square wave generator on each phase branch in turn, and adjust the position of the amplitude modulation and phase modulation knob corresponding to the corresponding high-frequency current transformer, that is, adjust the pulse signal transformation coefficient of the high-frequency current transformer, so that the discharge quantity indication of the partial discharge detection terminal is the smallest. Finally, inject interference pulses through all the square wave generators at the same time, and adjust the position of the amplitude modulation and phase modulation knob corresponding to each high-frequency current transformer again, that is, adjust the pulse signal transformation coefficient of the high-frequency current transformer, so that the indication of the partial discharge detection terminal still remains the smallest, thus suppressing external interference signals. After the transformer under test is powered on, the pulse signal measured by the high-frequency current transformer enters the partial discharge detection terminal through the amplitude modulation and phase modulation unit for display, completing the partial discharge detection of the transformer under test.

2. The partial discharge detection method for ultra-high voltage and extra-high voltage transformers according to claim 1, wherein The input end of the amplitude modulation and phase modulation unit is electrically connected to the high-frequency current transformer through a coaxial signal cable, and the output end of the amplitude modulation and phase modulation unit is electrically connected to the partial discharge detection terminal through a coaxial signal cable.

3. A partial discharge detection method for ultra-high voltage and extra-high voltage transformers according to claim 2, characterized in that, The highest measured current of the high-frequency current transformer is 300000A, and the highest measured frequency is 13MHz.

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