A digital simulator for testing a three-phase relay system using results obtained from simulating an induction motor using phase co-ordinate model

A simulator for testing relays in power systems is proposed which uses a PLC and an IBM-PC computer and brings together a FORTRAN program which simulates system transients. Turbo-Pascal programs and additional interfacing hardware were required to implement the Intel 8255 PPI chip required to achieve D/A conversion at the lowest acceptable sampling rate of 1 kHz. The PLC used for the application was limited to a maximum sampling rate of 50 Hz. The research which is on-going will consider alternative concepts to include the serial connection of PLCs necessary to monitor the state of other nodes in this system. Also the work includes analysing the serial signal to and from the relay over a 1 km communication link. These essential improvements are required to make the computer system proposed ideal for testing relays in remote areas without removal from their operating location