Em ii mannual

Er. PERUMAL MANIMEKALAI COLLEGE OF
ENGINEERING
DEPARTMENT OF ELECTRICAL& ELECTRONICS
ENGINEERING
EE8411 - ELECTRICAL MACHINES LABORATORY-II
MANNUAL
Prepared by
S.DEVARAJ
ASSISTANT PROFESSOR
DEPT OF EEE

EE8411 ELECTRICAL MACHINES LABORATORY-II L T P C
0 0 4 2
OBJECTIVES:
 To expose the students to the operation of synchronous machines and induction
motors and give them experimental skill.
LIST OF EXPERIMENTS
1. Regulation of three phase alternator by EMF and MMF methods.
2. Regulation of three phase alternator by ZPF and ASA methods.
3. Regulation of three phase salient pole alternator by slip test.
4. Measurements of negative sequence and zero sequence impedance of alternators.
5. V and Inverted V curves of Three Phase Synchronous Motor.
6. Load test on three-phase induction motor.
7. No load and blocked rotor tests on three-phase induction motor
(Determination of equivalent circuit parameters).
8. Separation of No-load losses of three-phase induction motor.
9. Load test on single-phase induction motor.
10. No load and blocked rotor test on single-phase induction motor.
11. Study of Induction motor Starters
TOTAL: 60 PERIODS
OUTCOMES:
At the end of the course, the student should have the:
 Ability to understand and analyze EMF and MMF methods
 Ability to analyze the characteristics of V and Inverted V curves
 Ability to understand the importance of Synchronous machines
 Ability to understand the importance of Induction Machines
 Ability to acquire knowledge on separation of losses

AIM:
To predetermine the regulation of the given alternator by EMF and MMF methods
APPARATUS REQUIRED:
S.NO Name of the apparatus Type Range Quantity
1. Voltmeter
2. Ammeter
3. Rheostat
4. Tachometer
5. TPSTS
6. Connecting wires
THEORY:
The regulation of a 3-phase alternator may be predetermined by conducting the
Open Circuit (OC) and the Sort Circuit (SC) tests. The methods employed for
determination of regulation are EMF or synchronous impedance method, MMF or
Ampere Turns method and the ZPF or Potier triangle method. In this experiment, the
EMF and MMF methods are used. The OC and SC graphs are plotted from the two tests.
The synchronous impedance is found from the OC test. The regulation is then
determined at different power factors by calculations using vector diagrams. The EMF
method is also called pessimistic method as the value of regulation obtained is much
more than the actual value. The MMF method is also called optimistic method as the
value of regulation obtained is much less than the actual value. In the MMF method the
armature leakage reactance is treated as an additional armature reaction. In both
methods the OC and SC test data are utilized.
Date : Ex. No:1
REGULATION OF ALTERNATOR BY EMF AND MMF METHODS

CIRCUIT DIAGRAM:
NAME PLATE DETAILS:
Excitation :
:
:
:
:
Voltage
Current
Speed




3- PHASE ALTERNATOR
 Capacity
Excitation :
:
:
:
:
Voltage
Current
Speed




DC SHUNT MOTOR
 Capacity

OBSERVATION TABULATION
1. O.CTEST:
Sl.No
Field current
If (Amps)
No-Load Voltage
Eo (Volts)
1.
2.
3.
4.
.
.
10.
2. S.C.TEST:
Sl.No
Rated Short circuit
current
Isc (Amps)
Field current
If (Amps)
1.
DETERMINATION STATOR ARMATURE RESISTANCE, Ra:
Sl.No V (Volts) I ( Amps) Rdc (Ω)
1.
2.
.
.
5.
Average Rdc (Ω) =
Stator resistance/phase ACvalue,Ra =1.3 xRdc= -------------------(Ω)

CALCULATION TABULATION:
i).EMF method:
Sl.No
Power
factor
cos ∅
sin ∅
No-Load phase
voltage, Eo (volts)
% Regulation
Lagging
p.f
Leading
p.f
Lagging
p.f
Leading
p.f
1. 0
2. 0.2
3. 0.4
4. 0.6
5. 0.8
6. 1.0
MODEL GRAPHS:
MODEL CALCULATION:

PRECAUTIONS:
1. Motor field rheostat should be at the minimum resistance position
while switching on and switching off the DPSTS.
2. The rheostat on the field circuit of generator should be kept at minimum
potential (output) position before closing the TPSTS.
3. The starter handle must be moved step by step to start the motor and
alternator set.
PROCEDURE:
O.CTEST:
1. Keep the TPSTS open.
2. Close the DPSTS switch.
3. Using the starter run the MG set.
4. Run the MG set at rated speed, by adjusting the field rheostat.
5. By adjusting alternator field rheostat in convenient steps of If. note down
V.(phase voltage)
S.C TEST:
1. Now close the TPSTS.
2. By adjusting alternator field rheostat, observe If for rated current in the
armature circuit of alternator

ii).MMF method:
Sl.No
Power
factor
cos ∅
Total field
current,
If (Amps)
No-Load phase
voltage, Eo (volts)
% Regulation
Lagging
p.f
Leading
p.f
Lagging
p.f
Leading
p.f
Lagging
p.f
Leading
p.f
1. 0
2. 0.2
3. 0.4
4. 0.6
5. 0.8
6. 1.0
MODEL GRAPHS:
MODEL CALCULATION:

RANGE FIXING:
Full load current of motor= A
On both O.C and S.C test the power delivered by the alternator is zero.
 The power drawn by the M-G set from source is equal to the no load power requirements
of M-G set, which is approximately 30-40% of full load current of DC motor.
 Fuse rating on DC side is A
 The rated current of alternator is A
 Fuse rating AC side is A
 Range of ammeter is(0- A)
 Rated phase voltage of alternator Vph =VL/√3
 Range of voltmeter is(0- V)
 The rated field current of alternator is A
 Range of ammeter If is(0- A)
 Rheostat on field circuit of motor and alternator
 Their current rating is to be based on their rated field current.
 Their ohmic value should be as high as possible (especially for alternator side).
 Therefore the range of field rheostat on motor side A Ω
 Therefore the range of field rheostat on alternator side A Ω
DISCUSSION QUESTIONS:
1. Define synchronous impedance.
2. Is regulation of alternator can be +ve, -veand zero? If so under what condition?
3. For which nature of load power factor the regulation of alternator is maximum?
4. Why EMF method is called as pessimistic method?
5. Why MMF method is called as optimistic method?
6. Mention the different methods available for pre determining the regulation of alternator
RESULT:

