Experiment No.
Date:
LOAD TEST ON SQUIRREL CAGE INDUCTION MOTOR
===============================================
AIM: Conduct the brake test on 3-phase squirrel cage induction motor using star delta starter
and plot the performance characteristics, viz. efficiency, line current, torque, slip, and
speed and power factor against output power. Also plot the speed – torque curve.
APPARATUS:
S.No.
Name of the apparatus
Type
1.
Voltmeter
MI
2.
Ammeter
MI
3.
Wattmeter
Dynamometer type
4.
Tachometer
5.
TPDT switch
Range
Quantity
PRINCIPLE:
The two types of 3-phase induction motors are i) squirrel cage induction motor and ii)
slip-ring induction motor. Three-phase squirrel cage induction motor is generally preferred
because it is rugged in construction, requires less maintenance and is economical as compared to
3-phase slip ring induction motor.
When the stator winding is connected to three phase ac supply, a rotating magnetic field
is established in the air gap which rotates at synchronous speed. Initially, rotor is stationary. Due
to relative speed between the rotating magnetic field and stationary rotor conductors, an
emf is induced in the rotor. As the rotor circuit is closed, currents will circulate through them.
According to Lenz’s law, these induced currents will flow in such a direction so as to oppose the
cause producing it. Here the cause is relative speed. In order to reduce the relative speed, the
currents in the rotor produce a torque tending to rotate the rotor in the same direction of rotating
field.
At synchronous speed of the rotor, the relative speed is zero, no emf and no torque is
developed, rotor tends to stop, hence rotor cannot attain synchronous speed. Motor runs at a
speed slightly less than synchronous speed.
CIRCUIT DIAGRAM
Machine Details
PROCEDURE:
Make the connections as shown diagram.
Precautions: i) Keep TPST switch open
ii) Keep TPDT in position 1 (Star connection)
.
iii) Keep belt on brake drum in loose position (motor on no load)
Switch on the 3 phase supply while the motor is on no load. When the motor gains speed,
change the TPDT switch to delta position (position 2). By tightening the brake drum, increase
the load on the motor up to rated value. Note down the speed, spring balance readings, and
voltmeter, ammeter and wattmeter readings. Now decrease the load in steps up to no load and
note down the readings each time. If any of the wattmeter readings shows negative on no load or
light loads, switch of the supply & interchange the terminals of pressure coils/current coils (not
both) of that wattmeter. Now, again starting the motor (follow above procedure forstarting), take
readings. Switch off the supply. Measure the radius of the brake drum.
TABULATION:
S.
No
V
I
W1
W2
Input W
=W1+W2
N
S1
S2
PF
Torque
N-m
Out-put
η (%)
1
2
3
4
5
6
7
8
SAMPLE CALCULATION (Set No. ____)
V= ______ V
I = ______ A
W1 = _______ W
N =_______ rpm
S1 = ________Kg
S2 =________Kg
Radius of brake drum R =
W2 = _______ W
m
Synchronous speed Ns = 1500rpm
(Note: N s  120 f ; For 50Hz induction motor, possible values of N s are 3000rpm, 1500rpm, 1000rpm,
P
750rpm etc)
Input Power W= W1 + W2 = _________ watts
Power factor, cosΦ1= cos(tan 1 3  (W1  W2 ) ) =__________
(W1  W2 )
Percentage slip, s = 
Ns  N
100 =_________%
Ns
Torque T  R  ( S1  S2 )  g = _________ N-m
Output power  2 NT = _________W
60
