Abstract

The presence of wide band gap devices (such as SiC MOSFETs) in the converters of future power network will introduce a new electrical constraint in the form of repetitive fast rising square voltage waveforms characterized by high repetition rate. These waveforms might influence the discharge mechanism of insulators in power equipment in a way different than AC sinusoidal waveforms.

Therefore, this thesis aims to investigate the partial discharge (PD) mechanism under square voltage waveform to address power electronic applications such as medium frequency transformer (MFT). To achieve this goal, at first a test bench generating square voltage is defined and developed during the timeframe of this thesis. A dV/dt in the range of 10-100 kV/µs is achieved around 20 kV during this work across a device under test filled with dielectric liquid.

Due to electromagnetic interferences produced by high-speed switching of semiconductor based HV switch, the PD detection is performed optically by deploying a photomultiplier tube (PMT), both under AC and square voltages; and compared. The measurements are also conducted by varying the square voltage parameters such as repetition rates, duty cycles and rise times.

Keywords: Partial discharge, optical detection, square voltage, fast rise time, high repetition rate, dielectric liquid.

Thesis director: Cyril Buttay (Ampère)

Thesis co-director: Eric Vagnon (Ampère)