Method and a device for fault location in the event of a fault on a power transmission line

A device for determining the location of a fault at a fault position (F) on a power transmission line between two stations (P, Q) and in which the power transmission line has an unknown conduction impedance (Z.sub.PQ), comprising at one of said stations (P):

• capacitive voltage measuring transformers means for measuring the phase voltage (U.sub.PM);
• means for measuring the phase currents (I.sub.p) or changes in the phase currents (.DELTA.I.sub.p) on the occurrence of a fault;
• means for low pass filtering said phase voltage and said phase currents or changes in the phase currents;
• and
• means for converting the filtered phase voltage, phase currents or the change in the phase currents from an analog to instantaneous digitized phase voltage, phase currents or changes in phase current values, respectively;
• said device further comprising:
• means for calculating a value of the fault distance .alpha. and a value of an apparent fault resistance R.sub.F at the fault location, using linear regression, on the basis of the relationship:
• U.sub.PM =.alpha.Z.sub.PQ I.sub.P +R.sub.F I.sub.P +.DELTA.U.sub.CVT ;
• where .alpha. represents a measure of the fault position, R.sub.F I.sub.P represents a voltage across the fault position and .DELTA.U.sub.CVT represents a fault voltage introduced by said capacitive voltage measuring means;
• and
• means for comparing said fault distance .alpha. with an upper (.alpha..sub.max) and a lower (.alpha..sub.min) limit value and for comparing said apparent fault resistance with an upper (R.sub.Fmax) and a lower (R.sub.Fmin) limit value and generating a tripping signal when the fault position and the apparent fault resistance, respectively, are within the aforesaid limit values.