Implementation of a numerical overcurrent relay for relay education

This paper proposes the design and implementation of a numerical over-current relay based on the single-chip microprocessor MSP430F449 for relay education. The over-current protection curves are established according to the international standard IEC 255-4. Using C language develops the relay control program. A graphical monitoring interface in the PC for the relay is designed by using the Borland C++ Builder program, in which the RS-232 data link is employed. Finally, a scaled-down 3-phase power system is built for test. Two experiments are offered to students. Through the experiments, students can understand the architecture and operation principles of modern numerical relays.