Post on 03-Apr-2018
7/29/2019 Electric Machines Lab I-Manual_1st Cycle
1/39
Electric Machines Lab IEEE 221
OBJECTIVES:
The objectives of laboratory experiments are:
i. To understand the principle of operation of all the electrical machines to supplement the theorylearned in the class room.
ii. Each electrical equipment is made to meet certain specifications. To verify whether theirspecifications are met, this is usually undertaken by a consumer or an authority lib Bureau of
Indian Standards.
iii. To gain experience in selecting appropriate instruments.SAFETY:
You are doing experiments with electric supply. It may cause even a fatal accident. To avoid this please
keep in mind the followings:i. When in DOUBT DO NOT DO IT is the first and foremost safety condition!
ii. You have to wear shoes compulsorily and stand on mats made by insulating materials toelectrically isolate your body from the earth.
iii. Dont wear loose neck chains or bangles.iv. You have to tuck in your shirts or wear an overcoat.v. Tighten the hair.
vi. While adjusting the rheostats, as far as possible use only one hand and keep other hand on yourback.
ATTENDANCE:
If you are absent for a lab class, then you have lost several things to learn. Laboratory should be treatedas temple, which will decide your career. So, dont fail to make your presence with your record
notebook having completed experiments, observation with completed experiments, that days
experiment particulars with required knowledge about it and stationeries.
MAKING CONNECIONS:
i. Get circuit diagram approval from your staff in charge.ii. Go to the respective worktable and start to give connections as per the circuit diagram from the
source side.iii. Make series connections first. Then make parallel connections like voltmeter, pressure coil etc.iv. Dont use meter terminals as junctions.v. Meters should be positioned properly so that they can be read conveniently without any parallax
error.
vi. Check the rheostat positions and connections. Check whether they have been connectedproperly or not.
vii. Before switching on the power, get circuit connection approval from the staff in charge .
7/29/2019 Electric Machines Lab I-Manual_1st Cycle
2/39
OBSERVATION:
i. Note all the required readings in their respective tables.ii. During the load test on motors, if the pointers of spring balances vibrate, then arrest the vibration
gently and take readings.
iii. If brake load is applied to the motor, then pour the water in the brake drum to avoid heating of belt.iv.
At the time of overloading, readings should be taken quickly.
CALCULATION:
i. Get verification of your observation and formulae for calculation from your staff in charge.ii. Calculate the required quantities by suitable formulae and tabulate them with units.
iii. Draw the necessary graphs and write the result and inference.
GENERAL PRECAUTIONS WHILE WORKING IN ELECTRICAL
LABORATORIES:
1. Understand the equipment to be tested and apparatus to be used.2. Select proper type (AC or DC) and range of meters. Moving coil meters should be used for DC
measurements. Moving iron meters should be used for AC measurements.
3. Do not touch live terminals.4. Use suitable wires (thin wires for parallel connection and thick wires for series connection).5. Make all the connections tight.6. Do not leave loose wires (Wires not connected).7. Get the connections checked before switching on the supply.8. Never exceed the permissible values of current, voltage and speed of any machine, apparatus,
load etc. For load test, one can load the machine up to 110% of its rated Capacity. Fuse rating
should not exceed 110% of the rated current for load test.
9. Switch on or off the load gradually and not suddenly.10.Under the load conditions, UPF wattmeters should be used for power measurement because of
high power factor.
11.Under no load conditions, LPF wattmeters should be used for power measurement because oflow power factor.
12.Following are the notations used in the manual:a. A1, A2Armature terminals.b. F1,F2 or E1,E2Shunt field terminals.c. D1, D2 or S1, S2Series field terminals.d. L, E, AStarter terminalse. SPSTSingle Pole Single Throw switch.f. DPSTDouble Pole Single Throw switch.g. TPSTTriple Pole Single Throw switch.h. MCMoving Coil instrument.
7/29/2019 Electric Machines Lab I-Manual_1st Cycle
3/39
i. MIMoving Iron instrument.j. +, -DC supply terminals.k. P, NSingle phase AC supply terminals.l. R, Y, B, NThree phase AC supply terminals.
Marking System (Total Marks: 100):
Evaluation Components are:
1. Observation : 15 Marks (Internal Component) The student needs to prepare a write up about the experiment in the observation page(s)
(in Record Sheets) before coming to the lab. The circuit diagram and the model graphsshould be on the left side of the observation. Neatness, correctness and proper
formatting will be considered as factors during the evaluation.
The faculty in charge can conduct a short viva related to the procedure of theexperiment. This short viva carries 5 mark weight-age
2. Viva : 20 Marks ( Internal Component): The student needs to prepare the theory related to the experiment before coming to thelab. Viva will be asked either before doing the experiment or during the experiment or
after completing the experiment. Questions related to previous experiments done or any
general topic related to electric machines could be asked for viva.3. Conduction: 15 Marks ( Internal Component):
Proper connections to the machine, measuring instruments and the mounting of theinstruments etc will be considered for evaluation.
