ELECTRIC MACHINE DESIGNUSING SPEED AND MOTOR-CAD

T.J.E. Miller and D.A. Staton

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Authors' Note

Electric Machine Design is one of the key engineering skills in the modern world,essential in the generation of electricity and its use in appliances, vehicles of all kinds,industrial machinery, and many other applications. Yet the art is taught in very fewcolleges; there is a worldwide scarcity of designers; and the theoretical background isdifficult to acquire without years of specialized study.

In this book two of the most experienced authors in the field have combined to presenta practical guide to the design of electric machines using the SPEED and Motor-CADsoftware packages, which were written to work together, one for the electromagneticand the other for the thermal aspects.

No fewer than ten different machine types are introduced, starting in each case from asimple specification and proceeding through to a credible prototype. Rules of thumb andbasic engineering principles are used throughout, to guide and inform the designprocess, and ample reference is made to the extensive documentation of both SPEED andMotor-CAD for a deeper theoretical understanding.

The book has been used and tested in training classes in the United States, Japan, andEurope. It can be used as a course text, either in intensive sessions covering up to 10days of instruction; or as a self-study text in conjunction with the SPEED andMotor-CAD software. We have chosen the "print-on-demand" route with wire-bindingto ensure that Electric Machine using SPEED and Motor-CAD fits comfortably on thedesk beside your computer, and is readily updated as the software itself develops.

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This book is dedicated to Jimmy Kelly

As a technician in the mechanical engineering workshop at the University of Glasgow, Jimmy Kelly built mostof the test rigs and prototype motors on which SPEED was built over a 25-year period. The workshop is in theJames Watt building, and anyone visiting the university may see the huge carved relief on the south wallfacing the Clyde, celebrating the practical art of the craftsman and engineer. This fine monument is a tributeto those whose genius is expressed through their hands, and perhaps a reminder that engineering is aboutmaking things.

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Preface

This book is a primer for engineers learning todesign electric machines using SPEED andMotor-CAD. It can be used in two ways:

• as part of a SPEED or Motor-CAD trainingcourse. Individual chapters can be used forthe design sessions that are so popular in thetraining courses. If you have the book inadvance, you can prepare the example onyour lap-top for each day of the training. Thisis the best way. It means you will arrive atthe class with momentum and questions.When the class is prepared, it becomespossible to go into more detail on theadvanced features of the programs, and totake the design examples further.

• for self-study. The book is designed for this.You can therefore use it as a substitute for thetraining course. However, please recognizethat the book is short and introductory. Itprepares the ground for more advanced work.If you prefer to work alone, you will findplenty of advanced documentation in thetutorials, the reference manuals, andSPEED’s Electric Machines to take youfurther into the capabilities of SPEED andMotor-CAD.

The book is organized as a collection of short“design stories”. Each design example isdeveloped from scratch in the same step-by-stepway we use in the SPEED training classes. Eachchapter is self-contained, and you can read line-by-line while executing the program.

You should achieve the same results as thosedisplayed in the book, and soon you’ll be able toimprove on them.

Most of the keystrokes for the SPEED part ofeach chapter are tabulated in the Appendix. Youcan use these tables to recover quickly ifsomething goes wrong. Instructors can use themfor the same purpose.

Each chapter except chapter 11 has a thermalsection. Once the design is established withSPEED, we pass it to Motor-CAD to begin thedesign for cooling and heat transfer.

SPEED and Motor-CAD are designed to worktogether. They were written by the same familyof engineers. The authors understand the mainrequirements in this type of design software:

• it must be fast

• it must rely on the engineering theory,— not just the physics

• it must be documented and supported almostwithout limit.

The book is not a reference book where you can“look something up”; that is the rôle of thereference manuals. (SPEED tutorials fallsomewhere in the middle: they provide step-by-step instructions to particular procedures, butthey contain no design guidance and they do notform a coherent approach to design).

The book is an introduction, covering only themost elementary aspects of each design. Manyadvanced concepts, parameters, and methodsavailable in SPEED and Motor-CAD are notmentioned here; some of them will be covered intraining courses, but ultimately the readershould refer to SPEED’s Electric Machines (SEM)and the reference manuals, and interact with theoriginal SPEED/Motor-CAD authors.

The book provides a little theory, but it is not asubstitute for proper training in the theory ofelectrical machines. Engineers who are qualifiedin this field will recognize the theoreticalprinciples described here, and they will see thelogic of the calculations more clearly. For a fulleraccount of machine and drive theory, consultSPEED’s Electric Machines (SEM), or the GreenBook (GB), [1].

