A medium voltage signal generator for the testing of voltage measurement transducers

Abstract

The importance of power quality monitoring in medium voltage (MV) systems has dramatically increased in the last years. It is well known that a measurement system with wide bandwidth and very low distortion is mandatory for this purpose. Usually, the performance bottlenecks are the transducers which have to be carefully selected according to the required accuracy. Therefore, it is very important to test them in real-world (nonsinusoidal) operating conditions. However, the characterization requires generating arbitrary voltage waveforms with amplitude of several kilovolts. This paper proposes a very simple MV waveform generator employing basic instrumentation which is very common in calibration laboratories. It consists in an arbitrary waveform generator (AWG) connected to a power amplifier which feeds the low voltage winding of a step up transformer. The secondary, high voltage winding is attached to a reference voltage transducer and to the device under test. In general, the shape of the secondary voltage waveform can be very different from the reference voltage of the signal generator. However, assuming that the nonlinearities of the system are negligible, it is possible to estimate the transfer function between the reference voltage of the signal generator and the secondary voltage. Then, it is possible to compute the reference voltage for the AWG in order to obtain the desired secondary voltage waveform. This technique has been implemented and its performance has been tested. The experimental activity has shown that an accuracy of a few percent can be easily achieved.