Evaluation on current transformer assessment method based on investigation result

The increase of current transformer (CT) failure rate in PLN P3B Jawa and Bali within the last five years has put CT as a critical asset. In order to prevent existing CTs from the similar failure, the assessment method needs to be evaluated. For this purpose, further investigation was conducted on three sister units of two failed CTs by performing measurements and tear down. The investigations reveal that the insulating medium of the high voltage conductor-to-ground of two investigated CTs were deteriorated due to moisture ingress. The presence of carbonized spots and residual material was also found in particular on the insulating paper. The physical conditions of each investigated CT are analyzed to determine the ageing stage which represents the failure risk. The correlation between the failure risk and its testing results is analyzed to evaluate the assessment method of CT operated under tropical climate.