School of Electrical Engineering, Xi'an Jiaotong University, Xi'an 710049, China Wang Guoli, Hao Yanzhong, Jia Zhidong, Li Yanming, Xi'an Transformer Factory (Xi'an 710077, China) Zhang Jiangang's broadband measurement system extracts its discharge pulse shape. The analysis shows that the discharge in the transformer oil is not stable, and there is an oscillation component in the discharge pulse; there are differences in the characteristic parameters of different discharge waveforms, and these characteristics can be used as the basis for the identification of the discharge type. Abstract 0 Introduction The partial discharge duration of the power transformer insulation system is very short, the pulse width is ns, and its corresponding frequency domain can be >1GHz. However, the commonly used current pulse method response frequency for partial discharge detection is usually the wideband measurement system developed in this paper. The characteristics of the discharge pulse of several typical transformer partial discharge models are analyzed to distinguish different types of discharges and establish a corresponding transformer partial discharge identification system. 1 The typical partial discharge model of a power transformer The partial discharge of a power transformer in operation : 1) Discharge of the oil gap in the middle of the oil separator in the winding; 2) Discharge in the oil gap at the end of the winding; 3) Discharge of the oil gap in contact with the insulated wire and electrical paper (lead insulation, lap joint insulation); 4) Lead wire connection, etc. Partial discharge in oil-paper insulation; 5) Oil gap discharge between coils (longitudinal insulation); 6) Partial breakdown of turn-to-turn insulation; 7) Flash discharge along the surface of electrical paper. Several discharge models have been designed on the discharge sites of some oil gaps, air chessboard air gaps, conductor conductor corners with suspended potentials, and solid surfaces. The insulation board was placed in a 105C oven for 6 days, followed by vacuum immersion. More than 5d oil; edges and corners of the cardboard smooth polished, no sharp corners or burrs.
For the simulation model of the corona discharge in the air, see (a) The needles and plates are all standard copper electrodes with a spacing of 25 mm. 1 2 The internal air gap discharge model of the internal discharge insulation board is shown in (b) The model medium is 2.5 mm thick in two layers. The oil-impregnated insulation board is sandwiched with a 1. 0mm thick insulation board with a diameter of 20. 0mm through holes. To prevent the transformer oil from entering the air gap and affect the measurement result, a very thin epoxy resin is used between the insulation boards. Adhesive.
1.3 surface discharge board surface discharge model see (c) high and low voltage electrodes are 0.2mm thick copper sheet, polished around the copper sheet and a guide turtle two electrodes with epoxy resin adhesive fixed on 2.5mm thick insulation board The distance between the high and low voltage electrodes is 15. 4 oil wedge discharge there is no oscillation, its rising edge ~ 10ns, the total pulse duration of 100 ~ 120ns, the falling edge is ladder-like waveform characteristics and band within the scope of the signal extraction R is basically purely resistive. It is input to the TDS680B digital oscilloscope through 50 RF coaxial cable. The input impedance of the oscilloscope is 50-speed, DC-coupled, and matched with the outgoing cable of the signal. 3 Measurement result of the discharge pulse and analysis 1 Performance of the system Verification The measurement system performance test uses the standard corona model in air.
At the voltage of 5kV, negative corona discharge is mostly used. Occasionally, very few waveforms have the same positive polarity discharge. For 6.5kV voltage and more, positive corona discharge is the stable discharge waveform measured at 8.0kV. Under the same applied voltage, the repeatability of the positive and negative polarity discharge waveforms is good, and the amplitude is basically the same. From the (a) positive pulse of the corona discharge (b) the negative pulse of the corona discharge at 0 kV, the corona discharge pulse waveform (b) at 0 kV shows that the negative polarity discharge is an oscillating waveform with the maximum peak at the first wave, The falling edge of this wave is about 4ns, and the total pulse duration is ~120ns. The positive corona discharge has two kinds of waveforms, one is basically the same as the negative polarity (the negative discharge waveform at this time is the same as the waveform at lower voltage, only Larger amplitude); Another feature such as (a), waveform base 3.2 typical discharge characteristics comparison Several discharge models and their waveform parameters can be known: Partial discharge is very random, comparing different voltage levels and discharge amplitude comparison Arbitrary, so measuring the characteristics of heavy discharge waveforms, there is no excessive attention to the characteristics of the amplitude.
