1
EASWARI ENGINEERING COLLEGE
RAMAPURAM, CHENNAI – 89
DEPARTMENT OF ELECTRICAL AND ELECTRONICS
ENGINEERING
EI2208- ELECTRICAL MACHINES LABORATORY - MANUAL
REGISTER NUMBER :
ROLL NUMBER :
NAME :
DEPARTMENT/SEM/SEC :
AC YEAR :
2
LIST OF EXPERIMENTS
1. OPEN CIRCUIT CHARACTERISTICS OF DC SHUNT
GENERATOR.
2. LOAD TEST ON DC SHUNT GENERATOR
3. SPEED CONTROL OF DC SHUNT MOTOR.
4. BRAKE TEST ON DC SHUNT MOTOR.
5. BRAKE TEST ON DC SERIES MOTOR.
6. REGULATION OF AN ALTERNATOR.
7. OC AND SC TEST ON SINGLE PHASE TRANSFORMER.
8. LOAD TEST ON SINGLE PHASE TRANSFORMER.
9. LOAD TEST ON THREE PHASE SQUIRREL CAGE
INDUCTION MOTOR.
10. BRAKE TEST ON SINGLE PHASE INDUCTION MOTOR.
11. V CURVES OF A SYNCHRONOUS MOTOR.
12. POWER MEASUREMENT IN THREE PHASE CIRCUIT
USING TWO WATTMETER METHOD
3
CYCLE - 1
Sl.
NO
DATE NAME OF THE EXPERIMENT PG.
NO REMARK
S
SIGN
OPEN CIRCUIT CHARACTERISTICS OF
DC SHUNT GENERATOR.
LOAD TEST ON DC SHUNT GENERATOR
SPEED CONTROL OF DC SHUNT MOTOR.
BRAKE TEST ON DC SHUNT MOTOR.
BRAKE TEST ON DC SERIES MOTOR
POWER MEASUREMENT IN THREE
PHASE CIRCUIT USING TWO
WATTMETER METHOD
CYCLE - 2
REGULATION OF AN ALTERNATOR.
OC AND SC TEST ON SINGLE PHASE
TRANSFORMER.
LOAD TEST ON SINGLE PHASE
TRANSFORMER.
LOAD TEST ON THREE PHASE
SQUIRREL CAGE INDUCTION MOTOR.
BRAKE TEST ON SINGLE PHASE
INDUCTION MOTOR.
V CURVES OF A SYNCHRONOUS MOTOR
4
Ex. No: OPEN CIRCUIT AND LOAD CHARACTERISTICS OF
Date : SEPARATELY EXCITIED DC GENERATOR
Aim:
To draw open circuit characteristics of the given separately excited
DC generator at rated speed and determine the critical resistance.
To determine load characteristics (Internal & External) of the given
DC separately excited generator.
Apparatus required:
Sl.No. Name Range Type Quantity
1 Voltmeter (0-300V) MC 1
2
Ammeter
(0-10A)
(0-2A)
MC
MC
1
1
3 Rheostat 300Ω/1.4 A Wire wound 2
4 Tachometer (0-1500) rpm Analog/Digital 1
5 Connecting wires Required
Formula:
Where, Rc – Critical resistance
∆Eg – Incremental generated EMF (measured from the linear portion
on the OCC)
∆If – Incremental field current (measured from the linear portion on the
OCC).
5
Circuit Diagram:
+
-
DPST
Switch
Fuse
220
Volts
D.C
Supply
+
-
220
Volts
D.C
Supply
LF
A
DPST
Switch
Fuse
F1
F2
A1
A2
3-Point Starter
Motor Name Plate Details
KW________
RPM________
Volts________
Amps________
Fuse
Fuse
Variable
Resistive
Load
(0-10 A) MC
(0-300 V)
MC
DPST
Switch
10 A
10 A
A
A
V
(0-2 A)
MC
F1
F2
Fuse
Fuse
300 Ω/
1.4 A
15 A
15 A
M G
15 A
15 A
300 Ω/
1.4 A
Fuse Rating Calculation
125% of Rated Current
Motor =
Generator = O.C & Load Characteristics of DC Separately Excited Generator
Generator Name Plate Details
KVA________
RPM________
Volts________
Amps________
6
Precaution:
1. The field rheostat on the motor side must be kept at minimum
resistance position at the time of starting.
2. The field potentiometer on the generator side must be kept at
minimum potential position at the time of starting.
3. DPST switches must be kept open at the time of power on.
Procedure:
1. Connections are given as per the circuit diagram.
2. Observing the precautions the motor side DPST switch is closed.
3. The motor is started with the help of three- point DC starter slowly.
4. The speed is measured with the help of a hand tachometer.
5. If the speed is below the rated value, then it is brought to the rated
value by adjusting the field rheostat.
6. With DPST switch on the generator field side open, the voltmeter
reading is noted down. (This is the residual voltage at the rated speed
at which the motor-generator set is running now.)
7. The DPST switch on the generator field side is closed.
8. By adjusting the potentiometer on the generator field side suitably for
various increasing field currents, note down the terminal voltages till
around 125% of the rated voltage. The speed is maintained constant
throughout this process.
9. The generator terminal voltage is minimized to zero.
10. The speed is brought down to minimum value and the motor is
switched off with the help of DPST switch. (Note the starter holding
coil releasing the handle else bring it back to start position)
7
Tabulation:
Speed = _________rpm
Residual voltage = ________ Volts
S. No. If (amps) Eg (volts)
Model graph:
Eg ∆E
g
∆If
If
8
Load Characteristics:
Precaution:
1. The field rheostat on the motor side must be kept at minimum
resistance position at the time of starting.
