Assisting users in specifying the functional requirements for transmission static synchronous compensator (STATCOM) systems using forced commutated technology based on voltage sourced converter topologies is the purpose of this guide. These systems may be hybrid,and also incorporate thyristor and mechanically switched inductors and capacitors. Reactive power compensation, voltage regulation and control, transient and dynamic stability, and control and protection are the functions included. Accepted engineering practices for the application of STATCOM systems are presented. Specifications, typical application requirements, engineering studies, main component characteristics, system functions and features, factory testing, commissioning, and operations are covered. Informative annexes that allow users to develop or modify specific clauses to meet the requirements of a particular transmission system application are included.