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Dept of EEEGNIT
MAGNETIZATION
CHARACTERISTICS OF A
D.C. SHUNT GENERATOR
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Experiment no: 2
MAGNETIZATION CHARACTERISTICS OF
A D.C. SHUNT GENERATOR
AIM : To obtain the Magnetization Characteristics of a D.C. Shunt Generator and to determine
its Critical field resistance & Critical speed.
NAME PLATE DETAILS:
Tpe DC S!"nt Motor DC S!"nt Gener#tor
R#tin$% &.'HP 2 ()
*o+t% 22' * DC 22' * DC
C"rrent ,2 A ,2 A
Ex-. *o+t% 22' * DC 22' * DC
Ex-. C"rrent '. A './ A
D"t S , S , In%. C+#%% 0 0
Spee1 ,'' rpm ,'' rpm
APPARATUS:
S.No App#r#t"% Re3"ire1 R#tin$ Tpe 4t
', *o+tmeter 5'6&''7* M.C ,
'2 Ammeter 5'6,7A M.C ,
'& R!eo%t#t &' o!m8,.2A 6 &
'9 R!eo%t#t &' o!m8,.2A 6' T#-!ometer 6 Di$it#+ ,
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THEOR:
I7 M#$neti;#tion C!#r#-teri%ti-%
The magnetization characteristics shows the relation between the no load generated emf
in armature, E and the field !or" e#citing current, $f at a gi%en fi#ed speed as shown in
model graph. These characteristics are also nown as the 'o load saturation characteristics or (pen
circuit characteristics. The shape of these characteristics is practicall) same for all
generators whether separatel) e#cited or self e#cited Due to the residual magnetism in the poles, some emf is generated e%en when $f *
represented b) (D++. ence, the cur%e starts a little wa) up. The slight cur%ature, DE++ at the lower end is due to magnetic inertia. $t is seen that the
first part of the cur%e, EC++ is practicall) straight. This is due to the fact that at low flu#
densities, reluctance of iron path being negligible !due to high permeabilit)", total
reluctance is gi%en b) the air gap reluctance, which is constant. ence, the flu# and
conse-uentiall) the generated emf are directl) proportional to the e#citing current. ow e%er at high flu# densities, where m is small, iron path reluctance becomes
appreciable and straight relation, C++ between Eo and $f no longer holds good, i.e.,
saturation of poles start.
!++ refers to the model graph"
II7 Criti-#+ re%i%t#n-e
$t is that ma#imum %alue of the field resistance, abo%e which the machine fails to e#cite
i.e. there will be no build up of the %oltage. This resistance corresponds to the straight/line position of the magnetization
characteristic because the magnetic circuit does not offer an) appreciable reluctance to
the magnetic flu#.
III7 Criti-#+ %pee1
$t is that speed for which the gi%en shunt field resistance will represent critical field
resistance5OR7$t is that minimum %alue of the speed of the machine below which the machine fails
to e#cite .
PROCEDURE:
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0. Connect the circuit as per the circuit diagram.
1. $nitiall) the starter must be in ( & S2ST Switch in open positions.
3. Switch on the D.C. Motor to 114 D.C. Suppl) b) closing the D2ST Switch.
5. Start the D.C. motor using the three point starter and thereb) ad6ust the speed of it to the rated
speed of the D.C.generator using field method of speed control.
7. 'ote down the %oltage of the %oltmeter which represents the residual %oltage of the generator
when S2ST switch is in open condition.
8. E#cite the field winding D.C.generator in steps b) decreasing its e#ternal resistance graduall)
and note down %arious corresponding readings of ammeter and %oltmeter till 0.0 to 0.17 times
the rated %oltage of the generator is reached, maintaining constant speed .
9. Graduall) reduce the field current of generator and mae it to zero finall) b) opening S2ST
switch. and disconnect the D.C. Motor from the 114 D.C. Suppl)
.
O0SER*ATION TA0LE:
At -on%t#nt %pee1 o< ,''r.p.m.
S.NoFie+1 C"rrent A Arm#t"re *o+t#$e *
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MODEL GRAPHS:
CALCULATIONS:
TO FIND CRITICAL FIELD RESISTANCE:
0. 2lot the magnetization cur%e.
1. Draw the tangent such that it touches most of the linear part of the cur%e. This line is the
Critical field resistance line.
