Environmental Engineering Reference
In-Depth Information
50.8
without DDC
with DDC
50.6
50.4
50.2
50
49.8
49.6
49.4
0
10
20
30
40
50
Time (h)
Figure 3.21
Simulation of frequency with wind on the system
A simulation was set up with the above wind generation connected, along with 3170 MW
reserve (providing both primary and secondary response), and a frequency dependent load
of 36 000 MW at 50 Hz. The level of reserve was chosen arbitrarily so that the maximum
frequency excursion would remain approximately within the statutory limits. Enough
base generation was provided such that the reserve was half-loaded when the wind
power was at its average for the 50 hour period - approximately 36 000
−
2500
−
(3170/2)
≈
32 000 MW.
Wind predictions were not used and the reserve requirements are large enough to compen-
sate for substantial but untypical large positive or negative variations of the wind resource
over several hours. The resulting grid frequency-time relationship for this simulation is
shown by the curve 'without DDC (dynamic demand control, see Section 3.8.3)' in Figure
3.21 .
Between 20 and 25 hours, the wind speed increased substantially to the extent that at 24
hours the base load plus the input from the wind exceeded the nominal demand. The conse-
quence was that the frequency increased excessively to a level determined by the frequency
dependence of the load. This undesirable situation could have been easily avoided by fi tting
wind turbines with a frequency dependent power regulator that reduces power generated at
higher frequencies.
At the opposite extreme between 40 and 42 hours, the output from the wind farms was so
low that the base load plus the total available reserve (the remaining half of 3170 MW) was
insuffi cient to balance the demand and the frequency had to drop to a level determined again
by the frequency dependence of the load. This undesirable situation would have been pre-
vented if at 37 hours use was made of meteorological data predicting a power decline from
the wind. Standby generating plant would then have been commissioned to provide the
expected shortfall in generation.
