number of synchronising relays are manu. factured commercially, most of which use dynamic relaying elements. They have employed electrically interlocked r+'lays i'.hich opt-rate each time the phase angle between the mach the and line voltages becomes zero. These automatic synchronisers have given excellent service in a variety of applications. However, it has become evident that.faster and more accurate synchronising could be obtained if the interlocking relays were eliminated and their functions performed by electronic means. The present trend has been to investigate the possibilities of, applying transistors and semiconductor components to the problems of an entirely static synchrotuising relay. All the necessary functions of voltage regulation, phase and slip measurements can be achieved successfully using static relaying principles. The automatic transistorised synchroniser described in the dissertation permits taking advantage of faster circuit breaker closing speeds and provides more accurate synchronising then the equipment 4th mecha-nical interlocking relays