How is Power Stepped Down?

By Scott Dreger

It’s more efficient to transmit electricity long distances at high voltages. So, to minimize losses, utilities increase-or step up-voltage after generation which is commonly 32-kV, transmitting power at up to 500,000 volts. Before this power can be distributed and used by customers, it must be stepped down or decreased in voltage so that it’s compatible with industrial or household appliances.

This is done with transformers—devices used to change one voltage to another. Southern California Edison steps down voltage one or more times with large substation transformers, and then again from distribution voltage, which is most commonly 12-kV, to 120/240V power that is delivered to residential customers. This final voltage reduction is done using distribution transformers that are attached to the pole, pad-mounted on the ground or buried underground.

A transformer is typically made of two wound copper coils separated by a magnetic core. The ratio of the windings to one another determines how much the voltage is stepped up or down. For instance, if one coil has 10 times the windings of the other, the voltage will change by a factor of 10.