Comparison of power frequency and impulse based Partial Discharge measurements on a variety of aerospace components at 1000 and 116 mbar

With the introduction of higher voltages in `more electric´ aircraft, the understanding of Partial Discharge (PD) performance has never been more critical. Power frequency PD testing of insulation systems according to IEC 60270 has been well established for some time. Less well established is the measurement of PD caused by voltage impulses with fast rise times and significant peak overshoots, as described in IEC 61934. This type of test is particularly applicable to machines fed by Pulse Width Modulation (PWM) voltages. An array of tests has been performed at The University of Manchester´s high voltage laboratory on typical aerospace components using both power frequency and impulse waveforms. The purpose of the tests has been to assess the performance of insulation systems under both atmospheric and simulated altitude (50,000 feet) conditions. Testing the samples using both sinusoidal and impulse waveforms provides a good opportunity to compare the practices described in the IEC standards, as well as the effect the type of waveform has on the PD performance of the test samples. Tests performed according to IEC 60270 have returned reliable results across a variety of test samples and atmospheric conditions. However, tests performed according to IEC 61934 have provided inconsistent results, and some unexpected behaviour has been observed. In particular, some test samples have shown an increase in the partial discharge inception voltage as the ambient pressure is reduced. As a result of these unreliable test results, a set of round robin tests have been proposed. Samples of identical specification have been dispatched for testing at a number of laboratories around the world. The results of these tests will be analysed and disseminated with the objective of improving PD qualification testing of aerospace components.