On-site calibration system for isolation current transformers

An on-site calibration system for three-phase isolation current transformers is described. It is based on precise power comparators which are shipped to the customer. Measurements can be done at test currents up to 120 A. The measurement uncertainties of the self-calibrating measurement system are in the order of 0.005% for the ratio error and 0.01 crad for the phase displacement at power frequencies.