I would have thought its was a 415V transformer that stepped down to 240V and 24V, so you had 240V for standard bulbs or suds pump etc and 24V for whatever needs 24V (control gear? or low voltage lamp?)
GReat that confirms what I thought it was...putting 415 across the two reds should give me the 24 volts I need and now I just need to remember what we spoke about ..although having just re read the thread it refreshed my memory and I need to change both contactors and provide the 24 volt to each of them........Seems pretty simple. If you have 415v use the two reds for input and you'll get 24v out of the whites. If you have 240V use the blues for input and you'll get 24v out of white.
Remember that putting 240v into blue will also cause the reds to be live with 415v so don't leave any wires hanging out thinking that it's not used so it's not live.
I was right then...its been a long time and memory fades quickly...Step up, step down, step sideways - doesn't matter. It's an dumb autotransformer if you put the labelled voltage into the relevant wires the other wires will generate their labelled voltages. That's why it's got a full length insulating cover, because everything is live if one thing is.
EDIT: actually I'll revise that comment a bit. It probably (almost certainly) is isolating between the 240 and 24v outputs, but it'll still work as I said above. You can put in 240v and get out 24 if you so wish.