3. The slope of the abo%e line gi%es the Critical field resistance.
TO FIND CRITICAL SPEED:
0. Draw the constant field resistance line ;f .1. rom point draw a line on to the Critical field resistance line.
'ow the Critical speed, 'c * !
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PRECAUTIONS:6
0. The field rheostat of the motor must be ept in minimum & for the generator in
ma#imum positions before switching on the D.C. suppl).
1. Ensure that the starter arm is at e#treme left position.
3.
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SPEED CONTROL OF
D.C. SHUNT MACHINE
Experiment no: &
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SPEED CONTROL OF DC SHUNT MACHINE
AIM : Determination of the speed characteristics of DC shunt machine b) a" ield control b"
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THEOR:
Speed control of DC shunt motor can be done in the following two wa)s ield control
method
Armature control method:-
This method is used when speeds below the no load speed are re-uired.
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Therefore at constant flu# !field current", as the %oltage across the armature increases, the speed
of the motor also increases and %ice %ersa.
PROCEDURE:
0. Connect the circuit as shown in the circuit diagram.
1. eep the armature rheostat resistance at ma#imum position and the field rheostat at minimum
position before starting the e#periment.
3. The DC suppl) is switched (' and motor is started with the help of a three point starter.
5. eep the field current constant and %ar) the rheostat in series with the armature.
7. 'ote down the corresponding readings of the %oltmeter across the armature and speed of the
DC shunt motor.
8. 'ow the rheostat of the armature is ept as it is and now the field rheostat is %aried and note
down the corresponding readings of field current and the speed of the DC shunt motor.
O0SER*ATION TA0LES:
FIELD CONTROL METHOD
At *# >
Spee1 N 5rpm7
ARMATURE CONTROL METHOD
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MODEL GRAPHS:
$ED C('T;( MET(D
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PRECAUTIONS:6
0. The field rheostat of the motor must be ept in minimum before switching on the 114 D.C
suppl).
1. Ensure that the starter arm is at e#treme left position.
3.
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S)IN0URNEBS TEST
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Experiment no: 9
S)IN0URNEBS TEST
AIM : To 2re/determine the efficienc) and performance characteristics of a DC Shunt machine.
!both as a generator & motor".
NAME PLATE DETAILS:
S.No Tpe DC S!"nt Motor
', R#tin$% &.'HP
'2 *o+t% 22' * DC
'& C"rrent ,2 A
'9 Ex-. *o+t% 22' * DC
' Ex-. C"rrent '. A
' D"t S ,
'/ In%. C+#%% 0
'= Spee1 ,'' rpm
APPARATUS:
S.No App#r#t"% Re3"ire1 R#tin$ Tpe 4t
', *o+tmeter 5'6&''7 M.C ,
'2 Ammeter 5'6,'7 M.C ,
'& Ammeter 5'67 M.C 2
'9 R!eo%t#t &' O!m 8 ,.2 A M.C ,
' T#-!ometer Di$it#+ ,
' F"%e 2' 2
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THEOR:
S)IN0URNEBS TEST:6
$t is a simple method in which losses are measured separatel) and from their nowledge,
efficienc) at an) load can be pre/determined in ad%ance. The onl)running test needed is
a no load test. Swinburne s test is applicable to those machines in which flu# is practicall) constant i.e.
Shunt wound and Compound wound machines. The machine is running as a motor on no/load at its rated %oltage and its speed be
ad6usted to its rated %alue using Shunt regulator. The no/load armature current $ao is measured using an ammeter, where as shunt field
current $sh is gi%en b) another ammeter. The no/load input current is gi%en b)
Io > I#o I%!
et the suppl) %oltage be 4 %olts
'o/load input * 4 $o watts
2ower input to armature * 4 $ao watts
2ower input to shunt * 4 $sh watts
'o/load input supplies Copper losses !
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Pre1etermin#tion o< e !(utput Total losses"
!Efficienc)"# * !# (utput" > !# output Ac ! # $ $sh"H ;a"
I ma) be J, K, L, full load !0"
Ma#imum Efficienc) condition : 4ariable losses !$aH ;a" * Constant losses ! Ac"
PROCEDURE:
0. Connect the circuit as per the Circuit diagram.
1. $nitiall) the starter must be in off position.
