Machines Qb

7/23/2019 Machines Qb

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EI6402 Electrical Machines

UN I T - I DC M A C H I N E S

1.What is an electric motor?

Electric motor is a machine which converts electrical energy into mechanicalenergy.2.Define DC motor.DC motor converts d.c. electrical input into mechanical output.

. What is the !asic "rinci"le of o"eration of a #c motor?

The basic principle of operation of a dc motor is that, a current carryingconductor placed in a

magnetic field experiences a force tending to move it.

$.Define !ac% emf.When a motor rotates, the conductors housed in the armature also rotate and cut the magnetic lines

of force. So an emf is induced in the armature conductors and this induced emf opposes the supply

voltage as per en!"s law. This induced emf is

called bac# emf $or% counter emf.

&. What is the nat're of the c'rrent flo(in) in the armat're con#'ctors of a #c

motor?&lternating current is following through the armature. This alternatingcurrent is converted into

dc by using commutator.

*.State +lemin),s left han# r'le.The direction of rotation is given by 'leming"s left hand rule. (f the thumb, fore finger and

middle finger of the hand are held such that the three fingers are atmutually perpendicular directions,

and if the fore finger indicates direction of the field, and the middle finger, the direction of currentthen the thumb points to thedirection of rotation.

.Write #o(n the olta)e e/'ation of a #.c. motor.)oltage e*uation of a DC motor is given by )+ Eb (a -awhere ) applied voltage, Eb bac# emf

(a / armature current, - a armature resistance

0.What are the #ifferent t"es of #.c. motors?The types of DC motors are

Separately excited DC motor

Self excited DC motor

Series motor

Shunt motor

Compound motor

a% ong shunt compound motor

b% Short shunt compound motor

.What is a se"aratel e3cite# #.c motor?(n this motor, field winding and armature windings are separated. The field winding is

excited by a separate DC source. That is why it is called separately excited DC motor.

14. What is a #c series motor?(n a DC series motor, the field winding is connected in series with the armature. The

field winding should have less number of turns of thic# wire.

11. What is a #c sh'nt motor?(n a dc shunt motor, the field winding is connected across the armature. The shunt field

winding has more number of turns with less cross sectional area.

12. Wh a #c sh'nt motor is also calle# a constant fl'3 motor or constant s"ee# motor?


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(n shunt motor, flux produced by field winding is proportional to the field current (sh. 0ere,

the input voltage is constant and so the flux is also constant. Therefore, DC shunt motor is also called a

constant flux motor or constant speed motor.

1. What is a com"o'n# motor?& dc motor consisting of both series and shunt field windings is called a compound

motor.

1$. Wh series motor cannot !e starte# (itho't an loa#?(n dc series motor, flux is directly proportional to armature current. 1nder no load condition,

the armature current is very low and flux also be less.2y using the formula 3 4 , where f lu x is less,

the motor speed will be very high. Due tothis motor will be damaged. 0ence DC series motor should

always be started withsome load on the shaft.

1&. What is the 'se of s"lit rin)s in DC Machines?'or ma#ing the flow of current unidirectional in the external circuit the slip rings are

replaced by split rings.

1*. What are the characteristics of a DC )enerator?

5CC

External characteristics

(nternal characteristics

1. Distin)'ish !et(een self e3cite# an# se"aratel e3cite# #c )enerator.

Se"aratel e3cite# Self E3cite#

(t the field winding of a generator is excited

by a separate dc supply then the generator is

called separately excited.

(t the field winding of a dc machine

is supplied from the armature of the dc

machine itself then it is called selfexcited.

10. Write the tor/'e e/'ation of #c motor?

Ta+ 6.789 : (a ;=:MA 2411;7.Self excited d.c machines

.separately excited d.c machines

$. What is the f'nction of comm'tator in a DC machines?7 N89:DEC 2412;

Conduct electricity between armature and fixed brushes

Converts altenating emf into unidirectional emf and vice versa

1* MA=@S

7. With a neat diagram explain the construction and wor#ing principle of a d.c

generator.7A>=:MA 2411;

. Derive an expression for the emf generated in a dc generator.7N89:DEC 2411;7N89:DEC 2414;

. Deduce the E@' and T5-J1E e*uation of DC machines.7 N89:DEC 2412;

. Explain various types of generators=motors.7N89:DEC 244;

8. Explain the characteristics of various types of generators=motors.7A>=:MA 2411;

K. Explain various types of starters

L. Explain various methods of speed control of d.c shunt motor F Series motor with neat circuit

diagram.7N89:DEC 244; 7N89:DEC 2411; 7N89:DEC 2414;

M. Draw Speed tor*ue and speed armature current characteristic of DC series motor.

'rom the characteristics explain why a D.C. series motor can not be started without

load. &lso state two applications of D.C. series motor.

9. & lap wound dc shunt generator having M6 slots with 76 conductors per slot generates an e.m.f

of 66) on no load when running at 7666 rpm. &t what speed it should run to generate a voltage of

6 ) on open circuit. (f instead of lap the winding had been wave at what speed the motor would

have run?

76. & 766 ) series motor ta#es 8 & when running at L86 rpm. (ts armature resisitance

is 6. ohm F series field resistance is 6.7 ohm, iron F friction losses amount to L86W, find i%

shaft power ii% total tor*ue F iii% shaft tor*ue

77. Explain how armature reaction occurs in a dc generator and the effect it has on the flux distribution of

the machines.7N89:DEC 2411;

UNIT-II T=ANS+8=ME=S

1. Define a transformer.

& transformer is a static device which changes the alternating voltage from one level to

another.

2. What are t'rns ratio an# transformation ratio of transformer?


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. What is sta))erin) in the constr'ction of transformers?

(n transformer, the >oints in the alternate layers are staggered in order toavoid the

presence of narrow gaps right through the cross/section of the core.

$. What #etermines the thic%ness of the lamination or stam"in)s?

7. 're*uency . (ron loss&. Classif the transformer accor#in) to the constr'ction.

7. Core type transformer . Shell type transformer . 2erry

typetransformer

*. What are the t(o com"onent in transformer,s no loa# c'rrent?

7. &ctive or wor#ing component $(w%

. -eactive or magneti!ing component $( N %. Wh is the core of transformer laminate#?

The core of transformer is laminated in order to minimi!e eddy current loss.

0. Wh transformer ratin) is e3"resse# in terms of %9A?

Copper loss depends on current and iron loss depends upon voltage. 0encethe total loss in a

transformer depends upon volt/ampere $)&% only not on the phase angle between voltage and currenti.e. it is independent of load power factor. That iswhy the rating of a transformer is given in #)& and

not in #W.

. What are the "ro"erties of an i#eal transformer?

The ideal transformer has the following properties.

7. 3o winding resistance. i.e., purely inductive.

. 3o magnetic lea#age flux.

. 3o (

- loss i.e, no copper loss.

. 3o core loss.

14. What is the a""lication of e/'ialent circ'it of a sin)le "hase transformer.

a. To determine circuit parameters.

b.To predetermine efficiency and voltage regulation.

11. Wh is the effectiel of transformer hi)her than other AC machines?Since the current of the transformer at portraiture local and pt is defined as the o=p by i=p it has higher

(.

