Inception time delay for internal partial discharges

Summary

Partial discharge measurement is a well-established method for testing the quality of solid insulation systems. Multiple standards for different assets and types of insulation are known. The testing time for partial discharge measurement of different assets varies from as little as 30 seconds up to 1 hour. In order for partial discharges to start, a free starting electron is needed. In absence of light, photoionization cannot create the first starting electron, but cosmic and terrestrial background radiation. The likelihood of a partial discharge to happen underlies the statistical probability of background radiation to create the first starting electron. At the same time, the electrical field must be high enough to accelerate the free electron sufficiently to start an ionisation avalanche effect. When partial discharge tests are carried out slightly above the partial discharge inception voltage, the possible time frame, where triggered start electrons can create the needed avalanche effect, is getting very small. This leads to an inception time delay, which depends on multiple factors. This paper shows multiple partial discharge tests on solid insulation systems, being measured slightly above the partial discharge inception voltage. The determined data shows a wide spread of time differences between the time when the AC voltage is applied until the first partial discharge in a solid insulation system can be detected. First tests indicate a strong dependence of the inception time delay based on the prior deposition of the tested sample to voltage. The longer the test object was not exposed to high voltage, the longer the inception time gets. These results may suggest to incorporate the inception time delay in future standards for partial discharge testing.

Additional informations

Authors

Koudela Lukáš, Kotlan Václav, Pánek David, Coenen Sebastian