Commissioned in 2006/7, the Tehri dam is something of a technical engineering marvel, providing 1400 MW of power as well as water for irrigation and consumption (see box text). And now the facility is being further enhanced, with the addition of a pumped storage plant (PSP). When operational, the PSP should add an extra 1000 MW capacity.
To give a brief description, the PSP involves the construction of an underground machine hall housing four reversible pump turbine units of 250 MW each on the left bank of river Bhagirathi. The main feature of the project is the large head variation of about 90 metres between the maximum and minimum head, under which reversible units shall operate. The operation of Tehri PSP is based on the concept of recycling of water between an upper reservoir and a lower reservoir. The Tehri Dam reservoir shall function as the upper reservoir and Koteshwar reservoir as lower balancing reservoir.
As might be expected when harnessing tremendous quantities of water, robust equipment is required for the Tehri PSP. Enter GE Renewable Energy’s Hydro Solutions, which was charged with manufacturing four 250 MW variable speed pumped storage units (units #5 to #8), including installation and commissioning.
Asked about some of the valves needed for this project, Hydro Solutions’ Project Director, Mr Ajai Shukla, replies as follows: “the main inlet valves (MIVs) are of the spherical type and work as the shut-off valve/isolating valve in the water conductor system. Located before the turbine, they allow water to flow from the penstock to the turbine.
The MIV acts as the closing valve and cuts the flow of water in the event of an emergency trip to ensure the safety of the powerhouse.”
The sheer scale of some of the items required for the PSP project is staggering. For example, the MIVs have a four-metre diameter, making them the largest spherical valves ever manufactured by GE’s Hydro Solutions team. Moreover, they weigh in at 350 tons each – without counterweights! To give a sense of scale, that is equivalent to 1.5 times the weight of the Statue of Liberty.
Comments Mr Philippe Feriol, Hydro Solutions’ Head of Hydro Valve Engineering: “this equipment is a real technological achievement in terms of design and product manufacturability.
It was the first time for GE’s Hydro engineering team to design a spherical valve with such a large diameter. This exceptional project pushed the boundaries of Hydro engineering, design and technology expertise.”
He continues: “the factor (size and pressure) was a challenge in terms of mechanical behavior and product dimensioning with multiple constraints such as the limitation of the steel making processes as well as the transportation limitation. Because of their size, these MIVs have to be disassembled, transported to the customer’s site, reassembled and finally retested. The tryptic of design, manufacturing and assembly must be at the right quality level to succeed.”
At the time of this interview, the PSP project was steadily progressing towards a successful conclusion. Mr Shukla indicates that GE’s Hydro Solutions client, THDC India Limited, had recently signed off the final acceptance test for the third MIV. That left just one final MIV for GE Hydro Solutions to focus on.
Nevertheless, Mr Shukla is keeping his eye on the ball. “Large projects such as the Tehri PSP can throw up surprises so flexibility and adaptability are the name of the game. It was the COVID-19 pandemic that created unforeseen challenges during 2020. My compliments to all at GE’s Hydro Solutions and THDC India Limited for their willingness to adapt and find workable solutions for all parties. For example, we changed the usual approach to inspection from in-person to remote inspection. Hence some inspections, such as checks, measurements and customer hold point, were successfully completed remotely, helping to keep the Tehri PSP project on track.”