On the calibration of direct-current current transformers

Modern commercial direct-current current transformers (DCCT) can measure currents up to the kA range with accuracies better than 1E-5. We discuss here a DCCT calibration method and its implementation with commercial instruments typically employed in low resistance calibration laboratories. The primary current ranges up to 2 kA; in the current range below \SI{100}{\ampere} the calibration uncertainty is better than 3E-7. An example of calibration of a high-performance DCCT specified for primary currents measurement up to 900 A is discussed in detail.