Determining reserve and interconnection requirements

UNTIL RECENTLY, the reserve requirements of a power system have been calculated either by applying a given percentage of reserve, or by counting on the outage of one or two of the largest machines. These standards generally are justified by the fact that satisfactory service has been obtained in the past by following them. Whether these rule-of-thumb standards will be valid under the conditions of the future is questionable, because the proportions of machine sizes to system size, as well as other characteristics that affect the required amount of reserve, can change considerably as time goes on. It is desirable to express a standard of service on a mathematical basis. Then all the factors that influence the standard can be analyzed separately, and any future system can be tested to see whether its service standard is equal to the present one.