Jawaharlal Nehru Engineering College
Laboratory Manual
ELECTRICAL MACHINE.
For
Second Year (EEP) Students
M a n u a l made by
Prof. Suradkar R.P. .
FORW ARD
I t is my g reat p leasure to p resent this laborator y m a n u a l for second y ear EEP
en g ineerin g students for the subject of Electrical Machine. Ke e p in g in view the vast
covera g e re q uired for visualization o f conce p ts of Electrical Machines with sim p le
lan g ua g e.
As a student, man y of you may be wonderin g with some of the q uestions in y our
mind re g ardin g the subject and exactl y what has been tried is to answer throu g h
this manual.
Facult y members are also advised that coveri n g these as p ects in initial sta g e itself,
w i l g r e a t l y relived them in future as much of the load w i l be taken care by the
enthusiasm ener g ies of the students once the y are conce p t u a l y clear.
H.O.D.
g
ÓAut hor J NEC , Aur an abad.
LABORATORY MANNUAL CONTENTS
This m a n u a l is intended for the second y ear students of EEP En g ineerin g branch
in the subject of El e ctri cal Machine. This m a n u a l t yp i c a l y contains p ractical/Lab
Sessions related electrical machine coveri n g various as p ects related the subject to
enhance understandin g .
Althou g h, as per the s ylabus, o n l y descri p tive treatment is p rescribed, we have
made the efforts to cover various as p ects of electrical machine subject coverin g
t yp es of different electrical machines, their o p eratin g p r i n c i p als, their
characteristics and A p p lications w i l be com p lete in itself to make i t meanin g ful,
elaborative understandable conce p ts and conce p t u a l visualization.
Students are advised to thorou g hl y go throu g h this manual rather than onl y to p ics
mentioned in the s y labus as p r a ct i ca l as p ects are the key to understandin g and
conce p t u a l visualization o f theoretical as p ects covered in the books.
Good Luck for y our Enjo y able Laborator y Sessions
Prof. Suradkar R.P.
SUBJECT INDEX
1. Do’s and Don’ts
2. Lab exercise:
1) To p lot ma g netization characteristics of d. c. g enerator.
2) To stud y load characteristics of d. c. com p ound g enerator.
y
p
3) To stud s eed control of d. c. shunt motor.
4) To p erform load test on d. c. shunt motor.
5) To stud y 3 p hase transformer connection & their volt a g e relations.
y
6) To stud d. c. motor starter.
3.
Quiz on the subject
4.
Conduction of Viva-Voce Examination
5.
Evaluation and Markin g S y stems
D Os and DO N ’T DO s in La bor ato r y :
1. Und erstand th e e q ui p m ent to b e tested and a p p aratu s to be us ed .
p
p
yp
.
.
g
2. Select ro er t e ( i e A. c. or D. C.) and ran e of m eters
3. Do not touch the liv e t erm inals
.
.
4. Us e suitable wir es ( t yp e and s i z e ) .
5. A l the conn ection sho uld be t i g h t .
1.
Do not leav e loos e wires ( i . e . wir es not conn ect ed) .
2.
Get the co nn ection ch eck ed b ef or e switchin g ‘ O N ’ the su p p l y .
3.
Nev er exc eed th e p erm issible values of c u r r e n t , volta g e , and / or s p eed of any m achine,
pp
a aratus, w i r e , l o a d , etc
.
g
y
y.
4.
Switch ON or OFF the load r a d u a l and not suddenl
5.
S t r i c t l y observ e th e instructions g iven b y the t eac h er/Lab I n s t r u c t o r
In s t r u c t i on f o r Labo ra tor y T ea che rs :
1.
Subm ission related to wh at ev er lab work has b ee n com p leted sho uld b e don e durin g th e n ext lab
session . Th e imm ediate arran g em ents for
g
assi nm ents
2.
p
r i n t ou t s related to subm ission on the day of
p
r ac tic a l
.
