Why transformers can’t operate on DC?
Transformers cannot operate on DC because a changing magnetic field is required to induce a voltage in a loop of wire.
If the primary of a transformer is connected to a DC supply, the primary will draw steady current and hence produce constant flux.
Consequently, no back e.m.f will be produced.
Additionally, there can be a saturation of the core due to which transformer draws very large current from the supply when connected to DC.