Case study on analysis of bus bar protection relay tripping due to improper logic configuration

-Modern numerical relays called as intelligent electronic device (IED), are embedded with advanced protection features to facilitate additional security features. Such security features eliminate the conventional topology of providing dual current transformers (CT) on either side of bus coupler circuit breaker (CB) to eliminate blind zones. Further, it also supports dynamic CT switching based on CB status, which assists elimination of blind spots, thereby eradicating the need for additional CT, thus providing a cost effective solution without compromise on protection. Such a solution implemented in a 220kV bus bar protection relay, encompassing double bus with transfer bus arrangement, located in Chindwara, Madhya Pradesh, has resulted in tripping of dual zones for a fault in a single zone, thus over riding the additional security logics. The analysis and precautionary measures carried out in this case, has been discussed in this paper to ensure that similar solutions can be adopted to inhibit analogous issues in future. This paper attempts to highlight the fact that the human errors may not be identified & eliminated during the installation, commissioning and testing phase at site. One has to remain vigilant throughout the product/ project lifecycle. This case is a live example of the same.