Interlock and phase-comparison schemes for the protection of overhead transmission lines

Abstract

Protective schemes based on Kirchhoff’s first law, namely those which determine the location of faults by comparing the instantaneous currents entering and leaving protected zones, were considered in Chapters 5–9. Their application to overhead lines and cables was described in Chapter 9, in which it was shown that there are factors which limit the lengths of circuits which may be protected when the comparisons are effected over interconnecting conductors (pilot wires). These limitations arise because of the need to convey continuous information with fairly high accuracy between the ends of protected circuits. To eliminate this need, alternative schemes were introduced in which only relatively simple signals need to be sent between the ends of protected zones, and because significant attenuation of these signals may be allowed it is possible to apply such schemes to very long circuits.