Government Engineering College
Kozhikode-5
Electrical Machines Lab Manual
(Version 1.0.04 - 08-08-2011)
Prepared by:- Mohammed Sadik(2010 AEI batch) <sadiqpkp(at)gmail(dot)com>
Ranjith A.R
(2010 AEI batch) <ranjithallath(at)gmail(dot)com>
Nikhil Narayanan (2010 AEI batch) <nikhil.sopanam(at)gmail(dot)com>
Guided by :- Smt. Sangeetha K(Associate Professor(EEE))
Verified by:- Smt. Sangeetha K(Associate Professor(EEE))
Type set in LATEX 2ε by Mohammed Sadik .P.K
Circuit Designs & Graphs in XCircuit by Mohammed Sadik .P.K
AEI logo in XCircuit by Mohammed Sadik,Ranjith AR,Mansoor M
Platform : GNU/Linux(Ubuntu)
Other Open Source softwares used: Bash,Gedit,Vim,Inkscape,Gimp. . . . . .
This work is licensed under :
Creative Commons Attribution-NonCommercial-ShareAlike 2.5 India License.
To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-sa/2.5/in/
or send a letter to Creative Commons, 444 Castro Street, Suite 900, Mountain View,
California, 94041, USA.
Thanks to:1. Smt. Sangeetha K(Associate Professor(EEE))
2. Sri. Asokan (Assistant Professor(EEE))
3. Dr. Reena P(Associate Professor(ECE))
4. Najmudheen P.K (Cherumukku)
5. Jazeel M (Kolappuram)
6. Selil C.P(MES Kuttippuram-EC)
7. Mansoor M (GECK-2008 AEI batch)
8. Sajith P.P (GECK-2010 AEI batch)
9. Misthah K.M (AWH Kozhikode-EEE)
10. Abhijit Navale (Mumbai)
11. Midhun M (GECK-2010 AEI batch)
12. Dijeesh K (GECK-2010 AEI batch)
13. Shaaz Khalid A.K (GECK-2010 AEI batch)
14. Mufeed Aslam (GECK-2010 AEI batch)
15. Musthafa M (GECK-2010 AEI batch)
Our
Manual,
sinere
thanks
espeially
our
to
everyone
lassmates
-
who
2010
have
helped
AEI
us
bath.
for
the
perfetion
of
this
CONTENTS
1. Load test on single phase transformer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Load test on 3−φ squirrel cage induction motor . . . . . . . . . . . . . . . . . . . 8
3. O.C.C of dc shunt generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
4. Load test on d.c shunt generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
5. Load test on dc series motor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
6. Measurement of coupling coefficient of transformer coils . . . . . . . . . . 32
7. O.C and S.C tests on single phase transformer . . . . . . . . . . . . . . . . . . . . 38
8. Three phase power measurement by two wattmeter method . . . . . . . 46
9. Calibration of single phase energy meter . . . . . . . . . . . . . . . . . . . . . . . . . . 52
10. Resistance measurement using Wheatstone’s bridge. . . . . . . . . . . . . .56
11. Resistance measurement using Kelvins double bridge . . . . . . . . . . . . 60
12. V-I Characteristics of incandescent lamp and linear resistance . . . 64
13. Open circuit and short circuit test on a three phase alternator . . . 68
14. No load & blocked rotor tests on 3φ slip ring induction motor . . . 74
License Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
meet me at https://launchpad.net/∼sadiq
3
CONNECTION DIAGRAM OF LOAD TEST
0-10A MI 150V,10A,upf
M
L
P
V
E
S1
V
0-150V
MI
C
P2
NL
0-250V
MI
S2
115/230V 1KVA
TRANSFORMER
Rated current on Primary side =
1000
115
=
Regulation and efficiency curves
Regulation
Efficiency
Efficiency
Output
Experiment 1
S
A
V P1
C
B
Regulation
N
A
10A
230V
1-φ
50 Hz
AC
0-5A MI
4
Load
Experiment 1
LOAD TEST ON SINGLE PHASE
TRANSFORMER
AIM
To conduct load test on the given single phase transformer at unity
power factor and determine the efficiency and regulation curve.
APPARATUS REQUIRED
1. Voltmeter 0-250V MI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2. Voltmeter 0-150V MI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
3. Ammeter 0-10A MI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
4. Ammeter 0-5A MI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
5. Wattmeter 150V,10A,upf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
6. Autotransformer(cont. variable) 0-270V,10A . . . . . . . . . . . . . . . . . . 1
no.
no.
no.
no.
no.
no.
THEORY
Regulation of a transformer is defined as the drop in terminal voltage of
a transformer expressed as a percentage of the no-load terminal voltage.
%Regulation =
Vno
load
− Von
load
Vno load
When a purely resistive load is connected across the secondary, the
transformer will be working at unity power factor.
Terminal voltage V = Induced emf [E2 ] − I2 r2 − I2 x2
Where r2 and x2 are the secondary winding resistance and leakage reactance respectively and I2 is the secondary load current
As the load current increases the power output increases. The iron loss
remains constant from no load to full load. The copper loss increases as
the square of the load current. Thus the efficiency curve starts from zero,
increases to a maximum value(When iron loss = Cu loss) and thereafter
starts decreasing.
5
OBSERVATION
Sl.
No.
V1
I1
W1
V2
I2
(volts)
(Amp)
(watts)
(volts)
(Amp)
Output Efficiency Regulation
(watts)
(%)
(%)
V2 at no load = VN L =
Sample Calculation (set no . . . . . . )
Primary Voltage (V1 ) = . . . . . . . . .
Primary Current (I1 ) = . . . . . . . . .
Wattmeter Reading (W1 ) = Input power = . . . . . . . . .
Secondary Voltage (V2 ) = . . . . . . . . .
Secondary Current (I2 ) = . . . . . . . . .
Output = I2 V2 = . . . . . . . . .
Output power
×100 = . . . . . . . . .
Input power
VN L − VL
×100 = . . . . . . . . .
Regulation =
VN L
Efficiency =
6
PROCEDURE
Connections are made as shown in the circuit diagram. The supply is
switched on keeping the autotransformer in the minimum position and at
no load. Adjust the autotransformer to get the rated voltage of the transformer. The readings of all the meters are noted down. The secondary
voltage is also noted down. This value is VN L . A small load is added on the
secondary side and the meter readings are again noted. The experiment
is repeated for different values of current till the current on the primary
side equals the rated value. The load is then reduced to zero, the autotransformer brought back to the zero position and the supply is switched
off. The readings are then tabulated as shown.
RESULT
Conducted load test on the given 1-φ transformer and plotted the regulation and efficiency curves.
VIVA QUESTIONS
1. What do you understand by regulation of a transformer?
2. What are the other methods of testing transformers?
3. What is the disadvantage of testing a transformer using load test?
4. Is a high or low value of regulation preferred for a transformer? Give
reasons.
5. What are the reasons for the drop in terminal voltage as the secondary
current is increased?
7
CONNECTION DIAGRAM
0-10A MI
R
A
600V,10A,upf
L
M
10A
V
V
S1
R
0-600V
MI
IM
Y
400V 3 - φ
50Hz AC
C
∆
Y
10A
B
B
10A
C
V
M
L
600V,10A,upf
D.O.L
STARTER
MACHINE DETAILS
Voltage
V - 415 V
Current
I - 7.5A
Power
- 5HP
Connection
-∆
Speed(rpm)
- 1440
Phase
- 3φ
Synchronous speed =
120f
P
= 120 4× 50 = 1500 rpm
Experiment 2
8
S2
Experiment 2
LOAD TEST ON 3−φ SQUIRREL CAGE
INDUCTION MOTOR
AIM
To conduct load test on the given 3-φ squirrel cage induction motor and
plot the performance characteristics.
APPARATUS REQUIRED
1. Voltmeter 0-600V MI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 no.
2. Ammeter 0-10A MI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 no.
3. Wattmeter 600V,10A,upf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 nos.
4. Tachometer - to measure speed
THEORY
A squirrel cage induction motor essentially consists of a stator and a
rotor. The stator is a hollow cylindrical structure with slots on the inner periphery and carries a three phase winding. The winding can be
connected in star or delta and is connected across a 3-φ supply.
The rotor is also a cylindrical structure with slots on the outer periphery.
The slots carry thick Al or Cu bars. These bars are short circuited at both
ends by means of end rings.
When a 3-φ supply is given to a 3φ winding displaced by 120◦ in space,
a magnetic field of constant magnitude but rotating at synchronous speed
is produced. This flux links with the stationary rotor, thus inducing an
emf in it. As the rotor circuit is closed, a current flows through it. The
direction of the induced current is such as to oppose the cause producing
it. The cause is the relative motion between the stator magnetic field and
the rotor. So the rotor starts rotating in the same direction as the stator
magnetic field and tries to catch up with it. But practically it is never
able to do so. Because if it does so, there would be no relative motion, no
emf and hence no torque.
9
OBSERVATIONS
Sl.
