We have a step up transformer 430/3300 volt. Now we want to use it as a step down transformer. Is it right that we can use step up transformer as step down?

 

yes, definately. The basic transformer is just a core and wire coils on its limbs, so if we put low voltage on one side it produce high voltage on other side and viceversa.

 

I think it is not possible, revise the equivalent circuit of the power transformer

 

We do this constantly, but only with 480/120 transformers with no issues. Not sure if there is any difference when using transformers with different Input/Output voltages, but my understanding is this will work with any transformer. Even have a scar on my arm from when I accidentally bumped into the the primary side of a 480/120 transformer that was being backfed.

 

Yes you can, as long as the transformer rating is not exceeded.

 

It is possible. basically a single Transformer is step up as well as step down.

BUT

within the Give KVA or MVA limitation.

The connection side either LV or HV you energize the other side you shall get respective voltage & Current with in design Limit. But remember HV side remain HV and LV side remain LV.