For the SPEED interface, the WinSPEED manualis recommended.

Parenthetic interjections are irresistible in atechnical book, so we use references [], footnotes,and doubly-indented paragraphs like the nextone. Some of these are introduced with thesomewhat precocious words “Design wisdom”.Here are two examples:

Design wisdom — e = L di/dt is not Faraday’s law. It’s only half of it. If that was allthere was to Faraday’s law, we wouldn’t have any electric machines, or even anytransformers. (We might have a few chokes and rinky-dink inductors).

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Design wisdom — Minor variations in results may arise with different versions. Theywill generally be unimportant. But it is also possible for one incorrect parameter to ruinthe entire calculation or even prevent the program from working. Computer programsare inflexible and curmudgeonly, and always contain errors, so if there is a problem andyou are sure your data is correct, contact your technical support engineer.

The units used in this book are predominantlymetric (mm, Nm, etc), as a reluctant concessionto the metric majority, and as a mark of respectfor the unarguable virtue of conformity inengineering units. However, TJEM’s preferenceis the English or Imperial system of units, (partlybecause of the familiar appropriateness of scale,and partly because of the power of fractions.

For example, 1½ pounds per square inch seemseasier than 20,700 newtons per square metre). Soinches and other English units appear here andthere, often in places where points can be scoredagainst the awkwardness of SI units. Alas, theshaku is not used in this book, but it would be funto try it.

Design wisdom — In a mathematical equation, units are strictly superfluous. In anengineering equation, units are a sine qua non.

The SPEED part of the book refers to the programfunctions using short-cut keys, and onlyoccasionally spells out the full menu item. Forexample, Static design is executed using [Ctrl+2],which is more concise and efficient than thecumbersome menu descriptor [Analysis | Staticdesign]. It is recommended to learn the short-cutkeys, especially the main ones. The WinSPEEDmanual provides a list of them, but they appearon the menus, so the only excuse for not usingthem is laziness.

Fonts: This work is set in 10pt Nimrod MT tosave paper, and because of its kerning qualitiesin equations. Boldface is used for parametersappearing in the SPEED programs, such as Rad1or Tph. The equivalent mathematical descriptormay be written in the classical form, so Tphbecomes Tph. Non-numerical parameter valuesare written in ordinary type, as for example inDrive = Square. In this example, Drive is theparameter name, and “Square” is the valuewhich will appear in the edit field in theTEMPLATE EDITOR, Ted. Menu items are writtenin boldface sans-serif, e.g., Analysis | Staticdesign. Short-cut keys are written in boldfaceenclosed in brackets: [Ctrl+1]. Italics are usedfor emphasis or for special terms like Dynamicdesign, which is a complete process, not simply amenu item. Main SPEED windows are in smallcaps, e.g., DESIGN SHEET, WINDING EDITOR.

Abbreviations: Generally acronyms aredeprecated, except classical ones, e.g. “i.e.”. Itwould be churlish not to use commonengineering abbreviations like PWM (pulse-width

modulation), RMS (root-mean-square), and p.u.(per-unit). But PM (permanent-magnet) is usedsparingly (to avoid confusion with PrimeMinister, or post meridiem. The TEMPLATE EDITOR

is referred to as Ted (though Hid might be moredescriptive), and individual pages by the formTed/Electrical, etc. Latin phrases such as mutatismutandis, ad hoc, etc. are used whereverpossible— the Romans were engineers too, andthey are still around.

Notation: Parameter names in SPEED aregenerally limited to 8 characters. There is noconsistent naming convention, and there aresignificant differences in nomenclature betweenthe individual SPEED programs (mainly becausethe originals were written at different times). Tcan mean torque or temperature; R can meanradius or resistance. W is often used for losses inwatts (having a connotation of “waste”); but itmight also mean width. Both prefixes andsuffices are used, often inconsistently: forexample, you might find wSlot or SlotWid bothreferring to the width of a slot.

Learn the parameter names (and their meanings,which are given in the reference manuals). Don’tguess. A smart programmer might be tempted torationalise it all, creating even greater chaos, forthe SPEED documentation will never berationalised in this way. The mathematicalconventions are followed more faithfully: forexample, lower-case letters are used forinstantaneous quantities like v or i, whileboldface is used for phasors, which are complex:thus V or I.

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Upper-case italic is generally used for averagequantities such as T for torque, but one cannotrely solely on the notation and one must get thedetailed meaning of parameters from theequations and the context (or from SEM or themanuals).