V
I
W1
W2
S1
S2
N
T
Output Input slip pf Efficiency
No. (volts) (Amp) (watts) (watts) (Kg) (Kg) (rpm) (N m) (watts) (watts) (%)
10
Thus an induction motor always runs at a speed slightly less than the
synchronous speed.
The term slip is of importance in an induction motor and is defined as
%slip =
Ns − N
× 100
Ns
Where,
120 × f
Ns - Synchronous speed =
P
N - rotor speed
f - frequency
P - no. of poles of the machine
An induction motor can never operate at s = 0. It always operates between
s = 0 and s = 1(starting).
The performance characteristics are plots of efficiency, torque, speed,
slip, pf and line current versus output.
Current and torque increases with increase in output. The induction
motor is essentially a constant speed motor. However speed reduces gradually with increase in output and slip increases gradually with increase in
output. The p.f is low at low loads and increases with increase in output.
The efficiency increases with increase in output, reaches a peak value and
then gradually drops with further increase in output.
PROCEDURE
The load on the motor is completely removed by loosening the brake
drum. The motor is to be always started and stopped at no load, The
supply is switched on and the motor is started using a Direct On Line
Starter (DOL Starter).
The readings of the voltmeter, ammeter, wattmeters and spring balance
are noted down. The speed is measured using a tachometer. The load is
then increased in steps, each time noting down all the above readings. The
experiment is repeated for different values of load currents till the rated
current of the machine is reached.
During the experiment, the machine may get heated up. It is cooled by
pouring some water into the brake drum.
11
Sample Calculation (set no . . . . . . )
Voltage (V ) = . . . . . . . . .
Current (I) = . . . . . . . . .
Wattmeter Reading 1 (W1 ) = . . . . . . . . .
Wattmeter Reading 2 (W2 ) = . . . . . . . . .
Spring balance Readings S1 = . . . . . . . . . S2 = . . . . . . . . .
Speed (N ) = . . . . . . . . .
Torque (T ) = (S1 − S2 )Rg Where,
R = Radius of brakedrum = . . . . . . . . .
g = 9.8 m/s2
120 × f
Synchronous speed =
= 120 4× 50 = 1500 rpm
P
(Ns − N )
slip(%) =
× 100 = . . . . . . . . .
Ns
Input power = (W1 + W2 ) = . . . . . . . . .
(W√
1 + W2 )
= .........
3V I
T
Output power= 2πN
60 = . . . . . . . . .
powerfactor(cos φ) =
Output
Efficiency = Input = . . . . . . . . .
Performance Characteristics
Slip pf T N
η
Efficiency
Speed
pf
Torque
Slip
Output
12
At low loads,(when the pf is < 0.5) one of the wattmeters read negative,
in such cases, the supply is switched off and the connections to the M and
L terminals of the wattmeter are interchanged. The meter now reads
positive, but it is to be recorded as negative.
The load on the machine is removed completely and the supply is
switched off.
The readings are tabulated and the performance characteristics are plotted.
RESULT
Conducted load test on the given 3-φ squirrel cage induction motor and
plotted the performance characteristics.
VIVA QUESTIONS
1. How are the meter ratings selected for this experiment?
2. Why does one of the wattmeters read -ve at starting?
3. What is ‘slip’ in an induction motor?
4. What are the two types of 3-φ induction motors and what is the
difference between the two?
5. What is the value of slip at starting?
6. What are the advantages and disadvantages of squirrel cage induction
motor?
7. What is the condition for maximum torque in an induction motor?
8. What are the different losses in an induction motor?
9. Give some applications of 3-φ squirrel cage induction motor?
10. Explain a typical Torque-slip characteristic.
11. What is the effect of increased rotor resistance on the performance
of an induction machine?
13
CONNECTION DIAGRAM
L F A
+
3 POINT STARTER
20A
600Ω
2A
Rh1
220V
DC
F1
S
A1
M
A2
20A
A1
+
G
-
F1
V
-
A2
A
F2
0-2A
MC
MACHINE DETAILS
MOTOR
GENERATOR
3.5 KW
3.5 KW
Speed - 1500rpm
Speed - 1500rpm
volts - 220V
volts - 220V
Amps - 18.6 A
Amps - 16 A
Winding - shunt
Winding - shunt
Field - 220V,0.46A Field - 220V,0.46A
OBSERVATION
Sl No. Field current Eo at rated speed Eo at 1000 rpm
To determine O.C.C at 1000 rpm
We have E ∝ N at same flux or field current
N1
N2
E1
=
⇒ E2 =
E1
E2
N2
N1
Where N2 is 1000 rpm
and N1 − Rated speed = 1500 rpm
Experiment 3
14
+ 0-300V
MC
V
+
0-30V
MC -
F2
600Ω
2A
Rh2
Experiment 3
O.C.C OF DC SHUNT GENERATOR
AIM
To conduct no load test on the given d.c shunt generator and determine
the following:1. Open circuit characteristics at rated speed.
2. Predetermine the O.C.C at 1000 rpm.
3. The critical field resistance at rated speed.
4. The critical speed of the machine.
APPARATUS REQUIRED
1. Voltmeter MC (0-300V). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 no.
2. Voltmeter MC (0-30V) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 no.
3. Ammeter
MC (0-2A). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 no.
4. Rheostat
600Ω,2A. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 nos.
5. Tachometer
THEORY
The O.C.C is a curve showing the relationship between the no load emf
generated and the shunt field current (Eo and If ). Even when the field current is zero there is some residual magnetism present in the poles. Hence
there is a small voltage generated even at zero field current, which is called
the residual voltage. As the field current is increased, Eo also increases
and the curve traced is almost a straight line. As If is further increased
the poles start getting saturated and the straight line relation no longer
holds good and the curve bends and becomes almost horizontal.
Critical Resistance:- It is that value of resistance in the field circuit
at which the generator will just excite (or voltage build up begins). If the
resistance is higher, the machine will fail to build up voltage.
15
MEASUREMENT OF SHUNT FIELD RESISTANCE
+
0-2A MC
100Ω,2.8A
+
+
220V
DC
V
A
F1
0-250V
MC
F2
-
OBSERVATION
Sl No.
V
I
16
Rf
It is given by the slope of the tangent drawn to the linear portion of the
magnetization curve from the origin.
Conditions for Voltage build up in a d.c shunt generator:1. There should be some residual magnetism in the poles.
2. For the given direction of rotation, the shunt field coils should be
properly connected ie, The coils should be so connected that the flux
generated by the field current aids the residual flux.
3. When excited at no load, the shunt field circuit resistance should be
less than the critical resistance.
Critical Speed :- It is that value of speed at which the given shunt field
resistance represents the critical resistance. It is determined as follows.
For the same value of If determine E1 and E2 from the field resistance
lines. Then
E1
N1
E2
=
⇒ Nc =
N1
E2
Nc
E1
Where,
Nc is the Critical speed
PROCEDURE
Connections are made as shown in the diagram. The motor field rheostat
(Rh1 ) is kept in minimum position, the generator field rheostat (Rh2 ) in
maximum position and switch ‘S’ is kept open at starting. Supply is
switched on. The starter handle is gradually moved to cut off the starter
resistance. The rheostat Rh1 is varied till the speed equals the rated speed
of the machine. With ‘S’ open, the residual voltage is measured using the
smaller range voltmeter. Switch ‘S’ is then closed. Rheostat Rh2 is then
decreased in steps, each time noting down the voltmeter and ammeter
readings. The process is repeated till the voltage equals 120% of the rated
voltage of the machine. [If Eo does not increase, it means that the machine
is not building up voltage. The field terminals F1 and F2 are interchanged
and the process is repeated] Rheostat Rh2 and Rh1 are brought back to
the original position and the supply is then switched off.
17
OPEN CIRCUIT CHARACTERISTICS
Eo
Critical Field
resistance
line
O.C.C at rated
speed
E1
O.C.C at 1000 rpm
Given shunt field
resistance line
E2
residual{
voltage
If1
Critical resistance at rated speed,
Rc =
E1
= .........
If 1
Critical speed of the Machine,
E2
N1 = . . . . . . . . .
Nc =
E1
18
If
Measurement of field resistance
Connections are made as shown in the diagram 2. For different values
of voltages determine the current. The ratio gives the field resistance. The
O.C.C and field resistance line is drawn and the critical speed of the machine is determined.
RESULT
No load test was conducted on the given d.c shunt generator and
the O.C.C was plotted.
Critical resistance at rated speed = . . . . . . . . .
Critical speed of the machine
= .........
VIVA QUESTIONS
1. What is the need for starter in a d.c motor?
2. How does a 3-point starter function?
3. Why is Rh1 kept in minimum position at starting?
4. Why is Rh2 kept in maximum position at start up?
5. What is residual voltage? How is it measured?
6. What is critical resistance? How can it be measured?
7. What are the conditions necessary for voltage build up in a d.c shunt
generator?