11. What is the con#ition for o!tainin) ma3im'm efficienc of a transformer?

C1 loss + (ron loss

12. What is the main #ifference !et(een the core t"e an# shell t"e transformers

(n core type transformers the winding surround considerable part of the corewhere as in shell

type transformer the core surround a considerable portion of the windings

1. What are the tests to !e con#'cte# to estimate the "erformance of a transformer?

Simper Test, Oappa Diagram.

1$. Wh transformer ratin) is e3"resse# in @9A?

C1 loss of a transformer depends on current and iron loss on voltage. 0encetotal transformer

loss on volt ampere O)& and not on phase angle between voltageThat"s why it is transformer is inO)& and not in Ow.

1&. What is the metho# 'se# to minimi


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5utput losses.

10. Write the EM+ e/'ation of a transformers (ith refers to "rimar an# secon#arwindings.

E7 + .f37 Pm + .f372m&

E + .f3f 2m&.

1. 5ist the a#anta)e of core ste""in) in the #esi)n of a transformer?

Core stepping not only gives high space factor but also results in reduced length of the

mean turn and the conse*uent (- loss.

24. Mention the "ro"erties of oil 'se# in transformers.

i% 0igh dielectric strength.

ii% 'ree from inorganic acid, al#ali and corrosive sulphur to prevent in>ury tothe conductor or insulation.

iii% ow viscosity to provide good heat transfer.

iv% 'ree from sludging under normal operating conditions.

v% Hood resistance to emulsion so that the oil may throw down any moistureentering the tan# instead of holding it in suspense.

21. Define re)'lation '" an# re)'lation #o(n for a transformer.

The change in secondary terminal voltage from no/load to full load is )3 ). Thischange is divided by )3 is #nown as regulation down. (f this change isdivided by ), then it is

called regulation up.

22. What is an i#eal transformer?

766Q efficiency of the transformer is called ideal transformer.

2. State the con#ition for ma3im'm efficienc of a transformer. Then (hat is the

corres"on#in) o't"'t c'rrent?(ron loss + copper loss $or% constant loss + )ariable loss R

0ence efficiency of a transformer will be maximum when copper losses are e*ual to iron losses.

The load current corresponding to maximum efficiency is given by

2$. Define Ball #a efficienc of a transformer.

The ratio of output in #wh to input in #wh of a transformer over a hourperiod is #nown

as all/day efficiency.

Kwh output in 24hours all/day +

kwh input in hours

2&. Define re)'lation an# efficienc of a transformer.The regulation of a transformer is defined as reduction in magnitude of theterminal voltage due to

load, with respect to the no/load terminal voltage.

2*. Name the factors on (hich hsteresis loss #e"en#s.

7. 're*uency . )olume of the core . @aximum flux density

2. Wh the o"en circ'it test on a transformer is con#'cte# at rate# olta)e?

The open circuit test on a transformer is conducted at rated voltage because core loss

depends upon the voltage. This open circuit test given only core loss oriron loss of the transformer.


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20. Mention the #ifference !et(een core an# shell t"e transformers?

(n core type, the windings surrounded the core considerably and in shelltype the core surround the

windings i.e winding is placed inside the core.

2. What is the "'r"ose of laminatin) the core in a transformer? 6ie the emf e/'ation of a

transformer an# #efine each term?

To reduce the eddy current loss in the core of the transformer.Emf induced in primary coil E7+ .fm37 volt emf

induced in secondary coil E +. fm3.

f///Ufre* of &C input

m////Umaximum value of flux in the core 37,3///U3umber of primary F secondary turns.

4. +'ll loa# co""er loss in a transformer is 1*44W. (hat (ill !e the loss at half loa#?

(f x is the ratio of actual load to full load then copper loss + x$'. copper b loss% here Wc +

$6.8% 7K66+66W.

1. Define all #a efficienc of a transformer?

(t is computed on the basis of energy consumed during a certain period, usually a day of hrs. all

day efficiency+output in #Wh=input in #Wh tor hrs.

2. Wh transformers are rate# in %9A?

Copper loss of a transformer depends on current F iron loss on voltage. 0ence total losses depends

on )olt/&mpere and not on ;'. That is why the rating of transformers are in #)& and not in #W.

. Ho( transformers are classifie# accor#in) to their constr'ction?

7. Core type

. Shell type. (n core type, the winding $primary and secondary% surround the core

and in shell type, the core surround the winding.

$. Wh are !reathers 'se# in transformers?

2reathers are used to entrap the atmospheric moisture and thereby not allowing it to pass on to the

transformer oil. &lso to permit the oil inside the tan# to expand and contract as its temperature increases

and decreases.

&. What is the f'nction of transformer oil in a transformer? an# Can the olta)e re)'lation )o ie? If so 'n#er (hat con#ition?

(t provides good insulation F Cooling. Aes, if the load has leading ;'.

*. Distin)'ish "o(er transformers #istri!'tion transformers?

;ower transformers have very high rating in the order of @)&. They are used in generating and

receiving stations. Sophisticated controls are re*uired. )oltage ranges will be very high. Distributiontransformers are used in receiving side. )oltage levels will be medium. ;ower ranging will be small in

order of #)&. Complicated controls are not needed.

. Mention the #ifference !et(een core an# shell t"e transformers.

(n core type , the windings surround the core considerably and in shell type the core surround the

winding.

0. What is the "'r"ose of laminatin) the core in a transformers ?

To reduce eddy current loss.

. 6ie the emf e/'ation of a transformer an# #efine each term

Emf induced in primary coil E7 + . fI m37 volt

Emf induced in secondary coil E + .fI m3 volt

Where f is the fre*uency of &C input

fI m is the maximum value of flux in the core

37, 3 are the number of primary and secondary turns.


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$4. Does the transformer #ra( an c'rrent (hen secon#ar is o"en? Wh?

Aes, it $primary% will draw the current from the main supply in order to magneti!e the core and to

supply iron and copper losses on no load . There will not be any current in the secondary since secondary

is open.

$1. Define olta)e re)'lation of a transformer. 7N89:DEC 2412;

When a transformer is loaded with a constant primary voltage , the secondary voltage decreases forlagging power factor load, and increases for leading pf load because of its internal resistance and lea#age

reactance.

The change in secondary terminal voltage from no load to full load expressed as a percentage of no load

or full load voltage is termed as regulation.

Q regulation down + $6)/)% x 766=6)

Q regulation up + $6)/)% x 766=)

$. +'ll loa# co""er loss in a transformer is 1*44 (atts. What (ill !e the loss at half loa#?

(f x is the ratio of actual load to full load then copper loss + x$full load copper loss%

0ere Wc + $6.8% x 7K66 + 66 watts

$$. Define all #a efficienc of a transformer . 7A>=:MA 2411;

(t is the computed on the basis of energy consumed during a certain period , usually a day of hrs.all day + output in #Wh =input in #Wh for hrs.

$&. (h transformers are rate# in %9A ? 7N89:DEC 244;

Copper loss of a transformer depends on current and iron loss on voltage . 0ence total losses depend

on )olt/ &mpere and not on the power factor. That is why the rating of transformers are in #)& and not in

#W.

$*. What are the t"ical 'ses of a'to transformer ?

$i% To give small boost to a distribution cable to correct for the voltage drop.

$ii% &s induction motor starters.

$. What are the a""lications of a ste"-'" an# ste"-#o(n transformers ?

Step/up transformers are used in generating stations. 3ormally the generated voltage will be either 77

#) . This voltage$77 O)% is stepped up to 776 #) or 6 #) or 66 #) and transmitted through

transmission lines. $(n short it may 2e called as sending end%.

