Electrical machines-lab-i-ee0209

15EE204L
ELECTRICAL MACHINES
LABORATORY-I
ACADEMIC YEAR: 2017-18
NAME :
REG.NO. :
DEPARTMENT OF ELECTRICAL & ELECTRONICS ENGINEERING
FACULTY OF ENGINEERING & TECHNOLOGY
SRM UNIVERSITY
(Under section 3 of UGC Act, 1956)
S.R.M. NAGAR, KATTANKULATHUR – 603 203
KANCHEEPURAM DISTRICT

SRM UNIVERSITY
(under Section 3 of UGC Act, 1956)
S.R.M. NAGAR, KATTANKULATHUR -603 203
KANCHEEPURAM DISTRICT
BONAFIDE CERTIFICATE
Register No__________________
Certified to be the bonafide record of work done by
________________________ of EEE , B.Tech Degree course in the Practical
15EE204L Electrical machines Lab - I in SRM UNIVERSITY,
Kattankulathur during the academic year 2017-2018
Lab Incharge
Date: Year co-ordinator
Submitted for University Examination held in
Electrical machines Lab, SRM UNIVERSITY, Kattankulathur.
Date: Examiner-1 Examiner-2

INDEX SHEET
C
Y
C
L
E
I
Exp
.
No.
Date
of
Exp.
Title of Exp. Pre and
Post Lab
(05)
Conduction of
Experiment
(15)
Calucation
and Result
(15)
Viva
(5)
Total
(40)
Faculty
Sign
1 Load Test on DC
Shunt Motor Using
Open Lab Sys
2 Load Test on DC
Series Motor
3 Load Test on DC
Compound Generator
4 OC & LC of Self &
Separately Excited DC
Generator
5 Swinburne’s Test
Using Open Lab Sys
6 Hopkinson’s Test
C
Y
C
L
E
I
I
7 Speed Control of DC
Shunt Motor Using
MATLAB
8 Load Test on Single
Phase Transformer
9 Load Test on Three
Phase Transformer
10 Sumpner’s Test
11 Transfer Function of
DC Machine
12 Three Phase to Two
Phase Conversion of
Transformer and Three
Phase Transformer
Connections
TOTAL
AVERAGE
COMPLETED SIGNATURE OF THE FACULTY WITH DATE

1. LOAD TEST ON DC SHUNT MOTOR USING OPEN LAB SYS
Pre-lab questions
1. State the working principle of a DC Motor
2. DC Shunt motor is called as constant flux motor. Justify.
3. What is the need of a three point starter?
4. Brief about significance of back emf?
5. At what condition a dc motor will develop maximum power?

LOAD TEST ON DC SHUNT MOTOR USING OPEN LAB SYS
Aim:
To conduct load test on DC motor with shunt excitation and plot the typical
characteristics using open lab systems.
Apparatus required:
Sl.
No.
Components Module Specification Qty
1 DC Shunt motor Open lab sys 42V/4A DC 1
2 Supply module DL10281 Fixed DC 32V/14A 1
3 Measurements module DC10282 DC Voltmeter (0-75)V 2
DC Ammeter (0-15)A 2
Speed sensor 1
4 Loads & Rheostats DC10283 - 1
5 Electromagnetic brake DC103004 G=3.5N, G=1.5N 1
Formulae:
Absorbed power : Pin – u I Watts
Output power : Pout = 0.1047 n M watts
Torque : M = G.b Nm
Efficiency : %𝜂 =
𝑃 𝑜𝑢𝑡
𝑃 𝑖𝑛
Where,
u = Supply voltage in volts
n = Load current in volts
I = Speed on shunt motor in RPM
M = Torque in Nm
G = Measuring weight
b = Distance of the arm in metres

Precautions:
1. In the supply module DL10281, select the selector switch “I” to position “a” for fixed
direct voltage 32V/14A and switch L+/L- to position “0”.
2. In the supply module DL01281, select the selector switch “IV” to position “c” for
variable direct voltage 40V/5A and control knob to 0%.
3. In the supply module DL10283, set the armature resistance (RA) to maximum value
(Control knob in position “b”) and switch R to position “0”.
4. In the supply module DL10283 set the field excitation Rheostat Rf = minium value
(Control knob in position “a”).
5. In the measurement module 10282 ensure the Ammeters and Voltmeters for DC
measurements and observe the polarities.
Procedure:
1. Activate the supply module by setting the L+/ L- switch from position “0” to “1”
2. Observe whether the motor runs in clockwise direction.
3. If not move the switch L+ . L- from “1” to “0” and interchange the field terminals F1 &
F6.

4. Repeat step (1) & (2)
5. In Rheostat module, to cut down the Ra (2) to minimum value, move the control knob
to position “a” and the switch “R” to position “1” (1)
6. Adjust the field excitation Rheostat RF in such a way that the field Ammeter reads If =
0.7A.
7. Balance the brake by moving the balance weight “g” until the water level shows
horizontal position and the speed measurements reads rated speed.
8. Now note down the No load measurements (u, I, G, b, n)
9. The motor is therefore loaded in steps by means of brake.
(The load is increased by moving the weight “g” to a distance “b” from the no load initial
position. Adjust the selector “IV” to balance the system again.
10. Perform the measurements as per previous step and repeat the procedure until rated
current condition.
11. Stop the system by setting the load voltage switch L+ / L- to position “0” to deenergize.
12. Bring back the RF to minimum and Ra to maximum and selector “II” to position “0”.
Tabular Column:
Sl.No. U(V) I
(A)
Pin
(W)
G
(N)
B
(m)
M
Nm
N
RPM
Pout
W
%


Model Graph:
Result:
The load test on DC shunt motor was carried out to determine the efficiency and plot the
typical characteristics.

