Investigation on Dielectric Failure of High Voltage Equipment in Substation Caused by Capacitor Bank Switching

This paper investigates transient phenomenon of electrical stresses caused by capacitor bank switching, damaging HV equipment in substation. The system of aged air-insulated 115 kV substation is modeled by using Alternative Transients Program-Electromagnetic Transients Program. The failed current transformer (CT) was comprehensively modeled and investigated. The comprehensive model for electrical transient simulation has been developed by using actual data and derived data from real physical dimension of equipment. The simulated results are challenged by comparison of the results from theoretical calculation according to international standard and the results from simulation including on-site measurement. The comparison results to verify the accuracy of the developed model are satisfactory. The results show that electrical stresses affecting CT by voltage stress exceeds CT’s 123 kV rating together with the frequent switching operations as hundreds of times per year. These lead to degradation of CT insulation, especially at the top insulation portion close to HV terminal due to non-linear voltage distribution. Consequently, CT explosion finally occurred. This developed model is used as an effective tool for switching transient investigation to determine electrical stresses caused by various switching operations. With the known electrical stresses, the proper rating of equipment in HV substation can be selected.