Dear sir
The rated voltage in our country is 415 v but I received medical machine of 480v , can we feed it by 415 v source or we have to install step up transformer .

Electrcial devices usually will operate with the voltage + or - 10%. 415 falls out of that tolerance from 480 volts.

You can use a "Buck-Boost" transformer(s) to boost the 415 to 480 volt, nominal.

Take a look at page 204 of:
http://www.solaheviduty.com/products/transformers/pdfs/bboost/bbselect3ph.pdf