Post-lab questions for load Test on Shunt Motor
1. How to reverse the direction of rotation of DC shunt Motor?
2. What are uses of DC Shunt motor?
3. What happens if the field circuit of a DC shunt motor is opened?

2. LOAD TEST ON DC SERIES MOTOR
Pre-lab questions
1. What will be the condition for attaining maximum efficiency in a DC motor?
2. Why does the DC series motor run dangerously at high speed under no load condition?
3. State Fleming’s Left Hand Rule.
4. Which type of starter is used to start a DC series motor?

LOAD TEST ON DC SERIES MOTOR
Aim:
To perform the load test on a given DC series motor and plot its performance
characteristics
Apparatus Required:
S.No. Apparatus Range Type Quantity
1 Ammeter (0-20)A MC 1
2 Voltmeter (0-300)V MC 1
3 Tachometer
(0-10000)
rpm
Digital 1
4 Connecting Wires 2.5sq.mm. Copper Few
Precautions:
1. The motor should be started and stopped under loaded condition.
2. Brake drum should be cooled with water when it is under loaded condition only.
Procedure:
1. Connections are to be made as per the circuit diagram.
2. Initially, the motor is loaded with 20 to 30% of the load. By closing DPST switch, the
supply is given to the motor and the motor is started using a two point starter.
3. For various load intervals, voltmeter, ammeter, speed and spring balance readings are
noted down.
4. After bringing the load to its initial position, DPST switch is opened.
Formulae Used
1. Input power = V × I Watts
2. Torque ,T= (9.81) × (S1 ~ S2) × R, N-m, where R is the radius of the brake drum,
Find the circumference of the brake drum. Using 2πR, R is obtained.
3. Output power =
2
60
NT
Watts

4. % efficiency = 100%
Output power
Input power


Tabular Column:
Sl
No.
V
Volts
I
Amp
N
RPM
Spring
Balance
Torque
N-m
Input
Watts
Output
Watts
Efficiency
%
S1
Kg
S2
Kg
S1-
S2
Kg

Model Graph:
Result:
Thus the load test was conducted on DC series motor and its characteristic curves are
drawn.
Torque,T(Nm)
Speed,N(rpm)
Efficiency,%
y3 y2 y1
Output Power (Watts)
N

T

Post-lab questions for load Test on DC Series Motor
1. What are applications of a DC Series Motor?
2. Define speed regulation in a DC Motor
3. Series motor has high starting torque. Justify.
4. Why series field winding is made thicker and has lesser number of turns?

3. LOAD TEST ON DC COMPOUND GENERATOR
Pre – lab Questions
1. What is compound generator?
2. Classify compound generator.
3. Mention the losses in compound generator
4. What is the difference between cumulative and differential compound generator?
5. Write down the applications of compound generator.

LOAD TEST ON DC COMPOUND GENERATOR
Aim:
To conduct a load test and to draw the external (or) load characteristics of the given
compound generator when it is,
(i) Cumulatively compounded
(ii) Differentially compounded
1 Ammeter (0-20)A MC 1
3 Rheostats 1200Ω, 0.8A Wire Wound 2
4 Loading Rheostat 5KW, 230V - 1
5 Tachometer (0-1500)rpm Digital 1
6 Connecting Wires 2.5sq.mm CopperFew
.
Precautions:
1. The field rheostat of motor should be at minimum position.
2. The field rheostat of generator should be at maximum position.
3. No load should be connected to generator at the time of starting and stopping.
Procedure
1. The generator is unloaded and the field rheostat of DC shunt generator is brought to
maximum position and the field rheostat of DC shunt motor to minimum position,
DPST switch is opened.
2. The connections of series field windings are reversed the above steps are
repeated.
3. The values of voltage for the particular currents are compared and then the
differential and cumulative compounded DC generator is concluded accordingly.

Cummulative Compound
VL (Volts) IL (Amps)
Differential Compound
VL (Volts) IL (Amps)

Result:
Thus load characteristics of DC compound generator under cumulative and differential
mode condition are obtained.

Post Lab questions:
1. What is the indication of an over loaded generator?
.
2. What are the causes of an overloaded generator?
3. What are the causes for the failure of generator to build up?

4. OPEN CIRCUIT AND LOAD CHARACTERISTICS OF SELF EXCITED
DC SHUNT GENERATOR
Pre-lab questions
1. State the working principle of a DC generator?
2. Why field winding of shunt generator is made thinner and has more number of turns?
3. List out the conditions to be satisfied for voltage build up process in a generator.
4. Define critical resistance of a generator
5. Define critical speed of a generator

OPEN CIRCUIT AND LOAD CHARACTERISTICS OF SELF EXCITED DC
SHUNT GENERATOR
Aim:
To perform a test on the given self excited DC shunt generator and to plot its open
circuit characteristics and load characteristics curves.
Apparatus Required:
1 Ammeter
(0-2)A MC 1
(0-10)A MC 1
3 Rheostats
300Ω/1.5A Wire Wound 1
600Ω/1A Wire Wound 1
4 SPST Switch - - 1
5 DPST Switch - - 1
7
Rheostatic or
lamp Load
5KW, 230V - 1
Formulate Used for Load Characteristics
1. Ia = IF + IL
2. Eg = Ia Ra + VL
Ia Armature current in ampere
If Field current in ampere
IL Load current in ampere
Eg Generated emf in volts
VL Load Voltage in Volts
Ra Armature resistance in ohms (Disconnect all the
connections and measure Ra using multimeter)
Precautions:
1. The motor field should be kept at minimum resistance position at the time of starting
and stopping of the machine.
2. The generator field rheostat should be kept at maximum resistance position at the time
of starting and stopping of the machine.
3. SPST switch has to be kept open while starting and stopping of the machine.
Procedure: Open Circuit Test
1. Connections to be done as per the circuit diagram.
2. By closing DPST switch 1, the supply is given to the motor. Using the three point
starter, the motor is started.
3. By varying the motor field rheostat, the motor has to be brought to its rated speed.
4. Voltmeter and ammeter readings are noted down when the SPST switch is kept open.
5. Now, the SPST switch is closed. The generator field rheostat is varied and its
corresponding voltmeter and ammeter readings are noted down.
6. The above procedure is repeated until 120% of the rated voltage of the generator has
reached.

