Nickel and chromium plated terminals in current transformer circuits

When nickel or chromium plated terminals are used in the circuits of precision current transformers, instabilities are often observed in their calibration. The nature of these instabilities suggests the cause to be small DC components flowing in the transformer windings. In the paper, the DC components are explained in terms of semiconducting oxides on the terminal contact faces. Experimental results indicate that chromium in contact with oxidised copper produces the worst effects. It is concluded that the problem would be solved if manufacturers simply used unplated copper or brass terminations.