AIM:
To predetermine the regulation of the given alternator by ZPF and ASA methods
APPARATUS REQUIRED:
1 Voltmeter
2 Ammeter
3 Rheostat
4 Tachometer
5 TPDTS
6 Connecting wires
THEORY:
ZPF method is based on the separation of armature leakage reactance and armature
reaction effects. To determine armature leakage reactance and armature reaction mmf
separately, two tests are performed on the alternator.
The two tests are
1. Open circuit test
2. Short circuit test
3. Zero power factor tests
ASA means American standard Association method. This is a modification of mmf
method. In these methods, the magnetic circuit is assumed to be unsaturated. If we
consider the saturated magnetic circuit, the resultant excitation is not If, but it is If’. This
additional excitation can be obtained by ASA method
Date : Ex. No:2
REGULATION OF ALTERNATOR BY ZPF AND ASA METHODS

CIRCUIT DIAGRAM:
NAME PLATE DETAILS:
Excitation:
:
:
:
:
Voltage
Current
Speed




3- PHASE ALTERNATOR
 Capacity
Excitation:
:
:
:
:
Voltage
Current
Speed




DC SHUNT MOTOR
 Capacity

OBSERVATION TABULATION:
1. O.CTEST:
Sl.No
Field current
If (Amps)
No-Load Voltage
Eo (Volts)
1.
2.
.
.
10.
2. S.C.TEST:
Sl.No
Rated Short circuit
current
Isc (Amps)
Field current
If (Amps)
1.
3. ZPF TEST:
Sl.No
Field current,
If (Amps)
EMF/Phase, E
(Volts)
1.
2.
3.
4.
5.
CALCULATIONTABULATION:
i).ZPF METHOD:
Sl.No
Power
factor
cos ∅
sin ∅
Field Current,
If(Amps)
No-Load phase
voltage, Eo (volts)
% Regulation
Lagging
p.f
Leading
p.f
Lagging
p.f
Leading
p.f
Lagging
p.f
Leading
p.f
1. 0
2. 0.2
3. 0.4
4. 0.6
5. 0.8
6. 1.0

MODEL GRAPHS:
MODEL CALCULATION:
ii).ASA METHOD:
Sl.No
Power
factor
cos ∅
Total field
current,
If(Total) (Amps)
No-Load phase
voltage, Eo (volts)
% Regulation
Lagging
p.f
Leading
p.f
Lagging
p.f
Leading
p.f
Lagging
p.f
Leading
p.f
1. 0
2. 0.2
3. 0.4
4. 0.6
5. 0.8
6. 1.0

MODEL GRAPHS:
MODEL CALCULATION:

PRECAUTIONS:
1. Motor field rheostat should be at the minimum resistance position while
switching on and switching off the DPSTS.
2. The rheostat on the field circuit of generator should be kept at minimum
potential (output) position before closing the TPSTS.
3. The starter handle must be moved step by step to start the motor and alternator set.
PROCEDURE:
O.CTEST:
1. Keep the TPSTS open.
2. Close the DPSTS switch.
3. Using the starter run the MG set.
4. Run the MG set at rated speed, by adjusting the field rheostat.
5. By adjusting alternator field rheostat in convenient steps of If. note down
V.(phase voltage)
S.C TEST:
1. Now close the TPSTS.
2. By adjusting alternator field rheostat, observe If for rated current in the armature
circuit of alternator
ZPF TEST:
1. Keep the field rheostat at minimum potential position.
2. Close the TPSTS switch to load position.
3. Vary the load and keep the load current as rated current.
4. Vary the field current by varying the field rheostat of alternator note the reading of
the voltmeter and ammeter.
5. Note that the load current should be rated full load current on all occasion. For
this purpose simultaneous adjustment of load and current may be done.
6. The speed should be rated speed.
1. Which method will give accurate result in predetermining the regulation of an
alternator? Why?
2. What is reactance?
3. What are the procedural steps for calculating the regulation by Potier method?
RESULT:

AIM:
To predetermine the regulation of the given three phase pole salient alternator by slip
test.
APPARATUS REQUIRED:
1 Voltmeter
2 Ammeter
3 Rheostat
4 Tachometer
5 Connecting wires
THEORY:
In non salient pole alternators air gap length is constant and reactance is also
constant. Due to this the mmfs of armature and field act upon the same magnetic circuit all
the time hence can be added vector ally. But in salient pole alternators the length of the air
gap varies and reluctance also varies. Hence the armature flux and field flux cannot vary
sinusoid ally in the air gap. So the reluctance of the magnetic circuit on which mmf act is
different in case of salient pole alternators. This can be explained by two reaction theory.
Date : Ex. No:3
REGULATIONOF THREE PHASE SALIENTPOLE ALTERNATOR
BY SLIP TEST

CIRCUIT DIAGRAM:
NAME PLATE DETAILS:
:
:
:
:
 Voltage
 Current
 Speed
3- PHASE ALTERNATOR
 Capacity
Excitation:
:
:
:
:
Voltage
Current
Speed




DC SHUNT MOTOR
 Capacity

Calculation of Xd and Xq:
DETERMINATION STATOR ARMATURE RESISTANCE, Ra
1.
2.
.
.
5.
Average Rdc (Ω) :
Stator resistance/phase ACvalue,Ra =1.3 xRdc=-------------------(Ω)

= ( )
= ( )phase
=
2
− 2
)
=
2
− 2
)
−
x100
=
=
co
co
−
+
−
+
(
(
)
)
=
=
−
−
s
(
(
)
)
si
co
n ±
±
)= tan
=
−1(
s
, =
FORMULA:
To find Xd and Xq:
Direct axis impedance per phase,
Quadrature axis impedance per ,
Direct axis reactance per phase, (
Quadrature axis reactance per phase, (
%Regulation =
Where,
s
For, + ← Generating mode
- ← Motoring mode
PRECAUTION:
1. Before switch on the supply the motor field rheostat must be in the
minimum resistance position.
2. Three phase variac on the alternator side should be kept in the zero position.

Sl.No
Power
factor
cos ∅
sin ∅
No-Load phase
voltage, Eo (volts)
% Regulation
Lagging
p.f
Leading
p.f
Lagging
p.f
Leading
p.f
1. 0
2. 0.2
3. 0.4
4. 0.6
5. 0.8
6. 1.0
MODEL GRAPHS:
MODEL CALCULATION:

PROCEDURE:
1. Observing the precautions switch on the supply. The motor will start run.
2. Adjust the motor armature/filed rheostat so that the motor runs at a slightly less than the
synchronous speed.
3. Adjust the three phase variac in convenient steps and setting note the maximum and
minimum value of voltmeter and ammeter needle oscillations.
1. Name the test by which xd and xq of a salient pole alternator is determined.
2. Name the theory by which salient pole synchronous machines analyised?
3. What is an infinite bus bar?
RESULT:

AIM:
To draw the V and inverted V curves of synchronous motor
APPARATUS REQUIRED:
1 Voltmeter
2 Ammeter
3 Wattmeter
4 Rheostat
5 SPSTS
6 Tachometer
7 Connecting wires
THEORY:
Synchronous motor is constant speed motor which are not self starting in nature, so
that we have to start this motor by any one of the following starting methods,
1. Pony motor method starting
2. Auto induction starting
3. DC exciter starting
4. Damper winding method of starting
By construction there is no difference between synchronous generator and
synchronous motor. It is capable of being operated under wide range of power factor;
hence it can be used for power factor correction.
The value of excitation for which back emf is equal to applied voltage is known as
1005 excitation. The other two possible excitations are over excitations and under
excitation if the back emf is more or less to the applied voltage respectively.
The variations of armature current with field current are in the form of V curves and
the variation of power factor with field current are in the form of Inverted V curves.
Date : Ex. No: 5
V AND INVERTED V CURVES OF SYNCHRONOUS MOTOR

CIRCUIT DIAGRAM:
NAME PLATE DETAILS:
3- PHASE SYNCHRONOUS MOTOR
 Capacity :
 Voltage :
 Current :
 Speed :

M.F=-----------
Sl.No
Line
Voltage
VL
(Amps)
Line
current
IL
(Amps)
Input Power
Pi (Watts)
Field
current
If(Amps
)
Power factor
cosφ
Reading Actual
1.
2.
.
.
7.
Note:
For each load setting, draw separate observation table.
MODEL GRAPHS:
MODEL CALCULATION:

meter
FORMULA:
Input Power, Pin=Watt readings
Power Factor, cosφ =
√3x VLx IL
Where,
VL -Voltmeter reading
IL -Ammeter reading
PROCEDURE:
1. Connect the circuit as per the circuit diagram.
2. Applied for rated voltage using autotransformer.
3. Apply the constant load to shaft of the synchronous motor and vary the field current
from minimum to maximum. i.e under excitation to over excitation.
4. Record the armature current (Ia) each step.
5. Also note down voltmeter, field ammeter (If), wattmeter readings. Repeat the above
procedure for other constant load setting.
DISCUSSION QUESTION:
1. What are the different methods of starting synchronous motor?
2. List down the application of synchronous motor.
RESULT:

AIM:
To the performance of the given 3-phase squirrel cage induction motor by direct
loading
APPARATUS REQUIRED:
1 Voltmeter
2 Ammeter
3 Wattmeter
4 Tachometer
5 Connecting wires
THEORY:
A 3-phase induction motor consists of stator and rotor with the other associated
parts. In the stator, a 3-phase winding is provided. The windings of the three phase are
displaced in space by 120º.A 3-phase current is fed to the 3-phase winding. These
windings produce a resultant magnetic flux and it rotates in space like a solid magnetic
poles being rotated magnetically
FORMULA:
Torque applied on the motor, T = (F1~F2) x r x 9.81 in Nm.
Where,
Circumference of the brake drum, 2 Π r =----------- m2
Radius of the brake drum, r =----------- m
Input Power, Pi = Wattmeter reading in Watts
Output, P0 =
2 Π N T
60
in Watts.
% Efficiency, η =
Po
Pi
x 100
Date : Ex. No: 6
LOAD TEST ON 3-PHASE SQUIRREL CAGE INDUCTION MOTOR

CIRCUIT DIAGRAM:
NAME PLATE DETAILS:
3- PHASE SQUIRREL CAGE INDUCTION MOTOR
 Capacity :
 Voltage :
 Current :
 Speed :

1. OBSERVATION TABULATION:
M.F=-----------
Sl.No
Line
Voltage
VL
(Amps)
Line
current
IL
(Amps)
Input Power,
Pi (Watts)
Speed
N
(rpm )
Spring Balance
Reading
Reading Actual F1( kg ) F2 ( kg )
1.
2.
.
6.
2. CALCULATION TABULATION:
Sl.No
Line
current
IL
(Amps)
p.f
Torque
(N.m)
% Slip
Output
Power
P0
(Watts)
Input
Power
Pi
(Watts)
%
Efficiency
η
1.
2.
.
6
MODEL GRAPHS:
MODEL CALCULATION:

√3x
−
L
x
V x
Power Factor, cosφ =
Po
IL
% Slip, S = 100
Where,
NS = Synchronous speed = 1500 rpm.
PRECAUTIONS:
1. The motor should be started without any load.
2. The supply should not be switched OFF before the motor is unloaded.
3. While running on load, the brake drum is cooled by pouring cold water.
PROCEDURE:
2. Switch on the supply at no load. Take one set of reading at no load.
3. Vary the load in suitable step and hence note down all the meter reading up to
100 % of full load. ( Observe one reading slightly above but less than 120%
rated current)
RANGE FIXING:
Rated voltage of motor =--------------V
 Range of voltmeter =--------------V
Rated current of motor =--------------A
 Range of ammeter =--------------A
The active power drawn by the motor and reactive power is less. So power factor
is normally more than 0.3.
 UPF wattmeter = ------------ V,------------- A
 Rated current of variac =--------------A
1. Compare induction motor with transformer?
2. Why induction motor draws more current on load than a transformer?
3. Can you identify the type of induction motor on visual inspection? If yes, How?
4. Which type of induction motor has more starting torque?
5. What is induction generator?
RESULT:

AIM:
Predetermine the performance characteristics of 3-phase squirrel cage induction
motor from the circle diagram and equivalent circuit using No-load and Blocked rotor
test.
APPARATUS REQUIRED:
1 Voltmeter
2 Ammeter
3 Wattmeter
4 Tachometer
5 Connecting wires
THEORY:
An induction motor is simply an electric transformer whose magnetic circuit is
separated by an air gap into two relatively movable portions, one carrying the primary
and the other the secondary winding. Alternating current supplied to the primary
winding induces an opposing current in the secondary winding, when later is short
circuited or closed through an external impedance. Relative motion between the
primary and secondary ie, stator and rotor is produced by the electromagnetic forces
corresponding to the power thus transferred across the air gap by induction.
NO LOAD TEST (OR) OPEN CIRCUIT TEST:
No load test is performed to determine the no load current, no load power factor,
wind age and friction losses, no load input and no load resistance and reactance. Since
there is no power output on no load, the power supplied to the stator furnishes its core
loss and the friction and wind age losses in the rotor.
Date : Ex. No:7
NO LOAD AND BLOCKED ROTOR TEST ON
3-PHASE SQUIRREL CAGE INDUCTION MOTOR

CIRCUIT DIAGRAM:
1. NO LOAD TEST
NAME PLATE DETAILS:
:
:
:
:
 Voltage
 Current
 Speed
 Capacity