8. What is critical speed?
9. Explain the shape of the O.C.C
19
LOAD TEST
+
3 Point Starter
L F A
Rh1
600Ω
2A
200V
DC
A1
A1
M
F1
-
S1
Rh2
+
F1
G
A2
A2
V
F2
0-2A
MC
F2
20A
600Ω
2A
+
0-300V
MC
20A
Load
A
-
S2
MACHINE DETAILS
MOTOR
GENERATOR
3.5 KW
3.5 KW
Speed - 1500rpm Speed - 1500rpm
volts
- 220V
volts
- 220V
Amps - 18.6 A
Amps - 16 A
Winding - shunt
Winding - shunt
Measurement of Armature Resistance
0-5A MC
+
-
A
20V
DC
+
50Ω
5A
V
0-10V
MC
Sl Voltage V
No.
(volts)
A1
G
A2
Current I Resistance R
(Amperes)
(ohms)
Armature Resistance Ra = . . . . . . . . .
Experiment 4
20
Ω
Experiment 4
LOAD TEST ON D.C SHUNT
GENERATOR
AIM
To conduct load test on the given D.C shunt generator and plot the
external and internal characteristics.
APPARATUS REQUIRED
1. Voltmeter MC (0-300)V. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 no.
2. Voltmeter MC (0-30)V . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 no.
3. Ammeter
MC (0-2)A. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 no.
4. Rheostat
600Ω,2A. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 nos.
5. Tachometer
THEORY
Load characteristics of the machine can be broadly classified into
1) External characteristics
2) Internal Characteristics
External Characteristics(V vs I2 ) :It is a curve showing the variation in terminal voltage of the generator
as the load on the generator is increased. The characteristics are as shown
in the figure.
At no load, the terminal voltage of the generator is at its rated value.
As the load current is increased the terminal voltage drops. The drop in
terminal voltage is due to the following reasons.
1) For a generator V = Eg − Ia Ra , as the load current increases, Ia
increases, Ia Ra drop increases, thus decreasing the terminal voltage V
2) As the load current increases, Ia increases, armature reaction effect
also increases. Due to demagnetizing effect of armature reaction, the induced emf Eg decreases, thereby decreasing V .
21
OBSERVATION - LOAD TEST
Sl
V
no. (volts)
IL
(A)
Ish
(A)
Ia
(A)
Eg
(V )
Sample Calculation (set no . . . . . . )
Terminal Voltage (V )
Load Current (IL )
Shunt Field Current (Ish )
Armature Current (IA ) = IL + Ish
Generated emf (Eg )
=
=
=
=
=
. . . . . . . . . volts
.........A
.........A
.........A
V + I a Ra
Internal and External Characteristics
V/ Eg
Drop Due
To Armature
Resistance
Drop due to armature
Reaction Effect
Internal Characteristics
Eg vs Ia
External
Characteristics
V vs IL
IL/ Ia
22
3)Due to reasons (1) and (2), the terminal voltage decreases, which in
turn reduces the field current Ish , thereby decreasing Eg causing further
decrease in V .
Internal Characteristics [Eg vsIa ] :- It is a plot of the internally generated emf (Eg ) and armature current (Ia ). It is a curve similar to the
external characteristics and lies above it.
E g = V + I a Ra
& Ia = IL + Ish
PROCEDURE
Connections are made as shown in the diagram. rheostat Rh1 is kept in
minimum position and Rh2 in maximum position. Switch S2 is kept open.
Supply is switched on and the motor is started using a 3-point starter. The
motor field rheostat Rh1 is varied till the speed equals the rated speed of
the motor. The generator field rheostat Rh2 is varied till the voltmeter
reads the rated voltage of the machine. Switch S2 is then closed. The
load on the generator is increased. The readings of the voltmeter and
ammeters are noted down. The experiment is repeated for different values
of load current till the rated current of the generator is reached. During
the experiment, the speed is to be maintained constant at the rated value.
The load is then switched off completely, the rheostats are brought back
to the original position and the machine is switched off.
Measurement of Ra
Connections are made as shown in the diagram. Keeping the rheostat
in the maximum position, supply is switched on. The resistance is then
increased in steps and the voltmeter and ammeter readings are noted. The
ratio gives the armature resistance.
The readings are then tabulated as shown. The external and internal
characteristics are then plotted.
RESULT
Conducted load test on the given DC shunt generator and plotted the
external and internal characteristics.
23
24
VIVA QUESTIONS
1.
2.
3.
4.
5.
6.
7.
8.
9.
What is the need for starter with a d.c motor?
How does a 3-point starter function?
Why is Rh1 kept in minimum position at starting?
Why is Rh2 kept in maximum position at starting?
Why does the terminal voltage of a generator decrease with increase
in load?
How are the meter ratings selected for this experiment?
What are the different losses in a d.c generator?
What is the condition for maximum efficiency in a d.c machine?
What is armature reaction? How does it effect the functioning of
the machine?
25
CONNECTION DIAGRAM
L A
+
2 Point Starter
+
-
A
20A
0-20A
F1
V
-
S1
0-300V MC
A2
20A
Machine Details
HP
Volts
Amp
speed
5
230 V
17 A
- 1500 rpm
Radius of brakedrum, R = . . . . . . . . .
Experiment 5
S2
A1
+
220V
DC
F2
26
BRAKE
DRUM
Experiment 5
LOAD TEST ON DC SERIES MOTOR
AIM
To conduct load test on the given d.c series motor and plot the performance characteristics.
APPARATUS REQUIRED
1. Voltmeter (0-250)V MC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 no.
2. Ammeter (0-20)A MC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 no.
3. Tachometer - to measure speed
THEORY
In a series motor, the field winding is connected in series with the armature winding. Thus the same current flows through the field and armature
windings.
Electrical characteristics(T1 Ia ) :- It shows the variation of torque
with the armature current.
We have
T ∝ φIa
where φ is the flux/pole
∝ Ia Ia
(as φ ∝ Ia up to the point of magnetic saturation)
Thus T ∝ Ia2
27
OBSERVATIONS
Sl.
V
I
S1 S2 Speed Torque Output Input
Efficiency
No. volts Amp. Kg Kg rpm N − m watts watts
Sample Calculation ( set no. . . . . . . )
Voltmeter reading (v) = . . . . . . . . .
Current (I)
= .........
Spring balance reaadings S1 = . . . . . . . . .
S2 = . . . . . . . . .
Speed(N ) = . . . . . . . . .
Torque(T ) = 9.8 (S1 − S2 ) R = . . . . . . . . .
Output power =
2πN T
= .........
60
Input power
= V.I = . . . . . . . . .
Efficiency
=
Output power
= .........
Input power
28
Where R is the radius
of brake drum
However after magnetic saturation φ remains almost constant, Hence
T ∝ Ia
Thus the curve is a parabola up to magnetic saturation and shows a
linear variation after the point.
Mechanical Characteristics(N1 vs T ):- It shows the variation of speed
with torque.
1
Eb
∝
as Eb is almost constant
where Eb is
We have N ∝
φ
φ
back emf
In a series motor φ ∝ Ia
1
∴N ∝
Ia
(ie) as Ia increases, Speed decreases.
The same pattern is followed in the N -T characteristics. The curve
traced is a rectangular hyperbola.
A series motor should never be started at no load. At no load, Ia is very
small, hence the speed of the motor becomes dangerously high(as N ∝ I1a ).
Performance characteristics shows the variation of speed, torque and
efficiency with change in output.
PROCEDURE
Connections are made as shown in the connection diagram. A small load
is applied to the motor by tightening the brake drum. Supply is switched
on and the motor is started using a 2-point starter. The voltage, current,
speed and spring balance readings are noted down. The experiment is
repeated for different loads till the rated current of the machine is reached.
During the experiment when the machine gets heated up, it is cooled
by pouring water into the brake-drum.
The load is then reduced till the current reaches a small value and the
supply is switched off.
29
Performance Characteristics
T η N
Torque
Efficiency
Speed
O
Output
Electrical Characteristics
Mechanical Characteristics
N
T
Ia
30
T
RESULT
Load test was conducted on the given DC series motor and the performance, electrical and mechanical characteristics are plotted.
VIVA QUESTIONS
1. What is the precaution to be taken when working with a d.c series
motor?
2. What is the need for starter with a d.c motor?
3. How does a 2-point starter function?
4. Explain the shape of the electrical and mechanical characteristics
5. What is the condition for maximum efficiency in a d.c motor?
6. What are the different losses occurring in a d.c machine?
7. How are the meter ratings selected for this experiment?
8. Give some applications of d.c series motor.
31
CONNECTION DIAGRAM
FLUX AIDING
0-250V
MI V
V1
C
N
P1
B
V3
2
0-250V
MI
E
S2
S1
P2
NL
0-150V
MI
230V
50Hz
1-φ
AC
240/120V,3kVA
Transformer
A
Auto
Transformer
P
0-500mA MI
1A
V1 ⋍ V2 + V3
FLUX OPPOSING
C
N
P1
B
0-250V
MI V
V1
0-250V
MI
S1
V3
2
S2
P2
E
NL
V1 ⋍ V2 − V3
MEASUREMENT OF RESISTANCE OF COILS
0-5A MC
+
A
0-20V
50Ω
5A
P1
S1
P2
S2
+
V
-
Experiment 6
0-150V
MI
230V
50Hz
1-φ
AC
A
Auto
Transformer
P
240/120V,3kVA
Transformer
0-500mA MI
1A
0-10V
MC
32
Experiment 6
MEASUREMENT OF COUPLING
COEFFICIENT OF TRANSFORMER
COILS
AIM
To determine the self inductance, mutual inductance and coupling coefficient of the given transformer windings.
