Rarely does the power supplied at a wellsite match with the power required by the ESP. Normally the ESP requires a medium voltage, while the site power is either high voltage line power to low voltage generator power. In order to adjust the available voltage to the required voltage, transformers are used.

The transformer needs to be designed for the application that considers factors such as ambient temperature, weather, VSD rating, phase shifting, etc. as well as the sizing. Off shore applications are also often concerned about foot print.