The following factors also will be considered for evaluation in this section:The way experiment is conductedReading are takenThe way rheostat is usedThe way spring loading is done etc...4. Result and Inference: 10 Marks (Internal Component)
Once the experiment is over, the student needs to enter the experimentreadings/associated data in the record sheets. Once the data entry and the necessary
graphs are sketched, the student should write the necessary result and inference. In theinference section students should write the reason behind the obtained results and
graphs.
The students should submit the record and get their record corrected on the day in whichthe experiment was done and before leaving the lab. Neatness, writing scale in graphsheets, writing units etc carries weight-age.
5. Term paper: 20 Marks ( Internal Component)6. End Semester Examination (20 Marks) ( External Component)
7/29/2019 Electric Machines Lab I-Manual_1st Cycle
4/39
List of Experiments (1st
cycle only):
Sl.
No.
Category Title of the Experiments
1. DC M/C a. Open circuit characteristics of DC shunt generator.b. Load test on DC shunt generator.
2. DC M/C Load test on DC series motor.
3. DC M/C a. Load test on DC shunt motor.b. Load test on DC compound motor.
4. Transformer Load test on 1- transformer.
5. Transformer Open circuit and short circuit on 1- transformer.
6. Transformer Separation of iron loss in 1- transformer.
7/29/2019 Electric Machines Lab I-Manual_1st Cycle
5/39
EX.NO:
DATE :
OPEN CIRCUIT CHARACTERISTIC OF DC SHUNT GENERATOR
AIM:
To obtain experimentally the open circuit characteristics of DC shunt generator at rated speed
and hence
i) To deduce the characteristic at two third of rated speed.ii) To predetermine the shunt field circuit resistance required to build up rated EMF at rated
speed, critical field resistance and critical speed.
APPARATUS USED:
(To find out from machine ratings)
THEORY:
In a DC generator, the expression for the voltage generated in the armature winding on no load can be
written as
EG= (ZN/60)*(P/A) volts
-flux per pole in webers which depends on field current
Z-number of armature conductors-constant for a given machine
P-number of polesA- number of parallel paths
N-speed in rpm
Open circuit characteristic is called magnetisation characteristic since it gives the variation of
flux per pole versus field current. At constant speed, EG is directly proportional to the flux per pole and
hence field current until the onset of saturation. So we get open circuit characteristic as a straight line
passing through origin. During saturation, a large change in field current is required to produce even a
small change in generated voltage.
Critical field resistance is the resistance of the shunt field winding beyond which the machine
will fail to excite. Critical field resistance is obtained by drawing a tangential line through origin for theinitial portion of the open circuit characteristic curve (Since the armature is open circuited) and finding
its slope.
Critical speed is the speed for which the given value of shunt field resistance represents the
critical field resistance. For self excited generator, there will be some EMF even when the field current
is zero due to residual magnetism.
7/29/2019 Electric Machines Lab I-Manual_1st Cycle
6/39
PROCEDURE:
Connections are made as per circuit diagram. Keeping the motor field rheostat at minimum
position, the generator field rheostat at maximum position and SPST open, the DC supply is given to
the motor. The starter handle is gradually brought from off to on position so that the resistance in thearmature circuit is cut down slowly and completely. Motor is brought to any desired speed using the
motor field rheostat. With the SPST switch open, the emf due to residual magnetism is noted down.Then SPST switch is closed and the field excitation of the generator is increased in steps with the help
of generator field rheostat and at each step generated emf is noted down. The procedure is continued
until the built up voltage of generator reaches about 110% of the rated voltage. The readings are
tabulated. Throughout the experiment, the speed must be maintained constant.
DATA OBSERVED:
Rated speed:
FIELD CURRENT
IF A
INDUCED EMF at rated
speed for increasing IF
EG V
To Deduce OCC at any other speed
( Let the new speed be two-third of rated speed i.e., N2 = (2/3)Nrated)
INDUCED EMF at rated
speed for increasing IF
EG1 V
DEDUCED EMF
EG2 V
GRAPHS DRAWN:
1. OCC at rated speed
2. OCC at two thirds rated speed.
7/29/2019 Electric Machines Lab I-Manual_1st Cycle
7/39
DATA PROCESSED:
1. A tangent is drawn to the initial linear portion of the OCC passing through the origin taken atrated speed.
Critical field resistance = slope of the tangent.
2. To obtain the OCC at two-thirds rated speed:At any given field current, emf induced is proportional to the speed.
EG1/EG2 = Nrated/N2.
Therefore EG2 = (N2/Nrated) EG1.
