Variable Transmission Voltage for Loss Minimization in Long Offshore Wind Farm AC Export Cables

Connection of offshore wind farms to shore requires the use of submarine cables. In the case of long HVAC connections, the capacitive charging currents limit the transfer capability and lead to high losses. This paper shows that the losses can be substantially reduced by continuously adjusting the cable operating voltage according to the instantaneous wind farm power production. Calculations for a 320 MW wind farm connected to shore via a 200 km cable at 220 kV nominal voltage show that an annual loss reduction of 9% is achievable by simply using a ±15% tap changer voltage regulation on the two transformers. Allowing a larger voltage regulation range leads to further loss reduction (13% for 0.4-1.0 p.u. voltage range). If the wind farm has a low utilization factor, the loss reduction potential is demonstrated to be as high as 21%. The methodology can be applied without introducing new technology that needs to be developed or qualified.