# Dc supply to transformer

• dhivakhar
In summary, the conversation discusses the accidental use of a DC supply on a transformer in a college lab, resulting in a blown fuse. It is explained that transformers typically work with AC voltage and that for DC voltage, they act like a short wire with low resistance. The speaker also suggests that the person asking for an explanation should already know the answer if they are working with transformers in a lab. It is also mentioned that the transformer's iron core acts like an electromagnet and produces a back emf which delays the increase of DC current, leading to the blown fuse.

#### dhivakhar

my friend gave a dc supply to a transformer in my college lab accidentally and the fuse went off can i get an explanation on why this happened?

Transformer work only with AC voltage. For DC transformer act just like a short wire (a very small resistance ).

Jony130 said:
Transformer work only with AC voltage. For DC transformer act just like a short wire (a very small resistance ).
Can you please explain how a transformer shows very small resistance to a DC supply?

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Actually this sounds like a disguised homework question. If you are messing with transformers in lab you should already know the answer to the question.

Because transformers is essentially just two or more coils of wire wrapped around the core. And wires has "low" resistance.

dhivakhar said:
my friend gave a dc supply to a transformer in my college lab accidentally and the fuse went off can i get an explanation on why this happened?
You have a careful smart friend

Actually, if your friend had been able to measure the way the current varied around the time of switch on, he would have found that the current value followed a curve, because the Iron core of the transformer behaves like an electromagnet. The magnetic field energy takes time to build up and it produces a 'back emf' which delays the DC current increase (This would be fairly quick with a mains transformer - only a few tens of milliseconds before the fuse started to blow.)