In SPEED, the parameters are entered and thena specific calculation is deliberately executedfrom the Analysis menu or one of the other utilitymenus such as the Tools menu. In Motor-CAD,the calculation is executed automatically whenthe relevant “results tab” is opened, for example,Temperatures or Transient.

In the Motor-CAD sections, menu items are set inthe same sans-serif font as in the SPEED sections;e.g., Geometry | Radial. Likewise the parameternames are set in boldface type ; e.g., SlotOpening. In Motor-CAD the parameter namesare not restricted to 8 characters, and they mayeven appear more like phrases with a smalldegree of abbreviation, e.g., Housing OuterCooling = Natural Convection, or Housing �Ohang [F/R] = 0. The abbreviation [F/R] means“front” or “rear”. The front end generally is thedrive end, and it appears at the left-hand side ofthe window in Geometry | Axial.

Blind cornering — Electric machine design involves guesswork and rules of thumb,techniques well known to engineers (in spite of their often-quoted sardonic disapproval).Anyone who loves motorcycles will know about blind cornering, but it is part and parcelof the creative engineering process : venturing into the unknown. So to keep this in mind,we will occasionally refer to certain design decisions as blind cornering.

With a new design, or a new type of motor, oreven a new engineer, we may have no idea of thedesign procedure (or even if one exists). We canoften get started by running SPEED to see whatwe get, and then use engineering common-senseand well-established principles to modify thedesign in the right direction.

The “engineering common-sense and well-established principles” are learned by analysis oftest data and calculations. The computer helpswith the calculations, but we must do the rest.

Almost certainly this book contains errors. Ifyou find any, please let us know.

Acknowledgements

SPEED and Motor-CAD form part of the electric machine design community. This is a close-knit world-wide community, and anyone who uses this book will be a part of that community.

Particular recognition should be given to Malcolm McGilp, the software engineer who designed theSPEED software architecture; Dougie Hawkins (Motor-CAD software manager); and Mircea Olaru, theauthor of PC-FEA.

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CONTENTS

1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.1 Rules of thumb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2 Fundamental laws . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.3 Guiding principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.4 SPEED and Motor-CAD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.5 How this book works . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.6 The SPEED system — basic design process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.7 The SPEED system — features, functions, and auxiliaries . . . . . . . . . . . . . . . . . . 51.8 Motor-CAD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61.9 SPEED and Motor-CAD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61.10 SPEED and Finite-Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71.11 Scripting, automation, optimization, and links . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81.12 Documentation, help, training, support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

2 Brushless DC Permanent-Magnet Motor with Squarewave Drive . . . . . . . . . . . 92.1 Specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92.2 Initial sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92.3 Starting PC-BDC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92.4 The numbers of slots and poles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112.5 Dimensions again . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142.6 The winding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162.7 Selecting materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172.8 Setting the controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182.9 Performance calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192.10 Static design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192.11 The design sheet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202.12 Custom output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212.13 Dynamic design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212.14 Next steps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252.15 Finite-element analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252.16 Effect of temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262.17 Demagnetization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272.18 Cogging torque . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282.19 Setting up the thermal analysis with Motor-CAD . . . . . . . . . . . . . . . . . . . . . . . . . 292.20 Thermal calculations using Motor-CAD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

3 Interior-Permanent-Magnet Motor (IPM) with Sinewave Drive . . . . . . . . . . . 373.1 Specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 373.2 Initial sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 373.3 Starting PC-BDC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 383.4 Engineering changes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 393.5 Winding editor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 403.6 Selecting materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 423.7 Estimating the number of turns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 433.8 Setting up the performance calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 433.9 Initial performance calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 443.10 Estimating the power available at 6,000 rpm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 503.11 Some of the many things we have not done . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 523.12 Setting up the thermal analysis with Motor-CAD . . . . . . . . . . . . . . . . . . . . . . . . . 533.13 Steady-state thermal analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 573.14 Transient Duty-Cycle Thermal Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 603.15 Conduction Heat Transfer in Slot Using Finite-Element Analysis . . . . . . . . . . . 60

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4 Synchronous Reluctance Motor with Sinewave Drive . . . . . . . . . . . . . . . . . . . 634.1 Specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 634.2 Initial sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 634.3 Starting PC-BDC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 644.4 No magnets! . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 684.5 The stator winding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 684.6 Estimating the number of turns per coil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 704.7 Wire size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 714.8 Selecting materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 714.9 Setting up the first calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 714.10 Setting up the thermal analysis with Motor-CAD . . . . . . . . . . . . . . . . . . . . . . . . . 754.11 Steady-State Thermal Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