3. Field circuit resistance required to build up rated emf is calculated from the OCC drawn at ratedspeed.
4. Critical speed at the given field current:Join the point of rated emf on the OCC drawn at rated speed to the origin. This is the field
resistance line to get rated emf at rated speed.Rcritical/Rfield = Nrated/Ncritical
Therefore Ncritical = Nrated (Rfield/ Rcritical)
RESULT:
1. Critical field resistance at rated speed =
2. Field Circuit resistance required to build up rated emf at rated speed =
3. Critical speed at the rated field current =
7/29/2019 Electric Machines Lab I-Manual_1st Cycle
8/39
CIRCUIT DIAGRAM:
OPEN CIRCUIT CHARACTERISTIC:
NAME PLATE DETAILS:
MOTOR: GENERATOR:
Capacity : Capacity :
Voltage : Voltage :
Current : Current :
RPM : RPM :
Excitation : Excitation :
Type : Type :
7/29/2019 Electric Machines Lab I-Manual_1st Cycle
9/39
EX.NO:
DATE:
LOAD TEST ON DC SHUNT GENERATOR
AIM:
To obtain the internal and external characteristics of a DC shunt generator.
PRECAUTIONS:
1. While starting the DC motor, starter handle should be moved from OFF to ONPosition slowly and steadily.
2. While measuring armature resistance, the armature of the machine should bestationary.
APPARATUS USED:
(To find out from machine ratings)
THEORY:
If a DC shunt generator, after building up to its rated voltage is loaded, its terminal voltage will
drop. This drop increases as load increases. There are three reasons of voltage drop in DC shunt
generator (i) Armature reaction (ii) armature resistance (iii) Drop in field current due to reduction in
terminal voltage. The different types of load characteristics are
(i)Internal or total characteristic (EG VS IA): It gives the relationship between the EMF actually induced
in the armature after allowing for the demagnetizing effect of armature reaction and the armature
current.
(ii)External or performance characteristic (VT VS IL ): It is drawn between the load voltage taking into
account both the armature reaction and armature resistance and load current. The drop in voltage is so
less that it can be considered as a constant voltage machine.
PROCEDURE:
On no load keeping the field rheostat of motor at minimum, the field rheostat of the DCgenerator at maximum and SPST switch open, DC supply is given to the motor. The DC motor is
started with help of the 3 point starter and it is adjusted from OFF to ON position slowly and steadily.
After the motor attains its rated speed, SPST switch is closed and the field rheostat of the DC generator
is adjusted so that the generator terminal voltage is built up to the rated value on no load.Load side DPST is closed. Maintaining the speed of the motor-generator set constant at the
rated speed of generator, load on the generator is increased gradually in proper steps from no load to
110% of full load. At each step, the terminal voltage and the load current are noted down. Throughout
the experiment, the field resistance must be maintained constant at no load value.
To find RA by V-I method:
The armature resistance of the generator is determined by V-I method.
7/29/2019 Electric Machines Lab I-Manual_1st Cycle
10/39
Connections are made as per the circuit diagram. The load is increased in steps and in each step the
corresponding armature current and voltage across the armature are noted down.
DATA OBSERVED AND PROCESSED:
Rated speed = ------rpm Field resistance=--------ohms.
LOAD CURRENT IL
A
FIELD CURRENT IFA
ARMATURE CURRENT
IA = IL + IF A
TERMINAL VOLTAGE
VT V
INDUCED VOLTAGE
EG V
To find RA by V-I method:
VOLTAGE ACROSS
ARMATURE
Va V
ARMATURE CURRENT
Ia A
ARMATURE RESISTANCE
RA = Va/Ia
TO FIND RA:
SAMPLE CALCULATION:
IA = IL + IF
7/29/2019 Electric Machines Lab I-Manual_1st Cycle
11/39
INDUCED EMF EG = VT + IARA
GRAPHS DRAWN:
1. Internal characteristics: EG VS IA2. External characteristics: VT VS IL
RESULT:
The internal and external characteristics were shown in the graph.
INFERENCE:
CIRCUIT DIAGRAM:
TO FIND INTERNAL AND EXTERNAL CHARACTERISTICS:
7/29/2019 Electric Machines Lab I-Manual_1st Cycle
12/39
TO FIND RA:
7/29/2019 Electric Machines Lab I-Manual_1st Cycle
13/39
Experiment No: LOAD TEST ON DC SERIES MOTOR
Date:
AIM:
To conduct load test on the DC Series Motor and to plot its performance characteristics.
APPARATUS REQUIRED:
No Apparatus Range Type Quantity
1. Ammeter ( 010 ) A MC 1
2. Voltmeter ( 0- 300 ) V MC 1
3. Digital Tachometer 1
PRECAUTION:
DC Series Motor SHOULD BE started with some initial load.
THEORY:
Load Test or Brake Test is the direct method of finding the efficiency of the DC motors of
smaller capacity. To determine directly the efficiency, the motor is loaded directly by means of Brakedrum - spring balance arrangement. The various performance characteristics of the DC Series motor
can also be obtained from the Load Test.
