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Image: Power grid monitoring
Southern California Edison employees in Alhambra monitor the utility's power distribution grid, with indicator lights lining the walls.
msnbc.com contributor

The electricity powering your computer as you read this may well have been generated at some power plant several states away, less than one second ago. How did it get from there, to you? You can thank some very interesting properties of electricity itself — and “The Grid,” which is the largest machine ever built by humans.

The grid is the giant network of high-voltage power transmission wires — those big ones up on those tall construction-set towers — that covers the entire United States and much of Canada. These wires are all interconnected at hundreds of substations, so power companies can buy and sell “product” from each other. Effectively it’s a single machine to distribute electricity, stretching 3,000 miles from east to west, and 3,000 miles from north to south.

The Grid has three main sections. The eastern part connects everything from the Rockies to the Atlantic, and from Florida up into Canada. The western network connects everything west of the Rockies from Mexico up to Canada. Most of Texas is on a grid of its own. (Back in the 1930s, Texas utilities didn’t want to deal with interstate government controls.)

For control purposes, the grid is broken down into 150 smaller subsections, so the Gridmeisters can monitor things on a more local basis.

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But those subsections are only organizational. The wires are all interconnected. It is technically possible to light up a light bulb in Seattle with a watt that was generated in Tallahassee.

Path of least resistance
The whole Grid idea wouldn’t work without a unique property of electricity. Electricity will travel down whatever path provides the least resistance, kind of like water running downhill.

Think of the Grid as if it were a huge network of hoses that carry water, connected at lots of places so the water in one hose can flow into another. Pump some water up into one of those hoses and, because of all the interconnections, the water can find its way into any of the hoses as it goes on its way. This imaginary giant network of hoses holds a cumulative reservoir of water.

Well, the electric power grid is a giant network of thick aluminum wires that holds a reservoir of electricity. The individual watts in any one of those wires might have come from any of the generating stations pumping power into the grid.

Substations, the crossroads on the grid, take in the high-voltage juice from transmission lines, redirect some of it back out onto other high-power lines, and transform some of it into lower-voltage power that goes into distribution lines on those poles on the street and finally into your house.

Every time you turn on anything plugged into the wall, you are drawing electrical power from the Grid, at the speed of light — 186,000 miles per second. When you switch on a lamp, it’s like sucking on a straw. The lamp draws power out of the wall plug. That draws power from the wire in your wall between the plug and your circuit breaker box. That in turn draws power from the line that runs between your house and the distribution line out on the local power pole. That draws power from the distribution line itself, which then draws power from one of the high-voltage grid transmission lines feeding the substation.

Looking for imbalance
The people at the 150 grid control stations spread across the United States and Canada are constantly watching for tiny variations in the frequencies of the electrical energy in the transmission wires, which tell them how to adjust things so the demand for electricity from consumers and the supply from the generators always matches. Balance in the grid is vital to protect it from failure. Here’s how imbalance can throw everybody into the dark:

Too much electricity in a transmission line can cause it to heat up, and sag. That can permanently diminish the wire’s capacity to carry electricity. If a line gets too hot — or sags too low, so it can zap people on the ground — the Grid Police turn it off. When that happens, the electricity from that line suddenly flows into all the others. They get hotter, and sag. So if anything makes even one line in the Grid too hot — like a sudden imbalance between supply and demand that encourages electricity to flow down one particular path — it can have a domino effect on the whole system. This was the basic problem that shut down the grids for Pennsylvania, New Jersey and Maryland for several hours in 1967.

A sudden loss of one major transmission line or a substation — due to a storm, a plane crash or a stupid bird landing in the wrong spot — can trigger the same chain reaction. The electricity that used to be in that line suddenly starts flowing in the others. The imbalance triggers safety equipment to turn everything off before it overheats. That’s what triggered the Northeast blackout in 1965.

Too much demand and not enough supply — as is “currently” the case in California — can also lead to an imbalance. That, in turn, can cause something called voltage collapse, which can shut down a major section of a regional grid. Voltage is like the pressure that pushes the electricity through the wire. If the voltage is strong where the power plant is making nice fresh watts and pumping them into the grid — but weak at the other end where too many customers are all drawing power from the grid — the imbalance in voltage between one end and the other interrupts the smooth electromagnetic field in the transmission system that helps the electricity flow.

This field is like an invisible lubricated lining inside the transmission wires. Interrupt that “lubrication,” and the electricity can’t flow. That’s what they call voltage collapse. Even if that happens in one major line, in seconds it can trigger a domino effect and shut down the wider system.

Since the balance between supply and demand is so important, bringing the Grid back online after a big shutdown is more than a matter of just flipping a switch. They have to restore the system one transmission line at a time, so they don’t suddenly shock things with more supply than there is demand. Which is why, after the ’65 blackout in the Northeast, it took nearly a day to restore power to everybody.

David Ropeik is a longtime science journalist and currently serves as Director of Risk Communication at the Harvard Center for Risk Analysis.

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