Stud ents should b e tau g ht for takin g the obs er vations /readin g s of d i f f e r e n t m easurin g instrum ents
und er the a ble o bs ervation of lab teach er .
3.
Th e p rom p tness of subm ission should be en coura g ed by way of m arkin g and evaluation p a t t er n s t h a t
w i l b en ef i t the sinc er e stud ents
.
2. Lab E xe r c is e s :
[ Purp os e o f t hi s exer ci s e i s t o i n t r o d u c e t h e st uden t s t o diff er ent D. C. a nd A. C. m ac hin es .]
–
E x e r c i s e N o 1 : ____________( 2 H o u r s )
1 Practical
M a g n e t i za t i o n c h a r a ct e r i st i c s o f a d . c .
g
A I M : To fin d m a n eti zati on c har ac t er isti cs of a d. c.
g
g
enerator.
en erat or
.
APPARATUS :
.
.
p
p
1 ) D C m ac hi n e wit h a c o u l ed rim e m o v er
2 ) Rh eo st at ( 3 0 0 / 1 . 7 ) ------------------- 1 n o.
3 ) D . C . Amm et er ( 0 - 1 A ) ---------------- 1 n o
4 ) D . C . vol tm et er ( 0 - 3 0 0 v ) ------------- 1 n o
THEO RY:
.
g
1 W h at i s r es i d ua l m a n et ism ?
2 . W h at i s O . C . C . ?
3 . Ho w v olt a g e i s d ev el o p ed in s elf exc it ed D. C. g en er at or s ?
PRO CEDURE :
1 ) Co n n ect as sh o wn in ck t . Di a .
2 ) Set th e p o t e n t i a l div id er t o zer o ou t p ut i . e . at m a x . r esi st an c e p osi tio n .
3 ) Ru n t h e g en er at or wit h t h e h e l p of its p rim e m ov er a t r at ed s p eed .
4 ) No t e th e r ea di n g of vo ltm et er c on n ect ed ac ro ss arm atu r e t erm in als of t h e g en er at or .
5 ) Switc h on D . C . Su p p l y t o t h e f i el d win di n g a nd p as s a sm al cur r ent by c ha n g i n g t h e s et ti n g of
p
.
g
g
.
t h e o t e n t i a l di vid er Not e th e fi el d c ur r en t & en er at ed vo lta e In cr ea s e th e fi eld
p
p
g
g
c u r r en t i n s t e s a nd n ot e c orr es o n din arm atu r e vo lta e
6 ) Plo t a rm atur e v olt a g e v ers us th e fi eld c ur r en t .
O SERVATION TABL E :
p
g
S eed of t h e en er at or = - - - - - - - - r. p.m .
.
Sr. No.
Fi el d c u rr en t r ea di n g t o b e t ak en in
i ncr ea si n g or d er of fi el d c urr en t I f am p s
1.
2.
3.
4.
5.
G RAPH:
0
g
Arm atu r e vo lta e E v olts
Va
CO NCL USION:
Becaus e of th e r esidual m a g netism the curv e do esn’t start from zero volt s .
Du rin
g
c ur r ent
g
th e s t ar ti n
.
g
p
A f t e r s at ur atio n o f
m a n etic cu rr ent
.
g
orti on of t h e c u r v e , t h e i nd u c ed vo lta e ri s es l i n ea r l
p
ol es c ur v e l oo s es it ’s lin ea rit
y
y
g
with m a n eti c
g
b et ween i nd u c ed v olt a e a n d
MAGNETISATION CHARACTERISTICS OF D C GENERATOR
230 V
D C SUPPLY
3- PHASE
INDUCT ION MOTOR
–
Exercise N o 2 : ( 2 ____ Hours)
1 Practical
L o a d c h a r a c t e r i s t i c s o f d . c . C o m po u n d
g
enerator.
