53759762 ee2403 special electrical machines question bank

8/12/2019 53759762 Ee2403 Special Electrical Machines Question Bank

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St. Josephs College of Engineering

St. JOSEPHS COLLEGE OF ENGINEERING, CHENNAI - 119

DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING

QUESTIONS BANK EE 2!" SPECIAL ELECTRICAL MACHINES

UNIT I S#NCHRONOUS RELUCTANCE MOTORS

PART - A

1. What are the different types of reluctance machines? Compare them.Reluctance machines are synchronous machines with certain unique features pertaining

primarily to their douly salient stator and rotor pole design. !he machines are roust" usesimple construction" and are suitale for high speeds. !hey include two types" switched andsynchronous.!hesynchronous reluctance motor is used in industry" where motors are required to operate

in synchronism or where highly regulated speed control is required using a #ariale$frequency dri#e. !he motors pro#ide constant" un#arying %or highly controlled& speed fromno load to full load with no slip.!heswitched reluctance motor %SR'& is e(cited y current pulses applied to each phase. !hecurrent pulses are applied ased on precise rotor position. !he inductance profile istriangular" with ma(imum inductance when it is in an aligned position. When #oltage isapplied to the stator phase" the motor creates torque in the direction of increasing inductance.)oth synchronous and SR's require a position sensor unless new" sensorless technology isemployed. *osition sensors are a source of increased cost and reduced reliaility.+. What is the principle of operation of reluctance machine?,n reluctance machines" torque is produced y the tendency of the rotor to mo#e to a positionwhere the inductance of the e(cited stator winding is ma(imi-ed %i.e." rotor tooth aligns withacti#e stator phase to minimi-e reluctance&. !he rotor is typically constructed of softmagnetic iron shaped so as to ma(imi-e the #ariation of inductance with rotor position.pposite poles form a phase and the phases are magnetically independent of one another.!he machines tend to e noisy/ a characteristic that has limited their applications in the pastand has also limited their use currently in #ehicles. Research has een on$going for years inan attempt to address the noise issue" ut little has een accomplished in actual noisemitigation. Reluctance machines are relati#ely low$cost machines" and they generally do notcontain *'s.0. What are the properties of Reluctance motor?

a. Comined reluctance and magnet alignment torque. ield wea2ening capailityc. 3nder e(cited operation for most loaded conditiond. 4igh inductancee. 4igh speed capailityf. 4igh temperature capaility

5. What are the #arious stator current modes used in synchronous reluctance motor?a. 3nipolar current modes

. )ipolar current modes6. 'ention the applications of distriuted anisotropy cage rotor of synchronous

reluctance motor?

!hese rotors are used for line 7 start %constant #oltage and frequency& applications.

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;. 'ention the applications of distriuted anisotropy Cageless rotor of synchronousreluctance motor?

!hese rotors are used for #ariale speed applications.


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,se the supply current which has two components ,dand ,q,d B Girect a(is current,q B Huadrature a(is current

sB Synchronous speed in rad sec.d B Girect a(is reactance

q B Huadrature a(is reactance16. S2ewing is required for Synchronous reluctance motor. Justify?

t the time of starting" reluctance motor are suIected to logging due to the saliency ofmotor. !his can e minimi-ed y the s2ewing of the rotor parts.

1;. What are the design considerations in Synchronous reluctance motor? *ower factor Copper loss and core loss Cost Efficiency

1


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1@. 1@ 4*" 5 pole" +5@A" ;@4-" reluctance motor operating under rated loadcondition has a torque angle of 0@K. Getermine%a& :oad torque on shaft%& !orque angle if the #oltage drops to ++5A%c& or the ao#e torque angle" will the rotor pullout of synchronism.

Solution

%a& * B ;.1== rads =

mNP

Ts

L == 6

%6'&

%& = >@0.51rel %


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stepping motor rotates through a fi(ed angle for e#ery pulse. !he rated #alue of this angleis called the step angle and e(pressed in degrees.

