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CAD for

Electrical Engineers

Dr. Indira M S Ph.D.(IISc) Principal, Sir MVIT, Bangalore

V D Sankarlal B.E., M.Sc.(Engg)Department of Electrical and Electronics Engineering (Former)

Sir MVIT, Bangalore D Beula M.E.

Department of Electrical and Electronics EngineeringSir MVIT, Bangalore

Second Edition

Sanguine Technical PublishersBangalore.

2015

CAD for Electrical Engineers 2nd Edition.Dr M S Indira, V D Sankarlal, D Beula.

This book contains information obtained from authentic and highly regarded sources. Reprinted material is quoted with permission, and sources are indicated. Reasonable efforts have been made to publish reliable data and information, but the author and the publisher cannot assume responsibility for the validity of all materials or for the consequences of their use.Neither this book nor any part may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, microfilming and recording, or by any information storage or retrieval system, without prior remission in writing from the publishers.The consent of SANGUINE TECHNICAL PUBLISHERS does not extend to copying for general distribution, for promotion, for creating new works, or for resale. Specific permission must be obtained in writing from SANGUINE for such copying.

The export rights of this book are vested solely with the publisher.

Direct inquiries: E-mail [email protected].

Visit our website at www.sanguineindia.com© 2015 by Sanguine Technical Publishers, Bangalore – 560 016.

Published by Lal Prasad for Sanguine.Production Editor: R.SubramanianTypeset by Sharvani Inc., BangalorePrinted in India at Regal Print Service, Bangalore.

Price: ̀ 285.00

Preface

An Electrical Engineer can analyze and design electrical equipments like transformers, DC machines, induction machines, synchronous machines and electrical power system elements comprising of transmission lines, circuit breakers, transformers, reactors, capacitors etc. Based on design information and specifications, engineering drawings are to be made. The drawing is an essential bridge between designer and manufacturer and also between the designer and commissioning/maintenance engineer. The manufacturer plans the details of processing, machining, material requirement and cost estimate, based on the drawing. The end user plans circuit connections, erection requirements, (mounting dimensions, space requirements, design of machine bed depending on the weight etc) and maintenance schedule. The technical drawings are created by using CAD software as against conventional method of using drafters and black ink. Use of standard CAD software has long moved past cutting-edge status and are presently considered a standard part of an engineer’s skill set. This book has been written with the aim of educating the students with the techniques of evolving electrical engineering drawing using CAD software. To design the equipment and elements as per the specification and the design information, ‘engineering drawings’ are to be evolved by technologists and drafting technicians. The drawings have to be scrutinized to check the dimensions, tolerances, material specification and quantity of the materials. These functions are performed by Computer Aided Design (CAD).The multiple skill of design and drafting is known as Computer Aided Design and Drafting ‘ (CADD).

• CADD drawings allow the designer to select the units of measure- inches, mm, m etc.

• Layers can be created and super imposed. • CADD drawings are accurate and the desired accuracy level can be pre-defined. • Extends flexibility for drawing large and small components on the same system. • Editing, plotting, storing and retrieval of the drawing are easier. • Drawings can be forwarded to the manufacturing shops, vendors, purchasers and

customers in the desired form.

Many Indian Universities have introduced the topic of ‘Computer Aided Electrical Drawing’ as a subject for the ‘Electrical and Electronics Engineering’/‘Electrical Engineering’ curriculum of the under graduate program. The subject of the Computer Aided Electrical Drawing is offered as a one semester course.

iv CAD for Electrical Engineers

The basics of theory of electrical machines and the knowledge of power system are a pre-requisite. However, at the beginning of each chapter a brief explanation of the related theory and conventions are explained. A detailed procedure for the execution of the required basic commands in Auto CAD with relevant screen shots is also given. A number of typical exercise problems in winding diagrams, single line diagram and assembly drawings are solved with the aid of ‘step by step’ list of CAD commands. The resulting figures after the execution of the listed commands are presented. This approach is very helpful for the beginners. Photographs of important substation equipments and a few assembly parts of DC machines, synchronous machines, induction machines and transformers are included in the book, for better understanding and visualization. Computer aided electrical drawing integrated with theory behind each topic makes this book unique. We believe that the electrical students will find this book very useful in practicing electrical drawings.