A I M - To stu d y lo ad c har a ct eristi cs of d. c. Com p ou n d g en erat or .
p
g
a ) Cum ul ativ e com ou nd en er at or
.
b ) D i f f e r e n t i a l c om p o un d g en era tor .
APPARATUSp
1 ) Rh eo st at ( 1 2 0 , 0. 6 am ) ---------------------------- 1 n o
2 ) Rh eo st at ( 5 0 0 , 1 .2 am p ) ---------------------------- 1 n o.
3 ) D. c. v oltm et er ( 0 - 3 0 0 v o l t )
----------------------- 1 n o
.
THEO RY:
.
p. g
1 W h at i s e f f e c t o f lo a d o n D. C. c om
en era tor ?
2 . W h at i s di ff er en c e b et ween cum ul ativ e & d i f f e r e n t i a l com p . g en er at or ?
3 . W h y terminal volt a g e dro p is ra p id in diff . Com p . D. C. g enerators as com p ared to comm . Com p .
g
en er at or ?
PRO CEDURE: 1 ) Ma k e t h e co n n ecti on as p er t h e cir c uit di a . Th e s eri es fi eld i s sh o wn co n n ect ed f o r t h e
c um ula tiv e c om p o un d c a s e , a s p er us ual m ar kin g .
2 ) S t a r t th e m oto r a n d a d j us t i t s s p eed wit h t h e h e l p f i ts fi el d r h eos tat to th e r at ed s p eed of
g
en er at or .
j
g
g
3 ) Ad u st t h e s hu nt f i el d r h eos tat of th e d. c . en er ato r t o obt ai n t h e sui ta bl e v olt a e at no
l o a d , s ay a l i t t l e h i g h er th a n it s ra t ed volt a g e at no lo a d . Not e t h e s am e .
4 ) L o ad th e g en era tor . Not e th e l oa d cu rr ent s a n d t h e cor r es p o ndi n g t erm i n a l vol ta g e s , (u p t o
r at ed l o ad c u r r e n t ) .
5 ) Dis co n n ect t h e s u p p l y an d r ev er s e th e s eri es fi eld c o nn ec tio ns . Th e g en er ato r n o w w i l wo rk
a s d i f f e r e n t i a l y c om p o u nd g en er at or .
p
p
6 ) Re ea t st e s ( 2 ) to ( 4 )
7 ) Plo t t h e t e r m i n a l v olta g e V/s lo ad c urr ent c urv e f o r b ot h t h e ca s es .
OBSERVATION TABLE: -
a)
Sr
No
1
2
3
4
p
g
For c um ulati v e c om ou n d en er at or
L o ad c urr en t in am p s ( I L) _ _ _
Term in al v olt a g e . ( V L) _ _
p
b)
g
For d i f f e r e n t i a l c om o un d en era tor
p
Sr. No
L o ad c urr en t in am s ( I L)
g
.
Term in al v olt a e ( V L)
1
2
3
4
G RAPH :
CO NCL USION: g
yp
p
Th e v ari atio n o f t er m i n a l v olta e wit h l oa d c urr ent f o r th e t wo t es o f d. c . com ou nd
g
.
en er at or ar e t ak en I t is ob s erv ed t h a t wit h t h e d i f f e r e n t i a l
g
p
t er m i n a l v olt a e f a l s m or e r a i d l
g
y
y
p
c om o u nd
g
en er at o r , the
wit h t h e l oad whil e wit h th e cum ula tiv e
t er m i n a l v olta e r em ai ns alm os t c on st ant
.
g
en era tor ,
LOAD CHARACTERISTICS OF D.C. COMPOUND GENERATOR
D.C. SHUNT MOOTR
3 HP, 2.2 KW
1500 RPM, 12.8 A, 230 V
Exercise No3: (
2 ____ Hours)
S pe e d c o n t r o l o f
y
a d .
c .
–
1 Practical
shunt motor
p
A I M : t o st u d t h e s eed c o n t r o l of a d. c. s h unt mo to r
.
