What type of HVDC system uses two conductors, one with a positive voltage and one with a negative voltage?

The bipolar HVDC system is characterized by its use of two conductors: one carrying a positive voltage and the other carrying a negative voltage. This configuration allows for efficient transmission of electricity over long distances while balancing the currents and minimizing the ground return currents, which can lead to interference or corrosion if not managed correctly.

In a bipolar system, the two conductors operate together, and the system can continue to function even if one of the conductors fails, making it more reliable than other configurations. The ability to transmit power with a positive and negative conductor helps in reducing losses and improving overall system stability.

In contrast, monopolar systems use a single conductor with the return path generally through the ground or via an earth return, which has certain limitations in terms of efficiency and reliability. Multiterminal systems include multiple connection points, which could be configured in various ways, and bidirectional systems simply indicate that current can flow in both directions but do not specifically define the conductor arrangement. Thus, bipolar systems are distinct in their design and function, making them the clear answer in this context.