. Gefine Getent torque of stepper motor?,t is defined as the ma(imum static torque that can e applied to the shaft of an une(citedmotor without causing continuous rotation.

1@. Gefine *ull 7 in torque of stepper motor?!hese are alternati#ely called the starting characteristics and refer to the range of frictionalload torque at which the motor can start and stop without loosing steps for #ariousfrequencies in a pulse strain.

11. Gefine *ull 7 out torque of stepper motor?!hese are alternati#ely called the slewing characteristics. fter the test" motor is started y aspecified dri#er in the specified e(citation mode in the self starting range" the pulsefrequency is gradually increased/ the motor will e#entually run out of synchronism. !herelation etween the frictional load torque and the minimum pulse frequency with which themotor can synchroni-e is called pull 7 out characteristics.

1+. Gefine Slewing frequency of stepper motor?!his is defined as the ma(imum frequency %stepping rate& at which theloaded motor can run without losing steps is alternati#ely called the ma(imum slewingfrequency.

10. Gefine Stepping frequency of stepper motor?!he speed of rotation of a stepping motor is gi#en in terms of the numer of steps per secondand the term stepping rate is often used to indicate speed.

15. Gefine 'a(imum starting torque of stepper motor?!his is alternati#ely called as ma(imum pull 7 in torque and is defined asthe ma(imum frictional load with which the motor can start and synchroni-e with the pulsetrain of frequency as low as 1@ 4-.

16. Gefine 'a(imum starting frequency of stepper motor?,t is the ma(imum control frequency at which the unloaded motor can start and stop withoutlosing steps.

1;. Gefine 'a(imum starting frequency of stepper motor?

,t is the ma(imum control frequency at which the unloaded motor can start and stop withoutlosing steps.1. Gefine 'a(wells stress,t is defined as cur#ing of magnetic lines of force at the end of the poles of the stator.

+@. Why interlea#ing is done in a stepper motor?,nterlea#ing is done in the stepper motor to decrease the step angle and thus increasing the

resolution.+1. E(plain AR type stepper motor?



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,t is a asic type of stepping motor in which the motor step y step rotation is achie#ed whenthe rotor teeth and stator teeth are in alignment such that the magnetic reluctance isminimi-ed and this state pro#ides a rest or equilirium position.

++. E(plain *' type stepper motor? stepping motor using permanent magnet in the rotor for step mo#ement is called a

permanent magnet motor.+0. E(plain 4yrid type stepper motor? hyrid motor has permanent magnet in its rotor. !he term hyrid deri#es from the fact thatthe motor is operated under the comined principles of permanent magnet and #arialereluctance motor.

+5. What is micro stepping and how is it achie#ed?,t is possile to sudi#ide on natural step into many small steps y means of electronics. !hismethod is 2nown as mini step or micro step.

+6. What is the effect of magnetic saturation in stepper motor? !he efficiency is impro#ed nd the losses are reduced.

+;. What are the classifications of dri#e system of stepping motor? pen loop system Closed loop system

+


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0(1@$52g 7 m+from f1B 1@@@4- to f+B +@@@4- during 1@@msec. !he frictional torque!fis @.@6 9m and the step angle is 1.=K.Solution

&5%155+.@

&5%@015.@1=@

L=.11=@

Ldeg

MmNT

MradreesinAngleStep

m

s

=

===

11%& What is the ma(imum acceleration of an initial load of 5(1@$52g 7 m+dri#en y amotor torque of @.0 9m. rictional loads are negligile and the step angle is 0K.

&;%[email protected]

&+%

+5Mstepsx

dt

dfonAcceleratiMaximum

Mdt

dfJT

sm

==

=

UNIT III S4ITCHED RELUCTANCE MOTOR

PART - A1. What is switched reluctance motor?!he switched reluctance motor is a douly salient" singly e(cited motor. !his means that it

has salient poles on oth the rotor and the stator" ut only one memer %usually the stator&carries windings. !he rotor has no windings" magnet is or cage windings ut is uilt up fromstac2s of salient pole laminations.

