Improving power quality by sub-cycle transfer switches: a criterion for the evaluation of alternate sources independence

The topic of fast load transfer sub-cycle transfer switches (STSs) at distribution medium-voltage (MV) level for power quality improvement is considered. Static switches for the MV level are available today, and there is the necessary industrial experience for practical application. The main actual difficulty for an effective fast load transfer is given by the availability of two MV sources, as independent as possible. A general criterion for the evaluation of the bus independence in an electrical net is proposed. The method is suitable for selection or planning of proper alternate sources for effective STS operation.