DEV BHOOMI INSTITUTE OF TECHNOLOGY
CHAKRATA ROAD,NAVGAOUN
MANDUWALA,UTTARAKHAND
Programs: B.TECH. (Electrical and Electronics Engineering)
EMEC 1 LAB
Laboratory Manual
PREPARED BY
Saurabh Rajvanshi
ASST.PROFESSOR,
ELECTRICAL ENGINEERING DEPARTMENT
1
LIST OF EXPERIMENTS
Electrical machine 1 Lab (PEE‐352)
1. To obtain magnetization characteristics of a d.c. shunt generator
2. To obtain load characteristics of a d.c. shunt generator and compound generator (a) Cumulatively
compounded (b) Differentially compounded
3. To obtain efficiency of a dc shunt machine using Swinburn’s test
4. To perform Hopkinson’s test and determine losses and efficiency of DC machine
5. To obtain speed control of dc shunt motor using (a) armature resistance control (b) field control
6. To obtain speed-torque characteristics of a dc shunt motor
7. To obtain speed control of dc separately excited motor using Conventional Ward-Leonard/ Static
Ward –Leonard method.
8. To study polarity and ratio test of single phase and 3-phase transformers
9. To obtain equivalent circuit, efficiency and voltage regulation of a single phase transformer using
O.C. and S.C. tests.
10 To obtain efficiency and voltage regulation of a single phase transformer by Sumpner’s test
2
LABORATORY MANUAL
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EXPERIMENT NO. 1
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PAGE: 3
LABORATORY Name & Code: PEE-352 EMEC 1Lab
SEMESTER: III
Experiment No-1
Theory and Concept
Objective: To conduct an experiment on a D.C shunt generator and draw the magnetization
characteristics (OCC) and to determine the critical field resistance and critical speed.
Apparatus: S. No
1
Apparatus
Voltmeter
Type
M.C
Range
0-250/500V
Qty
1
2
Ammeter
M.C
0-1/2A
1
3
Rheostats
400 /1.7A
1
4
Tachometer
Wire
wound
Digital
0-9999
1
Theory: Open circuit characteristics or magnetization curve is the graph between the generated emf
and field current of a dc shunt generator. For field cur-rent is equal to zero there will be
residual voltage of 10 to 12V because of the residual magnetism present in the machine If
this is absent there the machine cannot build up voltage to obtain residual magnetism the
machine is separately excited by a dc source from OCC we can get critical field resistance
and critical speed.
Critical field resistance: It is the resistance above which the machine cannot build up emf.
Critical speed: It is the speed below which the machine cannot build up emf.
3
Circuit diagram:
Procedure:
1.
2.
3.
4.
Connections are made as per the circuit diagram.
Start the motor and bring it to rated speed..
The switch SPST is opened and If=0
For the different values of excitations (I f) the generated voltage (Eg)from the voltmeter
is taken at rated speed, with increasing and decreasing orders.
5. Calculate average Eg from increasing and decreasing orders.
6. A graph is drawn between Avg Eg & If. From the graph (OCC) Critical field
resistance and critical speed are calculated.
Observation:
Field Current
Sl.
No.
4
Generated
Volgate
Graph:
Critical field resistance (Rc)
= OA/OC
Field resistance (Rf)
= OR
The maximum voltage the Generator can induce
With this field resistance.
= OM
Critical Speed
= PQ/PR * N
Result:
Precaution:
1. Make Sure that your connection are correct.
2. Do not touch the live wire.
3. Take observation carefully.
4. Experiment kit should be properly grounded.
5
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LABORATORY Name & Code: PEE-352 EMEC 1 lab
SEMESTER: III
Experiment No-2
Theory and Concept
Objective: To conduct a load test on the given DC Shunt generator and to obtain the performance
characteristics
Apparatus required:
1
Ammeter
2
Voltmeter
3
4
5
6
5
Rheostat
Rheostat
Load
Tachometer
Connecting wires
0-20A, MC
0-1A, MC
1
1
0-5A MC
0-250V, MC
0-30V, MC
400 /1.7A
100 /5A
3 Kw / 220V
1
1
1
1
1
1
1
Theory:
By conducting load test on DC shunt generator we can get load characteris-tics i.e,
Internal & External characteristics. By exciting the m/c, the field current increases and
voltage build up. After the machine has attained 220V the rated load is switched on. With
increase in load, the voltage will be dropped
6
Circuit diagram:
Armature Resistance (Ra):-
Procedure
1. Connections are made as per the circuit diagram.
2. Start the machine with the help of starter and bring to rated speed by vary-ing field
rheostat of motor, then by varying field rheostat of the generator set the rated
voltage of the generator.. Then close the DPST switch of the load and increase the
load by step 0.125Kw, up to full load of the generator.
