Hoover Dam is an icon of American ingenuity. Located about 30 miles southeast of Las Vegas, it controls water flow along the Colorado River, irrigates crops, supplies drinking water, contributes to recreation and wildlife habitats, and generates electricity.
Without the dam, far fewer people would be able to live in the southwestern United States.
President Franklin Delano Roosevelt dedicated what was originally known as Boulder Dam on 30 September 1935:
| Employment Opportunities at Hoover Dam Interested in working at Hoover Dam? If so, go to www.usajobs.gov. Among the 250 people who work there are electrical, civil and mechanical engineers. "We’re always on the lookout for good engineers," said Mark Cook, chief of engineering at Hoover Dam. "We have an incredible place to work." "And there’s definitely job security in water," Bureau of Reclamation spokeswoman Rose Davis said. |
“Today marks the official completion and dedication of Boulder Dam. This is an engineering victory of the first order – another great achievement of American resourcefulness, American skill and determination.”
Since the dam began producing low-cost, renewable energy in October 1936, it is one of the few things the federal government operates that makes money. The sale of electricity has fully paid for the cost of construction – with interest.
Hoover Dam generates an average of about 4 billion kilowatt-hours of hydroelectric power each year for use in Nevada, Arizona and California, enough to serve 1.3 million people. And modern technology allows it to produce electricity much more efficiently.
The Hoover Dam powerplant has 17 generating units (turbines) – nine on the Arizona side and eight on the Nevada side. In 2005, the dam was generating electricity at around 82 percent efficiency. It is now running at about 87 percent.
“We’ve increased the efficiency of Hoover Dam as a whole over the past few years tremendously,” said Mark Cook, P.E., chief of engineering at the dam.
“It’s been due to a kind of holistic view of the system," he said. "We replaced turbines that have helped; we’ve installed wicket gates – new, thinner wicket gates that have helped the efficiency, as well as capacity.”
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| Figure 1: This chart illustrates the dam’s powerplant efficiency increases between 2009 and 2013, when it grew from 84.1% to 87.3% — an improvement of 3.4%. |
New Control System
Another key factor in the efficiency increase is the installation in 2012 of a new software control system, which Cook, Brandon Hilliard and Terry Whittemore designed. A digital PLC-based (programmable logic controller) system, it continually monitors input data from connected field devices and executes a custom program to control the output devices.
"It allows us to move units faster, start units faster, more reliably monitor the units, and it’s allowed us to be able to set-point our units closer to their more-efficient operating points because we know that we can get another unit to respond, if need be," Cook said. "It actually allows us to condense more units, which is where a lot of the gains have come in. By condensing the unit, we still serve the spinning reserve needs, while still being able to reach the [automatic generation control] demands and the regulation demands of following the signal every four seconds or chasing it around all day long."
Hoover Dam primarily provides power during peak daytime demand – beginning around 3 p.m. Pacific Time during the summer – and carries a much lighter load later at night.
“When the Californians turn on their air conditioners,” said Rose Davis, a Bureau of Reclamation external affairs officer, “then we get [an automatic signal] to generate more power.”
New Turbines Compensate for Lower Water Elevation
When the Colorado River was dammed in Black Canyon at the Arizona-Nevada border, it produced Lake Mead. If you visit the dam, you’ll see white rocks on the banks of Lake Mead representing the highest water mark the reservoir ever reached, in 1983. The water elevation was so high that it was the only time in the dam’s history – outside of testing – that the spillways were used.
By September 1999, the reservoir was at 95 percent capacity. It fell to 38 percent in November 2010 before rebounding slightly to 41 percent in May 2014. On 8 July 2014, it had diminished to about 39 percent capacity. This drop in water level has reduced the efficiency of the dam’s powerplant.
“It has a direct correlation,” Cook said.”There’s less pressure on the turbines; not only is it hard on efficiency, but it also de-rates our units. The units are rated for 130 MW, but we’re only able to get closer to like a hundred right now.”
