Environmental Engineering Reference
In-Depth Information
turbine runner and into the tailrace below the elevation of the tail water.
The tube allows the full head of the plant to be used because it facilitates the
utilization of suction head.
Tailrace
A tailrace is a water conduit between the afterbay or tail water and the draft
tube or turbo machinery. A tailrace conveys water from the tail water during
pumping and into the tail water during generation.
Surge Tank or Chamber
Surge tanks can be provided both upstream and downstream of a water con-
duction system.
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The purpose of a surge tank is to dampen changes in pres-
sure, protecting the water conduits, turbine, and pumping equipment. A surge
tank allows the turbo generator to regulate its load. Figure 3.8 shows surge
chambers on the upstream and downstream sides of turbo machinery.
Iwabuchi et al.
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show that optimizing governor operation allows the sizing
of surge chambers to be minimized, thus leading to lower development cost.
Since surge chambers or tanks provide dampening mechanisms to water
conductors and mechanical equipment, it is logical to further develop these
devices to furnish more flexibility for PHES operations. A research group
in Austria is pursuing that via a project titled: “Design of Pumped Storage
Schemes.”
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A brief description follows.
The objective is the development of a new surge tank system for pumped
storage schemes (PSS) to govern the changing requirements of electric-
ity networks arising from the integration of renewable, volatile energy
sources. The novel design provides for splitting the lower chamber of a
two-chamber surge tank. The two separate portions of the lower chamber
are situated at different levels and connected via an overflow sill at the
lower end of the riser. Likewise, the water column is separated under the
critical loading conditions, and thus can accelerate the water column in the
tailrace tunnel while simultaneously building up the required back pres-
sure for the pump.
Turbo Machinery
Most PHES developments are designed with Francis style pump turbines.
These devices both pump and generate; they are generally categorized as
reaction turbines (Figure 3.9). Another option is the use of a separate pump
and turbine. This design may allow a project to utilize higher heads and
maintain higher technical efficiency during both generation and pumping
operations. Although higher technical efficiency can be achieved, the eco-
nomic penalty must be assessed against the financial benefit from the effi-
ciency gain. This system also allows the selection of an impulse turbine and
a centrifugal pump.
Figure 3.10 displays hydraulic reaction turbines at operational head ranges
versus turbine discharge.
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Power output increases with head and flow up