3. Note down all the meter readings at every step.
4. Do necessary calculations.
7
Observations:
S
no
IL, in
amps
If , in
amps
Ia= IL+if Vt in
in amps volts
Ia Ra in
volts
EG = Vt + IaRa
in volts
Graph:
Between Emf Generated (E) and Current (I)
Result:
Precautions:
1. Make Sure that your connection are correct.
2. Do not touch the live wire.
3. Take observation carefully.
4. Experiment kit should be properly grounded.
8
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PAGE: 9
LABORATORY Name & Code: PEE-352 EMEC 1 Lab
SEMESTER: III
Theory and Concept
Objective: To conduct load test on DC compound generator and to determine its characteristics
Apparatus:
S. No
Equipment
Range
Type
Qty
1.
Voltmeter
0-250 V
M.C.
1
2.
Ammeter
0-2A
0-20A
3.
4.
Rheostats
Tachometer
400 /1.7A
M.C.
M.C.
Wire wound
Digital
1
1
2
1
5
Connecting wires
Theory: D.C. Compound generator consists of both series and shunt field wind-ings. The shunt
and series fields can be connected in two ways.
1. Short shunt.
2. Long shunt.
When the MMF of series field opposes the MMF of shunt field, the generator is differentially
compound. The terminal voltage decreases sharply with in-creasing load current. Evidently this
connection is not used.
In cumulative compound the connections of the two fields are such that their MMF’s added and help
each other. If the series field is very strong, the termi-nal voltage may increase as the load current
increases and it is called over com-pounding. When terminal voltage on full load and no load are
equal, it is known as flat compounded generator. If the series field is not strong, the terminal voltage
will decreases with increase in load current (under compound)
9
Circuit diagram for cumulative compound generator:
Procedure:
1. Connections are made as per the circuit diagram.
2. The machine is run at rated speed and the rated voltage is obtained by vary-ing field
excitation
3. There the switch is closed so that load is connected across the generator.
4. Increase the load step by step with 0.125Kw and note down all the meter readings and
calculations are made accordingly and the characteristics are obtained.
5. Plot graph for internal external characteristics.
Observations:
10
Graph:
Internal characteristics
External characteristics
Result:
11
Precautions:
1. Make Sure that your connection are correct.
2. Do not touch the live wire.
3. Take observation carefully.
4. Experiment kit should be properly grounded.
12
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PAGE: 133
LABORATORY Name & Code: PEE-352 EMEC 1Lab
SEMESTER: III
Theory and Concept
Object: To perform Swinburne’s Test or no load test on dc motor and to predetermine the
efficiencies of the machine acting as a motor and generator
Apparatus:
S.No
Apparatus
Type
Range
qty
1
2
Voltmeter
Voltmeter
MC
MC
0-250v
0-30V
1
1
3
Ammeter
MC
0-5A
1
4
Ammeter
MC
0-2A
1
5
Rheostats
Wire wound
Wire wound
400 /1.7A
1
1
100 /5A
THEORY:
It is simple indirect method in which losses are measured separately and the efficiency at any desired
load can be predetermined. This test applicable to those machines in which flux is practically
constant i.e. shunt and compound wound machines. The no load power input to armature consist iron
losses in core, friction loss, windage loss and armature copper loss. It is convenient and economi-cal
because power required to test a large machine is small i.e. only no load power. But no account is
taken the change in iron losses from no load to full load due to armature reaction flux is distorted
which increases the iron losses in some cases by as 50%
Model calculations:
No load input=V IL
2
2
No load armature copper losses =Ia Ra =(Il –If) Ra
2
Constant losses Wc=V l–(Il-If ) Ra
Efficiency as a motor:
I= Assumed load current
Motor i/p=VI
Ia=IL-If
2
Motor armature losses=I a .Ra
2
Total losses=I a Ra+ Wc
2
Efficiency of motor= VI- I a Ra+ Wc / VI x 100
13
Efficiency as generator:
I=assumed load current
Generator O/P =VI
2
Generator armature cu. Losses= I a .Ra
2
Total losses= I a Ra+ Wc
2
Efficiency of generator=VI / VI+ I a Ra+ Wc
Circuit diagram:
Procedure:
1. Make connections as per the circuit diagram.
2. Show the connections to the lab instructor.
3. Keeping both rheostats at minimum, Start the motor with the help of starter and by adjusting
field rheostat bring the motor to rated speed.
