# Why Transformers can’t step Up or Step Down A DC Voltage or Current?

**URL:** <https://forumautomation.com/t/why-transformers-can-t-step-up-or-step-down-a-dc-voltage-or-current/12920>\
**Category:** Electrical\
**Tags:** interviewquestions\
**Created:** [December 31, 2024, 11:30am UTC](https://forumautomation.com/t/why-transformers-can-t-step-up-or-step-down-a-dc-voltage-or-current/12920 "2024-12-31T11:30:10Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Rabert](https://forumautomation.com/user_avatar/forumautomation.com/rabert/32/6784_2.png) [@Rabert](https://forumautomation.com/u/Rabert)\
**Post date:** [December 31, 2024, 11:30am UTC](https://forumautomation.com/t/why-transformers-can-t-step-up-or-step-down-a-dc-voltage-or-current/12920/1 "2024-12-31T11:30:10Z")

</div>

A DC voltage cannot be step up (or) step down using a [**transformer**](https://forumelectrical.com/what-is-an-on-load-tap-changing-transformer-oltc/). The transformer may start to smock & burn because, in the case of a DC supply, the frequency is zero.

 ![image](https://cdn.forumautomation.com/original/2X/f/fa7a989cd63362a79e6d089da1d7ca8d0e5d7080.jpeg)

Therefore, it is not advised to connect a DC supply to a transformer because, if a DC rated voltage is applied to the transformer’s primary coil, the flux generated in the transformer will not change in magnitude but rather remain the same.

As a result, EMF will not be induced in secondary coil except at the point of switching ON.

Since, the frequency of a DC supply is zero, applying voltage across a pure inductive circuit results in

**Xl = 2πfL**

 

If we set frequency to 0, the overall **X**** l** (inductive reactance) will be zero as well.

 

To calculate current,

 

Use the formula

 

I = V/R (or I = V/Xl for inductive circuits) (Basic [**Ohm’s Law**](https://forumelectrical.com/what-is-ohms-law/))

Therefore, a pure inductive circuit may start to smoke & burn if DC voltage is applied to it.

As a result, transformers cannot step up or step down a DC voltage.

Additionally, in such conditions, the primary coil will not experience self-induced EMF, which is only achievable with a variable flux linkage to counteract the applied voltage.

Since the primary coil has a low resistance, a high current passing through it will cause the primary coil to burn out from the extreme heat the current generates.

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