5 3-Phase Induction Motor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 815.1 Specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 815.2 Initial sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 815.3 Starting PC-IMD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 815.4 Initial sizing and dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 825.5 Rotor design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 835.6 Stator winding layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 855.7 Determining the number of turns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 875.8 Selecting materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 875.9 Setting up the first test calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 885.10 Operation at high speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 895.11 Checking the flux-densities with PC-FEA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 915.12 Other parameters to consider . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 915.13 Setting up the thermal analysis with Motor-CAD . . . . . . . . . . . . . . . . . . . . . . . . . 925.14 Steady-State Thermal Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 975.15 Fin Spacing Optimisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

6 Single-Phase Induction Motor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 996.1 Specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 996.2 Starting PC-IMD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 996.3 Stator winding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1006.4 Estimating the number of turns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1006.5 Selecting materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1026.6 Setting up the operating point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1026.7 Torque/speed characteristic and steady-state operation . . . . . . . . . . . . . . . . . . 1026.8 Further aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1046.9 Setting up the thermal analysis with Motor-CAD . . . . . . . . . . . . . . . . . . . . . . . . 1056.10 Steady-State Thermal Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1096.11 Further Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110

7 PM DC Commutator Motor (Brush motor) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1137.1 Specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1137.2 Initial sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1147.3 The armature winding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1177.4 Determining the turns/coil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1177.5 Selecting materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1197.6 Initial calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1197.7 Engineering changes required to meet the specification . . . . . . . . . . . . . . . . . . 1207.8 Precise kE, or the simple formula? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1207.9 Nominal performance calculation (still with high friction) . . . . . . . . . . . . . . . 1217.10 Calculation and graphical display of the torque/speed characteristic . . . . . . 1227.11 Setting up the thermal analysis with Motor-CAD . . . . . . . . . . . . . . . . . . . . . . . . 123

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7.12 Steady-State Thermal Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1267.13 Transient thermal analysis (Stall) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1277.14 Rating test using a flange-mounted plate as a heatsink . . . . . . . . . . . . . . . . . . . 127

8 AC Universal Motor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1318.1 Specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1318.2 Initial sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1318.3 Preliminary changes to the geometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1328.4 The armature winding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1358.5 Selecting materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1388.6 Setting the controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1388.7 Setting up the first test calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1398.8 Torque/speed characteristic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1418.9 Operation at 1,500 rpm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1428.10 Setting up the thermal analysis with Motor-CAD . . . . . . . . . . . . . . . . . . . . . . . . 1438.11 Transient heating of the rotor winding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148

9 Switched Reluctance Motor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1499.1 Specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1499.2 Initial sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1499.3 Initial performance calculation — low speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1519.4 Calculation at the high-speed point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1539.5 Checking the low-speed operation again . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1559.6 Setting up the thermal analysis with Motor-CAD . . . . . . . . . . . . . . . . . . . . . . . . 1569.7 Duty-cycle analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162

10 Salient-Pole Wound-Field Generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16510.1 Specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16510.2 Initial sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16510.3 Starting PC-BDC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16510.4 Engineering changes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16710.5 The armature winding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16710.6 Determining the number of turns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16710.7 The field winding and the excitation current . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16810.8 Selecting materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17010.9 Setting up the controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17010.10 First calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17010.11 Harmonic analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17110.12 Generator characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17210.13 Load calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17310.14 Finite-element calculation — the single-load-point GoFER . . . . . . . . . . . . . . . . 17610.15 Adding a damper (amortisseur) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17710.16 Short-circuit calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17810.17 Setting up the thermal analysis with Motor-CAD . . . . . . . . . . . . . . . . . . . . . . . . 17910.18 Steady-state temperatures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186

11 Axial-flux machine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19311.1 Specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19311.2 Initial sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19311.3 Starting PC-AXM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19611.4 The winding editor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20011.5 Selecting materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20111.6 Control settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20111.7 Static design calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20111.8 Dynamic design calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202

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Appendix I : Main short-cut keys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204

