Conditions Controlling the Economic Selection of Prime Movers

This paper attempts to clarify the effect of various controlling conditions on the magnitude of the evaluation constants used to select the optimum prime mover to be added to a system with a growing load. A hypothetical load has been set up which is assumed to grow at a known constant rate. Fixing on a policy of equal-sized units, two-unit installed reserve, and one-unit operating reserve regardless of load magnitude the progress of the individual generating units from the base to the top of the load curve can be readily studied. With the fundamental mechanics of the problem delineated the effects of unit availability, unit life span, rate of load growth, load cycle, load factor, unit capacity, and system reserve policy are analyzed. From this analysis certain principles are apparent, among the most important being: 1. Historical data of past and present prime-mover experience are of very limited value. 2. Evaluation constants for future prime movers are not fixed in magnitude and must be redetermined from time to time for each individual system. Having demonstrated the relative importance of the various controlling conditions this work is concluded with a recommended procedure for determining the evaluation constants for any practical case.