How can we use Transformer on Direct Current ?

The general answer to why a transformer doesn't work on a DC supply is that a DC voltage doesn't "change" and cause changes in the magnetic field in the core, and, thereby, cause changes in the voltage in the secondary windings. When we "turn on" the DC (direct current), a field will be built in the core, it will sweep the secondary windings and deliver a "pulse" as the field is built. But then the secondary voltage will drop to zero after the pulse. This is because there is a static magnetic field around the secondary windings, and a static field will not sweep the windings and generate a voltage. There will be no secondary voltage.

It is possible to generate pulses of voltage in a transformer by pulsing a DC voltage supplied to the primary. The ignition coil in an automobile works in this way. The 12-volt supply is pulsed to the coil to generate the high voltage to fire the spark plugs. It is possible to get a transformer to work on DC. But, in general, transformers need a dynamically changing voltage supplied to them to cause the changing magnetic field in the core. This changing magnetic field will sweep the secondary windings and generate a changing voltage there. AC (alternating current) works really well for this application, and we use this idea in the power grids around the world.

Read more: http://wiki.answers.com/Q/Why_doesn't_a_transformer_work_on_a_DC_supply#ixzz1c6CEOmx6

Direct current not possible to use transformer if must be necessary then we have to first convert dc current to ac current by using converter it first convert from DC current to AC current then we use Transformer after then we again convert AC to DC by using converters  

Mr. Sandeep

Thank you very much for your answer to my question but in reality i am not satisfied yet. Could you focus on it elaborately. 

The principal of transformer design is not allow us to use it for DC supply. Instead of this why you think in this way, the housing wiring of electricity may use the DC supply say fan bulb tube light etc. Resurch the comparision of power consume by AC system and DC system. If we convert the housing system into DC ther will not be harmonics generation, frequency variations.