Both aspects of this activity are intertwined (voltage change in an alternating current (AC) network is effected through production or absorption of reactive power), so within this article the term voltage control will be primarily used to designate this essentially single activity, as suggested by Kirby & Hirst (1997).
[3] Kirby & Hirst indicate three reasons behind the need for voltage control:[1] Use of specialized voltage control devices in the grid also improves the power system stability by reducing the fluctuations of the rotor angle of a synchronous generator (that are caused by generators sourcing or sinking the reactive power).
Electric grid equipment units typically either supply or consume the reactive power:[6] In a typical electrical grid, the basics of the voltage control are provided by the synchronous generators.
The proliferation of microgrids might make the flexible centralized approach more economical.
[17] The system should be capable of providing additional amounts of reactive power very quickly (dynamic requirement) since a single failure of a generator or a transmission line (that has to be planned for) has the potential to immediately increase the load on some of the remaining transmission lines.