Measurement of Dynamic Voltage Variation Effect on Instrument Transformers for Power Grid Applications

Within the framework of distribution and transmission grids, knowledge of Instrument Transformers (ITs) behavior in distorted conditions is a topics of great interest. Its relevance stems from the ITs wide use in metering, protection, monitoring and control applications, where their role is to reduce voltage and current to levels compatible with measuring instruments input. In force standards require that the performance of measuring instruments is assessed under realistic conditions. On the contrary, performance test of ITs are generally carried out only at rated conditions, so that their behavior under actual waveforms is not fully known. To cover this gap and starting from the hardware used for the Medium Voltage (MV) Voltage Transformer (VT) frequency characterization, a suitable setup is developed for the traceable test of VTs under a quite large set of static and time varying test waveforms. In the paper, after a short description of the setup, examples of its applications to the evaluation of the performances of ITs under different test voltage waveforms are given, including a realistic reproduction of a PQ event and focusing on the amplitude and phase modulation tests, as those suggested for the Phasor Measurement Units in IEEE Std. C37.118.1. Preliminary experimental results are shown.