LAUSR

Abstract The constant increase of switching power converters in distribution and transmission grids pushes the need for harmonic measurements. Recent literature has shown that inductive Voltage and Current Instrument Transformers (VTs and CTs) can be used for harmonic measurements, but their accurate frequency characterization involves the use of quite costly instrumentation. In this context, this paper proposes an industry oriented technique for frequency characterization of medium voltage inductive VTs, involving instrumentation that, typically, is present in accredited laboratories or at VT manufacturers premises. In fact, it requires the generation of only sine waves and the measurement of: i) ratio and phase errors in sinusoidal rated conditions, the same prescribed by the international standards, and ii) ratio and phase errors with sine waves at 7 V from power frequency up to the first resonance frequency. The proposed technique, named SINDICOMP-LV, has been applied to medium voltage VTs and validated by the INRIM reference system for frequency characterization of VTs. Accuracy improvement with respect to the use of a conventional low voltage frequency sweep is up to one order of magnitude for the ratio error and up to 5 mrad for the phase over the considered frequency ranges, depending on the frequency value