Difference Between Current Transformer (CT) and Potential Transformer (PT)


Difference Between Current Transformer (CT) and Potential Transformer (PT)

There are a few differences in current transformer (CT) and potential transformer (PT).  These are mentioned below:-

Sr. No.

Current Transformer (CT)

Potential Transformer (PT)


It is a basically step up transformer.

It is a basically step-down transformer.


Primary winding has one or a few turns of thick wire.

Primary winding has large number of turns of fine wire.


The secondary winding having large number of turns of fine wire.

The secondary winding has much smaller number of turns.


Current transformer is connected in series with one line and a small voltage exists across its terminals.

Potential transformer is connected in parallel with the circuit and full line voltage is impressed upon its terminals


The primary current of CT is independent of secondary circuit conditions rather it depends upon the line or load current

In PT, the primary current depends upon secondary burden.


In current transformer, line or load current vary over a large range, therefore exciting current in CT varies over a large range.

Under normal working conditions, the line voltage applied across the PT remains almost constant, therefore, the exciting current in a potential transformer varies only over a restricted range.


Ammeter is used in conjunction with a current transformer for measurement of current.

Voltmeter is used in conjunction with a potential transformer for measurement of voltage.


Current transformer works under short circuit conditions.

The secondary winding of potential transformer can be open-circuited without any damage being caused either to the operator or to the transformer.


From the constructional point of view, there are two types of current transformers :

(i)                 Wound Type:-  A current transformer having a primary winding of more than one full turn wound on core.

(ii)               Bar Type: – A current transformer in which the primary winding consists of a bar of suitable size and material is forming an integral part of transformer.

The potential transformer is made shell type because this condition develops a higher degree of accuracy.

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