Partial Discharge Measurements under DC Voltages Containing Harmonics Produced by Power Electronic Devices

Partial Discharge (PD) monitoring is one of the main diagnostic instrument to evaluate the reliability of modern electrical transmission and distribution systems. The widespread use of High voltage dc (HVDC) connections increase the demand of voltage source converters (VSCs) which, as a consequence, has brought about new challenges in the field of partial discharge measurements. In fact, the output voltage waveforms generated by AC/DC modular multilevel converters (MMCs) are affected by a significant harmonic content which influences the Partial Discharges (PDs) activity. For this reason, previous research mainly investigated the PD phenomenon on the AC side of the converter. The aim of the present work was to evaluate the PDs behavior applying a voltage waveform containing ripple at the DC side of the converter. At first, a pure DC voltage has been used to stress the tested specimen and then harmonic content has been added by chancing the number of modules of the simulated AC/DC converter. For the different generated waveforms, measurements of PDs have been carried out and a comparison of the different PDs pattern have been made. The effect on the PDs behavior has been also evaluated for different switching frequencies.