FIELD: electrical engineering; overcurrent and short-circuit relay protective gear. SUBSTANCE: resultant three-phase sequence of phase currents of respective lines is applied to primary windings of saturable current transformers incorporated in electromagnetic current relays. In the process, all kinds of faults occurring in defective line can be chosen and recorded by means of two electromagnetic current relays by single variable (sum of line phase currents). In this way, power direction relay and voltage circuits of substation (station) transformer buses may be dispensed with thereby eliminating voltage dead zone and, hence, reducing zone of its cascaded action. EFFECT: simplified design, reduced power requirement, improved sensitivity, reliability, and speed of response. 2 cl, 2 dwg
