Secondary current distortion of inductive current transformer in conditions of dips and interruptions of voltage in the power line

• The connection between magnetic flux and inductive CT transformation accuracy is discussed.
• The results indicate why variation of inductive CT's primary current rms value causes additional distortion of its secondary current.
• It is explained how rapid changes of inductive CT’ primary current cause overvoltage.
• Inductive CT operation for dips/interruptions of power line's supply voltage is analyzed.
• It is presented how to ensure repeatability of measurement results with the usage of FFT algorithm.

The aim of this paper is to present results explaining the phenomenon of inductive current transformers (CT) additional secondary current distortion in condition of variation of their primary current rms value caused by dips and interruptions of the power line's voltage. To assess its accuracy of current transformation for such transients, harmonics spectrums’ of primary and secondary currents are compared. To ensure repeatability of measurement results with the usage of FFT algorithm, regardless of the beginning of the sampling process, the window of 16 fundamental periods consisting 4 dips/interruptions cycles is used. Additional CT's secondary current distortion caused by repeatable transients results in increased error of indirect measurement of rms values of power line's current higher harmonics and additional inaccuracy of power quality estimation.