FIELD: electrical engineering; overcurrent and short-circuit protection of three-phase motors, transformers, power transmission lines, etc. SUBSTANCE: for detecting short circuit, current equal to geometric difference between currents at different ends of electrical installation is monitored. These currents are obtained by summing up currents of two phases passed through current transformer and current of third phase shifted 180 deg. from them. Proposed method for detecting emergency conditions enables using only one threshold element for recording different kinds of short circuits including single-phase ones in lines with solidly grounded neutral and those due to double ground faults with any phase combination of insulated-neutral lines. EFFECT: enlarged functional capabilities, enhanced sensitivity, simplified design. 5 cl, 3 dwg
