Pumped Hydroelectric Energy Storage - Large Energy Storage Systems - page 71

Upper
Surge Chamber

Upper
Reservoir

Lower
Surge Chamber

Headrace Tunnel

Pump-turbines

Lower
Reservoir

Penstock

Tailrace
tunnel

FIGURE 3.9
Upper and lower surge chambers of PHES design. (From Garrity, J. J et al. 1985. In Handbook
of Energy Systems Engineering Production and Utilization , Wiley Interscience: New York. With
permission.)

the y-axis and from left to right across the x-axis. Above the head range of
a reaction turbine, an impulse turbine is usable. Table 3.3 displays pump
turbine head limits.
Figure 3.11 depicts limits and ratings of a system developed by Rodrique 14 and
in operation since 1979. Data for single stage and multiple stage reversible pump
turbines and tandem units with impulse and Francis turbines are shown.

Impulse Turbines and Centrifugal Pumps

Very high head applications may utilize impulse turbines with separate cen-
trifugal pumps. Impulse turbines function by running the energy contained
in the raised water through a nozzle where the water becomes a jet and is
directed at the vanes or buckets of a wheel. The jet of water hitting the vane
is the impulse that removes the kinetic energy from the fluid and transfers it
to the turbine or wheel. An impulse turbine cannot pump and thus must be
matched to a separate centrifugal pump. Centrifugal pump sizing is covered
in a U.S. Bureau of Reclamation monograph. 15

Reaction Turbines
Most modern PHES facilities utilize reaction turbines. These turbines func-
tion by reactive forces. Unlike the arrangements of impulse turbines, the
nozzles or buckets of reaction turbines are attached to the scroll cases. As
a scroll case turns, the water either is pushed by the machine or pushes the
machine, based on the operating status—pumping or generating, respec-
tively. Reversible pump turbines fall into three subgroups: radial flow Francis
type, mixed flow diagonal, and axial flow 16
RadiallowFrancistypeturbines — Also known as Francis style pump
turbines, these types are the most common applications for PHES facilities.