Looks like it might be an obsolete part?
Max.

Seems to have been a Westinghouse owned company - but that was all I could find out.

 

measure from the star connection on the input side to the 'open' (unused) connection and compare to the other used terminal, you may be able to use the alternative Higher primary connection and lower it that way, probably by half

do you mean it might be connected to center tap not to the other end of the transformer and by connect it to the other end it will half the output?
if not can i put 3 phase controllers on the outputs?

Found it - its a; Hyreg AR2/250-15.

thanks, i will search for it or for replacment

 

do you mean it might be connected to center tap not to the other end of the transformer and by connect it to the other end it will half the output?

Yes, that's the general idea, if the transformers are on the lowest taps, wiring to a higher tap on the same voltage will lower the output.
Max.

 

Sadly the connection is on the higher tap already.
I'm considering putting three SSR before the rectifiers since I cannot find any phase controller in the local market.
Those SSR are usually used with heaters but I hope the capacitor will make it work with the motor
Is there any consideration I should take care of before using them (regarding the Yy configuration ) ?

 

3ph fed full wave bridge DC motor controlers are extremely pricey, if it were me I would look at replacing the transformers with either 3 singles or one single 3ph verion.
The rpm is directly relative to the DC supply, so it should be easy to calculate what AC you would need.
Max.