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.

cvk

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.

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

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).

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.

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

suraj

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..

gangadas

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...

M.KARTHIKEYAN

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..

Udhayakumar

Jul 1st, 2014

Transformer principle is basically of Mutual Inductance.. In DC supply there will be no induction so EMF wont be induced and so the Flux linkage.. so the primary winding of the transformer gets burned!!!

yuvaraja

Jul 2nd, 2014

There is no frequency in DC.Due to that the inductive reactance value will be zero.(In AC I=V/Z)
then Z=R,I=V/R,The large amount of current will flow through the coil and it get burst.

M.chandu naik

Jul 17th, 2014

The primary winding of transformer is damage due low resistance

NIKKI

Jul 17th, 2014

if dc is applied to transformer than produced flux will be constant so there will not be any induced emf in primary and secondary so there will not be any opposition to primary flux and a huge current will flow and wdg will get damage

Shashank Lohia

Jul 24th, 2014

Transformer coils are generally designed with a very high inductance and low resistance values. When DC voltage is applied to the primary of transformer, the change in flux would be zero, so no voltage would be induced in the secondary side. Moreover because of low resistance of winding, very high current will flow through it which would ultimately burn the insulation of the winding and inturn damage the transformer.

Current=voltage/impedance,
When DC is applied then Z=R =>I= V/R and R is low for transformer, so I increases very high, so heating as current is not allowed to flow further and hence intuitively you can assume current accumulate and hence heating is produced to a great extent and hence causing damage of coil.

M.SANTHOSH KUMAR

Aug 7th, 2015

Why we do not give DC supply in transformer means DC current is a direct current, so alternating flux is not produced, because input supply and flux will be same, so emf will not produced and same time more voltage is given, primary winding will be burn. This voltage do not affect the secondary winding because emf is not produce in primary winding.

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