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Design and analysis of coupling device in partial discharge detection

This paper presents design and analysis of a coupling device which is used for measurement of PD signal and AC voltage as the conventional partial discharge testing according to IEC 60270. The remarkable feature of the developed coupling device is the accuracy in PD signal measuring and the ability in eliminating noise signal Therefore, In the AC signal measuring part, the proper impedance was chosen to achieve appropriate voltage divide ratio and accuracy in PD signal measuring. In PD signal measuring part, the value of the components must be chosen properly to achieve the determined Upper and Lower limit frequency. In this part, noise signal elimination must be considered to gain less effect to PD signal, otherwise the PD signal waveform will distort. From intensive study, three different coupling device circuits were designed and constructed. The circuit of the first and second coupling device are collected from literatures. It is found that the PD signal was interfered by the testing AC voltage signal. Therefore, the last one was developed to overcome this problem. The last developed coupling device has the lower and the upper cut off frequencies of 30 kHz and 20 MHz, respectively. The results of the three coupling devices are compared to that of the commercial coupling device in the HV laboratory of King Mongkut's Institute of Technology Ladkrabang. The developed coupling devices can be used in conventional PD testing according to IEC 60270. The comparisons of the simulated and experimental results show that the performance of the developed coupling devices as same as the commercial one.