+. What is meant y self control?,n the open loop system" if a load is suddenly applied" the rotor momentarily slow down"

ma2ing the torque angle delta increase eyond >@ and leading to loss of synchronism. ,f therotor speed adIusts the stator frequency the dri#e system is called as self controlled dri#e.

0. What are the ad#antages of Switched Reluctance motor?

a. Rotor is simple and it tends to ha#e a low inertia. !he stator is simple to windc. ,n most applications the ul2 of the losses appear on the stator" which is

relati#ely easy to cool.d. Gue to the asence of magnet the ma(imum permissile rotor temperature

may e higher than in *' motors.e. 3nder fault conditions the open circuit #oltage and short circuit current are

-ero or #arying small.f. E(treme y high speeds are possile

5. What is the difference etween Switched Reluctance motor and #ariale reluctancestepper motor?

S5t'(0 R*'t&' /$t$) 6)7 )*'t&' +t88) /$t$)

Conduction angle for phase current iscontrolled and synchroni-ed with the rotor

position" usually y means of a shaftposition sensor

Stepper motor is usually fed with a squarewa#e of phase current without rotor

position feedac2.

!he SR' is designed for efficient powercon#ersion at high speed

,t is usually designed as a torque motorwith a limited speed.

6. What are the disad#antages of a Switched Reluctance motor?a. !he asence of free *' e(citation imposes the urden of e(citation on the

stator windings and the controllers and increases the per unit copper losses.. is limited

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c. torque ampere is limitedd. 9on uniform nature of the torque production which leads to torque ripple and

may contriute to acoustic noise.

;. Gistinguish etween co$energy and field energy

Co$energy ield energyCo$energy is defined as

=i

diw@

1

ield energy is defined as

=

@

idwf

. Ni#e asic features of Switched Reluctance motor.!he switched reluctance motor is a douly$salient" singly$e(cited motor. !his means that ithas salient poles on oth the rotor and the stator ut only one memer %usually the stator&carries windings. !he rotor has no windings" magnets" or cage windings" ut is uilt up froma stac2 of salient$pole laminations.

:ow inertia and simple manufacturing :osses appear only on the stator and easy to cool 9o magnets and so permissile rotor temperature is higher than in *' motors. !orque is independent of the polarity of phase current. Reduction in no of

semiconductor de#ices in controller pen circuit #oltage and Short circuit current are -ero or #ery small under faulty

condition. ,mmune from shoot through failure. 4igh starting torque" e(tremely high speeds possile.

1@. Write the relations etween the speed and fundamental switching frequency.

f B n 9r B %r.p.m.;@& 9r 4-9r B 9o. of rotor poles"

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,f there are q phases there are q 9r steps per re#olution and the step angle or stro2e is gi#eny O B + P %q 9r& rad.

!he no of stator poles usually e(ceeds the no of rotor poles.11. What is co$energy?

,n the Q 7i cur#e of a motor" the area etween the cur#e and hori-ontal i a(is is the co$energyW and the other part is the stored field energy W f.1+. Ni#e the e(pression for torque of a Switched Reluctance motor.!he torque is gi#en y ! B W MT iBconstr y ! B Wf MT QBconstWith magnetic saturation negligile and with Q 7i cur#e straight line "Q B : iW B Wf B %U& : i+

! B %U& i+ d: d M 9m10. E(plain torque speed characteristics of Switched Reluctance motor.or speed elow D the torque is limited y the motor current. 3p to ase speed it is

possile to maintain the torque constant y means of the regulators. ,n the speed range elowD the firing angles can e chosen to optimi-e efficiency of minimum torque ripple. !hecorner point or ase speed w is the highest speed at which ma(imum current can esupplied at rated #oltage with fi(ed firing angle. ,f these angles are still 2ept fi(ed" then thema(imum torque at rated #oltage decreased with speed squared. 4owe#er if the conductionangle is increased there is a considerale speed range o#er which ma(imum current can still

e forced into the motor and thus sustain the torque at a le#el high enough to maintainconstant power change. !his is shown etween points ) and *. !he angle Gis dwell orconduction angle of the main switching de#ice in each phase. ,t should generate can e

possile to maintain constant power up to +.0 times ase speed.

