You've been hearing a lot about power grids since the recent blackout. But do you know what they are and how they work? Today's lesson sheds light on how they keep you out of the dark.

Electrical energy is like air. You don't notice it until all of a sudden, it's not there. Though officials are still trying to figure out exactly what caused the latest blackout, it is certain that the failure happened somewhere in the massive power grid that supplies energy from New York to Detroit and even to Canada.

You've seen power lines. Take notice the next time you see them. They are part of a huge electrical distribution system called the power grid. These massive energy highways are almost hidden in plain sight, so commonplace that we don't even notice them - until they fail. Just what is a power grid and how does it work? It all begins at the power plant. Energy is produced by a spinning generator that can be powered hydraulically (using water), or with diesel fuel or gas; most often, steam is used. The steam is created using coal, oil, natural gas or nuclear energy.

Once the power leaves the generator, it enters a transmission substation that converts it to the extreme high voltage necessary for it to travel long distances.

High-voltage, transmission lines will transport up to 765,000 volts as far as 300 miles away. These are the huge steel towers you see near a power plant. These power towers usually have three wires and extra ones to attract lightning.

Next, the transmission reaches the power substation, where it is converted from the high voltage necessary for transmission to a lower voltage for distribution to our homes and businesses.

A power grid transfers electricity from the power plant to your home.

The substation delivers power to two sets of distribution lines at two different voltages. The smaller transformer goes down to standard line voltage, about 7,200 volts, while the higher voltage travels on.

There are regulators along the line to make sure there is enough voltage for use and also to prevent an overload.

The energy finally makes it to your house by way of power poles whose lines go directly into your house. Every home has its own power lines.

You can even see transformer boxes on the wire poles. They transfer the energy from the line to the house. The transformer reduces the 7,200 volts down to 240 volts, which is what powers appliances like your TV and washing machine. The voltage reaches your house through a watt hour meter. You've probably seen these on the outside of your house or in the basement. It looks like a series of moving dials that measure the electricity your house uses. This is also what the electric company uses to determine your monthly electric bill.

When the power enters your home, it hits a circuit breaker. The circuit breaker separates the power and determines which wires it will flow through to reach its final destination for use - outlets.

You should never touch a power line, circuit breaker or voltage meters in your own home, but know that they are part of a huge network, sometimes hundreds of miles away, that allows you to let there be light.

For more information about power grids, go online and check out www.howthingswork.com.

Today's lesson fulfills the following New York standards: English Language Arts: E1c, E3c, E3d; Science : S4a, S5c, S7b, S8c

Have a discussion with your class about the recent blackout. How did you manage without subways, television or lights?

Use today's paper to prepare a blackout safety kit. Make a list and find pictures of items to include.

It has been said that the current power- grid system is outdated. Choose a partner and create a new power system. Draw a diagram of how you think this system will work.