About this previous year paper
This question paper belongs to B.Tech Semester IV – Electrical Machines-I (KEE-402).
The exam duration is 3 hours and the total marks are 100.
The paper evaluates a student's understanding of: Electromechanical energy conversion principles
DC machines: generators & motors Windings, starters, speed control
Transformers: equivalent circuit, tests, regulation, efficiency
Special transformer connections & 3-phase configurations
Torque equations and energy balance in electrical machines
The paper is divided into three major sections – A, B and C.
2. Section A – Short Conceptual Questions (20 Marks)
This section contains 10 questions, each worth 2 marks, requiring brief explanations.
Topics include:
● Magnetic Circuit in Energy Conversion
Reason for using magnetic medium in electromechanical systems.
● Block Diagram of Energy Conversion
General structure showing electrical system → magnetic system → mechanical output.
● Commutator as Mechanical Rectifier
How commutation converts AC to DC in DC machines.
● Lap vs Wave Winding
Differences in conductor distribution, number of parallel paths, and current handling capability.
● Speed Control of DC Machines
Field control, armature control, voltage control, etc.
● Necessity of Starters
High starting current problem in DC motors.
● Condition for Maximum Efficiency of Transformer
ηmax occurs when copper losses = iron losses.
● Voltage Regulation
Definition, significance, and calculation method through no-load and full-load conditions.
● Conditions for Parallel Operation of Transformers
Same voltage ratio, polarity, impedance magnitude and angle, and phase sequence.
● 3-Phase to 2-Phase Conversion
Connection diagram (Scott connection) and naming.
This section tests the fundamentals and theoretical base of electrical machines.
3. Section B – Descriptive & Analytical Questions (30 Marks)
Students must attempt any three of the five questions.
Each question carries 10 marks, requiring detailed derivations, diagrams, and explanations.
The topics include:
● Singly-excited vs Doubly-excited Systems
Differences + derivation of electromagnetic torque for singly excited linear system.
● Characteristics of DC Shunt Generator
Magnetization, internal, and external characteristics.
● 3-Point Starter
Construction, working, no-volt coil, overload protection, modifications in 4-point starter.
● Equivalent Circuit of Transformer
Primary & secondary referred circuits with core loss and leakage reactances.
● Open-Delta (V-V) Connection
Construction, VA rating reduction, phase diagram, and applications.
This section evaluates understanding of machine models, tests, and characteristics.
4. Section C – Advanced, Application-Oriented & Problem-Solving Questions (50 Marks)
This section contains 5 parts (Q3–Q7).
From each part, the student must attempt one option, each worth 10 marks.
Part 3 – Energy Conversion & Torque
Choice between:
● Torques in Doubly-Excited System
Components: electrical torque, reluctance torque, field interaction torque with derivation.
OR
● Energy Balance Equation of Motor
Derivation using conservation of energy, explaining all mechanical and electrical energy terms.
Part 4 – Commutation & Generator Characteristics
Choice between:
● Commutation in DC Machines
Process, causes of poor commutation, and improvement methods (interpoles, capacitor, brush shifting).
OR
● Compound Generator Characteristics
External characteristics, applications + numerical problem for generated voltage (long-shunt & short-shunt).
Part 5 – DC Motor Control & Testing
Choice between:
● Speed Control Zones
Different speed regions + detailed field-flux control method and speed ranges.
OR
● Swinburne’s Test
No-load loss test, procedure, limitations vs Hopkinson’s test.
Part 6 – Transformer Tests & Autotransformer
Choice between:
● Transformer Equivalent Circuit + Efficiency + Regulation
Using open-circuit and short-circuit test data to compute efficiency & regulation.
OR
● Autotransformer Copper Saving
Derivation + numerical problem (power transformed vs conducted).
Part 7 – Transformer Vector Groups & 3-Phase System
Choice between:
● Vector Groups
Yy0, Dy11, Yd1 etc., connection diagrams, phasor diagrams, and applications.
OR
● 3-Phase Transformer Bank Problem
Star-Delta (Y-Δ) connection calculations: secondary voltage, current, and kVA output.
This section tests problem-solving ability, numerical accuracy, and practical understanding of electrical machines.
Final Summary (Purpose of WHAT DESCRIPTION)
This WHAT DESCRIPTION provides a complete, long, clear, structured explanation of:
The aim of the question paper
What each section contains
What type of questions are asked
Expected depth of answers
Key concepts covered in ELECTRICAL MACHINES-I
It helps students understand the entire exam structure and conceptual scope.