This guide assists users in specifying the functional requirements for Transmission Static Synchronous Compensator (STATCOM) Systems using forced commutated technology based on Voltage Sourced Converter topologies. This guide covers specifications@ applications@ engineering studies@ main component characteristics@ system functions and features@ factory testing@ commissioning@ and operations of the STATCOM Systems. A number of sections in the guide can be used for active filters and for industrial or distribution system applications. However@ reactive power compensation@ mitigation of load disturbances or phase unbalance compensation for industrial and distribution system applications are not included in this guide. Commercial terms and conditions for the purchase of the STATCOM Systems are also beyond the scope of this document. General terms and conditions forming the commercial part of a specification for a particular project are outside the scope of this document. Purpose This guide presents technical information that may be used as the basis of functional specifications for Static Synchronous Compensator (STATCOM) Systems. Functions covered include reactive power compensation@ voltage regulation and control@ transient and dynamic stability@ main components@ control and protection@ and accepted engineering practices for the application of STATCOM Systems applications. This guide also includes informative appendices that allow users to develop or modify specific clauses to meet a particular system application. The wording deliberately uses ??should?? rather than ??shall??@ given that the document is a guide@ not a standard specification. The user of this guide might wish to make this adjustment when converting specific sections into a specification. The guide describes i) newer developments in STATCOM components and particularly control systems ii) information on latest practices for STATCOM applications iii) an informative Annex to allow users to modify or develop specific clauses to meet a particular system application