Potential Risk of Failures in Switching EHV Shunt Reactors in Some One-and-a-half Breaker Scheme Substations

This paper reports the case of some EHV circuit- breaker repetitive failures during the opening of a 100 MVAR shunt reactor in a 400 kV substation in central part of Iran. By taking advantage of the simulation capabilities of EMTP-RV, the restructured version of the DCG-EMTP and its new GUI, major understanding of arc-circuit interaction phenomena was achieved. Simulation results show without any doubt that opposite-polarity high frequency arc- instability-dependant oscillations caused mainly by current transformers on each side of the breaker were responsible for its thermal failures and thus the non-interruption of the low 50 Hz reactor current by the 50 kA circuit-breaker. This paper represents a major contribution to the field of shunt reactor circuit-breaker applications. It is expected that large transient simulations with EMTP-RV incorporating circuit parameters frequency-dependency and dynamic arc modeling will contribute, in some cases, to a much safer shunt reactor installation.