DC Motor construction and working principle.pdf

Details of DC motor

1. Mechanic Electric Vehicle
(Motors)
Omkar Kore

2. DC Motor Construction and Working

3. •Electricmotorsarethemostimportantelementoftoday's
industrialworld.
•Fromasimpledrillmachinetoasophisticatedroboticarm
electricmotorsareusedeverywhere.

4. Types
There are two types of electric motors-
1.AC Motors
2.DC Motors
•In these, because of some important characteristics like fast reaction, better speed
control, simple construction, DC motors are very popular in automatic machines.
AC motor
DC motor

5. Construction
•The outer part of the motor is
generally static, which is
known as stator.
•Stator consist of a frame, and
it contains “Pole Shoes”
which are projected inward.

6. Construction
•Core of these poles are made from silicon
steel on which insulated copper wire is
wound to make windings.
•These poles are bolted and fixed inside the
frame.
Core

7. Construction
•When DC current is pass through the windings it creates a static magnetic field.
•There are two types of pole in a DC machine.
1.Main/ Field Pole
2.Inter Poles

8. Construction
•Theconnectionsofthesepolesarebroughtoutthroughconnectorsin
theterminalbox,sothatwecangiveelectricsupplytothemandeven
dothecheckforthefault.
•Main poles create static magnetic field, when current is pass to its
winding.

9. Construction
•Inthismagneticfieldrotatingpartofmotorlies,knownasRotororArmaturewhich
ismadebynumberofstampingsofhighlypermeablemateriali.e.siliconsteel,
whichallowsmagneticfieldtopassthroughiteasily.

10. Construction
•Slots are cut on the outer periphery of rotor or we can say “armature”, which
receive coils/windings made up of copper conductor.
•Each coil gets connected to an external DC source by a pair of commutator
segments arranged in the form of a Ring.

11. Construction
•This complete assembly is housed over a cylindrical shaft made up of high quality
steel.

12. Construction
•Because of the bearings at both side of the shaft the rotor is capable of rotate
between the field poles.

13. Working
•Whenelectriccurrentis
forcedtopassthroughthe
rotorconductorsbyasetof
carbonbrushesthrough
commutatorsegments,it
createstheirownmagnetic
fieldwhichtriestodistorts
themagneticfield,created
bythefieldpole.

14. •Duetointeractionbetweentwomagneticfieldsi.emagagnticfieldofmain
polesandtherotorconductors.ElectromagneticForcesactontherotor
conductorsandtheseforcesacttangentiallyontherotorsurface.
•Thereforeatorqueisproducedattherotorshaftandtherotorrotates.
.

15. •To understand the process more easily lets take a example of single loop having a
set of its own commutatorsegment.
Commutator
segments

16. •DuetotheDCvoltageappliedbyanexternalDCsourcecurrentwillflowinthe
coilingivendirectionfrompositivetonegativepotentialandbyFleming'sleft
handrule,wecanfindthatthissideofcoilreceiveforceinupwarddirection
andthissidewillreceiveadownwardforceandhencethelooprotates.
Current

17. •Duringtherotationofloopyoucanfindthatcommutatorsegmentscomesin
contactwithbrushesofoppositepolarityonebyone.
•Thiswaytheconductorofleftsidealwayscarrycurrentingivendirection,and
ofrightsideinoppositedirection.

18. •Thishelpstomaintainthecontinuousrotationofcoil.
•Wecanalsofindthatmagnitudeofforceonthecoilismaximuminthisregion
afterthat,magnitudereducereducesconsiderably.
•Thiscauseuneventorqueandmomentofrotor.
•Tomake“maximumtorque”alwaysavailableattheshaftofrotormultiple
numberofcoilswithapairofcommutatorsegmentsareplacedintherotor.

19. •Whenonecoilpassesthroughtheregionofmaximumtorquenextcoilwilltakeitsplace.
•Thiswayshaftofrotoralwaysprovidehigherandsmoothtorque.
•Coilsareconnectedtocommutatorsegmentinsuchawaythateveryinstantoftimeeachandeverycoil
carriescurrent,butthesidesofcoiltocomesatthelefthandsidecarriescurrentinonedirectionandthe
sideatrighthandcarriescurrentinoppositedirectionrespectiveoftherotorposition.
•Thiscanbeachievedbythelaporwaveconnectionwindings.
•ToensurethatthecurrentgiventothecommutatorsegmentswillnotreachtotheshaftMicaInsulation
isplacedbetweenthem.

20. •InsmallDCmotorpermanentmagnetcanbeusetocreatestaticmagneticfield,
buttheycanloosetheirmagnetismduetoheating,vibration,oraging,that’swhy
inhigherratingmotorelectromagnetsareusedandtheirmagnetic
fielddensitycanbecontrolledtocontroloutputtorque.

21. Letshavealookatthecoildesign,ifasingleturncoilofthickwireisusedhere
thenitallowhighercurrentandgivehighertorque.Whereas,ifmulti-turncoilof
thinwireisusedthencurrentandtorqueisalsoreducedbutwegethigherspeed
Single turn coil Multi-turn coil

22. •That means at the time of manufacturing we can decide whether we want high
torque low speed machine or low toque high speed machine.
•Here the work of interpole is to reduce sparking at the brushes over commutator
ring due to the effect of armature reaction.
•To energized the field poles we can use same DC source which runs our DC
motor or we can use a separated source , the method which is used will decide
the type of DC motor.
High torque low speed machine Low toque high speed machine

23. •At last all terminals are brought out through terminal box.

24. •And, “end covers” are fixed form both side, which holds bearings at both ends of
shaft.

25. •SothisisabouttheConstructionandWorkingofDCmotor
•YoucanwatchvideoofthisPresentationathttps://youtu.be/E9X_ZQDt670
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