Perfect to use for that 25VAC supply, using the 11kV tappings rather nastily and applying 400VAC to tappings 1 and 6 of the primary, and using the 400VAC side as secondary. You will need to do some rewiring of both primary and secondary transformer connections though, along with making sure the 11kV section that is unused is well insulated as it will have 11kV on it from autotransformer action. Rating will be much reduced, but regulation on the secondary will be very good.