Efficiency,  
output
100 = _________%
input
MODEL GRAPHS
Experiment No.
Date:
LOAD TEST ON 3Ф SLIP RING INDUCTION MOTOR
AIM
(i) Start the 3-phase slip ring induction motor using rotor resistance starter and conduct
the brake test.
(ii) Plot the performance characteristics, viz. efficiency, line current, torque, slip, and speed
and power factor against output power. Also plot the speed – torque curve.
APARATUS REQUIRED
S.No.
Name of the apparatus
Type
1.
Voltmeter
MI
2.
Ammeter
MI
3.
Wattmeter
Dynamometer type
4.
Tachometer
5.
TPDT switch
Range
Quantity
PRINCIPLE
The slip ring induction motor has phase wound rotor and therefore external resistance can be
added to improve starting torque. The machine is started with the help of rotor resistance starter.
The load test is conducted on the machine to find out the performance under different load
condition. Using the readings obtained, performance characteristics are plotted. The
calculations are done as follows.
Here efficiency, % slip and the power factor are found out as given below. Torque
developed, T = (S1-S2) x 9.8 x R Nm where R is the radius of the break drum and S1&S2 are
the spring balance readings.
Input Power W = W1+W2
The output power developed, P=2πNT/60 watts
Hence the efficiency = output power/ input power x 100 %
Ns =120f/P
% slip = (Ns - N)/Ns x 100 %
Power Factor cosФ = Input / √3 VLIL
CIRCUIT DIAGRAM
Machine Specification
3 Ф SLIP RING INDUCTION MOTOR
kW
rpm
Volts
Current
PROCEDURE
Connections are made as shown in figure. The machine is started on no load, using rotor
resistance starter. For this, first the starter switch is kept in start position. It is then gradually
switched step by step to the run position. Now, the load is increased to full load value. The
speed, loads S1 and S2 and different meter readings are noted. Then load is decreased and each
time, different readings are noted. This is continued up to no load. The speed of the motor is
measured using tachometer.
TABULAR COLUMN
Sl.
V
No. (V)
I
Wi
W2
S1
(A)
(W)
(W)
(Kg)
SAMPLE CALCULATION
Voltage V = ...... Volts
Current I = ........ Volts
Input Power W = W1+W2 ..... Watts
S1 = ………..Kg
S2= ………..Kg
R =…………..m
Speed N = ...... rpm
Torque T = (S1-S2) x 9.8 x R= ..... Nm
The output power developed, P=2лNT/60 watts
S2
N
(Kg) (rpm)
T
Input Output PF
(Nm) (W)
(W)
Efficiency ŋ = output power/ input power x 100 %
%slip = (Ns - N)/Ns x 100 %
Power Factor cosФ = Input / √3 VLIL
KVAR required to improve pf to 0.95 =KVAR of load-KVAR at pf 0.95
=Pin tanФ1- Pin tanФ2
Expected Graphs
Experiment No.
Date
NO LOAD AND BLOCKED ROTOR TESTS ON A 3 PHASE SQUIRREL
CAGE INDUCTION MOTOR
================================================
AIM: i) To conduct no load and blocked rotor tests on 3 phase squirrel cage induction motor
ii) To determine the equivalent circuit parameters
iii) To
draw the circle diagram and hence predetermine the performance
characteristics.
APPARATUS:
S.No.
Name of the
Type
Range
Quantity
apparatus
1.
Voltmeter
MI
2.
MI
3.
MC
4.
Ammeter
MI
5.
MI
6.
MC
7.
Wattmeter
8.
9.
Dynamometer
Dynamometer
Rheostat
Wire wound
PRINCIPLE:
The performance characteristics of induction motors can be determined approximately
by graphical method such as circle diagram. This is applicable both for the squirrel cage and
slip ring induction motors. From the approximate equivalent circuit,
I2 ' 
V
V
sin 

