Environmental Engineering Reference
In-Depth Information
Stiff
voltage
busbar
Power flow
1.06
Allowable
voltage range
1.0
0.94
Load distance (MW km)
Figure 4.8
Network voltage profile with voltage regulator
circuits supplied from the node. A little thought might suggest that a voltage
controller at the supply end of the circuit would be more useful, but the problem
with this is that a sudden cessation of wind power would expose customers at both
circuit extremities to a 12% voltage step, which lies far outside normal standards.
Indeed the potential 6% step in this example is unacceptable for frequent
switching, and therefore the generated output of the wind farm would have to be
reduced to ensure that the step seen by consumers is 3% or less. This approach
follows present deterministic rules and experience may show that this is too
conservative, i.e. a more probabilistic approach to step voltage may be taken.
There is evidence to suggest that very rarely does a wind farm with many WTGs
actually drop its entire generated output over a very short period - and that in
many cases the wind gusting which causes this could be predicted and the output
pre-curtailed, as noted above.
4.4
Thermal/active power management
4.4.1 Planning approaches/standards
Annual or periodic utility plans are prepared and developments authorised to
maintain a level of security in line with the network security standards. These
standards are effectively a benchmark document to ensure that customers in one
part of the network experience the same conditions as customers in another similar
part of the network. They generally have the status of strong guidance, rather than
regulation, to give flexibility for the wide variety of circumstances. Common
practice with the load security standard is that parts of the network that supply large
load blocks are more stringently secured. This gives rise to the much quoted
n-1, n-2, n-g-1, etc. security standards, where n refers to system normal running
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