Monopolar Metallic Return Operation of Long Distance HVDC Transmission Systems

This paper presents various design aspects of monopolar metallic return with particular reference to the operation of the Pacific NW-SW HVDC Intertie in this mode. Discussion includes the design considerations involved in determining the capacitor size, protective gap duty, insulation level required at the floating end, location of the grounding at the grounded end, additional control and protection required, etc. The paper then presents practical results of such an operation of the Intertie. Disadvantages and justifications of using monopolar metallic return are also discussed.