Effect on CT Ratio and Circuit Breaker Rating due to nearby New Mega Generating Station

Abstract

This paper presents the effect on the breaking capacity of previously installed circuit breaker due to the upcoming installation of new generating stations in the near vicinity. The MVA capacity of the circuit breaker and current transformer rating needs to be upgraded owing to increase in the symmetrical fault current level. The circuit breaker connected to the older generating station can maloperate. The circuit breaker parameters connected to the smaller generating unit at the generating and grid end have been calculated and tabulated with respect to symmetrical fault without and with the new transmission line connected to the same grid. The more the difference in the rating of the two generating unit the higher is the MVA rating required for circuit breaker upgradation. The current transformers connected at the generating and grid end saturates and affects the secondary output due to the change in fault current level with new generating unit nearby. This results in maloperation of the relay and circuit breaker. The current transformer new rating has been proposed to avoid its saturation and the output is compared with the older rating.