DLR-supported distance protection for blackout mitigation

Analyses of the recent decade blackouts has indicated overloads and power swings as being responsible for initiation and development of most large area failures. The overload and power swing conditions have also been found to correspond especially with the over-current and distance protection relays, often causing their over-function under allowable power system operating conditions. It is highly desired to improve the operation of protection relays for the sake of avoiding possible following blackout occurrences or at least lowering their scale. One of the possibilities to do so is an application of the Dynamic Line Rating algorithms into the standard distance protection relay with the hope of ensuring safe relay behavior during overloads and power swings. The Dynamic Line Rating is usually proposed to be used for increasing the line transfer capacity by monitoring of the overhead conductors temperature and weather conditions. It is clear that one must also take into account the impact of DLR-operated line on the existing protection devices. It is required to adapt their decision-making algorithms to the new conditions, while satisfying arbitrarily established protection principles. This paper firstly presents chosen recent decade blackouts, highlighting the main causes of their formation and development process. Applicable solutions for distance protection relay improvement are then proposed, which is followed by analyses of the new algorithms' operation during allowable overloads, power swings and faults. The enhanced distance protection solution described in this paper proved to be an efficient technique also for blackout prevention.