Impedance-measuring device for impedance protection

Claim 1

An impedance-measuring device for the impedance protection of an electric power line, comprising a comparator means built up from logic components for comparing the phase positions of a plurality of alternating current quantities which together contain information of such a nature that a phase comparison of said quantities is sufficient to obtain a criterion of whether the impedance in a fault loop lies inside or outside certain limits of an impedance zone which are defined by means of a model impedance, Z k =R+jX; said alternating current quantities being transformed into signals containing only polarity information, said signals each being supplied to an input of at least one comparator means which is adapted to supply a specified output signal only when the supplied signals constitute a combination of logic levels for which the impedance of the fault loop lies inside said limits, one of said signals corresponding to the current I in the fault loop, each of said comparator means comprises a first, a second and a third logic component; and that one of the inputs of said second logic component is connected via a delay element to the output of said first logic component; and that the input side of said first logic component is supplied with a signal corresponding to U k =IZ k -U, where U is the voltage of the fault loop, and with said I-signal; and further that said I-signal and a signal corresponding to IX are supplied to respective inputs of said second logic component; and that said third logic component has an input to which said U k -signal is supplied as well as an input which is supplied with a signal which is derived from the output signal of said second logic component.