Variable-characteristic generalised techniques for distance protection. Theory and initial performance studies

The paper outlines a method for dynamically varying the shape of polarised quadrilateral distance-protection characteristics using modified relay-signal arrays in conjunction with generalised phase-comparison techniques. Two extremes of variation corresponding to characteristic requirements during healthy and faulty circuit conditions are produced, and the possibility of providing a high degree of immunity to power swings and extreme loading emerges. The effect of measurement errors is considered, and the results of digital-computer studies of the relay response under faulted conditions on a typical 132 kV transmission line are presented. Results relating to each type of relay are presented, and it is shown that relays connected to healthy conductors restrain during faults on other phases.