Environmental Engineering Reference
In-Depth Information
Figure 13-5. Typical standard relating voltage excursions in utility power systems to the
minimum allowable time for the change to take place. [Ewart et al. 1978]
cutoffs of service occur at the local level, except under unusual circumstances like those that
caused the “Northeast Blackout” in 1968 and subsequent emergency events.
System Dynamic Stability
Relatively small amounts of wind-generated power will simply not be noticed on a utility
network, because normal consumer load fluctuations will dominate over the typical varia-
tions in the output of a wind power plant. However, as the capacity of a wind power plant
increases there may come a point at which the loss of the wind power is noticeable at the
system level. Normally, a high wind speed cut-out is the most severe loss-of-output test. If
a significant amount of the plant (conventional or wind) has been operating at full power and
then suddenly stops operating, two things happen: First, all the remaining generators slow
down slightly, causing the frequency of the power to drop. Secondly, a small voltage drop
occurs throughout the utility system.
Extra generators need to be brought up to load immediately to replace the dropped power.
For this reason all utilities maintain generators on partial load or as spinning reserve ( i.e. ,
turning without load), so that the power deficiency can be corrected along with the system
voltage and frequency. The converse occurs if a large consumer load is switched off without
warning or if a storm front moves across a wind power station and causes an upsurge in its
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