FIELD: electrical engineering. SUBSTANCE: device has zero-sequence current transformers 3, 4, current-to-dc-voltage changers 5, 6, storage members 7, 8, integrating members 11, 12, closing switches 9, 11 and 13, 14. threshold elements 15, 16, pulse stretchers 17, 18, final elements 19, 20, starting gear 21, zero-sequence potential transformer 22, control unit 23, short-pulse shaper 24, and OR gates 25-27, all mounted at connection points 1 and 2. Control unit 23 incorporates duration limiter 28, time delay element 29, and NOT gate 30. Newly introduced are pulse stretchers and closing switches as many as there are points of connection, OR gates, and short-pulse shapers common for all points of connection, and control unit built up of duration limiter, time delay element, and NOT gate. EFFECT: improved speed of device response, enlarged functional capabilities, simplified design. 1 dwg
