Coreless current measurement transducer and instrument for distorted and noisy currents

Accurate measurement of distorted, noisy and pulsed currents is still a challenge. Current transformers introduce unacceptable errors in magnitude and/or phase shift. Rogowski coils are useful for clamp-on field measurements, but can be cumbersome to use. This paper presents a transducer consisting of coreless transformer and a non-integrating electronic amplifier. Calibration of two prototype transducers, for primary currents of 20 A and 60 A rms, is presented, confirming excellent linearity throughout the range, both in terms of magnitude and frequency. Together with a dedicated stochastic instrument, these transducers can perform very accurate measurement of distorted mains currents, including the current harmonics as well as measurements of active and reactive energy. Measurement accuracy is confirmed in two cases of low-level, distorted and noisy currents.