| The insulation reliability of electrical installations is directly related to the stable operation of the power system, and Partial Discharge(PD) is not only a sign of electrical equipment insulation fault, but also a cause of insulation fault. Therefore, using efficient techniques to detect PD and using corresponding fault diagnosis in electrical equipment has been the focus of research in this field. Ultra High Frequency(UHF) detecting technology is the widely used way in PD detection, but there is no proper measuring criterion of UHF, and the calibration of UHF signal cannot be realized, which heavily constrains the full utilization of UHF technique. Based on the research status of such problem, a further study of UHF detecting technology is involved in this paper, an UHF signal simulation source is designed which can be used in the calibration of UHF detecting system at the same time. The main achievements are as follows.On the basis of electromagnetic radiation theory and the characteristics of UHF PD, after the in-depth study of active radiant and electric dipole radiation, the mathematical expression between the UHF electromagnetic energy and the current source could be obtained. Further, coupled with antenna radiation theory and rationale of impulse current method, results indicated that there is a quadratic function relationship between UHF electromagnetic energy and discharge quantity in both far-field and near-field measurement. Meanwhile, the experimental platform is set up, the UHF electromagnetic energy and apparent discharge of four typical PD are extracted, and corresponding spectrograms of PD areestablished. Plus, the quadratic function relationship between UHF electromagnetic energy and discharge quantity has been substantiated by experiment results, and a theory and method of calibration of discharge quantity by waveform of UHF PD are developed.Directing at the problem of current UHF PD signal simulator that its parameters cannot be adjusted, this paper comes up with a method to generate UHF signals by multi-channel signal synthesizing based on analyses of magnitude-frequency and phase-frequency characteristics of PD signal, and a related device simulating actual signals is designed. At the same time, the principle and system structure of this device is elaborated, and actual measurement analysis is carried out with respect to this device’s performance. The experiment results show that the simulated signal owns the time domain features at high frequency and phase characteristics at power frequency of the UHF PD signal. Besides, the bandwidth of the output electromagnetic signal is ranging from 0.3GHz to 1.429 GHz and the phase distribution characteristic is similar to the power frequency signal; the signal frequency, output power and φ-q、φ-n spectrograms can be adjusted smoothly; The real output power is high enough up to 25 d Bm. This simulator build up discharge type database by obtaining real PD signals, as well as modify and add field data of PD conveniently. Thus, in this way, this device can simulate various types of PD UHF signals efficiently. In addition, the sensitivity of measurement sensor has been studied by this simulator, showing such signal simulator is suited for the calibration of UHF detecting system.In a summary, through combing theory with related experiments, this paper discusses various factors which influence the sensitivity calibration of UHF signal, including the features of discharge source, the transmission characteristics of UHF signals and the performance of measurement sensor. Laboratory finds obtained suggest that the reliability of the relationship between UHF PD signal and apparent discharge quantity is different when it comes to disparate insulating defects; secondly, the UHF signalswith different frequencies have non-linear attenuation with different slopes when the measured distances and angles are changing; thirdly, the sensor’s bandwidth is dependent on the bandwidth of UHF signal energy in effective frequency range, the variation pattern of the UHF signal strength basically is consistent with that of the sensor’s gains and standing-wave ratio. Finally, this paper believes that by meas of an in-depth analysis of factors affecting the calibration of UHF signals, it could make certain contributions to the research of UHF signal calibration in both a comprehensive and systematic way. |
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