R2 ' 2
X

X2 '
1
(R1 
)  ( X 1  X 2 ')2
Where, sin  
X1  X 2 '
R2 ' 2
(R1 
)  (R 1  R 2 ')2
If the leakage reactance X1 and X2’ are assumed to remain constant regardless of load, and
the applied voltage V is constant, the above equation represents the polar equation of a circle
with diameter
. By changing the load RL (where R  R ' (1 s) ) and Φ, the value of the
V
X1  X 2 '
L
2
S
current I2’ changes. The locus of the current, however, lies on a circle (Figure 1).
V
X1  X 2 '
Thus in the case of induction motors, the locus of the current due to load lies on a circle and the
diagram is known as a circle diagram. If no load current taken by the motor is also to be
accounted for to obtain the stator current, the diagram can then be shown as in figure 2. The
stator current I1 is then the phasor sum of I2’ and Io.
No load and blocked rotor tests are conducted for determining the equivalent circuit parameters,
for predetermining the efficiency at any load and to draw the circle diagram. No- load test is
conducted at rated voltage keeping the motor on no-load. Since the no-load currentis only 2040% of the full load current, the I2R losses can be neglected. Input power is equalto constant
iron, friction and windage losses of the motor. In blocked rotor test, rotor is blocked and a
reduced voltage is applied to the stator through a 3-phase autotransformer. Due to low voltage
and no rotation, core and mechanical losses are neglected. Input power is equal to copper loss
only.
CIRCUIT DIAGRAM
a) No Load Test
b) Blocked Rotor Test
Machine Details
c) Stator Resistance Measurement
PROCEDURE:
a) No Load Test
Make the connections as shown in figure.
Precautions: i) Keep the autotransformer in minimum voltage position
ii) Keep belt on brake drum in loose position (motor on no load)
Switch on the 3 phase supply. Adjust the autotransformer and apply rated voltage to the stator.
Since the power factor of the induction motor under no load condition is generally less than
0.5, one wattmeter will show negative reading. Then switch off the supply and interchange the
connections of the pressure coil (or current coil) of that wattmeter. Note down the ammeter,
voltmeter and wattmeter readings after applying rated voltage. Switch off the supply
b) Blocked Rotor Test
Make the connections as shown in figure.
Precautions: i) Keep the autotransformer in minimum voltage position
ii) Rotor is blocked by tightening the belt on the brake drum.
Switch on the 3 phase supply. Adjust the autotransformer so that rated current (to get full load
copper loss) flows in the ammeter. Note down voltmeter, ammeter and wattmeter readings. (If
any of the wattmeter reads negative, switch off the supply and interchange the connections of
the pressure coil (or current coil) of that wattmeter and continue the above procedure). Switch
off the supply.
c) Stator Resistance Measurement
Make the connections as shown in figure.
Precautions: Keep the rheostat in maximum resistance position
Switch on 28V DC supply. Note down voltmeter and ammeter readings for different positions
3
of rheostat. (Note: Resistance/phase = x Delta resistance)
Procedure to draw the circle diagram: (Do not write in fair record)
1. Draw the lines by taking the current (I) in X-axis, voltage (V) in Y-axis. (V & I are line values)
2. From the No-load test find out the current Io and draw the OA vector with the magnitude of Io from
the origin by suitable current scale, which lags the voltage (Y-axis) V by an angle Φo where
o  cos 1 (
Woc
).
3Voc I oc
3. From the current Isc find out the ISN (short circuit current corresponding to the normal voltage)
through the formula I SN  I sc (
Vrated
) , draw the OB vector with the magnitude of ISN from the origin
Vsc
by the same current scale, which lags the voltage (Y-axis) V by an angle ΦSC where
 SC  cos1 (
Wsc
).
3Vsc I sc
4. Join the points B and A to get the output line.
5. Draw the parallel line for the X-axis from point A and for the Y-axis from point B upto the X-axis
(point E), let both the lines intersects at point D.
6. Then draw the bisector for the output line and extend it to the line AD let the point of intersection
be C.
7. By keeping the point C as center draw a semi circle with radius CA.
8. Let EB be the line of total loss [EB = ED + DB where ED = constant loss and DB = variable loss]
9. In the line DB locate the point G to separate the stator and rotor copper losses by using the formula,
Rotor Copper loss I 2 '2 R2 ' R2 '
=
where R1= stator resistance per phase and R2= rotor resistance

Stator Copper loss I 2 '2 R1
R1
per phase.
Or,
BG R2 '
Rotor Copper loss
.


BD Ro1 Stator Copper loss+Rotor Copper loss
10. To get the torque line, join the points A and G.
11. To find the full load quantities, draw line BK (=Full load output/power scale). Now, draw line PK
parallel to output line meeting the circle at point P.
12. Draw line PT parallel to Y-axis meeting output line at Q, torque line at R, constant loss line at S
and X-axis at T.
Note: Choose the current scale such that the circle diagram will be as large as possible. The larger the circle
diagram more will be the accuracy. Select power scale =
3  Vrated  Current Scale .
TABULATION
NO LOAD TEST
Voc
Ioc
W1
W2
BLOCKED ROTOR TEST
Woc
Vsc
Isc
W1
W2
Wsc
Stator Resistance Measurement
S.No.
V (volts)
1.
2.
3.
Rdc
CIRCLE DIAGRAM
Voc = 400V,
Ioc = ___ A ,
Vsc = _____ V,
Woc = _____ W
Isc = 7.8A, Wsc = _____ W
Per phase values are
Vo  Voc  _____ V
Io 
I oc
 ____ A
3
Vs  Vsc  _____ V
Is 
I sc
 ____ A
3
Rdc = _____ Ω
3
R1  1.2  Rdc = ______ Ω
2
Ro1 
Wsc
= _______ Ω
3I s 2
R2'  Ro1  R1 = _______ Ω
BG R2 '

