# What happens if dc supply is given to a transformer?

#### boda devsingh

• Mar 14th, 2013

If DC supply is given to the primary of Transformer then DC current flows through primary winding which is constant(time invarient).For production of emf in any winding the current flowing through that must be sinusoidal since e=L*(dI/dt).So in the given case ie, for DC input,no emf produced in primary winding. So net voltage in the primary winding will be (Vin-0) more due to which primary winding draws more current which leads to burning of winding.

In the case of AC voltage input emf produced in the primary,lets say e1 then net voltage in the primary is (Vin-e1) less, so the primary winding draws less current and the winding will be safe.

#### Prachurjya Parashar

• Mar 19th, 2013

When dc current is supplied to the X-mer, the primary side will draw a steady current due to which a constant flux is generated. Hence no back emf is produced. Thus the primary side of the X-mer which is a low resistance side draws excessive current ultimately resulting in burning out of the terminals.

Thus, to limit the effect of application of dc to X-mer a high resistance is connected in series to the primary side of the X-mer.

#### suryatejreddy Profile Answers by suryatejreddy Questions by suryatejreddy

• Apr 12th, 2013

transformer works on the principle of mutual induction which means rate of change of current or charges induces e.m.f..
hence alternating current is the one in which current varies with respect to time and when direct current is sent to transformer there will be no change in current and no mutual induction and hence transformer doesn't work..

#### aniruddha mani

• May 18th, 2013

The secondary winding of the tmer will burn as there is no back emf in the primary winding of the tmer.

#### waris

• Jun 25th, 2013

dc has no alternating waves so there is no induced emf in the secondary. so dc is applied to primary there is no impedance in the primary due to dc.hence only resistance which is very less in the tfrmr windings.due to that primary will burn out.

#### ripplenwinder Profile Answers by ripplenwinder Questions by ripplenwinder

• Dec 10th, 2013

I understanding what the question generally is asking, the question needs to be more specific to how the DC is being used when hooked up to a transformer. An example is a Balun which is a transformer or a coupled inductor (seen in switching power supplies, impedance matching networks ect) is used to pass DC or any current of different potentials. There is no specified voltage or current in the question so A direct current initially will "charge" or create a stored porential in the transformer and if the DC is removed it then creates a electrical current in the secondary of the transformer or "Material" in a coupled inductor. In magnetism the stored potential or Remanence is the amount of flux density which remains in the material after the external field is removed. Also when the transformer charges its resistance (or reactance) increases so it could be thought of as A open switch.

I would guess the burn up happens because no one converted the transformers designed volt-amp rating and frequency to what would be the "DC rating"; if done properly DC will make the transformer conduct then stop conducting when charged just like a capacitor. Capacitors are an analog of an inductor so too much voltage they too burn up.

#### billaragu

• Jan 29th, 2014

When DC current passed through the transformer.....the primary winding was burning.....

so only AC current use in the transformer......

#### shobhit nagar

• Feb 3rd, 2014

if we supply dc to the transformer then there will be no emf induced in the coil the emf generates only in case of ac and dc may also burn to the transformer.......

• Mar 2nd, 2014

transformer has high inductance and low resistance. in dc supply there is no inductance only resistance will act in the circuit so high current will flows through the primary of the transformer. for this reason coil and insulation will burn out.

#### chiragmistry

• Mar 14th, 2014

When DC supply applied to transformer the rate of change of flux is zero so output voltage iz zero.Thats why transformer is not work on dc supply.

#### VUYYURU AJAY KANTH

• Mar 27th, 2015

the t/f will be short ckt .because the t/f work on mutual induction when dc supply given it acts as self induction means the primary flux will not mutual to the secondary when given dc supply at primary flux increase during some time the t/f may get damage.the alternate cycle while required in ac only not in dc.depend on the form factor the step ration will be depend .these are the main condition we are giving ac supply to the t/f

#### vash

• Mar 29th, 2015

because
when dc supply is applied on xmer its primary winding is burned ......
2--- cause. waveform of dc is straight line and ac waveform is alternating.. dc is not good xmer....

