Abstract: A protection device for a power network performs a method to align measuring times of first and second measurements of an electric quantity, taken at different ends of a power network line transmitted with measuring times via a telecommunication network. In the method, a send transmission time from the local to remote end of the line and a receive transmission time from the remote to local end of the line are determined based on time signals from internal clocks. After a global time reference to synchronize the internal clocks is lost, a clock drift is determined between the internal clocks. The measuring times of the first and the second measurements are aligned using the send and receive transmission times as well as the clock drift. A sudden change in the clock drift is determined in order to recognize a route switching in the telecommunication network and the clock drift is corrected.

Abstract: A protection device for a power network performs a method to align measuring times of first and second measurements of an electric quantity, taken at different ends of a power network line transmitted with measuring times via a telecommunication network. In the method, a send transmission time from the local to remote end of the line and a receive transmission time from the remote to local end of the line are determined based on time signals from internal clocks. After a global time reference to synchronize the internal clocks is lost, a clock drift is determined between the internal clocks. The measuring times of the first and the second measurements are aligned using the send and receive transmission times as well as the clock drift. A sudden change in the clock drift is determined in order to recognize a route switching in the telecommunication network and the clock drift is corrected.

Abstract: 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), wherein, at one of the stations (P), capacitive voltage measuring transformers measure the phase voltage (U.sub.PM) and the phase currents (I.sub.P) or changes in the phase currents (.DELTA.I.sub.P) are measured on the occurrence of a fault. The phase voltage, phase currents or changes in the phase currents are low pass filtered; and the filtered phase voltage, phase currents or the change in the phase currents are converted from an analog to instantaneous digitized phase voltage, phase currents or changes in phase current values, respectively.The fault distance .alpha. and a value of an apparent fault resistance R.sub.F at the fault location are calculated, 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 .