BT-103 BEEE • Unit 4

BEEE Unit 4 Notes PDF

Download RGPV BEEE Unit 4 notes on Electrical Machines, DC Machine, Induction Motor, Synchronous Machine, Slip, Torque-Slip Characteristics and Losses.

Unit 4: Electrical Machines Overview

BEEE Unit 4 covers basic electrical machines such as DC machine, induction motor and synchronous machine. This unit is important for RGPV exams because questions are commonly asked from construction, working principle, slip, torque-slip characteristics and losses in electrical machines.

Students should focus on neat diagrams, definitions, working principles, comparison tables and numerical formulas.

Unit 4 Syllabus

Most Important Topics for Exam

DC Machine

Construction and working is a very important long-answer topic.

Induction Motor

Frequently asked with construction, working and applications.

Synchronous Machine

Important theory and comparison-based topic.

Slip

Very important formula-based numerical topic.

Torque-Slip Characteristics

Common graph and explanation-based question.

Machine Losses

Important short note and theory topic.

Short Notes for Quick Revision

1. DC Machine

A DC machine is an electrical machine that converts mechanical energy into electrical energy or electrical energy into mechanical energy.

2. Main Parts of DC Machine

Main parts of DC machine are yoke, pole core, pole shoe, armature core, armature winding, commutator and brushes.

3. Working Principle of DC Machine

DC machine works on Faraday’s law of electromagnetic induction. When conductors rotate in a magnetic field, emf is induced.

4. Applications of DC Machine

DC machines are used in electric traction, cranes, elevators, rolling mills and speed control applications.

5. Induction Motor

An induction motor is an AC motor in which rotor current is induced by electromagnetic induction.

6. Main Parts of Induction Motor

Main parts of induction motor are stator and rotor. The stator is the stationary part and rotor is the rotating part.

7. Working Principle of Induction Motor

When three phase supply is given to stator, rotating magnetic field is produced. Rotor conductors cut magnetic flux, current is induced in rotor and torque is produced.

8. Types of Rotor

There are two main types of rotor: squirrel cage rotor and slip ring rotor.

9. Synchronous Machine

A synchronous machine is an AC machine which operates at synchronous speed. It may work as a synchronous generator or synchronous motor.

10. Slip in Induction Motor

Slip is the difference between synchronous speed and rotor speed. It is necessary for torque production in induction motor.

11. Torque-Slip Characteristics

Torque-slip characteristics show the relationship between torque and slip. At low slip, torque increases almost linearly. At medium slip, maximum torque occurs. At high slip, torque decreases.

12. Losses in Electrical Machines

Losses in electrical machines include copper losses, iron losses, mechanical losses and stray losses.

Formula Sheet

Topic Formula / Key Point
Synchronous Speed Ns = 120f / P
Slip s = (Ns − Nr) / Ns
Percentage Slip %s = ((Ns − Nr) / Ns) × 100
Copper Loss Pc = I²R
Efficiency η = (Output / Input) × 100
Iron Loss Hysteresis Loss + Eddy Current Loss
Mechanical Loss Friction Loss + Windage Loss
Induction Motor Principle Electromagnetic Induction
DC Machine Principle Faraday’s Law of Electromagnetic Induction

BEEE Unit 4 Important Diagrams

Practice these important electrical machine diagrams for RGPV examination. Write 3–5 short explanation points after every diagram.

1

Construction of DC Machine

       ______________________
      /                      \
     |         YOKE           |
     |                        |
     |     N           S      |
     |  Pole Core   Pole Core |
     |        \     /         |
     |       ARMATURE         |
     |          │             |
     |      COMMUTATOR        |
     |       ▰   ▰            |
     |       BRUSHES          |
      \______________________/
  • Yoke provides mechanical support.
  • Poles produce the magnetic field.
  • Armature is the rotating part.
  • Commutator converts internal AC into DC.
  • Brushes collect current from the commutator.
Frequently asked diagram
2

Three-Phase Induction Motor

        _______________________
       /                       \
      |         STATOR          |
      |   Three-Phase Winding   |
      |      _____________      |
      |     /             \     |
      |    |     ROTOR     |    |
      |    |      ●        |    |
      |     \_____________/     |
       \_______________________/
                 │
               SHAFT
  • Stator is the stationary outer part.
  • It carries a three-phase winding.
  • Rotor is placed inside the stator.
  • Rotor rotates due to electromagnetic torque.
Important for 5–7 marks
3

Squirrel-Cage Rotor

          END RING
       _______________
      /               \
     |  │ │ │ │ │ │   |
     |  │ │ │ │ │ │   | ← Rotor Bars
     |  │ │ │ │ │ │   |
      \_______________/
          END RING
  • Rotor bars are placed inside rotor slots.
  • Bars are short-circuited by end rings.
  • Construction is simple and rugged.
  • It requires very low maintenance.
4

