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September 10, 2025Open Access

Measurement System for Current Transformer Calibration from 50 Hz to 150 kHz Using a Wideband Power Analyzer

MRMano RomVSL Dutch Metrology Institute HBHelko E. van den BromVSL Dutch Metrology Institute EHErnest HoutzagerVSL Dutch Metrology Institute

Key Points

The new calibration system reduces uncertainty in current transformer measurements, enhancing grid performance.
Uncertainty is maintained at 10 ppm up to 10 kHz and less than 120 ppm up to 150 kHz, supporting better accuracy.
This approach simplifies the calibration process, using a power analyzer directly without auxiliary equipment.
Operational setup details, like grounding and cable type, critically affect measurement uncertainty and repeatability.

Abstract

Accurate and reliable characterization of current transformer (CT) performance is essential for maintaining grid stability and power quality in modern electrical networks. CT measurements are key to effective monitoring of harmonic distortions, supporting regulatory compliance and ensuring the safe operation of the grid. This paper addresses a method for the characterization of CTs across an extended frequency range from 50 Hz up to 150 kHz, driven by increasing power quality issues introduced by renewable energy installations and non-linear loads. Traditional CT calibration approaches involve measurement setups that offer ppm-level uncertainty but are complex to operate and limited in practical frequency range. To simplify and expand calibration capabilities, a calibration system employing a sampling ammeter (power analyzer) was developed, enabling the direct measurement of CT secondary currents of an unknown CT and a reference CT without any further auxiliary equipment. The resulting expanded magnitude ratio uncertainties for the wideband CT calibration system are 10 ppm (k=2) up to 10 kHz and less than 120 ppm from 10 kHz to 150 kHz; these uncertainties do not include the uncertainty of the reference CT. Additionally, the operational conditions and setup design choices, such as instrument warm-up duration, grounding methods, measurement shunt selection, and cable type, were evaluated for their impact on measurement uncertainty and repeatability. The results highlight the significance of minimizing parasitic impedances at higher frequencies and maintaining consistent testing conditions. The developed calibration setup provides a robust foundation for future standardization efforts and practical guidance to characterize CT performance in the increasingly important supraharmonic frequency range.

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