Objective To familiarize the students with relevant CAD commands To enable them to develop basic CAD skills for electrical drawings like- • DC Winding Diagrams • AC Winding Diagrams • Single Line Diagrams of Sub Stations • Schematic of Power Generating Stations • Electrical Machine Assembly Drawings –

DC Machines ) Transformers ) Alternators ) Induction Machines )

Topics Chapter 1 DC winding diagram covers the method of drawing the developed

winding diagrams for Simplex, Multiplex, Lap and Wave winding. Chapter 2 AC Winding Diagram deals with drawing of 3-phase AC winding

diagram for Integral/Fractional slot, Lap/Wave winding, Un-bifurcated/ Bifurcated 2 and 3 tier windings. Pole changing winding for 2/4 Pole and 4/8 Pole are introduced.

Chapter 3 The symbols used for substation components, measuring and protective equipment are explained with relevant photographs. Single line diagram of generating substation and that for Main Unit Substations are illustrated.

Chapter 4 Schematics of Generating Plants- Hydel, Thermal and Nuclear are outlined.

Preface v

Chapter 5 The various parts of a DC machine are discussed. Sectional/half sectional drawings of general assembly and sub assembly drawings of parts like- yoke and pole assembly, armature on hub, commutator, laminated yoke and laminated pole- are covered.

Chapter 6 A brief discussion on various types of transformers, core sections and winding patterns is given. The procedure for drawing sectional views is included.

Chapter 7 The constructional details of salient pole rotor and cylindrical rotor of synchronous machine are discussed. A brief of brushless synchronous alternator with built in exciter and AVR is given. The drawings of longitudinal view and end view of typical parts are provided.

Chapter 8 Specifications, essentials of squirrel cage rotor and slip ring motors, frame size and mounting dimensions of induction machine are given. Sectional / half sectional views of general as well as sub assembly drawings are furnished.

Appendix I Basics of CAD commands with figures and examples are explained with screen shots. A study of these commands is essential for the beginners, to proceed with exercises on winding and machine assembly drawings.

Appendix Size of Papers, Important specifications of the insulating II -VI materials, Conductor materials, Electrical steel sheet and Fasteners.

Acknowledgements

We express our sincere gratitude to the following authorities, for the kind permission to include the photographs provided by them, in our text- Central Power Research Institute (CPRI), Bangalore Karnataka Power Transmission Corporation Ltd. (KPTCL), Bangalore Karnataka Power Corporation (KPC), Bangalore Vijay Power Control Systems, Bangalore Integrated Electric Company Pvt. Ltd. (IEC), Bangalore Sri Krishnadevaraya Educational Trust (KET), Bangalore Special thanks are due to Sri KET and Sir M. Visvesvararaya Institute of Technology

for facilitating and supporting us in the endeavor.

Dr. Indira M S V D Sankarlal

D Beula

vii

table of contents

1. Dc Winding Diagrams 1.0 Introduction 11.1 Basic Definition 11.2 Procedure for Lap Winding 4

1.2.1 Pitch Calculation 41.2.2 Winding Table 5

1.3 Procedure for Wave Winding 61.3.1 Pitch Calculation 61.3.2 Winding Table 6

1.4 Examples 71.5 Problems-for Self Study 34

2. three Phase ac Winding Diagrams 2.0 Introduction 352.1 Assembly of Windings 35

2.1.1 Coil, Coil Group 352.1.2 Layers 362.1.3 Numbering of Conductors 402.1.4 Calculation of Pitch 412.1.5 Selection of Pitch to Control Harmonics 422.1.6 Winding Layout 442.1.7 Slot Vector Diagram 46

2.2 Examples 472.3 AC Three Phase Winding with Parallel Paths 672.4 Pole Changing Windings 742.5 Problems for Self Study 78

viii CAD for Electrical Engineers

3. substations 3.0 Introduction 913.1 Classification 91

3.1.1 Functionality 913.1.2 Location 95

3.2 Single Line Diagram: 993.3 Symbols for Equipments in Substation 993.4 Various Equipments of a Substation 101

3.4.1 Bus-Bars 1013.4.2 Power Transformers 1023.4.3 Instrument Transformers 1053.4.4 Circuit Breaker 1063.4.5 Isolating Switches / Group Operating Switches 1083.4.6 Lighting Arresters / Surge Arrester 1093.4.7 Earth Switch 1103.4.8 Shunt Reactors 1113.4.9 Wave Trap/Line Trap 1123.4.10 Shunt and Series Capacitors 113

