Interconnection Services Their Classification and Evaluation

The services rendered by an interconnection between two or more electric power systems may be classified as: 1. Emergency service-by which assistance is given by one system to the other in event of breakdown of equipment or other abnormal conditions. 2. Load diversity-arising from the non-coincidence of the times of peak loads in the interconnected systems. 3. Firm power-transactions involving a definite advance commitment by one company to sell power and energy to the other for use in lieu of installed capacity. 4. Storage power-by which off-peak energy from one system is converted into peak capacity in the other through the medium of storage. 5. Intra-company use-referring to the use of interconnecting facilities for the internal purposes of one of the parties. 6. Economy flow-by which generation in one system is replaced by more economical generation in the other system; and 7. Unintentional flow. The foregoing services may be evaluated, as far as capital cost is concerned, by determining the aggregate saving in generating capacity and multiplying by the estimated cost per kilowatt of generating capacity and then comparing the result with the capital cost of the interconnection. The more important annual-cost comparison is made by: 1. Determining the difference between the fixed charges on the avoided generating station investment and the fixed charges, including operation and maintenance, on the interconnecting facilities. 2. Determining the saving in fixed element of production expense arising from the avoided capacity. 3.