What will happen rated voltage applied in transformer short circuit?

I can only answer this from an actual problem I had in relation to the question.

20-60VA 12V transformer supplying 2x20W lamps,both lamps had blown,so I bought 2x10W replacement lamps.

On replacing the lamps,when I fitted the first and tried to power up,the lamp glowed briefly,then went out.

It was only when I fitted the second lamp that both fittings lit up continuously,so in brief,the answer to the question is................the load won't operate.

The power rating of a load should never exceed the volt ampere rating of the transformer, otherwise the resulting load current may overheat the transformer. So the situation you describe is perfectly normal.

The reason for the problem encountered by the writer of the original answer is not clear. A 60-V.A transformer should supply two 20-W lamps without any difficulty whatsoever. I suspect that the problem had nothing to do with the power rating of the lamps vs that of the transformer, and more to do with the voltage. For example, was the secondary voltage of the transformer higherthan the rated voltages of the lamps? If so, then the lamps would have burnt out.