4. Note down all the meter readings at no load.
5. Do necessary calculations and find out the efficiency of the Machine as a motor and as a generator
6. Draw the graphs between output Vs efficiency of the Machine as a generator and as a motor.
14
Observations:
S.No
IL
IF
IA
V
N(Speed)
For Ra
S.NO
V
I
Ra=V/I
Expected graphs:-
Tabular Column to find out efficiency:
GENERATOR:
S.No
Voltage
in volts
Load
Current
in amps
Armature
Current Ia =
(IL+If)
Armature
Cu loss=
Ia XIaXRa
Total losses
Wt=Wc+
IaXIaXRa
15
InputVxIL
OutputInput-total
losses=
VxIL-Wt
η=
Output/
Input.
Motor:
S.No
Voltage
in volts
Load
Current
in amps
Armature
Current
Ia =(IL-If)
Armature
Cu loss=
Ia XIaXRa
Total losses
Wt=Wc+
IaXIaXRa
Output=
VxIL
Results:
Precautions:
1. Make Sure that your connection are correct.
2. Do not touch the live wire.
3. Take observation carefully.
4. Experiment kit should be properly grounded.
16
Input=output
+total losses=
VxIL+Wt
η=
Output/
Input.
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PAGE: 17
LABORATORY Name & Code: PEE-352 EMEC 1 Lab
SEMESTER: III
Theory and Concept
Object: To conduct a Hopkinson’s test on a two similar D.C shunt machines and find out the
efficiency
Apparatus:
S.No
Equipment
Range
Type
Qty
1
Volt meter
0-250V
M.C.
1
2
Ammeter
0-20A
M.C
2
0-2A
M.C
2
400 /1.7A
Wire wound
2
3
Rheostat
4
Connecting wires
THEORY: Hopkinson’s test is also called as regenerative test or back-to-back test. It is an indirect test or full
test, which is used to determine the efficiency of the two identical shunt machines. The two
machines are mechanically coupled and are also adjusted electrically that are of then run as motor
and other as a generator. The two-shunt machines are connected in parallel. The power input from
the mains is only that needed for supplying the losses of the two machines. The two machines can
be tested under full load conditions (for determining the efficiency and maxi-mum temperature rise).
17
Circuit Diagram:
Armature Resistance (Ra):-
Procedure:1. Connected the circuit as per the circuit diagram.
2. Keep the field regulator minimum resistance position and start the motor by using starter,
Keeping S.P.S.T switch open.
3. Adjust the regulator on generator side until the rated voltage equal to both in magnitude and
polarity as that of main supply. i.e; voltmeter reads zero.
4. The S. P. S.T switch is closed to parallel the machines, by adjusting the re-spective field
regulators, any load can now be thrown on to machines.
5. Calculate efficiency by applying load.(changing excitation)
18
Observation:
Input VoltGen If=I3
Input CurS. No
Gen Ia=I2
age in volts
Motor If=I4
rent=I1
To find out efficiency:
Motor:
S. No
Motor
input
Motor
Motor
Armature Field
Cu loss
Cu loss
Stray
loss
Total
losses
of motor
Out put
Of Motor
η of Motor
Generator:
S.
No
Generator Generator Generator Stray
output
Armature Field Cu loss
Cu loss
loss
Total
Input
η of
losses of Of
generator
generator generator
Calculations:
Armature Resistance of each machine =Ra
Generator Armature cu loss
=I1 x I2 x Ra Watts.
Motor Armature cu loss
= (I1 + I2)(I1 + I2)Ra Watts.
Armature power input to the set.
=VL x I1 Watts.
Ps, Stray losses of both machines
= VL x I1 Armature Cu loss of
(Gen +Motor)
Stray losses of each machine
= Ps/2
Efficiency of Generator:
Generator output
Generator Losses Pg
Efficiency of Generator
= VL . I2 Watts
= V.I3 + I2 x I2+(Ps/2)
=( VL .I2 )/ (VL .I2 +Pg)
Efficiency of Motor :
Motor in put:
Motor losses Pm
Motor Efficiency
=VL (I1 +I2 +I4).
=(I1 +I2)(I1 +I2)Ra +VxI4 +Ps/2 .
= {VL (I1 +I2+I4)}-Pm/ VL (I1+I2+I4)
19
Plot the following graphs:(a) Output Vs Efficiency for Generator.
(b) Output Vs Efficiency for Motor.