15. What are the types of power controllers used for Switched Reluctance motor? 3sing two power semiconductors and two diodes per phase %n V 1& power switching de#ices and %n V 1& diodes per phase *hase windings using )ifilar wires Gump 7 C 7 con#erter Split power supply con#erter

16. Why rotor position sensor is essential for the operation of Switched Reluctancemotor?,t is normally necessary to use a rotor position sensor for communication and speed

feedac2. !he turning 9 and operation of the #arious de#ices of power semiconductorswitching circuit are influenced y signals otained from rotor position sensor.

1;. What are the two types of current control techniques? 4ysteresis type control *W' type control

1


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Stator poles carrying field coils. !he field coils of opposite poles are connected in seriessuch that mmfs are additi#e and they are called X*hase windingY of Switched Reluctancemotor.1>. What is 4ysteresis current control?!his type of current controller maintains a more or less constant throughout the conduction

period in each phase. !his controller is called hysteresis type controller.+@. Gefine Chopping mode of operation of Switched Reluctance motor?,n this mode" also called low 7 speed mode" each phase winding gets e(cited for a period

which is sufficiently long.+1. Gefine Single pulse mode of operation of Switched Reluctance motor?,n this mode" also called high 7 speed mode" the current rise is within limits during the small

time inter#al of each phase e(citation.++. What is the step angle of an 6 phase Switched Reluctance motor and commutation

frequency in each phase for the speed of ;@@@ rpm. SR' ha#ing 1@ stator poles and 5rotor poles.

S$*t$&:

Step angle % & B % +P q9r& B % 0;@K 6L5& B 1=K

Commutation frequency at each phase B % 9rL D & +P B % 5L;@@@& ;@ B 5@@ 4-.D B +P9T

+0. What are the merits of Gump C 7 Con#erter? !his topology uses lower numer of switching de#ices and has only one

switch #oltage drop. !he con#erter has full regenerati#e capaility !here is faster demagneti-ation of phases during commutation

+5. What are the merits of split power supply Con#erter?

,t requires lower numer of switching de#ices. !here is faster demagneti-ation of phases during commutation

+6. What are the merits of classic con#erter? Control of each phase is completely independent of the other phases !he energy from the off going phase is feedac2 to the source" which

results in useful utili-ation of the energy.PART B

1. E(plain the construction and wor2ing of Switched Reluctance motor?+. With a loc2 diagram" e(plain the importance of closed loop control of SwitchedReluctance motor.0. Gescrie the 4ysteresis type and *W' type current regulator for one phase of SwitchedReluctance motor.5. E(plain in detail aout microprocessor ased control of Switched Reluctance motor.6. Gescrie the #arious power controller circuits to Switched Reluctance motor and e(plainthe operation of any one scheme with suitale circuit diagram.;. Gescrie the #arious operating modes of Switched Reluctance motor.. Giscuss the ad#antages and disad#antages of Switched Reluctance motor.1@. Giscuss in detail the frequency of #ariation of the inductance of each phase winding ofSwitched Reluctance motor.

UNIT I6 PERMANENT MAGNET BRUSHLESS D.C. MOTORSPART - A

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1. Why adIustale speed dri#es are preferred o#er a fi(ed speed motor?!he common reasons for preferring an adIustale speed dri#es o#er a fi(ed speed motor are1. Energy sa#ing e.g. an or pump flow process+. Aelocity and position control e.g. Electric train" portale tools" washing machine0. melioration of transients Starting and stopping of motors produce sudden transients. ,t

can e smoothened using adIustale speed dri#es.

