While there are many computer programs available for calculating time over current relay settings of coordination with the transformer highside fuse, few of these programs are usable to the relay technician. This project developed a computer-aided distribution substation protection coordination, which not only allows the technician to check the relay settings and fuse size but also allows the relay engineer to check the distance relay settings on the subtransmission system for coordination with the transformer fuse.
With the advent of digital relays for induction motor protection as well as increasing harmonic content in the ac lines, an experimental study has been initiated to determine the effect of this combination on the operation of the relay. In this experiment, we test the degree of protection with both sinusiodal and nonsinusoidal inputs. A microprocessor based motor protection relay (protecting a 3d induction motor against the harmonics the relay gives) was also tested under these conditions.
