# Difference between Current Transformer(CT) & Potential Transformer(PT)

Last Updated on October 14, 2023 by Electricalvolt

One of the major differences between a current transformer and a potential transformer is that the current transformer steps down the high value of current into a low value, whereas the potential transformer steps down high voltages into low voltage. Thus, CT and PT transformer decrease the current and voltage from high to low values.

CT Full form is current transformer, and PT full form is the potential transformer. Let us first discuss what the Current Transformer (CT) and Potential Transformer (PT) are.

The transformer is an electrical device used to either increase (i.e., step up) or decrease (i.e., step down) the electric voltage or current in a circuit. This device plays an important role in ensuring the safety of the electronic components of the circuit by preventing them from getting damaged due to high values of voltage applied across them. The step-up transformer increases the voltage magnitude for transmitting power at long distances. In contrast, a step-down transformer is used to reduce the voltage or current applied across the components of an electric circuit.

Depending on the type of application, there are three types of transformers:

• Instrument Transformer
• Distribution Transformer
• Power Transformer

Depending on the type of electric quantity to be stepped up or stepped down, instrument transformers are broadly classified into two categories as follows,

• Current Transformer (CT)
• Potential Transformer (PT)

## What is a Current Transformer (CT)?

A current Transformer is a kind of instrument transformer used for the purpose of converting high magnitudes of current into lower values in order to measure high current with the utmost safety. The Current transformer is comprised of the primary and secondary winding.

The symbol of CT is;

The AC current flowing in the secondary winding of the CT is directly proportional to the current across its primary winding from where it’s measured. The current transformer is also called a “series transformer”, as the primary winding of the transformer is in series with the current flowing across the conducting material. Moreover, the primary winding has a lesser number of turns as compared to the secondary winding of the transformer.

Depending on the type of primary winding, the current transformer is of three types:

• Wound Current Transformer – In this type of transformer, the primary winding is connected in series with the current flowing across the conductor.
• Toroidal Current Transformer – In this type of transformer, the primary winding is absent in the CT. Instead, the current conducting wire is inserted into the transformer directly.
• Bar-Type Current Transformer – In this type of transformer, the primary winding is the main conducting cable of the circuit, which is just one turn one long, completely insulated from the high voltage values.

## What is a Potential Transformer (PT)?

A potential transformer is a kind of instrument transformer used for the purpose of converting high voltage values into lower voltage values to help ease measurement and improve the protection of the electronic circuit and its components.

The Potential transformer is comprised of the primary and secondary winding, just like a current transformer. However, in contrast to the current transformer, the primary winding of the potential transformer has a lesser number of turns as compared to its secondary winding based on the ratio of the potential transformer.

The symbol of PT is;

The primary winding of the PT is connected to the power grid from where the voltage has to be measured. The secondary winding of the PT is linked to the voltmeter measuring device to read the voltage obtained at the output.

The PT can be divided into the following two types:

• Wound potential transformer – This type of transformer has its primary and secondary windings wounded to the core of the transformer, provided with appropriate insulation.
• Capacitor voltage potential transformer – This type of transformer has a capacitive divider and auxiliary transformer instead of the primary and secondary windings.

## Difference between Current Transformer (CT) and Potential Transformer (PT)

The most important differences between the Current Transformer (CT) and Potential Transformer (PT) are described in the table below –

### Conclusion

It can be concluded from the above discussion that although both current transformer (CT) and potential transformer (PT) are instrumentation transformers, they have some notable differences between them, as listed in the difference table. The most significant difference between CT and PT is that CT operates as a step-up transformer, while PT functions as a step-down transformer. Both these transformers work to ensure the protection of electrical power systems by preventing severe damage to them and easing the task of measuring electrical parameters like voltage and current.

CT and PT are widely used in measurement and protection circuits.

Satyadeo Vyas, M.Tech,M.B.A. is an electrical engineer and has more than 36 years of industrial experience in the operation, maintenance, and commissioning of electrical and instrumentation projects. He has good knowledge of electrical, electronics, and instrumentation engineering.