2. The field potentiometer on the generator side must be kept at
minimum potential position at the time of starting.
3. DPST switches must be kept open at the time of power on.
4. There should be no load at the time of starting.
Procedure:
1. Connections are given as per the circuit diagram.
2. Observing the precautions the motor side DPST switch is closed.
3. The motor is started with the help of three- point DC starter slowly.
4. The speed is measured with the help of a hand tachometer.
5. If the speed is below the rated value, then it is brought to the rated
value by adjusting the field rheostat.
6. By adjusting the potentiometer on the generator side the generator
terminal voltage is brought to the rated value.
7. Load side DPST switch is closed.
8. The load is applied gradually. For various load currents voltmeter and
ammeter readings are noted down till full current of the generator.
(Avoid sustained overload.)
9. The load is brought back to initial no load position.
10. DPST switch on the load side is opened.
11. Generator field circuit potentiometer is brought to minimum potential
position.
12. DPST switch on the generator field side is opened.
13. The speed is brought down to minimum value and the motor is
switched off with the help of DPST switch. (Note the starter holding
coil releasing the handle else bring it back to start position)
14. Disconnect and return the apparatus.
9
Tabular column:
Ra = _________ Ohms
Load
current
IL(amps)
Shunt
Field
current
I sh
(amps)
Load
voltage
VL
(volts)
Armature
current
Ia = IL + I sh
(amps)
Generated voltage
Eg = V + Ia Ra
Model graph:
I a & IL
Eg Vs Ia
V Vs IL
V
&
Eg
10
Ia = IL + I sh Amps
Eg = V + Ia Ra Volts
Ra – Armaure resistance ohms
Eg – generated voltage volts
V – Terminal voltage volts
I sh – Shunt field current Amps
Result:
The Open Circuit Characteristics of the given separately excited DC
generator was obtained and the Critical resistance at rated speed is found to
be ______ohms.
The Load Characteristics (Internal & External) of the given separately
excited DC generator was obtained.
11
Ex. No: LOAD CHARACTERISTICS OF SELF EXCITIED
Date : DC SHUNTGENERATOR
Aim:
To determine load characteristics (Internal & External) of the given DC self
excited generator.
Apparatus required:
Sl. No Name Range Type Quantity
1 Voltmeter (0-300) V MC 1
2 Ammeter (0-10) A MC 1
3 Ammeter (0-2) A MC 1
4 Rheostat 300 Ω / 1.4 A
100 Ω / 4 A Wire wound Each 1
5 Tachometer Analog / Digital
6 Connecting wires Required
Formulae:
Eg = V + Ia Ra
Ia = IL + I sh
Where,
Ra – Armature resistance
Eg – Generated voltage
V – Terminal Voltage
I sh – Shunt field current
IL – Load Current
12
Circuit Diagram:
+
-220 Volts
D.C
Supply
LF
A
DPST
Switch
F1
F2
A1
A2
3-Point Starter
M
FuseFuse
A
v
Fuse
Variable
Resistive
Load
(0-10 A)
MC
(0-300 V)
MC
(0-2 A)
MC
f1
f2
100 Ω/4A
DPST
SwitchFuse
300 Ω/
1.4 A
15 A
15 A 10 A
10 A
G
A1
A2
Motor Name Plate Details
KW________
RPM________
Volts________
Amps________
Generator Name Plate Details
KVA________
RPM________
Volts________
Amps________
Fuse Rating Calculation
125% of Rated Current
Motor =
Generator =
O.C & Load Characteristics of DC Shunt Generator
A
13
Precaution:
1. The field rheostat on the motor side must be kept at minimum
resistance position at the time of starting.
2. The field rheostat on the generator side must be kept at maximum
resistance position at the time of starting.
3. DPST switches must be kept open at the time of power on.
4. There should be no load at the time of starting.
Procedure:
1. Connections are given as per the circuit diagram.
2. Observing the precautions the motor side DPST switch is closed.
3. The motor is started with the help of three- point DC starter slowly.
4. The speed is measured with the help of a hand tachometer.
5. If the speed is below the rated value, then it is brought to the rated
value by adjusting the motor field rheostat.
6. By adjusting the field rheostat on the generator side the generator
terminal voltage is brought to the rated value.
7. Load side DPST switch is closed.
8. The load is applied gradually. For various load currents voltmeter and
ammeter readings are noted down till full current of the generator.
(Avoid sustained overload.)
9. The load is brought back to initial no load position.
10. DPST switch on the load side is opened.
11. Generator field circuit rheostat is brought to maximum resistance
position.
12. DPST switch on the generator field side is opened.
13. The speed is brought down to minimum value and the motor is
switched off (Note the starter holding coil releasing the handle else
bring it back to start position)
14
Tabular column:
Ra = ________ Ohms
S.
No. IL(amps)
I sh
(amps) V(volts) Ia = IL + I sh
(amps)
Eg = V + Ia Ra
Model graph:
Result:
Thus the Load Characteristics (Internal & External) of the given self-
excited DC shunt generator was obtained.
I a & IL
Eg Vs Ia
VL Vs IL
VL
&
Eg
15
Ex. No: LOAD TEST ON DC SHUNT MOTOR
Date :
Aim:
To perform load test on the given D.C shunt motor and to obtain the
performance characteristics.