While discussing the DC motor characteristics, the following two relations should be kept in
mind. Speed of the DC motor is given by
Where
Eb = Back EMF of the motor
= V- Ia Ra
The torque of the machine is given by
Where
Ia is armature current
Flux of the machine
7/29/2019 Electric Machines Lab I-Manual_1st Cycle
14/39
The flux of the machine is directly proportional to field current which also depends on the
load. From the above discussion,
Speed of the DC series motor is given by
For series motor, the field current is equal to armature current. So flux of the machine is
directly proportional to armature current Ia. So, when motor is loaded, field current (armature current in
case of DC Series motor) increases with increase in load causing the flux to increase thereby reducingthe speed. At high loads, flux becomes constant due to saturation and hence the speed remains nearly
constant.
The torque of the DC Series motor is given by
For DC Series motor, Flux is proportional to the armature current. So the torque is
proportional to the square of armature current. After saturation, flux becomes constant and hencetorque is linearly proportional to the armature current. As starting torque is higher for this motor, it is
preferred in traction.
CIRCUIT DIAGRAM
NAME PLATE DETAILS:
Capacity:
Rated Voltage:
Rated Current:
Rated Speed:
7/29/2019 Electric Machines Lab I-Manual_1st Cycle
15/39
PROCEDURE:
1. The connections are made as per the circuit diagram2. The DC Series Motor should be started with some initial load. So keep some initial load on the
motor before starting.
3.
Change the starter handle of Two Point Starter from OFF to ON Position slowly and steadily.
4. Load the motor using the Brake drum loading arrangement up to 110% of the rated current ofthe motor. Then in decremental steps reduce the load conveniently.
5. At each load observe and tabulate the followinga) Line currentb) Supply voltagec) Speedd) Spring balance readings.
FORMULAE USED:
1. Power Input
2. Torque
Where
R = Radius of the Brake Drum in metre (m).
3. Power Output
4. Efficiency
Where
N = Speed of the motor in rpm
T= Torque in Nm
GRAPHS DRAWN:
I) Performance Characteristics:
1. Po Vs Torque
2. Po Vs Speed
3. Po Vs Efficiency
4. Po Vs Line Current
II) Mechanical Characteristic:
5. Speed Vs Torque
7/29/2019 Electric Machines Lab I-Manual_1st Cycle
16/39
7/29/2019 Electric Machines Lab I-Manual_1st Cycle
17/39
DATA OBSERVED AND PROCESSED: Radius of the Brake Drum: R = _________ m
No.
Line
Voltage
VL (
V )
Line
Current
IL (
A )
Spring Balance
Reading
Total Force
Acting
( S1~ S2 )
kg
Speed
N(rpm)
Torque
T (Nm)
Power
Input Pi
(kW)
Power
Output Po
(kW)
Efficiency
(%)S 1 (kg) S 2 (kg)
7/29/2019 Electric Machines Lab I-Manual_1st Cycle
18/39
MODEL GRAPHS
(I) Performance Characteristics
(II) SpeedTorque Characteristics
TABULATION:
Loading
Line
Current
( A )
Speed
(rpm)
Torque
(Nm)
Efficiency
(%)
FL
th
FL
th
FL
FL
RESULTS:
7/29/2019 Electric Machines Lab I-Manual_1st Cycle
19/39
Experiment No: LOAD TEST ON DC SHUNT MOTOR
Date:
AIM:
To conduct load test on the DC Shunt Motor and to plot its performance characteristics.
APPARATUS REQUIRED:
No Apparatus Range Type Quantity
1. Ammeter ( 010 ) A MC 1
2. Voltmeter ( 0- 300 ) V MC 1
3. Rheostat 230 /1.7 A 1
THEORY:
Load Test or Brake Test is the direct method of finding the efficiency of the DC motors of smallercapacity. To determine directly the efficiency, the motor is loaded directly by means of Brake drum - spring
balance arrangement. The various performance characteristics of the DC Series motor can also be obtained from
the Load Test.
While discussing the DC motor characteristics, the following two relations should be kept in mind.
Speed of the DC motor is given by
Where
Eb = Back EMF of the motor
= V- Ia Ra
The torque of the machine is given by
Where
Ia is armature current
Flux of the machine
The flux of the machine is directly proportional to field current which also depends on the load.
From the above discussion, Speed of the DC shunt motor is given by
7/29/2019 Electric Machines Lab I-Manual_1st Cycle
20/39
For DC shunt motor, the flux is proportional to field current which is almost constant. When motor is
loaded, armature current increases with increase in load. This causing an increase in armature drop I aRa.Generally armature resistance Ra is quite small. So IaRa is quite small compared to applied voltage V. But, thiscauses small drop in the speed on loading. So, it is a constant speed motor which is used for constant speedapplications such as lathes, belts drives.
