Electrical Engineering - What will happen if we apply dc volt across transformer?

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What will happen if we apply dc volt across transformer?

Total Answers and Comments: 7

Last Update: November 15, 2009 Asked by: dhirendra singh

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Best Rated Answer

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Submitted 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

Above answer was rated as good by the following members:
aborayan317

July 21, 2007 07:56:12

pradeep

RE: What will happen if we apply dc volt across transf...

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

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July 24, 2007 09:14:09

Anandkumar Modakwar

Member Since: July 2007 Contribution: 3

RE: What will happen if we apply dc volt across transf...

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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October 06, 2007 08:28:02

cvk

RE: What will happen if we apply dc volt across transf...

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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April 21, 2009 04:05:02

bsk0bsk

Member Since: April 2009 Contribution: 1

RE: What will happen if we apply dc volt across transformer?

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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1 0

Overall Rating: +1

August 16, 2009 07:29:23

sainathdi

Member Since: August 2009 Contribution: 2

RE: What will happen if we apply dc volt across transformer?

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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November 09, 2009 08:57:25

sintayew

Member Since: November 2009 Contribution: 2

RE: What will happen if we apply dc volt across transformer?

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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November 15, 2009 03:23:44

ENG.Khatib

Member Since: November 2009 Contribution: 1

RE: What will happen if we apply dc volt across transformer?

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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