Apparatus Required:
Sl.No
Name of the apparatus
Range
Type
Quantity
1. Ammeter (0-2) A
(0-20) A MC Each 1
2. Voltmeter (0-300) V MC 1
3. Tachometer (0-1500) rpm Analog/Digital 1
4. Rheostat 300Ω/1.4 A Wire wound 1
5. Connecting wires Required
Formulae:
IL = Ia + I sh
Input power = V x IL (Watts)
Torque (T) = (S 1 ~ S 2) x 9.81 x R (Nm) S 1, S 2 – spring balance
readings (Kg)
Output power = 2 N T (Watts) N – speed of the motor in rpm
60
Efficiency = Output power x 100
Input power
Ia - Armature current (Amps) I sh – Shunt field current (Amps)
IL - Load Current (Amps) V – Supply voltage (Volts)
R – Radius of the brake drum = Circumference / 2 (m).
16
Circuit Diagram:
+
-220 Volts
D.C
Supply
DPST
Switch
A1
A2
Fuse
Fuse
15 A
15 A
M
LF
A
F1
F2
3-Point Starter
300 Ω/
1.4 A
A
A
V
(0-20 A) MC
(0-300 V)
MC
(0-2 A)
MC
Spring
Balance
Brake
Drum
S1 S2
Motor Name Plate Details
KW________
RPM________
Volts________
Amps________
Fuse Rating Calculation
125% of Rated Current
Motor =
Load Test on DC Shunt Motor
17
Tabular column:
Sl.
No
Input
voltage
(Volts)
(V)
Load
Current
(Amps)
(IL)
Field
Current
(Amps)
(Ish)
Armature
Current
(Amps)
(Ia = IL - Ish )
Speed
(N)
(rpm)
Spring Balance
Readings
Torque
(T)
(Nm)
Input
Power
(Watts)
Output
Power
(Watts)
Efficiency
(%) S1
kg
S2
kg
(S1~ S2)
kg
18
Model Graph:
ELECTRICAL CHARACTERISTICS MECHANICAL CHARACTERISTICS PERFORMANCE CHARS
Torque
(T)
(Nm)
1
2 3
4
1 – Output Vs Speed
2 – Output Vs % Efficiency
3 - Output Vs Torque
4 – Output Vs Armature
Current
Speed (N)
% Efficiency (η)
Torque (T)
Arm. Current (Ia)
Output power in
watts
Torque
(Nm)
Arm. Current (Ia) in
Amps
Speed (N)
(rpm)
19
Precautions:
1. The motor field rheostat must be kept at minimum resistance position at
the time of starting.
2. There should be no load at the time of starting.
Procedure:
1. Make the connections as per the circuit diagram
2. Switch on the supply and move the starter handle slowly and
gradually to start the motor
3. Now observe the speed. If the speed is less than the rated speed adjust
the field rheostat and bring the speed to rated value.
4. Readings are taken for no load.
5. Load on the motor is varied with the help of pony brake arrangement.
6. Spring balance, ammeter, voltmeter and speed-readings are noted
down for various line currents as the load is increased (till the rated
current is reached).
7. Pour water in the brake drum to avoid over heating.
8. Unload the machine and bring back the rheostat to minimum position.
9. Switch off the supply
Result:
Thus the load test on the given DC Shunt motor was conducted and its
performance characteristics were drawn.
20
Ex. No: LOAD TEST ON DC SERIES MOTOR
Date :
Aim:
To perform load test on the given D.C shunt motor and to obtain the
performance characteristics.
Apparatus Required:
Sl.No
Name of the apparatus
Range
Type
Quantity
1. Ammeter (0-20) A MC 1
2. Volt meter (0-300) V MC 1
3. Tachometer (0-1500) rpm Analog/Digital 1
4. Connecting wires Required
Formulae:
IL = Ia = ISe
Input power = V x IL (Watts)
Torque (T) = ( S 1 ~ S 2 ) x 9.81 x R (Nm) S 1 , S 2 – spring balance
readings(Kg)
Output power = 2 N T (Watts) N – speed of the motor in
rpm
60
Efficiency = Output power x 100
Input power
Ia - Armature current (Amps) I se – Series field current (Amps)
IL - Load Current (Amps) V – Supply voltage (Volts)
R – Radius of the brake drum = Circumference / 2 (m)
21
Circuit Diagram:
+
-220 Volts
D.C
Supply
DPST
Switch
A1
A2
Fuse
Fuse
15 A
15 A
M
2-Point Starter
A
V
(0-20 A) MC
(0-300 V)
MC
Spring
Balance
Brake
Drum
S1 S2
Motor Name Plate Details
KW________
RPM________
Volts________
Amps________
Fuse Rating Calculation
125% of Rated Current
Motor =
L A
S1 S2
Load Test On DC Series Motor
22
Tabular column:
Sl.
No
Input
voltage
(Volts)
(V)
Load
Current
(Amps)
(IL = Ia)
speed
(N)
(rpm)
Spring Balance
Readings
Torque
(T)
(Nm)
Input
Power
(Watts)
Output
Power
(Watts)
Efficiency
(%) S1
kg
S2
kg
(S1~ S2)
kg
23
Model Graph:
ELECTRICAL CHARACTERISTI MECHANICAL CHARACTERISTICS PERFORMANCE CHARS
% Efficiency
Speed Speed
(N) Torque
Torque (T) rpm Arm. Current
(Nm)
Arm. Current (Ia) in Amps Torque (Nm)
Output power in watts
1
2
3
4
1 – Output Vs Armature
Current
2 – Output Vs Torque
3 – Output Vs % Efficiency
4 – Output Vs Speed
24
Precautions:
1. The motor should be started with some load.
2. Brake drum should be cooled throughout the experiment.
Procedure:
1. Connections are given as per the circuit diagram
2. Observing the precautions the DPST switch is closed.
3. The motor is started with the help of two-point dc starter slowly.
4. Load on the motor is varied with the help of pony brake arrangement.
5. Spring balance, ammeter, voltmeter and speed readings are noted
down for various line currents as the load is applied. Care must be
taken to avoid the speed reaching dangerously high values while
reducing the load.
