Some notes on HVDC

Advantage of ground retuyrn:

• Earth resistance in case of dc for long lines is interdependent of length and this resistance is < that of metallic conductor if used.
• d.c line can be built in two stages.
• reliability increases in case of outage one monopolar out of the bipolar.

Disadvantages of  ground return:

• Electrolytic erosion of buried / immersed metallic structure.
• difficult design
• Ground currents can cause dangerous step and touch voltages.
• Ground current interferes with other services.