Transformer Overview

• Definition: A static electrical machine that transforms electrical power between circuits without changing frequency. It can increase or decrease voltage with a corresponding change in current.

Working Principle

• Mutual Induction: The core principle, involving two windings linked by mutual magnetic flux.
  • Primary winding connected to an AC source creates alternating magnetic flux.
  • Flux links with the secondary winding, inducing EMF as per Faraday's Law.
  • If the secondary circuit is closed, electrical energy transfers between circuits.

Construction

• Components: Two inductive windings and a laminated steel core.
  • Windings are insulated from each other and the core.
  • Core manufactured from high-silicon steel to reduce hysteresis and eddy current losses.

Types of Transformers

• Construction: Core type and Shell type.
• Purpose:
  1. Step-up Transformer: Increases voltage, decreases current.
  2. Step-down Transformer: Decreases voltage, increases current.
• Supply Type: Single-phase and Three-phase.
• Use:
  1. Power Transformer: For high-rating transmission network.
  2. Distribution Transformer: Lower rating, for distribution network.
  3. Instrument Transformer: Used in relays and protection (Current Transformer, Potential Transformer).

Testing Methods

• Open Circuit Test: Determines no-load loss and no-load current.
• Short Circuit Test: Determines copper losses and parameters of the equivalent circuit.

Transformer Losses

• Iron Losses (Core Losses): Includes eddy current and hysteresis losses.
• Copper Loss: Occurs due to resistance in windings.

Efficiency

• Calculation: Efficiency = Output/Input.
• Maximum Efficiency: Achieved when copper and iron losses are equal.

EMF Equation and Voltage Transformation

• EMF Equation: Derived for primary and secondary windings, involves turns ratio and maximum flux.
• Voltage Transformation Ratio (K):
  • K > 1: Step-up transformer.
  • K < 1: Step-down transformer.

Equivalent Circuit

• Representation: Includes resistances and reactances to model real transformer behavior.
• Approximate Circuit: Simplifies calculations by referring all parameters to either primary or secondary side.

Operating Conditions

• No Load: Secondary open-circuited; primary draws no-load current.
• On Load: Secondary connected to load; primary current adjusts to maintain flux.

Phasor Diagrams

• Inductive Load: Shows relationships between voltages, currents, and power factor when load is inductive.
• Capacitive Load: Similar representation for capacitive loads, illustrating leading power factor.