Proximity effect in high-currenct conductors - a case study of breakdowns in a hydropower plant

The proximity effect plays an important role when calculating the ampacity of high-current cables, transmission lines and busbars. If ignoring the distance between the conductors, the number of parallel circuits and the conductor phase orders, there will be excessive heat losses in conductors and screens. This was the case in a hydropower plant, where thermal overload was root cause for dielectric breakdowns in insulated busbars. Combined magnetic and thermal calculations provide examples of how pronounced the proximity effect is, by using the hydropower plant as case study. In one location, with three parallel circuits in a 3×3 arrangement, heat losses in the most exposed busbar were reduced by 39 % by simply optimizing phase order of the conductors. At other locations, with conductors in flat formation, the heat losses could be reduced by 11 % by increasing centre-centre distance from 400 to 600 mm. In the 500 m repaired section, heat losses were reduced by 23 % after reorganizing the busbar layout. This corresponds to heat losses of 255 kW and annual energy reduction of 2 GWh at continuous rated current.