CIRCUIT DIAGRAM:
2. BLOCKED ROTOR TEST

__A
=
__A
=
∅Wo = √3 x Vo x
I
∅ =
√3 × 0×
o
BLOCKED ROTOR TEST (OR) SHORT CIRCUIT TEST:
It is also known as locked rotor or short circuit test. This test is used to find the short
circuit current with normal voltage applied to stator, power factor on short circuit, total
leakage reactance and resistance of the motor as referred to stator and full load copper
loss.
FORMULA:
For Delta connected 3-phase squirrel cage induction motor
No-Load test,
No-Load applied Line voltage, Vo = V
No-Load applied phase voltage, Vo (ph)= Vo= V
No-Load Line Current, Io =
No-Load phase Current, Io (ph) = A
√3
No-Load totalPower, Wo= W
Blocked Rotor test,
Blocked rotor applied Line voltage, Vb = V
No-Load applied phase voltage, Vb(ph) = Vb= V
Blocked rotor Line Current, Ib =
Blocked rotor phase Current, Ib (ph) = A
√3
Blocked rotor total Power, Wb= W
i) To Find Equivalent Circuit Parameters
No Load Test:
x

1. NO LOAD TEST:
M.F= --------
Sl.No
No-Load
applied
voltage, Vo
(Volts)
No-Load
Current, Io
(Amps)
W1 W2
Total No-load
input Power,
Wo (Watts)
Reading Actual Reading Actual
1.
2. BLOCKED ROTOR TEST:
M.F= --------
Sl.No
Blocked Rotor applied
voltage, Vb (Volts)
Blocked Rotor
Current, Io (Amps)
Total Blocked Rotor input Power,
Wb (Watts)
Reading Actual
1.
DETERMINATION STATOR RESISTANCE, R1
1.
2.
.
5.
Average Rdc (Ω) :
Stator resistance/phase AC value, R1= Ra (ac) =1.3 xRdc =-----------------(Ω)

EQUIVALENT CIRCUIT:
Sl.No % Slip
IL
(Amps)
p.f
Speed
N
(rpm)
Torque
(N.m)
Output
Power
P0
(Watts)
Input
Power,
Pi
(Watts)
%
Efficiency
η
1. 1
2. 2
3. 4
4. 6
5. 8
6. 10
7. 12
MODEL CALCULATION:

CIRCLE DIAGRAM: (DO WRITE IN THE GRAPH SHEET)

using the formula
=
,
′
2
′
2 2
2 =′
2 1
′
2
1
Whe
1 =
re,
ℎ ′
=2
′
ℎ . or, = 2
01
1. In the line DB locate the point G to separate the stator and rotor copper losses by
2. To get the torque line, join A and G.
3. To find the load quantities, draw line BK (= full load output power/ power scale).
Now draw line PK parallel to output line meeting the circle at point P.
4. 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 a large as possible. The
larger the circle diagram more will be the accuracy. Select power scale = √3 x Vrated x
current scale
PROCEDURE:
i) NO-LOAD TEST:
2. By varying the variac, start the motor at no load.
3. Applied rated voltage to the motor and note down all the meter readings
ii) BLOCKED ROTOR TEST:
1. Make the circuit connections as per the circuit diagram.
2. Add some load initially so that the motor is blocked from rotating.
3. By varying the variac circulate rated current in the motor stator circuit.
4. Note down all the meter readings.

1. List out the method of starting of 3-phase induction motor.
2. What are the data needed for constructing circle diagram of an induction motor?
3. What should be minimum dimension for the diagram of circle diagram?
4. What is the limitation on capacity on induction motor for using DOL starter?
5. What is an induction generator?
RESULT:

AIM:
To separate the no load losses (Stator, Rotor copper losses, Iron and mechanical
losses) in induction motor
APPARATUS REQUIRED:
1 Voltmeter
2 Ammeter
3 Wattmeter
4 Tachometer
5 Connecting wires
THEORY:
The no load losses are the constant losses which include core loss and friction and
windage loss. The separation between the two can be carried out by the no load test
conducted from variable voltage, rated frequency supply.
When the voltage is decreased below the rated value, the core loss reduces as nearly
square of voltage. The slip does not increase significantly the friction and windage loss
almost remains constant.
The voltage is continuously decreased, till the machine slip suddenly begins to
increase and the motor tends to stall. At no load this takes place at a sufficiently reduced
voltage. The graph showing no load losses versus voltage is extrapolated to V =0 which
gives friction and windage loss as iron or core loss is zero at zero voltage.
Date : Ex. No:8
SEPARATION OF NO LOAD LOSSES IN INDUCTION MOTOR

CIRCUIT DIAGRAM:
NO LOAD TEST:
NAME PLATE DETAILS:
 Capacity :
 Voltage :
 Current :
 Speed :

DETERMINATION STATOR RESISTANCE, Ra (ac)
1.
2.
.
.
5.
Average Rdc (Ω) =
Stator resistance/phase AC value, Ra (ac) =1.3 xRdc =----------------(Ω)
M.F=-----------
Sl.No
Applied
Voltage,
V
(Amps)
No Load
current,
Io
(Amps)
W1(Watts) W2(Watts) No Load Input
Power,
W=W1+W2
(Watts)
Reading Actual Reading Actual
1.
2.
3.
.
.
7.

2
Ra (ac)
PROCEDURE:
3. Adjust the voltage applied to the induction motor in convenient steps, note
down the wattmeter readings.
4. Repeat this procedure up to rated voltage and slightly above the rated voltage.
Procedure for Separation of No Load Losses:
From no load test, Polt a graph W and V as shows.
For rated voltage read W. This represents the irion and mechanical losses, as stator Cu
loss on no load is negligible. Note it as Wo
Extend the graph so that it intercepts the y axis. This y axis intercept represents the
mechanical losses of the IM. Note this as Wm
For Rated Voltage,
No load Cu loss, Wcu = 3
No load Cu loss, Wcu is very small value; stator Cu loss on no load is
negligible No load Iron loss, Wi = Wo – Wm
RESULT:

AIM:
To the performance of the given 1-phase induction motor by direct loading
APPARATUS REQUIRED:
1 Voltmeter
2 Ammeter
3 Wattmeter
4 Tachometer
5 Connecting wires
THEORY:
The single phase induction motor is more or less a polyphase induction motor. The
only difference is that is given supply in single phase. This motor connect and motor
function without any initial start the motor having some part which is called starter and
rotor. These are two types of starting a 1 phase induction motor namely capacitor-start
and other is split-phase. These motors are widely used in domestic purpose.
FORMULA:
Torque applied on themotor, T = (F1~F2) x r x 9.81 in Nm.
Where,
Circumference of the brake drum, 2 Πr= ------------ m2
Radius of the brakedrum, r =----------- m
Input Power, Pi = Wattmeter reading in Watts
Output,P0 =
2 Π N T
60
in Watts.
Date : Ex. No: 9
LOAD TEST ON 1-PHASE SQUIRREL CAGE INDUCTION MOTOR

