The Limitation of Partial Discharge Inception Voltage Tests at Repetitive Impulsive Voltages Using Ultra-High Frequency Antenna and Possible Solutions

Partial discharge inception voltage (PDIV) measurements under repetitive impulsive voltages should be performed on turn to turn insulation of low voltage inverter-fed motors to ensure that the rated voltages is lower than PDIV and thus no partial discharge (PD) occur in insulation systems. Due to the fact that PD of the tested objects and the disturbance coming from impulsive voltage generator often have similar features in both time and frequency domains, ultra-high frequency (UHF) technologies are recommended to be used under repetitive impulsive voltage conditions because the UHF sensors (connected with high pass frequency filters) with appropriate bandwidth can receive PD signal and remove disturbance effectively. However, PD tests using UHF tests at impulsive voltage have the following limitations (1) the sensitivity of the UHF sensors is substantially lower compared with PD test methods using conventional sensors at sinusoidal voltages. (2) The signal-to-noise ratio (SNR) would not be satisfied when testing PD at impulsive voltages with very fast rise times (e.g. 50 ns). To address the above problems, this paper aims to study improvements when performing PDIV tests at impulsive voltages with very fast rise times, including designing a novel UHF sensor used especially for PD and PDIV tests under repetitive impulsive voltages, finding the reasonable distance between UHF sensor and the tested object and proposing a new method when testing PDIV by Software Assisted Trigger in oscilloscope to avoid triggering by disturbance and obtain the first PD pulse.