Model graphs:-
Result:
Precautions:
1. Make Sure that your connection are correct.
2. Do not touch the live wire.
3. Take observation carefully.
4. Experiment kit should be properly grounded.
20
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PAGE: 21
LABORATORY Name & Code: PEE-352 EMEC I Lab
SEMESTER: III
Theory and Concept
Object: To conduct speed controls on DC shunt motor. The methods are
1. Armature voltage control method 2. Flux control method
Apparatus required:
S.No Equipment
1
Ammeter
2
3
Voltmeter
Rheostats
4
5
Tachometer
Connecting Wires
Range
0-5A
0-2A
0-250V
100 /5A
400 /1.7A
0-2000rpm
Type
MC
MC
MC
Wire wound
Wire wound
Digital
Qty
1No
1No
1No
1NO
1No
1No
LS
THEORY:
i) Armature voltage control method:
For a load of constant Torque, the speed is proportional to the applied to the arma-ture.
Therefore speed voltage characteristic is linear and is a straight line. As the voltage is decrease
across the armature the speed falls. This method gives speeds less than rated speeds.
Eb α ΦN
Eb α N
V-Ia(Ra+R) α N
As the voltage are decreased speed decreases.
ii) Flux Control Method:
With rated voltage applied to the motor, the field resistance is increased i.e field current is
decreased. I t is observed that speed increases.
Eb/Φ α N
N α Eb/If
The characteristics If Vs N is inverse (or) if it is hyperbola.
21
Circuit diagram:
Armature Resistance (Ra):-
22
Procedure:
i) Armature Voltage Control Method
.
1) Make connections as per the circuit diagram.
2) Show the connections to the lab instructor.
3) Keeping both rheostats at minimum, Start the motor with the help of starter and by adjusting
field rheostat bring the motor to rated speed.
4) By increasing armature circuit rheostat in steps note down voltage, Ia and speed at every step.
5) The corresponding graph is draw between armature Voltage Vs speed
ii) Flux Control method:
1) The machine run at its rated speed and rated voltage obtained.
2) The voltage is kept constant and for different values of field current the speed is noted.
Observation Table:
Armature Voltage Control Method
S.No Armature
Voltage in
volts
Armature
current=Ia
in amps
Speed
in RPM
Eb=V-IaRa in
volts
Flux Control Method:
S.No Field Current in amps
Speed in RPM
Graphs:
N (Speed) Vs If (Field Current)
23
N vs Va (Armature voltage)
Result:
Precautions:
1. Make Sure that your connection are correct.
2. Do not touch the live wire.
3. Take observation carefully.
4. Experiment kit should be properly grounded.
24
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PAGE: 25
LABORATORY Name & Code: PEE-352 EMEC I Lab
SEMESTER: III
Theory and Concept
Object:
To conduct OC &SC tests on the given 1- Transformer and to calculate its
1) Equivalent circuit parameters
a).Referred to H.V side
b).Referred to L.V side
2) Efficiency at various loads.
3) Regulation at various power factors
4) Maximum Efficiency.
Nameplate Details:
1 φ- TRANSFORMER
T/F
Rated power
LV side
HV side
Rated voltage
Rated current
Frequency
Apparaturs Required:
SL.NO
Name of the Apparatus
Type
1
Ammeter
MI
2
Ammeter
MI
3
Voltmeter
MI
4
Voltmeter
MI
5
Wattmeter
EDM(LPF)
6
Wattmeter
EDM(UPF)
7
Single phase variac
25
Range
Quantity
Theory:
Open– Circuit (OC) or No-Load Test:
The purpose of this test is to determine the shunt branch parameters of the equivalent circuit of the
transformer. One of the windings is connected to supply at rated voltage, while the other winding is
kept open -circuited. From the point of view of convenience and availability of supply the test is
usually performed from the LV side, while the HV side is kept open circuited.
Voltage =V1; Current =I0and power input=P0
Indeed the no-load current, I0is so small (itisusually2-6% of the rated current) and R01 and
X01are also small, that V1can be regarded as = E1by neglecting the series
impedance.Thismeansthatforallpracticalpurposesthepowerinputonno-load
equals
the
core(iron)lossi.e.,
P0=V1 I0 cos0
cos0 = P0/V1I0
Iw=I0 cos0,  =I0sin0
R0=V1/Iw, X0=V1 / I
Short Circuit (SC) Test:
This test serves the purpose of determining the series parameters of a transformer. For convenience
of supply arrange mentioned voltage and current to be handled, the test is usually conducted from
the HV side of the transformer while the LV side is short-circuited. Since the transformer resistance
and leakage reactance are very small, the voltage Vsc needed to circulate the full load
currentundershortcircuitisaslowas5-8%of the rated voltage. The exciting current under the second it
ions is only about 0.1to0.5%of the full load current. Thus the shunt branch of the equivalent circuit
can be altogether neglected. While conducting the SC test, the supply voltage is gradually raised
from zero till the transformer draws full load current. The meter readings under these conditions are:
Since the transformer is excited at very low voltage, the iron loss is negligible (that is why shunt
branch is left out), the power input corresponds only to the copper loss, i.e
Vsc=Voltage, Isc=Current, Psc=Power Copper loss)
Z01= VSC/ ISC=√R201 + X201
Equivalent resistance, R01=PSC/ (ISC)2
Equivalent reactance, X01= √Z201-R201
26
Circuit Diagram: Diagram--1
PROCEDURE:
OC TEST:
(1) All the connections are done as per the circuit diagram of OC test
(2) Byusing1- variac apply rated voltage to the circuit.
