Experience with on-line insulation diagnostics of surge arresters by PD measurement in the field

Surges arresters are extremely important on high voltage stations. Because of their direct connections with to high voltage, any fault can have to serious consequences to the system. The evaluation of these equipments is therefore an important task to maintenance engineering. However, since removing all equipments from the system to perform proper laboratorial tests is not feasible, an evaluation in the field is often necessary. This paper describes the experience applying a simple methodology to evaluate surge arresters in the field, measuring PD through a high frequency current transformer (HFCT) connected on the grounding cable using a modular digital oscilloscope and a laptop PC. The objective this work is to check whether the surge arresters exhibit PD and, if so, obtain to evidence in the laboratory. After that, some of them equipment were retired and taken to the laboratory for further testing. The results obtained in field were confirmed in laboratory, approving this methodology.