>>1986016I heard of this recently and initially, I thought of this to be quite silly. But countries don't seriously consider spending billions on 'silly'. So what I thought of:
1. On a DC fed train you don't need to bother with a bulky transformer.
2. I think it would be sensible to quickly retrofit an existing rolling stock to run on increased voltage - all that would need is a simple, fairly compact inverter, some extra insulation and off you go.
3. Grid does not like having asymmetric 6MW loads, and that tends to happen on a pure AC system unless a substation does the conversion from 3 to single phase. Which I don't think makes sense. I mean - the AC-DC-AC link already exists on 25kV stock, thus why add another one?
4. 1500V catenary will happily run 9kV DC with some extra insulation, methinks.
Overall - the only issue I see is protection against arcing and the ability to extinguish them if they occur. DC arcs are notoriously hard to extinguish. Which is why contemporary DC systems top at 3kV, while AC will happily run 25kV or even 50kV.
But - there seem to be benefits to this 6/9/12 kV system.
