HVAC cables generate reactive power proportional to the length of the cable and proportional to the voltage squared. This dependency on cable length is illustrated in Figure 1, where it can be seen for example that for a 1000mm2 220kV cable compensated from both ends the possible transmitted power is 400MW if the cable is 50km, whereas the same cable would only be able transmit 280MW if the cable is 200km long. Likewise the stronger influence of system voltage due to the voltage squared dependency can be seen by comparing the blue curves for 132kV to the green curves for 220kV and likewise it becomes clear that full transmission power is only possible for relatively short distances at 400kV.
As can be seen from Figure 1 compensating with reactors from both ends increases the possible length of the cable, and breaking up the cable system in sections and compensating with reactors inserted between sections can further increase the possible cable length. A midpoint reactor would for example double the distance where close to maximum power can be transmitted to about 170km for a 1000mm2 220kV cable – which is basically why a midpoint reactor station is used for the Hornsea 1 offshore wind farm project.
A midpoint reactor station placed on an offshore platform is a fairly straightforward solution, as the platform is comparable to the offshore platforms used for offshore . It is however a costly construction which is why concepts for using submerged reactors is described in this document
transformerstations. It is however a costly construction which is why concepts for using submerged reactors is described in this document.