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Hydropower Flows Here
McNary Dam hits the rewind
4/23/2015 12:00 AM
A crew applies electrical insulation to the stator bar jumpers.
To the untrained eye, it’s a box of copper planks.
But these wands, called stator bars, are where the magic happens in hydroelectric generation.
Kathy Spillane says stators are the hidden key to transforming the muscle of the Columbia River into the low-cost, carbon-free electricity used across the Pacific Northwest. And Spillane – who has successfully led an $86 million federal project to replace 1,044 of the copper bars at McNary Dam – would certainly know.
“The stator windings are the invisible piece of the hydro plant, part of the mystery people don’t understand,” says Spillane, a project manager with the U.S. Army Corps of Engineers. “But they’re really the heart of the generator.”
Tim Roberts, the dam’s chief of maintenance, agrees: “It is like magic. It’s magnetic theory – you can’t see it; you just have to believe it. And that’s where it happens.”
McNary’s original stator windings had been producing electricity virtually 24/7 since the dam went into full service in 1957 near Umatilla, Ore. Its powerhouse, at mile 292 from the mouth of the Columbia River, produces 980 megawatts at full capacity – enough to support about 686,000 homes. That’s more than the households in the cities of Seattle and Portland combined.
After half a century of service, the trusty magic of McNary’s stators began to fade in the early 2000s. The old insulation wrapping the metal bars had deteriorated, raising the risk of high-voltage faults (electrical shorts) that jeopardized safe and reliable operations. Several of the generating units had to be indefinitely de-rated, meaning they could only be safely operated at partial capacity, something akin to always having to drive 20 mph below the speed limit.
That’s why the ratepayers of the Bonneville Power Administration are investing $86 million at McNary Dam to install new stator windings on 10 generators, helping secure its dependable value for the next half century. A nonprofit federal agency, BPA markets wholesale electricity from the region’s 31 federal dams, and in return funds the operations, maintenance and capital improvements related to power generation at the hydroelectric plants.
The Corps of Engineers, McNary Dam’s owner, and its partners are now in the home stretch of the project to replace the original Eisenhower-era windings with state-of-the-art components. Besides BPA, the project partners are contractor Andritz Hydro and the Corps’ own Hydroelectric Design Center in Portland, Ore.
The labor-intensive project is expected to wrap up this fall. During the painstaking installation process, the 1,044 bars must be bonded by hand in a high-temperature process called brazing, using a torch at more than 1,000 degrees.
“We had a steep learning curve on the project, but we improved every year,” Spillane said. “We’ve had some really great teamwork with BPA and HDC (the hydro design center). When we’ve hit challenges, we’ve done a lot of effective problem-solving. We’ve been tested over and over, and our team unity is very strong.”
McNary is known as the hydraulic bottleneck of the Federal Columbia River Power System, which makes its level of performance crucial to the overall system. It occupies a critical position just downstream of the confluence of the Snake and Columbia rivers, but due to its physical characteristics, McNary has less flow capacity than the combination of dams above and below it.
“The turbines only have the ability to pass a certain amount of water through them,” Roberts explained. “We, at the project, view water as fuel. And sometimes we have too much fuel.”
To have a revolving roster of two generators disassembled and out of service over the course of five years would pose a challenge at any FCRPS dam, but managing McNary’s array of vital and often competing objectives can be even more difficult. Beyond its main job of producing a certain amount of electricity to serve the Northwest’s demand hour to hour, the dam provides the voltage support to keep the regional transmission grid stable in the era of variable wind power. It also maintains calibrated water flows to support endangered fish. At times of peak demand, when every available generator is needed for such operational flexibility, subtracting units compounds an already difficult juggling act.
“When I saw the original schedule for the stator replacements, I said, ‘10 units in five years? Wow, that’s an aggressive schedule,’ ” Roberts said. “To get this done even close to five years is pretty impressive.”
The project is part of a sequence of capital investments in the FCRPS, which provides nearly a third of the electricity consumed in the Pacific Northwest. As part of their broader asset strategy, BPA and the Corps decided it would be cost-effective to invest in better stators, which will have the capacity to produce 18 percent more power from the same amount of water.