Internal discharge of 5kV voltage is low and the amplitude is very small. The amplitude of the discharge is strong as the voltage rises. The pulse amplitude is also large, but its waveform shape is almost constant, and the discharge is very unstable. When the voltage reaches 20.0kV, it discharges more. The discharges with visible positive and negative polarities are basically the same. Oscillating Waveforms The peaks on the first wave are the interference components. Wavelet denoising can be used to eliminate the intensity of discharge along the surface of the insulating paper in the oil. Partial discharge Occurs when the contact between the cardboard and the tip of the electrode leaves a dendritic carbonized trace. The discharge was measured at a voltage of 3.5 kV. The waveform was relatively stable, and the discharge was strong as the voltage increased, but the waveform was almost constant. 6. There is more discharge at 0kV, the waveforms are seen, the positive and negative polarity discharges are basically the same oscillating waveform; the peak of the 12th wave peak is almost the same; the discharge waveform is not smooth, each waveform is superimposed on the larger ground, etc. The oscillation component of the amplitude, which has obvious areas with other discharges. 1(a) Positive pulse of surface discharge (b) Negative pulse of surface discharge 60kV Insulation surface discharge pulse waveform has great randomness, discharge is not quite Stable, difficult to capture the pulse waveform waveform measured 15.0kV oil wedge discharge waveform see, see the positive and negative polarity discharges are basically the same oscillation waveform, the maximum peak appears on the first peak oil wedge discharge waveform similar to internal discharge However, its waveform parameters are significantly different from internal discharges. After the discharge occurs, it will quickly disappear. This may be caused by the bubbles in the oil bursting at a higher voltage, which causes the discharge to terminate, and the interference burrs in the oil wedge waveform may be removed by wavelet denoising.
(a) positive pulse in the discharge of the oil gap (b) negative pulse in the discharge of the oil gap 15.0kV discharge in the oil gap Pulsed discharge in the oil The intensity of the levitation discharge in the oil is large. After the discharge occurs, the part where the cardboard touches the tip of the levitation electrode will remain Under the carbonization trace, a positive pulse discharge occurred at a voltage of 5 kV, and a negative pulse discharge occurred at 6.0 kV, and the discharge was unstable. The discharge is obviously stronger with the increase of the voltage, but the discharge waveforms when the waveform parameters basically do not change at 8.0 kV are seen, and the positive and negative polarity discharges are also basically the same oscillation waveform, and the maximum peak appears on the first peak, and the waveform parameters Distinguishes its difference from the chessboard obviously (a) the positive pulse of the floating discharge (b) the negative pulse of the floating discharge The pulse waveform of the floating discharge of 8.0kV is the characteristic of the waveform of all kinds of discharges in a comprehensive way. The author has compiled a special calculation program for the waveform. After denoising, extract the characteristic parameters of each waveform. The results are shown in Table 1 (taking into account the similarity of positive and negative pulses, so only the positive pulses of each discharge are processed). Corresponding to each type of discharge, multiple models were made. Each model was made. Multiple sets of experiments Table 1 Characteristic parameters of various discharge waveforms ns discharge type internal discharge surface discharge oil wedge discharge suspension discharge where the pulse rising edge time tr is from 10% of the maximum amplitude to the maximum amplitude of 9 (% at the end The time of the pulse; the pulse falling edge time td is the time from the point where the maximum amplitude reaches 90% to the time when the maximum amplitude ends 10%. The amplitude pulse duration t5* is the maximum amplitude rising from the rising edge to 50%. The pulse wave 10% maximum amplitude pulse duration tw from the beginning to the end of the falling edge is defined as the same, except that the 50% maximum amplitude is replaced with the 10% maximum amplitude.The total duration including the oscillating wave ttota It is the time from the rising edge of the pulse to the time when there is almost no oscillation.
As can be seen from the table, the characteristic parameters of the discharge pulse waveforms of the different partial discharge models are quite different. By synthesizing the above parameters, a large number of experimental verifications are performed, and the waveform characteristic parameters corresponding to each discharge are extracted as the identification samples for simple discharge. Type identification another IJ. 4 conclusions The discharge in the transformer oil is not stable, and its discharge pulse has an oscillation component. The waveform of the discharge pulse rises (falls). The difference in characteristics of the time, waveform duration, and oscillation component is the use of discharge pulse identification. The type of discharge provides an interference component that can contain discharge pulse measurements. It has an effect on some waveforms. It is necessary to perform special processing on the waveform first, and then analyze the waveform characteristics. The measurement system provides valuable value for future fingerprint diagnosis and pattern recognition applications. Data can meet the actual measurement requirements
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