Testing Distribution Switchgear for Partial Discharge in the Laboratory and the Field

Over the past 30 years handheld instrumentation has been developed that enables the detection of partial discharge activity with the plant in normal service. The continuing challenge in making meaningful field based partial discharge measurements is to reliably relate the severity of any detected partial discharge activity to the risk of failure of the item under test. The risk will be a function of such factors as the location within the test item, ambient conditions, materials, the severity of the activity and the history of failure (if any). This paper describes some of the field experience gained whist using this equipment and also introduces results from recent laboratory based accelerated ageing tests on 11 kV vacuum switchgear that employed cast resin insulation material where surface partial discharge activity was observed from inception to failure.