3. Switch on the D.C. Motor to 114 D.C. Suppl) b) closing the D2ST Switch.
5. Start the D.C. motor using the three point starter and thereb) ad6ust the speed to its rated speed
using field rheostat.13
7. 'ote down the readings of 4oltmeter & * Io I#o R# )#tt% > )#tt%
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CALCULATION TA0LE:
I7 For Motor
S.No Inp"t*o+t#$e
5*7
Inp"tC"rrent
5I7
Fie+1C"rrent
5I%!7
Arm#t"reCopper
Lo%%e%
Tot#+Lo%%e%
Inp"tPoer
For Gener#tor
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S.No O"tp"t*o+t#$e
5*7
O"tp"tC"rrent
5I7
Fie+1C"rrent
5I%!7
Arm#t"reCopper
Lo%%e%
Tot#+Lo%%e%
Inp"tPoer
MODEL GRAPHS:
S)IN0URNEBS TEST
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PRECAUTIONS:6
0. The field rheostat of the motor must be ept in minimum before switching on the 114 D.C
suppl).
1. Ensure that the starter arm is at e#treme left position.
3.
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1. Ahat are the ad%antages & disad%antages of this testB
3. Ah) this test is not suitable for D.C series motorB
5. Ahat is the purpose of 3 point starterB
7. Ahat happens if field is open in D.C motorB
8. ow do )ou reduce the iron lossesB
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0RA(E TEST ON AD.C. SHUNT MOTOR
Experiment no:
0RA(E TEST ON A D.C. SHUNT MOTOR
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AIM : To obtain the 2erformance characteristics cur%es of a D.C. shunt motor b) conducting
brae test on it.
NAME PLATE DETAILS:
S.No Tpe DC S!"nt Motor
', R#tin$% &.'HP
'2 *o+t% 22' * DC
'& C"rrent ,2 A
'9 Ex-. *o+t% 22' * DC
' Ex-. C"rrent '. A
' D"t S ,
'/ In%. C+#%% 0
'= Spee1 ,'' rpm
APPARATUS:
S.No App#r#t"% Re3"ire1 R#tin$ Tpe 4t
', *o+tmeter 5'6&''7* M.C ,
'2 Ammeter 5'62'7A M.C 2
'& Ammeter 5'6,'7A M.C ,
'9 R!eo%t#t &' o!m8,.2A 6 ,
' T#-!ometer 6 Di$it#+ ,
' F"%e 2'A 6 2
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THEOR:
$t is a simple method of testing low rating DC machines and consists of appl)ing a brae
to a water/cooled drum mounted on the motor shaft. The four important characteristics cur%es of a D.C. Shunt Motor, namel), Tor-ue, Speed,
$nput power" # 0.
Speed ;egulation * P !'o oad speed " / ! ull load speed "Q > ull oad. Speed *
The size of the motor that can be tested b) this method is limited from the consideration
of the heat that can be dissipated at the brae drum
Ahere the output power e#ceeds about 1 .2., or where the test is of long duration, it s
necessar) to use a water cooled brae drum.
PROCEDURE:
0. Connect the circuit as per the Circuit diagram.
1. $nitiall) the starter must be in off position.
3. Switch on the D.C. Motor to 114 D.C. Suppl) b) closing the D2ST Switch.
5. Start the D.C. motor using the three point starter and thereb) ad6ust the speed to its rated speed
using field rheostat.
7. 'ote down the readings of 4oltmeter &
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O. Ahen the full load is reached, slowl) reduce the load and switch off the Motor from 114
D.C. Suppl) b) opening the D2ST Switch
O0SER*ATION TA0LE:
S.No Inp"t
*o+t#$e 5*7
Arm#t"re
C"rrent
Fie+1
C"rrent
Sprin$ 0#+#n-e% Spee1
5N7
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CALCULATION TA0LE:
Radius of the Brake Drum, R = ______ mts.
S.No Inp"t
*o+t#$e
5*7
Inp"t
C"rrent
Tor3"e
N6m
5T7
O"tp"t
Poer
Inp"t
Poer
PRECAUTIONS:
0. The field rheostat of the motor must be ept in minimum before switching (' the motor.
1. Ensure that the starter arm is at e#treme left position.
3.
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0" Ahat is Speed regulationB
1" Ahat are the different t)pes of motorB
3" Ahat are the characteristics of D.C shunt motorB
5" Ahat is the condition for ma#imum efficienc)B
7" Ahat are the different methods to reduce the iron lossesB
8" Ahat are the application of D.C Shunt MotorB
9."Define armature reactionB
O." Difference between interpole and compensating winding.
N. " Define breae horse power !=..2".
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