Slip-Ring Rotor

          ROTOR WINDING
             │ │ │
             │ │ │
          ┌──┴─┴─┴──┐
          │   ROTOR  │
          └──────────┘
             │ │ │
             O O O    ← Slip Rings
             │ │ │
         External Resistance
  • Rotor carries a three-phase winding.
  • Rotor winding is connected to slip rings.
  • External resistance provides high starting torque.
  • Used for heavy starting-load applications.
5

Synchronous Generator

          PRIME MOVER
               │
               ▼
       ┌─────────────────┐
       │      ROTOR      │
       │  DC Excitation  │
       │        ●        │
       │                 │
       │      STATOR     │
       │  3-Phase Winding│
       └─────────────────┘
               │
               ▼
         Three-Phase AC
  • Converts mechanical energy into electrical energy.
  • Rotor receives DC excitation.
  • Three-phase AC output is obtained from the stator.
6

Slip in Induction Motor

       Synchronous Speed = Ns
                │
                │ Difference
                │   = Slip
                ▼
          Rotor Speed = N

       Rotor Speed is always
       less than Synchronous Speed
  • Slip is the difference between Ns and N.
  • Slip is necessary for torque production.
  • At synchronous speed, rotor EMF becomes zero.
Slip % = [(Ns − N) / Ns] × 100
7

Torque-Slip Characteristics

Torque
  ↑
  │
  │                  ● Maximum Torque
  │                /   \
  │              /       \
  │            /           \
  │          /               \
  │________/___________________\____→ Slip
      0          Sm             1
  • At zero slip, torque is zero.
  • Torque initially increases with slip.
  • Maximum torque occurs at critical slip.
  • After maximum torque, torque decreases.
  • At starting, slip is equal to one.
Very important 7-mark diagram
8

Losses in Electrical Machines

            INPUT POWER
                 │
                 ▼
       ┌───────────────────┐
       │ ELECTRICAL MACHINE│
       └───────────────────┘
           │   │   │   │
           │   │   │   └─ Stray Loss
           │   │   └───── Mechanical Loss
           │   └───────── Iron Loss
           └───────────── Copper Loss
                 │
                 ▼
            OUTPUT POWER
  • Copper loss occurs in machine windings.
  • Iron loss includes hysteresis and eddy-current loss.
  • Mechanical loss includes friction and windage.
  • Stray losses are small additional losses.

Important Questions

  1. Explain construction and working of DC machine.
  2. Write main parts of DC machine and explain their functions.
  3. Explain working principle of DC generator.
  4. Explain construction and working of induction motor.
  5. Explain types of rotor in induction motor.
  6. Explain synchronous machine with applications.
  7. Define slip in induction motor and write its importance.
  8. Derive or write formula of slip.
  9. Explain torque-slip characteristics of induction motor.
  10. Explain losses in electrical machines.
  11. Compare DC machine, induction machine and synchronous machine.
  12. Solve numerical problems based on slip.
  13. Solve numerical problems based on synchronous speed.
  14. Solve numerical problems based on copper loss.

PYQ Analysis Table

Topic Repeated Pattern Importance
DC Machine Construction + working Very Important
Induction Motor Construction + working + applications Very Important
Synchronous Machine Definition + types + advantages Important
Slip Formula + numerical Very Important
Torque-Slip Characteristics Graph + explanation Very Important
Losses in Electrical Machines Short note + explanation Important
Comparison of Machines Difference table Important

Sample Numericals

Slip Numerical

Question: An induction motor has synchronous speed 1500 rpm and rotor speed 1440 rpm. Find slip.

Formula: s = (Ns − Nr) / Ns

Solution: s = (1500 − 1440) / 1500

s = 60 / 1500 = 0.04

Final Answer: Slip = 0.04 or 4%

Synchronous Speed Numerical

Question: Find synchronous speed of a 4-pole motor supplied with 50 Hz frequency.

Formula: Ns = 120f / P

Solution: Ns = 120 × 50 / 4 = 1500 rpm

Final Answer: Synchronous Speed = 1500 rpm

Download BEEE Unit 4 PDFs

Download complete Unit 4 notes, important questions and PYQ analysis for RGPV BEEE exam preparation.

Download Notes PDF

How to Prepare Unit 4

Frequently Asked Questions

Is BEEE Unit 4 important for RGPV exams?

Yes, Unit 4 is important because DC machine, induction motor, slip and torque-slip characteristics are repeatedly asked.

Which topic is most important in BEEE Unit 4?

Induction motor, DC machine, slip and torque-slip characteristics are the most important topics.

Are numericals asked from Unit 4?

Yes, numerical questions are commonly asked from slip, synchronous speed, copper loss and efficiency.

Is this website official?

No, this is an independent educational website created only for student support and exam preparation.

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