Transformer

A transformer is a passive electrical device that transfers electrical energy from one alternating current (AC) circuit to one or more other circuits, either increasing (step-up) or decreasing (step-down) the voltage. It operates on the principle of electromagnetic induction.

Key Points About Transformers

Basic Operation:

Primary Coil: When an alternating current flows through the primary coil (the winding connected to the power source), it creates an alternating magnetic field around the transformer's core.
Core: The core, typically made of laminated soft iron, concentrates and guides this magnetic field.
Secondary Coil: The alternating magnetic field passing through the core induces an alternating voltage in the secondary coil (the winding connected to the load).
Voltage Transformation: The ratio between the number of turns in the primary coil (N₁) and the secondary coil (N₂) determines the voltage change:
- Step-up transformer: If the secondary coil has more turns than the primary, the output voltage is higher than the input voltage.
- Step-down transformer: If the secondary coil has fewer turns than the primary, the output voltage is lower than the input voltage.

Key Characteristics:

✔ Works only with AC: A varying magnetic field is required for induction. Direct current (DC) produces a constant magnetic field and thus cannot induce voltage in the secondary coil.
✔ Passive device: It does not generate electrical energy but transfers and transforms it.
✔ No direct electrical contact: Energy is transferred via the magnetic field, providing galvanic isolation between primary and secondary circuits.
✔ Power conservation (ideally): Input power (voltage × current) equals output power (neglecting losses). Thus, if voltage increases, current decreases, and vice versa.

Common Applications:

Electric power distribution: Essential for transmitting electricity over long distances at high voltages (to minimize losses) and stepping it down to safe levels for household and industrial use.
Powering electronic devices: Many electronics use transformers to reduce mains voltage (e.g., 230V or 120V) to the required internal circuit voltage (e.g., 12V, 5V).
Galvanic isolation: Used to electrically separate two circuits, preventing electric shocks or ground loops.
Impedance matching: In audio and communication circuits, transformers match impedance between stages to maximize signal transfer.

Transformer Types

Type	Function	Example Use
Step-up	Increases voltage	Power plants → High-voltage transmission
Step-down	Decreases voltage	Substations → Household (230V/120V)
Isolation	Provides electrical separation	Medical equipment, lab instruments
Autotransformer	Single winding with taps	Voltage adjustment in industrial equipment

Efficiency & Losses

Transformers are highly efficient (typically 95–99%), but losses occur due to:

Copper losses (I²R heating in windings)
Iron losses (eddy currents & hysteresis in the core)
Leakage flux (magnetic field not linking both coils)