Influence of system design on reactive control requirement

The reactive power control requirements in the National Grid Company transmission system are determined by the system configuration and utilisation. The system interconnects several major load centres and has a diversity of generating sources. Since the system is meshed, with line thermal ratings 4-5 times natural loadings, system reactive demand increases considerably under outage conditions; the provision of reactive capacity is determined by the need for security under outages. Competition between generating companies and fuel sources causes variations in distribution of generating plant and the security of the system must be robust against such changes. The author describes how these factors combine to define the reactive control task confronting the system operators