+. What is the structure of an adIustale speed dri#e system?!he general structure of a motion control system or dri#e consists of the following elements

1. the load+. the motor0. the power electronic con#erter/ and5. the control.

0. Write riefly aout the construction and types of a )rushless GC machines.)rushless *' machines are constructed with the electric winding on the stator and *'s onthe rotor. !here are se#eral con#entional *' machine configurations and other more no#el

concepts concei#ed in recent years to impro#e performance. !he configuration of a *'machine and the relationship of the rotor to the stator determine the geometry and the shapeof the rotating magnetic field. *' machines in which the magnetic flu( tra#els in the radialdirection are classified as radial$flu( machines. !hey are cylindrical in shape" and the rotor isusually located inside the stator ut can also e placed outside the stator. *' machines inwhich the magnetic flu( tra#els in the a(ial direction are classified as a(ial$gap machines.!hey can ha#e multiple dis2 or panca2e$shaped rotors and stators. !he stator$rotor$statorconfiguration is typical.!he shape of the ac2$emf is a fundamental characteristic. !he shape of the ac2$emf of *'machines matches that of the dri#ing currents and can e trape-oidal or sinusoidal. lthough

oth 2inds are rushless and synchronous" *' machines with trape-oidal ac2$emf are oftencalled rushless dc motors %)GC's&" while *' machines with sinusoidal ac2$emf arereferred to as *' synchronous motors.5. What are the ad#antages of *' machine?,n general" *' machines ha#e a higher efficiency as a result of the passi#e" *'$ased fielde(citation. *' machines ha#e the highest power density compared with other types ofelectric machines" which implies that they are lighter and occupy less space for a gi#en

power rating. !he amount of magnet material that is required for a gi#en power rating is a2ey cost consideration. !he cost of magnet material is high compared with the cost of theother materials used in electric motors" and design attriutes that minimi-e the requiredamount of magnet material are important considerations in motor selection. !he stators of

*' machines are generally faricated in the same manner as induction machine stators/howe#er" modifications are sometimes necessary" such as the design of a stator lamination toaccommodate high flu( density.6. What are the types of *' machines? Compare.

1. ,nterior *' machine and +. Surface mounted *' machine.,n contrast to surface$mounted *' machines" uried$magnet or ,*' machines offer certainad#antages" their suitaility for high$speed operation eing perhaps the most o#ious. !hefundamental difference is that in a surface$mounted rotor" the flu( cannot e mo#edtangentially within the magnet to pro#ide a rotor$to$stator phase ad#ance" while in a uried$magnet rotor the flu( cane mo#ed tangentially ao#e the magnets in the rotor iron so that aquite significant rotor$to$stator phase ad#ance can result. ,*' machines can pro#ide torque

under certain conditions with less ,+

R losses than other *' machines.



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;. S2etch different types of ,*' machines


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properties" ut the onded #ersion can e made in more shapes and si-es. !he sinteredneodymium magnet ranges in strength from a )4ma( of +=$6@ mega$gauss$ersted%'Ne&. )onded magnets are cominations of magnetic powders and either thermo$elastomers or thermoplastic resins. !hese lended materials can e inIection molded orcompressed. Compression onded magnets ha#e greater magnetic output ut can e shaped

into only simple geometries. 9eodymium magnets offer the est #alue in performance andcost/ howe#er" designers should e aware that this type of magnet is temperature$sensiti#eand susceptile to o(idation if not properly coated. !he magnet is high in )r" 4c" and)4ma(. !ale 6.1 compares 2ey properties of selected neodymium magnets and the most

