Lecture Notes: Transformers

Introduction to Transformers

• Transformers are essential components in electrical systems, linking homes and power stations.
• Only work with alternating current (AC), not direct current (DC).
• Rated in VA (volt-amps) or kVA (kilovolt-amps).

Structure of a Transformer

• Consists of two coils of wire wrapped around an iron core.
  • Primary Side: Connected to the generator or power supply.
  • Secondary Side: Connected to the load needing power.
• Variants: Small (doorbells, chargers), Medium (homes, businesses), Large (regional power supplies).

Working Principle

• Transfers electrical energy between two circuits.
• Changes voltage and current levels.
• Uses electromagnetic induction, where a changing magnetic field induces a voltage in a second coil.

Types of Transformers

• Step-Up Transformer: Increases voltage, decreases current.
• Step-Down Transformer: Decreases voltage, increases current.
• Example Usage:
  • Power stations use step-up transformers to send electricity over long distances by increasing voltage.
  • Step-down transformers reduce voltage for local distribution and household use.

Efficiency and Power Transmission

• Higher voltages reduce current, minimizing energy loss over long distances.
• North America uses a three-wire system for 120/240 volts; most of the world uses 230 volts with a two-wire system.
• Energy loss due to resistance is minimized by high voltage and low current.

Electromagnetic Induction

• AC current creates a magnetic field that changes direction.
• A reversing magnetic field induces voltage in a nearby coil.
• DC cannot induce sustained voltage in a transformer.

Transformer Core Design

• Ferromagnetic iron core enhances efficiency by concentrating the magnetic field.
• Core made of laminated sheets to reduce energy losses from eddy currents.
• Copper losses occur due to resistance in wires.

Noise and Efficiency Considerations

• Humming sound caused by vibrations in core sheets due to AC.
• Transformer rated in kVA due to varying power factor and efficiency.

Applications and Calculations

• Widely used in electrical engineering for efficient power transfer.
• Rectifier Circuits: Convert AC to DC.
• Basic Calculations:
  • Voltage and turn ratios can be used to determine voltages on primary and secondary sides.
  • Power consistency (voltage x current) must be maintained across both sides.
• Example problems illustrate step-up and step-down transformer calculations.

Conclusion

• Critical role in electrical distribution and efficiency.
• Further learning encouraged through related videos and online resources.