Influence of power system protection on system blackouts

The important part that power system protection may play in a major power system blackout is well known. Many papers have been written to describe particular events and to analyse the causes of failure. The following paper is based on an actual protection failure on a major transmission system. The main purpose of the paper is not to describe the event in detail, but to describe how the occurrence of this event initiated a detailed review into the transmission system protection. This review was initiated to identify any limitations of protection systems or their application and maintenance which might result in a similar event occurring in the future and to recommend actions to correct any perceived limitations. The paper provides a general overview of the significance of protection operation on power system performance, provides a brief description of an actual event and gives details of the protection review which followed. The need to record both correct and incorrect protection operation events in order to be able to assess current and potential and future protection performance is also discussed