.
a ) b y va r y i n g fi el d c u rr en t wit h a rm atur e volt a g e k e p t c o nst a nt .
b ) By v ar y i n g arm at ur e v olt a g e wit h fi eld c u r r en t k e p t c o nst a nt .
APPARATUS: p
1 ) rh eo st at ( 1 0 0 F 1 .2 am )
--------------------------------------------------------------- 1 n
2 ) Rh eo st at ( 1 0 0 F o6 .0 am p)
3 ) D. c. v oltm et er ( 0 - 3 0 0 1
vn
o ol t ) ------------------------- 1 n o.
4 ) D . C . Amm et er ( 0 - 1 A ) --------------------------------- 1 n o
THEO RY:
1 . W h at i s e f f e c t o f v olt a g e on D. C. s h unt m ot or ?
.
p
2 W h at ar e d i f f e r e n t f a c t o r s whic h a f f e c t th e s eed o f D. C. sh unt m otor ?
PRO CEDURE: 1 ) Ma k e t h e co n n ecti on s a s p er c ir c uit di a
.
2 ) Set u p t h e fi eld an d arm atu r e rh eo st at t o t h ei r m axim um val u e .
3 ) Switc h on th e D . C . Su p p l y st art t h e m otor wi th th e h e l p of s t a r t e r . Ad j u st t h e fi el d c u rr en t t o
r at ed va lu e .
4 ) No t e th e s p eed wit h t h e h e l p of t a c h o m e t e r , th e vo lta g e a cr os s arm atur e an d t h e fi eld c u r r en t .
5 ) Ch a n g e t h e s p eed b y v ar y in g t h e rh eo st at i n t h e arm atu r e ci rc u it . Not e t h e s p eed a n d a rm atur e
v olt a g e , th e fi el d c ur r en t r em ai nin g co ns ta nt .
p
p
6 ) Re ea t st e s 4. an d 5. ab ov e, f o r d i f f e r e n t fi el d cu rr ent s
.
7 ) Plo t s p eed V/s arm at ur e v olt a g e
p
.
g
8 ) Kee th e r h eo sta t in t h e a rm atur e cir c uit to som e fi xed v al u e No t e t h e v olt a e a cr os s a rm atur e
p
No t e th e fi eld c ur r en t a nd s eed
.
9 ) Va r y t h e fi el d c u rr en t .
O BSERVATIO N TABL E: a ) Arm atur e vol ta g e v ari atio n .
1 ) Fi el d c ur r en t ( c o n s t a n t ) = _ __ _am p s .
Sr. n o.
1.
2.
3.
4.
5.
6.
Arm atu r e vo lta g e
( Va in v o l t s )
p
S eed (r
.p .
m)
.
b ) Va ria bl e Fi el d c u rr en t
g
1 ) Arm atur e volt a e ( c o n s t a n t ) = ---------- v olt s.
Sr.
No
1.
2.
3.
4.
5.
p
Fi el d c u rr en t ( I f i n am s) _ _
p
S eed (r
.p .
.
m)
G RAPH :
V
O
L
T
S
SPEED
CO NCL USION: Th e vari ati on of s p eed with arm at ur e v olt a g e an d fiel d c u r r en t h as b een s tu di ed . Th e s p eed of
d . c. Sh un t m ot or is d i r e c t l y p ro p o r t i o n a l to t h e arm at ur e volt a g e an d in v ers el y p ro p o r t i o n a l to t h e
fi el d c u r r en t . T h u s , t o in cr ea s e s p eed ab ov e r ated s p eed fi el d c u r r en t sh o uld b e d ecr ea s ed & t o
d ec r ea s e th e s p eed b el o w r at ed s p eed arm at ur e v olt a g e sh o uld d ecr ea s e .
