Abstract: To minimize the outlay for circuit engineering in a measuring system having at least one measuring instrument for measuring power and/or power factors at least one measuring point in an a.c. voltage network, a voltage transformer device having in each case one voltage transformer for each phase of the a.c. voltage network is arranged at a voltage-detection site of the a.c. voltage network. In addition, a current transformer for each phase is arranged at each measuring point, and to connect a measuring instrument assigned is connected to the particular measuring point at a current transformer input. The voltage transformer device and all measuring instruments are interconnected via a shared data-transmission device, in which predefined information on the detected voltages is digitally transmitted to the measuring instruments.

Abstract: Spectral values are calculated from sampling values of the network voltage or current using the discrete Fourier transformation. Of these values, only those that are greater than a predefined threshold value (SW) are transmitted or stored. The missing spectral values are assumed to be equal to zero to reconstruct the sampling values. In general only those spectral values are transmitted or stored that pertain to a fault and its previous and subsequent history of a few seconds.