APPARATUS REQUIRED
1. Transformer 240/120V,1kVA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2. Voltmeter
0-250V
MI. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2
3. Voltmeter
0-150V
MI. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
4. Voltmeter
0-10V
MC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
5. Ammeter
0-500mA MI. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
6. Ammeter
0-5A
MC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
7. Autotransformer 0-270v,10A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
no.
no.
no.
no.
no.
no.
no.
PRINCIPLE
The property of a coil due to which it opposes any change of current
through it is know as self inductance. The coefficient of self induction(L)
is defined as Weber turns per ampere in the coil.
N φ N N Iµ0 µr A N 2
=
=
(H)
I
Il
S
Mutual inductance is the ability of one coil to produce an emf in a
nearby coil by induction when the current in the first coil changes. The
coefficient of mutual inductance (M) is defined as the Weber turns in one
coil due to ampere current in the other coil.
L=
M=
N2 N1 I 1
N1 N2
N2 φ 1
=
=
I1
I1 S
S
33
OBSERVATIONS
Measurement of impedance of coils
Condition
Flux aiding
Flux opposing
V1 (v)
V2 (v)
V3 (v)
I(A)
Measurement of resistance of coils
Sl. No.
1
2
3
V (v)
I(A)
Winding Resistance R = r1 + r2 = . . . . . . . . .
34
R(Ω)
Z(Ω)
L(H)
Consider two coupled coils A and B
N12
L1 =
S
N22
L2 =
S
N1 I 1
Flux produced in A due to current I1 is φ1 =
S
Let a fraction k1 of this link with the second coil
ie, φ2 = k1 φ1
Then
M=
(k1 φ1 N2 ) (k1 N1 N2 )
=
I1
S
........................
Flux produced in B due to current I2 is φ2 =
Suppose a fraction k2 of this links with A
N2 I 2
S
ie, φ1 = k2 φ2
(k2 φ2 N1 ) (k2 N1 N2 )
M=
=
........................
I2
S
from (1) and (2)
M2 =
(1)
(2)
(k1 k2 N12 N22 )
N2 N2
= k1 k2 1 2
SS
S S
M
M 2 = k1 k2 L1 L2 or k = √
( L1 L2 )
√
where k = k1 k2
The constant k is called the coefficient of coupling and may be defined
as the ratio of mutual inductance actually present between the two coils to
the maximum possible value. If the flux due to one coil completely links
the other then k = 1. If the flux of one coil does not link the other coil at
all then k = 0.
35
CALCULATION
For coils connected in series with fluxes aiding each other
V1
= .........
Total impedance of coils ZA =
I
p
Reactance of coils XA = ZA2 − R2 = . . . . . . . . . Where, R = r1 + r2
is the total resistance
XA
Inductance LA =
= .........
of both windings
2πf
For coils connected in series with fluxes opposing
V1
Total impedance of coils ZB =
= .........
I
p
Reactance of coils XB = ZB2 − R2 = . . . . . . . . .
XB
Inductance LB =
= .........
2πf
When coils are connected with flux aiding each other
Total inductance, LA = L1 + L2 + 2M
(1)
When coils are connected with flux opposing each other
Total inductance, LB = L1 + L2 − 2M
(2)
subtracting (2) from (1), M =
L1
L2
=
N1
N2
2
=
240
120
2
(LA − LB )
4
=4
L1 = 4L2
Substituting in (1), LA = 5L2 + 2M or L2 =
L1 = 4L2 = . . . . . . . . .
Coupling coefficient k = √
M
= .........
L1 L2
36
LA − 2M
= .........
5
PROCEDURE
Measurement of impedance of coils
Connections are made as shown in the first figure. Supply is switched
on with autotransformer in the minimum position. The autotransformer
is adjusted to get the rated voltage in voltmeter1. The corresponding
readings in all meters are noted down. In this case the fluxes produced by
both the coils are additive in nature ( ie V1 = V2 + V3 ).
Next the connections of the second coil are reversed. The fluxes produced by the two coils are now in subtractive polarity(ie, V1 = V2 − V3 ).
The autotransformer is adjusted so as to get the same reading in V2 as
with the additive polarity. This is done to maintain the same flux in both
the cases. The readings of all meters are noted down and tabulated as
shown.
Measurement of Resistance
Connections are made as in the third figure. For different values of voltages the readings of both meters are noted down and tabulated.
RESULT
The coupling coefficient of the given transformer windings is . . . . . . . . . .
VIVA QUESTIONS
1. What is meant by coupling coefficient of a transformer? What are
the limiting values?
2. Why is the voltage V2 maintained constant in the second case?
3. How are the meter ratings selected for this experiment?
37
CONNECTION DIAGRAM(OPEN CIRCUIT TEST)
0-2A MI 150V,2A,lpf
L
M
2A
P
A
B
230V
1-φ
50Hz
AC
C
V
C
NL
N
V
P
0-150V
MI
h.v
l.v
E
115/230V,1kVA
Transformer
OBSERVATION
Vo
Io
Wo
CONNECTION DIAGRAM(SHORT CIRCUIT TEST)
0-5A MI 75V,5A,upf
M
L
5A
P
A
B
230V
1-φ
50Hz
AC
C
V
C
NL
N
V
0-50V
MI
h.v
E
l.v
115/230V,1kVA
Transformer
Rated Current =
1000
Rated KV A
=
= .........
Rated V oltage on h.v side
230
OBSERVATION
VSC
Experiment 7
ISC
38
WSC
Experiment 7
O.C AND S.C TESTS ON SINGLE PHASE
TRANSFORMER
AIM
To conduct open circuit and short circuit tests on the given 115/230 V,
1kVA transformer and predetermine the following:1. Equivalent circuit as referred to l.v side
2. Equivalent circuit a referred to h.v side
3. Efficiency curve at 0.8 pf
4. Regulation curve at 1 /2 Full load
INSTRUMENTS REQUIRED
1. Voltmeter 0-150V MI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2. Voltmeter 0-50V MI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
3. Ammeter
0-2.5A MI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
4. Ammeter
0-5A
MI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
5. Wattmeter 150V,2.5A,lpf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
6. Wattmeter 75V,5A,upf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
7. Autotransformer 0-270V,10A
no.
no.
no.
no.
no.
no.
PRINCIPLE
Open circuit test:- This test is usually conducted on the l.v side of
the transformer. It is conducted to determine the core loss ( iron loss or no
load loss). The low voltage side of the transformer is supplied with rated
voltage with the h.v side left open. The current, voltage and power on
the input side is noted. Since the no-load primary current is small (2-10
% of the rated current) the copper losses in the primary winding can be
neglected and the power loss read by the wattmeter is the core loss of the
transformer. Since the flux linking with the core is constant at all loads,
39
From O.C test (l.v side) :V 0 = . . . . . . . . . I0 = . . . . . . . . . W0 = . . . . . . . . .
W0
W0 = V0 I0 cos φ0 cos φ0 =
= .........
V 0 I0
sin φ0 = . . . . . . . . .
Iw = I0 cos φ0 = . . . . . . . . .
Iµ = I0 sin φ0 = . . . . . . . . .
Core loss component resistance as refered to l.v side R0 =
V0
= .........
Iw
V0
= .........
Iµ
The parameters R0 and X0 as referred to the h.v side are
′
R0 = R0 × k 2 = . . . . . . . . .
E2
230
N2
=
=
X0′ = X0 × k 2 = . . . . . . . . .
where k =
N1
E1
115
Magentising reactance as refered to l.v side X0 =
From S.C test (h.v side) :VSC = . . . . . . . . . ISC = . . . . . . . . . WSC = . . . . . . . . .
WSC
= .........
ISC
VSC
= .........
Total eqvt. impedance as refered to to h.v side Z02 =
ISC
q
Total eqvt. leakage reactance referred to h.v side X02 = Z022 − R022 =
Total eqvt. wdg resistance as refered to h.v side R02 =
The parameters R02 , Z02 , and X02 as referred to l.v side are
R01 = R02 |K 2 = . . . . . . . . .
X01 = X02 |K 2 = . . . . . . . . .
Z01 = Z02 |K 2 = . . . . . . . . .
EQUIVALENT CIRCUIT
as referred to l.v side
as referred to h.v side
I1
I'2
I0
115V
R0=
I1
R0=1
I0
X01=
Z'L
X0 =
I'2
230V
R'0=
40
R0=2
X02=
ZL
X'0=
the core loss remains same for all loads. The parameters R0 and X0 (the
shunt branch) are determined using this test.