Procedure: Load Test
1. The generator field rheostat is brought back to its initial position (i,e) maximum.
2. Now, the DPST switch 2 is closed.
3. By varying the generator field rheostat, the generator has to be brought to its rated
voltage. Corresponding reading of voltmeter and ammeter are noted down.
4. By varying the load gradually, the corresponding reading of voltmeter and ammeter
are noted down at regular intervals.
5. The above procedure is repeated until the rated current of generator has reached.
Open Circuit Characteristics:
S.No. If (Amp) Eg (Volts)
Model Graph for Open Circuit Characteristics:
Eo
If
Critical Resistance = Eo / If Ohms
Eo(Volts)
If (Amps)

Load Characteristics:
S.No. VL (Volts) If (Amps) IL (Amps) Ia (Amps) Eg (Volts)
Model Graph for Load Characteristics:
Result:
Open circuit and load test on the given self excited DC shunt generator was conducted
and its curves were drawn.
Internal (Eg Vs Ia)
External (VL Vs IL)
V(Volts)
I (Amps)

Post-lab questions
1. What is the role of SPST Switch in this experiment?
2. List out the methods available to give mechanical input for the DC generator
3. Why the shunt generator has drooping external characteristics?
4. Why the magnitude of field current in dc shunt generator is lesser as compared to
armature current?

4. OPEN CIRCUIT AND LOAD CHARACTERISTICS OF SEPERATELY
EXCITED DC GENERATOR
Pre-lab questions
1. State the Fleming’s Right Hand Rule
2. What is the difference between self and separately excited DC Generator?
3. What is the function of the commutators?
4. Define critical resistance and speed of generator
5. Define armature reaction

OPEN CIRCUIT AND LOAD CHARACTERISTICS OF SEPERATELY EXCITED
DC GENERATOR
Aim:
To perform a test on the given separately excited DC generator and to plot its open
circuit characteristics and load characteristics curves.
Apparatus Required:
1 Ammeter
(0-2)A MC 1
(0-10)A MC 1
3 Rheostats
300Ω/ 1.5A
Wire Wound
1
600Ω/ 1A 1
4 SPST Switch - - 1
5 DPST Switch - - 1
7
Rheostatic Load
or lamp load
5KW, 230V - 1
Formulae
1. Ia = IL= If
2. Eg = Ia Ra + VL
Ia Armature current in ampere
If Field current in ampere
IL Load current in ampere
Eg Generated emf in volts
VL Load Voltage in Volts
Ra Armature resistance in ohms (Disconnect all the
connections and measure Ra using multimeter)
Precautions:
1. The motor field should be kept at minimum resistance position at the time of starting
and stopping of the machine.
2. The generator field rheostat should be kept at maximum resistance position at the time
of starting and stopping of the machine.
Procedure: Open Circuit Test
1. Connections to be done as per the circuit diagram.
2. By closing DPST switch 1, the supply is given to the motor. Using the three point
starter, the motor is started.
3. By varying the motor field rheostat, the motor has to be brought to its rated speed.
4. Voltmeter and ammeter readings are noted down when the SPST switch is kept open.
5. Now, the SPST switch is closed. The generator field rheostat is varied and its
corresponding voltmeter and ammeter readings are noted down.
6. The above procedure is repeated until 120% of the rated voltage of the generator has
reached.

Procedure: Load Test
1. The generator field rheostat is brought back to its initial position (i,e) maximum.
2. Now, the DPST switch 2 is closed.
3. By varying the generator field rheostat, the generator has to be brought to its rated
voltage. Corresponding reading of voltmeter and ammeter are noted down.
4. By varying the load gradually, the corresponding reading of voltmeter and ammeter
are noted down at regular intervals.
5. The above procedure is repeated until the rated current of generator has reached.
Circuit Diagram
Open Circuit Characteristics:
S.No. If (Amp) Eg (Volts)

Model Graph for Open Circuit Characteristics:
Load Characteristics:
S.No. VL (Volts) If (Amps) IL (Amps) Ia (Amps) Eg (Volts)
Model Graph for Load Characteristics:
Internal (Eg Vs Ia)
External (VL Vs IL)
V(Volts)
I (Amps)
Eo
If
Critical Resistance = Eo / If Ohms
Eo(Volts)
If (Amps)

Result:
Open circuit and load test on the given seperately excited DC shunt generator was
conducted and its curves were drawn.

Post-lab questions
1. What are causes of overloading of generators?
2. Why saturation curve for the DC Generator does not start from zero?
3. Will the voltage of a shunt generator drop if load is applied to its terminal. Justify

5. SWINBURNE’S TEST USING OPNE LAB SYS
Pre-lab questions
1. What is the other name for Swinburne’s Test?
2. Mention the uses of Swinburne’s Test.

