Power transformers are at the heart of the substation. They step down the voltage from 735,000 volts (735 kV) to 120,000 volts (120 kV), the subtransmission level at which it is carried to regional substations.
Surge arresters are protective devices located on either side of power transformers. They’re connected at the top to a line conductor and at the bottom to the ground. Surge arresters protect the transformers and other electrical gear from voltage surges caused by lightning or substation switching operations.