= ______
BD Ro1
BG = _____
x BD
I (amps)
Rdc=V/I Ω
Selection of current and power scale
Current scale = 1cm = ______ A
Ioc = _______A (= ______cm)
V
I SN  ( rated ) I sc = _______A(= _______cm)
Vsc
o  cos 1 (
Woc
) = _______ ˚
3Voc I oc
 SC  cos1 (
Wsc
) = _______˚
3Vsc I sc
Power Scale =
3  Vrated  Current Scale = _______ W = 1cm
PERFORMANCE AT FULL LOAD FROM CIRCLE DIAGRAM
Full load output = 3000W = PQ = _____cm
Full load current = OP x current scale = ____ x _____ = ______A
Full load power factor = PT 100% = ______ lag
OP
Rotor copper loss at full load = QR x power scale = ____ x _______ = _______W
Stator copper loss at full load = RS x power scale = _____ x ______ = _______W
Constant loss = ST x power scale = ___ x ______ = ________W
Rotor input at full load = PR x power scale = _____ x ______ = _______W
Torque at full load = PR x power scale (sync. watts) = PR x power scale x 60 N-m
2 N s
= _____ x ______ x
60
2  750
= _______N-m
Motor input at full load = PT x power scale = _____ x _______ = ______W
Efficiency at full load = PQ 100% = ________%
PT
Slip at full load s = QR 100% = _________%
PR
Speed at full load = (1  s)  N s = ________ rpm
Starting torque = BG x power scale x 60 N-m
2 N s
= _____ x ______ x
60 =______N-m
2  750
Maximum torque = I I’ = ______ x _____ x
60 =______N-m
2  750
Maximum output = HH’ = ______ x ______ = ________W
Maximum input = JJ’ = ______ x ______ = ________W
TABULATION FROM CIRCLE DIAGRAM
Line Current Motor
Torque
Rotor Cu
Output
Loss
OP
PQ
PR
QR
cm
A
cm W cm N-m cm
W
Po
Motor Input Efficienc Slip
y
PT
PQ/PT QR/PR
cm W
%
%
P1
P2
P3
P4
P5
P6
P7
P8
2
Model Graph – Performance Characteristics from Circle Diagram
Power
Factor
PT/OP
Experiment No.
Date
VOLTAGE REGULATION OF 3-PHASE ALTERNATOR
================================================
AIM: To predetermine the voltage regulation of the given 3 phase alternator by i) emf
method and ii) mmf method.
APPARATUS:
S.No.
Name of the apparatus
Type
1.
Voltmeter
MI
2
3
Quantity
MC
Ammeter
MI
4
MC
5.
MC
6
Range
Rheostat
Wire Wound
7
8
9
Tachometer
PRINCIPLE:
The terminal voltage of an alternator under load conditions is different from the open
circuit voltage due to the effects of armature resistance, leakage reactance and armature
reaction. Voltage regulation is defined as the rise in voltage, expressed as per cent of rated
voltage, when the load current is reduced to zero, the field excitation and frequency being
maintained constant. Thus,
Voltage regulation =
E f V
100
V
The term rise in voltage used in the above definition pre-supposes a resistive or
inductive load. If the load is capacitive, the magnetizing effect of armature reaction, due to
the leading current, may cause V to be higher than Ef, thus causing a drop in voltage, when
the load current is reduced to zero. In that case, the regulation is negative.
The regulation of a synchronous generator can be predetermined by the following
methods: a) synchronous impedance or emf method, b) mmf or ampere-turn method c) zero
power factor or potier method.
Open circuit characteristic (OCC): The open circuit characteristic of an alternator is a curve
of the armature terminal voltage on open circuit as a function of field excitation when the
machine is running at synchronous speed.
Short circuit characteristic (SCC): It is the plot of short circuit armature current as a function
of field current when the machine is running at synchronous speed.
Zero power factor curve (ZPFC): Zero power factor characteristic of an alternator gives the
variation of terminal voltage with field current, when the alternator is delivering its full load
current to a zero power factor (lagging) load.
PROCEDURE:
i) Open Circuit & Short Circuit Characteristics (OCC & SCC)
Make the connections as shown in diagram.
Precautions/Initial settings:
i)
TPST in open position
ii)
DPST1 and DPST2 in open position
iii)
Motor field rheostat in minimum position
iv)
Potential divider in minimum voltage position
Switch on the DC supply to the DC motor by closing the switch DPST 1. Start the DC shunt
motor using 3-point starter. Increase the resistance of dc motor field rheostat and drive the
alternator at rated speed. Now, dc supply is given to the alternator field winding and for
different values of field current, note down the open circuit voltage across the armature
terminals. Take care to keep the speed constant (rated value) through out the experiment. The
above procedure is repeated till the open circuit voltage reaches 120% of rated value. Open
circuit voltage/phase Eo Vs field current If gives OCC.
For SCC, reduce the armature voltage to zero by bringing the potential divider to minimum
voltage position. Now, close the TPST switch. By varying the potential divider, increase the
current through the short circuited armature up to rated value. Note both the ammeter readings.
Isc Vs If gives SCC.
STATOR RESISTANCE MEASUREMENT
Make the connections as shown in figure.
Precaution: Keep the rheostat at maximum position.
Switch on 28V d.c. supply. Note down the voltmeter and ammeter readings for
different positions of rheostat (If possible, take readings for rated armature current).
OCC
Field Current If
OC Voltage Eo
SCC
Isc (A)
If (A)
Stator Resistance Measurement
S.No.
V (volts)
I (amps)
Rdc=V/I (Ω)
1.
2.
3.
4.
Rdc
EMF METHOD
Sl. No.
CALCULATIONS
EMF METHOD
Rated voltage/phase V =
p.f.
1
0
lag
2
0.2
lag
3
0.4
lag
4
0.6
lag
5
0.8
lag
6
1
7
0.8
lead
8
0.6
lead
9
0.4
lead
10
0.2
lead
11
0
lead
Full load Ia =
Ef
Regulation
Short circuit current corresponding to rated voltage from SCC, Isc = ______A
Synchronous impedance, Z s 
V
=_______Ω
I sc
Armature resistance, Ra  1.2  Rdc = _______Ω
Synchronous reactance, X s  Z s 2  Ra 2 = ________Ω
Regulation at full load and ____ pf. Lag
Full load current = 10.9A, V = 230V, X s = _____ Ω, Ra = ______Ω, cosΦ = ____ lag

