Partial discharge monitoring of power transformers using UHF sensors. Part I: sensors and signal interpretation
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Determining whether power transformers are suffering from internal arcing or dangerous levels of partial discharge (PD) is important because failure without warning can result in damage to neighboring equipment, customer dissatisfaction, disruption to economic activity, and the imposition of regulatory fines. This paper provides an overview of the excitation of UHF signals by PD inside transformers. The use of externally mounted sensors has been outlined, and the structure of a dielectric window that can be constructed on an inspection hatch has been outlined. Attenuation of UHF signals propagating inside a transformer tank has been shown to be relatively low. A new approach to locating PD sources in three dimensions has been presented, based on using a numerical model of the transformer materials, which defines electromagnetic propagation velocities on a mesh of 5-cm sub-cells. The concepts of the propagation-velocity matrix (PVM) and the propagation-time matrix (PTM) were thereby introduced. Once the PD source has been located to a specific region of the transformer, the PVM might be used to index a database of physical descriptions of the transformer that could provide additional information to assist with diagnosis.Keywords:
Electric arc
In order to evaluate the partial discharge Ultra High Frequency (UHF) detection device, the author conducted a laboratory simulation experiment on UHF Partial Discharge (PD) online monitoring system. The UHF signal is simulated by the pulse signal generated by the ns steep pulse generator. By comparing the characteristics of the generated UHF signal with the spectral features detected by the UHF partial discharge on-line monitoring system, the detection capability, pattern recognition ability, and anti-jamming capability of the UHF partial discharge on-line monitoring system are measured and evaluated. Through the research on the testing and evaluation of power equipment, it can ensure the normal operation of the partial discharge online monitoring system.
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We have designed and manufactured four types of typical defects found in power transformers to simulate partial discharge(PD) in oil insulated power transformers. Stable PD signals were generated by applying AC voltages on to the PD cells. We measured spectral response of PD signals from these defects using our Ultra-high frequency(UHF) PD measuring system and apparent discharge using IEC60270 PD detector simultaneously. Partial discharges from the defects in oil generated well detectable UHF signal up to about 2 GHz. UHF PD patterns were recorded and analyzed for each defect types. The phase resolved partial discharge(PRPD) patterns of defect obtained from UHF range were different from each other. The patterns of UHF PD signals were also different from those obtained from that of conventional method. Type of defect could be identified by obtaining PRPD patterns.
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Abstract In this paper, the causes of partial discharge in GIS and the existing detection methods are described, and signal processing and pattern recognition method of insulation defect in UHF detection method are introduced emphatically.
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GIS partial discharge detection is a scientific and effective way for insulation condition monitoring.A GIS model and the detection system based on UHF method has been set up.Several typical GIS partial discharge is studied and using power phase analysis a detailed analysis of characteristics under different voltage is made;Combined with conventional partial discharge detection method,the partial discharge quantity estimation of UHF signal is also made.All of these lay a foundation for the study of partial discharge intelligent recognition and the relationship between UHF signal and partial discharge quantity to improve the engineering utility of UHF partial discharge detection.
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This paper introduces GIS partial discharge detection by M-series ultra-high frequency(UHF) sensors made by Tsinghua University.The principle,characteristics and waveforms of GIS partial discharge under different discharge gaps are provided.Practical examples demonstrate that the method is convenient,accurate and effective.
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The possibility of UHF (ultra high frequency) method used in partial discharge detection in GIS is analyzed, and the UHF sensor, simulating passive filter, detecting the method of wide-band and narrow-band are studied, in order to avoid interferes of low-frequency. The authors develop an inner loop sensor in GIS model and investigate UHF method detecting partial discharge in GIS. The results indicate that the UHF system of detecting PD can effectively detect partial discharge and avoid outer corona interfere and Periodic pulse interfere. At the same time, narrow-frequency PD detection is an effective detection method to restrain UHF interferes.
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In order to explore the sensitivity and the parameters of relationship among the electrical research association(ERA),the ultra high frequency(UHF) and the UV imaging technology in partial discharge detection,using the simulation GIS to establish a set of partial discharge detection platform.The ERA,the UHF and UV imaging technology are applicated to carry out the measurement of partial discharge activity under several typical model of simulation GIS cavity,access to a large number of experimental data and maps.The studies show that the sensitivity of the ERA is the highest among them,the sensitivity of the UHF is higher than UV imaging technology.And the three kings have same trend reflecting the change of PD level,but there is not direct linear relationship among them.In order to accurately determine the severity of PD,a variety of detection method be should used.
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Several kinds of GIS partial discharging detection methods are introduced simply,and the UHF detection method is introduced specifically.The detecting,interfering and positioning principles of UHF are illustrated respectively.Through comprehensive analysis on waveform features,phase features and frequency features of partial discharge,the features of all kinds of partial discharge phenomena are summarized.Finally,UHF detection method was applied on partial discharge and the testing results were analyzed.
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Apparent discharge quantity is usually recognized as judgement standard for severity of partial discharge in the field of electrical equipment insulation diagnosis. In recent years, the ultra-high-frequency (UHF) method has been widely used due to its unique advantages on on-line monitoring and positioning, but the relationship between UHF partial discharge signals and discharge quantity is still a difficult problem of UHF method. In order to research relationship between UHF partial discharge signals and discharge quantity in GIS, a large number of experiments, based on four kinds of typical insulation defects in the GIS, are carried out. Degree of correlation, between parameters including UHF energy, quadratic integral, peak voltage, peak-to-peak value, wave area and discharge quantity, the square of discharge quantity, is studied based on coefficient of determination. The experimental results show there is linear relation between UHF signal energy and the square of discharge quantity with high related degree.
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In this study, to improve the sensitivity and accuracy of the detection of surface partial discharge (PD) in gas insulation switchgears (GISs), a combination of ultra‐high frequency (UHF) and optical methods is proposed based on an integrated sensor. The PD triggered by a fixed metal needle defect attached to the spacer is detected from PD inception to flashover in a real GIS. The characteristics of UHF and optical signals under different applied voltages are compared and analysed in terms of PD waveform, Phase Resolved Partial Discharge (PRPD) pattern, PD count and amplitude. The results show that the surface discharge process can be precisely divided into three stages according to the combined characteristics of the UHF and optical signals. The comparison of the two detection methods shows that the optical method can detect the weak avalanche PD under low voltage while UHF cannot, so it can detect more PDs than UHF method in an AC cycle. In addition, with the deterioration of solid insulation material, the amplitude of the optical signal increases significantly while the amplitude of the UHF signal only increases slightly.
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