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Reactive power supply is essential for reliable operation of the electric transmission system. Inadequate supply of reactive power can contribute to voltage collapse, as demonstrated in several recent major power outages. In examining the causes of the August 14, 2003 Northeast blackout, the U.S.-Canada Power System Outage Task Force found that "insufficient reactive power was an issue." 1 Reactive power is one of a class of non-energy power system operating needs collectively known as ancillary services. Other ancillary services include regulation, synchronized and non-synchronized reserves, and Black Start Service. Reactive power is unique among other ancillary services in that it must be delivered throughout the transmission system in close proximity to load centers. Reactive power is provided by an array of generation and network devices, including generators, capacitors, synchronous condensers, static VAR compensators, and Static Synchronous Compensators (STATCOMs). Distributed energy devices also have the capability of producing reactive power and voltage support. 2 Intuitively, there seems to be a good match between the requirement for reactive power supplies near load centers and the availability of distributed energy near or at customer loads. The statistics support the intuition that there is tremendous potential for distributed energy to be used for reactive power support. Over 10,000 MVAR of reactive power capability is estimated to be located close to the load. For comparison purposes, the entire New England Independent Service Operator has approximately 12,000 MVAR of available reactive power capacity.

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