On the high-frequency response of a Rogowski coil

Abstract

In this paper a Rogowski coil with a capacitive shieid is treated as a distributed circuit, so that the toroidally wound coil acts as a delay line. It is shown that, in general, the high-frequency response is limited by the transit time around this delay line, and for times greater than this transit time the individual circuit elements act as lumped impedances. However, if the flow of the current to be measured is such that it is symmetrical with respect to the toroidal coil (so that the voltage induced per unit length along the coil, when the current changes, is constant), the transient response becomes less than the transit time for a termination whose impedance is small compared with that of the toroidal coil. The best results may be obtained with an inductive termination whose impedance has the same phase angle as the impedance of the toroidal coil; and for this termination the output is proportional to the rate of change of current.