How Transformers Work
A transformer works on the principle of electromagnetic induction, where a changing current in one coil creates a changing magnetic field, which induces a voltage in another coil. This allows electrical energy to be transferred between circuits without direct electrical connection.
Step-by-Step Operation
-
AC Voltage Applied
An alternating voltage is applied to the primary winding. -
Magnetic Field Generated
The alternating current creates a changing magnetic field in the core. -
Magnetic Flux in Core
The magnetic field flows through the iron core, forming magnetic flux. -
Induced Voltage
The changing flux induces a voltage in the secondary winding. -
Energy Transfer
Electrical energy is transferred from primary to secondary.
Key Principle: Electromagnetic Induction
The operation of a transformer is based on Faraday’s Law, which states that a changing magnetic field induces an electromotive force (EMF).
The faster the magnetic field changes, the higher the induced voltage.
Voltage and Turns Ratio
The output voltage depends on the number of turns in each winding.
Vp / Vs = Np / Ns
This means:
- If Ns > Np → Voltage increases (Step-Up)
- If Ns < Np → Voltage decreases (Step-Down)
- If Ns = Np → Voltage remains the same (Isolation)
Ohm’s Law in Transformer Circuits
The current in the transformer windings depends on voltage and load resistance.
When the load resistance decreases, current increases, and the transformer draws more power from the source.
Power Relationship
In an ideal transformer, input power equals output power.
Vp × Ip = Vs × Is
This means:
- If voltage increases, current decreases
- If voltage decreases, current increases
Role of the Core
The magnetic core plays an essential role:
- Provides a path for magnetic flux
- Improves efficiency
- Reduces energy loss
Laminated cores are used to reduce eddy current losses.
Why Transformers Use AC
Transformers require a changing magnetic field to operate. Since direct current (DC) does not continuously change, it cannot induce voltage in the secondary winding.
Therefore, transformers only work with AC or pulsed signals.
Real Transformer Losses
In practical transformers, some energy is lost:
| Loss Type | Description |
|---|---|
| Core Loss | Due to hysteresis and eddy currents |
| Copper Loss | Resistance in windings |
| Leakage Flux | Magnetic flux not linking both coils |
| Heat Loss | Energy converted to heat |
Simple Example
If a transformer has:
- Primary turns = 100
- Secondary turns = 200
- Input voltage = 10V
Then:
Vs = (Ns / Np) × Vp = (200 / 100) × 10 = 20V
This is a step-up transformer.
Key Points
- Transformers work using electromagnetic induction.
- They transfer energy without direct electrical connection.
- The turns ratio determines voltage change.
- Power remains approximately constant (ideal case).
- They only work with AC or changing signals.