An overview of ancillary services in an open market environment

The worldwide restructuring of the electrical energy industry is followed by processes like deregulation, liberalization and commertialization. These changes introduce new paradigms such as competition in generation and the concept of electricity supply as a commodity market and creates a new set of transactions among utilities and new agents and end users. An important aspect is the role of competitive markets stressed by the new regulation in procurement and remuneration os ancillary services. These services are required to provide stability and security of supply. Ancillary services have a variety of terms used throught the world to name them (e.g. system services, support services) and it is not easy to define or classify them. The objective of this paper is to give a possible classification scheme for ancillary services to allow an easier identification of the roles of suppliers and buyers. Also, means by which the costs of various services can be measured, quantified and allocated are discussed and one method for cost allocation is proposed.