6. Pour water in the brake drum to avoid overheating.
7. At a minimum safe load the DPST switch is opened.
8. Disconnect and return the apparatus.
Result:
Thus the load test on the given DC Series motor was conducted and
its performance characteristics were drawn.
25
Ex. No: SPEED CONTROL OF DC SHUNT MOTOR
Date :
Aim:
To vary the speed of the given dc shunt motor by the following
methods.
(i). Armature control method (below rated speed)
(ii). Field control method (above rated speed)
Apparatus Required:
Sl. No Name of the apparatus Range Type Quantity
1. Ammeter (0-2) A M.C 1
2. Volt meter (0-300) V M.C 1
3. Tachometer (0-1500) rpm Analog/Digital 1
4. Rheostat 300 Ω / 1.4 A
100 Ω / 4 A Wire wound Each 1
5. Connecting wires Required
Precautions:
1. The field rheostat must be kept at minimum resistance position at the
time of starting.
2. The armature rheostat must be kept at maximum resistance position at
the time of starting.
26
Circuit Diagram:
Motor Name Plate Details
KW________
RPM________
Volts________
Amps________
+
-220
Volts
D.C
Supply
DPST
Switch
A1
A2
Fuse
Fuse
2 A
2 A
V
(0-300 V)
MC
Fuse Rating Calculation
10% of Rated Current
Motor =
F1
F2
300 Ω/
1.4 A
(0-2.5 A)
MC
M V
100 Ω / 4 A
Speed Control of DC
Shunt Motor
A
Model Graph:
(i) Armature Control method (ii) Field control method
Speed
(Rpm) Speed
(Rpm)
Armature voltage (volts) Fieldcurrent (amps)
27
Tabulations:
(i). Armature control method:
Field current (If) = ______ Amps kept constant
SL.
No
Armature voltage
(Volts)
Speed
(rpm)
(ii) Field control method
Armature voltage (Va) = ______ Volts kept constant
SL.
No
Field current
(Amps)
Speed
(rpm)
28
Procedure:
(i). Armature control method:
1. Make the connections as per the circuit diagram
2. Switch on the supply
3. Keep the field current constant and for different armature voltage (by
varying armature rheostat) note down the corresponding speed.
4. Bring back the rheostat to initial position and switch off the supply
(ii). Field control method
1. Switch on the supply
2. Start the motor by closing the DPST switch
3. Keep the armature voltage constant and for various field current (by
varying field rheostat) note down the corresponding speed.
4. Bring back the rheostat to initial position and switch off the supply
Result:
Thus the speed of the given DC shunt motor is varied by both armature
control and field control method and the graphs are plotted. The speed is
directly proportional to the armature voltage by graph (i) and inversely
proportional to the field current by graph (ii).
29
Ex. No: OC AND SC TEST OF SINGLE PHASE
Date : TRANSFORMER
Aim:
To perform open circuit and short circuit test on a single phase
transformer and predetermine the efficiency at various loads and also draw the
equivalent circuit.
Apparatus Required:
Sl.No
Name of the apparatus
Range
Type
Quantity
1. Ammeter (0-2) A
(0-5) A MI Each 1
2. Volt meter (0-150) V
(0-30) V MI Each 1
3. Watt meter 150V, 2A, LPF
30V, 5A, UPF Dynamo meter Each 1
4. 1- Autotransformer (0-270) V 1
5 Connecting wires Required
Formulae:
Transformer Ratings: 1 KVA, 220 V/ 110V, 50HZ
V1 = 220 V & V2 = 110 V
I 1 = 1000/220 = 4.55 A & I2 = 1000/110 = 9.09 A
K = V2 / V1 = 110/220 = 0.5
From open circuit test:
In the open circuit test the primary is open circuited and the meters are
connected on L.V side, which is secondary of the transformer. Thus O.C test
will give us no load current, I01. (i.e referred to secondary)
Since K = V2/V1, the corresponding no load primary current, I0 = I01 * K
W0 = V1 I0 Cos 0 ( watts)
Where,
W0 = No load input power = core (or Iron) loss = Wi
I0 - No load input current
V1 - No load rated input voltage
30
Cos - Power factor
Cos 0 = W0 / V1 I0
I w = I0 Cos 0 A ( Iron loss component)
I = I0 Sin 0 A ( Magnetizing component)
R0 = V1 / I w (Resistance to represent core loss)
X0 = V1 / I (Reactance to represent magnetizing component)
From short circuit test:
In the Short circuit test the secondary is short circuited and the meters
are on H.V side, which is primary of the transformer. Hence it gives
parameters referred to primary.
