Beyond the normal testing procedure-a closer look at the microcomputer based relay

The application of microcomputer-based relays grow rapidly and a number of microprocessor-based protective relays are applied in electric utility power systems. Since the performances of the protective relays are normally categorized by their function, the same test procedure is applied to a group of relays with the same protective function regardless of their operation mechanism. Unlike electromechanical or solid-state relays, a microcomputer based relay is a software-driven system. The performance of such a relay depends on the hardware design, the accuracy of the input signals and the algorithms embedded inside the unit. Though they may have similar protective functions, the physical capability and constraints of microcomputer-based relays may vary from one vendor to another. Some of these features are difficult to be tested or evaluated through traditional testing procedures. This paper discusses the hardware and software design issues and illustrates how they can affect the performance of a microcomputer-based relay system.