Short Circuit Test :- The short circuit test is conducted to determine the full load copper loss and the equivalent resistance and leakage
reactance referred to the winding in which the test is conducted. The test
is conducted on the h.v side with the l.v side short circuited by a thick
conductor. A low voltage just enough to circulate the rated current of the
transformer is supplied to the transformer. The voltage supplied is usually
only 5-10% of the normal supply voltage and so the flux linking with the
core is small. Thus core losses can be neglected and the wattmeter reading
gives the full load Cu loss of the transformer.
PROCEDURE
Open Circuit Test:- Connections are made as shown in the connection
diagram1. The h.v side is left open. The supply is switched on with the
autotransformer in the minimum position. The autotransformer is gradually varied till the voltmeter reads the rated voltage of the primary side of
the transformer. The corresponding ammeter and wattmeter readings are
noted down and tabulated as shown.
Short Circuit test:- Connections are made as shown in the diagram 2.
The l.v side is short circuited. Supply is switched on with the autotransformer in the minimum position. The autotransformer is gradually varied
till the ammeter reads the rated current of the transformer on the h.v side.
Rated volt Amperes of transf ormer
Rated Current =
Rated voltage on h.v side
41
Calculation of Efficiency :Efficiency of the transformer at any load and p.f is given by
η=
x × F.L(V A) × cos φ
P ower Output
=
P ower Input
x × F.L(V A) × cos φ + Wi + x2 WCu
Where,
Wi - is the core loss
WCu - full load Cu loss
x - is the fraction of full load
x Output Wi
1
/4
1
/2
3
/4
x2 WCu
Input Efficiency
1
Sample Calculation(set no. . . . . . . )
x = .........
F.L(V A) = . . . . . . . . .
p.f cos φ = . . . . . . . . .
Power output = x × F.L(V A) × cos φ = . . . . . . . . .
Power input = Power Output +Wi + x2 WCu = . . . . . . . . .
P ower Output
= .........
Efficiency
=
P ower Input
η
Efficiency curve
1/4
FL
1/2
FL
42
3/4
FL
O/P
FL
The corresponding voltmeter and wattmeter readings are noted down
and tabulated as shown.
Using the readings obtained from the two tests, the equivalent circuit
as referred to the l.v side and h.v side are drawn.
The efficiency at various fractions of full load are calculated and tabulated. The efficiency curve is then plotted.
Regulation of the transformer (which gives the variation of the secondary
terminal voltage from no load to full load expressed as a percentage of the
secondary terminal voltage with the primary voltage held constant) is then
calculated using the approximate formula at various power factors and half
the full load, Regulation curve is then plotted.
43
Calculation of Regulation
Regulation at any load and p.f is given by
%Reg =
I2 R02 cos φ ± I2 X02 sin φ
E2o
‘+’ for lagging
‘-’ for leading
Where I2 is the current at any load and
= xI2 F L
Where x → Fraction of full load
I2 F L → full load current on secondary side
E20 → rated voltage on secondary side
←− lagging
upf
leading −→
0 0.2 0.4 0.6 0.8 1 0.8 0.6 0.4 0.2 0
Sample calculation . . . . . .
(for one lead and one lag case)
Regulation Curve
%Reg
(upf)
0 0.2 0.4
p.f
(lead)
0.6
0.8
0.8
%Reg
44
0.6 0.4
0.2
0
p.f
(lag)
RESULT
O.C and S.C tests were conducted on the given 1-φ transformer and
predetermined the regulation and efficiency curves.
VIVA QUESTIONS
1. How are the meter ratings selected for O.C and S.C tests?
2. Why is the O.C test conducted on the l.v side of the transformer and
S.C test on h.v side?
3. What are the losses measured in an O.C test?
4. What are the losses measured in an S.C test?
5. What is the condition for maximum efficiency in a transformer?
6. What is meant by ‘regulation’ of a transformer?
7. Is a high or low value of regulation preferred? Why?
8. How can the parameters on one side of the transformer be transferred
to the other side?
45
CONNECTION DIAGRAM
600V,5A,upf
0-5A MI
R
M
A
5A
L
C
B1
50Ω,5A
400V 3 - φ 50Hz AC
C1
Y
5A
N
5A
NL
0-600V
3−φ
Inductive
Load
1-10A
B2
C2
B
V
E1
E2
50Ω,5A
B3
C3
E3
C
V
M
L
600V,5A,upf
PHASOR DIAGRAM
V BY
IB
V RY
VB
φ 30
30
φ
VR
IR
IY
VY
Experiment 8
46
50Ω,5A
Experiment 8
THREE PHASE POWER
MEASUREMENT BY TWO
WATTMETER METHOD
AIM
To measure the power factor and power consumed by a 3-φ RL load
using two wattmeter method.
APPARATUS REQUIRED
1. Voltmeter (0-500V) MI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 no.
2. Ammeter (0-5A) MI. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 nos.
3. Wattmeter 600V,5A,upf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 nos.
4. Rheostat
100Ω,5A. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 nos.
5. 3-φ Inductive load (0-10A) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 no.
6. 3-φ Autotransformer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 no.
PRINCIPLE
In the two wattmeter method current coils of two watt meters are connected in two phases and the potential coils between the corresponding
phase and the third phase. It can be proved that the sum of the wattmeter
readings gives the total power.
From the phasor diagram
Reading of Wattmeter 1,W1 = VRY IR cos(30 + φ)
Reading of Watt meter 2,W2 = VBY IB cos(30 − φ)
W1 +W2 = VRY IR (cos 30 cos φ−sin 30 sin φ)+VBY IB (cos 30 cos φ+sin 30 sin φ)
= VRY IR cos 30 cos φ + VBY IB (cos 30 cos φ)
Assuming balanced load
VRY = VBY = VBR = VL
& IR = IB = IY = IL
where VL and IL are the line values of voltage and current
47
OBSERVATIONS
Sl.
Case
No.
1 W1 and W2 read
+ve
2 W1 reads +ve, W2
reads zero
3 W1 reads +ve, W2
reads -ve
voltage Current
V(V )
I(A)
Wattmeter
Phase Power
Power
Reading
Angle factor
W1
W2 P(W )
φ
cos φ
Sample Calculation (set no . . . . . . )
Voltage V = . . . . . . . . .
Current I = . . . . . . . . .
Wattmeter reading W1 = . . . . . . . . .
Wattmeter reading W2 = . . . . . . . . .
Total Power P = W1 + W2 = . . . . . . . . .
#
"√
3(W1 − W2 )
= .........
Phase angle φ = tan−1
W1 + W2
Power factor = cos φ = . . . . . . . . .
48
= VL IL cos
√30cos φ + VL IL cos 30 cos φ
= 2VL IL 23 cos φ
√
= 3VL IL cos φ
For leading pf φ (When the load is capacitive)
W1 = VL IL cos(30 − φ)
W2 = VL IL cos(30 + φ) = Power in a 3φ circuit
W1 + W2 = VL IL cos(30 − φ) + VL IL cos(30 + φ)
=√
[2 cos 30 cos φ]VL IL
= 3 cos φVL IL
W1 − W2 = VL IL cos(30 − φ) − VL IL cos(30 + φ)
= [−2 sin 30 sin φ]VL IL
= − sin φVL IL
√ (W1 − W2 )
(W1 − W2 )/VL IL
√
= 3
tan φ =
(W1 + W2 )
(W1 + W2 )/ 3VL IL
When pf is unity, φ = 0 and W1 = W2
When 1.0 > pf > 0.5,
0 < φ < 60◦ both W1 and W2 read positive
When pf = 0.5 , φ = 60◦ and W1 = 0, hence W2 alone reads the total
power
When 0.5 > pf > 0, 60◦ < φ < 90◦
W1 reads negative and W2 positive
PROCEDURE
Connections are done as shown in the figure. The resistance is kept in
the maximum position and the inductive load is set to minimum. The
supply is switched on with the autotransformer in the minimum position.
The autotransformer is adjusted to get rated voltage in the voltmeter.
The load is purely resistive, the power factor is nearly unity and both
wattmeters read positive. Readings are taken corresponding to this condition. The inductive load is then increased till one of the wattmeter
becomes zero. This corresponds to a pf of 0.5. Again all readings are
noted. On further increasing the inductive load one of the wattmeters
starts deflecting in the negative direction. This indicates that the power
factor of the circuit is less that 0.5. The supply is now switched off and
the pressure coil(or current coil ie, C & V or M & L) connections of the
49
50
wattmeter reading negative is interchanged. Supply is switched on and
the readings corresponding to this condition are noted. The reading of
the wattmeter whose terminals are interchanged is be recorded as
negative. The power factor and power are calculated using the formula
given.
RESULT
Power consumed by a 3-φ RL load is measured using two wattmeter
method.
VIVA QUESTIONS
1. What is the expression for power in a 3-φ circuit?
2. Derive the expression for power factor in terms of the wattmeter
readings.
