How Undesired Non-Idealities of the Input Signal Affect the Accuracy Evaluation of Instrument Transformers at Power Frequency

This paper explores the calibration of Instrument Transformers (ITs) used in power grids metering. It highlights the lack of information in in-force standards regarding the non-idealities of the current and voltage generated for ITs calibration. Existing literature has proposed innovative calibration systems based on commercial ADC acquisition boards or digital multimeters. However, no studies have analyzed the impact of undesired non-idealities of the test signal on the measurement of power frequency ratio and phase errors. The paper aims to investigate and quantify the influence of Total Harmonic Distortion and frequency variation of the input voltage and current on IT accuracy assessment. The study is carried out through numerical simulations generating various THD levels and frequency variations and evaluating ratio and phase error through common algorithms. The simulation results show that especially for industrial laboratories in which uncertainty targets are more relaxed, THD levels higher than 2% can be tolerated by choosing proper measurement algorithms.