Principle, type and accuracy of current transformer

Principle of Current Transformer

Like transformers, current transformers are instruments that convert large primary currents into small secondary currents for measurement based on the principle of electromagnetic induction.

Current transformers are composed of a closed iron core and windings.

Its primary winding has few turns and is connected in series in the circuit of the current to be measured.

The secondary winding has many turns and is connected in series in the measuring instrument and protection circuit.

When the current transformer is working, its secondary circuit is always closed, so the impedance of the series coil of the measuring instrument
and protection circuit is very small, and the working state of the current transformer is close to short circuit.

Type of Current Transformer

Metering current transformer: electricity bill settlement.

Measurement current transformer: measure current, calculate electricity, etc., the accuracy is generally lower than the dual-purpose transformer, not used for settlement.

Protection current transformer: current speed protection, overcurrent protection, overload protection, etc.

Accuracy of Current Transformer

The accuracy of the current transformer for calibration: 0.1S level. The error of 0.1% is often used to calibrate the accuracy of the current transformer for measurement.

The accuracy of the current transformer for measurement: 0.2S 0.5 level. The error of 0.2% and 0.5% is used as the basis for electricity bill settlement, and 0.5 level is also used in some occasions.

Measurement level current transformer: 0.5 level, 1.0 level, 2.0 level, etc. are generally used for ammeters.