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What will happen if we apply dc volt across transformer?

Asked by: Interview Candidate | Asked on: Jul 21st, 2007
Showing Answers 1 - 12 of 12 Answers
pradeep

Answered On : Jul 21st, 2007

If we apply a DC voltage across transformer, after some time the coil gets burn

  
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The principle of transformer is depend on flux linkage.In DC, there is no linkage.So the primary of transformer gets burn if the DC voltage level is higher than the transformer rating.

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cvk

Answered On : Oct 6th, 2007

It depends on the magnitude of applied voltage.  Since reatance is absent in DC circuit and no back emf as transformer action is absent, application of DC voltage equal in magnitude to rated AC voltage will burn the winding.

  
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bsk0bsk

Answered On : Apr 21st, 2009

View all answers by bsk0bsk

When a.c is applied: When ac voltage is applied to a transformer
winding, as that circuit is closed & based on the impedance present in that
winding current starts flowing but the nature of this current is also a.c. This
a.c current produces a magnetic flux which is of a.c in nature i.e time varying
nature (because flux = mmf/reluctance = current x no. of turns/reluctance, if
current is ac flux will also be ac )


Now according to Faraday's Law- if any conductor links time varying nature of
flux then emf will be produced in that conductor & the direction of this emf
will be exactly opposite to the applied voltage.  In this case the total
current flowing through that winding will be


applied voltage-induced emf

       impedance




When d.c is applied: When dc voltage is applied to a transformer
winding, as that circuit is closed & based on the impedance present in that
winding current starts flowing but the nature of this current is also dc. This
d.c current produces a magnetic flux which is of d.c in nature i.e constant
magnitude (because flux = mmf/reluctance = current x no.of turns/reluctance, if
current is dc flux will also be dc ) flux is constant, i.e


d(flux) = 0

dt


so emf produced will be 0 & the total current flowing through that winding
will be


applied voltage-0

impedance


eg.

200-0 = 2000A

.1


So if the magnitude of dc is higher enough, then in that case the current
flowing through the winding may exceed the current carrying capacity of that
winding thus the winding will be damaged


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sainathdi

Answered On : Aug 16th, 2009

View all answers by sainathdi

When AC supply is given to the primary of the transformer current flows through the primary windings, inducing an EMF in the winding & creating a magnitic flux around the winding (i.e production of flux around the windings)

Here since supply is AC-alternating current, so if the applied voltage is alternative then the current flowing through the windings is alternative and flux developed in the windings is also alternative.. then all these takes place in primary windings, and the flux produced in this primary windings links with the secondary producing an EMF in the secondary winding and current flows through it if secondary is closed (since the flux linkages of primary are alternative the EMF induced in secondary is also alternative) and the voltage appears across secondary (if open or load is connected).

If DC supply is applied at primary, no induced emf in primary, so no emf in secondary too, and if the applied voltage is greater than the rated current then the windings burn (damage).

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When DC voltage is applied to a transformer winding as that circuit is
closed & based on the impedance present in that winding current starts flowing
but the nature of this current is also dc. This DC current produces a magnetic
flux which is of DC in nature i.e constant magnitude


Induced emf=d(flux) = 0

dt


From this we do not expect any induced EMF on the the secondary winding too.

we have to careful that if the magnitude of dc is higher enough then in that
case the current flowing through the winding may exceed the current carrying
capacity of that winding thus the winding will be damaged.


  
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ENG.Khatib

Answered On : Nov 15th, 2009

View all answers by ENG.Khatib

Nothing because the transformer needs variable excitation field, but DC is fixed, in this case the transformer will be as Magnets only.

  
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saginala13

Answered On : Jun 19th, 2010

View all answers by saginala13

There wil not be any back emf so the net current flowing through primary winding will increase and cuases damage.

  
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if dc is applied to transformer the magnetising current will be very high and might burn the winding

  
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suraj

Answered On : Jan 30th, 2012

AC having some frequency but DC doesnt have any frequency means "ZERO"..Morever coil which presents inside the transformer also having some frequency so it allows only AC..suppose if DC is applied to the transformer more time then coil will burn or damage..

  
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gangadas

Answered On : Feb 1st, 2012

as we know DC is of zero frequency ,and the current is uniform ,no change in current associated with the wdg turns, therefore flux would be zero...

  
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M.KARTHIKEYAN

Answered On : Dec 31st, 2013

First of all a Transformer designed to AC supply only. They required a AC supply to function operation.

In case of AC supply:
There is a Alternating Flux produced in primary winding. This changing flux induces EMF in secondary winding of a transformer.

In case of DC supply:
There is no any Alternating Flux or Magnetic field produced. Also there is no EMF induced in secondary coil. Then the very high current and low resistance causes burning of winding..

  
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