SPEED CONTROL OF D.C. SHUNT MOTOR
(0-300 V)
D.C. SHUNT MOTOR
3 HP / 2.2KW 230 VOLT
1500 RPM, 12.8 AMP.
Exercise No4: ( 2 Hours) –
1 Practical
Load test on D.C. shunt motor.
p
.
.
A I M - To er f o rm l o a d t e s t o n D C s h u n t m ot o r
APPARATU S 1 ) Rh eo s t a t ( 5 7 0 o h m , l Am p ) ---------------------------- 1 n o
2 ) Rh eo s t a t ( 3 0 0 o h m , 1 . 7 am p s ) ------------------------ 1 n o .
3 ) D. c . v o ltm et er ( 0 - 1 0 o hm ) -------------------------------- 2 n o .
4 ) D. c . v o ltm et er ( 0 - 3 0 0 v ) ----------------------------------- 2 n o
5 ) Ta c h om et er
.
THEO RY:
.
1 W h at i s e f f e c t o f l o a d o n D. C. s h u n t m ot o r ?
.
y
2 W hat is the relation b etween effici en c & load of D. C. shunt m otor ?
3 . W h y c u rr en t & t or q u e i n c r ea s es l i n e a r l y wi t h t h e l o a d ?
PRO CEDURE
1 ) Ma k e t h e c o n n ec t i o n a s p er c i r c ui t d i a .
2 ) Set t h e f i el d r h eo s t a t of m o t o r t o zer o a n d f i el d r h eo s t a t o f
g
maximum .
en er a t o r t o
3 ) Swi t c h o n D . C . s u p p l y a n d s t a r t t h e m o t or wit h th e h e l p o f s t a r t e r .
j
p
.
g
g
4 ) Ad us t fi eld rh eo st at f or m ot or t o obt ai n r at ed s eed Fo r on e s et of r ea di n s th e s etti n of
f i el d r h eo s t a t s h o u l d n ot b e a l t er ed .
5) Ad j ust D . C . s hunt g en er ator v olt a g e to it ’s r at ed v olt a g e with th e h el p of it ’s fi el d rh eosta t .
6 ) L o a d t h e g en er a t o r wit h k ee p i n g i t ’s t er m i n a l v o lt a g e c o n s t a n t .
7 ) No t e t h e r ea d i n g o f a m m et e r s , v o ltm et er s a n d s p e ed .
8 ) Re p ea t ( 6 ) a n d ( 7 ) a b o v e t o a c o v er t h e r a n g e o f n o l o a d t o f u l l o a d of m o t or .
p
p
p
y
p
q
p
9 ) Plot s eed v s. o u t u t, a rm atur e cur r ent Vs o u t ut, effi ci en c Vs ou t ut, t o r u e vs. o ut ut
c u r v es
SAMPL E CAL C UL ATI O N y
g
Ef f i ci en c o f en er a t o r i s a s s um ed a s 8 7%
G en er a t o r o u t p u t – Vg I g wa tt s .
p
g
p
G en er a t o r i n u t = en er a t o r o u t u t /
0
.
87
G en er a t o r i n p u t = m ot o r o ut p u t .
p
Mo t o r i n ut – Vm Im wa t t s
.
y
p
p
% Mo t o r ef f i ci en c = (m o t o r o u t ut / m ot o r i n u t ) * 1 0 0
q
p
Mo t o r To r u e = (m o t o r o u t u t i n w a t t s ) * 6 0
2n
N-M
O BSERVATIO N TABL E :
GENE
R
ATO
Sr.No.
Vg R
1
2
3
4
5
Ig
MOTO
R
Vm
SPEED
(rpm)
Im
MOTOR MOTOR
EFFI.
