dem part b-problems final

7/26/2019 DEM PART B-Problems Final

1/22

UNIT-1:

PROBLEM 1.2 (P-1.25) Calculate the specific electric and magnetic loading of 100HP

3000V,3,50Hz,8 pole, star connected flame proof induction motor having stator core length

05m and stator !ore 0""m#urns$phase%&8"'ssume full load efficienc(%0)38 and po*er

factor %08" +-C.&013/8 mar2

PROBLEM 1.1(P-1.23) ' 004,500V ,50 rpm," pole C generator is !uilt *ith an

armature diameter of 086m and core length is 03&m#he lap *ound has ""0 conductors

Calculate the specific electric loading and magnetic loading


2/22

PROBLEM 1.8(P-1.46) ' field coil has a heat dissipating surface of 015 m &and a length of

mean turn of 1 m 7t dissipates loss of 150,the emissivit( !eing 3 $m & C -stimate the

final stead( temperature rise of the coil and its time constant if the cross section of the coil is

100950 mmhe specific heat of copper is 3)0 :$g C#he space factor is 05"Copper

*eighs 8)00 g$m3

+;'


3/22

PROBLEM 1.13(P-1.62) #he temperature rise of a transformer is &5?C after one hour and

365?C after & hours of starting from cold condition Calculate its final stead( temp rise and

the heating time constant if its temperature falls from the final stead( value to 0?C in &5

hours *hen disconnected, calculate its cooling time constant #he am!ient temperature is

30?C +;'< &015./8mar2

UNIT-2:

PROBLEM 2.6(P-2.22) etermine the airgap length of a C machine from the follo*ing

particulars = gross length of core % 01& m @ Ao of ducts %1 @ and is 10mm *ide @ slot pitch

%&5mm@slot *idth % 10 mm@CarterBs co.efficient for slots and ducts %03&@gap densit( at pole

centre % 06!$m&@field mmf per pole % 3)00'#,mmf reuired for iron parts of magnetic

circuit %800'# +;'


4/22

PROBLEM 2.1(P-2.14) #he stator of a machine has a smooth surface !ut its rotor has open

t(pe of slots *ith slot *idth s% tooth *idth, t% 1 mm and length of air gap lg%3mm Eind

the effective length of air gap if the CarterBs coefficient%1$F1G5Flg$s

PROBLEM 2.2(P-2.16) Calculate the ;;E reuired for the air gap of a machine having core

length % 03&m, including ducts of 10 mm each@ pole arc%01)m@slot pitch % "5 mm@ slot

opening % 5mm@ air gap length % 5mm @ flu9 per pole % 5&m! Iiven carterBs coefficient is

018 for opening$gap%1@ and is 0&8 for opening$gap% &

+-C.&01, &013, &010 . 8 mar, -C.&015F1" mar2

PROBLEM 2.3(P-2.17) ' 154 , &30 V , pole dc machine has the follo*ing armature

diameter % 0&5m @ armature core length % 01&5 m, length of air gap at pole center % &5


5/22

mm@ flu9 per pole % 116J10.3!,ratio pole arc$pole pitch% 0"" Calculate the ;;E

reuired for the air gap

Fi 7f the armature surface is treated as smooth

Fii 7f the armature is sloted and the gap contraction factor is 118

PROBLEM 2.9(P-2.34) etermine the apparent flu9 densit( in the teeth of a dc machine

*hen the real flu9 densit( is &15 !$m&@ slot pitch &8 mm@ slot *idth 10 mm and the gross

core length % 035m#he num!er of ventilating ducts is , each 10 mm *ide #he

magnetizing force for a flu9 densit( of &15 !$m&is 55000 '$m #he iron stacing factor is

0) +;'


6/22

ventilating ducts %",each 10mm *ide@ real flu9 densit( % && !$m &@ permea!ilit( of teeth

corresponding to real flu9 densit(%31 J 10."H$m @ stacing factor is 0)

PROBLEM 2.11(P-2.45) ' 54, pole,&50V ,1500 rpm shunt generator is designed to have

a suare pole face #he loadings are ='verage flu9 densit( in the gap %0&!$m& and ampere

conductor per metre % 15000Eind the main dimensions of the machine 'ssume fill load

efficienc( 086 and ratio of pole arc to pole pitch %0""

+;'


7/22

+'K.CL7;M'#LN-.;'< &0132


8/22

PROBLEM 2.12(P-2.47) ' design is reuired for a 504, pole, "00rpm, dc shunt generator

