Ancillary services definitions, markets and practices in the world

Ancillary services are some operational reserved services procured by the Transmission System Operator (TSO) for keeping a balance between supply and demand, stabilizing the transmission system and maintaining the power quality on an economical basis in any competitive electricity market environment. This paper discusses different types of ancillary services and their characteristics and challenges in the power market in order to find an efficient combination of ancillary services with the least reservation cost that secures reliable transmission system operation. An overview of practical experiences regarding performance of ancillary services in several competitive markets in the Europe, Australia and New Zealand will be discussed. Further, wind power as a disputable ancillary service will be presented in brief. In addition, some efficient proposals for revising the design and implementation of those markets will be mentioned in conclusions.