The torque of the DC Shunt motor is given by
For DC Shunt motor, Flux is constant. So, torque is proportional to the armature current and we willget a straight line for torque-armature current characteristic passing through origin.
CIRCUIT DIAGRAM
NAME PLATE DETAILS:
Capacity:
Rated Voltage:
Rated Current:
Rated Speed:
PROCEDURE:
1. On no load keeping the resistance in field rheostat of motor at minimum position, DC supply is given tothe motor.
2. The DC shunt motor is started with help of the 3 point starter and it is adjusted from OFF to ON positionslowly and steadily.
7/29/2019 Electric Machines Lab I-Manual_1st Cycle
21/39
3. On no load, line voltage, line current, spring balance readings and speed are noted down.4. The motor is loaded directly with the help of brake drum loading arrangement.5. For each load, observe and tabulate the following
a. Line currentb. Supply voltagec. Speedd. Spring balance readings.
6. The procedure is repeated until the line current is 110% of the rated value.FORMULAE USED:
1. Power Input
2. Torque
Where, R = Radius of the Brake Drum in metre (m).
3. Power Output
4. Efficiency
Where, N = Speed of the motor in rpm
T= Torque in Nm
GRAPHS DRAWN:
I) Performance Characteristics:1. Po Vs Torque
2. Po Vs Speed
3. Po Vs Efficiency
4. Po Vs Line Current
II) Mechanical Characteristic:
5. Speed Vs Torque
7/29/2019 Electric Machines Lab I-Manual_1st Cycle
22/39
DATA OBSERVED AND PROCESSED: Radius of the Brake Drum: R = _________ m
No.
Line
Voltage
VL (
V )
Line
Current
IL (
A )
Spring Balance
Reading
Total Force
Acting
( S1~ S2 )
kg
Speed
N(rpm)
Torque
T (Nm)
Power
Input Pi
(kW)
Power
Output Po
(kW)
Efficiency
(%)S 1 (kg) S 2 (kg)
7/29/2019 Electric Machines Lab I-Manual_1st Cycle
23/39
MODEL GRAPHS
(i) Performance Characteristics
(ii) SpeedTorque Characteristics
TABULATION:
Loading
Line
Current (
A )
Speed (rpm) Torque (Nm) Efficiency (%)
th FL
th FL
th FL
FL
RESULTS:
7/29/2019 Electric Machines Lab I-Manual_1st Cycle
24/39
EX.NO:
DATE : LOAD TEST ON DC COMPOUND MOTOR
AIM:
To conduct load test on the DC Compound motor and to plot its performance
characteristics.
APPARATUS REQUIRED:
THEORY:
A DC compound motor has two field windings: shunt and series field. The series field
is decided by the motor current and this mmf aids or opposes the shunt field depending upon
whether it is cumulative or differential type. The characteristic between output and speed willlie between those of the shunt and series motors. As the compound motor is loaded, the motor
current increases and current through series field also increases. In cumulative type, due to
increase in series flux, the net flux increases. So, speed decreases as N (Eb/)
PROCEDURE:
On no load, keeping the resistance in shunt field rheostat of motor at minimum, DC
supply is given to the motor. The DC motor is started with help of the 3 point starter and it is
adjusted from OFF to ON position slowly and steadily. On no load, line voltage, line current,
spring balance readings and speed are noted down. The motor is loaded directly with the help
of brake drum loading arrangement in steps and for each load, the spring balance readings,
the line voltage, line current and speed are noted down. The procedure is repeated until theline current is 110% of the rated value.
SAMPLE CALCULATION:
Power input Pi = VL IL x10-3 kW
Torque T = (S1S2) x r x 9.81 Nm,
where r is the radius of the brake drum in m.
Power output Po = [2NT/60] x 10-3 kW
% efficiency = (Po/Pi ) x 100
7/29/2019 Electric Machines Lab I-Manual_1st Cycle
25/39
DATA OBSERVED AND PROCESSED:
LINE VOLTAGE
VL V
LINE CURRENTIL A
SPRING BALANCE READING
S1 kg
SPRING BALANCE READING
S2 kg
TOTAL FORCE ACTING
(S1S2) kg
SPEED
N rpm
POWER INPUT
Pi Kw
TORQUE
T Nm
POWER OUTPUT
PO kW
EFFICIENCY
%
GRAPHS DRAWN:
I) PERFORMANCE CHARACTERISTICS:
1. Po Vs TORQUE
2. Po Vs SPEED
3. Po Vs EFFICIENCY
4. Po Vs LINE CURRENT
II) MECHANICAL CHARACTERISTIC:
5. SPEED Vs TORQUE
7/29/2019 Electric Machines Lab I-Manual_1st Cycle
26/39
MECHANICAL CHARACTERISTIC: PERFORMANCE CHARATERISTICS
RESULT:
Load test is conducted on the DC Compound motor and the following results are
obtained .
