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What Is A Current Transformer?

A current transformer is a device that helps in measuring alternating currents. It converts the high primary current into a measurable low safety level secondary current.

Current transformers can be used to increase or decrease the alternating current. A typical current transformer is a series-connected electromagnetic device consisting of an iron core, electrical-grade laminations, and a copper-wound coil.

Why use a current transformer?

Current transformers are often used when the voltage or current is too high to measure directly. In this case, the CT performs its usual function of reducing the current.

The resulting lower or secondary currents are suitable for processing into electronic devices. In this way, the actual current flowing in the AC transmission line can be safely monitored by reducing the high current to an equivalent low current. Therefore, the current transformer is an indispensable part of the power system.

CTs are also used to protect precision measuring equipment. By increasing the number of windings, the current in the CT can be significantly smaller than the current in the primary circuit under test.

How does it work?

Current transformers follow the principles of Faraday's law of electromagnetic induction.
A current transformer is also known as a low-voltage current transformer (LTCT) because it takes a low-voltage and high current as input.

A CT consists of 2 windings - primary and secondary. The primary is connected to the power supply, while the secondary is connected to the distribution terminal. Instead of making electrical contact with each other, the two windings are twisted together around a sealed circuit of magnets called the core.

AC current flows through the primary winding. According to Faraday's law, an equivalent magnetic flux will be generated. This magnetic flux strikes the secondary winding and produces a proportional alternating current.

The primary current is determined by a separate external load, while secondary current is rated at 1A or 5A, making it suitable for measuring instruments.

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