Appendix II : Summary of keystrokes and changes for each chapter . . . . . . . . . . . 205Keystrokes Chapter 2 — Brushless PM Motor with Squarewave Drive . . . . . . . . . . . . 205Keystrokes Chapter 3 — IPM Motor with Sinewave Drive . . . . . . . . . . . . . . . . . . . . . . . 207Keystrokes Chapter 4 — Synchronous Reluctance Motor with Sinewave Drive . . . . 209Keystrokes Chapter 5 — 3-Phase Induction Motor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211Keystrokes Chapter 6 — Single-Phase Induction Motor . . . . . . . . . . . . . . . . . . . . . . . . . 212Keystrokes Chapter 7 — PM DC Commutator Motor (Brush Motor) . . . . . . . . . . . . . . . 213Keystrokes Chapter 8 — AC Universal Motor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215Keystrokes Chapter 9 — Switched Reluctance Motor . . . . . . . . . . . . . . . . . . . . . . . . . . . 217Keystrokes Chapter 10 — Wound-field AC Generator . . . . . . . . . . . . . . . . . . . . . . . . . . . 218

Appendix III : Typical values of TRV and airgap shear stress . . . . . . . . . . . . . . . . . 220

Appendix IV : Numbers of stator and rotor slots for small induction machines . . . 221

Appendix V : Options | General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223

References and Further Reading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225

Electric Machine Design using SPEED and Motor-CAD Page 1

Fig. 1.1 Crompton alternator, Walmsley

v ����t

, (1.1)

E � 4�44kw1 Tph�m1 f [V RMS]. (1.2)

1 Introduction1.1 Rules of thumb

There are many “rules of thumb” for designingelectric machines, but no such rule applies in allcases. As an example, we have the idea that thepole-face of a synchronous machine should beroughly square.

This idea has deep theoretical roots. It cansometimes be observed in production, thoughthere are many more exceptions. It is an old idea,as we can see in Fig. 1.1.

However, a square pole-face would not be suitablein a down-hole drilling motor, which mustproduce a huge torque with a severely limiteddiameter. Such motors may have a rotordiameter of a few inches, with an axial lengthmeasured in metres, so that with two poles theratio of the axial length to the pole-arc is of theorder of ten times the value that would give a“square pole”.

1.2 Fundamental lawsAt the same time, there are fundamental physicallaws that do apply rigorously in all cases, thoughnot necessarily in an obvious way. One of themost basic laws of electric machines is Faraday’slaw. A general form of it is expressed in terms offlux-linkage �:

but an engineer designing an AC machine ismore likely to use

Even the units of eqns. (1.1) and (1.2) are not thesame. Eqn. (1.1) is in instantaneous volts,whereas eqn. (1.2) is in RMS volts. Moreover, eqn.(1.1) is always true in all circumstances, whereaseqn. (1.2) is true only when the flux-linkage of thewinding is varying sinusoidally with time.

The form of eqn. (1.1) is of limited use to thepractical design engineer, even though eqn. (1.2)is derived from it.

Conversely eqn. (1.2) is utterly useless outside theAC machine, or when the time variation of thewinding flux-linkage is not sinusoidal. SPEEDmust use both forms: (1.1) for time-steppingsimulation and for the underlying theory, and(1.2) for calculating E in a form that can readilybe checked by the expression

4�44 * kw1 * Tph * PhiM1 * Freq1

which can be entered exactly in that format inthe CALCULATOR, [F4].

Page 2 Electric Machine Design using SPEED and Motor-CAD

1.3 Guiding principlesThe design engineer is thus faced with rules ofthumb that don’t always work, and equationsthat may be applicable only in special cases.Nowadays s/he is also faced with software thatmay require a considerable learning period,making the overall learning process even morecomplicated. Additional complexities can arisebecause of interactions with power-electronics,control, protection, heat transfer, failure modes,manufacturability, production issues, materialproperties, costs, and many other factors.

What guidance can be given to design engineers(especially young design engineers) facing thesecomplex challenges? The authors can do no morethan offer a few points of advice based on theirown experience, which covers 45 years ofengagement in industrial companies and in theSPEED laboratory:

• Keep company with experiencedengineers. This is by far the mostvaluable external source of wisdom andknow-how. While personal experienceand initiative is also important, no-onecan encompass the subject alone, and“only a fool learns by his own mistakes”.1

• Keep a firm grip on the fundamentalphysical principles such as Faraday’slaw, and many others. In the authors'experience it seems that the top engineersalways have an unshakeable grasp of thebasics. They are rarely the ones who usesophisticated theories. They seem to becharacteristically skilled in dealing witha mosaic of interacting factors, whilebeing able to see the essential physicallaws at work behind them. Often whensomething isn’t right, they will notice aconflict with one of the essential physicallaws. For example, when one thing goesup, another goes down (especially when itshouldn’t).

