The improvement in the reliability problem for air current breaker's over current protect function

Almost all plants have the experience of ACB's overcurrent relay (OCR) unexpectedly trip event. Each accident will cause a huge production loss. But manufacturers of OCR can't afford the cost-effective solution of problem. The most used solution is to install an additional relay (ex. ABB Relay B) to replace the function of the ACB's OCR or to adopt a new ACB to replace the old one. These two uneconomical solutions are not only high cost but also time consumption on annual PM. Thus, authors proposed a novel solution by interlocking the main ACB's relay and the feeder ACB's OCR function to prevent the ACB tripped by OCR false tripping signal. This method does not require additional relay and current transformer. Therefore, it is a cost-effective and time saving solution.