TORQUE
I/P
O/P
OF
(N.M)
(watts)
(watts) MOTOR
G RAPH :
M
T
O
C
U
R
N
O
R
R
E
T
OU T PU T
T O R Q U E
V s
M OT OR CU R RE N T V s OU T PU T
O U T P U T
E
F F
I
C
E
I
S
P
N C
Y
E E
OU T PU T
D
OU T PU T
E FFI CIE N CY V s OU T PU T
SPE E D V s OU T PUT
CO NCL USION From th e a bo v e
g
ra p h s , t h e m oto r cu rr ent i ncr ea s es wit h t h e l o a d , an d th e s p eed d ecr ea s es
sli g htl y with increase in load . Th e efficienc y initial y increas es with th e l o a d , and then rea ch es i ts
m a xim um (at ab ou t 8 0 t o 90 % of th e f u l l o a d ) a nd t h en d ecr ea s es .
LOAD TEST ON D.C. SHUNT MOTOR
Exercise No5: ( 2 Hours) –
Three
p
1 Practical
hase transf ormer connection
y
p
y
y
A I M : To st ud th e Th r ee h as e Tr an sfo rm er Co nnec ti o ns, whic h ar e c omm onl u s ed & To st ud t h ei r
Vol ta g e r elati o n .
APPARATUS : 1.
3 Ph as e Tra n sfo rm er .
2.
Vol tm et er ( 0 - 6 0 0 V )
THEO RY:
.
1 W h at ar e th e d i f f e r e n t t r a n s f o rm er co nn ec tio n s ?
.
p
p
.
.
p
2 W hat is hase shift bet ween rim & sec of 3 hase transform er ?
.
3 W h at ar e th e d i f f e r e n t a
pp
l ic atio n s o f tr an sf orm er ?
PRO CEDURE :
1 ) Ta k e th r ee p h as e tr a nsf orm er .
2 ) Ma k e c o nn ecti o ns as p er t h e c ir c uit di a g ram
3 ) For th at co n n ecti on s, m ea su r e Li n e & Pha s e Volt a g e for Prim ar y & Seco nd ar y si d es .
4 ) Re p ea t thi s p r oc ed ur e f o r a l t yp es of c on n ecti on . .
O BSERVATIO NS:
1.
p
(V 1 ) =
For Y -Y Co nn ect ed T r a n s f o r m e r : Mea su r ed v al u e
, (V1 1) =
2.
(Vp1 ) =
p
, (V 2 ) =
For M - M Con n ect ed T r a n s f o r m e r : Mea su r ed v alu e
, (V1 1) = , (V p 2 ) =
3.
p
, (V1 1) = , (V 2 ) =
4.
p
, (V1 2) =
For M - Y Con n ect ed T r a n s f o r m e r : Mea su r ed
p
v al u e ( V 1 ) =
, (V1 2) =
For Y - M Con n ect ed T r a n s f o r m e r : Meas ur ed v alue
p
(V 1 ) =
, (V1 2) =
, (V1 1) = , (V 2 ) =
, (V1 2) =
CAL CUL ATIO NS :
1.
Find [(VP2) / ( V p 1)] = & [( V12) / (V11)] =
& Ch ec k t h e Rel ati on as b e l o w: -- -1 . For M- M Co n n ecti on
(Vp1 ) = ( V I I )
p
Fin d [ (VP2) / (V 1)] = K & [( V12 ) / ( V11 )] = K
2.
For Y-M Connection
(Vp1 ) = 3. Vp1;
p
[(VP2) / (V 1)] = K & [( V12) / (V11)] = K
3.
For M - Y Connection
p
p
(V 11) = 3. V 1;
p
p
[(V 2 ) / (V 1)] = K & [( V12) / (V11)] = K /3
4.
For Y-Y Connection
(Vp1 ) = ( V I I ) ; (Vp2 ) = (V12) / 3;
[(Vp2 ) / (Vp1)] = K & [( V12) / ( V I I ) ] = 3. K
CONCLUSION :
Al the Transformer Voltages verifies the Relation given between Line & Phase Voltages.