Such observations appear to be based onan almost intuitive grasp of the essentialphysical laws. But these laws are notactually intuitive. For centuries, greatminds were frustrated searching for the“simple” laws of mechanics andelectromagnetism. Therefore it isnecessary to learn them, and to go onlearning them, by applying them

repeatedly and questioningly to theexamples one encounters in the course ofone’s work as a designer.

• Collect rules of thumb. Only experiencewill tell whether or not they are reliable.Some rules of thumb may yield theirsecrets to scientific analysis; but otherswill defy analysis, and in such cases theymay be risky. They must necessarily bebroken in many cases, but with scientificjustification or experimental proof whenthis is possible.

• Measure and test everything in the lab.Spend as much time as possible on thefactory floor.

• Keep in shape. Do lots of practice. Reada lot. Study. Keep asking questions.

1.4 SPEED and Motor-CADSPEED and Motor-CAD are designed to helpengineers who follow these principles. Theycollect many of the methods and calculations thatdesigners do every day. These calculations arecommonly done thousands of times during adesign exercise, as different combinations ofdimensions and parameters are changed in thesearch for an “optimum” design or even one thatsimply meets the requirements. For this reasonSPEED and Motor-CAD are designed to be fast.

Primarily one should think of SPEED and Motor-CAD as a numerical and theoretical companion.

In skilled hands, SPEED and Motor-CAD arecapable of accurate and sophisticated designcalculations. Both programs are primarilyanalytical, supported by PC-FEA for 2-dimensional magnetostatic and thermalcalculations. They can be used in conjunctionwith other specialist software — for example,FLUX™ for finite-element analysis, or STAR-CCM+™ for fluid flow.

SPEED and Motor-CAD can be used for self-learning about electric machines, or as a tool inthe teaching of electric machine performance anddesign. Until the publication of this book, the useof SPEED and Motor-CAD for these educationalpurposes was not documented, so this book isintended as a “grand tutorial” for most of thebasic steps. Of course, much more can be foundin the extensive internal documentation and thetheory references and books.

1 This maxim should be relaxed for engineers. “Nothingventured, nothing gained”.

Electric Machine Design using SPEED and Motor-CAD Page 3

Fig. 1.2 The basic design process in SPEED

1.5 How this book worksIt teaches how to use SPEED and Motor-CAD, andit does this by example.

In every example the objective is to design amachine to a specification. So the steps are setout in “do-this-do-that” fashion. The narrativeincludes a few comments about manufacturingpractice, usually to explain or justify designdecisions. Manufacturing practice varies widely,and it is beyond the scope of SPEED or Motor-CAD to make pronouncements about it. Theimportant thing is to recognize the interactionbetween theory on the one hand, and practicalmanufacturability on the other.

The narrative also contains elements of theory,by way of support for the design function withoutoverwhelming it. For some calculations, thedesigner must know the theory.

In each chapter, the SPEED marker appears inthe margin at the point where the data is readyfor export to Motor-CAD. If you are following theinstructions step-by-step, this is where the exportto Motor-CAD should be executed. Alternatively,save the file at this point for later use in Motor-CAD.

1.6 The SPEED system — basic design process

The SPEED system is shown in Fig. 1.2. At itscore is the design loop process. We start with aMotor performance requirement, or a generatorperformance requirement.

Design parameters are defined. These begin withphysical dimensions, so there is an OUTLINE

EDITOR where the dimensions can be specified.The OUTLINE EDITOR displays the cross-section inthe transverse or longitudinal plane, and givesinstant visualization of the design.

Design parameters include electrical details ofwindings, and of the power supply and thecontrols. To assist in the layout and specificationof the windings, the WINDING EDITOR providesimmediate visualization of the winding layout.

The WINDING EDITOR also has many powerfulanalytical functions to help obtain a winding ofthe right quality and characteristics, and toanalyze its winding factors, MMF harmonics, andphase sequence.

Materials must be specified. To assist in materialselection, a MATERIAL SELECTION DIALOG providesaccess to the materials databases (for steels,permanent magnets, and brushes). Thesedatabases can be populated and edited by theuser, using the materials database editors on theTools menu.

Finally the TEMPLATE EDITOR is provided fordesign parameters related to the drive andcontrol, and other program settings.

Design wisdom — the SPEED OUTLINE EDITOR helps to develop an eye for suitableproportions. We often refer to this as the “designer's eye”.

