Basic ConceptsDC CircuitsEE Questions / AnswersInductance & Magnetism

Why an Inductor acts as a Short Circuit in DC Supply?

What is the Role of Inductor in DC Circuit?

In short, there is no frequency in DC supply i.e. frequency in DC = 0.

We know that inductive reactance:

XL = 2πfL

If we put frequency as zero then inductive reactance of the inductance would be zero.

XL = 2 x 3.1415 x 0 x L … ( L = Inductance i.e. Value of Inductor)

XL = 0Ω.

This is the reason why inductive reactance is zero in DC power supply.Why an Inductor acts as a Short Circuit in DC Supply

OK with theory but what is the exact reason behind the scene in real scenario and what if we connect an inductor to the DC source?

What is the Effect of DC Supply on Inductor?

An inductor which is a passive device acts as a short circuit when DC applied across it. Actually, inductor stores energy in the form of magnetic field and restores back to the circuit when needed.

When DC applied across an inductor, the sudden changes of current produces self inducted EMF in it which opposes it producing cause i.e. change in the current (Len’z law) when flowing through inductors.

VL = – L (di/dt)

This opposition (- L (di/dt) will slow down the changes of current in the inductor. This process will lower the produced EMF across the inductor until the changes in current stable. This way, inductor will stop to oppose the current as changes in current is zero i.e. the energy storage in the inductor is over and the value of induced EMF.

VL = 0

At this stage, there is no resistance (opposition to flow of current through inductor) and the induced EMF is zero as well. This way, the inductor is acts like a conductor.

When the resistance or inductive reactance of the inductor is zero, then

IL = V /XL

If we put XL = 0, the current flowing through inductor would be infinite i.e. short circuit.

In short, the working principle of inductor is based on changing of magnetic flux, but there is no changing magnetic flux due to no frequency in DC supply. This is the reason why an inductor acts as a short circuit in DC supply.

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