The Current Transformer ( C.T. ), is a type of “instrument transformer” that designed to produce an alternating current in its secondary winding which is proportional to the current being measured in its primary.
Potential transformer or voltage transformer gets used in electrical power system for stepping down the system voltage to a safe value which could fed to low ratings meters and relays. Commercially available relays and meters used for protection and metering, designed for low voltage. This is a simplest form of potential transformer definition.
1. The secondary of a P.T can be open circuited without any damage being caused either to the operator or the transformer.
2. P.T may be considered as a parallel transformer.
3. The primary current of a P.T depends upon the secondary circuit conditions (burden).
4. The primary winding P.T is connected across the line of voltage to be measured. Hence the full line voltage impressed across its terminal.
5. With the help of P.T, a 120V voltmeter could be used to measure very high voltages like 11KV.
1. The secondary of a C.T cannot be open circuited on any circumstance when it is under service.
2. A CT may be considered as a series transformer.
3. The primary current in a C.T is independent of the secondary circuit conditions (burden).
4. The primary winding of the CT connected in series with the line carrying the current be measured. Hence it carries of the full line current.
5. With the help of CT, a 5A ammeter could be used measure a high current like 200A.