Page 4 Electric Machine Design using SPEED and Motor-CAD

Design wisdom — At the beginning of a design, a complete set of design parametersmust be specified. A complete set of design parameters is just sufficient to define themachine and to run it at one or more more operating points.

The Performance calculation is the next maincontribution that SPEED makes to the designprocess. We will see that there are many differenttypes of performance calculation, but in all casesthere is a definite Result in the form of a DESIGN

SHEET and SIMULATION GRAPHS.

The DESIGN SHEET is a complete set of datadescribing the performance at one operatingpoint. It often contains several hundrednumbers, collected into numbered sections.

In fact the DESIGN SHEET is the complete collectionof all input and output parameters, often farexceeding the few that are of immediate interest.

SIMULATION GRAPHS include waveforms ofcurrent, voltage, torque, and other time-varyingquantities. There are also numerousdistributions (for example, flux-density in theairgap); special graphs such as energy-conversionloops and other operating loci; and graphicalrepresentations of equivalent circuits.

In principle we have defined the basic designprocess :

• Machine specification

• Definition of parameters

• Performance calculation

However, it is extremely unlikely that thecalculated performance will match the machinespecification after only one pass. For this reasonit is common to repeat the whole process,changing parameters in an orderly way, until thecalculated performance does meet the machinespecification.

“In an orderly way” sounds simple. But there areso many parameters, and the relationshipsbetween them are often nonlinear ordiscontinuous. Some parameters can be variedcontinuously, while others can take only integervalues. All parameters are subject to practicallimits or constraints.

SPEED does nothing more than the performancecalculation itself, so it falls to the designer, theuser, to make the decisions about parameterchanges. “In an orderly way” is really aparaphrase for the skill of the designer, inknowing what parameters to change, and by howmuch.

“Repeat the whole process” also sounds simple, iftedious. SPEED provides two methods to assistthe process of repetition : Ranging and Scripting.Ranging is a straightforward matter of varyingone or more parameters synchronously, so that agraph can be plotted showing the variation of oneor two parameters with each other.

Scripting is much more powerful because it canemploy SPEED as the calculating “engine” in asearch or optimization process written in anexternal environment such as Excel™ orMATLAB.™ However, there is a danger thatscripting can create data that is impractical orbeyond the analysis capability of the program, soit should be used only by skilled designers.

Design wisdom — It is helpful to make up a CUSTOM DESIGN SHEET, or a CUSTOM OUTPUT

panel, containing only the parameters of interest. See p. 21. The same applies to theTEMPLATE EDITOR; see p. 22. This is a good way to simplify the appearance of theprogram, and to collect all the parameters of immediate interest in one place.

Electric Machine Design using SPEED and Motor-CAD Page 5

Vs VCdc

iDC

Cdc

R_sRdc

Ldc

0

ICdc

iLdc

iA iB iC

e1

i1 i2 i3

e2 e3

Rph

Lph

Rac

Lac

Q1 Q3 Q5

Q4 Q6 Q2

D1 D3 D5

D4 D6 D2

Frame

Leads

v1

Vt

iRec

A B CvAB

TORQUE SPEED

FC-IV CONTROLLERMACHINE INVERTER LOAD INVERTER

Resolver

Gate drives

Current SPEEDReference

TestMachine

LoadMachine

Fig. 1.3 The SPEED system

1.7 The SPEED system — features, functions, and auxiliaries

In Fig. 1.3 the basic design process of Fig. 1.2 isillustrated with some of the features alreadymentioned, such as the OUTLINE EDITOR, theWINDING EDITOR, the DESIGN SHEET, and theGRAPHS. At the lower left of Fig. 1.3 is acondensed figure of a dynamometer and a circuitdiagram for an inverter-fed AC machine,referring to the simulation of the drive and itsdigital control found in many SPEED programs.

Fig. 1.3 also shows a number of importantauxiliary functions and links.

The finite-element GoFER — this is a closelylinked finite-element program (PC-FEA) which isprovided to assist with electromagnetic fieldcalculations. “GOFER” stands for “Go to Finite-Elements and Return”. The data transfer fromSPEED to PC-FEA is automatic, although it canbe controlled and modified by the user at allstages of the process.2 “Return” refers to datathat can be passed back to SPEED for directlyimproving the design calculations in severaldifferent ways.

The finite-element process is also used internallyin some SPEED programs as an embeddedsolver. In this case the finite-element results areincorporated in the design calculations withoutdisplaying the flux-plot or other graphicsavailable with the GOFER. Some calculationsrequire this solver.

