reserve capacity must be added if the system reliability is to be maintained. The magnitude of the assumed reliability criterion is not critical; whatever the criterion, it should not change when the SPS is added to the power pool. The most important simplications made in this study and a description of the effect that each would have on the required total installed generating capacity in the power pool are given below: • The conventional generators in the power pools were assumed to be identical in their maintenance characteristics, fuel economy and power generating capacity (1 GWe) . This assumption tends to increase the required generating margin. Gas turbines are usually used to provide the reserve margin. The maximum expected size of these units in 1995 is 300 MWe. • The assumed forced outage rate of .05 is relatively low for thermal units; large fossil fired units can have forced outage rates as high as .2. This assumption tends to reduce the required margin. • The twenty percent scheduled maintenance requirements assumed for all plants, SPS ground station and conventional, is the upper limit on this parameter. This assumption tends to increase the required margin. • Individual power pools were assumed to be controlled by a central dispatcher. This assumption tends to reduce the margin from what would be required if the power pool had the transmission system appropriate to a centrally controlled system.
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