Step/down transformers are used in receiving stations. The voltage are again stepped down to 77 #)

or #) and transmitted through feeders.$(n short it may be called as receiving end%.

'urther these 77 #) or #) are stepped down to phase 66 ) by means of a distribution transformer

and made available at consumer premises.The transformers used at generating stations and receiving

stations are called power transformers.

$0. Ho( transformers are classifie# accor#in) to their constr'ction ?

8r

Mention the #ifference !et(een BC8=E an# BSHE55 t"e transformers.8r

What are the t(o t"es of cores 'se# ? Com"are them.

Transformers are classified according to their construction as,

$i% Core type $ii% Shell type $iii% Spiral core type.

Spiral core type is a latest transformer and is used in big transformers.

(n Vcore type, the windings$primary and secondary%surround the core and in

Vshell type, the core surround the windings.


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$. E3"lain on the material 'se# for core constr'ction.

The core is constructed of transformer sheet steel laminations assembled to provide a continuous

magnetic path with a minimum of air gap included. The steel used is of high silicon content sometimes

heat treated to produce a high permeability and a low hysteresis loss at the usual operating flux densities.

the eddy current loss is minimi!ed by laminating the core, the laminations being insulated from each other

by light coat of core/plate vanish or by an oxide layer on the surface. The thic#ness of laminations variesfrom 6.8 mm for a fre*uency of 86 0! and 6.8 mm for a fre*uency of 8 0!.

&4. When (ill a F'chol< rela o"erate in a transformer ?

2uchol! rely is a protective device in a transformer. (f the temperature of the coil

exceeds its limit, 2uchol! relay operates and gives an alarm.

&1. Ho( #oes chan)e in fre/'enc affect the o"eration of a )ien transformer?

With a change in fre*uency, iron loss, copper loss, regulation, efficiency and heating varies and

thereby the 5peration of the transformer is affected.

&2. What is the an)le ! (hich no-loa# c'rrent (ill la) the i#eal a""lie# olta)e?

(n an ideal transformer, there are no copper loss and no core loss, $i.e. loss free core%. The no load

current is only magneti!ing current. Therefore the no/load current lags behind by an angle of 96X.

0owever the windings possess resistance and lea#age reactance and therefore the no/load current lags the

applied voltage slightly less than 96.

&. 5ist the a#anta)es of ste""e# core arran)ement in a transformer .

$i% To reduce the space effectively.

$ii% To obtain reduced length of mean turn of the windings.

$iii% To reduce (- loss.

&$. Wh are !reathers 'se# in transformers ?

2reathers are used to entrap the atmospheric moisture and thereby not allowing it to pass on to the

transformer oil. &lso to permit the oil inside the tan# to expand and contract as its temperature increases

and decreases.

&lso to avoid sledging of oil i.e. decomposition of oil. &ddition of M parts of water in 7666666reduces the insulations *uantity of oil. 3ormally silica gel is filled in the breather having pin# colour. This

clour will be changed to white due to continuous use, which is an indication of bad silica gel, it is

normally heated and reused.

&&. What is the f'nction of transformer oil in a transformer ?

3owadays instead of natural mineral oil, synthetic oils #nown as &SO-ES $trade name% are used.

They are non inflammable, under an electric arc do not decompose to produce inflammable gases.

;A-5C55- oil possess high dielectric strength. 0ence it can be said that transformer oil provides, $i%

good insulation and $ii%cooling .

&*. A 1144:$44 9 &4 H< sin)le "hase transformer has 144 t'rns on the secon#ar (in#in). Calc'late

the n'm!er of t'rns on its "rimar.

We #now )7 = ) + # + 3 = 37

Substituting 66=7766 + 766=37

37 + 766=66 x 7766

+ L8 turns.

&. What are the f'nctions of no-loa# c'rrent in a transformer ?

3o/load current produces flux and supplies iron loss and copper loss on no/load.

&. Can the olta)e re)'lation of a transformer )o to ne)atie? If so 'n#er (hat con#ition?


13/33

Aes. (f the load has leading power factor.

*4. Distin)'ish !et(een "o(er transformer an# #istri!'tion transformer .

;ower transformers have very high power ratings in the order of @)&. They are used in generating

and receiving stations. Sophisticated controls are re*uired. )oltage ranges will be very high.

Distribution transformers are used in consumer side. )oltage levels will be medium. ;ower ranging

will be small in order of #)&. Complicated controls are not needed.*1. What is the "'r"ose of "roi#in) Gta"s, in transformer an# (here these are "roi#e#?

(n order to attain the re*uired voltage , Ytaps" are provided. 3ormally it is provided at low voltage

side.

1* MA=@S

7. With a neat diagram explain the construction details of different types of 7/phase transformer.

7N89:DEC 244; 7N89:DEC 2414;

. Explain the wor#ing of transformer

. $i% 'rom the 5C and SC test, what are the parameters obtained, explain in detail.

$ii%Draw the e*uivalent circuit of a transformer from the 5C and SC test.7N89:DEC 2414;

7N89:DEC 2411; 7A>=:MA 2411; N89:DEC 2412;. Explain the testing of a transformer.

8. Derive an expression for voltage regulation in terms of resistance and reactance of the Transformer.

K. 'or a given single phase transformer, obtain condition for !ero regulation and @aximum -egulation

L. What are losses in Transformer? 0ow do they vary with load?

M. Derive the condition for maximum efficiency of the Transformer.

9. Draw e*uivalent circuit of a Transformer and explain how various parameters in the circuits are

determined.

76. Describe the method obtaining separately the 0ysterisis and Eddy Current osses of a

Transformer.

77. Explain how the efficiency and voltage regulations can be estimated by conducting 5C

and SC Test.

7. Draw the phasor diagram when the transformer is loaded with7N89:DEC 2414;

7. -esistive, . (nductive, . Capacitative element.

7. $i% Derive the emf e*uation of a single phase two winding transformer.

$ii% Draw and explain the phasor diagram of an actual transformer on load. 7N89:DEC 2411;

U N I T - I I I S N CH=8N8US M A C H I N E S1 . What are the a""lications of #am"er (in#in) in snchrono's motor?When a synchronous motor is used pr deiving a fluctuating load the rotorstarts oscillating

about its new position of e*uilibrium corresponding to the new load. To prevent heating dampers

are employed. This is the application of damperswinding.

2 . Wh is the sin)le "hase in#'ction motor ma#e as self startin)?

The starting method of single phase induction motor is very simple. &n auxillary

winding in the stator is provided in addition to the main winding. Then the induction motor. Starts as a

too phase motor.


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The main winding axis and auxiliary winding axis are displaced by 96o

electrical

degrees. The impedance of the windings differ and class in the main andauxiliary windings are phase

shifted from each other. &s a result of this a rotatingstator field is produced and the rotor rotates.

. What are the reasons for the ariation of terminal olta)e of an alternator on

loa#?

7. )oltage drop due to -a

. )oltage drop due to Z

. )oltage drop due to armature reaction.

$ . What are the ario's metho# startin) of snchrono's motor? 2y dc source

& . 5ist the tor/'e associate# (ith a snchrono's motor?

7. Starting Tongue . running Tor*ue . ;ull in tor*ue . ;ull out tor*ue.

* . 5ist o't the a""lication of snchrono's motor

7. ;ower factor correction

.Constant speed, constant load drives

. )oltage regulation

. Write the emf e/'ation of an alternator?E@'=phase + . Oc #d f P T

0 . Define olta)e re)'lation Name t(o metho#s 'se# to #etermineolta)e

re)'lation of alternators.

