Design of standard instruments, relays or equipment normally does not permit them to be considered directly to the high voltage system. Potential transformers therefore play a key role hereby performing the following functions:

1. For electrically isolating the instrument and relays from the high voltage side.

2. For transferring voltage from higher values to proportional lower values upto 63.5, 100V or 110V as per the standard of the equipment.

Potential transformers are of:

1. Indoor resin cast & oil cooled type.

2. Out door oil cooled type.

The class of accuracy of metering PT are 0.1, 0.2, 0.5, 1.0 and protection PT is 3P