#### timmmi khan

• Apr 8th, 2015

Voltage in a transformer is developed only with a frequency. Since a dc supply has a zero frequency, voltage in a transformer will remain zero also.

#### jitendra

• Apr 25th, 2015

the winding will be burnt only when the current through the winding becomes so much that the winding cannot withstand it.if i apply 3v dc to a 160MVA transformer,nothing will happen to the primary winding.

#### vineethprasath vcet

• May 2nd, 2015

Transformer works in the mutual induction principle so AC current only use because AC source only changes with times, DC current does not change with time so transformer does not work in DC, if we passed DC in transformer the primary winding are burned

#### Faran

• May 18th, 2015

A constant current through the primary winding produces a non-changing magnetic field (Faradays Law). The transformer doesnt work properly since a non-changing magnetic field doesnt produce a current in the secondary winding. This is the reason why the power grid uses AC instead of DC: because transformers only operate with AC voltage and not DC.

#### javed khan

• May 25th, 2015

Simply and shortly the transformer working ac supply the ac flux plus and negative. And dv fluc is constant.

#### Ayaz Shaik

• Jun 29th, 2015

Lets us speak some think about A.C and D.C first.....A.C is a form of voltage which flows in a form of wave and has some certain amount of frequency..but D.C is completely just passage through the given media for translation...now coming to transformer for its operation basic requirement in mutual induction..

If you apply DC there would be alternating flux.. according to our basic laws any one either conductor should be in motion or magnetic field.. in transformer it is static if you apply DC it is also static them there is transformation of flux so it does not cause transformation i.e induction and further causes insulation failure.

#### aneesh k

• Jul 3rd, 2015

Could you please explain how the secondary winding will burn?

#### Khushali Thacker

• Jul 7th, 2015

AC means alternating voltage. When AC supply is given to the transformer, there will be rate of change of flux w.t.time. so EMF will be induced in the coil. If we apply DC supply, there will not be any change of flux so EMF will not be induced. If we apply DC supply then coil will come in saturation condition so we cant apply DC supply to transformer.

#### DAVID

• Jul 8th, 2015

Basically transformer only using in device with AC(sinusoidal), using DC in Transformer will not make transformer work. The principle of the transformer is induced magnetic field of the primary winding to the secondary winding. This induction should change and continuous. If the transformer is energized DC then there initially occurs induction but not change (aka fixed) magnetic field so that the next energized no voltage on the secondary winding.
But instead of DC current can not be entirely incorporated in the transformer, if the DC current is made pulse (on - off) is continuous with the oscillator can be energized voltage on the secondary winding.

#### Dipanjan Biswas

• Jul 13th, 2015

Transformer is like an inductor coil. For inductor V=L(di/dt); for DC there is no change in current, so i=constant. So (di/dt)=0; so output voltage is 0. So if DC supply is given to a transformer then output voltage will zero.

#### Lavkush Kumar Tripathi

• Aug 29th, 2015

Since the induced EMF in a coil=Ldi/dt thus in case if we apply a DC to the primary coil of transform the inductance will be infinite and hence the primary will be burn out.

#### Jarrod1937 Profile Answers by Jarrod1937

• Aug 31st, 2015

This is sort of a trick question. A transformer works off of a changing current, you can get a perfectly working transformer using DC, it just depends on the frequency. For example, switch mode power supplies will take an AC signal, rectify it, then use a chopper circuit that may be a full inverter, or may just be a PWM in DC. Feed this to a transformer, and youll have a working transformer. Most seem to assume a DC signal is zero hz for some reason.

#### thala

• Sep 4th, 2015

When DC supply is given to primary side of the transformer it does not create magnetic field between primary and secondary hence transformer does not operate in DC supply.

#### divya

• Sep 4th, 2015

If we give an DC supply to transformer means, it produce steady state flux, it makes the transformer surface heated up and damage the windings of transformer

#### Lava kumar.V

• Sep 27th, 2015

When DC supply is given to the transformer primary side it does create the the magnetic field between primary and secondary, hence transformer does not work in DC supply.

