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

A device for calibrating large de instruments ranging up to 320 kA has been designed. The calibrating coil simulates the actual busbar and its turns c an readily be changed to meet various required measurement ranges, The cali brating coil is arranged in the shape of a cross so that we can determine t he influence of the external magnetic field, The accuracies are 6x10(-6) wh en a differential current measuring method is adopted and 200x10(-6) when a differential voltage measuring method is adopted. The stability of the pow er supply is 0.02% per hour. The error due to the current fluctuation is ve ry small and thus can be neglected.