HVDC system performance with a neutral conductor

The poles of bipolar HVDC transmission systems are often required to be capable of independent operation. In order to maintain the independence of the poles a return path for the current is needed. If a ground return cannot be used a neutral conductor must be installed, either on the same structures as the pole conductors or on separate structures. A fault on one pole of such a system may cause a fault on the neutral and a fault on the other pole; therefore, a fault must be efficiently cleared. This paper examines the effect a neutral conductor has on HVDC system reliability and the effectiveness of fault clearing devices such as arcing horns and neutral grounding breakers.