METHOD FOR PROTECTION AGAINST EARTH SHORT CIRCUITS IN THREE-PHASE MAINS AND A DEVICE FOR THE REALIZATION OF THE METHOD

The proposed method for protection against short circuits in three-phase mains consists in measuring the amplitudes and phase differences of the high-frequency components of load currents in two phase circuits and controlling the amplitude of the zero-sequence voltage at the operating frequency. As the said high-frequency signals in a phase circuit with a fault are opposite in phase to the signals in the same phase circuit without a fault, a fault in one of the phase circuits causes the signal that is proportional to the difference of the phases of the high-frequency current components to increase comparing with the same signal when there is no fault. The proposed device for the realization of the method is distinctive by its enhanced sensitivity and reliability at simple design. The device can be used in mains with an insulated neutral and mains with a neutral connected to the ground via a resistor.