How Electricity Makes Its Way From Power Plants To The Plugs In Your House

(Karim D. Ghantous/Flickr)
(Karim D. Ghantous/Flickr)

Turn back the clock just a couple of centuries, and to our ancestors, the alchemy of electricity would seem like magic: With the single flip of a switch, our rooms are bathed in light.

But how does electricity makes its way to the plugs in your house?

Step 1: Generation

As I stood on the floor of the Millstone nuclear plant in Waterford, Connecticut, it did seem like some futuristic feat of engineering.

I was inside a massive room that looked like the hold of a multi-storied space freighter. Countless pipes twisted on the walls around me as I walked over a latticed corridor of metal stairs.

The nuclear reaction at Millstone happens elsewhere — uranium atoms are split; heat is produced, and used to make steam. But I was looking at where that steam goes — into a massive high-pressure turbine, about 250 feet long. It's the start of our electricity's journey.

"That's spinning at 1,800 revolutions per minute," said Ken Holt, a spokesperson for Millstone, who took me through the plant.

As we walked and tried to talk over the noise, steam flowed into the turbine, hitting blades, and twisting the shaft of a generator. It was all spinning a magnet inside huge coils of wire, converting mechanical energy into electricity. In this case, it was about 1,200 megawatts.

"Each megawatt, in New England ... can power 1,000 homes," Holt said. "So, Unit 3 is about 1.2 million homes."

In 2016, Millstone and other nuclear plants provided about 30 percent of New England's power generation. Natural gas pumped out about 50 percent. And the rest came from a mix of renewable energy and coal. It has many points of generation, which all feed into the same thing: our grid.

This got me curious about the next step: How does all that electricity move across all those wires?

Step 2: Transmission Lines

Eversource uses helicopter flights, in part, to monitor power lines for debris and vegetation, which could fall and compromise electricity flow. (Courtesy of Eversource)
Eversource uses helicopter flights, in part, to monitor power lines for debris and vegetation, which could fall and compromise electricity flow. (Courtesy of Eversource)

To understand that part of the story, I hopped into a helicopter with Christine Naktenis from Air Ocean Aviation. We flew a few hundred feet over a trail of high-voltage transmission lines running through Connecticut towns. Transmission lines are the big power wires you see, often in fields, up on giant metal scaffolds. In the backseat was Tony Johnson from Eversource.

You can think of electric wires as pipes — only instead of water, they’re carrying electricity. They're two things we wouldn’t want to mix, but for the sake of this analogy, they'll do just fine.

As the helicopter zipped and dipped, I asked Johnson about something key to electricity’s journey. When a line is "live," is it always carrying the same amount of power?

"Lines are always running at voltage level 115,000 volts or 345,000 volts," Johnson said. "But amperage — the current — is actually how much power is flowing."

Back to our analogy. Pipes have pressure that moves water through them. Wires have voltage that moves amperage, or current, along its way. And just like you can’t track a drop of water as it moves through pipes, you can’t track an electron as it moves along on a wire. But you can track and change its flow.

"Depending on the time of year — the loads, the heat — you can have a very high current running through these," Johnson said. "If you take some lines out, other lines will be loaded up, so they’ll have very high current running through them."

The process isn’t perfect. The federal Department of Energy says around 5 percent of electricity is lost in transmission and distribution in the U.S. Some is lost in the form of heat. And on really hot days, it’s physics you can see, power lines dipping toward the ground, as heat and electricity cause the wires physically to expand and slacken.

And here’s the part of the story where, for me at least, the whole thing gets a little bit mind-boggling: The entire electric system needs to be kept in near-perfect balance. If too much power is dumped into the grid, lines could, quite literally, burn up.

So who the heck watches that? Naturally, I had to find out.

Step 3: Dispatch

(Courtesy of ISO New England)
(Courtesy of ISO New England)

"It's from this room, here in Holyoke, Massachusetts, that we dispatch virtually all of the electricity that consumers use from Maine down to Connecticut," said Ellen Foley, with ISO New England. They dispatch electricity over 9,000 miles of high-voltage transmission lines across the region’s electric grid — to millions of homes and businesses.

We were in a conference room talking about electricity, when suddenly, Foley jumped up to make a call. And in Wizard-of-Oz-like fashion, one side of the room ascended, as she literally pulled back the curtain on a large control center.

Because of security, I couldn't go in. But behind the glass were the workers responsible for keeping the grid operational.

"Electricity is used as soon as it's produced," Foley said. "So we have to make sure that we keep supply and demand in almost constant balance."

Helping with that was a giant screen about 12 feet tall by 50 feet wide. It was a visual schematic of hundreds of power plants, substations and transmission lines across New England, which need to be tweaked as demand varies.

Foley said workers also keep close tabs on news and the weather — and use a "neural network" to make short-term forecasts about energy demand, "which is sort of an artificial intelligence computer that takes a look at consumer behavior for electricity demand over the past 35 years on the grid," she said.

This enables ISO to run forecasting models. For example: "How much electricity will we need on a Wednesday morning in the middle of winter, with this kind of temperature?" Foley said.

Step 4: Substation

Back up in the helicopter near Wallingford, Connecticut, Naktenis swooped in to observe two large transmission lines running parallel. I asked Johnson where it’s going next.

"It will end up going to a substation," he said.

Remember when we said voltage was like pressure for electrons? Well, just like you wouldn't take a shower with a fire hose — for fear the water pressure would obliterate your loofah — too much electric pressure, or voltage, could blow out your appliances.

So substations knock that electricity down to a lower voltage. Eversource runs more than 200 of those in Connecticut.

"And then, from there, you'll have these smaller lines come from that station to other substations, where it breaks it down to the distribution voltage," Johnson said.

Energy hits those small cylindrical transformers on your utility poles, where the voltage is massaged down one more time, traveling through distribution lines.

Finally, that power flows into your home, ready for you when you turn on your TV, or flip on your light.

This story comes via the New England News Collaborative and was first published by WNPR



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