Design of matching impedance for ultra wideband partial discharge detection

Abstract

Partial Discharge (PD) detection in the ultra wideband (UWB) at frequency from 100 kHz up to and above 1 GHz give some benefits especially for nature observation of PD pulse shape and frequency spectrum. One of the methods to measure the UWB PD signal is a method of impedance matched. Impedance of 50 ohm corresponding to the characteristic impedance of the coaxial cable and the internal impedance of oscilloscope is used as a coupling device to maximize the power transfer of PD current so that it can obtain real PD signals. This paper designs a matching impedance which composed from attenuator as detecting impedance and UWB amplifier as signal amplifier and evaluates the performance using S-parameter value. The matching impedance has good reflection loss below ~10 dB over low frequencies up to 3 GHz frequency bandwidth, with a minimum value of S11 is ~28.8 dB at a frequency of 322 MHz and ~18.3 dB at 3 GHz. The input impedance and output impedance values are close to 50 ohm over the frequency bandwidth. The gain (S21) of the impedance matching circuit is 14 dB at a frequency close to DC and down to a 6 dB at a frequency of 100 MHz and have flat value of 6 dB up to 3 GHz frequency. From the simulation results, the designed matching impedance has frequency bandwidth from DC up to 3 GHz that can be implemented as a coupling device for UWB PD detection.