SWINBURNE’S TEST USING OPNE LAB SYS
Aim:
To conduct No load test on DC motor with shunt excitation and predetermine the
efficiency of DC machine when running as motor and generator.
Apparatus required:
Sl.
No.
Components Module Specification Qty
1 DC Shunt motor Open laysys 42V/4A DC 1
2 Supply module DL10281 Fixed DC 32V/14A 1
3 Measurements module DC10282 DC Voltmeter (0-75)V 2
DC Ammeter (0-15)A 2
Speed sensor 1
4 Loads & Rheostats DC10283 - 1
Precautions:
1. In the supply module DL10281, select the selector switch “I” to position “a” for fixed
direct voltage 32V/14A and switch L+ / L- to position “0”
2. In the supply module DL10283, set the armature resistance (RA) to maximum value
(Control knob in position “b”).
3. In the supply module DL10283 set the field excitation Rheostat Rf = minimum value
(Control knob in position “a”).
4. In the measurement module 10282 ensure the Ammeters and Voltmeters for DC
measurements and observe the polarities.

Procedure:
1. Activate the supply module by setting the L+ / L- switch from position “0” to “1” .
2. Observe whether the motor runs in clockwise direction.
3. If not move the switch L= / L- from “1” to “0” and interchange the field terminals F1
& F6.
4. Repeat step (1) & (2).
5. In the supply module DL10283 vary the field excitation Rheostat RF till the rated
speed of the motor.
6. Now note down the No load measurements (Vo, Io, If)
7. Bring back the RF to minimum and the switch L+ / L- to position “0”
Tabular Column:
Sl.
No.
Vo(V) Io(A) If(A) IA = Io+If

Efficiency when running as motor:
IL
(A)
Assume
IA=IL-IF
(A)
IA
2
RA
(W)
Wc
(W)
WT=Wc+IA
2
RA
(W)
I/P Power
= Vo IL
(W)
O/P Power =
I/P – Total
Losses (W)
%
motor
Efficiency when running as a generator:
IL
(A)
Assume
IA=IL-IF
(A)
IA
2
RA
(W)
Wc
(W)
WT=Wc+IA
2
RA
(W)
O/P
Power =
Vs IL (W)
I/P Power =
O/P power+
Total Losses
(W)
% g
Formulae:
Constant loss Wc = Input power – Armature copper loss
= Vo X Io – (Io – IF)2
X RA
For Motor
1. IA = IL – IF
2. IA
2
RA / RA = 1.3 / phase
3. Total loss WT = Wc + IA
2
RA

4. Input power Vo IL
5. Efficiency m (%) =
𝐼𝑛𝑝𝑢𝑡 𝑝𝑜𝑤𝑒𝑟−𝑇𝑜𝑡𝑎𝑙 𝑙𝑜𝑠𝑠
𝐼𝑛𝑝𝑢𝑡 𝑝𝑜𝑤𝑒𝑟
× 100
For Generator
1. IA = IL + IF
2. IA
2
RA / RA = 1.3 / phase
3. Total loss WT = Wc + IA
2
RA
4. Output power Vo IL
5. Efficiency G (%) =
𝑂𝑢𝑡𝑝𝑢𝑡 𝑝𝑜𝑤𝑒𝑟
𝑂𝑢𝑡𝑝𝑢𝑡 𝑝𝑜𝑤𝑒𝑟+𝑇𝑜𝑡𝑎𝑙 𝑙𝑜𝑠𝑠
× 100
Where,
Io = No load Input current in Amps
If = No load field current in Amps
IA = No load calculated armature current in Amps
IL = Assumed load current in Amps
Vo = No load input voltage in volts
RA = Armature resistance in  (measured)
Model Graph:
Result:

Thus Swineburne’s test was conducted on a DC shunt machine using open lab
systems and efficiency of motor and generator were predetermined.
Post-lab questions
1. State the disadvantages of Swinburne’s Test.
2. Is it possible to conduct Swinburne’s test on DC series motor? Justify.

6. HOPKINSON’S TEST ON DC MACHINES
Pre-lab questions
1. What is the other name for Hopkinson’s Test.
2. Mention the uses of Hopkinson’s Test.

HOPKINSON’S TEST ON DC MACHINES
Aim:
To perform Hopkinson’s test on the given pair of DC machines and to obtain the
performance characteristics.
Apparatus Required:
1 Ammeter
(0-10)A
(0-2) A
MC
MC
2
2
2 Voltmeter
(0-300) V
(0-600)V
MC
MC
1
1
3 Rheostats
300, 1.5A
600, 1A
Wire
Wound
2
4 Tachometer (0-3000) rpm Digital 1
Precautions:
1. The motor field rheostat should be kept at the minimum position at the time of
starting and stopping the machine.
2. The generator field rheostat should be kept at the maximum position at the time of
starting and stopping the machine.
3. SPST switch should be kept open at the time of starting and stopping of the
machine.
Procedure:
2. Now, by closing the DPST switch, supply is given to the motor and motor is
started using 3-point starter.
3. The motor has to be brought to its rated speed by varying the motor field rheostat.
4. By varying generator field rheostat, the voltmeter 1 is made to read as zero and
SPST switch is closed (If the reading of voltmeter 1 reads higher voltage, the
terminals of armature winding of generator or motor is interchanged such that the
voltmeter 1 reads zero).
5. Various Ammeter readings, voltmeter readings are noted.
6. The rheostats and SPST switch are brought to their original positions and then
DPST switch is opened.

