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Application of a fast hybrid transfer switch (HTS) as a suitable tool for protection of sensitive electrical loads against power quality problems has attracted much attentions these days. In this paper, methods for desired control of a HTS which consists of a fast fault-detection method and a suitable firing and transfer strategy are proposed. Simulation results of a HTS under various operating conditions for two types of medium-voltage electrical systems, i.e. grounded (star connection) and ungrounded (delta connection) systems, with respect to total transfer time are presented. The results show the capability of the HTS and the proposed control methods in fast transferring of sensitive loads in case of various power quality problems in the system. It is also shown that the transfer process in an ungrounded electrical system is somewhat complicated compared to a grounded electrical system, but it does not necessarily result in longer total transfer time.