Electric Power Facilities - the basic system

After power is generated at a generation plant, the voltage is "stepped up" by a transformer to give it the "push" to travel long distances. High voltage allows electric power to be carried efficiently over the transmission system. Long distance transmission lines in Ontario are 115 kilovolts (kV), 230 kV or 500 kV. Transmission lines are usually on steel lattice towers, steel poles or double wooden poles.

Close to the location where it will be used, electric power is then stepped down at a transformer substation station to a lower voltage for distribution to a local area. Typical local "distribution" voltages are 44 kV, 27.6 kV, 13.8 kV and 6.9 kV. These are the power lines you see on city streets, strung on concrete or wooden poles.

Before electric power enters your home, it is further reduced in voltage, usually by a small "pole-top" or "pad-mounted" transformer. Power coming into your residence is usually 120 V or 220 V.

Electrical substations perform many functions in controlling and transferring power in an electric system. Many stations contain transformers to convert power from one voltage to another. They can also contain circuit breakers to turn lines on and off, or switches to divert power from one line to another.

In North America, the entire electrical system uses alternating current (AC), as opposed to direct current (DC) produced by batteries. Electric power flows back and forth or "alternates" at a frequency of 60 cycles per second or 60 Hertz (Hz). In many other locations in the world, including Europe, electrical systems operate at 50 cycles per second or 50 Hz.