A voltage control system and method for multiple windfarms (810, 815, 820) with transmission lines (898). Voltage is regulated at a point of regulation (825) on the system, such as a high voltage substation or other system bus. At least one other constraint point in the system may be monitored and controlled to prevent voltage exceeding the limit at the point of constraint. Regulation is achieved at the point of regulation (825) by sensing the voltage, comparing to a reference voltage (847), and adjusting the reactive power output of the wind turbines (60) and other equipment in the system. The regulation point (825) may be shifted to at least one other constraint point (805) needed to respect voltage limits at that points of the system after attempting to shift reactive load to restore voltage within limits at the other points in the system. The reference voltage (847) may be adjusted to minimize losses for the system of multiple windfarms and transmission lines. A loss optimizing algorithm (890) is applied to the combined multiple windfarm and transmission lines (898) to shift reactive load (850, 851, 852) among local windfarms (810, 815, 820) and transmission lines (898) to minimize losses and to shift reactive load among individual wind turbines (60) within an individual windfarm.