Transformer is static device. two or more stationary electrical circuit mutually linked by magnetic circuit. assumptions of ideal transformer: 1. there are no losses. 2. whole magnetic flux constant no leakage. 3. permeability of core is infinite.
transformer works on principle of faraday's law of electromagnetic induction. So if D.C supply use, no indction are produced and due to this E.M.F not induced in winding and transfer of electrical energy is not possible.
EXAMIANS