Experience with on-line PD measurements on generators in frequency and time domain

This paper presents a method to perform online time domain partial discharge measurements in a high noise and disturbance environment. The method combines the sensitivity of an online VHF PD (very high frequency partial discharge) measurement with the power of a time domain measurement.. Two measurements on running turbogenerators are presented: one on an 150 MVA generator without disturbances and. one on an 650 MVA turbo generator in a high disturbance environment. The paper shows that it is possible to detect and record partial discharges in an environment with disturbance pulses over 1000 times their size. Using frequency analysis a signal to noise ratio can be obtained, which can be used to determine the optimum measuring frequencies for online VHF PD measurements. Using typical time and frequency wave shape parameter extraction it is possible to separate the recorded pulses into PDs and disturbances.