Measuring partial discharges under pulsed voltage conditions

Partial Discharges (PDs) measurement deserves a specific study when in the presence of fast rising/falling voltages, as the output of IGBT switching devices. In such operating conditions, the choice of a proper detection system is crucial in order to have the best signal to noise ratio and to solve some problems linked to the specific characteristics of the voltage waveform. This work proposes a comparison between a high frequency ultra wide band (HF UWB), and two different low frequency selective wide band (LF SWB) PD detection systems. The performance of such systems have been assessed during tests performed on twisted pair enameled wire specimens. These tests have been carried out applying pulsed voltage waveforms, while having different amplitudes and rise times, reproducing the output of a switching device. The outcome evidence is that, in the considered conditions, the HF UWB systems cannot provide correct information about the intensity of PD stress and the severity of the relevant degradation. It is also demonstrated that with proper optimizing of the output signal of the LF SWB system, it is possible to obtain reliable quantities that can be used to implement empirical models. Such models can be useful to predict the residual duration of twisted pair specimens, after a short monitoring of PD activity during aging tests.