powerful samarium coalt magnets. 9eodymium magnets clearly ha#e a potential for greatermagnetic strengths ut do not ha#e the high temperature capaility of the samarium coaltmagnets. Gepending on the specified grade" neodymium magnets may ha#e a wor2ingtemperature of up to +@@ C and samarium coalt magnets a wor2ing temperature of up to 0. What are the methods for containing the magnets in *'):GC motor?s the ase speed increases" magnet containment ecomes a critical prolem. or a machine

with surface$mounted magnets operating as a rushless direct current motor %)GC'& withtrape-oidal ac2$emf" there are four options1. Wrap the magnets with a suitale )$stage.+. Encase the rotor in a non$magnetic can.0. 3se an Xinside$outside configurationY in which the stator is inside the structure containingthe magnets and rotor laminations. !he centrifugal forces on the magnets are then restrained

y this structure.5. 3se an a(ial gap configuration. ,n this arrangement" the stator and rotor are in the shape ofa toroid. !he armature current is in the radial direction and the magnets are charged in thea(ial direction. !he air gap is in the a(ial direction and the centrifugal force on the magnets isin the radial direction. !hus a restraining ring can e used that does not impact the air gap#olume.1@. Compare rushless GC motor with *.'. commutator motor.

B)*+(++ DC /$t$) P.M. C$//*tt$) /$t$)

1. 9o )rushes. 'aintenance prolems%R," spar2ing" ignition and fire accidents&eliminated.+. 'ore cross sectional a#ailale forarmature windings. Conduction of heatthrough the frame is impro#ed.

0. ,ncrease in electric loading is possile"pro#iding a greater specific torque. 4igherefficiency.5. Space sa#ing" higher speed possile"with reduced inertia.6. 'a(imum speed limited y retention ofmagnet against centrifugal force.;. Shaft position sensor is a must.


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switch conducts for the period 1+@ or 1=@ degree as per the mode. Commutation from oneconducting de#ice to another ta2es place at e#ery ;@ degree inter#als.1+. Why the shape of the emf wa#eform of a ):GC is trape-oidal?!he ideal shape of the emf wa#eform is rectangular. !he effect of slotting and fringingcauses its corner to e rounded and hence the shape is trape-oidal with flat top portion with

1+@ degree

10. Ni#e the emf and torque equations of the square wa#e ):GC motor.!he emf equation is gi#en y E B 2\D and the torque equation is gi#en y ! B 2\,.where 2 is the armature constant depending on the numer of turns in series per phase in thearmature winding"D is rotor speed in rad sec and\ is the flu( % mainly contriuted y the *ermanent 'agnet on the rotor&., is the load current.15. Ni#e the e(pression for torque speed characteristics of ):GC motor.!he emf equation is gi#en y E B 2\D and the torque equation is gi#en y ! B 2\,.

E B A $ ,Rt no load " , B @" so the no load speed D@is gi#en y D@ BA %2\&%Since at no load ,B@" EB AB 2\ D@ &!he stall torque% motor at -ero speed& is gi#en y !@B 2\,@"where ,@ is the stall current.t -ero speed E B @ " AB ,@R" R B A ,@.E B A$ R,]\D B A 7 %A ,@& ,B A%1$, ,@&

D B %A]\&% 1$, ,@&B D@ %1$! !@& since ! is proportional to ,.

!his is the equation descriing the torque speed characteristics of ):GC motor.16. Compare 1+@ degree and 1=@ degree operation of ):GC motor.!he 1=@ degree magnetic arc motor uses 1+@ degree mode of in#erter operation. !he motorwith 1+@ degree magnetic arc uses 1=@ degree mode of in#erter operation.,n 1=@ degree mode of in#erter has 1.6 times copper losses ut produce same torque withonly +0 of magnetic material. 'otor operation is less efficient.1;. Ni#e the e(pression for self and mutual inductances of a ):GC motor.Self inductance is gi#en y :g B %Qi& B %P^@9+lr1 &%+gY& wheregY B g V lm ^recg B ]cg

