Microprocessor-based busbar protection relay

For differential protection of busbars, current transformer (CT) saturation must be considered. In cases of CT saturation, the waveform of the CT secondary current in each cycle consists of two periods: a saturation period and nonsaturation period. If CT saturation occurs during an external fault, differential current does not flow during the nonsaturation period. Utilizing this phenomenon, the low-impedance solid-state differential relays which incorporate a CT saturation countermeasure have long been used. Regarding the CT saturation countermeasure, however, the CT output cannot be determined during the intervals between sampling instants. For CTs generally used in Japan for differential protection of busbars, this drawback offers no problem for the digitized busbar protection relay that adopts proper CT saturation countermeasures. Hence, the authors put the digitized busbar protection relay to practical use to utilize the advantages mentioned