Partial discharges field tests in a 230kV circuit breaker

This paper shows a case study of a partial discharge (PD) test in a 230kV/2000A circuit breaker that was performed in a substation. Two sorts of sensors were used: a high frequency current transformer (HFCT) installed in equipment's grounding conductor and an antenna that is used to estimate the location of discharge source. Partial discharge signatures obtained previously at the laboratory were used to analyze the high frequency current obtained by HFCT [1, 2]. After the equipment was disassembled, DGA analysis was performed into insulating oil when combustible gases were found, indicating internal electrical discharges. Analysis and visual inspection of the inner surface of the equipment showed electrical discharges paths inside of a porcelain column, confirming the partial discharge measurements. Those results showed the effectiveness of partial discharges field test for the predictive maintenance of high voltage equipment. This technique has many advantages, for instance, the low cost, tests are performed keeping the equipment under normal operation, fast diagnosis, and can be used for most of the equipment in a substation.

I. Introduction

Partial discharges consist in small electrical discharges inside of high voltage equipments caused by insulation flaws or voids, or by high electrical gradients in the insulation, in general. Those fast electrical current pulses generate radiated electromagnetic waves [3], [4] and they could be detected by means of high frequency current transformer (HFCT) applied to the equipment grounding conductors, or using an antenna.