%Efficiency,η =
Po
x100
Pi
1. OBSERVATIONTABULATION.
M.F=------
Sl.
No
Line
Voltage
VL
(Amps)
Line
current
IL
(Amps)
Input Power
Pi (Watts)
Speed
N
(rpm )
Spring Balance
Reading
Reading Actual F1( kg ) F2 ( kg )
1.
2.
.
6.
2. CALCULATIONTABULATION.
Sl.No
Line
current
IL
(Amps)
p.f
Torque
(N.m)
% Slip
Output
Power
P0
(Watts)
Input
Power
Pi(Watt
s)
%
Efficiency
η
1.
2.
.
6.
MODEL GRAPHS:
MODEL CALCULATION:

VLx
−
L
x
I
PowerFactor,cosφ =
Po
%Slip,S = 100
Where,
NS = Synchronous speed = 1500 rpm.
PRECAUTIONS:
1. The motor should be started without any load.
2. The supply should not be switched OFF before the motor is unloaded.
3. While running on load, the brake drum is cooled by pouring coldwater.
PROCEDURE:
2. Switch on the supply at no load. Take one set of reading at no load.
3. Vary the load in suitable step and hence note down all the meter reading up to
100 % of full load. ( Observe one reading slightly above but less than 120%rated
current)
RANGE FIXING:
Rated voltage of motor =--------------V
 Range of voltmeter =--------------V
Rated current of motor =--------------A
 Range of ammeter =--------------A
The active power drawn by the motor and reactive power is less. So power factor is
normally more than 0.55
 UPF wattmeter =------------V,--------------- A
 Rated current of variac=----------------A
1. Why single phase induction motors are not self starting?
2. How would you reverse the direction of a single phase capacitor start induction
motor?
3. Mention few applications of single phase induction motor?
4. Name the theory by which the working of single phase induction motor?
5. Classify the single phase motors based on their construction and method
of starting
RESULT:

AIM:
To draw the approximate equivalent circuit of 1-phase squirrel cage induction motor by
conducting No-load and Blocked rotor test.
APPARATUS REQUIRED:
1 Voltmeter
2 Ammeter
3 Wattmeter
4 Tachometer
5 Connecting wires
THEORY:
The equivalent circuit of a single phase induction motor can be developed by using
double field revolving theory. By using the equivalent circuit the performance of the single
phase induction motor can be obtained.
The single phase induction motor can be visualized to be made of single stator winding
andtwoimaginaryrotors.Thedevelopingtorquesoftheinductionmotorisforwardtorque and
backward torque.
When the single phase induction motor is running in the direction of forward revolving
field at a slip S, then the rotor currents induced by the forward field has frequency sf. The
rotor mmf rotates at slip speed with respect to the rotor but at synchronous speed with
respect to the stator. The resultant forward stator flux and the rotor flux produce a forward
air gap flux. This flux induces the voltage in rotor. Thus due to the forward flux, the rotor
circuit referred to stator has an impedance of R2’ /2s + jX2’/2.
Date : Ex. No:10
NO LOAD AND BLOCKED ROTOR TEST ON
1-PHASE SQUIRREL CAGE INDUCTIONMOTOR

CIRCUIT DIAGRAM:
1. NO LOAD TEST:
NAME PLATE DETAILS:
M.F=---------------
Sl.No.
No-Load Voltage
V0 (Volts)
No-Load Current
I0 (Amps)
No-Load Power , P0 (Watts)
Reading Actual
1.
 Capacity :
 Voltage :
 Current :
 Speed :

CIRCUIT DIAGRAM:
2. BLOCKED ROTOR TEST
M.F=----------------
Sl.No.
Blocked Rotor Voltage
Vb (Volts)
Blocked Rotor Current
Ib (Amps)
Blocked Rotor Power, Pb (Watts)
Reading Actual
1.

NO LOAD TEST OR OPEN CIRCUIT TEST:
No load test is performed to determine the no load current, no load power factor, wind
age and friction losses, no load input and no load resistance and reactance. Since there is no
power output on no load, the power supplied to the stator furnishes its core loss and the
friction and wind age losses in the rotor.
BLOCKED ROTOR TEST OR SHORT CIRCUIT TEST:
It is also known as locked rotor or short circuit test. This test is used to find the short
circuit current with normal voltage applied to stator, power factor on short circuit, total
leakage reactance and resistance of the motor as referred to stator and full load copper
loss.
FORMULA:
i) NO LOADTEST:
No load power factor (CosФ0) = W0/ V0I0
Where W0 = No load power in watts
V0 = No load voltage in volts.
I0 = No load current in amps
Working component current (Iw) = I0 CosФ0 amps
Magnetizing component current (Im) = I0SinФ0amps
No load resistance R0 = V0 / Iw ohm
No load reactance X0 = V0 / Im ohm

DETERMINATION STATOR RESISTANCE, R1
1.
2.
.
5.
Average Rdc (Ω)=
Stator resistance/phase AC value, R1=Ra(ac) =1.3 xRdc= -------------------(Ω)
DETERMINATION STATOR IMPEDANCE, ZS
Sl.No VS(Volts) IS ( Amps) ZS (Ω)
1.
2.
.
5.
Average ZS (Ω) =

′
=2 01 − 1,
2
−
2
1
Where,
R1- Stator winding resistance a.c value
R1= Ra(ac) = 1.3 x Rdc
Rotor Reactance referred to stator side
Where, Stator winding reactance, X1=
Where,
Zs-Stator winding Impedance
Magnetizing reactance, Xm = 2(Xo –X1 – X2’/2)
PROCEDURE:
i) NO-LOADTEST:
2. By varying the variac, start the motor at no load.
3. Applied rated voltage to the motor and note down all the meter readings
ii) BLOCKED ROTORTEST:
1. Make the circuit connections as per the circuit diagram.
2. Add some load initially so that the motor is blocked from rotating.
3. By varying the variac circulate rated current in the motor stator circuit.
4. Note down all the meter readings.

Approximate Equivalent Circuit (Without Core Losses):
MODEL CALCULATION:

REGULATION OF THREE PHASE ALTERNATOR BY EMF AND MMFMETHOD
1. What are synchronous machines?
The machines generating ac emf are called alternating or synchronous generators.
While the machine accepting input from ac supply to produce mechanical output are called
synchronous motors. Both these machines work at a specific constant speed called
synchronous speed and hence in general called synchronous machines.
2. Define voltage regulation. Name two methods used to determine voltage regulation of
alternators.
%Reg = (E-Vrated / Vrated)
*100 Where,
E = No load voltage
Vrated = Rated voltage
3. Two methods to determine voltage regulation:
a) EMF method
b) MMF method
4. What are the two types of alternators?
a) Non salient pole alternator
b) Salient pole alternator.
5. State the principle of alternator.
When the rotor is rotated by the prime mover, the stator windings or conductors are cut
by the magnetic flux hence an emf is induced in the stator conductors. (Faraday’s law of
electromagnetic induction)
6. Is EMF method an accurate method?
No, it is not an accurate method because the value of synchronous impedance found is
always more than the original value.
7. Write the emf equation of an alternator.
E = 4.44f ФTKcKd
volts Where,
f = frequency in hertz
Ф = flux perpole
T = Number of turns in stator windings
Kc = Pitch factor
Kd = Distribution factor
8. What is known as Armature reaction?
The effect of armature flux on main flux is called as armature reaction.
9. What is meant by synchronous reactance?
Synchronous reactance Xs = XL + Xa
Where,
XL = leakage reactance
Xa = Armature reactance
10. Can a DC generator be converted into an alternator? How?
Yes, by providing two collector rings on end of the armature and connecting these
two rings to two points in the armature windings 180 degree apart.

