Contribution to the calibration of current transformers with a rated secondary current of less than 1A

Standardized values of current transformers with the rated secondary currents of 5 A and 1 A are defined according to the requirements of analog measuring and relay techniques that were typical for the technology of the last century. The development of microprocessor technics and technology as well as digitalization processes in transmission and distribution sectors of power industry requires rated secondary currents of current transformers of less than 1A. That implies different technical and technology difficulties in manufacturing such transformers as well as its accuracy testing. This paper is contribution to the calibration of current transformers with the rated secondary currents of less than 1A. The paper presents a new, modified differential measurement method that enables the calibration of the current transformers with the rated secondary current of less than 1A using a standard current transformer with the rated secondary current of 5A.