LOAD LINE CURRENT
A
SPEED
rpm
TORQUE
Nm
EFFICIENCY
%
FL
FL
FL
FULL LOAD
7/29/2019 Electric Machines Lab I-Manual_1st Cycle
27/39
NAME PLATE DETAILS:
Capacity :
Voltage :
Current :
RPM :
Excitation :
Type :
7/29/2019 Electric Machines Lab I-Manual_1st Cycle
28/39
Experiment No.: LOAD TEST ON SINGLE-PHASE TRANSFORMER
Date :
AIM:
a. To determine the transformation ratio of the given single phase transformer fordifferent input voltages.
b. To plot the variation of iron loss with different input voltagesc. To conduct the load test on the given single phase transformer and to
determine its performance characteristics.
APPARATUS REQUIRED:
SerialNo.
Apparatus Range and Type Quantity
1 Voltmeter (0-300)V, (MI) 2
2 Ammeter (0-10)A, (MI) 2
3 Watt meter 300V 10A, UPF 1
4 Variable Resistive Load 1
5 Single phase variac 250V,8A 1
6 Single Phase Transformer 230 V /230 V 1
THEORY:
The transformation ratio of the given single phase transformer is defined as the ratio
of secondary voltage to the primary voltage. When it is on no load, the copper losses will be
very less. So the input power can be taken as approximately equal to iron loss. This iron loss
varies with input voltage. When the transformer is loaded, the secondary terminal voltage
changes and load dependent losses will be present in its windings. The change in terminal
voltage depends on the magnitude and the phase of the current (or load impedance). Thecopper losses vary as the square of the winding currents. The voltage applied across the
primary winding should be kept constant throughout the test. Voltage regulation of
transformer is defined as the change in secondary voltage from no load to full load expressed
as the percentage of either no load voltage or load voltage, keeping the primary voltage
constant.
PROCEDURE:
Connections are made as per the circuit diagram. The single phase AC supply is
switched ON, keeping no load on the secondary side of the transformer and single phase
variac at zero voltage position. By adjusting the variac, the voltage is applied to the primaryside of the transformer in steps. At each step, the voltmeter, ammeter and wattmeter readings
are noted. This is done up to its rated primary voltage of transformer. The DPST on the load
side is closed and the transformer is loaded in steps up to 110% of the rated secondary
7/29/2019 Electric Machines Lab I-Manual_1st Cycle
29/39
current. At each load, corresponding input current, load current, primary voltage, secondary
voltage and input power are noted down. The primary voltage should be kept constant
throughout the experiment.
CIRCUIT DIAGRAM:
DATA OBSERVED AND PROCESSED:
TRANSFORMER PRIMARY VOLTAGE = ----------V
TRANSFORMER SECONDARY NO-LOAD VOLTAGE = ----------V
On no load:
MF for primary watt meter = ------ Primary winding resistance R1 =------------ohms
Sl
No
Primary
Voltage
V1
Primary
Current
I1
Input
Power
(Pin)
( Kw)
Copper
Loss
I12R
(Kw)
Iron Loss
(PinI12R)
(kw)
Secondary
Voltage
V2
On load:
MF for primary wattmeter = ------ MF for secondary wattmeter = -------
7/29/2019 Electric Machines Lab I-Manual_1st Cycle
30/39
Sl
No
Primary
Voltage
(Volts)
Primary
Current
I1 (A)
Input
Power
P1 (Kw)
Secondary
Voltage
V2
Secondary
Current
I2
Output
Power
P2
%
Efficiency
%
Regulation
SAMPLE CALCULATIONS:
TRANSFORMATION RATIO = SECONDARY VOLTAGE/PRIMARY VOLTAGE
Power input Pin = ----------kW
Power output, Pout = V2 I2 x 10-3 = -----kW
% efficiency = (Pout/Pin) x 100%
% voltage regulation = [(V2 (NL)V2 (L)) / V2 (NL)] x 100
MODEL GRAPH:
RESULT:
LOAD %EFFICIENCY %REGULATION
FULL LOAD
FL
FL
FL
7/29/2019 Electric Machines Lab I-Manual_1st Cycle
31/39
EX.NO:
DATE
OPEN CIRCUIT AND SHORT CIRCUIT TESTS ON SINGLE PHASE TRANSFORMER
AIM:
To conduct open circuit and short circuit tests on given single phase transformer and
to (i) determine its equivalent circuit parameters (ii) predetermine its performance
characteristics
APPARATUS REQUIRED:
THEORY:
Efficiency and regulation of transformer are determined either by direct loading orfrom calculations based on its equivalent circuit parameters which can be determined from
open circuit and short circuit tests (indirect method). In second method, efficiency and
regulation are predetermined without actually loading the transformer. Power consumption is
less in the second method. So, it is mostly applied for large size transformers. Open circuit
test is used to determine the shunt branch parameters and short circuit test is used to find out
series branch parameters. Open circuit test gives core loss as copper loss is negligible and
short circuit test gives copper losses as core loss which depends on the applied voltages is
negligible.