Three new wide-head turbines have recently been installed at Hoover Dam, allowing it to operate at lower water elevations. These turbines, with two more set to go in by 2016, create less vibration and are a lot more stable than the 1980s turbines they replaced. This translates to high energy efficiency.
“It’s pretty incredible,” Cook said. “Any time you’re getting over 90 percent energy conversion is just amazing.”
Cook has worked at the dam since January 2007, a month after graduating from Utah State University with a B.S. in electrical engineering. He earned his professional engineering designation in March 2011.
Wicket Gates
Wicket gates control the amount of water that reach a turbine’s blades. In generate mode, falling water hits and rotates the blades, which in turn rotates the connecting shaft and turns the generator. Electricity is produced by magnets spinning inside the generator’s copper coils.
The majority of Hoover Dam’s turbines have new wicket gates that are made of stainless steel and are thinner than the gates they replaced.
“These thinner gates allow more water [to go through] and they pass it with less velocity losses,” Cook said. “So we’re able to pick up quite a bit of efficiency by using this new gate design.”
The new software control system also helps boost efficiency when a generator goes into synchronous condense mode. This happens when the wicket gates are closed and pressurized air is injected into the turbine to keep it spinning. Cook explained that with the air bubble, the turbine only consumes 3 MW of power from the grid instead of 12.
“It keeps spinning until we need it again to produce power,” he said. “Once we do need it to produce power, we’re 30 seconds away from being able to do that.”
When the decision to go into condense mode was left up to a human operator, it took 2-3 minutes to bring a unit back online.
Being able to go between generate and condense mode quickly is important because the Western Area Power Administration tells the dam how many megawatts of electricity to produce and how much capacity – or spinning reserve – to have online. Hoover Dam receives these signals automatically every four seconds.
“They do move us around quite a bit,” Cook said.
Electrical engineers continue to play a key role in the dam’s multifaceted success, including its ability to generate electricity more efficiently.
“From the electrical engineering standpoint,” Cook said, “the big triumphs have been the software change and the programmable logic controller (PLC) upgrades, taking all those controls and making them more reliable and being able to control the units more precisely.”
Twin Engineering Marvels
Hoover Dam is one of the greatest engineering achievements in the world. On 27 September 2001, the American Society of Civil Engineers designated it the “Civil Engineering Monument of the Millennium.” A plaque outside the dam proclaims it:
“One of the finest examples of how civil engineering’s ingenuity shaped the development of society’s quality of life in the 20th Century”
A separate plaque honors the 96 men who lost their lives while constructing the dam:
“They died to make the desert bloom.”
Another engineering marvel is the nearby Mike O’Callaghan-Pat Tillman Memorial Bridge. Open to traffic since 2010, it was built primarily as a Hoover Dam bypass for travelers who used to have to drive over the dam to go between Arizona and Nevada.
At 1,060 feet, the central span of the bridge is the longest single-span concrete arch in the Western Hemisphere. A pedestrian lane allows visitors to see Hoover Dam from a perspective never before seen – about 1,500 feet south of the dam and 880 feet above the Colorado River.
The bridge is named after two selfless men who dedicated their lives to the service of others. Mike O’Callaghan was a decorated Korean War veteran who lost partial use of a leg in battle. He served as Nevada governor from 1971-79 and then dedicated his life to newspaper journalism and philanthropy.
Pat Tillman was an honors graduate of Arizona State University who gained fame and fortune playing football for the Arizona Cardinals. He left it all behind to enlist in the Army soon after 9/11. He was killed in Afghanistan in 2004 at age 27.
U.S. Transportation Ray Secretary Ray LaHood dedicated the Mike O’Callaghan-Pat Tillman Memorial Bridge on 14 October 2010. What he said that day could also have been said of Hoover Dam upon its dedication 69 years ago:
“This magnificent bridge is proof positive that America is not afraid to dream big. The jobs supported by this project are undeniable, and its economic benefits to the American southwest and the nation as a whole will be felt for generations to come.”
Chris McManes, IEEE-USA’s public relations manager, used to live in Las Vegas and considers Hoover Dam one of his favorite places on earth.
