Emission and propagation mechanisms of PD pulses for UHF and traditional electrical measurements

Partial Discharge (PD) measurements are considered as a very powerful technique for testing and monitoring the condition of high-voltage (HV) insulations. PD activity is generally accepted as an early breakdown indicator, which is also reflected in numerous standards. In the present contribution, the authors describe the fundamentally different propagation mechanisms of electrical impulses in the conventional (according IEC 60270) and the ultra-high frequency (UHF) range. The low-frequency components of the PD signals propagate mainly via the conductor, whereas the high-frequency components (UHF signals) are radiated as electromagnetic waves. The sensitivity and spectrum of the measurement depends strongly on the geometric position of the PD, damping and resonances of the propagation path, and the frequency response of the receiver. Field simulation has been used as an appropriate tool for calculating PD signal propagation in HV apparatus.