On the page here, they support both (20 and 22 kV).
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When it comes to traction devices, you never really know where the power for that comes from. When the mains would drop in the city I used to live in, the trams running at 5kV still had power. Where did the power come from ? Batteries ? :-) The trams didn't have the "emergency traction" option (cheep), so if one stalled in the middle of an intersection, it just sat there.
Maybe the train running at 25kV, is a kind of flag indicating the power comes from some sort of parallel network.
Paul