VGB POWERTECH 11 (2019)

A journey through 100 years VGB | VGB POWERTECH 4 (2006)
Pumped Storage Power Plants
Adapting Power Plant Deployment
and Resulting Effects
Flexibility of Peak Load Covering
Whereas 1 pump cycle and 1 to 2 turbine cycles
were run every day in the past, today's
plants are started more frequently, and often
for shorter periods of time. With this hitherto
unknown mode of operation, one can react to
foreseeable events such as tariff switches
with foresight.
Figure 9. Effects of trading on grid frequency.
f
in Hz
50.10
50.05
50.00
49.95
49.90
C
in MW
25
0
– 25
– 55
13 min
Pump operation
Capacity
Primary control
Frequency
6 min
Secondary control
38 min
16 min
Primary control
Pump operation
Grid controller
22:30 23:00 23:30 00:00 00:30 1:00 1:30
Time
Figure 10. Example: Operation of a pumped storage plant.
Turbine
Pump
When significant wind power capacity is
feed in into the grid, pumps are often taken in
operation and can be shut down whenever
wind strength decreases – an expected, albeit
not precisely predictable event. Instead of using
a pump, a turbine can be run at partial
load, ready to be run up further whenever the
need for additional capacity arises.
Running pumps and turbines with this kind
of foresight often results in pumps or turbines
being shut down after a few minutes of operation
if the expected event does not occur.
PSP thus provide the dispatcher with additional
room for manoeuvre and increased
flexibility in controlling the grid and power
plants.
A Contribution to Grid Balancing
PSP help balance power in the grid via the
automatic balancing of sudden frequency
variations using the primary control (PC).
Within 30 seconds the full compensation
must be effective. In such cases, the turbine
is usually run at minimum load in order to
make positive PC capacity available when
needed, which causes substantial thermodynamic
loss and costs when provided by thermal
units. By contrast, negative PC capacity
can be supplied at low cost in combined heat
and power plants as well. In PSP with nongoverned
pumps, when in pump mode, PC
capacity can only be supplied if one renounces
additional input by load shedding.
An example of this mode of operation can be
seen in Figure 10. First the frequency
must be kept constant by capacity variation.
If grid frequency decreases, turbine capacity
is increased. Then, whenever the frequency
rises above 50 Hz, the pump is started in order
to draw capacity from the grid, and shut
down soon thereafter to pass the baton to the
turbine, which then runs for a limited period
of time. After a good 20 minutes, the pump is
started again and the turbine is shut down.
The secondary control (SC) is also automated
and relieves the PC of its work after 15 minutes.
Within the 30-minute period, the SC
equalises the operated grid zone, which is influenced
by the PC and undesired transits.
Figurs 11. Changes in operation of selected pumped storage plants.
When the 30-minute period is exceeded, grid
control is also handled by the PSP, using the
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