PROCEDURE:
OPEN CIRCUIT TEST:Connections are made as per the circuit diagram. The high voltage side of the
transformer is kept open and the single phase variac is kept at zero voltage position. The
single phase AC supply is switched ON. Then the rated voltage is applied to the low voltage
side of the transformer by adjusting the variac and corresponding primary current and the
power input are noted down.
SHORT CIRCUIT TEST:
Connections are made as per the circuit diagram. The low voltage side of the
transformer is shorted and the single phase variac is kept at zero voltage position. The single
phase AC supply is switched ON. Reduced voltage is applied to high voltage side of the
transformer by using the variac such that rated current is circulated through the winding andthe applied voltage and power input are noted down.
DATA OBSERVED:
OPEN CIRCUIT TEST: ON HV SIDE
INPUT VOLTAGE, VO = -------- V
INPUT CURRENT, IO = -------- A
INPUT POWER (iron loss), PO = -------- W
SHORT CIRCUIT TEST: ON LV SIDE
INPUT VOLTAGE, VSC = -------- V
INPUT CURRENT, ISC = -------- A
7/29/2019 Electric Machines Lab I-Manual_1st Cycle
32/39
INPUT POWER (copper loss at full load), PSC = -------- W
Wattmeter constant (wattmeter multiplication factor)
= ( voltage setting)(current setting)(PF of wattmeter)/ full scale deflection
MF for OC test = -------- MF for SC test = --------
DATA PROCESSED:
FROM OPEN CIRCUIT TEST :( Referred to LV side, since readings were taken on
LV side)
Vo Io Coso = Po
Coso = Po/Vo Io
Zo = Vo/ Io
Il = Io Coso
Im = Io Sino
Ro = Vo/ Il
Xo = Vo/ Im
FROM SHORT CIRCUIT TEST :( Referred to HV side, since readings were taken
on HV side)
Psc = Isc2 Req
Req
= Psc/ Isc2
Zeq = Vsc/Isc
Xeq = (Zeq2Req
2)1/2
1) TO DRAW EQUIVALENT CIRCUIT :
K = ( Vrated-h v/ Vrated-l v)
a) REFERRED TO HV SIDE
RO' = RO K2
XO' = XO K2
b) REFERRED TO LV SIDE
Xeq' = Xeq/K2
Req' = Req/K2
PREDETERMINATION OF PERFORMANCE CHARACTERISTICS:
Assuming any load power factor & for any fraction of full load, efficiency and regulation can
be predetermined as follows :-
2) EFFICIENCY :
Iron loss, Po = ----------x 10-3kW Rated load, Qrated = ----------- kVA
7/29/2019 Electric Machines Lab I-Manual_1st Cycle
33/39
LOAD POWER
FACTOR, Cos1 0.8
FRACTIONAL
LOAD, x
0.2 0.4 0.6 0.8 1 1.25 0.2 0.4 0.6 0.8 1 1.25
COPPER LOSS
W
TOTAL LOSSES
W
OUTPUT POWER
W
INPUT POWER
W
% EFFICIENCY
3) VOLTAGE REGULATION at RATED kVA (i.e., x = 1):
LOAD POWER FACTOR
Cos ZERO 0.2 0.4 0.6 0.8 1.0
Req Cos Xeq Sin %REGULATION,LAGGINGPF
%REGULATION,LEADINGPF
SAMPLE CALCULATIONS: Reading number : ---------
PRE-DETERMINATION OF EFFICIENCY AND REGULATION:
Load Power factor = ----------
Fraction of full load, x = ----------
Copper loss at any load Pc= x2 Psc = ---------kW
Total loss PL= Po + Pc = ---------kW
Output power,Pout = x .(QratedCos) = ---------kW
Input power, Pin = Pout + PL = ---------kW
7/29/2019 Electric Machines Lab I-Manual_1st Cycle
34/39
% efficiency = {x .(QratedCos) /[x.(QratedCos) + Po + x2 Psc] } x 100 = ---------
% regulation = (xI/V)[Req Cos Xeq Sin] x 100 = --------
+ for lagging and - for leading
where, I = rated current (full load current) I and V referred to HV side
V = rated voltage since Req and Xeq are referred
at HV side.
4) MAXIMUM EFFICIENCY :
Fraction of full load at which maximum efficiency occurs,
Xm = (Po/PSC)1/2
Load at which maximum efficiency occurs = Xm(Qrated )
To find Maximum efficiency, substitute x =Xm in the efficiency formula.
