1. Dept. of EEE, CUET
EEE 240 Electrical Machine Design
(Credit: 0.75)
Prof. Dr. Nur Mohammad
Email: nur.mohammad@cuet.ac.bd
Website: https://www.cuet.ac.bd/members/191
Office: 2229,Academic Building-2,
Dept. of EEE, CUET
https://classroom.google.com/
Class code: 6agw2aio
Introduction, Machine Design
Principles, Limitation
Economic, Energy Conversion
Basics,Types of Machine,
Specification and Standards,
Testing.
Lecture -1
Joined in EEE CUET: September 2008
PhD from QUT Australia: February 2019
Promoted Professor: March: 2021
2. Syllabus
General design principles of electrical apparatus involving electric and magnetic circuits, specification
design of electromagnets, solenoids, chokes, starters, etc, design of rotating machines and transformers.
1.Fundamental Design Concepts:
1. Design philosophy, output equations, and
specific loadings
2. Selection of core and winding materials
2.Magnetic Circuit Design:
1. Core dimensions and flux calculations
2. Magnetic leakage and reluctance networks
3.Electrical Circuit Design:
1. Winding arrangements (concentric/layered)
2. Current density, voltage stress, insulation
considerations
4.Thermal and Cooling Design:
1. Estimation of losses
2. Cooling methods (ON, ONAF, forced air
3. Tank and radiator sizing
5. Mechanical Design Considerations:
5. Shaft, bearings, frame, housing
6. Vibration, mounting, and balance
6.Transformer Design:
1. Core-type and shell-type transformer structure
2. Regulation and efficiency optimization
7.Design of Rotating Machines:
8.Standards and Modern DesignTools:
1. Application of IEC/ standards
2. Use of simulation tools (e.g., MATLAB, Python)
for design validation
9.Economic and Practical Considerations:
1. Cost-effective design choices
2. Manufacturability and serviceability
3. Environmental and energy-efficiency compliance
Key Areas Covered:
4. 4
Purpose and Scope
To introduce students with the knowledge and practical skills
required to design electrical machines by integrating electromagnetic,
thermal, and mechanical principles to meet specified performance,
reliability, and economic criteria.
The course on Electrical Machine Design covers the theoretical
foundations and practical aspects of designing electrical machines.
It integrates knowledge from various engineering domains to develop
skills necessary for the optimal design, evaluation, and documentation
of electrical machines used in power systems, industry, and consumer
applications.
5. Course Outcomes (COs)
CO No. Course Outcome Description Knowledge Mapping with
PLOs
CO1 Describe the design procedure and key design parameters
of electrical machines.
Level 2:
Understand
PLO1 – Engineering
Knowledge
CO2 Calculate main dimensions of transformers using loading
and output equations.
Level 3:Apply PLO2 – Problem
Analysis
CO3 Analyze magnetic, electrical, and thermal circuits of
electrical machines for loss minimization and thermal safety.
Level 4:Analyze PLO1, PLO2
CO4 Design core, winding, and cooling systems of different types
of machines based on performance and safety constraints.
Level 5: Evaluate PLO3 –
Design/Development
CO5 Use relevant standards (e.g., IEC, NEMA, BIS) and software
tools to ensure design compliance and accuracy.
Level 3:Apply PLO5 – Modern Tool
Usage
CO6 Prepare and present comprehensive technical
documentation of an electrical machine design, including
justification of choices and constraints.
Level 6: Create PLO10 –
Communication
6. 6
Course Objectives
Upon completion of the course, students will be able to:
Apply fundamental principles of electromagnetic, thermal, and mechanical
engineering to design electrical machines.
Develop optimal designs for transformers, induction machines, and
synchronous machines considering cost, materials, losses, and performance.
Interpret technical standards and specifications to ensure safety, compatibility,
and manufacturability.
Utilize analytical and empirical methods for machine dimensioning and
performance prediction.
Incorporate sustainability, environmental, and economic factors in the machine
design process.
7. 7
Suggested Reading
Attendance 10%
– 90% up
Performance Tests 20%
– Assignment: 1, 2, 3,4
Assignment Reporting 70%
– Answer 6 questions out of 8
Total 100%
Book-1) Electrical Machine Design andTesting by M.V. Deshpande.
Book-2) A Course in Electrical Machine Design by A.K. Sawhney.
Evaluation Process
8. 8
Overview of Power Systems
Machine Design Principles
Design is where science meets economy—
every watt saved echoes over decades of
operation
9. 9
Core Design Principles
Objective: Economical construction meeting performance
needs.
Key Factors:
– Material selection (magnetic, conductive, insulating).
– Magnetic/electric circuit efficiency.
– Insulation integrity and cooling systems.
– Mechanical robustness.
Design Art: Optimal space allocation for iron, copper,
insulation, and cooling paths.
10. 10
Design Limitations
Constraints:
– Magnetic saturation (limits flux density).
– Insulation breakdown (voltage/temperature dependent).
– Temperature rise (dictated by insulation class).
– Efficiency targets (IEC/IEEE standards).
Standards: IS/IEC specifications for safety and interoperability.
11. 11
Economic Balance in Design
Trade-offs:
– Low initial cost High losses/maintenance (e.g., thin
→
laminations).
– Low losses High material cost (e.g., grain-oriented steel).
