Lecture Notes: Transformers and Their Applications

Introduction to Transformers

• Transformers are essential in modern life, connecting homes to power stations.
• Operate only with alternating current (AC), not with direct current (DC).
• Transformers change voltage and current levels, rated in Volt Amps (VA) or Kilovolt Amps (kVA).

Construction and Function

• Consist of two coils of wire (primary and secondary) around an iron core.
• Transfer energy between coils by electromagnetic induction.
• Only work with AC as it allows the magnetic field to change polarity and induce current in the secondary coil.

Types of Transformers

• Step-Up Transformer: Increases voltage, decreases current.
  • Used for long-distance power transmission to reduce energy loss.
• Step-Down Transformer: Decreases voltage, increases current.
  • Used to step down the voltage for safe residential use.

Efficiency and Losses

• Copper Losses: Due to resistance in the wire.
• Iron Losses: Include eddy currents and hysteresis losses.
• Laminated iron cores reduce eddy current losses.
• The humming sound is caused by vibrations of the iron core laminations.

Power Transmission

• High voltage reduces current, thus minimizing energy loss over long distances.
• Power remains constant: Voltage × Current (V×I = constant).
• Homes in North America use 120/240V due to a three-wire system.
• Most of the world uses around 230V (simplified two-wire system).

Calculations and Formulas

• Transformer Voltage Formula: ( \frac{V_s}{V_p} = \frac{N_s}{N_p} )
• Transformer Current Formula: ( \frac{I_p}{I_s} = \frac{N_s}{N_p} )
• Power remains constant: Apparent Power (VA) = Voltage (V) × Current (A).
• Use of kVA due to unknown load which decides the power factor.

Applications and Examples

• Used in rectifier circuits to convert AC to DC.
• Example calculations to determine voltage, turns, and current using formulas.

Additional Resources

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