| 摘要 |
In an impedance-measuring device for impedance protection, the phase positions of a plurality of alternating-current quantities are compared with the aid of a phase comparator. From the output signal thereof it is clear whether the impedance in a fault loop with a voltage U and a current I lies inside or outside an impedance zone, which is defined by means of a model impedance, Zk=R+jX. The comparator is supplied with input quantities corresponding to IX, Uk, I and preferably also Up, where Uk=U-IZk, whereas Up relates to a voltage which is phase-shifted -90 DEG with respect to U. Quantities corresponding to IX, Up and I are each supplied to one input of a second logic component. This second logic component also has an input which is connected, via a delay element, to the output of a first logic component, the two inputs of which are supplied with quantities corresponding to I and Uk, respectively.
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