The current from rectifiers can be measured by using Rogowsky coils which are installed on each leg of the rectifier giving the derivative of the current. Current signals (channels) are integrated and added to give the total current. The individual channels are checked for polarity to detect reverse current -
a condition which will shut down the system. Measurement of current and reverse current detection using the signals from Rogowsky coils are replaced by a digital system using PLC devices by Comp. Beckhoff.
The goal of the project was the accuracy and error analysis of the measurement system for all channels, using MATLAB and other simulation tools. The hardware details of the measurement and computational system are as follows:
The signals from Rogowsky coils are pre-processed by a RC-filter which decreases the slope of the signal. Using a RC-filter reduces problems with aliasing and clipping in the A/D converter which accepts signal amplitudes from -10 to 10 volts (Beckhoff a/d limits). The sampling rate is increased by a parameter factor by using an interpolation algorithm developed by AREVA which takes into account the signal specific information about the shape of the Rogowsky pulses. The methods of Rogowski signal integration, e.g. numerical integration by a trapezoidal rule with step size T or other numerical integration methods, are the key problem of the project. After large simulations with MATLAB and other simulation tools the accuracy goal for the hard- and software project could be reached.

• Prof. Dr.-Ing. Hans-Rainer Langner (Projektleitung)

AREVA GmbH

• Söral AG