Design of pumped storage schemes

The Integration of renewable energy sources and the liberalisation of the European electricity market has fundamentally changed the setting for the generation of electrical energy. The steadily rising amount of wind energy is one of these changes. In Germany 15,000 MW of installed wind energy share about 1/8 of the total installed capacity. In Austria the installed capacity from wind energy is expected to reach 800 MW at the year 2008. Wind power plants are able to produce energy only when the wind in blowing. They cannot react on demands from the network. Besides demand load management, which is to be developed, it is therefore necessary to provide or to store large amounts of energy. These conditions have recently led to an increased demand for readily available peak energy, and this in turn has aroused a growing interest in the design and construction of pumped-storage schemes (PSS). The requirements to be met today by both the hydraulic equipment, such as water conveyance structures, and the mechanical equipment - the pumps and turbines - have tightened considerably in respect of such factors as response times, etc. as compared with the equipment of the past.

The objective of the project is the development of a new surge tank system for pumped storage schemes. The novel design provides for splitting the lower chamber of 2-chamber surge tanks into two. Situated at different levels, these two separate portions of the lower chamber are connected via an overflow sill 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.

The Project will be carried out by use of both a numerical-model and scale-model tests.

The Project consists of four Work packages:

• Work package 1 (WP 1): Numerical analyses:
  Comparative studies will be conducted to find the main parameters, such as chamber volumes, relative levels, etc., for the new type of surge tank by use of a one-dimensional computation program. In addition, potential limits of applicability will be defined. Studies on damping of oscillations are included.

• Work package 2 (WP 2): Scale model tests - Overflow sill:
  Hydrodynamic effects on the overflow sill between the two lower chambers will be studied on a scale model. Studies will be conducted for a fixed and movable installation.

• Work package 3 (WP 3): Scale model tests - Tailwater system:
  A characteristic tailwater system will be modelled with the purpose of studying the general performance of the three-chamber surge tank (uniting the water flows, surge phenomena, air intake, de-aeration, etc.).

• Work package 4 (WP 4): Net integration - Design guidelines:
  Comparative calculations will be performed for the new and a conventional system on the basis of actual load demand curves. Design guidelines for general application will be prepared.

Goals of the project

• Cost optimized construction of new PSS (minimizing excavation of chambers and power shaft),
• Cost effective upgrading of existing PSS,
• Positive effects on the load managements of the power utilities,
• Shorter response times,
• Higher plant availability of the PSS,
• Improved damping on mass oscillations.
• The potential of volume savings for water conduits and power stations as against conventional two-chamber systems.
• A cost optimized adaptation of existing pumped storage systems
• The knowledge of a further damping effect on the oscillation
• A higher operational availability of pumped storage power stations

Most important results

• Substantial reduction in lower-chamber volumes
• Sufficient areation and de-areation of the chambers
• Design of the sill concerning shape and flexibility

Risks of the project

• The main hydraulic requirements to be met by the designers of surge tanks include damping the water-hammer effect, accelerating and deceleration tunnel flow, and improving the response capabilities of the mechanical equipment.
• Integration of the lower chambers into the water conduit as against separate lower-chamber systems (technical feasibility).
• The technical and economic benefits by integration of the lower chambers into the condiut.

ProjektleiterIn:
Dr. Dominik Mayr
TU Graz, Institut für Wasserbau und Wasserwirtschaft
Stremayrgasse 10/II, A-8010 Graz
Tel.: 0043/316/873-8859; Fax DW: 8357
E-Mail: Dominik.mayr@TUGraz.at
Internet: www.hydro.tugraz.at

Institut/Unternehmen:
TU Graz, Institut für Wasserbau und Wasserwirtschaft
Stremayrgasse 10/II, A-8010 Graz
Tel.: 0043/316/873-8851; Fax DW: 8357
Internet: www.hydro.tugraz.at

Projekt- bzw. KooperationspartnerInnen:

• EnBW Kraftwerke AG
• VERBUND Austrian Hydro Power AG
• Vorarlberger Illwerke AG