Abstract
Metallized polypropylene film capacitors are prone to failure under high pulsed voltage
and current waveforms. A set of specifications are given by the International Electrotechnical
Commission (IEC) that defines the required performance characteristics of
these capacitors. The proposed test setup is very involved and requires a skilled operator
who is responsible for ensuring that the prescribed test conditions are accurately applied
to the capacitor. Automated test and measurement equipment was developed to conduct
these tests according to the IEC specifications. The test equipment generates large crest
factor current discharge waveforms in the capacitor with peaks reaching 1000 A. A new
method was also developed for measuring the rms value of these current waveforms
using a low-end microcontroller, together with an inexpensive current transformer. The
recommended IEC discharge circuit is powered by a switching power supply, utilizing
feedback control, which also enables the rms current through the capacitor to be
regulated. By automating the system, important responsibilities are isolated from the
operator, allowing a less skilled person to effectively conduct the capacitor tests.
Prof. W.A. Cronje
Prof. I.W. Hofsajer