This final paper describes current measuring transformers, their application and classification. Their operating principle is also explained and they are compared with power transformers in characteristic operating states. The second chapter discusses current measuring transformers in general, their design, connection methods and their behavior in no-load and short-circuit conditions. In no-load conditions, large overvoltages occur and the transformer is destroyed, therefore the secondary must never be left open. Each current measuring transformer is defined by current and angular errors and accuracy class. Their explanations, calculation methods and the impact of reducing the number of turns of the secondary winding are discussed in the third chapter. The fourth chapter explains the behavior of a current measuring transformer in conditions of increased primary current, methods of obtaining a current multiplier and the selection of current transformers. The last chapter presents in detail the characteristics of all current measuring transformers located in the TS 110/35/10 kV Vrboran.