V  V 0  2300


I  I     10.9   for lag ( I  I     10.9   for lead)

E f  V 0  I    ( Ra  jX s )  E f   =________V
(OR E f  (V cos   I a Ra ) 2  (Vsin  I a X s ) 2 =________V)
% regulation =
E f V
V
100 =___________%
MMF METHOD
Regulation at full load and ____ pf. Lag

V  V 0  2300 V
cosΦ = ____ lag


I  I     10.9   for lag ( I  I     10.9   for lead)

E r  V 0  I    Ra  Er     =________V
Refer OCC and find Ifr corresponding to Er.

I f r  I fr (  90) =_________A
Ifa is the field current required to circulate rated current on short circuit (from SC test)


I f a  I fa (   180) for lag ( I f a  I fa (   180) for lead)



I f  I fr  I fa =_________A= I f (90   )
Hence, If = ______A, δ = ______˚
Refer OCC and find Ef corresponding to If.

E f  E f   =________V
% regulation =
E f V
V
*100 =__________%
PHASOR DIAGRAMS – MMF METHOD
TABULATION – MMF method
Power factor
1
0 lag
2
0.2 lag
3
0.4 lag
4
0.6 lag
5
0.8 lag
6
1
7
0.8 lead
8
0.6 lead
9
0.4 lead
10
0.2 lead
11
0 lead
MODEL GRAPHS