3.5 Bus-Bar Arrangement in Substation 1143.5.1 Single Bus-Bar Arrangement 1143.5.2 Single Bus-Bar with Sectionalisation 1153.5.3 Duplicate Bus-Bar or Double Bus-Bar Arrangement 1163.5.4 Sectionalised Double Bus-bar Arrangement 1183.5.5 Double Main and Auxiliary Bus-bar Arrangement 1193.5.6 Breaker and a Half Scheme/1.5 Breaker Scheme 1203.5.7 Main and Transfer (Auxiliary) Bus Scheme 1233.5.8 Ring Bus-bar Scheme 124

3.6 Examples 1253.7 Problems for Self Study 136

4. Generating stations 4.0 Introduction 1374.1 Hydro Electric Power Plants 137

4.1.1 Low Head Hydro Electric Plant 1374.1.2 Medium Head Hydro Electric Power Plant 1394.1.3 High Head Plant 141

4.2 Thermal Power Plant 1434.3 Nuclear Power Plant 147

table of contents ix

5. Dc Machines 5.0 Introduction 1495.1 Constructional Details 149

5.1.1 Yoke or Stator 1495.1.2 Poles 1515.1.3 Rotor 1515.1.4 Armature 1515.1.5 Commutator 1525.1.6 Fan 1545.1.7 End Shields 1545.1.8 Brush and Brush Holder Assembly 1545.1.9 Assembly 154


6. transformers 6.0 Introduction 1756.1 Transformer Core 175

6.1.1 Core Type Transformer 1766.1.2 Windings 177

6.2 Shell Type Transformer 1786.3 Transformer with Accessories 179

6.3.1 Assembly 1796.4 Examples 187

6.5 Problems for Self Study 202

7. alternators 7.0 Introduction 2037.1 Construction 203

7.1.1 Stationary Field 2047.1.2 Rotating Field 2047.1.3 Types of Rotor Construction 2077.1.4 Cooling 208


x CAD for Electrical Engineers

8. Induction Motor 8.0 Introduction 2218.1 Construction 222

8.1.1 Frame or Housing 2228.1.2 Stator Core 2228.1.3 Rotor Core 222

8.2 Slot Forms 2228.3 Types of Rotor 224

8.3.1 Aluminum Die Cast Rotor 2248.3.2 Fabricated Squirrel Cage Rotor 2248.3.3 Slip Ring Rotor 224

8.4 End Shields, Fan and Bearings 2268.5 Frame Size and Mounting Dimensions 2268.6 General Assembly of Induction Machine 2278.7 Examples 2288.8 Problems for Self Study 230

appendix I - Introduction to caD commands 231

appendix II - size of Papers 293

appendix III - Insulating Materials 293

appendix IV - conductor Materials 295

appendix V - electrical steel sheet 297

appendix VI - Metric fasteners 299

Index 305

references 307

1

Chapter

1DC Winding Diagrams

1.0 IntroductIon

Any rotating electrical machine consists of stator, rotor, end shields, fan and ventilating system, bearing system and mounting system. In a DC machine, the stator consists of a yoke which houses poles attached to the yoke and the field windings. The rotor consists of armature with supports, commutators and bearings. The armature has slots in which the windings are placed. The winding terminals are connected to the commutator. The winding placement and the connections to the commutator follow a systematic procedure, so as to get the required formation and function as a generator or as a motor. The developed DC winding diagram furnishes the details of the coil end connections to the commutator segments. From this, position of poles, brushes and current directions are visualized. The following are some of the terminologies related to the winding.

1.1 BasIc defInItIon

i) Coil: A coil is made by winding over the ‘formers’ with the designed value of number of ‘turns’ of round copper conductor of suitable diameter / copper strips of suitable cross sectional area. The coil will have distinct ‘start’ and ‘end’ terminals with a span to cover the required number of slots in the armature. A multi-turn coil represented as a single turn coil is shown in the Fig.1.1.