TRANSFORMER CONNECTIONS
1. Y - Y CONNECTION
3. A - A CONNECTION R
TRANSFORMER CONNECTIONS
3 . Y - A CONNECTION
Yz
4. A - Y CONNECTION
Exercise No6: ( 2 Hours) – 1 Pr a ct i c a l
D .
C . motor starter
At starting, Eb =0 because sp eed of motor is zero . Armature current of motor is e q ual t o ,
Ia = V- Eb / Ra
so Ia =V/ Ra (Eb = 0)
Since Ra is ver y smal so motor w i l draw lar g e armature current . To limit the armature current in
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safe value we add some external resistance in armature circuit A mechanism which adds resistance
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durin startin onl is known as starter
THEORY
There are two t ypes of starters which are commonl y used for d. c. shunt motor
1) 3-point starter
2) 4 - point starter
3- POINT STARTER
Three p oint starter is shown in the f i gure 1 , when motor is st a r t e d, starting arm is moved slowl y
towards the ON position
1)As soon as arm touches the stud no. 1 f u l starting resistance get connected in the armature circuit .
1) Field current receives su ppl y di rect l y
The starting armature current is e qual t o ,
Ia = V / (Ra + Rs t )
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2) The arm is moved a ainst the s rin force towards the ON position.
3) When the arm travels towards ON position , the startin g resistance is gradual y removed from
armature circuit . since motor takes f u l speed, motor develo ps f u l back E. M. F . the starting arm
carries a soft iron piece which is held by attraction of the hold on coil . starter remains in ON
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osition because the electroma gnetism formed by NO VOLT COIL
FUNCTION OF HOLD ON (NO VOLT COIL)
1) In case of su ppl y failure NO VOLT COIL gets de-ener gized and the startin g arm w i l be released to
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OFF osition This is automatical done by s rin action
2) I t hold the plunger in ON position
3) I t gives the protection a gainst field failure
FUNCTION OF OVERLOAD COIL
Overload coil is a electroma gnet connected in series with armature . when current exceeds be y ond
certain predetermined value the electroma gnet w i l become strong and i t attracts plung er. Due to this
voltage across NO VOLT COIL becomes zero . this w i l make hold on coil de –ener gized due to which
arm gets to OFF position and motor gets disconnected from su ppl y.
L I M I T A T I O N S O F THREE POI NT STARTER
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1 ) W hen m oto r is in O N ositi o n t h e s t ar t i n r esist a nc e ets r em ov e f orm arm atu r e ci r cu it at t h e
s am e tim e i t g et s at ta ch ed to fi eld c i r c u i t , whic h is d an g er ou s t o t h e m ot or .
2 ) W hen we c o n t r o l s p eed of m otor b y fi el d c o n t r o l m e t h o d , r es ist an c e i n fi el d cir c ui t r ed uc es
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fi el d c u r r en t whic h i ncr ea s es t h e s eed of m otor at th e s am e tim e th er e is ch an c e u nd er O N
c o ndi tio n m ot or c ou ld d is co nn ec t from su
l es s fi eld c u r r en t
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l d u e t o d e en er i sati o n of HOL D ON C O I L , du e to
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4 - POI NT STARTER
4-
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oint starter with brass arc covers lim itations of 3 .
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oint starter; usi n
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brass arc covers f i r s t
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lim itati on Maki n f i el d c ir c uit a th i nd e en d en t of h ol d c o i l ci rc ui t b y m akin f o r t h oi nt i n a ddi tio n
wit h 3 - p oi nt cir c ui t c ov er s s ec o nd l im itatio n .
W hen field current is reduc ed while controli n g s p eed of m otor wil not effect on m a g netic field of
hold on coil becaus e circuit of hold coil is s e p arate than field coil circui t as shown in the f i g . 2 .
