Easy Measurement of PD transfer impedance using Network Analyzer

Summary

IEC60270 requires to measure the transfer impedance Z(f) of the Partial Discharge (PD) measuring system for type, routine and performance tests. ZT(f) is the ratio of the output voltage and input current of the PD measuring system. In many cases this measurement is performed only at few fixed frequencies using a function generator (converted into a current source) and reading the output voltage either from an additional oscilloscope or the PD detector display. Determine the -6dB and-20dB cut off frequencies requested in the IEC 60270 standard may require interpolation between two frequencies. Covering all main filters and coupling impedance combinations is difficult, leading manufacturers to limit the measurement to a single set up. In this paper, a quick and easy method is presented, to measure ZT(f) based on a Vector Network Analyzer (VNA). The VNA performs the frequency sweep, measures the input current and output voltage, performs the calculation and automatically determines the -6dB and -20dB cut off frequencies. Two setups are covered where one is using T/R gain-phase test ports and the second one is using S-parameter test ports. The PD detector offers an analog output to direct connection to the VNA. The Z(f) measurement relies only on one traceable measuring Equipment hence avoiding complex test Arrangements.

Additional informations

Authors

Wattanawongpitak Sarawut, Ruankon Sayan, Suwanasri Cattareeya, Lipirodjanapong Sumate