Online monitoring of partial discharge in high voltage switchgear using a differential electric field sensor

High voltage switchgear has been widely used in recent years, meanwhile, electrical faults in switchgear happen time and again, resulting in not only power failure, but also damage to electrical equipment and personal safety. Among amounts of electrical faults, insulation faults take a leading role, which regard partial discharge (PD) signal as an early manifestation, thus PD monitoring is an effective method to predict insulation fault. This paper designs a differential field sensor(D-dot sensor) based on the radio-frequency (RF) technique used for PD on-line monitoring, which benefits at simple structure, small size, flexible location and strong anti-interference performance compared with conventional methods such as ultrasonic detection, electromagnetic detection, heat detection, chemistry detection and so on. This paper builds the simulation model of D-dot sensor using the CST software to study the influence of the sensor structural parameters and material characteristics on the sensor performance. On this basis, the physical D-dot sensor was made. Besides, for verifying the performance of D-dot sensor, a switchgear PD testing platform was built in laboratory based on aforementioned research. The results show that the D-dot sensor designed by this paper can effectively detect most types of switchgear PD faults, and a quadratic relationship between the cumulative energy captured by the D-dot sensor and the apparent charge of PD is as well proved.