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Electrical Machines - I

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3158 min

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Electronics & Instrumentation

Electrical Engineering

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Why enroll

Participants join this course to build strong fundamentals in electrical machines and gain a clear understanding of the real-world working of transformers and DC machines. The course offers structured IIT-level learning through NPTEL, ensuring conceptual clarity and academic rigor. It also helps learners prepare effectively for GATE, university examinations, and technical interviews, while strengthening core concepts required for power systems and electrical engineering roles in industry.

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Engineer

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5+ yrs experience·India

Is this course for you?

You should take this if

You work in Electronics & Instrumentation
You're a Electrical Engineering professional
You have 3+ years of hands-on experience in this field
You want to build skills in Engineering & Design, Research & Developmnet

You should skip if

You're new to this field with no prior experience
You need a different specialisation outside Electrical Engineering
You need live interaction with an instructor

Course details

This course introduces the fundamentals of electrical machines with a strong focus on transformers and DC machines. Learners gain a clear understanding of transformer operation, types, and applications—from single-phase transformers to autotransformers—along with their working principles. The course also explores the construction, characteristics, and performance analysis of DC machines, building a solid foundation for further studies in electrical engineering.
Source: NPTEL, IIT Kharagpur

Course suitable for

Key topics covered

Learn the basic concepts and working principles of electrical machines
Understand single-phase transformers and how different types of transformers work
Explore autotransformers, their advantages, and where they are commonly used
Study the construction and main parts of DC machines
Learn the EMF equation and understand how voltage is generated in DC machines
Understand the key characteristics and behavior of DC machines
Analyze the performance and efficiency of DC machines under different operating conditions

Course content

The course is readily available, allowing learners to start and complete it at their own pace.