R01 = Wsc / Isc 2
Z01 = Vsc / Isc
X01 = Z012 - R01
2
I21 = I2 * K & I1 = I0 + I2
1
Where,
R01 - Equivalent resistance of transformer referred to primary side
X01 - Equivalent reactance of transformer referred to primary side
Z01 - Equivalent impedance of transformer referred to primary side
Wsc – Full load copper loss
Isc – Short Circuit Current
Vsc – Short circuit voltage corresponding to Isc
Equivalent Circuit Parameters referred to secondary side:
R01 = R0 * K
2 I0
1 = No load current from O.C Test
X01
= X0 * K 2 I w
1 = V1
1 / R0
1
R02 = R01 x K 2
I1 = V1
1 / X0
1
X02 = X01 x K 2
Where, V11 = V1 * K
Z02 = Z01 x K 2
I11 = I0
1 + I2
Regulation = [ I2 R02 Cos + I2 X02 Sin / V2 ] X 100
+ Ve for lagging Power factor
- Ve for leading power factor
(X * KVA * P.f)
% Efficiency at various loads = x 100
[(X * KVA * P.f ) + (Wi + X 2 Wsc)
]
X-Load ratio
31
Circuit Diagram:
DPST
Switch
Fuse
230 V
1-φ 50 HZ
AC Supply V
A
C
M L
V
Fuse
5 A
5 A
(0-270 V) 1φ
Auto
Trnsformer
(0-150 V)
MI
(0-2 A) MI
150 V, 2A, LPF
Wattmeter
110 V 220 V
Open Circuit
Name Plate Details
Single Phase Transformer
Auto TransformerFuse Rating Calculation
KVA________
Voltage Ratio________
20 % of Rated Current
(Max. Load of A.T )
Maximum Load =
Maximum KVA =
Input =
0 V 0 V
Open Circuit Test on Single Phase Transformer
P
N
32
Circuit Diagram:
DPST
Switch
Fuse
230 V
1-φ 50 HZ
AC Supply V
A
C
M L
V
Fuse
5 A
5 A
(0-270 V) 1φ
Auto
Trnsformer
(0-30 V)
MI
(0-5 A) MI
30 V, 5A, UPF
Wattmeter
220 V 110 V
Fuse Rating Calculation
Short Circuit
0 V 0 V
Isc = KVA / V
= Short Circuit Test on Single Phase Tranformer
P
N
33
Equivalent circuit referred to primary side:
V1
I21
I0
I1
IW Iµ
X0R0
R01 X01
ZL1
V21
Equivalent circuit referred to secondary side:
V11
I11
I01
I2
IW1 Iµ
1
X01R0
1
R02 X02
ZL
V2
34
Model Graph:
UPF
%Reg.
% 0.8
Leading P.F Lagging P.F
O/P Power (Watts) %Reg.
Tabulations:
Open circuit test:
Short circuit test:
Sl.
No
Vo
(Volts)
Io
(Amps)
Wo
(Div)
Wo x M.F
(Watts)
Sl.
No
Vsc
(Volts)
Isc
(Amps)
Wsc
(Div)
Wsc x M.F
(Watts)
35
Tabulation to determine the Efficiency:
Sl.
No
Load
ratio
(X)
Output power
(Watts)
Wi
(Watts)
Wcu
(Watts)
Input Power
(Watts) % Efficiency
UPF 0.8 UPF 0.8 UPF 0.8
1 ¼
2
½
3
¾
4
1
Tabulation to determine the Regulation:
Sl.No Power Factor (Cos )
% Regulation
Leading Lagging
1 0
2 0.2
3 0.4
4 0.6
5 0.8
6 1.0
36
Precautions:
Autotransformer must be kept at minimum potential point during starting
condition.
Procedure:
Open circuit test:
1. Make the connections as per the circuit diagram
2. Switch on the supply and vary the autotransformer to get rated voltage
3. Note down ammeter, voltmeter and wattmeter readings.
4. Bring back the autotransformer to original position.
5. Switch off the supply
Short circuit test:
1. Make the connections as per the circuit diagram
2. Switch on the supply and vary the autotransformer to get rated short
circuit current.
3. Note down ammeter, voltmeter and wattmeter readings.
4. Bring back the autotransformer to original position.
5. Switch off the supply
Result:
Thus the open circuit and short circuit tests were performed on a
single-phase transformer and the efficiency was predetermined at various
loads.
37
Ex. No: LOAD TEST ON SINGLE PHASE TRANSFORMER
Date :
Aim:
To perform load test on a single phase transformer and determine its
performance characteristics
Apparatus Required:
Sl.no
Name of the apparatus
Range
Type
Quantity
1. Ammeter (0-5) A
(0-10) A MI Each 1
2. Volt meter (0-150) V
(0-300) V MI Each 1
3. Watt meter 150V, 5A, UPF
300V, 10 A, UPF Dynamo meter Each 1
4. 1- Autotransformer (0-270) V 1
5 Connecting wires Required
Formulae:
Input power = W1 x M.F1 watts
Output power = W2 x M.F2 watts
% Efficiency = Output power / Input power X 100
% Regulation = (E02 – V2) / E02 x 100
E 02 - No load secondary voltage
V 2 - Secondary voltage at various loads
M.F – Multiplication factor
W1, W2 - Wattmeter readings
V I cos
Multiplication factor (M.F) =
No of divisions in the watt meter
38
Precautions:
1. Autotransformer must be kept at minimum potential point during
starting condition.
2. There should be no load at the time of starting the experiment
Procedure:
1. Make the connections as per the circuit diagram.
2. Switch on the supply and vary the autotransformer to get rated
primary voltage.
3. Note down the no load readings.
4. Add the load in steps and note down all the meter readings till the
rated secondary current is reached.
5. Remove the load and bring back the autotransformer to original
position.
6. Switch off the supply.
39
Circuit Diagram:
DPST
Switch
Fuse
230 V
1-φ 50
HZ AC
Supply
A
C
M L
V
Fuse
15 A
15 A
(0-270 V)
1φ Auto
Trnsform
er
(0-150 V)
MI
(0-5 A) MI
150 V, 5A, UPF
Wattmeter
110 V 220 V
Fuse Rating Calculation
0 V 0 V
Load Test on Single Phase Tranformer
C
M L
V
A
DPST
Switch
Fuse
Fuse
10 A
10 A
(0-10 A) MI
300 V, 10A, UPF
V V(0-300 V)
MI
Wattmeter
Load
Name Plate Details
Primary Side Secondary Side
Power =
Voltage =
Current =
Power =
Voltage =
Current =
Primary Side: 125 % of Rated Current
=
Secondary Side: 125 % of Rated Current
=
P
N
40
Tabulation:
Sl.
