Pole Voltage Balancing in HVDC Systems: Analysis and Technology Options

Maintaining balanced voltage during normal operation and rebalancing pole voltages after a pole-to-ground fault are both necessary to prevent high insulation stresses on the DC cable in a HVDC system. The state-of-the-art solution requires two separate devices to deal with normal and post-fault operation separately. This paper proposes pole rebalancing solutions using a single device applicable to both normal and post-fault operations, thus leading to reduced cost and footprint for pole rebalancing. The proposed circuits use fast switches to dynamically adapt the connected impedance in order to fulfil the requirements for rebalancing voltages during both situations. The performance of the proposed circuits are verified in a four-terminal HVDC test network using EMTP simulations.