Reactive power control in a metro system

The reactive power problem will become intensified in the future with the increasing use of EHV overhead lines and high-voltage cable in densely populated areas. Generators alone, with their underexcited limitations during light load periods, may not have sufficient capability to control voltages in some systems in which substantial amounts of high-voltage cable are used. Turbine generators with automatic voltage regulators, however, can be operated successfully in the underexcited region to minimize the problem of excessive system capacitive reactive loading. Although shunt reactors are an effective solution, economics may suggest other methods. Nevertheless, shunt reactors are helpful in controlling voltage during a system-start-up. Finally, more experience with the daily switching of 138-kV and 345-kV circuit breakers is necessary before definite conclusions can be drawn as to the advisability of operating them so frequently.