3. What are the other methods of measuring 3-φ power.
4. What does a zero reading in one of the wattmeters signify?
51
CONNECTION DIAGRAM
250V,5A,upf
0-5A MI
L P.C
M
N1
A
V
C
P1
5A
P
B
230V
1-φ
V
50Hz
AC
NL
E
ERROR CURVE
% ERROR
N
C
0-250V
MI
LINE CURRENT
Experiment 9
52
C.C
N2
Energy
Meter
K=
240V,5A
P2
Experiment 9
CALIBRATION OF SINGLE PHASE
ENERGY METER
AIM
To calibrate the given 1-φ energy meter at unity power factor by direct
loading.
APPARATUS REQUIRED
1. Energy meter 240V,5A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2. Wattmeter 250V,5A,upf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
3. Ammeter (0-5A)
MI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
4. Voltmeter (0-250V) MI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
5. 1-φ Autotransformer (0-270V,13A) . . . . . . . . . . . . . . . . . . . . . . . . . . 1
6. Stop watch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
7. Connecting wires
8. Lamp load
no.
no.
no.
no.
no.
no.
PRINCIPLE
An energy meter is an instrument used to measure electrical energy. It
keeps a record of the total energy consumed in a circuit during a particular
period. It is an integrating type of instrument. It essentially consists of
two electromagnets called the shunt magnet and series magnet. A coil
having a large number of turns of fine wire is fitted on the shunt magnet
called the pressure coil and is connected across the supply mains. The
series electromagnet is wound with a few turns of heavy gauge wire called
the current coil and is connected in series with the load. An aluminium
disc is mounted on a vertical spindle and is free to rotate between the
two magnets. The reaction between the magnetic fields setup by the two
electromagnets and eddy currents set up a driving torque in the disc and
the disc starts rotating. The average torque thus produced is proportional
to the true power of the circuit.
53
OBSERVATIONS(direct loading)
Sl. no. V(v)
I(A)
W(w)
T(s)
A.R(kwh) I.R(kwh) % Error
Sample Calculation(set no. . . . . . . )
Energy meter constant k = . . . . . . . . .
Voltmeter Reading (V ) = . . . . . . . . .
Ammeter Reading (I) = . . . . . . . . .
Time for 5 rev. of energy meter disc (t) = . . . . . . . . .
1
= .........
k
5
Indicated energy for 5 revolution of energy meter disc = = . . . . . . . . .
k
Wattmeter Reading (W ) = . . . . . . . . .
True energy for ‘t’ seconds (T R) = W × t = . . . . . . . . .
I.R − T.R
× 100 = . . . . . . . . .
% Error =
T.R
Indicated energy for 1 revolution of energy meter disc =
54
Calibration involves comparing the energy measured by an energy meter
with a standard instrument. The standard chosen here is a wattmeter.
Since the wattmeter measures only the power, it has to be multiplied with
time to get the energy reading. The readings are then compared to find
the error in the energy meter.
Calibration can be done either by direct loading or phantom loading. In
direct loading both the current and pressure coils are fed from the same
supply at rated voltage. Energy meters of high rating when tested by direct loading would involve large amount of power. Such meters are thus
tested using phantom loading.
PROCEDURE
Connections are made as shown in the connection diagram. The supply
is switched on, keeping the autotransformer in the minimum position. The
autotransformer is then varied to get the rated voltage. The lamp load
is then switched on and the ammeter adjusted for a small value of current. The corresponding readings of voltmeter, ammeter and wattmeter
are noted down. The time for five revolutions of the energy meter disc is
also noted. The experiment is repeated in steps adding loads till the rated
current of the energy meter is reached. The true energy and indicated
energy is evaluated and the error found out. The error curves are then
plotted as shown.
RESULT
The given energy meter is calibrated by direct loading at upf and the
error curve plotted
VIVA QUESTIONS
1. What is meant by ‘calibration’ of the energy meter?
2. What is the standard used for calibration of energy meter?
3. How does an induction type energymeter work?
4. What is the disadvantage of direct loading method?
5. How are the meters selected for this experiment?
55
WHEATSTONE’S BRIDGE
P
Q
I1
G
I2
R
G
5
1000
100
M1000
10
G
A
L
V
O
S
6
5
7
4
8
M100 3
1
.01
.001
M10
2
1
5
7
4
GALV
EXT
2
9
MIN
MAX
SENSITIVITY
CONTROL
B
50Ω,5Α
7
8
2
9
1
10
EXT
10
x10
G
EXT.
BATT.
10
4
x1
G
9
8 3
3
1
INT
2
SERIES x100
ARM 5 6
6
10V
8
1
10
x1000
RATIO
7
3
9
.1
6
4
B
INT
X
R1
R2
V
0-30V
PORTABLE FORM OF WHEATSTONE’S BRIDGE
Experiment 10
56
Experiment 10
RESISTANCE MEASUREMENT USING
WHEATSTONE’S BRIDGE
AIM
(a) To measure the resistance of given voltmeter (0-30V) using Wheatstone’s Bridge.
(b) To draw the circuit for extending the range of the given voltmeter
(0-30V) to read up to 300V.
APPARATUS REQUIRED
1. Wheatstones Bridge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2. Voltmeter (0-30V) MC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
3. Galvanometer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
4. High Resistance box . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
5. D.C source (0-30V). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
no.
no.
no.
no.
no.
PRINCIPLE
This is the best and most common method of measuring medium resistance (from 1Ω - 0.1 MΩ). The general circuit arrangement is shown in
the figure. P and Q are two known and fixed resistances. S is a known
variable resistance and R is the unknown resistance. When the bridge is
balanced, no current flows through the galvanometer, then
I1 × P = I2 × R
P
R
P
I1 × Q = I2 × S, ie,
=
or R =
×S
Q
S
Q
The unknown resistance can then be determined.
In the portable form of the Wheatstone’s Bridge the ratio(P/Q) can be
set to values of 1,10,100,1000. The standard resistance S can be adjusted
using decade dials of x1,x10,x100 and x1000. R can be found out using
the above formula.
57
OBSERVATIONS
Sl. Unknown
no. resistance
P
Q
S1 × S2 × S3 × S1 × S = S1 + S2
Mean
XΩ
1000Ω 100Ω 10Ω 1Ω
+S3 + S4
X
Voltmeter
(0 − 30V )
Resistance of the given voltmeter is . . . . . . . . .
EXTENSION OF INSTRUMENT RANGE
RS
V
RV
0-30V
VV
VT
300V
Let Rv
Rs
Vv
VT
be the resistance of the voltmeter
the resistance to be connected in series
the range of the given voltmeter
the range to which the extension is to be made
The value of the resistance to be connected in series to extend the range
is
VT
Rs =
− 1 Rv
Vv
58
PROCEDURE
The given voltmeter (unknown resistance) is connected to the terminal
marked R1 and R2 on the bridge. The toggle switches are adjusted for
external battery and galvanometer. An external battery is connected to
terminals BB′ through a rheostat. A galvanometer is connected to the
terminals marked Galvo. on the bridge. The P/Q ratio (range selector) is suitably selected. The resistance ‘S’ is varied by varying the four
decade resistances (one at a time starting from the highest range) till null
deflection is observed in the galvanometer, when the ‘B’ and ‘G’ keys are
pressed. Adjustments are made till null deflection is obtained, The reading
of the ‘Range selector’ and the four dials of the variable resistance ‘S’ are
noted. The readings are tabulated as shown. The experiment is repeated
for different values of range selecter(P/Q ratio)
Extension of range of meter:- First the resistance of the given voltmeter Rv is measured using Wheatstone’s bridge. To extend the range of
given voltmeter a resistance Rs is connected in series with voltmeter as
shown in the figure.
Since they are in series, current is the same through voltmeter and series
resistance.
Vv
(VT − Vv )
I=
=
Rv
R
s VT
Rv
=
− 1 Rv
Rs = (VT − Vv )
Vv
Vv
RESULT
1) Resistance of given volt meter is . . . . . . .. Ω
2) Resistance to be connected in series to extend its range to 300V
is . . . . . . . . . Ω
VIVA QUESTIONS
1. What is the range of resistances that can be measured using a
wheatstones bridge?
2. Why can’t a wheatstones bridge be used for measurement of small
value of resistance?
3. How can a low range voltmeter be used for measurement of high
voltages?
59
P
Q
G
p
R
q
S
r
R1
E
KELVINS DOUBLE BRIDGE
10V
+C1
45Ω,5Α
G
DC
SOURCE
GALV.
20
5
100
6
0-2.5A
4
A
+P1
x10
3
x.01
x100
x1
7
X.00002Ω/DIV
9
1 0 10
-P2
CURRENT SWITCH
-C2
PRESS KEY
FOR.
REV.
INITIAL FINAL
Experiment 11
60
0
8
2
x.1
10
10
OFF
Experiment 11
RESISTANCE MEASUREMENT USING
KELVIN DOUBLE BRIDGE
AIM
a) To measure the resistance of the given ammeter(0-2.5A) using Kelvin’s
double bridge.
b) To draw the circuit for extension of range of the meter to read up to
25A.