The material property databases areimportant repositories for material property datain a form that is readable by theSPEED programs. Given the critical importanceof material property data, it is essential thatusers prepare their own data records formaterials used in their products. This data isoften proprietary, particularly when it has beenhard-won by painstaking efforts in the testlaboratory, or by negotiation with suppliers. Thematerial data supplied with the SPEED programsis generic and unqualified. It should only be usedas a “starter”, or as representative of certaingeneral classes of material, for example, “high-silicon steel”, or “neodymium-iron-boron”.

There is an important link to Motor-CAD™ forheat-transfer analysis and cooling calculations.

Finally there are facilities for linkingSPEED data to manufacturing design databasessuch as those used with product inventories.

2 The FLUX™ finite-element software by CEDRAT can readSPEED datafiles of type .bd4, .im1 and .srd directly.Thereafter FLUX™ can be used flexibly for a wide range offinite-element calculations. Moreover, FLUX™ has excellentfacilities for modifying the geometry with holes, flats,notches, and imperfections such as eccentricity.

Page 6 Electric Machine Design using SPEED and Motor-CAD

1.8 Motor-CADMotor-CAD is a unique software for thermalanalysis of electric machines and generators,closely linked to SPEED. The Motor-CAD solveris based on analytical network (lumped-circuit)analysis. Nodes at which temperatures will bepredicted are set at important points throughoutthe machine geometry, e.g., the stator bore,halfway down a stator tooth, halfway through thestator back iron, at the winding hotspot, etc. Thenodes are joined by thermal resistances topredict heat transfer due to conduction, radiationand convection. Power is injected at nodes atwhich losses occur, e.g. winding copper loss,tooth iron loss, stator yoke iron loss, etc. Thenetwork is solved to calculate the steady-statethermal performance. Results appear as nodetemperatures and heat-flows through resistances.

Thermal capacitances are also defined at nodes toaccount for heat storage, so that the transientthermal response can also be calculated, e.g.temperature vs. time at the nodes. Transientcalculations include the thermal response tointermittent operation and user-defined loadduty-cycles.

Several cooling systems are modelled, includingNatural Convection, Forced Convection, LiquidCooling, Submersible, and Through Ventilation.All thermal parameters such as conductionthermal resistances, convection and radiationheat transfer coefficients are calculatedautomatically. The solver quickly calculates thethermal performance, instantaneously for steady-state results and within a few seconds or minutesfor the transient response (depending on thelength of the transient to be calculated).

Motor-CAD also has inbuilt multi-parametricsensitivity analysis capabilities. The sensitivityanalysis is useful for gaining an in-depthunderstanding of the main constraints todissipation, allowing informed design decisionsto be made to improve the cooling. Sensitivityanalysis is often run on manufacturing process-dependent parameters such as the “goodness offit” between stator lamination and housing, orthe goodness of the impregnation system. Theparameters are defined in Motor-CAD usingdescriptions and units that are designed toproduce accurate results with confidence.

Details are provided for parameters based on avast amount of testing and numerical analysisperformed on various machines to gain a detailedknowledge of typical minimum, maximum andnormal values. Default values are set to typicalvalues to give realistic temperature predictions.Subsequent calibration will improve accuracyand allow for particular manufacturingprocesses.

1.9 SPEED and Motor-CADOne thing we find when we run Motor-CAD usingSPEED design data is that the temperaturedistribution is not quite what we assumed orexpected during the SPEED phase of the designprocess. Sometimes the temperatures are lower,but more usually they are higher. Motor-CAD notonly draws our attention to the importance of thecooling and the temperature distribution ; itgenerally suggests improvements in the design,and increases confidence in it.

What Motor-CAD has that SPEED does nothave:

• Loss scaling with speed or torque,without changing the datafile

• Sensitivity analysis

• Vast database of materials and data onheat transfer and fluid flow

• Thermal equivalent circuit with largenumber of nodes and steady-stateschematic

• Axial variation of temperatures

• Temperatures overlaid on the cross-section

• A wide range of housing configurationswith fins, water-cooling jackets, ducts,etc.

• Finite-element thermal diffusion model

• Layered diffusion model for heat transferacross windings in slots

• Duty-cycle editor (including duty-cyclesimported from files).

• Slot geometry editor showing the spacingof conductors .

T.J.E. Miller D.A. Statonwww.motor-design.comwww.speedlab.co.uk