A current transformer (CT) is a type of transformer that is used to measure AC Current. It produces an alternating current (AC) in its secondary which is proportional to the AC current in its primary. Current transformers, together with voltage transformers (VTs) or potential transformers (PTs), which are designed for measurement, are known as an Instrument transformer.
The main tasks of instrument transformers are:
− To transform currents or voltages from a usually high value to a value easy to handle for relays and instruments.
− To insulate the metering circuit from the primary high voltage system.
− To provide possibilities of standardizing the instruments and relays to a few rated currents and voltages.
When the current to be measured is too high to measure directly or the system voltage of the circuit is too high, a current transformer can be used to provide an isolated lower current in its secondary which is proportional to the current in the primary circuit. The induced secondary current is then suitable for measuring instruments or processing in electronic equipment. Current transformers have very little effect on the primary circuit.
Current transformers are the current sensing units of the power system. The output of the current transformers are used in electronic equipment and are widely used for metering and protective relays in the electrical power industry.
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