Using instrument transformers in a wider frequency range

The introductory part of this paper presents the theory of instrument current and voltage transformers with a view to using them in a wider frequency range. A general substitution diagram is presented, including the parasitic capacitances which take effect when using a transformer at frequencies higher than mains frequency. An important parameter is the resonant frequency of the transformer, which is defined in the paper. Methods for determining the frequency dependence of the instrument current and voltage transformer are given at the end of the paper.