FIELD: electric instruments. SUBSTANCE: device has three-phase power supply 1, three-phase protection switch 2, current transformers 7, voltage transformers 6, 8, three-phase active load 9, frequency meter 10, unit 11, which transforms primary voltage to secondary one, unit 12 for calculation of voltage difference, unit 13 for calculation of average voltage, current derivative unit 14, dividing unit 15, unit 16 which transforms inductance to nominal frequency, unit 17, which calculates average inductance for given period, deviation calculation unit 18, setting unit 19, inductance deviation unit 20, protection unit 21. Device provides possibility of monitoring state of windings of power transformers without their switch off line. Protection is switched on when destruction of windings or their distortion is detected. EFFECT: increased reliability.
