System-services: several questions, in an integrated utility perspective [ancillary services]

Ancillary services, interconnected operation services, system services-the variety of terms used throughout the world shows the difficulty, not only to name, but also to define these services, and to integrate them in electricity supply planning and operation procedures. Since such system services are still an unresolved issue, the author does not give definite statements. Rather, he considers several questions raised by system services, and identifies possible answers, together with their advantages and drawbacks