Differential protection in electrical power networks

摘要

A method in a three-terminal differential protection includes measuring a terminal phase current (IT1(y), IT2(y), IT3(y)) at each terminal (T1, T2, T3) of a protected zone of the differential protection in each phase (L1, L2, L3) to be protected, and determining a bias current (Ib(y)) of the phase on the basis of the terminal phase currents (IT1(y), IT2(y), IT3(y)). The bias current determination includes subtracting phasor values of the terminal phase currents of two terminals from the phasor value of the terminal phase current of one terminal. The terminal phase current, which is a minuend in the phasor difference computation, is selected on the basis of the phase angles or amplitudes of the terminal phase currents.

主权项

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.