International Hydropower Association (IHA)
|IHA Electronic Newsletter, January 2005|
Research Project on a new type of surge tank for pumped storage
The requirements to be met by pump storage schemes by both the hydraulic equipment, such as water conveyance structures, and the mechanical equipment, the pumps and turbines, have tightened considerably in respect to such factors as response time etc., compared to the equipment in the past.
Recent trends include the need for improving what may be called the surge-tank strategy for the downstream portion of pumped-storage schemes. It is above all the increased speed and frequency of the change-over between the pumping and generating modes that have become an important criterion to be allowed for in the design of chamber volumes. Where the tailrace tunnel is long, it is a general practice to select a surge tank of the two-chamber type. This system, however, is supposed to meet two contradicting requirements. During start-up of the pump units, the back-pressure head should be high to avoid cavitational damage. So the axis of the lower chamber should be situated as high as possible. This is opposed by the need for the maximum possible differential head between the water level in the surge tank and the lower basin, to ensure a speedy acceleration of the water column. This is why the axis of the lower chamber should be situated at a low level. The two requirements can be satisfied only by locating the pump unit as low as possible. Therefore, installation of the pump unit in a shaft-type power station will involve a substantial rise in the cost of constructing the shaft and ancillary structures. The three-chamber surge tank is a design idea developed by Professor GŁnther Heigerth to reconcile the opposing requirements. This novel design provides for splitting the lower chamber into two. Situated at different levels, these two separate portions of the lower chamber are connected via an overflow hump at the lower end of the riser. Likewise, the water column is separated under the critical loading conditions, thus being able to accelerate the water column in the tailrace tunnel and at the same time build up the required back pressure for the pump.
At present, this new type of surge-tank design still lacks basic information, and problems of detail such as uniting the water flows in the chambers need to be studied. This gap is to be closed with the help of our Research Project, which will also include studies to solve the problem of ensuring adequate aeration for the two chambers. The three-chamber surge tank with the two separate and continuously water-filled lower chambers represents an entirely novel configuration for pumped-storage schemes. Although separating and then reuniting the water column in a power-conduit system is usually avoided in the design of hydraulic structures, this very concept may in this case involve decisive cost advantages. The new type of surge tank is expected to afford the following benefits, which are reflected in reduced construction cost: - Integrating the lower chambers into the power conduits - Reducing the volumes of the lower chambers - Reducing the shaft depth necessary for the pump-turbine unit.
If you are interested
in our Research Project, please contact:
Dipl.-Ing. Dr.techn. Dominik Mayr
Institut fuer Wasserbau und Wasserwirtschaft,
TU-Graz Stremayrgasse 10/II, A-8010 Graz
Tel: +43 (0)316 873 8859
Fax: +43 (0)316 873 8357