FACTS in transmission systems involves dynamic devices of SVC and STATCOM type. Both use power semiconductors to control the exchange of Mvar over a shunt connection with the grid. Thanks to the fast controllability, SVC and STATCOM can counteract event the most rapid voltage transients that will appear in the grid and consequently reduce the risk of serious voltage depressions and/or voltage collapse.
Additionally SVC and STATCOM can under steady state conditions, through continuous control of reactive power injection or absorption, control the grid voltage profile according to a given optimal characteristic. The benefits for the grid owner/operator are that the stability limit dictated by system voltage will be raised and that the voltage profile will be more controlled. The grid capacity will be enhanced at the same time as its behavior will be more robust, flexible and predictable.