HVDC Classic transmission losses

An optimized HVDC transmission line has lower losses than AC lines for the same power capacity.

HVDC cables also have lower losses than AC cables. One reason for this is that there is no dielectric losses in an DC cable as there are in AC cables. Also the full current capacity can be used for the power transmission as there is no 50 or 60 Hz charging current that causes conductor losses without any contribution to the active power.

The losses, calculated acc. to IEC 61803, in the HVDC Classic converter stations amount to about 0.6 - 0.7 % of the rated HVDC transmission capacity (per station) at rated load. The no-load (standby) losses are about 0.1 %. The main contributors to these losses are the converter transformers (» 50 %) and the thyristor valves (» 30 %). The rest comes from the AC filters, the smoothing reactor, the station service power and the DC filter.

If the HVDC link is operated in parallel with AC lines, there is a possibility to adjust the power on the HVDC link to minimize the total grid losses. (See example!)