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How to choose a current transformer

How to choose a current transformer

Current transformers are used in systems for measuring electric current and relay protection of power systems.

The main requirement for such transformers - high precision.

Transformers must also ensure the safety of the measurement, which is achieved by isolation of the measuring circuit of the high voltage circuit.

Selecting the transformer requires some calculations.



Before you select the transformer, it is necessary to find out the required output parameters of the electrical circuit: output voltage (U in) and load current (Ir).


Calculate the output transformer power (Pout) by the formula:
Pout = U in x In-


Now select the size of the transformer within the power of calculated (based on the existing product range). Pay attention to the physical size (dimensions) of the transformer.


transformers can be in different climatic design: sealed and open. Consider this when choosing a design feature. It is important to choose the type of execution for the environment in which the transformer will actually be used.


Taking into account possible additional requirements for current limiting idling, open-circuit voltage and overheating, it is advisable to take the output from the reserve.


The essential criteria for choosingthe transformer will be the presence of a special impregnation and thermal fuse, especially fastening devices, types of terminals. Please note that a complete set of options different from the standard version may be slightly more expensive.

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