Impact of CT errors on protective relays - Case studies and analysis

Current transformers (CTs) are the basic interconnection between the power system and almost all measurement devices such as protective relays. CTs step the primary current down to a nominal secondary level for use by protective relays, meters, and other monitoring devices. One of the practical concerns for the protection engineer is the actual ability of a CT to replicate the primary current. This paper discusses several actual relay operations, and the root cause of the events behind the relay operations.