Answer / elango.k

In dc the rate of change of flux is zero .when dc is
applied to primary windings there is no back emf to oppose
the supply voltage . the winding acts as resistance -where
high current flow through the coil and transformer is burnt.

I=V-Eb/R

Eb-BACK EMF
V- DC SUPPLY
I- CURRENT IN PRIMARY
R- RESISTANCE OF COIL(small)

Answer / deepa james

when ac is applied to the primary winding an alternating flux is produced in the core which then links with the secondary winding of transformer and induces emf ..
when dc is applied to the primary winding no alternating flux is produced and secondary cannot be linked..thus emf is not induced..
as we know a emf is induced only when a conductor is cut by an alternating magnetic field...so ac is applied to transformer..

Answer / jagadeesh

because d.c current has no frequency. so that d.c current is
not used in transformer


jagadeesh.p.

Answer / sk panda

If you apply a DC Voltage across the winding a high
current will flow thru the winding as a result of which the
winding will get burnt due to high temperature.

Answer / prasanna

In Generator, rotating conductor cuts the stationary flux
and so an emf induces which is called generator EMF.
Whereas in Transformer, rotating flux cuts the stationary
conductors. This way of induced emf is called Transformer
EMF. By applying DC, flux and conductor both are
stationary, that does not results any emf in secondary of
transformer.

Answer / chiranjit ghosh, hetc

WE KNOW XL=2(pi)FL.IN CASE OF DC F=0. AS F=0, XL=0 ALSO. SO
THERE IS NO INDUCTIVE REACTANCE IN THE PRIMARY CIRCUIT IF DC
IS FED TO TRANSFORMER.THE PRIMARY WINDING BEHAVE LIKE SIMPLE
CONDUCTOR.NOW ITS LOOK LIKE U GIVE A DC VOLTAGE ACROSS A
CONDUCTOR. THE PRIMARY WINDING(CONDUCTOR) WILL HEATED UP AND
WINDING BURN DUE TO HEATING.

Answer / arun

dc only produce the steady flux

Answer / master ramunni raja.v

When we apply the DC supply to the Transformer there is no
emf is produced. But it act as a ElectroMagnet. Electro
magnet Having Magnetic flux. That flux also can induce the
emf in secondary side. But There is no frequency in the
Secondary side output voltage. So finally the output is also
a DC supply.
EX: We can operate a relay in DC supply. In side the Relay
There is a coil is there.

Answer / swati

If you apply DC Voltage with sufficient capacity across
the primary or secondary of a transformer the current
flowing in the transformer will depend only on the
resistance of the winding . since the resistance is very
low high current will flow thru the winding and if it
continues for a resonable time the winding will get
burnt.

Answer / robert harper (ee tech)

This is directly related to another thing. Think of this...
If you have a 24VAC coil and a 24 VDC coil and you check
the resistance of both, you will see that the AC coil has a
low resistance and the DC coil has a high resistance. This
is b/c the impedance that is introduced upon energization
of the coil and the CEMF This is not present in DIRECT
current b/c of the lack of an alternating current therefore
no frequency. Oscillators are a whole other subject but
very interesting.

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