What will happen to a transformer if rated output voltage is injected to the secondary terminal?
No, you would not get 415 volts at the primary, at least if this is a regular symmetrical 3-phase transformer in open delta configuration. 
The turns ratio in that case would be would be (415 x √3)/ 240 = 3. However, if you feed the secondary you lack the 120⁰ phase shift resulting in only 1/2 of the voltage over the individual secondary windings (now primary), therefore 120V instead of 138V. The primary will drop proportionally to 360V. 

You may want to check if the transformer is truly a symmetrical 3-phase transformer.