HVDC 고장감소 및 정비시간 단축을 위한 전력변환 밸브 냉각시스템 개선방안

Abstract

This dissertation presents the improvement of HVDC thyristor valve cooling system to reduce HVDC fault and its maintenance time. The actual HVDC system is linked between Jeju island and mainland electricity system In case of either HVDC system failure of delay of repair time, power outage brings out not only enormously economic loss but also the significant decrease of the power system stability. Since HVDC convertor valve cooling system is located in confined space, the inspection of cooling system is visually impossible. Therefore, it is important to prevent the failure of valve in advance. In this study, first of all, the failure factors and recovery time in each failure point were analyzed by investigating operation-case of Jeju - Haenam HVDC which has been operating since 1998. Then, the improvement of maintenance for HVDC convertor valve cooling system was proposed by applying the six-sigma technique which currently is a highly recommended quality improvement tool in the industrial sites. Priority, bellows material which is the most frequently defected was improved in order to reduce the failure rate. And then, additional stop valves were placed in the proper position to shorten the maintenance time of failures. Moreover, a demonstration was performed to validate the effectiveness of the proposed improvements. The demonstration proved the significant improvement. It is concluded that the proposed improvements with some modifications possibly apply to cooling system for AD-DC convertor, and it can surely contribute to reliability improvement of HVDC system which currently installed.