E ES S

Fig.1.1: Representation of a multi-turn coil

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2 CAD for Electrical Engineers

ii) Pole Pitch or Full Pitch: The pitch is specified in terms of number of slots. If the machine is having ‘P’ number of poles and ‘N1’ number of armature slots, then the Pole Pitch or Full Pitch is given by ‘N1/P’. This may be an integer or fraction, depending on the number of slots and the number of poles.

iii) Coil Pitch: The coil pitch denotes the number of slots the coil will cover, on insertion in to the slots. The coil pitch is usually selected to cover one pole pitch. If the coil pitch is less than the pole pitch, it said to be ‘short chorded coil’. If the coil pitch is more than the pole pitch, it said to be ‘over chorded coil’. If the pole pitch is a fraction, the coil pitch is usually selected closer to the next lower integer. The coil pitch is always an integer. It is to be noted that one side of the coil will be under the influence of the North Pole, whereas the other side of the coil will be under the influence of the South Pole.

iv) Coil Sides per Slot or Number of Layers per Slot: If one coil side is inserted in a slot, then it is known as ‘Single Layer’. If two coil sides are inserted in one slot, then it is known as ‘Double Layer’ and so on. Depending on the design, the coil sides per slot may be 1,2,3,4 etc. The symbol for number of coil sides is denoted by ‘m’.

v) Numbering of conductors:

The total number of conductors, Z = Number of slots × Number of coil sides

The numbering of conductors is as shown in Fig.1.2.

Coil Side = 1(Single Layer)

Coil Side = 2(Double Layer)

Coil Side = 4

17

Conductors Placed in Slots of Armature

Conductors Positioned for Drawing the Developed Winding DiagramFig.1.2: Convention for numbering of conductors

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DC Winding Diagrams 3

For DC winding various pitches are defined in terms of conductors and very rarely in electrical degrees.

vi) Back Pitch, Yb: The distance between two sides of a coil, measured in terms of conductors, at the back end of the commutator is known as the back pitch.

vii) Front Pitch, Yf: The distance between the two sides of coil connected to the commutator segment, measured in terms of conductors, at the front of the commutator, is known as the front pitch.

viii) Average Pitch, Yav: The average pitch is the average of the back pitch and front pitch. This will be nearer to the pole pitch measured in terms of conductors.

Yb

Yc Yc

Yb

Yf Yf

Fig.1.3(a): Lap winding Fig.1.3(b): Wave winding

ix) Commutator Segments: The commutator will have number of segments, related to the number of armature slots and the coil sides per slot is given below -

Number of commutator segments = 1N m

2

×

x) Commutator Pitch, Yc: It is the distance, measured in commutator segments, between two ends of the coil.

xi) Lap Winding: In a lap winding the finish-end of one coil is connected via the commutator segment to the start-end of the adjacent coil situated under the same pole. As the sides of the adjacent coils overlap each other, it is known as lap winding.

xii) Wave Winding: In a wave winding the finish-end of one coil under one pole- pair is connected to the start of a coil under the next pole- pair. The process is continued till all the armature coils are connected and the winding closes onto itself.

The back pitch Yb, front pitch Yf and commutator pitch Yc are marked in Fig.1.3(a) and in Fig.1.3(b) for Lap and Wave winding, respectively.

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1.2 Procedure for LaP WIndIng

1.2.1 Pitch Calculation

Sequence of steps involved Symbol Remarks Example

Number of slots in the armature

N1 17

Number of coil sides per slot

m 2

Number of Poles P 4

Total number of conductors

Z = N1 × m 34

Pole Pitch in terms of conductors

Yp = Z/P 8 12

Modified integer value of the Pole Pitch

Yp If the value is a fraction an integer lower than the obtained fractional number is selected

8

Commutator Pitch Yc= X X Type of Winding

11 Simplex

2 Duplex

3 Triplex

4 Quadraplex

Back Pitch (unmodified)

Yb The values are obtained by solving the two equations- Yb + Yf = 2Yp, Yb - Yf = ±2Yc ‘+’ for Progressive lap winding ‘-’ for Retrogressive lap winding

