Short Answer:

The working principle of a transformer is based on Faraday’s law of electromagnetic induction. It transfers electrical energy between two circuits through a changing magnetic field, without any direct electrical connection. When alternating current (AC) flows through the primary coil, it creates a varying magnetic field that induces a voltage in the secondary coil.

This process only works with AC because the changing current creates a changing magnetic flux. The amount of voltage induced in the secondary coil depends on the number of turns in both coils. This principle allows the transformer to either step up or step down the voltage levels efficiently.

Detailed Explanation:

Working principle of a transformer

A transformer operates on a fundamental law of electromagnetism called Faraday’s Law of Electromagnetic Induction. This law states that when the magnetic flux linked with a coil changes, an electromotive force (EMF) is induced in the coil. In the case of a transformer, this change in magnetic flux is created by an alternating current (AC) passing through the primary coil.

This AC current generates a time-varying magnetic field around the primary coil. A magnetic core, usually made of laminated soft iron, guides this magnetic flux and links it to the secondary coil. Because the magnetic flux is alternating, it also changes in the secondary coil. According to Faraday’s Law, this changing magnetic flux induces a voltage in the secondary winding.

The whole energy transfer from primary to secondary happens without any electrical contact. The magnetic field acts as the medium for energy transfer, which also makes the transformer an effective electrical isolation device. The frequency of the voltage remains the same during this process, only the voltage level changes depending on the turns ratio of the coils.

Let’s understand the sequence step-by-step:

1. AC Current in Primary Coil:
   When an AC voltage is applied to the primary winding, alternating current flows and produces a changing magnetic field.
2. Magnetic Flux Generation:
   This changing current produces alternating magnetic flux in the transformer’s core.
3. Flux Linkage with Secondary Coil:
   The core guides this flux to the secondary coil. Since the flux is changing, it links with the secondary winding and induces EMF in it.
4. Induced Voltage in Secondary:
   The voltage induced in the secondary depends on the number of turns. If the secondary has more turns than the primary, the output voltage is higher (step-up). If it has fewer turns, the voltage is lower (step-down).
5. Turn Ratio Relation:
   The voltage ratio is directly proportional to the turns ratio:
   V₂ / V₁ = N₂ / N₁
   Where:
   V₁ = Primary voltage
   V₂ = Secondary voltage
   N₁ = Primary turns
   N₂ = Secondary turns

This entire process takes place continuously as long as AC power is supplied. The magnetic field acts as the energy carrier between the two electrically isolated windings.

Important Points:

• It only works with alternating current.
• Energy transfer is magnetic, not electrical.
• Voltage is transformed according to the coil turns ratio.
• Provides both voltage transformation and isolation.

This principle is used in power transformers, distribution transformers, and even in small electronic circuits for signal conditioning and voltage matching.

Conclusion:

The working principle of a transformer depends on electromagnetic induction, specifically Faraday’s Law. Alternating current in the primary coil creates a changing magnetic flux that induces a voltage in the secondary coil through the core. The voltage level depends on the coil turns ratio, and the transformer works without any moving parts or electrical contact. This simple yet powerful principle enables the efficient transfer and control of electrical energy in modern power systems.