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the balance between generation and demand. However, if
the loss of generation is large this results in a
substantial drop in frequency, a reduction in the
capability of auxiliary plant supplying the other sets
running on the system and hence a reduction in their
output and finally a complete shut-down of the system.
It is therefore essential that no set running on the
system carries an excessive proportion of the demand
on the system. Operational experience has established
that no generating set should normally carry more than
25% of the demand at any time. The winter night load is about 28% of the system maximum demand; and 25% of the
winter night load would be 7% of the maximum demand.
So the new sets must be capable of being operated down
to 7% of the maximum demand which means, assuming an
operational minimum part-loading of 33% of machine-
rating, that the maximum size of the new generating
sets should not exceed 21% (7/0.33) say 20% of the system
maximum demand.
Maximum Size of Sets for the Next Phase of Generation
Development
At present, 200 HW, 275 MW, 350 MW, 500 MW and 660 MW are standard in the UK and in order