# Why Transformer does not work on DC supply?

- Link: https://studyelectrical.com/2015/07/why-transformer-does-not-work-on-dc-supply.html
- Published: 2015-07-30T11:56:00+00:00

Did you ever think about what will happen to a transformer on dc supply? In this
article, you will learn why the transformer does not work on the DC supply.

You already know that dc supply cannot be used for the transformers. The transformer
does not work on the DC supply. The reason why the transformer does not work on 
dc supply is explained below.

>  * [Why Transformers are rated in KVA and not in KW?](http://www.studyelectrical.com/2014/08/why-transformers-are-rated-in-kva-not-in-kw.html)
>  * [Working Principle of Tranformer ](http://www.studyelectrical.com/2015/04/working-principle-of-transformer.html)

The [transformer works on the principle](http://www.studyelectrical.com/2015/04/working-principle-of-transformer.html)
of mutual induction, for which current in one coil must change uniformly. If dc 
supply is given, the current will not change due to constant supply and the transformer
will not work. 

Practically winding resistance is very small (Read [Practical Transformer](https://studyelectrical.com/2018/06/ideal-transformer-and-practical-transformer-diference-comparison.html)).
For dc, the inductive reactance X_(L )is zero as dc has no frequency. So the total
impedance of the winding is very low for dc.

[⌊Core and Winding of a Transformer⌉⌊Core and Winding of a Transformer⌉[

Core and Winding of a Transformer

Thus winding will draw very high current if dc supply is given to it. This may cause
the burning of windings due to extra heat generated and may cause permanent damage
to the transformer.

There can be a saturation of the core due to which transformer draws very large 
current from the supply when connected to dc.

If the primary of a transformer is connected to dc supply, the primary will draw
steady current and hence produce constant flux. Consequently, no [back e.m.f](https://studyelectrical.com/2015/02/back-emf-and-significance-in-dc-motor.html)
will be produced. The primary winding will draw excessive current due to the low
resistance of the primary.

The result is that the **primary will overheat and burn out or the fuses will blow**.
Care must be taken not to connect the primary of a transformer across the d.c. supply.

Thus dc supply should not be connected to the transformers. 

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