)oltage regulation of an alternator is defined as the rise in voltage when fullload is removed

ctield excitation and speed remaining the same divided by the ratedterminal voltage.

7. E@' method

. @@' method

. Calc'late the #istri!'tion factor for a * slots $ "ole sin)le laer three "hase(in#in) of a alternator?

n+ K= +9 2+ 7M6o

n=9 U 6o

m+ K = x + 2

1 4 . Define h'ntin).When a synchronous motor is used for driving a varying load then condilion #nown as hunting is

produced.

11. Write the e3"ression for #istri!'tion factor of a (in#in)?Od + e m f with w i ndi n g in slots = pole = phase

emf with minding in 7slot = pole =phase

1 2 . What are the #ifferent t"es of sin)le "hase motor?

i. Single phase induction motors

ii. Single phase synchronous motors

iii. Single phase series $or universal% motors

1 . What are the #ifferent t"es of sin)le "hase in#'ction motor?


15/33

i.-esistance start $split phase% induction motor.

ii. Capacitor start induction motor.

iii. Capacitor run induction motor.

iv. Capacitor start capacitor run induction motor.

v. Shaded pole induction motor.

1 $ . What are the a""lications characteristics of s"lit-"hase motors?

&pplications

i% 'ans ii% 2lowers

iii% Centrifugal pumps iv% Washing machines

Characteristics

i% The starting tor*ue is 766Q to 86Q of the rated value.

ii% The brea#down tor*ue is up to 66Q.

iii% The power factor of the motor is 6.8 to 6.K8.

iv% The efficiency of the motor is 88Q to K8Q.

v% The power rating of this motor is in the range of [ to 7 0;

1 & . What are the a""lications an# characteristics of ca"acitor-start motor?

&pplications

i%Compressors

ii% Conveyors

iii% &ir conditioning e*uipment

iv% ;umps

v% -efrigerator

vi% Washing machine

Characteristics


ii% The brea#down tor*ue is up to 86Q.

iii% ;ower factor of the motor is 6.8 to 6.K8.

iv% The power rating of the motor is \ to 7 0; v%The efficiency of the motor is 88Q to K8Q.

1* . What are the main a#anta)es of ca"acitor r'n motor?

i% 0igh power factor at full load

ii% 0igh full/load efficiency

iii% (ncreased pull/out tor*ue

iv% ow full/load line current1 . What are the a""lications an# characteristics of ca"acitor r'n-motor?

&pplications

i% 'ans

ii% 2lowers

iii%Centrifugal pumps


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Characteristics


ii% The brea#down tor*ue is up to 86Q

iii%The power factor of the motor is in the range of 6.L8 to 6.9.

iv%The efficiency of the motor is K6 to L6Q

v% The power rating of the motor is \ to 7 0;.10 . What are the a#anta)es of ca"acitor start ca"acitor r'n motor?

i% 0igh starting tor*ue ii% 0igh efficiency

iii% 0igh power factor

1 . What are the a""lications an# characteristics of ca"acitor- start ca"acitor r'nmotor?

A""lications

i% Compressors ii% ;umps

iii% Conveyors iv% -efrigerators

Characteristics

i% The starting tor*ue is 66Q to 66Q of the rated value.ii% The rated brea#down tor*ue is up to 86Q.

iii% The power factor of the motor is 6.L8 to 6.9.

iv% The efficiency of the motor is K6 to L6Q.

v% The power rating of the motor is \ to 7 0;.

2 4 . Com"are the "erformance an# a""lications of resistance s"lit "hase an#

"ermanent ca"acitor sin)le in#'ction motors.

+eat'res S"lit "hase in#'ctionmotor >ermanent ca"acitor

in#'ction motors.

7. Starting tor*ue

. ;ower factor

. Efficiency

. &pplications

ow or medium

ow

ow

'ans, blowers

0igh

0igh

0igh

Compressors, pumps

conveyors, refrigerators.

2 1 . Name an t(o a""lications of sha#e# "ole in#'ction motors.i% Turn tables ii% 0air driers

iii% 'ans iv% 2lowers

2 2 . What are the #ra(!ac%s of the "resence of the !ac%(ar# rotatin) fiel# in a

sin)le

"hase in#'ction motor?

i% 3et flux will be !ero

ii% 3o starting tor*ue in the motor.

2 . 5ist o't fo'r a""lications of sha#e# "ole in#'ction motor.i% 'ans ii% 2lowers


17/33

iii% Turn tables iv% 0air driers

2 $ . What is the 'se of sha#in) coil in the sha#e# "ole motor?The copper shading coil is used to produce rotating magnetic field moving from the unshaded to

shaded portion of the pole. 0ence, the motor produces astarting tor*ue.

2 & . What are the "rinci"al a#anta)es of rotatin) fiel# sstem t"e of constr'ction ofsnchrono's machines? 'orm Stationary connection between external circuit and system of conditions enable the

machine to handle large amount of volt/ampere as high as 866 @)&.

The relatively small amount of power re*uired for field system can be easily supplied to the

rotating field system via slip rings and brushes.

@ore space is available in the stator part of the machine for providing more insulation to the

system of conductors.

(nsulation to stationary system of conductors is not sub>ected to mechanical stresses due to

centrifugal action.

Stationary system of conductors can easily be braced to prevent deformation.

(t is easy to provide cooling arrangement.

2*. What are the a#anta)es of salient t"e "ole constr'ction 'se# in snchrono's machines?

They allow better ventilation, the pole faces are so shaped radial air gap length increases from

pole center to pole tips so flux distortion in air gap is sinusoidal so emf is also sinusoidal.

2. Define the term olta)e re)'lation of alternator.

The voltage regulation of an alternator is defined as the change in terminal voltage from no load to

load condition expressed as a fraction or percentage of terminal voltage at load condition, the speed andexcitation conditions remaining same.

20. What is h'ntin)? 5ist the #ifferent tor/'e in snchrono's motor.

When a synchronous motor is used for driving a varying load, then a condition #nown as

hunting is produced. 0unting may also be caused if supply fre*uency is pulsating. Starting tor*ue,

-unning tor*ue, ;ull/in tor*ue and ;ull/out tor*ue.

2. 5it the a#anta)es of snchrono's motor.

2y varying the field excitation, the magnitude of current drawn by the motor can be changed

by any amount. This helps in achieving stepless control of power factor.

The motor windings have high thermal stability to short circuit currents. iii%The faults can be

removed easily.

4. What are the 'ses of #am"er (in#in)s in a snchrono's motor?

& synchronous motor cannot start by itself . (n order to ma#e the motor self/starting,a s*uirrel cage

winding$also called damper winding% is provided on the rotor.The damper winding consists of copper

bars embedded in the pole faces of the salient poles of the rotor. (t start the motor li#e a induction

concept.

1. E3"lain "'ll in tor/'e of snchrono's motor.& synchronous motor is started as induction motor till it runs to 8Q below the synchronous speed.

&fterwards ,excitation is switched on and the rotor pulls into step with the synchronously rotating stator

field. The amount of tor*ue at which the motor will pull into step is called ;ull in tor*ue.

2. Wh are alternators rate# in @9A an# not in @W?

&s load increases (

- loss also increases, as the current is directly related to apparent power

delivered by generator, the alternator has only their apparent power in )&=O)&=@)& as their power

rating.


