When DC power is supplied to the primary transformer, no self-induced EMF is generated (no back EMF). Therefore, in the primary winding of the transformer flows a strong current, which can lead to the burning of the primary winding of the transformer.
Means, When a DC voltage is applied to the primary winding of a transformer due to the low resistance, the winding acts as a short circuit between the terminals of the DC source, resulting in a large current flow through the winding, which leads to overheating of the winding.
What happens if D.C. supply is given to the transformer?
The transformer works on the principle of mutual induction, in which the current in a coil must change evenly. With DC power supply, the current does not change due to the constant supply and the transformer does not work.
Practically resistant to wraps is very small. For DC, the inductive reactance is zero because DC has no frequency. Therefore, the total impedance of the winding for DC is very low. The winding therefore draws a very high current when DC is supplied. This can cause the coil to burn off due to additional heat generation and permanently damage the transformer. It can lead to a saturation of the core, due to which the transformer draws a very large current from the supply when connected to DC.
What will happen if a DC voltage is given to the transformer primary?
- We know that for an inductance v = Ldi / dt, since v is constant here, the i (current) follows a ramp waveform and continues to increase until the core is saturated.
- This means that I rise to a dangerously high level and then stop changing. When I stop changing, the induced voltage across the primary winding is zero (as di / dt = 0), shorting the DC source.
- There is a strong short-circuit current that overheats the coils, resulting in quadratic R losses. The temperature rise exceeds safe levels and the device eventually catches fire.
- Short-circuit currents lead to radial magnetic forces, which tear the winding and expose the windings to the atmosphere. Transformer oil can ignite under short circuit conditions.
- Therefore, under operating conditions, we must never apply a DC voltage to a transformer.
In Short,
Transformers can not be DC powered because the electric field generated by the DC power supply is not rotating but linear and not a rotating field. The AC power supply generates a changing EMF, which is a rotating EMF. This causes the primary winding of the transformer to generate an electromagnetic field that is detected by the secondary winding of the transformer. However, when the transformer is supplied with DC power, the field is not generated and EMF is converted to heat. Your transformer has burst.
