DC supply to Transformer

Why the transformer will burn if DC supply is given?

Questions by harry4u   answers by harry4u

Showing Answers 1 - 32 of 32 Answers

If DC supply is fed to a transformer's primary, then inductive reactance X1 and magnetising reactance X0 becomes zero. The no load branch contain a parallel combination of R0 and X0. As X0 is zero so that the impedance of no load branch is zero. and current being the ratio of Supply Voltage and no load impedance is very high as it burn the primary winding.

Because the transformer is working with Mutual induction principle. This will happen only in AC supply. In DC this is not happend. When applying DC supply to transformer the positive and negative terminal is shorted by transformer winding. So the winding is burnout.

In transformer coil introduced reactance which cause sufficient reduction of
current, but in case of DC supply frequency is 0 so the reactance hence a large
current flow which cause burning of coil as heat produced depend upon current.
Heat Energy is directly proportion to current.


  • Jul 19th, 2011

DC supply is always constant its magnitude dosent varies at al ,so when it is passed through a wounded coil(i.e primary of transformer) due to its constant magnitude no change in flux so no emf is produced,hence no flux linkages(i.e no mutual inductance) is produced.

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  • Jul 26th, 2011

Because dc supply would encounter a very low overall impedance due to the reactance disappearing in case of DC. This would cause overheating due to increased current and transformer winding failure!

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  • Aug 1st, 2011

infarct transformer can work on dc by varying the dc with the help of a rheostat to make the supply vary conterminously.

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  • Aug 9th, 2011

Transformer is an electromagnetic device. It works on the principle of electromagnetic induction i.e., an emf is generated when a changing flux is set up in the core. To produce a changing flux, a changing voltage has to be applied. If a constant voltage i.e., dc is applied, a constant magnitude flux will set up Which will not induce any emf and no opposing voltage of primary. As resistance of transformer is very small which will cause of large current to flow in the primary.This may burn the primary.No emf will induce in the secondary.

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yuvraj sahu

  • Aug 10th, 2011

transformers work with the principal of electromagnetic induction if we provide dc supply to primary
winding there is no emf and flux generated in winding and finally winding burned.

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  • Aug 17th, 2011

reactance of the inductor will come in to picture when ever there is an alternating current.,as inductance it self property to oppose change in current.so when dc supply is given there is no question of inductive reluctance which is zero& one more known thing is resistance of the inductor is very small,there fore large current will flow even for small voltages which leads burning of winding

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  • Aug 26th, 2011

when dc is applied to transformer primary,which is constant in magnitude and reluctance is neglected frequency is zero .so the core become saturated and no induction occur.the winding being heated and burn out.

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  • Aug 31st, 2011

As the frequency of a D.C supply is zero, thus it will burn the transformer.

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bharath B.E

  • Sep 8th, 2011

if dc is supplied to tfr,there ll be no emf. if primary is supplied with dc,the flux produced in the core and hence there ll be no varying of voltage is possible.and the resistance of primary is low,therefore heavy current may burnout the winding hence dc is not used in transformer.

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  • Sep 9th, 2011

transformer is a AC stationary machine,it works based on the inductive principle,so you cannot give dc supply

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  • Sep 22nd, 2011

as u see the phase of transformer u will recognize that if there is no ac supply, no change in flux will produce and principle of induction will not satisfy, because with dc supply flux is stationary.

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  • Oct 3rd, 2011

in transformer we can give dc . but DC is not varying with time..... hence there is no variation inn the production of flux . if there is no variation in flux then there is no production of emf.. e=(d(flux)/dt). so induction process thus not take place.... And also the reactance value go to zero.. and the resistance value also low with no load ,. then high current passes through it causes burning of primary winding

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  • Oct 12th, 2011

Mainly transformer has high inductance and low resistance.In case of DC supply there is no inductance ,only resistance will act in the electrical circuit. So high electrical current will flow through primary side of the transformer.So for this reason coil and insulation will burn out.

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saurabh singh

  • Nov 4th, 2011

it will burn ....because there is no meaning of reactance in case of direct current.As a result the the impedance of the winding has no component of reactance and the overall impedance of the circuit becomes very low.....and consequently the value of current becomes very high.This leads to the burning of the winding of the primary side of the transformer.....that's all......

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Current through primary coil is limited by emf induced in primary. Since i=(V-E)/Z. but DC won't be able to induce emf in primary since static flux is generated(dynamic flux can only induce emf).

So, connecting DC in primary of transformer cause heavy current((V-0)/Z) if rated voltage is applied and winding will burn out.

That's what many of us answered and its very true.........

But lets come in detail analysis........ What we explained were the scenario "when rated DC voltage applied". what if very lower DC voltage will be applied??? will winding burn out??? No, then what?

Actually if DC is very lower than rated one then it won't produce current which will cause to burn the winding.
At the instant when switch is ON(at t=0), V will also be 0 and attain steady state after few second. During this instant you will feel a "pulse" of output voltage in secondary. But when voltage attains steady state, Output will become 0.

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  • Jan 21st, 2012

What if i apply DC pulse to transformer will there be Transformation

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  • Jan 21st, 2012

If transformer is fed with DC pulse for short duration it will have transformation to secondary, but if width is more than transformer will go in saturation. But pure DC is a problem

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sundar raj M.Tec

  • Mar 11th, 2013

Give DC supply of the transformer the DC supply is the constant magnitude. Does not operate on the transformer. The reason for XC Xl is the reluctance and one of the resistance. DC supply frequency is 0. The formula is Xl = 2pif and Xc = 2pi / fc so Xl=0 and XC=1/0 so the resistance value is infinite. So their is no current flow of transformer.

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suman suwal

  • Mar 11th, 2013

The primary winding of transformer oppose the current in two way that is by 1.the resistance of the wire and depends upon the material length and cross section and 2.by the inductance of a coil(primary and secondary winding merely behaves as inductor). So when dc is fed to transformer primary reactance due to inductor is not present the only opposition felt by current is the resistance of the coil only. the resistance of the coil is very low and hence large current flow in the coil there by heating the coil and finally destroy by burning.

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prateek "gnit"

  • Nov 19th, 2014

If dc source if applied then no flux is generated

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  • Nov 27th, 2014

Since DC is constant in magnitude so it does not generate alternating flux so no counter EMF E1 is generated in primary side which allow huge amount of current through transformer and gets burnt.

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  • Dec 28th, 2014

if u r giving dc to the t/f dc means there is no voltage polarities and current flow direction remains unchanged

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  • Jan 3rd, 2015

the induced emf in transformer is change of flux linking with number of turns.... if we apply dc to the transformer there is no flux changes in transformer..... emf not induced...mainly winding will be burn.

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  • May 25th, 2017

As AC power DC power also produces flux but it is not alternating. This flux will be constant, since the flux are constant there is no chance to back EMF. Hence there is no opposition to applied. It causes high voltage and current to flow through primary, it causes burning of winding of a transformer. That is why we do not use DC in transformer.

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  • Oct 2nd, 2017

The induced emf in transformer is change of flux linking with number of turns.... if we apply dc to the transformer there is no flux changes in transformer..... emf not induced...mainly winding will be burn

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Gajendra Singh

  • Oct 30th, 2017

If we apply DC at input end then there will be no emf induced in the primary winding, As e=N*d(flux)/dt. Also leakage reactance (X1)and magnetizing reactance (Xm) will also be zero, coz (X=2πf) and frequency being zero for DC. No load Current I= V-e/Z, the magnetizing shunt branch containing Xm and Rc will become zero, Z will contain only R1, this leads to very high current at primary side and may cause the burning of primary winding of transformer.

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