FIELD: relay protection of power supply devices, in particular, method for differential protection of transformers. SUBSTANCE: device has adaptive filters 6 and 8 which provide possibility to analyze first half-wave of transient currents when information loss caused by transformer saturation does not occur. This analysis is done for time which is less than half-period of voltage frequency using additional information characteristics of current spectrum. This involves detection of levels of odd harmonics and levels of free constituents of measured and differential currents, detection of maximal levels of free constituent and odd harmonics of measured currents and five operations of comparison of levels to pre-set values. First comparison involves measurement of level of odd harmonics of differential current to first pre-set value, second comparison -- level of free constituent of differential current to second pre-set value, third comparison -- level of odd harmonics to level of free constituent of differential current, fourth comparison -- level of odd harmonics of differential current to maximal level of odd harmonics of measured currents, fifth comparison -- level of free constituent of differential current to maximal level of free constituent of measured currents. If simultaneously during first, third and fourth comparison operations first operands are greater than second ones, inrush of magnetization current in transformer is detected. If during second and fifth comparison operations first operand is greater than second one, short circuit in transformer is detected. EFFECT: increased speed of detection of inrush or short circuit current in transformer. 7 dwg