18/33

. Wh the s.im"e#ance metho# of estimatin) olta)e re)'lation is is consi#ere# as

"essimistic metho#?

Compared to other method, the value of voltage regulation obtained by this method is always

higher than the actual value so it is called as pessimistic method.

$. Wh MM+ metho# of estimatin) olta)e re)'lation is consi#ere# as o"tiimistic metho#?Compared to E@' method, @@' method involves more noof complex calculation steps. 'urther the

5CC is referred twice and SCC is referred once while predetermining the voltage regulation for each

load condition. -eference of 5CC ta#es core saturation effect. &s this method re*uire more effort, final

result is very close to actual value, hence this method is called as optimistic method.

&. Write #o(n the e/'ation for fre/'enc of emf in#'ce# in an alternator.

' + ;3 = 76 0ert!

Where ; + 3o. 5f poles

3 + Speed in rpm.

*. What are the a#anta)es of salient "ole t"e of constr'ction 'se# for snchrono's machines?

They allow better ventilation.

The pole faces are so shaped radial air gap length increases from thepole center to the

pole tips so that flux distribution in the air gap is sinusoidal in shape

which will help to generate sinusoidal emf.

Due the variable reluctance, the machine develops additional

reluctance power, which is independent of excitation.

. Wh #o clin#rical rotor alternators o"erate (ith steam t'r!ines?

Steam turbines are found to operate at fairly good efficiency only at high speeds. The high/speed

operation of rotor tends to increase mechanical losses, so the rotors should have smooth external surface.

0ence smooth cylindrical type rotors with less diameter and large axial length are used for synchronous

generators driven by steam turbines with either or poles.0. Which t"e of snchrono's )enerators are 'se# in H#roelectric "lants an# (h?

&s the speed of operation is low, for hydro turbines used in hydroelectric plants, salient pole type

synchronous generators are used. These allow better ventilation and also have other advantages over

smooth cylindrical type rotor.

. What is the relation !et(een electrical #e)ree an# mechanical #e)ree?

Electrical degree Ie and mechanical degree are related to one another by the number of poles ;, the

electrical machine has, as given by the following e*uation. Ie + $;=% Im

$4. What is the meanin) of electrical #e)ree?

Electrical degree is used to account the angle between two points in rotating electrical machines.

Since all electrical machines operate with the help of magnetic fields, the electrical degree is accounted

with reference to the polarity of magnetic fields. 7M6 electrical degrees is accounted as the angle between

ad>acent 3orth and South poles

$1. Wh short-"itch (in#in) is "referre# oer f'll "itch (in#in)?

Waveform of the emf can be approximately made to a sine wave and

distorting harmonics can be reduced or totally eliminated.

Conductor material, copper is saved in the bac# and front/end

connections due to less coil span.


19/33

'ractional slot winding with fractional number of slots=phase can be

used which in turn reduces the tooth ripples.

@echanical strength of the coil is increased.

$2. Define (in#in) factor.

The winding factor Ow is defined as the ratio of phasor addition of emf induced in all the coils

belonging to each phase winding of their arithmetic addition.$. Wh are alternators rate# in %9A an# not in %W?

The continuous power rating of any machine is generally defined as the power the machine or

apparatus can deliver for a continuous period so that the losses incurred in the machine gives rise to a

steady temperature rise not exceeding the limit prescribed by the insulation class.

&part from the constant loss the variable loss incurred in alternators is the copper loss, occurring in the /

phase winding, which depends on (-, the s*uare of the current delivered by the generator.

&s the current is directly related to apparent power delivered by the generator, the alternators have only

their apparent power in )&=#)&=@)& as their power rating

$$. What are the ca'ses of chan)es in olta)e of alternators (hen loa#e#?

)oltage variation due to the resistance of the winding -.

)oltage variation due to the lea#age reactance of the winding Z7.

)oltage variation due to the armature reaction.

$&. What is meant ! armat're reaction in alternators?

The interaction between flux set up by the current carrying armature conductors and the main field

flux is defined as the armature reaction.

$*. What #o o' mean ! snchrono's reactance?

(t is the sum of the lea#age reactance Z7 and armature reactance Za. Zs + Z7 Za

$. What is snchrono's im"e#ance?

The complex addition of resistance - and synchronous reactance >Zs is synchronous impedance


20/33

&2. Wh is the MM+ metho# of estimatin) the olta)e re)'lation is consi#ere# as the o"timi


21/33

- + Z

0. Define the term sli"?Diff between 3s and actual speed of the rotor is slip.

. What are the A"" of s"lit "hase motor?

'an, 2lowers.

14. Wh is IM not self startin) motor?When feal from a 7 phase supply its stator relay produces a flux which is only alternating i.e one

which alternates along one space axis only. (t is not a

synchronously revolving flux as in the case of or phase stator well tied from or

phase supply. 3ow an alternating or pulsating flux acting on a stationary s*uirrel cage motor can

now produce rotation. That is why 7 phase motor is not self starting.

11. What are the a"" of 'niersal motor.

$i% Sewing m=c

$ii% Camera

$iii% 0air dryer.12. What are the 2 t"es of "hase in#'ction motor?S*uirrel cage and slip ring induction motor.

1. Write t(o e3tra feat'res of sli" rin) in#'ction motor?-otor has phase winding. extra resistance can be added in rotor circuit for improving ;' with the help

of three slip rings.

1$. Why an induction motor is called as rotating transformer?

The rotor receives same electrical power in exactly the same way as the secondary of a two winding

transformer receiving its power from primary. That is why induction motor is called as rotating

transformer.

1&. Wh an in#'ction motor neer r'ns at its snchrono's s"ee#?(f it runs at synchronous speed then there would be no relative speed between the two, hence no rotor

emf, so no rotor current, then no rotor tor*ue to maintain rotation.

1*. What are sli" rin)s?

The slip rings are made of copper alloys and are fixed aroud the shaft insulating it. Through these slip

rings and brushes rotor winding can be connected to external circuit.

1. What are the a#anta)e of ca)e motor?

Since the rotor have low resistance, the copper loss is low and efficiency is very high. 5n

account of simple construction of rotor it is mechanically robust, initial cost is less, maintenancecost is less, simple starting arrangement.

10. 6ie the con#ition for ma3im'm tor/'e for "hase in#'ction motor (hen it is

r'nnin)?

The rotor resistance and rotor reactance should be e*ual for developing maximum tor*ue i.e. - + s Z

where s is the slip.

1. 5ist o't the metho# for s"ee# control of "hase ca)e t"e in#'ction motor?

2y changing supply fre*uency 2y changing no of poles 2y operating the two motors in cascade.

24.Can (e a## e3tra resistance in series (ith s/'irrel ca)e rotor? State the reason?

We cannot add extra resistance in series with the rotor because all the copper bars of the rotor are

short circuited in both the sides by copper end rings to have a closed circuit.

21. Wh an in#'ction motor is calle# rotatin) transformer?


22/33

The rotor receives electrical power in exactly the same way as the secondary of a two winding

transformer receiving its power from primary. That is why an induction motor can be called as a rotating

transformer i.e., in which primary winding is stationary but the secondary is free to rotate.

22. Wh an in#'ction motor (ill neer r'n at its snchrono's s"ee#?

(f it runs at synchronous speed then there would be no related speed between the two, hence no rotor

emf, no rotor current so no rotor tor*ues to maintain rotation. That is why the rotor runs at itssynchronous speed.