9 B 9umer of conductors in the slot.

, B currentlmB magnet length in radial directiong B air gap" gY B air gap including radial thic2ness of the magnet^rec B relati#e recoil permeaility.'utual inductance is gi#en y 'gB $ %10& :g1


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!hese de#ices operate at #ery high switching frequencies for *W' method of operation. !heduty cycle of the *W' decides the a#erage #oltage applied to the motor and hence the speedis adIusted. !hese de#ices are easy to commutate y using microprocessor or microcontroller

ased software. %)ase dri#e&1>. Write the dynamic equations of the *'):GC motor.

!he dynamic model equations of *'):GC motor is gi#en ydiadt B% #an7 R ia7 ea %M& & :didt B% #n7 R i7 e %M& & :dicdt B% #cn7 R ic7 ec%M& & :dDdt B !e7 !l7 ) D T JdMdt B * D +where the !orque de#eloped is gi#en y!e B %ea%M&iaVea%M&i V ea %M& ic& D!: B :oad torque applied" ) is the coefficient of friction and J is the moment of inertia.+@. What are the relati#e merits and demerits of rush less GC motor dri#es?'erits

Commutator less motor Specified electrical loading is etter 4eat can e easily dissipated 9o spar2ing ta2es place due to rush Source of E', is a#oided

Gemerits o#e 1@ 2W" the cost of magnet is increase Gue to centrifugal force the magnet may come out.

+1. 4ow the direction of rotation is re#ersed in case of *'):GC motor!he direction of rotation can e re#ersed y re#ersing the logic sequences in *'):GC

motor++. What are the difference etween con#entional GC motor and *'):GC motor?

DC PMBLDC

)rushes are present )rushes are not presentSpar2ing may occur due to rush Spar2ing will not occur as rush is not

present)rush tend to produce R1 R1 prolem does not occur !here is a need for rush maintenance 9o need of rush maintenance+0. Write the torque and emf equation of square wa#e rushless motor

!lr"NT

lr"Ne

gphe

gpn

1

1

5

+

=

=

+5. What are the #arious 2inds of permanent magnets?!here are asically three different types of permanent magnets which are used in small GC

motors lnico magnets errite or ceramic magnet" and Rare $ earth magnet %samarium 7 coalt magnet &

+6. )ring out the differences etween con#entional and rushless GC motors?Gescription Con#entional motors )rushless GC motors'echanical structure ield magnets on the stator ield magnets on the rotor.

Similar to C synchronousmotor.

Gistincti#e features Huic2 response and :ong 7 lasting



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e(cellent controllaility Easy maintenance

Commutation method 'echanical contact etweenrushes and commutator

Electronic switching usingtransistors

+;. Write the difference etween square wa#e *'): and sine wa#e *'): motor.S.9o. Square wa#e *'): Sine wa#e *'): motor 1. ,t has rectangular distriution of

magnetic flu( in the air gap.,t has sinusoidal or quasi 7 sinusoidaldistriution of magnetic flu( in the air gap.

+. ,t has rectangular current wa#eforms. ,t has sinusoidal or quasi 7 sinusoidalcurrent wa#eforms.

0. ,t has concentrated stator winding ,t has quasi 7 sinusoidal distriution ofstator winding %conductors& which is short

pitch and distriuted or sometimesdistriuted in some cases.

+


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;. E(plain in detail the #arious rotor position sensors used in permanent magnet rushlessGC motor.. E(plain in detail the magnetic circuit analysis of rushless GC motor on open circuit.

1@. Giscuss in detail the #arious dri#ing circuits used in permanent magnet rushless GCmotor.UNIT 6 PERMANENT MAGNET S#NCHRONOUS MOTORS

PART - A

1. Compare *'S' and *'):GC motors.PM B)*+(++ DC /$t$) PMSM

1. Rectangular distriution of magneticflu( in the air gap.+. Rectangular current wa#eforms.

0. concentrated stator windings.