, the full load terminal voltage !eing &&0V7f the ma9imum gap densit( is 083!$m&and the

armature ampere conductors per meter are 30000 Calculate suita!le dimensions of armature

core to give a suare pole face

'ssume that the full load armature voltage drop is 3 percent of the rated terminal voltage, and

that the field current is 1 percent of rated full load current Natio of pole arc to pole pitch is

0"6 +;'


9/22

PROBLEM 2.13(P-2.50) Eind the main dimesions of a &00,&50V,"pole ,1000rpm

generator#he ma9imum value of flu9 densit( in the gap is 086!$m& and the ampere

conductors per metre of armature peripher( are 31000the ratio of pole arc to pole pitch is

0"6 and the efficienc( is )1O'ssume the ratio of length of core to pole pitch is 065

PROBLEM 2.19(P-2.78) etermine the diameter and length of armature core of a 554

110V, 1000rpm, pole shunt generator, assuming specific electric and magnetic loadings of

&"000 ampcond$m and 05!$m&respectivel( #he pole arc should !e 60O of pole pitch and

length of core a!out 11 times the pole arc 'llo* 10amperee for field current and assume a

voltage of volts for the armature circuit pecif( the *inding used and also determine

suita!le values for the num!er of armature conductors and num!er of slots+;'


10/22

average gap densit( of 055 !$m&and ampere conductors per meter as 16000 L!tain the

main dimensions of the core and particulars of a suita!le armature *inding

+;'


11/22

+;'


12/22

stacing factor %0)#he net iron area is 05"d&in a cruciform core *here d is the diameter of

circumscri!ing circle 'lso the *idth of largest stamping is 085d +-C.&012

PROBLEM 3.7(P-3.25

) Calculat a!!"#$%&at #'"all %&*%#* +#" a &00 4V'""00$00V, 3 phase core t(pe transformer#he follo*ing data ma( !e assumed= emf per

turn%10V,ma9imum flu9 densit(%13!$m&,current densit(%&5,&&2 *indo* space

factor% 03,overall height % overall *idth,stacing factor%0)Kse a 3 stepped core for *hich

net iron area is 0" d&and *idth of largest stamping is 0)d +-C.&01&,&0102

PROBLEM 3.16(P-3.65) ' ""00 V, "0 Hz single phase transformer has a core of sheet steel

#he net iron cross.sectional area is &&" S 10D3 m&, the mean length is &&3 m, and there are

four lap Roints -ach lap Roints taes T times as much reactive mmf as is reuired per metre

of core 7f Mm % 11 !$m&, determine

i #he num!er of turns on the ""00 V *inding and

ii #he no load current 'ssume an amplitude factor of 15& and that for given flu9

densit(, mmf per metre % &3& '$m@ specific loss % 16" $g pecific gravit( of

plates % 65


13/22

+;'


14/22

PROBLEM 3.19(P-3.77) ' 10004V',""00V$0V,50Hz,3 phase,delta$star core t(pe,oi

immersed,natural cooled transformer#he design data of the transformer is=

istance !et*een centers of adRacent lim!s%06m,outer diameter of high voltage *inding

0m,height of frame%1&m

Core loss%36 and 7&

N loss%105esign the suita!le tan for the transformer#he average temperature rise of oil should not

e9ceed 35oC

#he specific heat dissipation from the tan *alls " and "5$m&.oC due to radiation and

convection respectivel( 'ssume that heat convection is improved !( 35O due to provision of

tu!es

PROBLEM 3.2/(P-3.80) #he tan of a 1&504V' natural oil cooled transformer has the

dimensions length, *idth and height 155mU0"5mU185m respectivel( #he full load loss is

131 Eind the num!er of tu!es for this transformer 'ssume $m&C due to radiation %"

and that due to convection is "5improvement in convection due to provision of tu!es is

0O;a9imum temperature is 0Clength of each tu!e is 1miameter of the tu!es is

50mmAeglect the top and !ottom surfaces of the tan as regard to cooling +;'


15/22

UNIT-4:

PROBLEM 4.1(P-4.11) Eind the main dimensions of a 154,three phase 00

volts,50Hz,&810 rpm suirrel cage induction motor having an efficienc( of 88O and full load

po*er factor of 0) pecific magnetic loading is 05 *!$m& and specific electric loading %

&5000'$m#ae rotor peripheral speed as appro9imatel( &0m$sec at s(nchronous speed+-C. &012

PROBLEM 4.2(P-4.13) etermine main dimensions of a &50 HP, 3 phase, 50 Hz, 00 volts,

110 rpm, slip ring induction motor 'ssume Mav % 05*!$m&, % 30000 ac$m, efficienc( %

