Patent ID: 9106076
Filing Date: 2015-08-11
Classification: H02H

Abstract:
1. A method in a three-terminal differential protection in an electrical power network, the method comprising: measuring a terminal phase current at each terminal of a protected zone of the differential protection in each phase to be protected; determining a bias current of the phase on the basis of the terminal phase currents; determining whether a fault exists in the protected zone based on a threshold value computed as a function of the bias current; and sending a control signal to a terminal of a respective protected zone upon the existence of a fault, wherein the determination of the bias current includes subtracting phasor values of the terminal phase currents of two terminals from the phasor value of the terminal phase current of a remaining one terminal, and wherein the terminal phase current, which is a minuend in the subtraction of phasor values, is selected on the basis of a comparison of phase angles or amplitudes of the terminal phase currents among the terminals.