REGULATION OF THREE PHASE ALTERNATOR BY ZPF AND ASA METHOD
1. Why is the field system of an alternator made as arotor?
The field system of an alternator is made rotating to avoid interaction of mechanical
and electrical stress. So with rotating field system, it is easier to collect currents at very high
voltages from stationary member. The insulation required is less; the problem of sparking is
avoided.
2. Define the terms distribution factor and pitch factor.
The factor by which there is a reduction in the emf due to distribution of coils is called
distribution factor, denoted by Kd.
The factor by which induced emf gets reduced due to short pitching of coil is called
pitch factor, denoted by Kc.
3. Potier method is also called Potier reactance method. Why?
It is based on the separation of armature leakage reactance and armature reaction
effects. The armature leakage reactance XL is called Potier reactance in this method, hence
this method is also called as Potier reactance method.
4. What are the experimental data required for Potier method?
i). Data’s obtained from open circuit test to draw the OCCcurve
ii). Field current required to obtain the zero armature voltage and the field current to
obtain the rated armature current. These two field currents are required to draw the ZPF
curve.
5. What is ASA method?
This is American Standard Association method. Both the EMF and MMF method is
capable of giving the reliable values of the voltage regulation, the error is present. So to
rectify that a modification of MMF method is introduced called as ASA method. It includes
the additional excitation.
6. Whether the results obtained by ASA method is reliable for salient pole machines.
Yes, it is reliable for salient pole and Non salient pole machines.
7. Compare EMF method and Potier method.
Sl.No EMF METHOD POTIER METHOD
1. Regulation of alternator of any load
condition and power factor condition can be
determined.
Separate curves foe every load condition
are to be plotted if regulation at various
load condition is required.
2. It is also called as pessimistic method. It is also called as Potier reactance method.
8. State the reason of errors in EMF and MMF method
a) The magnetic circuit is assumed to be unsaturated. This assumption is unrealistic.
b) In salient pole alternators, it is not correct to combine field ampere turns and armature
ampere turns .This is because the field winding is always concentrated on a pole core
while the armature winding is always distributed.

9. Compare MMFmethod and Potier method.
Sl.No MMF METHOD POTIER METHOD
1. This method which gives regulation lower The results obtained are nearer to
than actual, hence called optimistic method. reality.
2. Energy is not wasted. Energy is wasted.
10. What are the different methods available to determine the voltage regulation of an
alternator?
a) Direct loading method
b) Synchronous Impedance method or EMF method
c) Ampere Turn method or MMF method
d) Zero Power Factor method or Potier method
e) ASA method
f) Two reaction theory
REGULATION OF THREE PHASE SALIENT POLE
ALTERNATORBY SLIP TEST
1. What is meant by salient pole type rotor?
The rotor poles projecting out from the rotor core of large diameter but small length.
This is used in low and medium speed (engine driven alternator)
2. What is the necessity of damper winding?
Most of the alternators have the pole shoes slotted for receiving copper bars of a grid
or damper winding. They are useful in preventing the hunting in generators and are needed in
synchronous motors to provide the starting torque.
3. What is meant by Two Reaction theory?
The method of analysis of the distributing effects caused by salient pole construction is
called Two Reaction theory.
4. State Two Reaction theory.
The armature mmf can be divided into two components as
i). Component acting along the pole axis called direct axis (d)
ii). Component acting along at right angles to the pole axis called quadrature axis (q).
5. What is d axis and qaxis?
The reluctance offered to the mmf wave is lowest when it is aligned with the field
pole axis. This axis is called direct axis of pole.
The reluctance offered is highest when the mmf wave is oriented at 90 to the field
pole axis which is called quadrature axis.
6. What is meant by magnetizing and cross magnetizing component?
The component along direct axis can be magnetizing and the component acting along
the quadrature axis is called cross magnetizing component.
7. What is called sliptest?
The method used to determine Xd and Xq, the direct and quadrature axis reactance’s
is called sliptest.
Page: 73

8. What is meant by power angle?
The angle δ between Eo and V is called the power angle.
6. Compare salient pole and Non salient pole rotor.
S.no SALIENT POLE ROTOR NON SALIENT POLE ROTOR
1. Large diameter and small axial length. The diameter of the rotor is reduce,
to reduce the peripheral velocity of
rotor
2. It is employed with hydraulic turbines or
diesel engines.
Used in high speed turbine like steam
turbines.
10. What is meant by Auto – Transformer?
It is a transformer with one winding only, part of this being common to both
primary and secondary. In this transformer the primary and secondary are not electrically
isolated from each other.
V AND INVERTED V CURVES OF THREE PHASE SYNCHRONOUS MOTOR
1. Define V and Inverted V curves.
The magnitude of armature current varies with excitation. If graph of armature
current drawn by the motor against field current is plotted then we get V curves.
If the power factor is plotted against field current then the shape of the graph looks
like an inverted V and are called as Inverted v curves.
2. When Synchronous motor is is said to receive 100%excitation?
The value of excitation for which back emf is equal to the applied voltage is known as
100% excitation or when the power factor of the synchronous motor is unity.
Eb = V (or) cosФ =1
3. Define critical excitation.
When the excitation is changed, the power factor changes. The excitation for which
the power factor of the motor is unity is called critical excitation.
4. What do you mean by under excitation and over excitation?
When the excitation is adjusted in such a way that the magnitude of induced emf is
less than the applied voltage the excitation is called under excitation (lagging power factor)
When the excitation is adjusted in such a way that the magnitude of induced emf is
greater than the applied voltage the excitation is called over excitation (leading power factor).
5. What is synchronous capacitor?
When synchronous motor is over excited it takes leading power factor current. This
characteristic is similar to a normal capacitor which always takes leading power factor
current.
Hence over excited synchronous motor operating on no load condition is called as
synchronous condenser or synchronous capacitor. This is the property due to which
synchronous motor is used as a phase advancer or as a power improvement device.