No
Primary
Voltage
Primary
Current
Input Power Secondary
Voltage
Secondary
Current
Output Power Efficiency Regulation
W1 W1 X M.F W2 W2 X M.F
(Volts) (Amps) (Div) (Watts) (Volts) (Amps) (Div) (Watts) % %
42
Model Graph:
% Vs Output Power
% Efficiency
&
% Regulation % Reg. Vs Output Power
Output power in watts
Result:
Thus the load test on a single-phase transformer was performed and
its performance characteristics were determined and plotted.
43
Ex. No: REGULATION OF ALTERNATOR BY EMF & MMF
METHOD
Date :
Aim:
To pre-determine the regulation of alternator by EMF & MMF methods.
Apparatus required:
Sl.No. Name Range Type Quantity
1 Voltmeter (0-300) V MI 1
2 Ammeter ( 0-2 ) A MC 1
3 Ammeter ( 0-10 ) MI 1
4 Rheostat 300 /1.4 A
100 /1 A Wire wound
1
1
5 Connecting wires Required
Formula:
(i) EMF Method:
Open circuit voltage, V0 (From graph)
Zs = at constant field current
Short circuit current, ISC (From graph)
Re = 1.6 x Ra
XS = √ ZS2 –
Re2
ZS → Synchronous impedance (Ω)
XS → Synchronous Reactance (Ω)
Re → Effective Resistance (Ω)
44
E0 = √ (Vcosφ + IaRe)2 + (Vsinφ ± IaXS)
2
+Ve → lagging p.f
-Ve → leading p.f
V → Rated voltage (volts)
Ia → Rated armature current (Amps)
Cosφ→ power factor
E0 – V
% Regulation = ---------- x 100
V
(ii) MMF Method:
Ifr = √ If12 + If2
2 + 2 If1 If2 Cos (90±φ)
+ → lagging p.f
- → leading P.f
If1 → Field current required to generate rated terminal voltage
If2 → Field current required circulating rated short circuit current
Ifr → Resultant field current
E0 → The generated emf corresponding to Ifr (from graph)
E0 – V
% Regulation = ---------- x 100
V
45
Precautions:
TPST switch must be kept open.
Motor side rheostat must be kept in minimum position and
alternator side rheostat in maximum position.
Procedure:
Open circuit test:
Make the connections as per the circuit diagram.
Switch on the supply.
Start the motor – alternator set by using starter.
Adjust the field rheostat of the motor to get the rated speed.
Increase the alternator field current in convenient steps and note down
all the meter readings up to 125% of the rated voltage.
Bring back the rheostat to the original position.
Short circuit test:
Close the TPST switch and adjust the potential divider such that the
maximum full load current flows through the armature winding.
Note down all the meter readings.
Bring back the rheostats to original position and switch off the supply.
46
Circuit Diagram:
+
-
DPST
Switch
Fuse
220 Volts
D.C Supply
FF1
R
YB
TPST
Switch
Fuse
+
-
220 Volts
D.C Supply
LF
A
DPST
Switch
Fuse
F1
F2
A1
A2
3-Point Starter
Motor Name Plate Details
KW________
RPM________
Volts________
Amps________
Alternator Name Plate Details
KVA________
RPM________
Volts________
Amps________
A
Regulation of Alternator By EMF and MMF Method
FF2
(0-300 V)
MI
(0-2 A)
MC
(0-10 A)
MI
300 Ω/
1.4 A
Fuse
Fuse
V
100 Ω/
4 A
M
10 A15 A
10 A
10 A
10 A15 A
A
47
Tabulation:
Open circuit test:
S. No If
(Amps)
Open circuit voltage
E0 (Volts)
Short circuit test:
S. No If (Amps) Isc (Amps)
To find Regulation (for EMF Method):
S. No Cosφ
% Regulation
Leading Lagging
E0 (V) % R E0
(V) % R
1 0
2 0.2
3 0.6
4 0.8
5 1
To find the Regulation (for MMF Method):
S. No Cosφ Lagging pf Leading pf
Ifr E0 %R Ifr E0 %R
1 0
2 0.2
3 0.6
4 0.8
5 1
48
MODEL GRAPH (for EMF Method):
V0
E0
Isc
ISC
If
Fig.1 O.C & S.C Characteristics
%Reg.
Leading P.F Lagging P.F
%Reg.
Fig.2 Regulation Graph
49
Model Graph (for MMF Method):
E0
E0
Isc
If
Fig.1 O.C & S.C Characteristics
%Reg.
Leading P.F Lagging P.F
%Reg.
Fig.2 Regulation Graph
If1 If2
Ifr
50
Result:
Thus the regulation of the alternator was predetermined by EMF &
MMF method and the graphs were plotted.
51
Ex. No: LOAD TEST ON 3φ SQUIRREL CAGE INDUCTION
MOTOR
Date :
Aim:
To determine the performance characteristics of the given 3φ squirrel cage
induction motor by conducting load test.
Apparatus required:
Sl.No. Apparatus Range Type Quantity
1 Voltmeter (0-600V) MI 1
2 Ammeter (0-10A) MI 1
3 Wattmeter 600V,10A,UPF Dynamometer 2
4 Tachometer (0-1500) rpm Analog/Digital 1
5 Connecting wires Required
Formula:
Input power = W1 x MF1+ W2 x MF2 (watts)
Torque (T) = (S1 ~ S2) x 9.81 x r (N-m)
Output power = 2 Π NT / 60 watts
Efficiency = output power / input power x 100%
% Slip = [(NS – N) / NS] x 100
Power Factor = Input Power / √3VL IL
52
VI cosφ
Multiplication factor =
No. of divisions in the wattmeter
S1, S2= Spring balance readings in Kg.
r = Radius of the brake drum in m (circumference / 2Π)
N = Actual speed of the rotor in rpm
T = Torque in N-m
NS = Synchronous speed in rpm
Precautions:
There should be no load at the time of starting.