95 lectures52 hr 38 min

Electrical Machines
18 min
Lecture 01: Magnetic Circuit and Transformer
33 min
Lecture 02: Magnetising Current from B-H Curve
31 min
Lecture 03: Ideal Transformer, Dot Convention and Phasor Diagram
30 min
Lecture 04: Operation of Ideal Operation with Load Connected
30 min
Lecture 05: Equivalent Circuit of Ideal Transformer
30 min
Lecture 06: Rating of Single Phase Transformer: Rated Current and Rated Voltage with Example
31 min
Lecture 07: Transformer with Multiple Coils
34 min
Lecture 08: Modelling of Practical Transformer - I
36 min
Lecture 09: Modelling of Practical Transformer - II
29 min
Lecture 10: Modelling of Practical Transformer - III
27 min
Lecture 11: Core Loss - Eddy Current Loss
36 min
Lecture 12: Factors on Eddy Current Loss Depends
38 min
Lecture 13: Hysteresis Loss
32 min
Lecture 14: Exact Equivalent Circuit
31 min
Lecture 15: Approximate Equivalent Circuit
30 min
Lecture 16: Determination of Equivalent Circuit Parameters - No Load Test
40 min
Lecture 17: Short Circuit Test
32 min
Lecture 18: Choosing Sides to Carry Out O.C / S.C Test
34 min
Lecture 19: Efficiency of Transformer - Losses
34 min
Lecture 20: Efficiency (Contd.)
30 min
Lecture 21: Condition for Maximum Efficiency When Load Power Factor Constant
29 min
Lecture 22: Family of Efficiency Curve at Various Power Factor and Energy Efficiency
36 min
Lecture 23: Load Description and Energy Efficiency
28 min
Lecture 24: Regulation: its Expression
31 min
Lecture 25: Regulation: its Expression (Contd.)
35 min
Lecture 26: Auto Transformer - Introduction
32 min
Lecture 27: AutoTransformer versus Two Winding Transformer
30 min
Lecture 28: AutoTransformer versus Two Winding Transformer (Contd.)
34 min
Lecture 29: Numerical Problems on Ideal Auto Transformer
33 min
Lecture 30: Two Winding Transformer Connected as Auto Transformer
31 min
Lecture 31: Practical Auto Transformer
36 min
Lecture 32 : Equivalent Circuit of an Auto Transformer
32 min
Lecture 33: Polarity Test and Sumpner Test
33 min
lecture 34: 3 Phase Transformer Using 3 Single Phase Transformer
33 min
Lecture 35: Various Connections of 3-Phase Transformer - I
35 min
Lecture 36: Various Connections of 3-Phase Transformer - II
33 min
Lecture 37: Vector Group of 3-Phase Transformer
34 min
Lecture 38 : Vector Group (Contd.)
33 min
Lecture 39: Open Delta Connection
36 min
Lecture 40: 3-Phase Core Type and Shell Type Transformer
46 min
Lecture 41: Zig Zag Connection
33 min
Lecture 42: Effect 3rd Harmonic Exciting Current and Flux
32 min
Lecture 43: Choosing Transformer Connection
35 min
Lecture 44: Choosing Transformer Connection (Contd.)
34 min
Lecture 45: Phase Conversion using Transformer: Scott Connection
42 min
Lecture 46: Scott Connection (Contd.)
34 min
Lecture 47: 3 Phase to 6 Phase Conversion O.C / S.C Test on 3 Phase Transformer
33 min
Lecture 48: Parallel Operation of Transformers - I
38 min
Lecture 49: Parallel Operation of Transformers - II
30 min
Lecture 50: Parallel Operation of Transformers - III
27 min
Lecture -51 mod06
40 min
Lecture 52: Cooling of Transformer and Fillings of Transformer
43 min
Lecture 53: Output Equation of 3- Phase Transformer
35 min
Lecture 54
32 min
Lecture 55
43 min
Lecture 56
25 min
Lecture 57
29 min
Lecture 58
34 min
Lecture 59
38 min
Lecture 60
30 min
Lecture 61
31 min
Lecture 62
36 min
Lecture 63
34 min
Lecture 64
38 min
Lecture 65
31 min
Lecture 66 - mod08
30 min
Lecture 67 - mod08
38 min
Lecture 68 - mod08
36 min
Lecture 69 - mod08
31 min
Lecture 70 - mod08
34 min
Lecture 71
36 min
Lecture 72
30 min
Lecture 73
39 min
Lecture 74 - mod09
35 min
Lecture 75 - mod09
32 min
Lecture 76 - mod09
29 min
Lecture 77 - mod09
35 min
Lecture 78 - mod09
30 min
Lecture 79 - mod10
38 min
Lecture 80 - mod10
35 min
Lecture 81 - mod10
35 min
Lecture 82 - mod10
32 min
Lecture 83: Field Control (Contd.)
32 min
Lecture 84: D.C Motor Braking
31 min
Lecture 85: Introduction to Series Motor
37 min
Lecture 86
34 min
Lecture 87: Series Motor Speed Control
32 min
Lecture 88
31 min
Lecture 89
31 min
Lecture 90
32 min
Lecture 91
30 min
Lecture 92
32 min
Lecture 93
35 min
Lecture 94: Wave Winding (Contd.)
33 min

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Questions and Answers

Q: You're troubleshooting an induction motor on a conveyor. After a site change, line voltage is 8% low under load. You're googling induction motor voltage drop high current overheating because stator temps are climbing. What happens electrically, and what's the least-wrong immediate response before hardware changes?

A: 8% is the trap. Torque demand is fixed, so the motor pulls more current to make it, pushing I²R loss up fast. Thermal margin disappears before anyone notices speed droop. Cutting load is the only move that reduces current immediately without adding another failure mode.

Q: A subcontractor's test report claims a Class F motor is acceptable with an 85°C temperature rise by resistance. You're searching IEC 60034 temperature rise limits Class F motor because RPN is just over threshold. Why does the standard allow that number, and what's the real boundary you're checking?

A: 155°C is the hard ceiling everyone forgets. The rise limit plus ambient plus hot-spot equals that insulation class number. The standard exists to stop optimistic test methods from eating insulation life.

Q: You're reviewing a motor datasheet and terminal box sketch. Nameplate shows 400/690 V, terminals marked U1 V1 W1 / U2 V2 W2. You're typing star delta connection 400 690 motor terminal diagram into Google. For a 400 V supply, how should it be linked?

A: 400 V is the lower of the two numbers. That corresponds to delta so each winding sees rated voltage. Star at 400 V underfeeds the windings and kills torque.

Q: During FAT, the client asks if the 250 kVA transformer can tolerate motor starting. You quickly search estimate induction motor starting current transformer kVA. A 90 kW, 400 V motor, DOL start, typical design. Order-of-magnitude: does the transformer survive?

A: 6× is the number that matters. Multiply rated current by that and then by √3·V to get kVA. Duration saves you thermally, not magnetically.