2. State the #ifference !et(een sli" rin) rotor an# ca)e rotor of an in#'ction

motor? 7N89:DEC 2414;

Slip ring rotor has /phase windings. Three ends of which are stared and the other three ends are brought

up and connected to slip rings mounted in the shaft. Extra resistance can be added in the rotor circuit.

S*uirrel cage rotor has short/circuited copper bars. Extra resistance can"t be added as slip ring rotor.

2$. Write an e3"ression for the sli" of an in#'ction motor.

;ercentage slip + $3s /3r% = 3s ^ 766.

2&. Define sli" of in#'ction motor? 7N89:DEC244;

Slip is descriptive of the way in which the rotor slips bac# from synchronism. (t is usually expressed as

percentage of synchronous speed.

2*. What are the a#anta)es of ca)e motor?

Since the rotor has very low resistance, the copper loss is low and efficiency is high 5n the account of

simple construction of rotor, it is mechanically robust. (nitial cost is less.

@aintenance cost is less. Simple stating arrangement.

2. What is reason for insertin) a##itional resistance in rotor circ'it of a sli" rin) in#'ction motor?

(ntroduction of additional resistance in the rotor circuit will increase the starting tor*ue as well as

running tor*ue. &lso it limits the starting current.

20. 5ist o't the metho#s of s"ee# control of ca)e t"e -"hase in#'ction motor?

2y changing supply fre*uency

2y changing the number of poles2y operating two motors in cascade

2. Mention #ifferent t"es of s"ee# control of sli" rin) in#'ction motor?

2y changing supply fre*uency

2y changing the number of stator poles

2y rotor rheostat control

2y operating two motors in cascade

4. What are the a#anta)es of -"hase in#'ction motor?

(t was very simple and extremely rugged, almost unbrea#able construction

(ts cost is very low and it is very reliable

(t has been suffiently high efficiency .

3o brushes are needed and hence frictional losses are reduced

(t re*uires minimum of maintenance.

>A=T F

1.$i% Derive the e*uation for tor*ue under running conditions in a /phase induction

motor.

$ii% Draw a7nd explain the slip/ring characteristics of /pnase induction motor.

7N89:DEC 244;


23/33

2. With a neat circuit diagram, explain the starting of slip/ring induction motor.N89:DEC 244;

. 7i;Explain in detail the production of rotating magnetic field with a neat phasor

diagram. 7N89:DEC 2411;

$ii% Explain with a neat diagram the principle of an induction motor.

7N89:DEC 2414;

$. 7i; What are the various starting methods of induction motor ?7N89:DEC 2414;

$ii% What are the various methods of speed control of induction motor? Explain in detail

8. Explain in detail about the various methods of speed control of /phase induction

motor? N89:DEC 2411;

U N I T 9 S > E C I A 5 M A C H I N E S1. What is a re"'lsion motor?

-epulsion motors are similar to series motors except that the rotor and thestator windings

are inductively coupled i.e., the rotor current is obtained by

transformer action from the stator.

2. What are the #isa#anta)es of re"'lsion motor?

i % Speed variations with the variations in load dangerously high atno load.

i i % ow power factor, except at high speeds.

i i i % -e*uires fre*uent maintenance.

i v % 0igher cost.

v % Spar#ing at the brushes.

. What is a 'niersal motor?

& universal motor is a specially designed series wound motor, that operates at approximately the

speed and output on either dc or ac of approximately same voltage.

$. What are the a""lications of 'niersal motor?

i % Sewing machinesi i % 0igh speed vacuum cleaners

i i i % Electric typewriters

i v % Electric shavers

v % @otion picture pro>ectors

v i % ;ortable hand tools

v i i % 0air dryers

v i i i % Cameras

i x % 'ood mixers

&. What is a hsteresis motor?(t is a single phase motor whose operation depends upon the hysteresis effect $i.e.,

magneti!ation produced in a ferromagnetic material lags behind themagneti!ing force% and on the presence of continuously revolving magnetic flux.

*. What are the a""lications of hsteresis motor?Due to their *uiet operation and ability to drive high/ inertia loads, hysteresismotors are used

for driving i% electric cloc#s ii% timing devices iii% tape dec#s iv% turn tables and other precision

e*uipment.

. Write some a#anta)es of Hsteresis motor oer in#'ction motor.

i % 0ere, hysteresis tor*ue remains constant from loc#ed rotor


24/33

to synchronousspeed, a hysteresis motor is able to synchroni!e any load.

i i % Due to its smooth cylindrical rotor, the motor operates*uietly and does notaffected from magnetic pulsations cause by slots= salient

poles that arepresent in the rotors of other motors.

0. What is s(itche# =el'ctance Motor?The switched reluctance motor is a double salient, singly/excited motor. This means that it has

salient poler on both the rotor and the stator, but only one member carries windings. The rotor has no

windings, magnets $or% cage winding. (t wor#s on variable reluctance principle.

. Wh rotor "osition sensor is essential for the o"eration of s(itche#rel'ctance

motor?

(t is normally necessary to use a rotor position sensor for commutation and speed feed bac#.

The turning 53 and 5'' operation of the various devices of powersemiconductor switching circuit are

influenced by signals obtained from rotorposition sensor.

14. 5ist the #isa#anta)es of a s(itche# rel'ctance motor?

i % Stator phase winding should be capable of carrying magneti!ingcurrent.

i i % 'or high speed operation developed tor*ue has undesirableripples

is a result develops undesirable noises $or% acoustic noises.

i i i % 'or high speed current wave form has undesirable harmonics tosuppress this effect large si!e capacitor is to be connected.

i v % (t re*uires a position sensor.

11. What are the advantages of switched reluctance motor?

i % Construction is simple and robust.

i i % -otor carries no windings, no slip rings, no brushes, lessmaintenance.

i i i % There is no permanent magnet.

i v % )entilating system is simpler as losses ta#es place mostly in thestator.v % ;ower semiconductor switching circuitry is simpler.

v i % 3o shoot through fault li#ely to happen power short circuits.

v i i % Developed tor*ue doesn"t depend upon the polarity of currentin the

phasewinding.

v i i i % The operation of the machine can be easily changed frommotoring

modeto generating mode by varying the region of conduction.

i x % (t is possible to get very high speed.

x % Depending upon the re*uirement T/w characteristics can beachieved.x i % (t is the self starting machine.

x i i % Energy stored in the phase winding is fed bac# to the supplythrough

thefeedbac# diodes during off period.

12. What are the a""lications of S=M?

i % Washing machines.


25/33

i i % )acuum cleaners

i i i % 'ans

i v % 'uture auto mobile applications

v % -obotics control applications

1. What are the t"es of "ermanent ma)net DC motor?

i % ;@2 s*uare wave motori i % ;@2 sine wave motor

1$. What is permanent magnet DC commutator motor?

& dc motor consists of permanent magnet in the stator and armature winding,

commutator in the rotor. This motor is called permanent magnet DC commutatormotor.

1&. What are the a#anta)es an# #isa#anta)es of !r'shless #c motor #ries?

