Current transformers with secondary current rating lower than 5 A

Current transformers (CT) designed for protective relaying applications with secondary current ratings substantially lower than 5 A offer advantages when lead resistance tends to predominate over the relay burden. The lower current rating may allow the use of a smaller wire size or a smaller CT core as well as providing improved transient performance. With the longer lead runs associated with EHV stations, and the advent of low-burden solid-state relays, the picture has become favorable for such lower current rating, and their advantages and disadvantages are considered. Also addressed are working voltage levels, open-circuit voltages, noise sensitivity, circuit breaker interchangeability, relay stocking requirements, and CT costs.<
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