What is a key factor in measuring an electrical system's availability?

Measuring an electrical system's availability primarily revolves around understanding how often and for how long the system can effectively provide its intended service. The long-term average fraction of time the system is functional is a direct indicator of its reliability and readiness to generate power when needed. This metric captures both planned maintenance outages and unplanned downtimes, giving a comprehensive view of how dependable the electrical system is over time.

In contrast, factors such as total operational cost, capacity of the generators, and the rate of energy production can influence the performance and efficiency of an electrical system, but they do not directly quantify its availability. Total operational cost encompasses various expenses and does not speak directly to reliability. The capacity of the generators refers to their maximum output, but this does not indicate how often they are actually available to produce electricity. Similarly, the rate of energy production provides insights into performance during operation but fails to account for periods of downtime or unavailability. Therefore, the measure of how long the system functions correctly over a specific timeframe remains the critical aspect of assessing availability.