Transformer works on the principle of mutual induction and for mutual induction polarity of current should change continuously. This is possible only for ac current not for dc current. So, transformer works only in ac not in dc current.
Transformer work only on ac supply because A transformer needs an alternating current that will create a changing magnetic field. A changing magnetic field also induces a changing voltage in a coil. This is the basis of how a transformer works: The primary coil is connected to an AC supply.
Since high voltages are more efficient for sending electricity great distances, AC electricity has an advantage over DC. This is because the high voltages from the power station can be easily reduced to a safer voltage for use in the house. Changing voltages is done by the use of a transformer.High voltage overcomes voltage drop over long distances. The reason that AC is transmitted instead of DC is that it is much cheaper and easier to boost and reduce AC voltage than DC. In fact, DC has fewer losses in long distance transmission. The longest transmission lines are, in fact, DC; often over a million volts.
A.C. is said to be four to five times more dangerous than D.C. For one thing, A.C. causes more severe muscular contractions. For another, it stimulates sweating, which lowers the skin resistance. ... The frequency of the AC has a lot to do with the effect on the human body.A transformer is not designed to convert AC to DC or DC to AC. The transformer can step-up or step -down current. A transformer that increases the voltage from the primary to secondary is called a step-up transformer.