APPARATUS REQUIRED
1. Kelvin’s Double Bridge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2. D.C source (0-30V). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
3. Ammeter (0-2.5A) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
4. Galvanometer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
5. High Resistance box . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
6. Rheostat 45Ω,5A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
no.
no.
no.
no.
no.
no.
PRINCIPLE
This method is best available for the precise measurement of low resistances(less than 1Ω) in the figure ‘R’ is the low resistance to be measured
and ‘S’ is a standard variable resistance of the same order of magnitude,
P,Q, p and q are four non-inductive resistances, one pair of which are variable. These are connected to form two sets of ratio arms, which are used
for range selection. The ratio Q/P is kept same as q/p ratio along with
‘S’ being varied till null deflection of the galvanometer is obtained.
R Q q
Q
Then
= = or R = × S
S
P
p
P
61
OBSERVATIONS
Sl. Unknown
Range
S1 S2 × 10−4 S = S1 + S2 X mean
remarks
No. resistance
multiplier mΩ
Ω
mΩ
mΩ mΩ
Ammeter direct
1
+leads
reverse
Leads
direct
2
alone
reverse
Resistance
Resistance
Resistance
Resistance
of
of
of
of
ammeter + leads = . . . . . . . . .
leads alone = . . . . . . . . .
ammeter alone = . . . . . . . . .
the given ammeter (0-2.5A) = . . . . . . . . .
Extension of range of ammeter
To extend the range of ammeter a resistance is connected in shunt as
shown
IT=25A
A
IM
2.5A
RA
RSH
Let RA be the resistance of the ammeter
RSH the resistance to be connected in shunt
IM the range of the given ammeter
IT the range to which the extension is to be made
The value of resistance to be connected in shunt to extend the range of
the given ammeter to (0-25A)
= RSH =
(IM × RA )
(IT − IM )
62
PROCEDURE
Connections are made as shown in the figure. Choose a suitable range
multiplier . Set the current switch in forward position. Press the galvanometer initial key first and adjust main dial and slide wire to get
null deflection in the galvanometer. Then press the galvanometer final
key and check whether the galvanometer reads null deflection. If not, adjust the dial readings to get null deflection. The readings of the main dial
and slide wire are noted down.
The current switch is then put to the reverse position. This reverses
the direction of current in circuit. The main dial and slide wire are adjusted to get null deflection and the readings are noted again. The mean
of the two is taken as the correct value. This is done to eliminate errors
due to thermal effect. The ammeter is then disconnected and the resistance of the connecting leads alone is measured using the same method.
The experiment is repeated with different values of range multiplier. The
readings are tabulated as shown.
Resistance of ammeter = Resistance of ammeter + leads - Resistance of
leads alone
Extension of Range
To extend the range of ammeter a resistance is connected in shunt as
shown. Since both are in parallel, voltage across both is the same.
RSH
IM × RA = ISH × RSH
IM
(IM × RA )
=
× RA =
ISH
(IT − IM )
RESULT
1) Resistance of given ammeter( 0- 2.5A) = . . . . . . . . . Ω
2) Resistance to be connected in shunt to extend its range to (0-25A)
= .........Ω
VIVA QUESTIONS
1. How does a Kelvins double bridge differ from a wheatstones bridge?
2. What is the range of resistances that can be measured using a Kelvin’s
double bridge?
3. How can a low range ammeter be used for measurement of larger
values of currents?
63
CIRCUIT DIAGRAM FOR LINEAR RESISTANCE
+
0-1A
2A
+
A
-
+
220V
DC
-
V
300Ω
1.7A
0-250V
1000Ω
1.2A
-
2A
CIRCUIT DIAGRAM FOR INCANDESCENT LAMP
+
0-1A
2A
+
A
LAMP
+
220V
DC
-
Experiment 12
V
300Ω
1.7A
-
2A
64
-
0-250V
Experiment 12
V-I CHARACTERISTICS OF
INCANDESCENT LAMP AND LINEAR
RESISTANCE
AIM
To determine the V-I Characteristics of linear resistance and incandescent lamp.
APPARATUS REQUIRED
Rheostat
- 300Ω, 1.7A
Voltmeter
- 0-300V MC
Ammeter
- 0-2A MC
Incandescent lamp - 240V, 100W
Rheostat
- 1000Ω, 1.2A
PRINCIPLE
The resistance of a material is practically a constant at constant temperature, so for the linear resistance, according to ohm’s law the current
flowing through the circuit is directly proportional to the voltage applied.
ie,
I∝V
V = IR
where,
V is voltage applied, I the current, R the resistance
Here R is a constant therefore we get a linear relationship between
voltage and current. But in the case of incandescent lamp, large amount
of heat is produced so there is a considerable change in the resistance thus
as the voltage increases we get a non linear relationship between voltage
& current.
65
OBSERVATION AND CALCULATION
Linear Resistance
Incandescent lamp
Sl. Voltage Current Resistance Voltage Current
no.
V
I
R=V /I
V
A
V-I CHARACTERISTICS
V
Linear
Resistance
Incandescent
Lamp
I
66
PROCEDURE
The connections are made as per the circuit diagram. The linear resistance is connected in the circuit first. Keeping the potential devider in
the minimum output voltage positions, the supply is switched on. The
rheostat(300Ω, 1.7A) is adjusted to get different voltages till the rated
voltage is reached and corresponding current readings are noted down.
The experiment is repeated by connecting incandscent lamp in place of
the rheostat. The V-I characteristics of linear resistance and incandescent
lamp are plotted.
RESULT
V-I characteristic of linear resistance and the incandescent lamp are
plotted.
67
CIRCUIT DIAGRAM- OCC & SCC
15A
+
0-10A MI
L F A
A
Rh1
300Ω
1.7A
220V
DC
M
F1
-
N
B
A2
15A
V
R
A1
0-300V
MI
S3
R
Y
Y
B
F1
F2
F2
S1
2A
+
Rh2
D.C motor
V -230V
I-17A
H.P -3.5
rpm-1500
1000Ω 1.2A
+
-
S2 2A
A
-
0-2A MC
MEASUREMENT OF ARMATURE RESISTANCE
+
5A
+
0-5A MC
-
A
50Ω 5A
R
+
20V
DC
-
Experiment 13
0-10V
MC
V
N
5A
68
alternater
V -415V
I-5A
KV A-3.5
rpm-1500
Conn.-Star
Experiment 13
OPEN CIRCUIT AND SHORT CIRCUIT
TEST ON A THREE PHASE
ALTERNATOR
AIM
To conduct open circuit and short circuit tests on a three phase alternator and predetermine the regulation curve by emf method at half load
and full load.
APPARATUS REQUIRED
Voltmeter - 0-300V,MI
- 0-10V, PMMC.
Ammeter - 0-10A,MI
- 0-2A,PMMC
- 0-5A,PMMC.
Rheostat - 300Ω,1.7A
- 1000Ω,1.2A
- 50Ω,5A
PRINCIPLE
As the load on the alternator is varied the terminal voltage also varies.
This is due to
1.Voltage drop due to armature resistance IR.
2.Voltage drop due to armature reactance IXL .
3.Voltage due to armature reaction effect.
The voltage regulation of a synchronous generator is defined as the rise
in voltage at the terminals when the load is reduced from full load rated
value to zero, speed and field current remaining constant
%reg =
E−V
× 100
V
Where E - Generated emf
V - Terminal voltage
69
OBSERVATIONS AND CALCULATIONS
S.C TEST
Ia
If
O.C TEST
If
VOC
Measurement of Ra
V
I
Ra
Regulation curve
%Reg
(full load)
(half load)
(upf)
0 0.2 0.4
p.f
(lead)
0.6
0.8
0.8
0.6 0.4
0.2
0
p.f
(lag)
%Reg
Line voltage
= .........
VL
VP H
= √ = .........
3
Ra (dc) = . . . . . . . . .
Effective value Ra
= 1.6 × Ra (dc) = . . . . . . . . .
From graph
VL
Zs =Vp
OC /ISC = . . . . . . . . .
∴ Xs = Zs2 − Ra2 = . . . . . . . . .
70
For small machines the regulation may be found by direct loading. For
large machines the voltage regulation is predetermined by using indirect
methods like emf method, mmf method, Potier and ASA methods All
these methods require open circuit characteristics and short circuit characteristics.
The open circuit characteristics [also called open circuit saturation curve
or magnetization curve] is a plot of no load terminal voltage versus field
excitation with the machine running at rated speed. Under these conditions the induced voltage is directly proportional to the flux. The shape of
curve is therefore a typical B-H curve or magnetization curve. The short
circuit characteristics is a plot between armature current and field excitation with a symmetrical short circuit applied across the terminals. Under
this conditions current in the armature winding wholly depends on the internal impedance consisting of synchronus reactance Xs and the winding
resistance Ra .
Now Ra being small compared to Xs the pf under short circuit condition
is zero power factor lagging and therefore the armature reaction mmf is
almost wholly demagnetizing.
The short circuit characteristics is a straight line. From O.C.C & S.C.C
the synchronous impedance is evaluated.
