(SEM IV) THEORY EXAMINATION 2022-23 ELECTRONICS ENGINEERING

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.