A calibrating device for large direct current instruments up to 320 kiloampere-turns

A device for calibrating large dc instruments ranging up to 320 kA has been designed. The calibrating coil simulates the actual busbar and its turns can readily be changed to meet various required measurement ranges. The calibrating coil is arranged in the shape of a cross so that we can determine the influence of the external magnetic field. The accuracies are 6/spl times/10/sup -6/ when a differential current measuring method is adopted and 200/spl times/10/sup -6/ when a differential voltage measuring method is adopted. The stability of the power supply is 0.02% per hour. The error due to the current fluctuation is very small and thus can be neglected.