Formulae Used
1. Power drawn from supply: VI2
2. Armature copper loss of generator= (I1+I3)2
Ra
3. Shunt copper loss of generator=VI3
4. Armature copper loss of motor= (I1+I2-I4)2
Ra
5. Shunt copper loss of motor=VI4
6. Total stray loss of both machines,
Ws=VI2 – [ (I1+I3)2
Ra + VI3+ (I1+I2-I4)2
Ra + VI4]
7. Stray loss of each machine(generator (or) motor) =
2
sW
Generator:
1. Total loss of generator= WTg =
2
sW
+ (I1+I3)2
Ra + VI3
2. Output of generator=VI1
3. g = 100
of generator+Total Loss
Output of generator
Output

Motor:
1. Total loss of motor= WTm =
2
sW
+ (I1+I2-I4)2
Ra + VI4
2. Input of motor=V (I1+I2)
3. m =
Loss
100
Input of generator
Input of motor Total


Readings obtained from Measurement
Applied
Voltage
V
(Volts)
Current taken
from supply
I2
(Amp)
Motor Field
Current
I4
(Amp)
Output current
of Generator I1
(Amp)
Generator
Field Current
I3
(Amp)
Predetermination of efficiency for Generator for various I1
I1
*
(Amperes
)
Generator
Armature
Copper
Loss
(I1+I2-I4)2
Ra
(Watts)
Genera
tor
Shunt
Copper
Loss
VI4
(Watts)
Stray
Loss
Ws
(Watts)
WT
(Total
Loss)
(Watts)
Output
VI1
(Watts)
Input=
Output+Tota
l Loss
(Watts)

%
20%
40%
60%
80%
100%
Table 3: Predetermination of efficiency for Motor
I1
*
(Amperes)
Motor
Armature
Copper
Loss
(I1+I2-
I4)2
Ra +
(Watts)
Motor
Shunt
Copper
Loss
VI4
(Watts)
Stray
Loss
Ws
(Watts)
WT
(Total
Loss)
(Watts)
Input
V (I1+I2)
(Watts)
Output=
Input-
Total
Loss
(Watts)
 %
20%
40%
60%
80%
100%
*I1=% of rated current of the machine (either generator or motor)

Model Graph:
Result:
Thus Hopkinson’s test on the given pair of DC machines was conducted and the
performance characteristics were drawn.
OUTPUT POWER P0 ()
% η
As a Motor
As a Generator

Post-lab questions
1. What are the advantages of Hopkinson’s Test?
2. What are the disadvantages of Hopkinson’s Test?

7. SPEED CONTROL OF DC SHUNT MOTOR
Pre-lab questions
1. Write the speed relation equations of DC shunt motor
2. What are the factors that control the speed of a DC motor?
3. State Fleming’s Left Hand Rule.
4. Which type of starter is used to start a DC series motor?
5. Define Stalling Current

SPEED CONTROL OF DC SHUNT MOTOR
Aim:
To control the speed of a given DC shunt motor using
a. Field control method
b. Armature control method
c. MATLAB
Apparatus Required:
1 Ammeter (0-2) A MC 1
2 Voltmeter (0-300) V MC 1
3 Rheostats
300, 1.5A Wire
Wound
1
100, 2.8A 1
4 Tachometer (0-10000) rpm Digital 1
Precautions:
1. Motor field Rheostat should be kept at the minimum resistance position at the time of
starting and stopping the motor.
2. Motor armature Rheostat should be kept in the maximum resistance position at the
time of starting and stopping the motor.
Procedure:
1. Connections are made as per the circuit diagram.
2. Now, DPST switch is closed.
(i) Armature Control:
1. The field current is kept constant and the armature voltage is varied in steps with the
help of motor armature rheostat and the corresponding speeds are noted down,
2. The above procedure is repeated for different values of field current.
3. The motor field rheostat and motor armature rheostat are brought to the initial
position.
(ii) Field Control:
1. The armature voltage is kept constant and the field current is varied in steps and the
corresponding speeds are noted.
2. The above procedure is repeated for different values of armature voltage.

3. The motor field rheostat and motor armature rheostat are brought to the initial
position.
4. The DPST Switch is opened.
Armature Control Method
If1 = If2 =
Sl.No. V
Volts
N
Rpm
V
Volts
N
RPM
Field Control Method
Va1= Va2=
Sl.No. If
A
N
RPM
If
A
N
RPM

Model Graphs:
Armature Control Field Control
Result:
The speed control of a given DC shunt motor using field control and armature control
method and using MATLAB were performed.
SpeedN(rpm)
SpeedN(rpm)
If (Amps)
Va (Volts)
If1
If3
If2
Va3
Va1
Va2

Post-lab questions
1. Why the armature control method is not employed above the rated speed in DC shunt
motors?
2. Why the field control method is not employed below the rated speed in DC shunt
motors?
3. Why the field control method is superior as compared to armature control method for
DC shunt motors?

8. LOAD TEST ON SINGLE PHASE TRANSFORMER
Pre-lab questions
1. What is the working principle of transformer?
2. State principle of mutual induction
3. Write down the EMF equation of a transformer

LOAD TEST ON SINGLE PHASE TRANSFORMER
Aim:
To perform load test on the given single phase transformer and to draw its
performance characteristics.
Apparatus Required:
1 Ammeter
(0-10)A MI 1
(0-5) A MI 1
2 Voltmeter
(0-150)V MI 1
(0-300) V MI 1
3 Wattmeter
(300V, 5A) UPF 1
(150V, 10A) UPF 1
4 Auto Transformer 1, (0-260)V - 1
5
Resistive Load or
lamp load
5KW, 230V - 1
6 Connecting Wires 2.5sq.mm Copper Few
Precautions:
1. Auto Transformer should be kept at minimum position.
2. The transformer should be kept under no load condition.
3. The ‘M’ and ‘C’ terminal of primary and secondary side watt meters should be
shorted.
4. The AC supply is applied and removed from the transformer under no load condition.
Procedure:
2. DPST switch is closed.
3. Under no load condition, ammeter, voltmeter and wattmeter readings on both primary
side and secondary side are noted down.
4. The load is gradually increased and for each load intervals, corresponding reading of
voltmeter, ammeter and wattmeter on both primary and secondary sides are noted
down.
5. The experiment is repeated until the rated current of the transformer (take the
minimum rated current of the transformer side) has reached.
6. The transformer is brought to the no load condition. The auto-transformer is brought
to its minimum position and then the DPST switch is opened.

