Pole-mounted Current Transformer

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Working Principle of Pole-Mounted Current Transformer

The working principle of current transformer is made based on the electromagnetic induction principle. A current transformer consists of a closed core and windings. Its primary winding has very few turns and is connected in series with the line where the current needs to be measured, hence the entire current of the line often flows through it. The secondary winding has more turns and is connected in series with the measuring instruments and protection circuit. When the current transformer is in operation, its secondary circuit is always closed, thus the impedance of the series coil of the measuring instruments and protection circuit is very small, and the operating state of the current transformer is close to a short circuit. The current transformer converts the high current of the primary side into a low current on the secondary side for measurement, and the secondary side should not be open-circuited.

Current Transformers are mainly used to convert large currents in AC circuits into smaller, proportionate currents(standardized at 5 amperes), for measurement and relay protection purposes. You might have seen an electrician's clamp meter, which is a device used to measure AC current; the "clamp" is a through-core current transformer.

A current transformer consists of a primary coil, a secondary coil, a core, insulating supports, and output terminals. The core of the current transformer is made of stacked silicon steel sheets, and its primary coil is connected in series with the main circuit, carrying the measured current T1, which generates an alternating magnetic flux in the core, inducing a corresponding secondary current T2 in the secondary coil. If excitation losses are ignored, then T1n1 = T2n2, where n1 and n2 are the turns of the primary and secondary coils, respectively. The transformation ratio of the current transformer K=T1/T2=n2/n1.