#### tanuj

• Sep 28th, 2015

It will explode.

#### SANDHIYA E

• Oct 23rd, 2015

In order to produce induced EMF, there should be either space variation (conductor moving) or time variation (AC signal). Since transformer is a static device (no rotating parts), the flux that is produced is steady state. Hence, time variation is needed to produce induced EMF. Moreover, since the DC supply is unidirectional, it will cause overheating of winding and burn them out.

#### SHYAM SUNDER

• Nov 25th, 2015

Yes this ia perfect answer. There is no need of back EMF or constant flux in addition. The main reason is what you said.

#### VEERA

• Dec 17th, 2015

In case of supplying DC to a transformer, it is nothing but connecting DC source to an inductor having a very less resistance. So after attaining steady state a very high current flows in the circuit, which damages the insulation.

#### Ebenezer

• Jul 26th, 2016

Whenever the primary or secondary terminals are connected with a DC source, the connection becomes short circuited which will lead to larger amount of current flowing in the system. Great heat will be generated as a result insulation break down...the coil gets burnt

#### AB

• Sep 16th, 2016

The Transformer has inductive load AC supply has high inductance and low resistance but DC supply has no inductance and high resistance so in case of DC supply flow into primary side core, insulation burned so then only DC supply is not given to transformer.

#### GAURAV THAM

• Sep 29th, 2016

In the DC current, reactant is zero and resistance high and in the copper winding of primary is of low resistance, then if we connect the DC supply to the primary high amount of current flows throw the primary winding which will burn the primary winding.

#### mukesh mahilange

• Oct 3rd, 2016

If a DC suppy is given to a transformer than the primary will draw more current which may result in burning of winding (f=2πfL, f= 0) due to small reactance & may cause core saturation

#### SP SINGH

• Oct 9th, 2016

DC having 0 frequency so transformer coil will behave like a short circuit having very low resistance so huge current flow and transformer winding will burn.

#### Ash

• Feb 17th, 2017

Instead if DC if you apply Pulse DC will it be ok

#### ravindra kushwah

• Mar 30th, 2017

The transformer works on the principal of mutual inductance for which current in one coil must change uniformly. if DC supply is given, the current will not change due to constant supply and transformer will not work.

Practically, winding resistance is very small. For DC, the inductive reactance is zero as it has no frequency. So total impedance of winding is very low for DC. Thus winding will draw very high current if DC supply is given to it.

This may cause the burning of winding due to extra heat generated and may cause permanent damage to the transformer.

#### Sunil Kumar kumawat

• Jul 19th, 2017

When dc supply is applied across the primary winding then a constant current of higher magnitude will flow through it due to low resistance of winding. It will setup a constant flux in the core so no emf is induced in secondary winding. If DC continuously given then primary winding will burn and damage the transformer.

• Sep 13th, 2017

Windings get burned

#### MOHAMMED MUZAMMIL

• Apr 1st, 2018

So net voltage in the primary winding will be (Vin-0) more due to which primary winding draws more current which leads to burning of winding. ... But when a particular High DC voltage is applied to the rated value of transformer, the windings will get damage and the core of the transformer will also get saturated.
Transformer is nothing but a pair of inductor coils which is wound on a magnetic core. One is called primary winding, to which you apply source. Other will be secondary winding.

You can now understand, when AC is applied to primary, the constant change in current produce changing magnetic field which is now linked with secondary winding - We know that change in magnetic flux linking to a conductor induces an EMF. So, an emf is induced on the secondary coil. If load is connected to it, the current will flow through it.

If you apply DC to it, there wont be varying magnetic flux, so since there is no change in magnetic flux linking to the coil, emf is not induced on the secondary. So no DC output.

But, when you apply DC pulses (constantly turn on and turn off power supply) there will be sudden change in the current, which inturn produces changes in the magnetic flux and hence can give you pulse output.