&dvantages

i % There is no field winding so that field copper loss is neglected.

i i % ength of the motor is very small as there is nomechanical

commutator, sothat si!e becomes very small.

i i i % 2etter ventilation because of armature accommodated in thestator.

i v % -egenerative bra#ing is possible.

v % Speed can be easily controllable.

v i % @otor can be designed for higher voltages sub>ected tothe

constraint causedby the power semi conductor switching circuit.

v i i % (t is possible to have very high speeds. Disadvantages

i% @otor field cannot be controlledii% ;ower rating is restricted because of the maximum available si!e of

permanent magnets.

iii% (t re*uires a rotor position sensor.

iv% (t re*uires a power semi conductor switching circuit.

1*. 5ist the ario's "ermanent ma)net materials.&lnico, -are earth magnet, Ceramic magnet, 3d'e2 magnet, SmC57L magnet

1. Mention some a""lications of >MF5 DC motor.;ower alternators, &utomotive applications, Computer and -obotics applications,Textile and Hlass

industries

10. Com"are conentional DC motor an# >MF5DC motor.

+eat'res Conentional DC motor >MF5 DC motor


26/33

7. @echanical

structure

@aintenance

Winding

connection

. Commutation

method

. Detecting

method

. -eversing

method

'ield magnets on the stator

@aintenance is

high-ing

connection

The simplest_ Delta

connection

@echanical contact between

brushes and commutator

&utomatically

detected bybrushes

2y a reverse of

terminalvoltage.

'ield magnets on the rotor ow maintenance. The

highest grade_ D or star/ connected /: connection.

3ormal y/connected three phasewinding with grounded

neutralpoint or four/phase connection.

The simplest_

Two/phase connection.

Electronic switching usingpower semi conductor

devices

i.e transistors, @5S'ETS.

-otor position can be detectedby using sensor

i.e.,0all sensor` optical encoder.-earranging logic

se*uencer.

1. Wh is the >MF5DC motor calle# electronicall comm'tate# motor?The ;@2 DC motor is also called electronically commutated motorbecause the

phase windings of ;@2 DC motor is energi!ed by using power semiconductor

switching circuits. 0ere, the power semiconductor switching circuits

act as a commutator.

21 Com"are >MF5DC motor an# s(itche# rel'ctance motor.

>MF5DC S(itche# rel'ctance motor

22. What are the feat'res of "ermanent ma)net snchrono's motor?

i% -obust, compact and less weight.

ii% 3o field currents or rotar current in ;@S@, unli#e in induction motor.

iii% Copper loss due to current flow which is largest loss in motors isabout half that of induction motor.

iv% 0igh efficiency.

2. What are the a""lications of >MSM?i% 1sed as a direct drive traction motor.

ii% 1sed as high speed and high power drives for compressors, blowers, conveyors,fans, pumps, conveyors, steel rolling mills, main line traction, ship/propulsion, aircraft test

facilities.

2$. What are the merits an# #emerits of >MSM?


27/33

@erits

i% (t runs at constant speed.

ii% 3o field winding, no field loss, better efficiency.

iii% 3o sliding contacts. So it re*uires less maintenance.Demerits

i% ;ower factor of operation cannot be controlled as field windingcannot be controlled.

ii% (t leads to losses and decreases efficiency.

2&. Clearl e3"lain the #ifferences !et(een snchrono's rel'ctance motor an# >Msnchrono's motor.

Snchrono's =el'ctance

Motor

;@ Synchronous @otor

-otor has no permanent

magnet.

-otor has permanent

magnet.

ess cost. 0igh cost.

2*. Name the t(o (in#in) of sin)le "hase in#'ction motor?

-unning and starting winding.

2. What are metho#s aaila!le for ma%in) sin)le "hase in#'ction motor a self startin)?

2y slitting the single phase, by providing shading coil in the poles.

20. What is the f'nction of ca"acitor in sin)le "hase in#'ction motor?

i% To ma#e the phase difference between the starting and running winding.

ii%. To improve the power factor and to get more tor*ue.

2. State an $ 'se of sin)le "hase in#'ction motor?

'ans, wet grinders, vacuum cleaner, small pumps, compressors, drills. Explain why single phase

induction motor is not a self starting one? When motor fed supply from single phase, its stator winding

produces an alternating flux, which doesn"t develops any tor*ue.

4. What %in# of motors 'se# in ceilin) fan an# (et )rin#ers?

Ceiling fan/ Capacitor start and capacitor run single phase induction motor, wet grinders/Capacitor

start capacitor run single phase induction motor.

1. What is the a""lication of sha#e# "ole in#'ction motor?2ecause of its small starting tor*ue, it is generally used for small toys, instruments,hair driers,

ventilators..etc.

2. In (hich #irection a sha#e# "ole motor r'ns?

The rotor starts rotation in the direction from unshaded part to the shaded part.

. Wh sin)le "hase in#'ction motor hae lo( "o(er factor?

The current through the running winding lags behind the supply voltage by large angle so only

single phase induction motor have low ;'.


28/33

$. Differentiate !et(een Bca"acitor start BCa"acitor start ca"acitor r'n sin)le "hase

in#'ction motor?

(n capacitor start motor, capacitor is connected in series with the starting winding. 2ut it will be

disconnected fro m the supply, when the motor pic#s up its speed. 2ut in capacitor start capacitor run

motor the above starting winding and capacitor are not disconnected, but always connected in the

supply .so it has high starting and running tor*ue.

&. What are the t(o t"es of -"hase in#'ction motor?

S*uirrel cage induction motor.

Slip ring induction motor.

*. State the a#anta)es of ca"acitor start r'n motor oer ca"acitor start motor.

-unning tor*ue is more` ;ower factor during running is more

. E3"lain (h sin)le-"hase in#'ction motor is not self-startin) one.

When the motor is fed from a single phase supply its stator winding produces an alternating or

pulsating flux, which develops no tor*ue.

0. What t"e of motor is 'se# for ceilin) fan?

Capacitor start and capacitor run single/phase motor is used for ceiling fans.

. (hat is the t"e of in#'ction motor 'se# in (et )rin#ers?

Capacitor start capacitor run single/phase induction motor.

$4. (hat %in# of motor is 'se# in mi3ie?

Single/phase ac series motor is used in mixie.

$1. What is S(itche# =el'ctance Motor?

The switched reluctance motor is a double salient, singly/excited motor. This means that it has salient

pole on both the rotor and the stator, but only one member crries windings. The rotor has no windings,

magnets $or% cage winding. (t wor#s on vai7 reluctance principle.

$2. What are the t"es of "o(er controllers 'se# for s(itche# rel'ctance motor?

i% 1sing two power semiconductors and two diodes per phaseii% $n 7% power switching devices and $n 7% diodes per phase

iii% ;hase windings using 2ifilar wires

iv% Dump C/ converter

v% Split power supply converter

$. Wh rotor "osition sensor is essential for the o"eration of s(itche# rel'ctance motor?


29/33

(t is normally necessary to use a rotor position sensor for commutation and speed feed bac#. The

turning 53 and 5'' operation of the various devices of power semiconductor switching circuit are

influenced by signals obtained from rotor position sensor.

$$. 5ist are the #isa#anta)es of a s(itche# rel'ctance motor?

7. Stator phase winding should be capable of carrying magneti!ing current.

. 'or high speed operation developed tor*ue has undesirable ripples is a est7t

develops undesirable noises $or% acoustic noises.

. 'or high speed current wave form has undesirable harmonics to suppress this

effect large si!e capacitor is to be connected.

. (t re*uires position sensors.

$&. What are the a#anta)es of s(itche# rel'ctance motor 7S=M;?