)0 O and po*er factor % 0), *inding factor % 0)55, current densit( %35 a$mm&

+;'


16/22

PROBLEM 4.5(P-4.28) -stimate the stator core dimensions and the total num!er of stator

conductors for a 3phase, 1004, 3300V, 50Hz, 1& pole star connected slip ring induction

motor 'ssume average gap densit( % 0*!$m&, conductors per meter %&5,000'$m

efficienc( %0), po*er factor%0) and *inding factor%0)" Choose main dimension to give

!est po*er factor #he slot loading should not e9ceed 500ampconductors

+;'


17/22

PROBLEM 4.1/(P-4.61)' 11, 3 phase, 50Hz, "pole &00V, star connected induction motor

has 5 stator slots, each containing ) conductors Calculate the current in rotor !ars #he

num!er of rotor !ars is " #he machine has an efficienc( of 08" and a po*er factor of 085

#he rotor mmf ma( !e assumed as 85Oof stator mmf 'lso find the !ar and end ring sections

if the current densit( is 5'$mm

&

+;'


18/22

PROBLEM 4.17(P-4.95) ' 15 , 00v, 3phase, 50Hz, "pole 7nduction motor has a diameter

of 03m and the core length of 01&m #he num!er of stator slots is 6& *ith &0conductors per

slot #he stator is delta connected Calculate the value of magnetizing current per phase if the

length of airgap is 055m #he gap contraction factor is 1& 'ssume the mmf reuired for theiron parts to !e 35O of the air gap mmf Coil span%11slots

+ -C. &01&2

UNIT-5

PROBLEM 5.4(P-5.17) Eind the main dimensions of a &5004V', 1865rpm, 50Hz, 3phase,

34V, salient pole s(nchronous generator #he generator is to !e vertical *ater *heel t(pe

#he specific magnetic loading is 0"*!$m&and the specific electric loading is 3000 '$m use

circular poles *ith the ratio of core length to pole pitch %0"5pecif( the t(pe of pole

construction used if the runa*a( speed is a!out & times the normal speed

+;'


19/22

PROBLEM 5.2(P-5.12) Eind the main dimensions of a 100;V',114V, 50Hz,150 rpm 3phase

*ater *heel generator #he average airgap flu9 densit( % 0"5*!$m &and ampere conductors

per metre 0000 #he peripheral speed should not e9ceed "5 m$s at normal running speed in

order to limit runa*a( speed +;'


20/22

appro9imatel( 0) *!$m&'ssume sinusoidal distri!ution Kse single la(er *inding and star

connection for stator

+-C&015, ;'


21/22

PROBLEM 5.8(P-5.36) etermine the main dimensions of a 1&;V',138 4V, 50Hz,150 rpm

3phase alternator 'verage airgap flu9 densit( % 0" #esla ac$m% &000,peripheral speed % 80

m$sEind also the ma9imum flu9,num!er of ststor slots if one conductor per slot is

used,num!er of turns per phase

PROBLEM 5.1/(P-5.41)' 5004V', 334V,50Hz,"00rpm

3 phase salient pole alternator has

180 turns per phase -stimate the length of air gap if the average flu9 densit( is 05 *!$m &

the ratio of pole arc to pole pitch%0"5, short circuit ratio%1&, gap concentration factor %115

and the *inding factor%0)55 #he mmf reuired for gap is 80 percent of no load field mmf

PROBLEM 5.11(P-5.43) #he follo*ing is the design data availa!le for a 1&50 4V',3

phase,50Hz,3300V star connected, 300 rpm alternator of salient pole t(pe=

tator !ore %1)m,stator core length %0335m,pole arc$pole pitch%0"",turns per

phase%150, single la(er concentric *inding *ith 5 conductors per slot, short circuit ratio%1&

'ssume that the distri!ution of gap flu9 is rectangular under the pole arc *ith zero values in

the interpolar regionCalculate

Fi pecific elctric loading Fiiarmature mmf per pole


22/22

Fiiigap densit( over pole arc Fivair gap length

#he mmf reuired for the air gap is 088 of no load field mmf and the gap concentraction

factor is 115

PROBLEM 5.15(P 5.65, 5.67)#he field coils of a salient pole alternator are *ound *ith a

single la(er *inding of !are copper strip 30mm deep, *ith separating insulation 015mm

thic etermine a suita!le *inding length, num!er of turns and thicness of conductor to

develop an mmf of a 1&000' *ith a potential difference of 5V per coil and *ith a loss of

1&00$m&of total coil surface #he mean length of turn is 1&m #he resistivit( of copper is

00&1>$m +;'

dem part b-problems final

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