Bandwidth of Current Transformers

Bandwidth is one of the important performance parameters of current transformers. Transformers are required to have adequate bandwidth to regenerate the measured current, apart from uncertainties that are caused by the nonsinusoidal waveforms along with harmonics. An expression for the transresistance of the current transformer in terms of parasitic components is derived. Approximate expressions for lower cutoff frequency, upper cutoff frequency, and bandwidth are derived from the equivalent models of the current probe in the corresponding frequency range. The expressions are validated by experimental results for a current transformer using a Ferroxcube ferrite core 528T500-4C4. An overview of the effects of different parasitic components, such as magnetizing inductance, leakage inductance, and stray capacitance, on the bandwidth of a current transformer is presented.