A never-finished report: Power system loads and stability

Electrical power systems are connected collections of many and various instances of com-ponents from several basic groups — e.g. generators and transformers — and are jus-tifiably claimed as the largest and most complex systems that ever have been made. Advances in computers, telecommunications and control techniques keep extending the possible amount and precision of measurement, control, and off-line and real-time plan-ning. Changes in system components, especially in the type and location of generating plant, provide new potentials for control action but also for problematic interaction. Use of these advanced methods and new resources to allow higher utilisation of trans-mission and distribution systems has been encouraged by recent competitive cost-cutting drives consequent to the deregulation that has happened to the power industry in many countries over the past decade, also by increasing pressures against the building of new lines and power stations. The transfer capacity of power systems is increasingly limited by constraints of stabil-ity rather than thermal limits, within which the critical constraint is increasingly that of voltage stability. The shift in critical security limit is due partly to improvements in othe