Auto transformer must be kept at minimum position
Procedure:
Make the connections as per the circuit diagram.
Switch on the supply and adjust the autotransformer to get the
rated voltage and note down the no load readings.
Adjust the loads and for various loads note down the
corresponding meters reading till the rated current is reached.
Unload the motor, bring back the autotransformer to minimum
position and switch off the supply.
53
CircuitDiagram:
VC
M L
C
M L
V
Spring
Balance
Brake
Drum
S1 S2
415 Volts
Three Phase 50Hz
AC Supply
TPST
Switch
R
Y
B
V
A
(0-600 V)
MI
(0-10 A) MI
10 A
10 A
10 A M1
L1
M3
M2
L3
L2
(0-470) Volts
Three Phase Auto
Transformer
600 V, 10 A, UPF
600 V, 10 A, UPF
Dynamometer
DynamometerMotor Name Plate Details
KW________
RPM________
Volts________
Amps________
Frequency________
Fuse Rating Calculation
125 % of Rated Current
=
Load Test on Three phase Squirrel cage Induction Motor
Fuse
Fuse
Fuse
54
Tabulation:
S.
No
V
(volts)
IL
(Amps)
W1
(div)
W2
(div)
W1x
Mf1
(Watts)
W2xMf2
(Watts)
Input
Power
(Watts)
Spring balance
readings
Speed
N
(rpm)
Torque
(N-m)
T
Output
power
(Watts)
η
%
Power
Facto
r
Slip
%
S1
Kg
S2
Kg
(S1 ~ S2)
kg
55
Model Graph:
Result:
Thus the performance characteristics of the given Three – Phase
squirrel cage induction motor were determined by conducting load test.
Torque in N-m
Speed in
rpm
PF Vs O/P
IL Vs O/P
Efficiency Vs
O/P
N Vs O/P
T Vs O/P
Slip Vs O/P
Output power in watts
Efficiency
Slip
Speed
Power
factor
Load
current
Torque
56
Ex. No: LOAD TEST ON SINGLE PHASE SPLIT PHASE
Date : CAPACITIVE START INDUCTION MOTOR
Aim:
To determine the performance characteristics of the given single phase
split phase capacitive start induction motor by direct loading.
Apparatus required:
Sl.No Apparatus Required Range Type Quantity
1 Voltmeter
(0-300) V MI 1
2 Wattmeter 300V, 20A, UPF Dynamometer 1
3 Ammeter (0-20) A MI 1
4 1- Autotransformer (0-270) V 1
4 Tachometer (0-1500) rpm Analog/Digital 1
5. Connecting wires Required
Formulae:
Cos = W/VI
%S = (NS - N) / N *100%
NS Synchronous Speed = 1500 rpm
Torque T = (S1 S2) 9.81 * r N-m
r Radius of the brake drum in m.
Output power P0 = 2 NT/60 watts
% Efficiency = [O/P Power / I/P power] *100.
57
Circuit Diagram:
C
M L
V
230 Volts
Single Phase 50Hz
AC SupplyDPST
Switch
P
N
A
(0-300 V)
MI
(0-20 A) MI
10 A
10 A
(0-270) Volts
Single Phase Auto
Transformer
300 V, 20 A, UPF
Dynamometer
Motor Name Plate Details
KW________
RPM________
Volts________
Amps________
Frequency________
Fuse Rating Calculation
125 % of Rated Current
=
Load Test on Single phase Induction Motor
V
Spring
Balance
Brake
Drum
S1 S2M1 S1
M2 S2
Main
WindingStarting
Winding
Rotor
C
CS
Fuse
Fuse
58
Tabulation:
S. No
Current
(Amps)
I
Voltage
(Volts)
V
Input Power (Watts) Speed
(rpm)
N
Spring Balance
(Kg) COS
Slip
(%)
Torque
(Nm)
T
Output
Power
(Watts)
Efficiency
(%)
η W WxM.F S1 S2
59
Model Graph:
PF Vs O/P
IL Vs O/P
Efficiency Vs
O/P
N Vs O/P
T Vs O/P
Slip Vs O/P
Efficiency
Slip
Speed
Power
factor
Load
current
Torque
60
O/p Power
Precautions:
1. Auto – transformer should be kept at the minimum position during starting.
2. Load should be kept free during the starting condition.
Procedure:
Make the connections as per the circuit diagram.
Switch on the supply and adjust the autotransformer to get the rated voltage and note down the no load
readings.
Adjust the loads and for various loads note down the corresponding meters reading till the rated current is
reached.
Unload the motor, bring back the autotransformer to minimum position and switch off the supply.
Result: Thus the performance characteristics were determined for the given single phase split phase capacitive
start induction motor by direct loading.
61
Exp. No : MEASUREMENT OF 3 PHASE POWER USING TWO
Date: WATTMETER METHOD
Aim:
To measure the three phase power p.f using two-wattmeter method.
