What is a Transformer?

Contents

Introduction Why Transformer Works on AC Only Step‑by‑Step Working Turn Ratio (n) Transformation Ratio (K) Mutual Induction (Simple Words) Why Laminated Silicon Steel Core EMF & Key Formulas Power Transfer Mechanism Advantages Applications Inside a Transformer – Summary FAQs Conclusion

Introduction

A transformer is a static electrical machine that transfers AC power from one circuit to another at the same frequency while changing the voltage level as required. It consists of two insulated windings—primary and secondary—wound on a laminated steel core. There is no electrical connection between the windings; power transfers via a magnetic field in the core.

Why Transformer Works on AC Only

With AC

• Changing flux → emf induced → transformer works.
• Flux varies sinusoidally; Faraday’s law applies.

With DC

• Flux becomes constant → practically no induced emf.
• Primary draws dangerously high current → overheating & damage.

Remember: Never connect a conventional power transformer directly to DC.

Step‑by‑Step Working

1. Apply V₁ to primary: An alternating current flows.
2. Create flux ϕ(t): Core provides a low‑reluctance magnetic path.
3. Link windings: The alternating flux links both primary and secondary.
4. Induce emf: E₂ appears across secondary terminals (mutual induction).
5. Load current: When a load is connected, current I₂ flows, and power transfers.
6. Balance: Primary current adjusts so that input power ≈ output power + losses.

Turn Ratio (n)

The turn ratio relates primary to secondary turns:

n = N₁ / N₂

• If N₂ > N₁ ⇒ Step‑up transformer (voltage increases).
• If N₂ < N₁ ⇒ Step‑down transformer (voltage decreases).

Transformation Ratio (K)

The transformation ratio tells how much voltage is increased or decreased:

K = V₂ / V₁ = N₂ / N₁

• K > 1 → Step‑up
• K < 1 → Step‑down
• K ≈ 1 → Isolation transformer

Mutual Induction (Simple Words)

• Changing current in the primary → changing flux in the core.
• This flux links with the secondary coil.
• Because the flux changes, a voltage is induced in the secondary.

Why Laminated Silicon Steel Core

• Reduces eddy current losses (thin laminations increase resistance to circulating currents).
• Improves magnetic properties; lowers hysteresis loss.
• Controls heating; increases efficiency and reliability.

EMF & Key Formulas

Induced RMS emf in a winding:

E = 4.44\,f\,\phi_m\,N

Alternatively, using flux density and core area:

E = 4.44\,f\,B_m\,A_core\,N

Other useful relations (ideal):

• V₂/V₁ = N₂/N₁ (Voltage ratio = turns ratio)
• I₂/I₁ = N₁/N₂ (Current ratio)
• Z_in = Z_L (N₁/N₂)² (Impedance reflection)

Power Transfer Mechanism

Even though windings are insulated from each other, power transfers efficiently via the magnetic core.

Ideal Power Balance: V₁I₁ = V₂I₂

Step‑up: Voltage ↑, current ↓   |   Step‑down: Voltage ↓, current ↑

Advantages

• High efficiency (≈95–99%)
• No moving parts → low maintenance
• Quiet operation
• Easy voltage transformation
• Essential for transmission and distribution

Applications

1. Power Transmission: Long‑distance, high‑voltage transfer.
2. Distribution Networks: Step down for homes and industry.
3. Electronics: Chargers, adapters, SMPS.
4. Instrumentation: CT and PT for metering and protection.
5. Isolation: Medical and sensitive circuits.

Inside a Transformer – Simple Summary

Step	Description
1	AC supply applied to primary
2	Primary current creates alternating flux
3	Flux passes through the core
4	Flux links the secondary winding
5	EMF induced in secondary (mutual induction)
6	Load connected → current flows → power transfer

FAQs

Does frequency affect transformer voltage?

Yes. From E = 4.44 f ϕ_m N, at a fixed core flux and turns, induced voltage is proportional to frequency.

Why are cores laminated?

Laminations reduce eddy currents and heating, improving efficiency.

What is an isolation transformer?

A transformer with nearly equal turns on primary and secondary (K ≈ 1), used for safety and galvanic isolation.

Is DC ever acceptable for a transformer?

Not for conventional iron‑core power transformers. DC‑DC converters first switch DC to high‑frequency AC, then use a small ferrite transformer.

Conclusion

The working principle of a transformer depends on Faraday’s Law, mutual induction, and alternating magnetic flux. A transformer can step up or step down voltage efficiently, making it the backbone of electrical infrastructure. Remember: Transformers work only on AC; applying DC can cause severe damage.