Planning for power systems is essentially a projection of how the system should grow over a specific period of time, given certain assumptions and judgment about the future loads and the size of investment in generating capacity additions and transmission facilities expansion and reinforcements.

Any plan can become technically and economically obsolete. New inventions in electrical utilization equipment or unforeseen industrial, commercial or residential projects can change load forecast. Breakthroughs in new generation and transmission technologies, unexpected inflation in equipment or labor costs or change of national income can all mean that system plans may take another direction.