Reliability of power supplies and systems

Summary form only given. The author presents the reliability of electricity supplies experienced by the IBA throughout the UK in terms of frequency of interruptions, durations and the corresponding annual downtime, ADT, and for supplies up to and including 11 kV. The supply arrangements are described and the necessity and difficulties of obtaining detailed records are emphasised. IBA data is presented and this data may be considered as a guideline to the kind of power supply reliability to be expected. The data is divided into two sections: those for fault outages, which include voltage deviations beyond +6% and -10% tolerances, and those pre-notified outages required by the electricity utilities for preventive maintenance purposes. Using the computed values of reliability indices, suggestions are proposed as to the cost viability of available options to enhance electricity supply reliability