I
Er
Ifr
Ifa
If
Ef
% VR
Experiment No.
Date
SLIP TEST ON THREE PHASE SALIENT POLE SYNCHRONOUS
MACHINE
================================================
AIM: i) To conduct the slip test on 3-phase salient pole synchronous machine
ii) To determine the direct axis and quadrature axis synchronous reactance
iii) To predetermine the voltage regulation at different loads and power factors
APPARATUS:
S.No.
1.
Name of the apparatus
Voltmeter
Type
MI
3
MC
Ammeter
5.
Quantity
MI
2.
4.
Range
MI
MC
6.
Rheostat
7.
Tachometer
Wire Wound
PRINCIPLE:
The direct and quadrature axis reactance can be measured by slip test. The machine is
driven by a dc motor at a speed slightly less or slightly more than synchronous speed. The field
winding is kept open circuited and a low voltage 3 phase supply (about 25% of the rated
voltage) is applied to the armature terminals. The direction of rotation should be same as the
direction of rotating field. If this condition is fulfilled, a small ac voltage would be indicated by
the voltmeter across the field winding.
The relative velocity between armature mmf and field poles is equal to slip speed i.e.
difference between synchronous speed and rotor speed. The stator mmf moves slowly past the
field poles at slip speed. This would cause the armature current to vary cyclically at twice the
slip frequency. When the peak of the armature mmf is in line with the field poles, the reluctance
offered by the magnetic circuit is minimum, the armature current, required for the
establishment of constant air-gap flux, will be minimum. Constant applied voltage minus the
minimum impedance voltage drop (armature current being minimum) in the leads and 3- phase
autotransformer gives maximum armature-terminal voltage. The ratio of maximum armature
terminal voltage per phase to minimum armature current per phase gives Zsd. After one quarter
of slip cycle, the peak of armature mmf is in line with q-axis and the reluctance offered by the
magnetic circuit is maximum. The armature current, required for the establishment of constant
air-gap flux, will be maximum and the armature terminal voltage will be minimum. The ratio
of minimum armature terminal voltage per phase to maximum armature current per phase gives
Zsq.
When the armature mmf is in line with field poles, the armature flux linkage with field winding
is maximum and rate of change of this flux linkage is zero, so that induced voltage across the
field winding is zero. On the other hand, when armature mmf is in line with q-axis, the flux
linkage with field winding is minimum and rate of change of this flux linkage is maximum, so
that induced voltage across the field winding is maximum.
PROCEDURE:
SLIP TEST
Make the connections as shown in figure.
Precautions: i) Keep the autotransformer at minimum voltage position
ii) Keep DPST, TPST and SPST switches open
iii) Keep dc motor field rheostat at minimum resistance position
Switch on the d.c. supply by closing the DPST switch. Using the three point starter, start
the motor. Run the motor at synchronous speed by varying the motor field rheostat. Close the
TPST switch. By adjusting the autotransformer, apply 20% to 30% of the rated voltage to the
armature of the synchronous machine. Make sure that the direction of rotation of the prime
mover and the direction of rotation of the magnetic field produced in the armature are the
same by closing the SPST switch. If the voltmeter reading across the
Alternator field winding is very small, both the directions are correct. If the voltmeter reading
is high, interchange the two lines of 3 phase supply after switching off the 3 phase supply. SPST
switch is kept open.
Machine Details
The speed is slightly reduced/increased from synchronous speed, so that slip is
increased and the voltmeter and ammeter readings are oscillating. The maximum and minimum
readings of voltmeter and ammeter are noted. The above said procedure can be repeated with
two more different autotransformer settings.
(During slip test, it would be observed that swing of the ammeter pointer is very wide, whereas
the voltmeter has only small swing because of the low impedance voltage drop in the leads and
3-phase autotransformer).
STATOR RESISTANCE MEASUREMENT
Make the connections as shown in the diagram.
Precaution: Keep the rheostat at maximum resistance position.
Switch on 28V dc supply. Adjusting the rheostat for different values of current, note
down the ammeter and voltmeter readings.
TABULATIONS
Slip Test
Sl.No.
Vmax
Vmin
Imax
Imin
Z sd
Z sq
Xd
1.
2.
3.
Stator resistance measurement
Stator Resistance Measurement
S.No.
V (volts)
I (amps)
Rdc=V/I Ω
1.
2.
3.
4.
SAMPLE CALCULATION (SET No. ___ )
Armature resistance, Ra  1.2* Rdc =1.2 x _____ = ____Ω
Vmax = _____V, Vmin = _____V, Imax = ____A, Imin = _____A
Z sd 
Vmax
=______Ω
I min
Z sq 
Vmin
=______Ω
I max
X d  Z sd 2  Ra 2 =_______Ω
X q  Z sq 2  Ra 2 =________Ω
Note: Need not write in the fair record
Mean Rdc
Xq
Ef
C
O

Iq

jIqXq
V
IaRa
 
E

Ia
D Id
A
B
jIdXd
ΔODE and ΔABC are similar. Hence, AC  BC
OE
AC 
DE
BC  OE jI q X q  I a

 jI a X q
DE
Iq

OC  V  I a Ra  jI a X q  V  I a ( Ra  jX q )

