Transient Earth Voltage Sensor Measurements as a Nonintrusive Tool for Partial Discharge Analysis in Switchgears

Partial discharges (PDs) are a major cause of electrical stress and insulation failure, but their presence is also a symptom of insulation problems. Online PDs measurement allows for continuous monitoring of the insulation system. An online PDs measurement system for air-insulated switchgear (AIS) is developed, based on transient earth voltage (TEV) sensors, and evaluated for morphological analysis of insulation defects. The evaluation is conducted comparing the developed system with a conventional PD measurement system based on the IEC 60270 standard. The aim of the proposed system is to facilitate its integration with minimal retrofitting and operational disruption assuring the possibility to identify and analyze the defects. A pilot system, employing an AIS, is designed and tested. The results from both the PDs measurement systems are presented and discussed. Furthermore, the impact of a high capacitive load connected to the switchgear is investigated, and the possible effects of a capacitive load due to an MV cable is considered by simulating the realistic cable geometry.