Analysis and Improvement of Line-Capacitance Effect on Three-Phase 161-kV Bus Potential Transformers

This paper is concerned with the analysis and improvement of line-capacitance effect on three-phase 161-kV bus potential transformers (BPT). The slow discharging overcurrent through the inherent line capacitance of underground inter-substation power cables may result in large magnetic force shifting and damaging BPT primary windings of local substation when opening circuit breaker (CB) of remote substation located several kilometers away. The simulation models are built according to field parameters and the discharging current simulation results agree closely with those of field tests in electric power laboratory. BPT primary winding relocation may cause strongly different effects. Calculations are given to determine whether BPT can survive over the mechanical force resulted from the magnetic field generated by the aforementioned three-phase peak transient currents or not. Based on the newly improved BPT and its line-capacitance withstanding test, recommendations of BPT specification with respect to the maximum allowable line capacitance are also given.