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Juice from water: hydroelectric refittings aim to squeeze new power out of old plants. (Professionally Speaking).

THE U.S. ENERGY INFORMATION ADMINISTRATION attributes 20 percent of the world's electricity to renewables, and almost all of that, the EIA says, comes from falling water.

According to the EIA, hydroelectric plants generated about 11 percent of the electricity consumed in the United States in 1999. That's one-ninth of the world's largest electricity market.

Although they are classed as renewables, hydro plants are not always considered environmentally correct. For instance, Egypt's high dam at Aswan has provided electricity to the country and has controlled the flow of water for agriculture, but there is a downside. The dam flooded ancient historical sites in Nubia, where rescue efforts could save only some of the legacy of vanished cultures. The jury is still out concerning the long-term effects of the dam on Egypt's environment. Right now, the biggest dam ever is under construction. China's Three Gorges Dam is expected to have a generating capacity of 18 gigawatts.

The volume of controversy and the size of the budgets put the construction projects squarely in the news. But in the past few months, GE and Alstom have announced a number of smaller projects as far apart as the Columbia River in North America and a wilderness preserve in southern New Zealand. Job specs include refitting generators with new windings or replacing machinery. The aim is to make older plants more efficient, and to get more power out of water that is already flowing through turbines.

Alstom landed the New Zealand contract, which is for hardware to refurbish a 30-year-old plant after an ambitious tunneling project improved the efficiency of its watercourse. The plant lies 200 meters underground inside an environmentally, and politically, sensitive nature preserve.

Meanwhile, a couple of time zones west, GE Power Systems has been hired to help a local power producer work out a plan to improve the performance of a hydroelectric plant in Tasmania. GE and the utility, Hydro Tasmania, plan to look at options and go from there.

Developments in the United States for GE include repowering work at Grand Coulee Dam.

Meridian Energy Ltd., New Zealand's largest electricity generator, hired Alstom to repower seven generators in the Manapouri hydroelectric station on the Southern Island of New Zealand. The generators are rated at 135 megavolt-amperes each. Site work will start next March, and completion is scheduled for the end of 2005.

"The building of new power plants is more and more restricted and costly due to environmental parameters and due to the difference in return of investment compared to thermal combined-cycle plants," according to Albert Kopp, manager of service and sales for hydro generator refurbishment at Alstom (Switzerland) Ltd. in Birr. "The refurbishment business is very economical and interesting, as the cost for a power increase of 1 MW is around one-third compared to the cost of 1 MW for a new plant."

Alstom will install replacement stators for the generators and refurbish the rotors. The contract also calls for refurbishment and replacement of auxiliary components and systems. Alstom said the deal is worth about $15 million.

The upgrade will bring the plant in line with the increased efficiency of its water flow, which was greatly improved by a major tunneling project completed 18 months ago. The plant was literally carved out of a mountain to take advantage of the natural outflow of the lake above. Some of the lake water is diverted through a tunnel to the station and then through a tailrace to a cove below. The water falls 178 meters, or almost 600 feet.

Excavation and construction at Manapouri lasted from 1963 to 1971. When the plant came on line, unexpectedly high friction in the tailrace tunnel reduced the hydraulic head of the flow. Instead of the predicted capacity of about 700 MW, the station put out about 590.

In the 1990s, studies led to a plan to bore a second tunnel parallel to the first tailrace, and free the restricted flow. As a consequence, the plant would generate more electricity from roughly the same volume of water. Meridian Energy's predecessor company, Electricity Corp. of New Zealand, commissioned the project in the summer of 1996.

The project would use a large tunnel boring machine and would need an outage of only 21 days. Earlier plans would have put the station out of business for as long as 3 1/2 years.

The new tunnel would be almost 10 km long and 10 meters wide. It would branch off the original tailrace just after the machine hail, where the turbines and generators are located. People have dug bigger tunnels, but few have cut through real estate like this. The plant draws water from Lake Manapouri and sends it to Deep Cove. The cove is in Doubtful Sound, named by Captain Cook (actually, he called it Doubtful Harbor), when he explored the Tasman Sea in the 1770s.

Sound, cove, lake, and power plant all sit in New Zealand's Fiordland National Park, part of a stretch of southern wilderness that has been designated a World Heritage Site by the United Nations.

According to Beth Masser, who was environmental manager for the project, the tunnel cost 200 million New Zealand dollars (about $95 million U.S.) and about 5 percent of that was spent on environmental matters.

Meridian Energy was required to clear its plans with the Minister of Conservation. According to Masser, who now works for the Department of Conservation, Meridian Energy spent three years consulting with various interested parties, including regional and local authorities, fish and game regulators, and the indigenous Iwi-Maori people.

Plans for curbing environmental disturbance covered everything from clearing vegetation and road building, to secure waste removal and sanitation.

The digging was led by an international consortium, Fletcher, Dillingham & Ilbau.

The tunnel boring machine was 25 meters long. The combination of the borer and its trailing gear stretched to nearly 500 meters and weighed approximately 15,000 metric tons, It had a crew of 25 men working three shifts around the clock.

Waste rock was carried by a conveyer belt from the cutting face to the tunnel entrance at Deep Cove. The digging started in June 1998 and broke through to the original tailrace in March 2001.

With the extra tunnel relieving the jam in the tailrace, the plant's capacity leaped to 760 MW, an increase of almost 30 percent.

The borer was made by Robbins Co. of Solon, Ohio. At the time, to build something of that size, the company had to use the facilities of Markham's Ltd. in Sheffield, England, according to Lok Home, Robbins' president. Robbins also supplied some of the machines for the Channel Tunnel between Britain and France.

On the far side of the Tasman Sea, GE Hydro, a unit of GE Power Systems in Atlanta, has entered what it calls an "alliance relationship" with Hydro Tasmania to upgrade the utility's 300-MW Poatina hydropower station. A joint project management team will assess the current condition of the power station, specify the work to be done, and develop a budget for the project.

The plant, located near Launceston, is Hydro Tasmania's second largest power station. The underground facility was brought into service in 1965 and houses six 50-MW generators.

The project is part of a 10-year plan by Hydro Tasmania motivated by Australian national legislation and by the entry of Tasmania into the country's wholesale power pool. To raise the share of its electricity generated by renewable sources, Australia is offering financial incentives to companies that upgrade hydroelectric plants.

The same unit of GE also landed a $3.8 million deal that will boost the power output of the Grand Coulee Dam in the United States. GE will deliver two 125-MVA stator cores and windings. According to GE, its bar windings, which have been in use for about 30 years, will increase the efficiency of the current generators.

The equipment will be built by GE Hydra in Lachine, Quebec. GE Installation and Repair Service of Salt Lake City, Utah, is expected to have the first unit in place by the start of the third quarter next year. The unit is scheduled to return to commercial operation in February 2004.

GE has a separate contract with the Bureau of Reclamation, which operates the Grand Coulee and other dams on the Columbia River in the state of Washington. Under that agreement, GE will replace 18 Francis turbines at Grand Coulee in a project scheduled for completion in 2007.
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Comment:Juice from water: hydroelectric refittings aim to squeeze new power out of old plants. (Professionally Speaking).
Author:Hutchinson, Harry
Publication:Mechanical Engineering-CIME
Geographic Code:1USA
Date:Nov 1, 2002
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