This improvement was possible with next-generation insulation, which provides more protection in a thinner epoxy material. Streamlined insulation makes more room for larger, more powerful copper stator bars nested in the same space.
Each of the 1,044 new copper stator bars is 8 feet long and weighs about 70 pounds.
Each copper bar contains the potential to generate a particular amount of electricity, BPA electrical engineer Jack Kolze explained: “The plant at McNary has 1,044 bars of copper. Each one produces about 67 kilowatts – enough power to run 45 hair dryers. Put all of them together and you would be able to operate 46,980 hair dryers at high heat at the same time.”
The current work sets the stage for the next major project: the likely replacement of the dam’s 14 aging hydroelectric turbines with more efficient models in the coming decade. The new stators contain about 35 percent more copper, which will lift the capacity of each generator to 100 megawatts from its historic 84.7 MW after turbine upgrades.
“This shows foresight for the future,” Roberts says. “McNary is a really robust plant. They built it to last. With this project, you’ve reset the asset, as far as windings, for another 50 years and you’ve also provided the potential for increased capacity. That’s a win-win.”
- Reported by Sarah Smith, Public Affairs
Behind the magic: How stators work
By Rod Aho, BPA Power-Up Academy instructor
A generator’s two main components are the stator and the rotor. As the name suggests, the stator is a stationary piece of equipment, essentially a large iron donut into which coils of wire or metal bars are inserted—the stator windings. They are connected to the generator’s electrical output terminals.
The rotor is a cylindrical shaft supporting a cluster of magnets, each with a north and south pole. This magnetic assembly rotates inside the stator’s donut hole, driven at a fixed speed by a turbine.
The rotating magnetic field piles electrons toward one end of the stator windings, a consequence of Faraday’s law of electromagnetic induction. A voltage — electrical pressure that causes current to flow in a circuit — is induced in the stator windings and appears at the generator’s output terminals.
As the rotor’s N and S poles alternately sweep past the stator windings, the electrons respond to the reversing magnetic polarity. Like synchronized swimmers, they move first in one direction, then the other — 60 times a second. This is the familiar 60 Hz alternating-current (AC) frequency standard used in power grids throughout North America and elsewhere.
The electrons don’t really go anywhere; they just jiggle back and forth at the 60 Hz line frequency, traveling at most a fraction of an inch in either direction. They do not “flow across the grid,” contrary to our intuition.
Here comes the really interesting part. The undulating, back-and-forth motion of the current launches an invisible wave of electromagnetic energy that travels at nearly the speed of light throughout the power system. The wave is enabled in its trek from generator to load by the current flowing in the grid circuitry.
So in a figurative sense, the stator windings serve as the staging area and launch pad for the generator’s electrical energy output. Transmission wires serve as the guidance system. The wires do not “carry” the energy, nor do the electrons; the energy resides in the electromagnetic wave between and around the wires, not in them.
The various electrical loads connected to the grid receive the incoming wave of electrical energy and convert it into other forms: light (by fluorescent tubes), heat (by electric space heaters), sound (by loudspeakers), chemical energy (by battery chargers), and so on. Electric motors convert the energy into rotational mechanical energy, the same driving force that spun the generator to begin with.
Two hundred years ago Michael Faraday discovered that mechanical energy could be transformed into electrical energy. He observed that if a magnet moves past a wire, or a wire past a magnet, a voltage is induced in the wire. Power plants today make use of Faraday’s law of induction to generate 99 percent of the electric power in the world.
The same curious principle — the relative motion between a magnet and wire — is used in electric guitars, dynamic microphones, hearing aids, seismographs, computer disk drives, smart traffic signals, credit card readers, audio tape players and ATM machines. When a salmon with an implanted PIT tag passes a detector, or you card-in at a BPA facility, Faraday’s law is at work!
Next time you flip a light switch or plug in your Fender Stratocaster, think about Professor Faraday and his discovery. And tip your hat to the diligent engineers and technicians of today for safeguarding McNary Dam’s reliability.
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