What is a Transformer?

An illustrated guide

Have you ever wondered what those gray metal cylinders are on power poles? How about those green metal boxes you see on the ground in some neighborhoods? They are transformers. This equipment transforms electricity to a voltage that is safe for use in homes and businesses. How do they work?

At the power plant the electricity produced by generators is stepped up by transformers to a very high voltage, often to 350,000 or 500,000 volts. High voltages help to send electricity on transmission lines over long distances.
Transmission lines connect to neighborhood substations that contain within their fences transformers and other control gear. Here the transformers step down the voltage to safer levels for distribution power lines. Depending upon the distance involved to the furthest member served, distribution voltages can range from 12,500 to 34,000 volts.
Nearby transformers again step down the electricity for delivery to your home at 240 volts.
Regardless of the shape and size of the transformer, they all work in the same manner. They have two sides, a high-voltage side and a low-voltage side. In normal operation, electricity flows into the transformer on the high-voltage side, where it goes into a coil of wire usually wound around an iron core. Each coil has a different number of turns. The greater the number of turns, the higher the voltage. The coil on the high side will have more turns than the one on the low side. As a result, the voltage on the low side is less.
Transformers can be found everywhere in our daily lives. The best example is the charger that all cell phones and many other electrical devices come with. These small cousins of utility transformers basically perform the same function. Charging your cell phone with 120 volts will fry it instantly. So, the charger converts the voltage to a more tolerable 5 volts or so.

Click on the image above to follow the path of electricity through transformers.