→
Optimal Goal: Minimize total lifecycle cost (initial +
operating costs).
12. 12
Sources of Heat in Electrical Machines
Copper (I²R) Losses: Flow of current through resistance in windings (armature, field, stator, rotor).Type:
Resistive heating .Location: Mostly in stator and rotor windings.
Core (Iron) Losses: Occur in the magnetic core (e.g., stator or transformer core).
– Hysteresis Loss. Due to repeated magnetization/demagnetization.
– Depends on material and frequency.
– Eddy Current Loss: Induced circulating currents in core laminations.
Stray Load Losses: Caused by leakage flux, harmonics, and slot effects. Usually estimated as a percentage
(~0.5%) of full-load power.
Mechanical Losses
In rotating machines only.
Include:
– Friction losses (in bearings)
– Windage losses (air resistance on rotating parts)
Dielectric (Insulation) Losses
Small amount of heat generated in insulation under high voltage (more in HV equipment)
13. 13
Temperature Rise in Electrical Machines
WhyTemperature Rises:
The heat generated by the above losses raises the temperature of windings,
core, and oil (in transformers).
Effects of HighTemperature:
Accelerates insulation aging
Reduces machine life
May cause thermal breakdown or failure
Heat and temperature must be managed to protect insulation and
maintain efficiency.
Table shows safe limits based on insulation class
14. 14
How to Manage Heat?
Cooling Methods:
Natural Air Cooling (AN): Passive, for small machines.
Forced Air Cooling (AF): Fans or blowers used.
Oil Natural (ON), Oil Forced (OF): Used in transformers.
Water Cooling: For large and high-performance machines.
Thermal design: Proper material, geometry, and insulation.
Sensors: Monitor hot spots and control overload.
Coolants:
Air, mineral oil, water, or synthetic liquids used to carry away heat.
HeatTransfer Modes:
Conduction: Heat flows through solid parts (e.g., core to frame).
Convection: Heat transfer to air/oil by fluid motion.
Radiation: Heat emitted from hot surfaces (minor role).
15. 15
Energy Conversion Basics
Generator: Mechanical Electrical energy (counter-
→
torque opposes rotation).
Motor: Electrical Mechanical energy (back EMF
→
opposes supply voltage).
Reversibility: Losses (heat) make conversion
irreversible.
16. 16
Fundamental Laws & EMF,Torque, Power
Faraday’s Law: (induced EMF).
Rotational EMF: (B: flux density, l: conductor length, v: velocity).
Force Production: (Lorentz Force Law: force on current-carrying
conductor).Torque: (: radius from axis).
Power: (
: angular velocity in rad/s).
Generator/Motor Duality: Same machine can operate in both
modes.
17. 17
Types of Electrical Machines
Synchronous:
– Rotor DC field + Stator AC windings.
– Constant speed (e.g., alternators).
Induction:
– Stator AC field induces rotor currents.
– Slip-dependent speed (e.g., industrial motors).
DC Machines:
– Commutator brushes + stationary poles.
– Variable speed (e.g., traction motors).
Transformers
– Transfers electrical energy between circuits at different voltages
18. 18
Difference Between Transformer and Electrical Machine
Feature Transformer Electrical Machine (Motor/Generator)
Function
Transfers electrical energy
between circuits at different
voltages
Converts energy between electrical and
mechanical forms
Type of Energy
Conversion
Electrical Electrical
↔ Electrical Mechanical
↔
Moving Parts
❌ No moving parts (static
device)
✅ Has rotating/moving parts (rotor, shaft,
etc.)
Power Supply
Type
Works only on AC supply
Works on both AC and DC depending on
type
Examples
Power transformer,
distribution transformer
Induction motor, synchronous generator,
DC motor
Operating
Principle
Based on Faraday’s Law of
electromagnetic induction
Based on Lorentz Force (motor) or
Faraday’s Law (generator)
Application Voltage conversion, isolation Producing or using mechanical power
#1:"Welcome! Today, we explore the Electrical Machine Design, driven by technology, sustainability, and resilience.
#9:Design starts with selecting materials that align with performance specs and cost constraints. For example, high-silicon steel reduces core losses but increases material costs. The ‘art’ lies in distributing space efficiently—balancing copper windings for conductivity, iron cores for flux paths, and insulation for safety
#10:Designers face hard constraints: Exceeding flux density causes saturation; poor insulation leads to failure at high temps. Standards like IS-1271 define temperature limits (e.g., Class B: 130°C). Ignoring these risks machine failure or inefficiency."
#11:A cheap machine with high losses costs more long-term. Example: Using lower-grade steel increases iron losses by 20–30%, raising operating costs. The sweet spot? A design where marginal cost of loss reduction equals savings from lower energy consumption
#15:All machines follow Faraday’s law. In generators, mechanical torque induces voltage; in motors, current creates torque. The process is reversible, but 5–15% energy is lost as heat due to resistance and hysteresis
#16:EMF generation relies on flux change. In rotating machines, e=Blve=Blv simplifies design—e.g., doubling rotor speed doubles voltage. Force F=BlIF=BlI explains why high-current motors need strong magnetic fields to avoid oversized conductors
#17:Synchronous machines lock to grid frequency—ideal for power generation. Induction motors are robust and cheap but slip under load. DC machines offer easy speed control but need commutator maintenance
