Compensating Nonlinearities in Voltage Transformers for Enhanced Harmonic Measurements: The Simplified Volterra Approach

The number of nonlinear devices in distribution grids has rapidly grown in the last years, and this trend is likely to increase in a near future. In this scenario, power quality monitoring and identification of disturbance sources are critical aspects. Inductive transformers are often employed for this purpose, although their metrological performances are guaranteed only near rated frequency. Secondary voltage harmonics are affected by the filtering behavior of the transformer, but also by nonlinearities due to the iron core that may have remarkable impact. In this work a novel post-processing technique allowing to dramatically reduce the detrimental effects of nonlinearities is proposed and discussed. After explaining the methodology, it has been applied to enhance the harmonic measurement accuracy that can be obtained by using an inductive medium voltage instrument transformer. Experimental tests carried out in laboratory show the significant performance improvement achieved thanks to the proposed approach.