Apparatus required:
S.No APPARATUS TYPE RANGE QUANTITY
1. Three phase variac - (0-415) V 01
2. 3 phase Inductive load 01
3. Wattmeter Dynamometer 600V/15A 02
4. Ammeter MI (0-15A) 01
5. Voltmeter MI (0-600V) 01
Theory:
Three-phase circuits may be balanced or unbalanced. In case of the balanced circuits, if three-watt meters are
connected (one in each phase), equal readings will be obtained. Therefore, only one wattmeter may be connected in any one
phase, and the total power will be obtained by multiplying the power per phase by three.
In case of an unbalanced circuit, three-watt meters may be connected, one in each phase. The total power will then be
obtained by adding the three-wattmeter readings. However, there are some practical difficulties in doing so. For example,
62
the load neutral may not be available in case of Y-connected load (and then the supply neutral must be connected) or in a
delta connected system; it may not be possible to cut through the delta to connect the meters. (In the later case of the delta-
connected load, one has to connect using the supply neutral).
r
r r
r
r
V
A
(0-600V)MI
600V/10A
UPF
600V/10A
UPF
(0-10A)10A
10A
10A
3
415V
50 Hz
AC
SUPPLY
R
Y
B
N
T
P
S
T
S
CIRCUIT DIAGRAM FOR POWER AND p.f MEASUREMENT BY TWO WATTMETER METHOD
3 LOAD
MIM
M
L
L
C
CV
V
63
TABULAR COLUMN:
Sl.No. VRY
(Volts)
IR
(Amp)
W1
(Watts)
W2
(Watts) P=W1+W2
cos =(P1/P)* 3
Where P1= W1-W2
1.
2.
3.
4.
5.
Observation and calculation of power & p.f in 3 balanced ckt with 2-watt meters.
A more convenient and a popular method of measuring three-phase power are to use two-watt meters in a particular
way. The method is known as
“TWO WATTMETER METHOD”, since two watt meters are required.
They are connected as shown in the circuit diagram. It does not require the neutral point. It also does not need
opening or cutting through in case of the delta connected system.
Another important point is that this method is valid for both the balanced as well as the unbalanced conditions.
Further, the method of connecting is same irrespective of the delta or Y- connections of the supply or the load.
64
The circuit diagram using method needs the connections of the two current coils in series with the load in series with
the load in two phases, and the two pressure coils are connected between these two phases and the third phase respectively.
For example, as in circuit diagram the current coils carry iR and iY and the pressure coils are VRB and VYB.
In terms of the instantaneous currents iR, iY, iB and the instantaneous phase voltage vR, vY and vB, the instantaneous
total power (=p) is given by
p = vR iR + vY iY + vB iB -------------- eqn. (1)
The sum of the three phase currents must be zero, in case of three wire systems (i.e., without the neutral wire).
Hence, at all instants,
iR + iY + iB = 0 -------------- eqn. (2)
(or) iB = (iR + iY) – This equation is true for delta or Y-connected, balanced or unbalanced, 3 wire 3 phase systems.
Since, iB is not being passed through the meters, it should be eliminated from eqn. (1)
p = vR iR + vYiY + vB (-iR – iY)
= (v0 – vB) iR + (vY – vB) iY
= VRB iR = VYBiy ------------- eqn. (3)
The average power is obviously obtained by taking the r.m.s values and the power factor.
Note: The wattmeters read only the average power.
The eqn. (3) suggests that two-watt meters can obtain the power in 3 phase circuits as follows:
Wattmeter No.1 (i.e., W1) current coil carrying iR
65
Pressure coil across VRB
Wattmeter No.2 (i.e., W2) current coil carrying iY
Pressure coil across VYB
This is exactly what has been shown in fig. 6.1 in terms of average power, r.m.s voltage and currents, and the power
factors, eqn. (3) can be rewritten as follows:
P = VRB IR cos 1 + VYB IY cos 2 -------- eqn. (4)
= (Reading of wattmeter No.1) + (Reading of wattmeter No.2)
Thus, the total (time averaged) power for a 3 circuit is obtained by adding the two-wattmeter readings.
In eqn. (4), the power factors, cos 1 and cos 2 have the phase angle 1 between VRB and IR. The above method is
valid for both balanced as well as for unbalanced conditions.
For balanced loads: There are certain simplifications for the balanced loads. The three-phase quantities are equal and
have a mutual phase difference of 120 .
Fig.6.2 shows the phasor diagram for the balanced conditions. The voltage, current and the phase angles between
them are given below for the two-watt meters.
Using eqn. (4), with values substituted for the 3 Ph. Balanced load having a p.f of cos (lagging), we have
P = VRB IR cos (30+ ) + VYB IB cos (30- ) -------eqn. (5)
= ( 3 Vph) Iph (cos 30 * cos - sin 30 * sin )
+ ( 3 Vph) Iph (cos 30 * cos + Sin 30 * Sin )
66
= 3 Vph Iph (2* cos 30 * cos )
= 3 Vph Iph (2* ( 3/2)* cos
= 3 Vph Iph cos = 3 VL IL cos -------- eqn. (6)
The eqn. (6) is valid for delta as well as Y – connected systems.
Thus, P = W1 + W2 = Total power in the circuit.
Precautions:
1. Check the mains before connection wires.
2. The three phase variac should be in zero position.
3. The ammeters are connected using thick wires.
4. The voltmeters are connected using thin wires.
Procedure:
1. Connections are made as per the circuit the circuit diagram
2. Set the variac to zero output and switch on the main.
3. Adjust the variac output to obtain about 200 volts as the line voltage.
4. Note down the readings of the ammeters, voltmeters and the two-watt meters.
5. Calculate the total power consumed from these readings to verify the method. Note that for purely resistive
loads, the p.f is unity.
67
6. Repeat steps (3) to (6) above for different readings.
Result:
Thus we find the three-phase power & p.f using two-wattmeter method
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