A transformer is a static machine that modifies alternating voltages through electromagnetic induction.
Suppose the power plant generates at 20,000V. To transport it with fewer losses, we step it up to 400,000V. Then we step it down to 20,000V in the city, and finally to 230V for your outlet.
How do we change the voltage without cutting the wires and without using complex electronics? By using the magnetic induction we saw in Module 5.
How does it work?
A transformer consists of three basic parts:
- Primary Winding: Where we connect the input (e.g., 230V).
- Ferromagnetic Core: A ring of iron laminations that connects the two coils.
- Secondary Winding: Where we connect the output (the load).
The Physical Process
We feed Alternating Current into the Primary.
As the current varies, it creates a Variable Magnetic Field (Ampère/Oersted’s Law).
The iron core “channels” that magnetic field and carries it to the other side.
The Secondary “senses” a magnetic field that changes within it.
By Faraday’s Law, the Secondary generates (induces) its own voltage.
The transformer only works with Alternating Current (AC). If you feed it Direct Current (DC), the magnetic field would be constant, there would be no change (
The Transformation Ratio (
In the ideal model, the relationship between voltages depends on the number of turns (
It’s a simple rule of three:
- 𝑉₁, 𝑁₁: Voltage and turns of the Primary.
- 𝑉₂, 𝑁₂: Voltage and turns of the Secondary.
- 𝑚: Transformation ratio.
Practical Example
We want to step down from 230V to 12V (a halogen transformer).
- If the primary has 1000 turns.
- How many turns does the secondary need?
If we put fewer turns on the output, the voltage goes down (Step-Down). If we put more turns on the output, the voltage goes up (Step-Up).
Conservation of Power
If we use a transformer to raise voltage from 10V to 1000V… have we created energy from nothing? Obviously not.
Power remains constant (ideally):
This implies a fundamental law:
If Voltage GOES UP, Current GOES DOWN proportionally.
If you multiply the voltage by 10, the available current is divided by 10.
In a real transformer, the output power is slightly lower due to losses in the copper and the core.
Galvanic Isolation
Apart from changing voltages, the transformer has a critical safety function: There is no electrical connection between the input and the output.
The electrons from the 230V outlet never touch your phone. The energy passes through magnetism. This is called Galvanic Isolation.
Why is it important?
- Protection: If there is a brutal short circuit in the high voltage grid, the surge does not pass directly to your equipment (although the magnetic field could induce a spike, there is no direct path for current).
- Floating References: The secondary has no reference to Earth unless you provide one. If you touch a single wire of the secondary of a 1:1 isolation transformer, you do not get a shock, because there is no return path to ground.
