Tonight the rock bank AC/DC plays a concert in Wellington's railyard stadium, appropriately featuring a locomotive in its stage set. The band's name is also appropriate as the issue of ac versus dc electric traction has been a problematic one for railways internationally including in NZ.
New Zealand Railways' first three electrification schemes (Otira-Arthur's Pass, Christchurch-Lyttelton and Wellington-Johnsonville) used 1.5 kV DC as this was a common choice in Europe at the time (the Copenhagen suburban system was electrified with this in 1934), but since WW2, the advantages of high voltage AC have made it the standard choice for new schemes.
The problem is that once you've opted for a particular system you are pretty much stuck with it for every extension. Thus Wellington's new Matangi electric units will be 1.5 kV dc, while the new units planned for Auckland will be 25 kV ac, as are the locomotives that run between Palmerston North and Hamilton. At this stage there are no plans to connect up the Wellington system with Palmerston North, but if that happened new dual voltage locomotives would be needed. The photo shows one of Slovakia's dual voltage ac/dc electric locomotives.
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