Formulae:
1. % Efficiency, = 100
Ws
Wp

2. % Regulation = 100
No load Load
No Load
V V
V


Tabular Column
Vp
(Volts)
Ip
(Amps)
Wp (Watts) Vs
(Volts)
Is
(Amps)
Ws (Watts) %  %
RegulationOBS *ACT OBS *ACT
*ACT=OBS × Multiplication Factor,
Where, factor
Full Scale Deflection used
wattmeter wattmeterV I Power factor
Multiplication
 


Model Graphs:
Result:
Thus load test on the single phase transformer was carried out and efficiency was
determined.
Efficiency%
RegulationR%

R

Post-lab questions
1. What are the disadvantages of Load Test?
2. Transformer is rated in KVA. Justify.

9. LOAD TEST ON THREE PHASE TRANSFORMER
Pre-lab questions
1. List out various three phase transformer connections
2. What are the advantages of open delta connections?
3. What is other name for Scott connection and state its applications?

LOAD TEST ON THREE PHASE TRANSFORMER
Aim:
To connect the primary and secondary of the given 3 phase transformer in star-delta
and to perform the load test on the same & to plot its performance characteristics.
Apparatus Required:
S. No. Name of the Apparatus Range Type Quantity
1 Ammeter
(0-10A)
MI
1
(0-15A) 1
2 Voltmeter
(0-600V)
MI
1
(0-300V) 1
3 Wattmeter
600V, 10A
300V, 15A
UPF
2
2
4 Three Auto Transformer 3, (0-440)V - 1
5
Three phase Resistive Load or
lamp load
3KW, 415V - 1
Precaution:
1. 3 phase auto transformer should be kept at minimum position.
2. The transformer should be kept under no load condition.
3. The ‘M’ and ‘C’ terminal of primary and secondary side watt meters should be
shorted.
4. The AC supply is applied and removed from the transformer under no load condition.
Procedure
2. TPST 1 switch is closed.
3. Under no load condition, ammeter, voltmeter and wattmeter readings on both
primary side and secondary side are noted down.
4. The load is connected to the transformer through TPST switch 2. Then the load is
gradually increased and for each load intervals, corresponding reading of
voltmeter, ammeter and wattmeter on both primary and secondary sides are noted
down.
5. The experiment is repeated until the rated current of the transformer (take the
minimum rated current of the transformer side) has reached.
6. The transformer is brought to the no load condition. The three phase auto-
transformer is brought to its minimum position and then the TPST switch is
opened.
Formulae Used
1. Input = Wp = Wp1 + Wp2 (watts)
2. Output power = Ws = Ws1 + Ws2 (watts)
3. % Efficiency = Ws / Wp × 100 %

Tabular Column 1
Wp1 (Watts) Wp2 (Watts) Wp=
Wp1+ Wp2
(Watts)
Ws1 (Watts) Ws2 (Watts) Ws=
Ws1+ Ws2
(Watts)
OBS *ACT OBS *ACT OBS *ACT OBS *ACT
Where, factor
Multiplication
 


Tabular Column 2
Vp
(Volts)
Ip
(Amps)
Wp (Watts) Vs
(Volts)
Is
(Amps)
Ws (Watts) %  %
Regulation
Model Graphs:
Result:
Load test was conducted on three phase transformer and regulation efficiency were
determined.
Efficiency%
RegulationR%

R

Post-lab questions
1. List out the difference between single phase and three phase transformer.
2. What are the disadvantages of load test?

10. SUMPNER’S TEST ON SINGLE PHASE TRANSFORMER
Pre-lab questions
1. What is the other name for Sumpner’s test?
2. Define all day efficiency of transformer?

SUMPNER’S TEST ON SINGLE PHASE TRANSFORMER
Aim:
To perform Sumpner’s test on the given single phase transformers and
1. To draw its equivalent circuit
2. To predetermine its efficiency and regulation
Apparatus Required:
S. No. Name of the Apparatus Range Type Quantity
1 Wattmeter
150 V, 2A LPF 1
75 V, 5 A UPF 1
2 Ammeter
(0-2) A
MI
1
(0-5)A 1
3 Voltmeter
(0-150) V
MI
1
(0-75) V 1
(0-600)V 1
5 DPST Switch - - 1
Precautions:
1. Both the autotransformers should be kept at its minimum potential position.
2. SPST switch should be kept open, at the time of starting.
Procedure:
1. Connections are to be made as shown in the circuit diagram.
2. DPST switch 1 is closed. Rated voltage of 110V is varied to get in voltmeter by
adjusting the Auto Transformer 1.
3. The readings of voltmeter 1, ammeter 1 and wattmeter 1 are noted on the primary side
(LV Side).
4. The voltmeter 3 reading connected across the SPST switch is noted down.
5. If the reading of voltmeter 3 reads higher voltage, the terminals of any one of
secondary coils (HV side) is interchanged such that the voltmeter 3 reads zero.
6. Then DPST switch 2 is closed after ensuring zero reading in the voltmeter 3.
7. The auto-transformer 2 is varied so that full load rated secondary current flows.
8. Corresponding readings of wattmeter 2, ammeter 2 and voltmeter 2 are noted down.

