High Voltage Insulation Failure on HV Current Transformer: A Case Study in Diagnosis of HV CT Failure at Bekasi 150 kV Substation

Abstract

Insulation in high-voltage equipment has a very important function as a part that separates the voltage from other parts, failure of insulation in high voltage equipment causes losses in operating of electric power transmission. High voltage Current Transformer (CT) with OIP type is a type of high voltage CT that is widely used to measure current in electrical power installations. Insulation on high voltage equipment is designed to be able to operate reliably, but the presence of stress such as voltage, heat, vibration, environmental conditions on the equipment causes a decrease in the insulation ability which can cause insulation failure. The conventional diagnostic methods to determine dielectric conditions in high voltage CT are by electrical testing including the tan delta test, capacitance and insulation resistance. A case study of the failure of the 150 kV CT occurred at the 150 kV Bekasi Substation in Indonesia, based on the results of the last electrical test that was carried out showed that the CT insulation condition was still in normal condition, for tan delta test with <1%, capacitance with <10% nameplate and insulation resistance > 11 GΩ but a major breakdown occurs on March 2021, according to this case study a comprehensive diagnostic method for dielectric conditions is needed to determine the insulation condition correctly and to avoid a breakdown due to insulation failure. The diagnostic method for high voltage CT that will be explained is by knowing the increase or grading of the tan delta test and combined with nonconventional method by dielectric frequency response test and partial discharge test.