Partial Discharge Detection in Power Electronic Substrates Exposed to Pulse Voltage Waveforms
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- Institutt for elkraftteknikk 
An increasing number of power electronic converters are integrated in power systems. The fundamental functionality of electronic converters is turning on and off semiconductor switches to form the wanted voltage shape. This causes fast repetitive voltage pulses which can have negative effects on the insulation systems. The increased degradation of the insulation systems is due to several mechanisms, but partial discharges (PD) is considered most harmful. The insulation of the electronic converter itself is also vulnerable to PD. Today, power electronic devices are tested for PD when the system voltage is above a certain level. They are not tested with the pulsed voltages they are exposed to, but rather using a conventional method applying a sinusoidal voltage. The conventional method for PD detection is unsuited for pulsed voltage conditions, and new detection methods must be developed. The objective for this project has been to create a system for detection of PD in semiconductor substrate test objects at a fast-rising square voltage. The current through the test objects has been investigated using a frequency analyzer to identify the frequency content of the applied voltage and PD pulses. Three different interfaces for measuring the current through the test object has been made for direct, inductive and electromagnetic measurements respectively; resistive shunt, high frequency current transformer (HFCT) and antenna. Three different methods of suppressing the influence of the applied voltage has also been tested; filter, wavelet analysis and subtraction by average. A functioning PD measuring system has been made utilizing a standard oscilloscope connected to a computer with Matlab for data collection. Current measurements were done using the resistive shunt. A Matlab script was made to suppress the influence of the applied voltage using the subtraction by average method. This script was also used to extract and plot the amplitude and location of the detected PD pulses. Optical detection with a photomultiplier was utilized as a method of confirming the electrical measurements.