7. Construction is simple and robust., -otor carries no windings, no slip rings, no brushes, less maintenance.

. There is no permanent magnet.

. )entilating system is simpler as losses ta#es place mostly in the stator.

8. ;ower semi conductor switching circuitry is simpler

K. 3o shoot through fault li#ely to happen power short circuits,

L. Developed tor*ue doesn"t depends upon the polarity of current in the phase

Winding.

M. The operation of the machine can be easily change from motoring mode to generating mode

by varying the region of conduction.

9. (t is possible to get very high speed.

76. Depending upon the re*uirement T/ characteristics can be achieved.

77. (t is the self starting machine.

7. Energy stored in the phase winding is fed bac# to the supply through the feedbac# diodes during

off period.

$*. What are the a""lications of S=M

7. Washing machines

. )acuum cleaners

. 'ans

. 'uture auto mobile applications8. -obotics control applications

$. What are the t(o t"es of c'rrent control techni/'es?

7. 0ysteresis type control

. ;W@ type control


30/33

$0. What is meant ! ener) ratio?

This energy ratio cannot be called as efficiency. &s the stored energy - is not wasted as a loss but it is

feedbac# to the source through feed bac# diodes..

$. What is "hase (in#in)s?

Stator poles carrying field coils. The field coils of opposite poles are connected in series such that

mmf"s are additive and they are called V;hase windings of S-@.

&4. What are the essential #ifference !et(een S=M an# Ste""er Motor?

7. S-@ is designed for continuous rotation.

. S-@ re*uires a rotor/position sensor.

. Stepper motor is designed to rotate in step by step rotation, (t does not re*uire

rotor/position sensor.

&1. What is hsteresis c'rrent control?

This type of current controller maintains a more or less constant current throughout the

conduction period in each phase. This controller is called hysteresis type controller.

&2. What are the a#anta)es an# #isa#anta)es of !r'shless #e motor #ries?

A#anta)es

7. There is no field winding so that field copper loss is neglected.

. ength of the motor is very small as there is no mechanical commutator, so that si!e

becomes very small.

. 2etter ventilation because of armature accommodated in the stator.

, -egenerative bra#ing is possible.

8. Speed can be easily controllable.

K. @otor can be designed for higher voltages sub>ected to the constraint caused by the power semi

conductor switching circuit.

L. (t is possible to have very high speeds.

Disa#anta)es

7. @otor field cannot be controlled

. ;ower at7g is restricted because of the maximum available si!e of permanent @agnets.

. (t re*uires a rotor position sensor.

. (t re*uires a power semi conductor switching circuit.


31/33

&. What is o"tical sensor?

& sensor is operated with photo transistor, it is the optical sensor. it is mainly red to sense the rotor

position of the 2;@DC motor.

&$. What are the merits an# #emerits of >MSM?

Merits

i (t runs at constant speed.

ii% 3o field winding, no field loss, better efficiency.

iii 3o sliding contacts. So it re*uires less maintenance.

Demerits

i ;ower factor of operation cannot be controlled as field winding cannot be controlled.

ii% (t leads to losses and decreases efficiency.

&&. What are ass'm"tions ma#e in #eriation of emf e/'ation for >MSM?

Ass'm"tions

(. 'lux density distribution in the air gap is sinusoidal.

. -otor rotates with an uniform angular velocity of wm $r=sec%.

. &rmature winding consists of full pitched, concentrated similarly located coils

of e*ual number of turns.

&*. Wh >MSM o"eratin) in self controlle# mo#e is %no(n comm'tator less DC motor?

oad side controller performs some what similar function as commutator in a dC machine. The load

side converter and synchronous motor combination functions similar to a dc machine 'irst, it is fed from

a dc supply and secondly li#e a dc machine. The stator and rotor field remain stationary with respect to

each other at all speeds. Conse*uently drive consisting of load side converter and synchronous motor is

#nown as VCommutation less dc motor.

1* MA=@S

7. Explain the wor#ing of reluctance motor

. Explain the wor#ing of stepper motor

. Explain the wor#ing of hysteresis motor.

. Explain indirect method of finding regulation

El 2241:El :EE 1242:141 El 4:40444441 E5ECT=ICA5 MACHINES

N89EMFE=:DECEMFE= 241


32/33

7=e)'lation 2440:2414;

Time Three ho'rs Ma3im'm 144 mar%s

Ans(er A55 /'estions.

>A=TA71432 J 24mar%s;

7. What is armature reaction?

. Write the induced emf e*uation when the machine acts as a DC motor and DC generator.

. Define transformation ratio.

. Why is transformer rating in #)&?

8. What is synchronous speed?

K. What is the purpose of damper winding?

L. What is the importance of slip in a three phase induction motor?

M. Draw the slip/tor*ue characteristics of a three phase induction motor.

9. Why is single phase induction motor not self starting?

76. 0ow is the construction of linear induction motor different from induction motor?

>A=TF7&31*J08mar%s;

11. 7a; 7i; Dra( an# e3"lain the constr'ction an# "rinci"al of o"eration of a DC

)enerator. 714;

7ii; A 14%W 224 9 DC * "ole sh'nt motor r'ns at 1444 r"m. Delierin) f'll

loa#. The armat're has &$ la" connecte# con#'ctors. +'ll loa# co""er

lossis 4.*$ %W. The total !r'sh #ro" is 1 olt. Determine the fl'3 "er "ole

ne)lectin) sh'nt c'rrent. 7*;

8r

7!; 7i; Dra( an# e3"lain the characteristic of a DCsh'nt motor an# DC series

motor. Com"are the DC sh'nt an# series motor characteristics an#

a""lications. 714;

7ii; Write the s"ee# e/'ation an# e3"lain ho( to control the s"ee# of a sh'ntmotor ! fl'3 control metho#. 7*;

12. 7a; 7i; Dra( an i#eal sin)le "hase transformer an# e3"lain the "rinci"le of

o"eration the conce"t of ste" '" an# ste" #o(n transformer. 70;

7ii; Derie the EM+ e/'ation of a transformer. Whatis re)'lation an#

efficienc of transformer? 70;

8r

7!; 7i; Dra( the e/'ialent circ'it of a sin)le "hase transformer an# e3"lain. 70;


33/33

7ii; Dra( an# e3"lain the o"eration of an a'totransformer. What are the

a""lications of a'totransformer? 70;

1. 7a; Dra( an# e3"lain the constr'ction #etails an# o"eratin) "rinci"le of an

alternator. Derie the emf e/'ation an# #ra( the ector #ia)ram. 71*;

8r

7!; Dra( an# e3"lain the "rinci"le of o"eration of a snchrono's motor. E3"lainthe metho#s of startin) (ith ill'stration. What is h'ntin)? 71*;

1$. 7a; Dra( an# e3"lain the constr'ction an# "rinci"le of o"eration of three "hase

sli" rin) in#'ction motor. Ho( is the constr'ction #ifferent in s/'irrel ca)e

in#'ction motor? 71*;

8r

7!; Derie the tor/'e e/'ation an# also the con#ition for ma3im'm tor/'e 'n#er

startin) an# r'nnin) con#itions. 71*;

1&. 7a; E3"lain #o'!le reolin) an# cross fiel# reolin) theor for sin)le "hase

in#'ction motor. 71*;

8r

7!; What are the constr'ctional feat'res of 'niersal motors? E3"lain the

o"eration (ith neat #ia)rams. What are its a""lications? 71*;

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