An apparatus for determining a fault location distance or distance protection in a multi-phase power transmission medium, configured to; determine a set of line fault parameters based on a measurement of voltage and current at a point of said power transmission medium and a fault type, the line fault parameters determined at a plurality of sample times determine a derivative with respect to time of a line fault parameters representative of an inductive part of measured faulty phase current; determine a set of phasors using a Fourier transformation of the derivative and of the remaining line fault parameters at the plurality of sample times and use said set of phasors to determine a fault location distance or distance projection distance along the power transmission medium; wherein, the determination of the fault location distance or the distance protection distance is based on the line equation;

[00001]${\stackrel{.}{U}}_P={\stackrel{.}{U}}_F+\left[R_1.Math.{\stackrel{.}{I}}_{\mathrm{PR}}+\frac{X_1}{{}_0}.Math.{\stackrel{.}{I}}_{\mathrm{PX}}\right].Math.D_F.$

The present disclosure relates to a method for distance protection of a transmission line carrying a plurality of phases for a phase-to-phase-to-ground fault comprising a first phase and a second phase of the plurality of phases as faulted phases in the phase-to-phase-to-ground fault, wherein the first phase is different from the second phase, the method comprising: obtaining a first impedance of a first electrical loop formed by a first phase carried on the transmission line and a ground potential based on a zero-sequence current (S601); obtaining a second impedance of a second electrical loop formed by a second phase carried on the transmission line and a ground potential based on the zero-sequence current (S602); computing an apparent impedance of the transmission line and a ground potential based on the transmission line seen at a first terminal based on the first impedance and the second impedance (S603); and performing the distance protection based on the apparent impedance (S604). The present disclosure also relates to a respective device, computer-readable medium, and system.

The present disclosure relates to a method for controlling a protection system for an electrical power system comprising a transmission line terminated by first and second terminals coupled to respective power sources. The method comprises: obtaining voltage and current measurements of the first terminal; determining phase angle boundaries of a fault current based on the voltage and current measurements; determining a first apparent impedance based on a first phase angle within or at one of the phase angle boundaries starting from the first terminal; determining a second apparent impedance based on a second phase angle within or at one of the phase angle boundaries starting from the first terminal; determining third and fourth apparent impedances starting from the first terminal based on the first and second apparent impedances; and controlling the protection system based on the third and fourth apparent impedances.