Abstract: A method of and apparatus for determining which if any phase of duplex supply lines wherein each phase w is assigned two conductors w1 and w2. The method and apparatus use an asymmetry value, for example a function of the relationship (output of 9) of the difference Iw1-Iw2 (output of 5) to the sum Iw1+Iw2 (output of 6) of the currents in the conductors w1 and w2. If the asymmetry level exceeds in absolute value a threshold level K(see 12 and 13), the conductor passing the current having the lowest amplitude is indicated as being sound.

Abstract: The invention concerns a method of direct measurement of a parameter characterizing a fault on an electricity line 1, such as the distance x or the resistance R.sub.d of the fault, the method being based on Ohm's Law including the line inductance L and the resistances R, R.sub.d. The signals respectively associated with the variation of current i(t) and of voltage v(t) at the measuring point M are operated upon by transfer functions the ratio of which is equal to:(2/.tau.) tan .omega..tau./2,.tau. corresponding to the propagation time of a wave over double the distance between the measuring point M and a zone boundary P. The method thus takes into account the distributed capacitances C of the line.

Abstract: A directional relay for providing indication of the direction of a fault on an electric power transfer network has an adder (9), a subtractor (10) and filters (11) which receive signals from voltage and current transformers (6,7) and derive signals related to fault-induced forward and backward transient waves on the network. To ensure reliable operation even when the relay is close to a low impedance element such as a generator (2), the forward wave related signal is delayed in a delay unit (12) by an amount equal to the propagation time of the wave along the section protected by the relay, before the difference between its square and that of the backward wave related signal are integrated (16) to derive the fault direction signal.

Abstract: A method for the directional detection of faults on power transmission lines is described.According to one embodiment applied to a link comprising several lines in parallel each provided, towards each of their respective ends, with a directional relay, the indications from all of these relays in response to the detection of a fault on the link, are combined to determine the presence or the absence of the fault on the lines under consideration. In particular, this method is applicable to lines compensated with series capacitors at the beginning of the line.