Why transformer doesn't work on DC supply???

• Before understanding this concept first we need to know working principle of transformer.

Fig (a) Working principle of transformer

• Working principle of transformer:-

➝ Transformer is works on the principle of MUTUAL INDUCTION.

➝ According to principle of MUTUAL INDUCTION, if time varying current (AC CURRENT) is given to the primary winding of transformer then it produces the time varying flux and due to this time varying flux EMF is induced in the primary winding, we already discussed in the previous article some amount of this primary winding flux is linked with secondary winding also, so EMF is induced in seconady Winding due to rate of change of current in the primary winding.

• Consider the equation of induced voltage in inductor or Coil;

Induced voltage V = -N di/dt ................(1)

                Where; - (minus) sign is due to LENZ LAW

                                 di/dt = Rate of change of current

❇️ CASE NUMBER :-1 INPUT IS AC

Fig (b) Input Sine wave

⇨According to Faraday's law we know that voltage is induced in the coil if and only there is relative motion between Conductor and Magnetic field.

⇨Suppose if we connect Sinusoidal input supply with primary of transformer then it produces time varying flux so EMF is induced in the primary winding and we know that supply is Sinusoidal EMF is also induced in the secondary winding due to rate of change of flux in the primary.

⇨So if we connect AC SUPPLY to the primary winding of transformer then transformer is satisfactory work with ac supply.

❇️CASE NUMBER :-2 INPUT IS DC

Fig (c) Input DC supply

⇨Suppose if we connect DC supply with primary winding of transformer, then it produces CONSTANT FLUX, Because DC is constant source it's value remain constant.

⇨Due to DC rate of change of flux will be Zero, so induced voltage in the primary winding will be ZERO.

                V = -N di/dt 

HERE di/dt = zero so V=0 means short circuit

• PLEASE OBSERVED VOLTAGE ZERO MEANS SHORT CIRCUIT, SO RESULT IS THAT THERE IS AN EXCESSIVE LARGE CURRENT IS FLOW THROUGH THE PRIMARY OF TRANSFORMER, DUE TO THIS LARGE CURRENT PRIMARY OF TRANSFORMER IS DAMAGED AFTER FEW TIME.
• So, from above discussion we conclude that TRANSFORMER DOESN'T WORK ON DC SUPPLY.

            ....................... Thank you 🙂.....................