Redesign of traditional relays with microcontroller-based relays can be used to achieve a higher level of reliability. In this study, the results of redesign and prototyping of a synchrocheck relay using an 8952 microcontroller with improved reliability is discussed. These relays are usually used for paralleling two load-generation islands, or for closing an open loop in an electric power system. The designed circuit measures voltage, frequency and phase angle difference between the voltage signal on the two sides of an open circuit breaker; evaluates the existence of necessary conditions for synchronism, and then decides whether or not a command should be issued to allow the circuit breaker to close. If these conditions do not exist when the circuit breaker closes, the power system equipment on the two sides of the circuit breaker may be damaged due to the inrush current at the instant of closing the circuit. The integration of three timer-counters, internal code and data memory plus the single-bit handling and 8-bit divide and multiply instructions of 8952 make it suitable for this application. No external RAM or EPROM are needed and the processor internally performs all the necessary computations. [Journal of

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