(3) At this rated voltage note down voltmeter, ammeter & wattmeter readings.
(4) From the values we can find R0and X0
SC TEST:
(1) All the connections are done as per the circuit diagram of SC test
(2) By using1- variac apply rated voltage to the circuit.
(3) At this rated current note down voltmeter, ammeter & wattmeter readings.
(4) From this values we can find out R01&X01
27
TABULAR COLUMNS
Observations:
OC TEST:
Vo
(Volt)
Io
(Amps)
Wo
(Watts)
Vsc
(Volts)
Isc
(Amps)
Wsc
(Watts)
SC TEST:
Graphs:
Result:
Precautions: 1. Make Sure that your connection are correct.
2. Do not touch the live wire.
3. Take observation carefully.
4. Experiment kit should be properly grounded.
28
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PAGE: 29
LABORATORY Name & Code: PEE-352 EMEC I Lab
SEMESTER: III
Theory and Concept
Object: To convert three phase system to two phase system with the help of Scott Connection.
Nameplate Details
1φ- TRANSFORMERS
T/F-1
T/F
Rated power
HV side
LV side
T/F-2
HV side
LV side
Rated voltage
Rated current
Frequency
Apparaturs Required:
SL.NO
Name of the Apparatus
Type
1
Ammeter
MI
2
Ammeter
MI
3
Voltmeter
MI
4
Voltmeter
MI
5
Wattmeter
EDM(LPF)
6
Wattmeter
EDM(UPF)
7
Voltmeter
MI
29
Range
Quantity
THEORY:
Sumpner's test or back to back test on transformer is another method for determining transformer
efficiency, voltage regulation and heating under loaded conditions. Short circuit and open circuit tests
on transformer can give us parameters of equivalent circuit of transformer, but they cannot help us in
finding the heating information. Unlike O.C. and S.C. tests, actual loading is simulated in Sumpner's
test. Thus the Sumpner's test gives more accurate results of regulation and efficiency than O.C. and
S.C. tests.
Both transformers are connected to supply such that one transformer is loaded on another. Primaries
of the two identical transformers are connected in parallel across a supply. Secondaries are connected
in series such that emf's of that are opposite to each other. Another low voltage supply is connected in
series with secondary’s to get of them are connected in voltage opposition, i.e. E EF and EGH. Both
the emf's cancel each other, as transformers are identical. In this case, as per superposition theorem,
no current flows through secondary. And thus the no load test is simulated. The current drawn from
V1 is 2I0, where I0 is equal to no load current of each transformer. Thus input power measured by
wattmeter W1 is equal to iron losses of both transformers.
i.e. iron loss per transformer Pi = W1/2.
Now, a small voltage V2 is injected into secondary with the help of a low voltage transformer. The
voltage V2 is adjusted so that, the rated current I2 flows through the secondary. In this case, both
primaries and secondary’s carry rated current. Thus short circuit test is simulated and wattmeter W 2
shows total full load copper losses of both transformers.
i.e. copper loss per transformer PCu = W2/2.
From test results, the full load efficiency of each transformer can be given as -
30
CIRCUIT DIAGRAM:
Procedure:
1. The circuit is connected as per circuit diagram.
2.
Both the transformers are energized at rated voltage & frequency.
3. With the secondary open, noted down the readings of W1 which gives core loss.
4. Secondary is connected in phase opposition and checked trough voltmeter connected
across the secondary.
5. Voltage is induced in secondary with help of booster transformer which is connected to
source. Readings of W2 are noted down.
Observation:
S.NO
W1
31
W2
Formule:
Graph:
Result:
Precautions:
1. Make Sure that your connection are correct.
2. Do not touch the live wire.
3. Take observation carefully.
4. Experiment kit should be properly grounded.
32