Microcomputer based out-of-step protection for large generator

A microcomputer based out-of-step protection for generator is proposed. The identification scheme is based on tracing the measured impedance locus and measuring speed and direction of the impedance variation. It can not only identify an out-of-step from a stable swing or a fault, but also give signals of the speedup or slowdown out-of-step when the swing angle less than 180°. The algorithm of the apparent impedance measuring is proposed. Logic blocks and program flow charts are described. Test of prototype shows that it meets the engineering requirements