For any value of excitation if VOC is the open circuit volage & ISC is
the short circuit current, then synchronous impedance Zs =VOC /ISC . The
value of Zs is calculated for the unsaturated region. For the computation
of regulation, it is convenient to take Zs at such a value of excitation which
give rise to Vph [normal voltage per phase]on open circuit. The armature
resistance is measured using ammeter,voltmeter method. Under working
conditions the effective value of Ra is increased due to skin effect and
temperature effect. The effective value of Ra is generally taken as 1.6
times the d.c value.
71
VOC
Ia
O.C.C and S.C.C of 3φ alternator
S.C test
O.C test
Isc
Voc
I f1
If
Sample Calculation
1/2
Eo = (V cos φ + IRa )2 + (V sin φ ± IXS )2
‘-ve’ for leading
‘+ve’ for lagging
% regulation =
Eo − V
× 100
V
←− lagging
leading −→
0 0.2 0.4 0.6 0.8 upf 0.8 0.6 0.4 0.2 0
Reg.(FL)
Reg.(HL)
72
p
Synchronous
reactance
per
phase
X
=
Za2 − Ra2 Ω per phase. Eo =
s
p
(V cos φ + IRa )2 − (V sin φ ± IXs )2
where +ve sign for lagging power factor and -ve for leading. Now percentage regulation for each case is computed as
% regulation =
Eo − V
× 100
V
PROCEDURE
O.C test
Connections are made as shown in the connection diagram. Switches
S3 and S2 are kept in the open position. The motor field rheostat Rh1
is kept in minimum position and the alternator field rheostat Rh2 in the
maximum position. Supply is switched on by closing switch S1 . The dc
motor is started using the 3-point starter. The motor field rheostat Rh1 is
varied till the speed becomes equal to the rated speed. Switch S2 is closed.
Rh2 is varied in steps and the field current and voltmeter reading are noted
down. The experiment is repeated for different values of field current till
the voltmeter reading shows 120% of the rated voltage of the alternator.
Rheostat Rh2 is brought back to the maximum resistance position.
S.C test
Switch S3 is closed and rheostat Rh2 is varied till the ammeter reading in the alternator (A2 ) reads the rated current of the machine. The
corresponding value of field current is noted down.
Armature resistance was found by voltmeter-ammeter method.
The regulation is then determined at various power factors for half and
full loads and the regulation curve is plotted.
RESULT
The open circuit and short circuit test was conducted on alternator and
O.C.C and S.C.C were conducted. The graph is plotted.
73
CONNECTION DIAGRAM - NO LOAD TEST
600V,5A,lpf
0-5A
R
A
400V 3 - φ 50Hz AC
10A
10A
L
E1
V
R1
R
V
C
B1
C1
Y
M
0-500V
B2
B
Y
STATOR
C2
B
10A
R2
R3
ROTOR
E2
B3
C3
E3
C
V
M
L
600V,5A,lpf
BLOCKED ROTOR TEST
250V,10A,upf
0-10A
R
A
400V 3 - φ 50Hz AC
10A
Y
M
10A
E1
V
0-250V
B2
B
Y
STATOR
C2
B
10A
S1
R1
R
V
C
B1
C1
L
R3
ROTOR
R2
E2
B3
C3
E3
C
V
M
L
Machine Details
Voltage - 415V
Current - 7.5A
speed -1440rpm
3-φ
H.P -5.0
250V,10A,upf
Experiment 14
74
BLOCKED
ROTOR
S2
Experiment 14
NO LOAD AND BLOCKED ROTOR
TESTS ON 3 PHASE SLIP RING
INDUCTION MOTOR
AIM
To perform no load and blocked rotor test on a three phase slip ring
induction motor and determine the equivalent circuit.
APPARATUS REQUIRED
Voltmeter
- (0-500V) MI
- (0-250V) MI
- (0-30V) PMMC.
Ammeter
- (0-5A) MI
- (0-10A) MI
- (0-10A)PMMC
Wattmeter
- 500V,5A,lpf
- 250V,10A,upf
Rheostat
- 9Ω,8.5A
Autotransformer
PRINCIPLE
Slip ring motors are always started with full line voltage applied across
the stator terminals. The value of starting current is adjusted by inducing
a variable resistance in the rotor circuit. The controlling resistance is in
the form of resistances connected in star. The resistance is gradually cut
out of the rotor circuit as the motor gathers speed.
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OBSERVATIONS AND CALCULATIONS
No load test:
V0 (V )
I0 (A)
W1
W2
W0 =W1 + W2
Blocked rotor test:
VSC (V )
ISC (A)
W1 (w)
W2 (w) WSC =W1 + W2
MEASUREMENT OF STATOR RESISTANCE
0-5A
5A
+
+
A
-
R
50Ω 5A
+
220V
DC
0-20V
5A
-
V
Y
B
For finding stator resistance; Rs :
No.
V (V )
I(A)
Rs
Rs (dc) = . . . . . . . . . Ω
Rse f f = 23 × 1.6 × Rs (dc)= . . . . . . . . . Ω
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By introducing the rotor resistance, the rotor current is reduced at starting and the starting torque is increased the latter due to the improvement
in power factor.
No load test:If the motor is run at rated voltage and frequency without any mechanical load, it will draw power to supply the no load losses. The no
load current will have two components. The active components and the
magnetizing component, the former being very small as the no load losses
are small. The power factor at no load is therefore very low. The no
load power factor is always less than 0.5 and hence at no load one of the
wattmeter at input side reads negative.
The no load input W0 to the stator consists of
1. Small stator copper loss
2. Core losses
3. The loss due to friction and windage.
The rotor copper loss can be neglected. Since slip is small under no load.
Blocked rotor test :The stator is supplied with a low voltage of rated frequency and with the
rotor blocked and short circuited, so that full load current flows through
the stator. The power input, current and the voltage applied are noted
down.
The power input during the blocked rotor test is wholly consumed in
the stator and rotor copper losses. The core loss is low because the applied
voltage is only a small percentage of the normal voltage. Again since the
rotor is at stand still the mechanical losses are absent. Hence the blocked
rotor input can be taken as approximately equal to the copper losses.
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No load test:V0 = . . . . . . . . .
I0 = . . . . . . . . .
W0 = . . . . . . . . .
V0 /ph = V0
= .........
Line current(IL ) =I0
= .........
IL
phase current(I0 /ph) = √ = . . . . . . . . .
3
Power consumed =W0
= .........
cos φ0
= √
W0
3V0 I0
= .........
∴ φ0
= .........
sin φ0
= .........
R0 /ph
=
V0 /ph
I0 /ph cos φ0
= .........
X0 /ph
=
V0 /ph
I0 /ph sin φ0
= .........
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PROCEDURE
No load test:The connections are made as shown in the diagram for no load test.
Brake drum is made free to rotate by loosening the belt. The autotransformer is placed in zero position. Then the supply is switched on and the
auto transformer is adjusted to supply the rated voltage to the machine.
The handle of the starter is rotated to cut out the rotor resistance. Readings of the wattmeters, voltmeter and ammeter are noted and tabulated.
Blocked rotor test:Connections are made as shown. The rotor is blocked by tightening the
belt on the brake drum. The auto transformer is set to the zero voltage
position. Then the three phase supply is switched on. By adjusting the
autotransformer, the ammeter reading is made equal to rated current of
the machine. Readings of the two wattmeters, voltmeter and the ammeter
are noted and tabulated.
Measurement of stator resistance :Connections are done for the stator resistance measurements. It is measured using the voltmeter-ammeter method.
79
From blocked rotor test:-
VSC = . . . . . . . . . ISC = . . . . . . . . . WSC = . . . . . . . . .
VSC /ph
= VSC
WSC /ph =
= .........
WSC
3
= .........
ISC /ph
ISC
= √
3
R01 =
WSC /ph
2 /ph
ISC
= . . . . . . . . . (Total winding resistance as referred
VSC /ph
ISC /ph
= .........
= .........
to the stator side)
Z01
=
X01
q
= Z021 − R021
R2′
RL
= .........
(Total leakage reactance as referred
= R01 − RS(ef f ) = . . . . . . . . .
to the stator side)
(Rotor resistance as referred to the
stater side)
= R2′
1−s
s
(Electrical equivalent of the mechanical load)
R0=1
V/ph=
X01=
RL
R0=
X0=
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RESULT
No load and blocked rotor tests were conducted on the given three phase
slip ring induction motor and the equivalent circuit parameters were determined.
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License information
Currently this Manual is licensed under Creative Commons AttributionNonCommercial-ShareAlike 2.5 India (CC BY-NC-SA 2.5).
But later on I’m intending to release the LATEX source of this book in
any GNU General Public License(GPL) compatible licenses (visit this:
http://www.gnu.org/licenses/license-list.html). I will be releasing the source
after some standardisation of LATEX codes (at my spare time), anyway now
you can get the vector images (Xcircuit editable postscript images) at my
site linked at https://launchpad.net/∼sadiq . If you can’t find anything
there, you might also request them via my email (I’m happy to do so :))
at sadiqpkp at gmail dot com .
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