Tabular Column
Vo
(Volts)
Io
(amp)
Wo
(Watts)
Vsc
(Volts)
Isc
(Amp)
Wsc (Watts)
OBS *ACT OBS *ACT
Where, factor
Multiplication
 


Formulae Used:
Vo = V1
Io = I1/2
Wo = W1/2
Vsc = V2/2
Isc = I2
Wsc = W2/2
1. Cos 0 =
oo
o
IV
W
2. Sin 0 = oCos 2
1 or 0 = Cos-1 o
o o
W
V I
 
 
 
Open Circuit parameters referred to LV side (test conducted on LV side):
3. RoLV =
oo
o
CosI
V

where Io cos 0 = Iw = working component
4. XoLV =
oo
o
SinI
V

where Io sin 0 = I = magnetising compent
Short Circuit Parameters referred to HV side (test conducted on HV side):
5. Z1eHV =
SC
SC
I
V
6. R1eHV = 2
SC
SC
I
W
7. X1eHV = 2 2
1 1e eZ R
1. Equivalent circuit referred to LV side
Note: The OC test is conducted on LV side. The SC test is conducted on HV side. Hence the
obtained open circuit parameters are referred to LV side and the obtained short circuit
parameters are referred to HV side. To obtain the complete equivalent referred to LV side, it
is necessary to transform short circuit parameters referred to LV side. This can be carried out
using the transformation ratio KLV. The open circuit parameters are retained as such.
1. KLV =
Voltage(115)
High Voltage(230)
Low
2. R2eLV = K2
LV ×R1eHV
3. X2eLV = K2
LV ×X1eHV

R1eHV
RoHV XoHV
Vo
’
Io
’
I1
’
P
N
Equivalent Circuit referred to LV Side:
2. Equivalent circuit referred to HV side
Note: To obtain the complete equivalent referred to LV side, it is necessary to transform open
circuit parameters referred to HV side. This can be carried out using the transformation ratio
KHV. The short circuit parameters are retained as such.
1. KHV =
High Voltage(230)
Low Voltage(115)
2. RoHV = K2
HV ×RoLV
3. XoHV = K2
HV ×XoLV
Equivalent Circuit referred to HV Side:
X2eLVR2eLV
RoLV XoLV
Vo
Io
I1
P
N
L
O
A
D
X1eHV
L
O
A
D

3. Predetermination of efficiency for various load conditions at any given power factor
1. From OC test, Core loss = Wo
2. From SC Test, Copper loss = Wsc (copper loss at full load) % Efficiency at any load
for the given power factor can be calculated using the formula,
3. % Efficiency at any load = 2 2
2
2 2
cos
cos ( )
rated rated
rated rated o sc
n V I
n V I W n W



   
(or)
4. % Efficiency at any load = 2
(rating)cos
(rating)cos ( )o sc
n VA
n VA W n W



   
Where n is the fraction of load
4. Predetermination of Regulation for various power factors at any given load
For Lagging PF,
2 2 2 2
2
( cos ) ( sin )
% 100rated eLV rated eLV
R
rated
n I R n I X
V
V
   
 
For Leading PF,
= 2 2 2 2
2
( cos ) ( sin )
% 100rated eLV rated eLV
R
rated
n I R n I X
V
V
   
 
Predetermination of Efficiency:
Sl
No.
Fraction of Load (n) %
p.f=1 p.f=0.8
1 1
2 3/4
3 1/2
4 1/4

Predetermination of Voltage regulation:
Cos  % Regulation for load fraction
n=1
% Regulation for load fraction
n=0.5
Lag+
Lead-
Lag +
Lead-
0
0.2
0.4
0.6
0.8
1
Model Graphs:
Efficiency%
Output power (Watts)
Drawn
for
p.f=0.8

Result:
Thus sumpner’s test was conducted to determined efficiency and regulation and the
equivalent circuit were also drawn.
Power factor
%VR for lagging
% VR for
leading
Drawn for Rated Full
Load Current

Post-lab questions
1. State the merits of Sumpner’s test
2. State the demerits of Sumpner’s test

11. TRANSFER FUNCTION OF ARMATURE CONTROLLED DC MOTOR
Pre-Lab Questions
1. State DC motor principle
2. Define poles and zeros
3. What is the significance of deriving the transfer function

TRANSFER FUNCTION OF ARMATURE CONTROLLED DC MOTOR
Aim
To obtain the transfer function of armature controlled DC motor
Apparatus Required
Sl. No. Apparatus Type & Range Quantity
1 Rheostat 50 / 5A
300 / 1.2A
1
1
2 Ammeter (0-10A) MC
(0-200mA) MI
1
1
3 Voltmeter (0300V) MC
(0-30V) MI
2
1
4 1-phase Variac -- 1
Formula
Transfer function =
])1)(1[()(
)(
bama
a
a KKSTST
K
sV
s



BR
K
K
a
t
a

 where Kt is the slope of T – Ia curve (motor gain constant)
radKgm
dt
dN
N
P
J
tt
t
PP /
0106.0
.
'
' 2









21
loglog
12
N
e
N
e
m
m
tt
T
T
J
B



b
a
a
a K
R
L
T  = back emf constant volt / rpm from no load test curve
Procedure
Load Test
1. The supply is switched on and the motor is started with a 3-point starter
2. Motor field rheostat is adjusted and the motor is brought to rated speed
3. Speed, Ammeter, Voltmeter and spring balance readings are noted down
4. Motor is loaded gradually till rated current and corresponding readings are
noted down.

Circuit diagram: Load Test
Tabulations: Load Test
Sl.
No.
V
(volts)
I
(A)
Spring balance readings Speed
(rpm)
T
(N-m)S1
(Kg)
S2
(Kg)
S1 ~ S2
(Kg)
II Procedure: Retardation Test
1. Motor is started on noload using 3-point starter
2. Adjust motor field rheostat and run motor at speed slightly greater than
rated speed.
3. Using DPST switch cut off the supply and allow the motor to retard
4. Various values of speed changes to corresponding time are taken.
5. Motor is started again and brought to the rated speed
6. DPST switch is used to cut off armature supply but a known resistance is
added to armature circuit & motor is allowed to retard.
7. Time for 5% fall on speed & corresponding voltmeter, ammeter readings are
noted down.

