Unit availability is a measure of the unit's capability to generate power when it is required for use by the system or for sale to other users. Availability is comprised of two sub-elements. Reliability is a measure of the unit's ability to continue to operate at the rated load, and maintainability is a measure of the ease with which corrective action can be carried out once the unit has become unavailable.

As a turbine generator unit is built to an engineering specification, it is inevitable that errors will occur in achieving full compliance with the engineering defined optimum requirements. These nonconforming conditions can occur as a result of manufacturing, assembly, or installation problems. In each case, it is the responsibility of the design engineering function to evaluate these conditions and establish the extent to which they can affect the total performance of the unit in respect to efficiency and availability. It can be anticipated that as a unit is put into service it is in a condition that meets with design approval. While it may contain a number of nonconforming conditions, these have been determined, as they occur, to not compromise performance, or, if their occurrence was significant, then the condition was corrected. In operation, similar nonconforming conditions can occur as a consequence of operation and/or maintenance.

Such situations must be evaluated by plant or supplier engineering personnel and a determination must be made of the most expeditious corrective action. When such errors exist, they represent a...