Verfahren zum Erfassen des Stromes in einem Leiter eines Wechselstrom-Energieübertragungsnetzes

摘要

The invention relates to a method of determining the current in an AC power transmission network. With the aid of a current transformer, a measurement quantity is obtained and digital samples converted. In order to prevent erroneous current measurements resulting from a fading direct current member in the current transformer, two initial measurement auxiliary quantities (Mh1, Mh2) at right angles to each other are formed by means of at least two FIR filters (8, 9). These quantities, together with two additional measurement auxiliary quantities (Mh3, Mh4) which are likewise at right angles to each other, are used to produce a measured value corresponding to the current amplitude and a measured value proportional to a differential angle. The additional measurement auxiliary values are produced from samples formed from older measurement quantities obtained before a quarter period of the current to be measured has elapsed. The differential angle is formed from the two measurement quantities. An output signal is produced from the two measured values in an evaluation device whenever the measured values exceed pre-set threshold values.