Unit 1 consderations and limitations in design

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1. Unit 1
INTRODUCTION

2. Electrical designer
A electrical designer must be familiar with the,
1.National and international standards
Indian Standard (IS),
Bureau of Indian Standard (BIS),
India British Standard (BS), England
International Electro technical Commission (IEC)
NEMA (The National Electrical Manufacturers Association).
2.Specifications (that deals with machine ratings, Performance requirements etc., of
the consumer)
3. Cost of material and labour
4. Manufacturing constraints etc.

3. Factors for consideration in electrical
machine design
•1.Magneticcircuitorthefluxpath:Shouldestablishrequiredamountof
fluxusingminimummmf.Thecorelossesshouldbeless.
•2.Electriccircuitorwindings:Shouldensurerequiredemfisinducedwith
nocomplexityinwindingarrangement.Thecopperlossesshouldbeless.
•3.Insulation:Shouldensuretroublefreeseparationofmachineparts
operatingatdifferentpotentialandconfinethecurrentintheprescribed
paths.
•4.Coolingsystemorventilation:Shouldensurethatthemachine
operatesatthespecifiedtemperature.
•5.Machineparts:Shouldberobust

4. Additional Factors
•The art of successful design lies not only in resolving the conflict for space
between iron, copper, insulation and coolant but also in optimization of cost
of manufacturing, and operating and maintenance charges
Limitation in design ( saturation, current density, insulation, temperature rise
etc.,)
Customer’s needs
National and international standards
Convenience in production line and transportation
Maintenance and repairs
Environmental conditions etc.

5. Limitations in design
1.Saturation:(Ferro Magnetic Materials )
Higher flux density reduces the volume of iron but drives the iron to
operate beyond knee of the magnetization curve or in the region of
saturation.
Saturation of iron poses a limitation on account of increased core loss and
excessive excitation required to establish a desired value of flux.
It also introduces harmonics.

6. Limitations in design
2.Currentdensity:
Highercurrentdensityreducesthevolumeofcopperbutincreasesthelosses
andtemperature
3.Temperature:
Posesalimitationonaccountofpossibledamagetoinsulationandother
materials
Lifeoftheinsulatingmaterialdependsontemperatureriseofmachines.
Propercoolingandventilationtechniquesarerequiredtokeepthe
temperaturerisewithinsafelimits.

7. Limitations in design
4.Insulation (which is both mechanically and electrically weak):
posesalimitationonaccountofbreakdownbyexcessivevoltagegradient,
mechanicalforcesorheat.
Shouldwithstandelectrical,mechanicalandThermalstresses(eg
transformer)
Sizeoftheinsulationdecidesthemaximumvoltagestressandthe
mechanicalstress.
Thickerinsulationisusedforlargesizeconductorsthensmallsize
conductors.

8. Limitations in design
5.Highefficiencyandhighpowerfactor
posesalimitationonaccountofhighercapitalcost.(Alowvalueof
efficiencyandpowerfactorontheotherhandresultsinahigh
maintenancecost).
Poorpowerfactorresultsinlargevaluesofcurrent,conductorsize
increases.(egIM)
ForhighefficiencythemagneticandelectricLoadingsshouldbesmall
whichrequireslargeamountofmaterials.Capitalcostishighbut
runningcostislow.

9. Limitations in design
6.Mechanicalstrengthofthematerials
posesalimitationparticularlyincaseoflargeandhighspeedmachines.
rotorslotdimensionsshouldbeselectedsuchthatthemechanical
stressesdevelopedatthebottomoftherotorteethshouldnotexceed
themaximumlimit.
Sizeoftheshaftshouldbesuchthatitshouldnotgiverisetoexcessive
unbalancedmagneticpullwhendeflected.
Sizeoftheshaftdependsonthecriticalspeed.

10. Limitations in design
Bearingsaresubjectedtotheactionsofrotorweightexternalloads
inertiaforces.(Verticalorhorizontalmounted)
Constructionshouldbesimple,technologicallygoodandeconomicalwith
littlelabourwithoutcompromisingperformance,reliabilityanddurability
.

11. Limitations in design
7.Commutation
Commutation conditions limits the maximum output that can be taken
from a machine .
8.Consumer Specifications .
9.Standard specifications.