6. What is hunting?
When synchronous motor is on no load, the stator and rotor pole axis coincide with
each other. When motor is loaded, the rotor pole axis falls back with respect to stator.
If the load connected to motor is suddenly changed by a large amount, the rotor tries to
take its new equilibrium position. But due to inertia of rotor, it cannot achieve equilibrium
instantaneously while achieving new position, it passes beyond its final position
corresponding to new load. This will produce more torque than demanded. So the load angle
is reduced and rotor swings in other direction.
Such oscillations of the rotor about its new equilibrium position, due to sudden
application or removal of load is called hunting.
7. Mention some application of synchronous motor.
a) Constant speed load service
b) Reciprocating compressor drives
c) Power factor correction
d) Voltage regulation of transmission lines
8. What could be the reasons if a synchronous motor fails to start?
It is usually due to the following reasons
a) Voltage may be to low
b) Some faulty connections in auxiliary apparatus
c) Too much starting load
d) Open circuit in one phase or short circuit
e) Field excitation may be excessive.
9. A synchronous motor starts as usual but fails to develop its full torque. What could be
due to?
a) Exciter voltage may be too low
b) Field spool may be reversal
c) There may be either open or short circuit in the field
10. What are the various methods of starting synchronous motor?
a) Pony motor method starting
b) Auto induction starting
c) DC exciter starting
d) Damper winding method of starting
11. What significant characteristic of a synchronous motor is revealed by itsV-curves?
The V curves of synchronous motor reveals the fact that its power factor is
controllable by means of its excitation.
LOAD TEST ON THREE PHASE INDUCTION MOTOR
1. What is the function of slip rings and brush assembly in three phase induction motor?
Slip rings are used to connect external stationary circuit to the internal rotating
circuit. Hence in induction motor, the external resistances can be added with the help of
brushes and slip ring arrangement in series with each phase of rotor winding.

2r = S
+
2 d)
)
.I2r
2. List the difference between squirrel cage rotor and slip ring rotor
S.no SLIP RING ROTOR SQUIRREL CAGE ROTOR
1. Rotor consists of winding similar to the Rotor consists of bars which are short
stator winding. circuited at the ends with the help of
end rings.
2. Resistances can be added externally. External resistances cannot be added.
3. Define the term slip
Slip of the induction motor is defined as the difference between the synchronous
speed and actual speed of rotor expressed as a fraction of the synchronous speed.
4. How the direction of rotation of three phase induction motor can be reversed?
The direction of rotation of three phase induction motor can be reversed by
interchanging any two terminals of the three phase windings while connecting to the three
phase supply.
5. Under what condition, the slip in an induction motor is zero, one, negative and
greater than one.
a) Zero: when N = Ns, S=0 which is not possible for an induction motor.
b) One: when N = 0, S=1. At start motor is at rest and hence its speed N is zero.
c) Negative: When the rotor is running at a speed above synchronous speed, slip is
negative.
d) Greater than one: When the motor is rotated in opposite direction to that of rotating
field,
e) Slip is greater than 1. When slip is greater than one, the machine works in breaking
mode.
6. What are the fundamental characteristics of a rotating magnetic field?
a) The resultant of three alternating fluxes separated from each other by 120 degree has
constant amplitude of 1.5 Фm, where Фm is maximum amplitude of an individual flux
due to any phase.
b) The resultant always keeps on rotating with certain speed in space, and the speed is
given by Ns = 120f /P
7. What is induction generator?
When run faster than its synchronous speed, an induction motor runs as a generator
called as induction generator. Slip is negative.
8. What is the effect of slip on frequency, induced emf, current, power
factor, Reactance, Impedance?
a). Fr=Sf b).E2r = SE2c).X X = E2r /Z2r
e).Cos Ф 2r= R2/Z2r f).Z2r= (
9. What are the types of three phase induction motor?
a) Squirrel cage induction motor
b) Slip ring induction motor

10. Can N = Ns in three phase induction motor?
When rotor starts rotating it tries to catch the speed of rotating magnetic field.
If it catches the speed of rotating magnetic field, the relative motion between rotor
and RMF will vanish. In fact the relative motion is the main cause for the individual emf in
the rotor. So induced emf will vanish and hence there cannot be rotor current and rotor flux
which is essential to produce the torque on the rotor. Eventually motor will stop. The
induction motor never rotates at synchronous speed.
NO LOAD AND BLOCKED ROTOR TEST ON THREE PHASE SQUIRREL
CAGEINDUCTION MOTOR
1. Enumerate the possible reasons if a three phase motor fails to start?
a) One or more fuses may be blown
b) Voltage may be too low
c) The starting load may be too heavy
d) Worn bearings due to which the armature may be touching field laminae,
thus introducing excessive friction.
2. What happens if single phasing occurs when the motor is running? And when it is
stationary?
a) If already running and carrying half load or less, the motor will continue running as a
single phase motor on the remaining single phase supply, without damage because
half loads do not blow normal fuses.
b) If motor is very heavily loaded, then it will stop under single phasing and since it can
neither restart nor blow out the remaining fuses, the burn out prompt.
c) A stationary motor will not start with one line broken. In fact due to heavy stand
still current, it is likely to burn out quickly unless immediately disconnected.
3. What is meant byplugging?
Plugging means stopping a motor by instantaneously reversing it till it stops.
4. What are the starters used in three phase induction motor?
a) Primary resistance starter
b) Auto transformer starter
c) Direct on line starter
d) Star Delta starter
e) Rotor resistance starter
5. What are the different methods of speedcontrol of three phase induction motor?
a). Control from stator side:
i).By changing the supply voltage
ii).By changing the supply frequency
iii).By changing the number of poles
b). Control from Rotor side:
i).Rotor rheostat control
ii).By operating two motors in cascade or concatenation
iii).By injecting an emf in the rotor circuit

6. What is meant by crawling?
Induction motor particularly the squirrel cage type, sometimes exhibit a tendency to
run stably at speeds as low as one seventh of their synchronous speed. This phenomenon is
known as crawling.
7. What is meant by cogging or magnetic locking?
The rotor of a squirrel cage induction motor sometimes refuses to start at all,
particularly when the voltage is low. This happens when the number of stator teeth is equal to
the number of rotor teeth and is due to the magnetic locking between the stator and rotor
teeth. That is why this phenomenon is also called as teeth locking.
8. What are the advantages of skewing?
a) It reduces magnetic humming.
b) It helps in reducing the locking tendency of the rotor. ie, the tendency of the rotor
teeth to remain under the stator teeth due to the magnetic attraction between the two.
9. What is jogging?
Jogging means inching a motor ie, make it to move a little at a time by constant
starting and stopping.
10. What are the indications of winding faults in an induction motor?
a) Excessive and unbalanced starting currents
b) Some peculiar noises and
c) Overheating
SEPERATION ON NO LOAD LOSSES IN THREE PHASE SQUIRREL
CAGEINDUCTION MOTOR
1. Mention the losses that occur in induction motor.
a) Stator core loss
b) Stator copper loss
c) Rotor Copper loss
d) Mechanical losses
2. What are the no load losses?
The no load losses are the constant losses which include core loss and friction and
windage loss.
3. In which type of induction motor can resistance be introduced in the rotor circuit?
In slip ring induction motor the resistance can be introduced in the rotor circuit.
4. The squirrel cage rotor is also known as short circuited rotor. Why?
In squirrel cage rotor, the copper bars are placed in the slots. These bars are short
circuited at each end with the help of conducting copper ring called end ring. The entire rotor
resistance is very small. Hence this rotor is also called as short circuited rotor.
5. Why air gap length is minimum in an induction motor?
The air gap length is kept minimum in induction motor
a) To reduce the magnetizing current which is required to set up the flux
b) To improve the power factor.

