what is potential transformer

A potential transformer (PT), also known as a voltage transformer (VT), is an instrument transformer used for the protection and measurement purposes in power systems. It is a step-down transformer that reduces high-level voltage to safer low levels. The output voltage of the potential transformer can be measured by connecting an ordinary voltmeter. Potential transformers are connected across or parallel to the line being measured to record phase angle errors or ratio errors. The primary winding of a potential transformer usually has many turns, while the secondary winding has few turns. The stepped-down voltage by the potential transformer can be measured using a low range AC voltmeter. The secondary winding of the potential transformer is usually grounded on one terminal to provide proper protection to the operator. There are three primary types of potential transformers: electromagnetic, capacitor, and optical. The basic construction and operation principle of a potential transformer is similar to that of a standard electric transformer.