5. Future prospects

Possible improvements based on current techniques should make it possible to achieve significant unit powers: almost 1,500 MVA at 225 kV, 2,500 MVA at 400 kV and over 4,000 MVA at 750 kV.

These limits would be reached with externally forced-cooling cables; they would be linked to mechanical (maximum cable diameter of 150 to 160 mm) and thermal constraints, as well as to the physical characteristics of the components. However, we already believe that these limits can be pushed back to higher values, for example by adopting internal water cooling.

However, there are a number of drawbacks to these prospects:

• forced cooling required (from 1,300 MVA at 400 kV) ;

• high reactive power (on the order of 16 to 17 Mvar/km for a 400 kV cable);

• ...