Circuit diagram: Retardation Test
Retardation Test:
(Without load R) (With load R)
N (rpm) Time (s) N (rpm) V (volts) I (A) Time, T(s)
No Load Test
Sl. No. Speed (rpm) V (volts) Ia (A) Eb (V)
8. Time for 5% fall in speed without R is noted
Model Graphs

Model Calculation:
Find Kb and Kt from Eb Vs N and TVs Ia graphs
Find La from Ra and Xa measurements
Determine dN / dt, the slope of NVs Time graph
)(
2
1
)(
2
1
' 2
2
2
12211 aa RIRIIVIVP  from retardation test values with load
t1
= Time in ‘sec’ for retardation of the machine with resistive load
t = Time in ‘sec’ for retardation of the machine without resistive load
find
dt
dN
N
P
J
tt
T NNm
0109.0
,
loglog 21
12





where
mT
J
B
tt
t
PP 







'
'
BR
K
K
a
t
a

 . Obtain transfer function by substitution of constants.
III To find Ra:
1. The connections are given as per the circuit diagram
2. By varying the rheostat, different values of V and I are noted
3. From these above values, the value of Ra is computed.

To find Ra:
Va(V) Ia (A) Ra = Va / Ia ()
Average
IV To find La
To find La:
1. The connections are given as per the circuit diagram
2. By varying the 1 phase variac, different values of V and I are noted
3. From these values, the values of Z are obtained. From Z and Ra, the value of
Xa (and hence La) are computed.
To find La:
Va(V) Ia (A) Za = Va / Ia () Xa () La (H)
Average

Result
Hence the transfer function of the given armature controlled DC motor was found to
be

TRANSFER FUNCTION OF FIELD CONTROLLED DC MOTOR
Aim
To determine the transfer function of a field controlled DC motor.
Apparatus Required
Sl. No. Apparatus Type & Range Quantity
1 Ammeter (0-10A) MC
(0-2A) MC
(0-2A0 MI
1
1
1
2 Voltmeter (0-300V) MC
(050) MC
1
2
3 Rheostat 300 / 1.2A
100 / 3A
1
1
Formula
The transfer function of a field controlled DC motor is
)}1)(1{()(
)(
mf
m
f STST
K
E 



Tm = Mechanical time constant of rotor = J/B
J = Moment of Inertia of rotor = Kg m2
/ rad – sec
Lf = Field inductance (H)
Km = Determined Using Load Test
T = R x 9.8 X (S1 ~ S2) N-M
Tf = Time constant of field circuit Lf / Rf
Procedure
I) To determine motor gain constant – Km (Load test):-
1. Motor field rheostat is kept at minimum position
2. Supply is given and the motor is started
3. Adjust the motor field rheostat and bring the motor to rated speed
4. Voltmeter, ammeter and spring balance readings are noted.
5. Readings are taken for different field event keeping armature current cut.
LOAD TEST
3 Point Starter

Load Test:
Sl.
No.
V
(Volts)
If
Ia kept
emf)
N
(rpm)
Spring balance readings Torque
T=9.81 R X S1 ~ S2 N-
m
S1
(Kg)
S2
(Kg)
S1 ~ S2 (Kg)
To find Rf:
To find Rf :
1 Connections are given as per the circuit diagram
2 By varying rheostat different ammeter and voltmeter readings are obtained.
Sl.No. V (volts) I (A) Rf = V/If ()
Average
II) Retardation Test:-
1. Connections are given as per the circuit diagram
2. Motor sis started on no load
3. Motor field rheostat is adjusted to bring the motor slightly above the rated
speed
4. Using DPDT switch supply is cut off and motor is allowed to retard
5. Different values of speed changes to the corresponding time are noted
6. Now motor is started as usual and brought to rated speed
7. DPDT switch is thrown off such that supply to armature is cut off, but a
known resistance R is connected to the armature and the motor is allowed to
retard.

8. Time taken of 5% fall in speed, voltmeter voltmeter and current readings are
noted.
9. Similarly time taken for 5% fall in speed without R is obtained.
To find Lf:
Model Graph:

To find Ra:
To find Ra:
Sl.
No.
Va
(Volts)
Ia
(A)
Ra
(Ω)

Retardation Test:
Retardation Test:
Without load resistance With load resistance
N (rpm) Time (s) I (A) V (volts) N (rpm) t (sec)
To fine Lf:
1 Connections are given as per the circuit diagram
2 The variac is adjusted to obtain different voltages and currents
Sl. No. V (volts) If (mA) Zf (Vf/If () Xf Lf
Average

Model Calculation
Obtain s
f
t
I
T
K


 from T – If curve
dT
dN
is calculated from N-t curve obtained from Retardation test without R
)( 1
1
tt
t
PP


where P1
power consumed in the load resistor during retardation test
)(
2
1
)(
2
1 2
2
2
12211 aa RIRIIVIV 
t = Time taken for speed reduction during retardation test without load R
t’ = Time taken for speed reduction during retardation test with load R.
Now, P = 0.0109 JN
dt
dN
J can be determined now.
21
loglog
12
NNm
tt
T
 

 obtained from speed time curve
Find B =
mT
J
BR
K
K
f
t
m


Substituting the values for different constants in the general formula for TF, we get the
transfer function of the given M/C
Result
Hence the transfer functions of the field controlled DC motor was found to be

Electrical machines-lab-i-ee0209

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