Is direct electric current used in transformers?

no direct current is not used in transformers. the reason is that, if dc is used, there would be no counter emf to oppose it in the primary winding.

since the constant flux will be flowing in the dc, there would be no rate of change of flux. as a result, the total current will be applied at the primary winding only. this results in the burning of the total primary winding.

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The practical application is:

If transformer input is DC, transformer output is smoke.