The Field Test and Dissection of a New Type of Composite Insulated Dry Current Transformer Made of Synthetic Materials

This paper introduces the performance of a new type of composite insulated dry current transformer (dry CT in the paper). It is made of synthetic materials and designed distinctively from traditional oil and gas insulation. The results of the test and dissection of three 110 kV units of dry CTs which have operated for three and a half years in a power system are presented. They indicate that such components sustain excellent insulation performance, withstanding higher AC voltage, showing lower dielectric dissipation factor (tandelta), smaller magnitude of partial discharge and higher insulation margin. This provides a higher operational reliability and safety along with maintenance-free operation. This kind of dry CT is being widely adopted in the Chinese power grid as more than 10,000 of such CTs have been operating without a single failure since 1998. The causes for such distinctive reliability and low deterioration rate are discussed