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 🙂.....................

Why in LARGEST POWER STATION per phase individual transformers are used instead of one big transformer???

 ⇨I visited in ADANI THERMAL POWER STATION Mundra Gujarat. The capacity of the power station is approximately 4650MW in this power station I seen that in per phase one individual transformer are kept Instead of One Big three phase transformer.

⇨It is because for such big power station if we used one transformer then it becomes too much large approximately some MW to Few GW rating of transformer are required.

⇨If we assume to use such big transformer then it becomes too difficult to handle it and also the weights of core and winding, volume of oil in the tank, Auxiliary equipments like breather, Colling system, conservator tank, Buchholz relay etc. The Summation of weight of all this accessory are in TONNES so it is too much difficulty in transportation.

⇨Also suppose any major fault is occurs in such big transformer then first it is isolate and it's all the parts are overhauling and then faulty parts are repair after this repairing agin all parts are assemble during this entire period all the consumers are Deprived of Electricity it is big disadvantage of Use of one Big transformer.

Fig(a) Approximate Specifications of Power transformer

⇨Please observed in above table, in this table technical specifications of some MW power transformer are given from it we know that the total weight of transformer is in TONNE specially for above specifications the total weight is 233.2 tonne (1 tonne =1000 kg).  so it not easy to transport it from Manufacturers to power station site.

➝ To avoid this all above difficulty in transportation and handling of power transformer and to increases the reliability of the power system it is preferable to use PER PHASE INDIVIDUAL TRANSFORMER INSTEAD OF ONE BIG TRANSFORMER.

        ...............THANK YOU 🙂............