THREE POINT STARTER
P - SOFT IRON PIECE
H - HANDEL
S - SPIRAL SPRING
M 1 - HOLD ON COIL
M 2 - OVER LOAD COIL
C -CUREENT CONTROL RELAY
4 POINT STARTER
KNOB
C - CURRENT CONTROL RELAY
M 2 - OVER LOAD COIL
P - SOFT IRON PIECE
H - HANDLE
S - SPIRAL SPRING
M - HOLD ON COIL
3. Quiz o n _ _ t h e s u b j e c t :
W hat is the workin g p r i n c i p le of D. C. Generator?
W hat are the different t yp es of D C Generator?
W hat is the workin g p r i n c i p le of D. C. Motor?
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W hat are the different t es of D C Motor?
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W hat is the workin r i n c i p le of three p hase Induction Motor?
Load characteristics of D.C. Com p ound Generator.
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a. What are the different t es of D.C. com ound Generator?
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b. What is the difference between flat com ounded & over com p ounded g enerator.
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c. Why the terminal volta e dro s when the enerator is loaded?
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d. What ha ens i f we connect the shunt field of com ound enerator in
series with the armature & series field across the armature?
e. What are the a pp lications o f d. c. com p ound g enerator?
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f. How to identif the series field & terminal at the terminal box?
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7. S eed control of D.C. Shunt motor
a. What are the factors on which s p eed of D.C. Shunt motor de p ends?
b. Name the different s p eed control methods.
C. W hat is the disadvanta g e of armature rheostat method?
d. What is the advanta g e of Ward Leonard method?
e. Where the D.C. S h u n t motor is a pp licable?
8. Load test on d. c. shunt motor.
a. What is the p ur p ose of Load test on d. c. shunt motors?
b. What is the relation between Ia and Armature Cu loss?
c. What are different losses in D.C. sh u n t motor.
9. Generators
a. Why s p eed control methods are not needed in d. c. g enerators?
b.W hat is the use of commutator & brushes in D C Generator?
c. How ener gy conversion takes p lace in D C Generator. d.W hat is the
effect of increasin g load on terminal volta g e in D C shunt
Generator.
10. Motor
A. How ener gy conversion takes p lace in D C Generator.
B. Why D C Motor is known as constant s p eed motor?
C. Why starter is necessar y for startin g of D C motor?
D. Ex p lain the disadvanta g e of 3 p t. Starter.
E. How to reverse the direction of rotation of D C shunt Motor.
F. What is the use of commutator & brushes in D C Motor? )
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2.
3.
4.
5.
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4 . C o n d u c t i o n o f _____ Viva -V oc e
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E x a mi n a t i o n s :
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Teacher should oral exams of the students with ful re aration Normal , the ob ective uestions with uess
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are to be avoided To make it m eani n ful, the uestions should be such that d e th of the students in the
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sub ect is test ed O r a l exam inations are to b e c ond ucted in co -cordial environm ent am on st the teachers
takin g the examination . Teachers taki n g such examinations should not have il tho u g hts about each other
and courtesies should be offered to each other in case of difference of o p i n i o n , which should be c r i t i c a l y
su p p r ess ed in f r o n t of the students .
5 . E v a l u a t i o n a n d _ _ _ _ m a r k i n g s ys t e m :
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Basic hon est in the evaluation and m arkin s st em is absolutel es s en t ial and in the roces s im a r t i a l
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nature of th e evaluator is r e uired in th e exam ination s stem to b ecom e o ular am on st the stud ents I t
is a wron g a p p roach or conce p t to award the stud ents by way of eas y m arkin g to get ch ea p
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o p ular it y
am on g the stud ents to which th e y do not d es erv e . I t is a p rimar y res p onsibilit y of the t ea ch er t h a t r i g h t
students who ar e r e a l y p u t t i n g up lot of hard work with r i g h t kind of i n t e l i g enc e are c o r r e c t l y a ward ed .
Th e m arkin g p a tt er n s should be j u stifi abl e to the stud ents without any am bi g uit y and teach er sho uld see
t h a t students ar e fac ed with un j ust circum stances .