System Tests for Paralleling, Parallel Operation, and Deparalleling of the Nelson River HVDC Bipoles 1 and 2

This paper reports on paralleling, parallel operation, and deparalleling tests on the Nelson River HVDC Bipoles 1 and 2, at the normal voltage of 463 kV, performed in the summer of 1985 following completion of Bipole 2. Control system development and testing of the sequences at low voltage (150 kV) are described in earlier papers. The present paper provides oscillograms and analyses of the most significant system tests performed along with paralleling overvoltage considerations. The tests are significant in the fact that for the first time two dissimilar HVDC poles have been paralleled and deparalleled at 463 kV using high-speed switches and have successfully undergone all the required transient tests while in parallel operation, proving that the concept of parallel operation is a viable technique for a major HVDC transmission system. The positive results should enable other electrical utilites to approach parallel operation, and as a logical extension multi-terminal operation, with much greater confidence than in the past.