Maximum efficiency at UPF = %
Maximum efficiency at 0.8 PF = %
5) POWER FACTOR AT ZERO REGULATION :
For zero regulation, Req Cos = Xeq Sin
Tan = Req/Xeq
= Tan 1 ( Req/Xeq)
Hence power factor at zero regulation = Cos (Tan-1(Req/Xeq)) leading.
GRAPHS DRAWN:
1. %Efficiency at UPF and at 0.8 PF Vs Output in kW.
2. %Voltage regulation Vs Powerfactor.
7/29/2019 Electric Machines Lab I-Manual_1st Cycle
35/39
RESULT:
1. Maximum efficiency of transformer at UPF = .. %2. Maximum efficiency of transformer at 0.8 PF = %3. Load power factor corresponding to zero regulation = ---------- leading4. Load kVA corresponding to maximum efficiency = kVA5. Voltage regulation at rated output & at UPF = .. %
CIRCUIT DIAGRAM:
7/29/2019 Electric Machines Lab I-Manual_1st Cycle
36/39
NAME PLATE DETALIS
KVA=
PH=
RATED VOLTAGE=
RATED CURRENT=
7/29/2019 Electric Machines Lab I-Manual_1st Cycle
37/39
EX.NO:
DATE :
SEPARATION OF IRON LOSSES IN A SINGLE PHASE
TRANSFORMER
AIM:
To separate the iron losses of a single phase transformer into the components of hysteresisloss and eddy current loss, at various frequencies.
APPARATUS REQUIRED:
PRECAUTION:
1. Motor field rheostat should be kept at minimum resistance position and motor armature rheostatshould be kept at maximum resistance position.
2. The alternator field rheostat should be kept at maximum resistance position.3. Motor should be run in anti clock wise direction.THEORY:
Iron losses in a transformer = Hysteresis loss + Eddy current loss
Hysteresis loss Bm1.6
f
Eddy current loss Bm2f
2
Therefore, if Bm is maintained constant ,Iron losses can be expressed as Pi = A.f + B.f2
(or) Pi/f = A + B.f
Bm-flux density in the core in Wb/sq.m.
f-frequency in Hz
This is the equation of a straight line. So if the iron losses are measured at different frequencies, graphcan be plotted with Pi /f in the y axis and the frequency in x-axis. Slope and y intercept of theresultant straight line will give the constant B and A respectively. But A and B will remain constant atall frequencies only if the Flux density is kept constant. The flux density can be kept constant by
keeping E/f as constant as the emf equation of transformer is given by
E1 = 4.44 f Tph (or) E1/f = 4.44 Tph
Where Tphnumber of turns per phase.
PROCEDURE:
1. Circuit connections are given as per circuit diagram.2. The prime mover is started with the help of the three point starter and is made to run at rated
speed.3. By varying the alternator field rheostat, gradually the rated primary voltage is applied to the
transformer keeping its secondary side open.4. By adjusting the speed of prime mover the required frequency is obtained and corresponding
readings are noted.
7/29/2019 Electric Machines Lab I-Manual_1st Cycle
38/39
5. Frequency is calculated corresponding to this new speed ( f = PN / 120 ). Now the value of Eis determined by calculation, so as to keep the value of E/f constant as before. Alternator fieldis excited to get this new emf. The corresponding wattmeter reading is noted. The procedureis repeated for different speeds.
6. The prime mover is switched off using DPST switch after bringing all the rheostats to initialposition.
7. From the tabulated readings, iron loss is separated as eddy current loss and hysteresis loss byusing respective formulae.
Graph drawn:
Pi / f Vs f Hysteresis loss Vs f and Eddy current loss Vs f in the same graph.
DATA OBSERVED & PROCESSED:
S.No. Induced
voltage, E
(volts)
Frequency,
f
(Hz)
Speed, N
(rpm)
Iron loss,
Pi
watts E / f Pi/f
A.f
Hysteresis
loss,
watts
B.f2
Eddy current
loss,
watts
1.
2.3.4.5.6.
FORMULAE USED:
1) Frequency (f ) = Ns P / 120PNo of poles
Nssynchronous speed in rpm.
2) Hysteresis loss (Wh) = A x f in Watts where Aconstant.
3) Eddy current loss (We) = B x f^ 2 in watts
4) Iron loss or core loss (Wi) = (We + Wh) in watts
Wi = A x f + B x f ^2
Wi /f = A + Bf
Here the constant A from the origin to the print distance at where the line cuts the y-axis in the graphdrawn between (Wi/f) and frequency (f). The constant B = (Wi / f) / f.
7/29/2019 Electric Machines Lab I-Manual_1st Cycle
39/39
RESULT:
Thus separation of no load losses in single-phase transformer is done and hence eddy current andhysteresis losses of a single phase transformer are found out at various frequencies.
SEPARATION OF IRON LOSSES OF SINGLE PHASE TRANSFORMER: