How to choose the current transformer

How to choose the current transformer

Transformers of current are used in the systems of measurement of electric current and devices of relay protection of power systems. The main requirement to such transformers – ensuring high accuracy. Transformers have to ensure also safety of measurements that is reached by isolation of measuring chain from chain with high tension. The choice of the transformer demands some calculations.


1. Before choosing the transformer, it is necessary to find out the required output parameters of electrical circuit: tension of exit (Uv) and load current (In).

2. Calculate the output power of the transformer (Rvykh) by formula: Rvykh =uv x In;

3. Now choose transformer standard size within the counted power (proceeding from the available listed products). Pay attention to the physical sizes (dimensions) of the transformer.

4. Transformers can be in different climatic modification: pressurized and opened. Consider this design feature when choosing. It is important to choose execution type for conditions in which the transformer will be really operated.

5. Taking into account possible additional requirements for restriction of current of idling, tension of idling and overheating, it is reasonable to take output power with stock.

6. As essential criteria in favor of the choice of the transformer will serve availability of special impregnation and the thermal switch, feature of fastening of the device, types of conclusions. Consider that the complete set options other than basic execution can be slightly more expensive.

Author: «MirrorInfo» Dream Team