FIELD: electrical engineering; selective short-circuit relay protective gear for all circuit configurations. SUBSTANCE: information about current through three-phase electrical installation and about voltage across line under control is conveyed by means of one signal whose frequency corresponds to voltage frequency of line under control. Protective gear incorporates time relays changed over by means of secondary-winding sections of summing transformers in preset time intervals which ensures selectivity of proposed device. EFFECT: simplified design, enhanced sensitivity, enlarged functional capabilities. 4 cl, 3 dwg
