The transmission of measured values and, if necessary, diagnosis data by the high-voltage devices or from the high-voltage part of an electric filter is necessary for controlling the power electronics of the high-voltage devices used for producing the high voltage.  The measured values are required, inter alia, in order to detect any flashovers occurring.  For this purpose, signal sampling of usually 10 ksamples/s per measured value is required. 
At each high-voltage device, at least two measured values are detected, namely a measured value for the voltage and a measured value for the current.  It is also possible to detect diagnosis data.  It is possible to detect further measured values at the high-voltage device, for example for the temperature, the transformer primary voltage of the high-voltage device and the like. 
The high-voltage devices or their high-voltage transformers are usually arranged on the roof of a housing in which the electric filter is accommodated.  In contrast, the control units, including the power electronics, are accommodated in a control room which, in the case of large electric filters, is at a spacing of approximately 100 m to 700 m from the electric filter and thus from the high-voltage devices. 
During operation of the high-voltage devices, voltages are used which are of the order of magnitude of 100 kV, with the result that electrical signal lines for signal transmission are not very suitable for transmitting signals between the measuring heads associated with the high-voltage devices and the control units. 
In the case of a high-voltage supply device known from the prior art for electric filters, the measured values are transmitted from the measuring heads associated with the high-voltage devices to the control units using a suitable transmission protocol via optical waveguides.  This transmission method gives the required signal qualities.  In the case of this high-voltage supply device for electric filters, each of the measuring heads of a high-voltage device is connected via an optical waveguide path to the control unit associated with the relevant high-voltage device. 
In particular in the case of comparatively large spacings between the control room accommodating the control units and the power electronics, on the one hand, and the high-voltage devices arranged close to the electric filter, on the other hand, considerable financial outlay for the installation and laying of the optical waveguide cable results in the case of the known point-to-point connections between in each case one high-voltage device and the control unit associated with it.  This aspect is particularly important when modifying existing high-voltage supply devices of this type, in which generally copper cables have already been laid, and often results in copper cables continuing to be used for signal transmission for financial reasons, although the signal quality which can be achieved with copper cables is considerably worse.