9

Front Pitch (unmodified)

Yf 7(Progressive lap winding)

Final Back Pitch Yb If the values of Yb and Yf are even , then the next lower values of odd integers for both Yb and Yf are selected

9

Final Front Pitch Yf 7

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1.2.2 Winding Table

-7

1 10+9

12

14

3

5

167

189

2011

2213

2415

2617

2819

3021

3223

3425

227

429

631

833

1.2.3 The drawing is made for the developed lap winding, using the winding table.1.2.4 The position of poles, brushes and current direction are shown in the developed winding

diagram.1.2.5 For duplex lap winding, width of the brush will be equal to twice the width of commutator segment.

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1.3 Procedure for Wave WIndIng

1.3.1 Pitch Calculation

Sequence of steps Symbol Remarks ExampleNumber of slots in the armature

N1 17

Number of coil sides per slot m 2Number of Poles P 4Total number of conductors Z = N1 × m 34Pole pitch in terms of conductors

Yp = Z/P 8 12

Commutator Pitch Yc= (Z±2X)/P ‘+’ for Progressive wave winding ‘-’ for Retrogressive wave winding

X Type of Winding 9 (Progressive

wave winding)

1 Simplex2 Duplex3 Triplex4 Quadraplex

Back Pitch Yb Choose Yb and Yf such that-i) They are odd numbersii) Yb + Yf = 2 Yciii) The values are nearer to Yp

9

Front Pitch Yf9

1.3.2 Winding Table

+9 +91 10 19 28

3 12 21 30

5 14 23 32

7 16 25 34

9 18 27 2

11 20 29 4

13 22 31 6

15 24 33 8

17 26 1

+9

Chapter 1.indd 6 19/01/2015 11:21:23 AM


1.3.3 The drawing is made for the developed lap winding, using the winding table.1.3.4 The position of poles, brushes and current direction are shown in the developed winding diagram.1.3.5 For duplex wave winding, width of the brush will be equal to twice the width of commutator

segment.

1.4 examPLes

1.4.1

Example 1.1Draw the developed DC Lap Winding Diagram for the following data- Number of Slots = 16, Number of Poles = 4, Type: Single Layer Simplex Lap Winding

SolutionTotal number of conductors, Z =16Number of Poles, P = 4Pole Pitch, Yp = Z/P = 16/4 = 4Yb = Back Pitch and Yf = Front PitchYb+Yf = 2 × Yp = 2 × 4 = 8 , Yb - Yf = 2 Solving for Yb and Yf , Yb = 5 and Yf = 3 Select Yb and Yf such that they are odd and differ by 2 Also to note that (Yb+Yf)/2 should be closer to YP

Winding Table

61

83

105

127

149

1611

213

415

1

+5

-3

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Steps for drawing the winding diagram

Command Details Evolving FigureUnits Set Units to mmLimits To set paper size

as A4, Lower left corner:0,0 Upper right corner:297, 210

Zoom To view all objects in the window Select:Zoom Option:all

Remark: Preliminary setting such as units, limits, zoom-all are set at the beginning of the drawing

Line To draw one conductor of 40unitsFirst point: 30,130 Next point: @40<270 Next point: Enter key

Array To draw multiple conductorsRows:1 Columns:17 Row offset:0 Column offset:10 Select Object: Select the above conductorEnter key, Ok.

Text The conductors are numbered using the Multitext command Font:Times New Roman Height:4Width factor:1

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Osnap Polar Tracking Line

Overhang is drawn using the Line command Draw a line from end point of conductor 1 at an angle 450 (Osnap and Polar tracking to be ‘ON’ for better selection) Draw another line from end point of conductor 6 at an angle 1350 Similarly for the lower side

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1

Trim The extended lines are trimmedSelect objects: upper and lower overhangs Enter keyclick on the object to be trimmed

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1

LineOsnap-ON

To draw one extension line from the diamond, Line command is usedFirst point: Select tip of the lower diamondNext point:@15<270

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1

Diamond

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CAD For Electrical Engineering

Publisher : Sanguine Publishers ISBN : 9789383506309 Author : Dr. Indira, V DSankarlal & D Beula

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