Current transformer TOPA 0,66-B is used in AC installations operating in climatic conditions "U". It allows taking readings of the level of the electrical signal using measuring instruments. Such transformers are installed at electric power facilities operated in various sectors of the national economy: industrial, agricultural, municipal, etc. The rules for the placement of transformers are established by DSTU 15150-69. They work in any position. The material for their measuring winding is a nanocrystalline alloy. Its use makes it possible to take characteristics in a wider linear dynamic range, even if the currents are less than 1%. At the same time, long-term stable characteristics are achieved throughout the entire service life of the transformer, and the magnetic circuit remains insensitive to the effects of short-circuit currents that can lead to magnetization by unipolar pulses.