BEEE R23 Unit-2

DC Generator

Generator Principle

  • Converts mechanical energy into electrical energy through dynamically induced e.m.f.

  • Based on Faraday’s Laws of Electromagnetic Induction.

  • Requires a magnetic field and a conductor that moves to cut the magnetic flux.

Construction

  • Consists of a rotating copper coil in a magnetic field from permanent magnets or electromagnets.

  • Coil ends are connected to slip-rings to collect induced current.

  • The rotating coil is termed the ‘armature’ while magnets are called ‘field magnets.’

Working

  • Coil rotates, changing the flux linked with it:

    • At 0°, maximum flux but minimum change in flux linkages leads to no induced e.m.f.

    • At 90°, maximum change in flux linkages results in maximum induced e.m.f.

  • After 90°, e.m.f. decreases back to zero at 180°.

  • Split-rings can replace slip-rings for unidirectional current flow.

Construction of D.C Generator

  1. Yoke: Provides mechanical support and carries magnetic flux.

  2. Pole Core & Shoes: Create and spread the magnetic field.

  3. Pole Coil (Field Coil): Produces magnetic field.

  4. Armature Core: Rotates within the magnetic field.

  5. Armature Winding: Coils that produce mechanical movement when current flows.

  6. Commutator: Converts AC to DC current.

  7. Brushes: Transfer current to armature winding.

  8. Bearings: Support rotating parts.

Applications of DC Generators

  • Power and lighting,

  • Arc lamps,

  • Voltage drop compensation in feeders.

DC Motor

Working Principle

  • Converts electrical energy into mechanical energy.

  • Current-carrying conductor in a magnetic field experiences a force (F = BIL).

Parts of a DC Motor

  • Same as for the DC generator.

Applications of DC Motor

  • Machines (e.g., washing machines, disc drives, toys).

Single Phase Transformer

Definition

  • Static device that transforms electrical energy without direct electrical connection.

Construction

  • Comprises a magnetic core and winding/coils.

Types of Transformers

  1. Shell Type:

    • Uses a three-limbed iron core.

    • Preferred for low voltage transformers.

  2. Core Type:

    • Uses two-limbed iron core for easy maintenance and better cooling.

Working Principle

  • Operates on mutual inductance between two inductively coupled coils.

Applications

  • Voltage regulation in devices, power supplies, and local distribution.

Three-Phase Induction Motor

Definition

  • AC motor operating on three-phase supply.

Construction

  • Consists of two parts:

    • Stator: Stationary part creating a rotating magnetic field.

    • Rotor: Rotating part experiencing induced currents creating torque.

Types of Rotor

  1. Squirrel Cage Induction Motor: Simple, rugged construction.

  2. Slip-ring Induction Motor: Allows for speed control by adding resistance.

Principle of Operation

  • Rotor conductors, experiencing a rotating magnetic field, induce torque.

Applications

  • Commonly used in residential and industrial settings for various machines.

Alternator (Synchronous Generator)

Definition

  • Converts mechanical power into AC electric power.

Construction

  • Stator: Carries armature winding.

  • Rotor: Generates main field flux.

Working Principle

  • EMF is induced when the armature is subject to a rotating magnetic field.

Applications

  • Power generation in various fields including automotive and industrial.

Permanent Magnet Moving Coil (PMMC) Instrument

Construction

  • Uses a permanent magnet and a moving coil within its magnetic field.

Principle of Operation

  • Current induces a force causing a torque that moves a pointer over a scale.

Advantages

  • High torque-to-weight ratio, less power consumption.

Disadvantages

  • Only suitable for DC measurements, high cost.

Moving Iron Instrument

Definition

  • Measures voltage or current using a movable piece of iron in a magnetic field.

Working Principle

  • Moving iron deflects in response to magnetic attraction in a fixed coil.

Advantages

  • Can measure both AC and DC, robust and reliable.

Disadvantages

  • Non-uniform scale, not suitable for low-cost manufacturing.

Wheatstone Bridge

Definition

  • Circuit for measuring unknown resistance using null detection.

Principle

  • Adjust ratio arms until the galvanometer shows zero current.

Sensitivity

  • Depends on bridge voltage, parameters, and galvanometer sensitivity.