1. Sinusoidal or quasi7sinusoidaldistriution of magnetic flu( in the air gap.+. Sinusoidal or quasi$sinusoidal currentwa#eforms.0. Huasi$sinusoidal distriution of statorconductors. %short pitched and distriutedor concentric stator windings&

+. Ni#e the e(pression for torque and emf of a *'S' motor.! B %0+& , _+ P r1 l B9ssin%`&T+" where ` is the torque angle V#e for motoringEphB + P %2w19ph& '1 f T _+0. Compare the performance of *'S' with ):GC motor.With equal r.m.s. phase currents the torque of the square wa#e motor e(ceeds that of sinewa#e motor y a factor 1.5


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s B Synchronous reactance' B 'agneti-ing reactancel B :ea2age reactance


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Rolling mills Cement mills Ship propeller Electric Aehicles Ser#o and rootic dri#es Starters generator for air craft engine

10. E(plain the difference etween synchronous motor and *'S'S%&'()$&$*+ M$t$) PMSM

0 phase C or si( step #oltage or currentsource in#erter is used as supply

0 phase sine wa#e ac or *W' ac is used assupply

!his type of motor is used in #ery largecompressor and fan dri#es

4ere it is used in low integral 4* industriesdri#es" fier spinning mills.

15. What are disad#antages of *'S' relati#e to the commutator motor?

9eed for shaft position sensing ,ncreased comple(ion in the electronic controller

16. What are the assumptions made in deri#ation of emf equation for *'S'? lu( density distriution in the air gap is sinusoidal Rotor rotates with an uniform angular #elocity of Dm% radsec& rmature winding consists of full pitched" concentrated similarly located

coils of equal numer of turns1;. What are the ad#antages of load commutation?

,t does not require commutation circuits requency of operation can e higher.

,t can operate power le#els eyond the capaility of forced commutation.1. What are the features of closed$ loop speed control of load commutated in#erter fedsynchronous motor dri#e?

4igher efficiency. our quadrant operation with regeneration ra2ing is possile 4igher power ratings and run at high speeds % ;@@@ rpm&

+@. Write down the emf e(pressions of *'S'?

EphB 5.55 f m]w1!ph#olts!his is the rms #alue of induced emf per phase" wheref B requency in 4ert-" mB flu( per pole

]w1B Winding factor" !ph B !urns per phase+1. What is load commutation?Commutation of thyristors y induced #oltages of load is 2nown as Xload commutationY.

4ere" frequency of operation is higher and it does not require commutation circuits.++. What is meant y slotless motor?,n slotless motor" the stator teeth are remo#ed and resulting space is partially filled with

addition copper.+0. Gistinguish etween self control and #ector control of *'S'?

Jayarama *radeep 8 9.C.:enin 1>


20/20


S.N$. S; '$&t)$ 6't$) '$&t)$

1. Gynamic performance is poor Gynamic performance is etter+. Control circuit is simple Control circuit is comple(+5. State the two classifications of *'S'?

Sinusoidal *'S' !rape-oidal *'S'

+6. Write down the e(pressions for the self and synchronous reactance of *'S'?sB % 0 P ^@9s+l r1D& = p+g+

PART B

1. Geri#e the E' equation of ):*' Sine wa#e motor.+.E(plain the microprocessor ased control of permanent magnet synchronous motors with

a neat loc2 diagram.0.Geri#e the torque equation of ):*' Sine wa#e motor.

5.E(plain in detail the #ector control of permanent magnet synchronous motor.6.With neat s2etch" discuss the torque 7 speed characteristics of *'S'.

;.What are the ad#antages and disad#antages of permanent magnet synchronous motor?.What are the differences in the constructional features of *'):GC and *'S'[email protected](plain the principle of operation of a sine wa#e *' synchronous machine in detail.

53759762 ee2403 special electrical machines question bank

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