6. Define operating torque, starting torque and breakdown torque. Which of these is the
largest?
Operating Torque : Torque from light load to full load
Starting Torque : Torque at start ie, speed = 0 or slip = 1
Breakdown Torque : Maximum torque that motor can develop.
I floaded beyond this torque the motor will decelerate and come to standstill.
Breakdown torque is the largest among these for normal induction motor.
7. Why do induction motor runs at low power factor when lightly loaded?
At no load an induction motor draws large magnetizing current to create flux in the
air gap. This current has very low power factor of the order 0.2 lag. The power is mainly
drawn to provide for core loss. As the motor is loaded, it draws a load component of current
with much higher power factor. Therefore the power factor of the net current drawn from
main increases with load. It rises to 0.8 - 0.85 at full load. At light load the power factor will
be slightly more than that at noload.
8. Why an induction motor is not operated under conditions of maximum load?
Maximum power output condition corresponds to matching of the load resistance in
the circuit model to the circuit impedance as seen by the load resistance. This condition
corresponds to much larger than the normal operating slip and hence larger current than the
full load value. As copper loss is proportional to square of motor current, the motor efficiency
under condition of maximum power output is well below 50% which is unacceptable for a
power device. Acceptable efficiencies are about 85% or higher.
9. Why an induction motor is called asynchronous motor?
Since the induction motor runs always at a speed lesser than the synchronous speed,
it is called asynchronous motor.
10. Why is the efficiency of a three phase induction motor less than that of a
transformer?
In induction motor, there are mechanical losses due to the rotation of the rotor. Hence
the efficiency of an induction motor is less than that of the transformer.
LOAD TEST ON SINGLE PHASE INDUCTION MOTOR
1. A single phase induction motor is not self starting. Why?
When a single phase supply is connected across a single phase winding, a pulsating
magnetic field is produced. The force experienced by the upper conductors of the rotor will
be downward and the force experienced by the lower conductors will be directed upward.
The two sets of force will cancel and the rotor will experience no torque. Hence the rotor
will not rotate.
2. What is the rating of single phase machines? State its applications.
The rating of the single phase machine is from 1/8 to ¾ hp range. They are widely used
for fans, washing machines, refrigerators, blowers, centrifugal pumps etc.
3. How will you change the direction of rotation of a split phase induction motor?
The direction of rotation of a split phase induction motor can be changed by changing the
direction of current either in the starting winding or in the running winding.

4. What type of motor is used for ceiling fans?
Permanent magnet capacitor motor is used for ceiling fans.
5. Why single phase induction motor has low power factor?
The current through the running winding lags behind the supply voltage by a very large
angle. Hence the power factor is low in single phase induction motor.
6. What is the use of shading coil in the shaded pole motor?
The copper shading coil is used to produce rotating magnetic field moving from the
unshaded to shaded portion of the pole. Hence the motor produces a starting torque.
7. Why are centrifugal switches provided on many single phase inductions motor?
The centrifugal switches are provided on many single phase induction motors, because
when the motor is running at 75% of the synchronous speed, the centrifugal switch connected
in the auxiliary winding operates and disconnect the auxiliary winding from the supply.
8. What could be the reasons if a split phase motor runs toos low?
a) Wrong supply voltage and frequency
b) Overload
c) Grounded starting and running windings
d) Short circuited or open winding in field circuit
9. What could be the reasons if a split phase motor fails to start and hums loudly?
It could be due to the starting windings being grounded or burnt out.
10. What is universal motor?
Universal motor is a series motor of rating less than 1Kw which is designed to operated on
both dc and ac supply. They are widely used for food mixers, vaccum cleaners, hair driers,
electric shavers, portable drills, sewing machines etc.
NO LOAD AND BLOCKED ROTOR TEST
ONSINGLE PHASE INDUCTION MOTOR
1. What is the function of capacitor in a single phase induction motor?
Capacitor is used to improve the power factor of the motor. Due to the capacitor
connected in series with the auxiliary winding, the capacitive circuit draws a leading current
which increases the split phase angle α between the two current I m and Ist.
2. Define double field revolving theory.
According to this theory, any alternating quantity can be resolved into two rotating
components which rotates in opposite directions and each having magnitude as half of the
maximum magnitude of the alternating quantity.
3. What are the classifications of single phase induction motor based on the method of
starting?
a) Split phase motor
b) Capacitor start motor
c) Capacitor run motor
d) Capacitor start Capacitor run motor
e) Shaded pole motor

4. What design features are incorporated in a split phase motor to make it starting?
The split phase motor is provided with windings, main winding and auxiliary winding.
These two windings are excited from the same voltage. The currents in the two windings can
be made out of phase by adjustment of the impedance of the auxiliary winding in relation to
the main winding. As a result the mmf of main winding and mmf of auxiliary winding
constitute an unbalanced field set with 90 degree electrical space phase relationship. The two
symmetrical components now being unequal the forward rotating field is made stronger than
the backward rotating field, which results in the net production of starting torque. Thus the
two windings with phase difference make the split phase motor self starting.
5. What is the advantage of a capacitor start motor over a resistance split phase motor?
In case of capacitor start, it is possible to have the phase angle between the two
currents. Therefore this type of motor has high starting torque as compared to resistance split
phase motor and used for heavy loads such as compressors, conveyors, pumps, certain
machine tools, refrigerators and air conditioning equipment.
6. In which direction does a shaded pole motor runs?
It runs from the unshaded to the shaded part.
7. Give the function performed by induction motor starter.
a) To improve the starting torque
b) To limit the initial in rush of current during starting conditions, which would
otherwise produce larger line voltage drop affecting equipments connected to the
same line.
8. What do you mean by synchronous condenser?
A single machine which is available to convert ac to dc is known as synchronous
converter or rotary converter. A synchronous converter combines the function of a
synchronous motor and a dc generator.
9. What type of motor is used in computer drives and wet grinders?
For computer drives – Permanent magnet dc motors
Wet grinders – Universal motor
10. What is the difference between the dc motors and single phase induction motor?
An important difference between the two is that the dc motors are self starting while
single phase induction motors are not self starting.
Page: 81

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