About this previous year paper
This question paper is for B.Tech – Semester IV, subject Electrical Machines-I (KEE 402).
The maximum marks are 100, and the duration is 3 hours.
The paper checks students’ understanding of:
Electromechanical energy conversion
DC machines (motors & generators)
Windings, characteristics, commutation
Starters & speed control
Transformers (tests, regulation, efficiency)
Special connections & 3-phase transformer concepts
Torque production and energy balance equations
The paper is divided into three sections – A, B, and C, each assessing different levels of knowledge.
2. Section A – Short, Fundamental Questions (20 Marks)
This section contains 10 brief questions, each carrying 2 marks, covering core definitions and basic understanding.
Topics include:
● Magnetic Circuit as Coupling Medium
Why a magnetic field is essential for electromechanical energy conversion.
● Block Diagram of Energy Conversion
Electrical input → magnetic coupling → mechanical output.
● Commutator as Mechanical Rectifier
How commutation converts internally generated AC into DC output.
● Lap vs Wave Winding
Difference in number of parallel paths, applications, and current-handling ability.
● Speed Control of DC Machines
Field control, armature voltage control, armature resistance control, etc.
● Need for Starters
High starting current & protection of DC motor windings.
● Maximum Transformer Efficiency Condition
When copper losses = iron losses.
● Voltage Regulation
Significance & determination using no-load and full-load values.
● Parallel Operation of Transformers
Conditions like polarity, voltage ratio, impedance magnitude & angle, phase sequence.
● 3-Phase to 2-Phase Conversion Diagram
Scott connection and its naming.
This section checks basic conceptual clarity.
3. Section B – Descriptive & Analytical Questions (30 Marks)
Students must attempt any three questions; each question carries 10 marks.
These answers require diagrams, derivations, and detailed explanation.
Topics include:
● Singly vs Doubly Excited Systems
Differences + torque derivation for a singly-excited magnetic system.
● Characteristics of DC Shunt Generator
Magnetization curve, internal and external characteristics.
● 3-Point Starter (with protection)
Construction, purpose of no-volt coil & overload protection; modification for 4-point starter.
● Transformer Equivalent Circuit
Drawing and explaining the two-winding equivalent circuit.
● Open-Delta (V-V) Connection
Diagram, VA rating reduction (≈ 57.7%), phasor diagram, and practical applications.
This section tests design, derivation ability, and theoretical understanding.
4. Section C – Application-Based, Numerical & Advanced Questions (50 Marks)
Section C contains five parts (Q3 to Q7).
Students must attempt one question from each part.
Each selected question carries 10 marks.
Part 3 – Torque & Energy Concepts
Choice between:
● Torque in Doubly Excited Systems
Electrical torque + alignment torque + derivation.
OR
● Energy Balance Equation of a Motor
Derivation using conservation of energy and explanation of all energy terms.
Part 4 – Commutation & Generator Analysis
Choice between:
● Commutation in DC Machines
Process, cause of sparking, poor commutation, and improvement methods.
OR
● Compound Generator
Characteristics + applications + numerical calculation for long & short shunt connections.
Part 5 – Speed Control & Testing
Choice between:
● Different Zones of Speed Control
Below-rated, rated, and above-rated speed + detailed flux control method.
OR
● Swinburne’s Test
Procedure, estimation of losses, limitations vs Hopkinson’s test.
Part 6 – Transformer Tests, Efficiency & Autotransformer
Choice between:
● Transformer Test Problems
Equivalent circuit, efficiency at 90% load, voltage regulation at lagging pf.
OR
● Autotransformer Copper Savings
Derivation + numerical calculations for power transformed and conducted.
Part 7 – Three-Phase Transformers
Choice between:
● Vector Groups
Yd11, Dy1, Yy0 etc., diagrams and corresponding phasor diagrams.
OR
● Y–Δ Connection Problem
Secondary voltage, current, and kVA calculation using turns ratio.
This section tests numerical ability, diagram understanding, real-world applications, and deep technical concepts.
Final Summary (Meaning of WHAT DESCRIPTION)
This WHAT DESCRIPTION gives a complete, long, structured explanation of:
The structure of the question paper
What each section contains
Type and depth of answers expected
Key topics in Electrical Machines-I
Why each section is included
It helps a student understand the purpose and layout of the entire KEE-402 exam.