Computer prediction of IDMT relay settings and performance for interconnected power systems

The application of the inverse definite minimum time (IDMT) overcurrent relay to power system protection is reviewed, and the present methods for determining its settings are briefly described. A computer program to calculate relay settings based on a generalised procedure, and therefore suitable for both radial and interconnected ring systems, is then proposed. Its application to a specific interconnected system is explained. Two further programs have been developed to be used in conjunction with the first one. These assess, by a simulated circuit breaker tripping facility, how the IDMT protection would perform on an interconnected ring power system when there occurs either a failure of the main protection or a circuit breaker on the faulted section.