Determining suitable settings for auto reclosing schemes of the Sri Lankan transmission system

The majority of faults in the transmission network can be successfully cleared by the proper use of protective relays to trip the respective circuit breakers and to bring back the system to normalcy using high speed autoreclosing. Thus, autoreclosing can significantly reduce the outage time due to faults and provide a higher level of service continuity to the customer. Furthermore, successful high-speed reclosing on transmission circuits can be a major factor when attempting to maintain system stability during fault clearing. Initial studies revealed that a detailed study of Autoreclosing settings in the transmission network of Ceylon Electricity Board and their performance based on failure analysis has not been carried out since the review of the protection system and settings by Lahmeyer International in 1996. Further there has been a brief analysis by the PB power consultants in their report on the CEB transmission system and organizational arrangements for operation and maintenance in October 1999. Since then there has been a comprehensive expansion of the CEB transmission network. Existing settings were reviewed along with failure incidents recorded during the period of November 2006 to August 2012 in the selected transmission lines. The stability analysis was carried out with the existing settings and prospective settings using the existing CEB power system which is modeled in PSSE software. Based on the simulated results, analysis of failure incidents, review of existing settings and the literature available on the practices followed in determining Auto reclose settings a set of Auto reclose settings for 220kV and 132kV transmission lines were proposed. These new settings and recommendations will improve the AR success rate thereby improving the reliability of the network. It will also minimize the risk of major failures resulted due to the definitive tripping of important transmission lines due to transient faults