Angle of OC will give δ. (Taking V as reference)
     for lag
     for lead
(or use the following formula for finding ψ,
tan  
V sin   I a X q
V cos   I a Ra
)
E f  V cos   I a Ra cos   I a X d sin 
a) To find Percentage regulation at full load and 0.8 p.f. lag

V  2300 V, cosФ=0.8, Ф = 36.87˚, I a  11.5   A

OC  V  I a ( Ra  jX q )  _____________  OC 
Hence, δ = _____º
    =
E f  V cos   I a Ra cos   I a X d sin 
% regulation =
E f V
V
100 = ______%
b) To find Percentage regulation at full load and 0.8 p.f. lead
V  2300 V, cosФ=0.8, Ф = 36.87˚, I a  11.5   A

OC  V  I a ( Ra  jX q )  _____________  OC 
Hence, δ = _____º
   
E f  V cos   I a Ra cos   I a X d sin 
% regulation =
E f V
V
100 = ________%
a) % regulation at full load
power factor
Ф
0
lag
90
0.2
lag
78.46
0.4
lag
66.42
0.6
lag
53.13
0.8
lag
36.87
1
Ψ
δ
Eo
Regulation
Ψ
δ
Eo
Regulation
0
0.8
lead
-36.87
0.6
lead
-53.13
0.4
lead
-66.42
0.2
lead
-78.46
0
lead
-90
b) % regulation at Half full load
power factor
Ф
0
lag
90
0.2
lag
78.46
0.4
lag
66.42
0.6
lag
53.13
0.8
lag
36.87
1
0
0.8
lead
-36.87
0.6
lead
-53.13
0.4
lead
-66.42
0.2
lead
-78.46
0
lead
-90
MODEL GRAPH
Experiment No.
Date
PERFORMANCE EVALUATION OF SINGLE PHASE INDUCTION
MOTOR
AIM
To conduct load test on the given single phase induction motor and to plot its
performance characteristics.
APPARATUS REQUIRED:
S.NO
1
APPARATUS
VOLTMETER
SPECIFICATIONS
(0-300V) MI
2
AMMETER
(0-10A) MI
1
3
WATTMETER
(300V,10A,UPF)
1
4
5
TACHOMETER
Connecting wires
(0-10000 RPM)
As required
1
FORMULAE
Load test
1. Circumference of the brake drum = 2πR (m)
R = Radius of the brake drum
2. Input power =W (watts)
W = wattmeter readings
3. Torque (T) = 9.81x R x (S1 ~ S2) (N-m)
S1, S2 = spring balance readings (Kg)
2NT
4. Output power =
(watts)
60
N- Speed in rpm
5. % Efficiency (η) =
output power
input power
W
6. Power factor, cos Φ=
VI
x100
QUANTITY
1
Ns  N
100
Ns
7. % Slip, s =
NS = synchronous speed =
120 f
P
(rpm)
P = no. of poles f=frequency of supply (Hz)
PRECAUTIONS
Load test
1. The auto transformer must kept at minimum voltage position.
2. The motor is started at no load condition.
3. The motor should not be stopped under loaded condition
MODEL GRAPH
CIRCUIT DIAGRAM
300V, 10A, UPF
(0-10)A
MI
Fuse
P
D
15A
P
S
T
L
C
V
S1 S2
M1
Auto Transformer
230/(0-270) V
230V,
50Hz 1
AC
Supply
M
A
S
W
I
T
C
H
V
C
Kg Kg
(0-300)V
MI
M2
Rotor
N
Link
S1
S2
Brake Drum
PROCEDURE
Load test
1. Connections are given as per the circuit diagram
2. The DPST switch is closed and the single phase supply is given to the motor.
3. By adjusting the autotransformer, the rated voltage is applied and the correspondingno
load values of speed, spring balance and meter readings are noted down. If thewattmeter
readings show negative deflection on no load, switch of the supply & interchange the
terminals of current coils (M & L) of the wattmeter. Now, again start the motor (follow
above procedure for starting), take readings.
4. The procedure is repeated till rated current of the motor is reached.
5. The motor is unloaded, the auto transformer is brought to the minimum voltage
position, and the DPST switch is opened.
6. The radius of the brake drum is measured.