How To Select The Precise Current Transformer?

       There are many precision current transformers on the market, so it is easy to be fussy. If you want to improve the measurement accuracy, you should consider the following two aspects when choosing a precise current transformer.

I Influence of primary current

        When the primary current of the precision current transformer is very small, the error will increase; when the primary current is larger than the rated current for a long time, the error will also increase. Therefore, generally, the primary measured current should be greater than 25% and less than 120% of the rated current of the transformer. Therefore, the primary side current of the transformer should be selected according to the rated range of the product.

II Influence of secondary load

       When the secondary load of precision current transformer increases, the error (ratio difference and angle difference) also increases. Therefore, the secondary load should not exceed its rated value (volt ampere or ohm number) in use. The secondary load capacity of the precision current transformer depends on the rated capacity of the current transformer. The rated capacity of the precision current transformer is the apparent power consumed when the rated secondary current I2E passes through the rated load Z2e, that is, S2E = I2E²xZ2e. In the production process of transformer, the magnetic core and cross-sectional area of current transformer can affect the rated capacity of current transformer, which is not discussed here. The linear relationship between input current of current transformer with 1:1000 turns and output voltage under different loads is shown in the figure above. 

       In the use of current transformer, its accuracy can be guaranteed only when the total impedance of secondary connection and instrument current coil does not exceed the rated capacity (volt ampere or ohm number) specified on the name plate. The rated load capacity of the current transformer with 10A / 10mA turns of 1:1000 generally does not exceed 200 ohm. When the load is greater than the load capacity of the current transformer, the input current may be saturated when the full scale is not reached, resulting in transformer conversion distortion.

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