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Pump Simplifies Concrete Placement

Gammon India Ltd. is using a BP 4000 HDR 180/125 pump manufactured by Schwing Stetter of Germany to pump concrete for construction of the two inclined pressure shafts for the 800 MW Parbati 2 hydroelectric project. This project, being developed by NHPC Limited (formerly National Hydroelectric Power Corporation), is under construction on the Parbati River in Himachal Pradesh, India. Use of this pump allows Gammon India to deliver concrete to a height of 770 meters, compared with a maximum of 535 meters with other available pumps.

Project background

Parbati 2 is a run-of-river plant that will take advantage of 862 meters of head between the Parbati River and the powerhouse, located 33 km away in Sainj Valley, to produce electricity. Development of this project includes construction of an 85 meter-high concrete dam with a 30 meter-long spillway section that features four bays controlled by radial gates. Water is diverted via a 6 meter-diameter, 31.5 km-long headrace tunnel to a 17 meter-diameter, 130 meter-high surge shaft. From there, two 3.5 meter-diameter, 1,546 meter-long inclined pressure shafts carry water to the surface powerhouse. This powerhouse will contain four Pelton turbine-generator units.

The pressure shafts for Parbati 2 are inclined at a 30 degree angle. They consist of a steel lining backed by self-compacting concrete. The shafts run from elevation 1335 meters to elevation 2105 meters — a total height of 770 meters.

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Using the BP 4000 HDR pump from Schwing Stetter enables Gammon India to pump concrete to a height of 770 meters. Pumping to this height is needed to build the two inclined surge shafts for the 800 MW Parbati 2 project in India.

Choosing the pump

NHPC realized the high elevation to which concrete would need to be pumped for these inclined pressure shafts presented a problem. There is no company in India that manufactures equipment that can pump concrete to that height. The maximum height to which equipment manufactured in the country can pump concrete is 535 meters. The other option was to place concrete by gravity from the top of the shafts. However, this would lead to segregation of the concrete and compromise the consistency of the concrete placed.

NHPC has several other hydro projects under construction in India, and Schwing pumps are being used at several of these projects to pump concrete for tunnels and surge shafts. To determine if one of Schwing's pumps would be suitable for use at Parbati 2, NHPC and Gammon India requested a detailed technical demonstration of the BP 4000 HDR 180/125 pump. As a result of this demonstration, NHPC and Gammon India determined that the pump could be used to build the pressure shafts at Parbati 2.

Building the pressure shafts

Gammon India, the main civil contractor for construction of Parbati 2, bought a BP 4000 HDR 180/125 pump at the end of 2006 at a cost of INR24.1 million (US$511,000). This pump was manufactured specifically for the work to be performed at Parbati 2. Work to place the pressure shafts began in March 2007. The pump is being used to place self-compacting concrete in the annular space behind the steel liners of the inclined pressure shafts. The pump can provide 35 to 57 m3 of concrete per hour through high-pressure pipes.

In December 2008, about 30 percent of the total concrete had been placed for the inclined pressure shafts. This equates to a total length of 900 meters. No problems have been encountered during pumping of the concrete, and results from using the pump have been satisfactory.

Work to place concrete for the inclined pressure shafts at Parbati 2 is scheduled to be complete by September 2010. The project is anticipated to begin operating in December 2010.

Once this work is complete, Gammon India plans to move the Schwing Stetter pump to another location where pumping to this height is required.

— By Virender Salman, chief engineer, NHPC Limited. For more Ideas in Action, visit www.hydroworld.com.

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