Why DC voltage is not Applied in Transformer Input

What Happen if DC Voltage is Apply to Transformer Input?

Considering the importance we can say transformer is the most efficient electrical machine ever invented on the earth.

The main function of transformer to step up or step down the voltage to desired voltage level keeping the power level same at both primary and secondary or in simple input power and output power is equal.

So, we can define as a transformer  is a static device which convert electrical power from one circuit to another without changing its frequency and  it Steps up or Steps down the level of AC Voltage and Current.

Finally we draw the working principle of transformer that works on the principle of mutual induction of two coils or Faraday Law’s Of Electromagnetic induction.

When current in the primary coil of transformer is changed the flux linked to the transformer secondary coil also changes; hence an EMF is induced in the secondary coil due to Faraday law’s of electromagnetic induction.

Actually transformer is based on two principles:

i> an electric current can produce a magnetic field or electromagnetism;

ii> a changing magnetic field within a coil of wire induces a voltage across the ends of the coil.

Changing the current in the primary coil changes the magnetic flux that is developed. The changing magnetic flux induces a voltage in the secondary coil.

So far, we understand that transformer works with an Alternating Current or AC voltage.

What is the Effect of Giving a Constant DC Voltage to a Transformer Input?

Observing the following steps we can see the effects of applying a constant DC voltage input to a transformer:

1. As we know the properties of an inductor v=Ldi/dt, since v is constant here, the i(current) will follow a ramp waveform and will keep on increasing till the core saturates;

2. This means, i will rise to a dangerously high value and then stop changing, if i stops changing then the induced voltage across the primary will be zero(as di/dt=0) thus short circuiting the DC source;

3. Heavy short circuit current will flow, overheating the coils, resulting in i squared R losses. Temperature rise will exceed safe values and eventually the apparatus will catch fire;

4. Short circuit currents will result in radial magnetic forces that will rip apart the winding and the wingdings become exposed to the atmosphere. Transformer oil may catch fire under short circuit conditions;

5. So we must never apply a DC voltage to a transformer during operating conditions.

Pulsating DC can be applied to transformers, such the flux reset occurs in the negative pulse period. 

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