Sensitivity check for radio frequency partial discharge detection for power transformers

Power and distribution transformers form important components in the electricity grid. Failure of such important components can give rise to high costs (such as costs for repair and cost for non-delivery). Therefore methods to determine the risk of failure of transformers are of importance. It is known that failure due to insulation defects is often preceded by partial discharge activity. Over recent years, on-line diagnostic means for power transformers have been investigated. In this paper the sensitivity of one of these methods, the UHF PD detection technique, has been analyzed on several transformers. From these experiments, the sensitivity of the UHF technique to detect partial discharges in power transformers has been established. Based on these results, a sensitivity check similar to the one used for GIS is proposed in this paper. Some of the additional challenges posed by the transformer structure will be discussed in terms of their effect on the detection sensitivity that is needed and the PD levels that might be present while transformers are in service. Some alternative practical methods for applying the technique during on-site tests will also be outlined