Comparison of reliability performance of group connected and conventional HVdc transmission systems

A group connected HVDC transmission scheme is a variant of the unit connection where instead of a single generator, a group of generators are directly connected to the power converter. Studies conducted in the past indicated that significant cost reduction can be achieved using this scheme. This is mainly due to the elimination of many components which results in considerable capital and operating cost savings to the utility. Concerns regarding the reliability performance of unit connected schemes were raised, however, there has not been a detailed reliability study conducted. This paper addresses the reliability evaluation aspect of a group connected scheme and compares the reliability performance of the group connected scheme with that of the conventional common collector system. Reliability models for both schemes were developed using a hypothetical model based on the Nelson River power system. Practical power system component outage data was used to examine the reliability performance of both schemes