Power Measurement Errors Using Current and Voltage Transformers in the Extended WB2 Optional Accuracy Class

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Original abstract

Modern power systems increasingly operate under distorted waveform conditions caused by distributed generation, renewable energy sources, and power-electronic loads. In medium- and high-voltage networks, power measurement accuracy depends on voltage and current transformers, whose ratio and phase displacement errors vary with frequency. This paper investigates how these errors propagate into indirect measurements of active, reactive, and apparent power. The analysis considers the conventional 0.2 accuracy class at 50 Hz and the extended 0.2 WB2 optional accuracy class for individual higher harmonic components up to the 400th order. Analytical expressions are derived for power measurement errors, and the results are presented as deterministic error envelopes. In addition, 16 global sign scenarios are evaluated to determine how different combinations of transformer error signs affect total power measurement. The results show that apparent power errors are mainly determined by ratio errors, whereas active and reactive power errors are additionally influenced by differential phase displacement errors. For higher harmonics, the WB2 frequency band limits produce step changes in the error envelopes, and relative errors may become large when the reference active or reactive power of a harmonic component is small. The proposed method extends conventional power error propagation analysis by linking harmonic power components with the frequency band limits of the IEC 61869 WB2 optional accuracy class and by introducing deterministic error envelopes and global sign scenarios for worst-case-oriented assessment under nonsinusoidal operating conditions.

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