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CHRISTU JYOTI INSTITUTE OF TECHNOLOGY & SCIENCE
Colombonagar,Janagoan,Warangal
ANDHRA PRADESH-506167
2013-14 1st Semester
LABORATORY MANUAL
of
ELECTRICAL MACHINES II
Prepared by
P.ANIL KUMAR
Assistant Professor
for
III B.Tech EEE
DEPARTMENT OF
ELECTRICAL & ELECTRONICS ENGINEERING
Electrical Machines-II Lab Manual
INDEX
Page No
List of experiments as per university
3
List of experiments to be conducted for this
semester
Cycle indicate schedule and the batch size
4
Laboratory Practice Safety Rules
Guidelines For Laboratory Notebook
Sl. No
5-7
8-10
Experiment Name
1.
OC & SC test on single phase transformer
11-16
2.
Sumpners’s test on a pair of single phase transformer
17-22
3.
23-26
4.
No-load & Blocked rotor tests on three phase induction
motor
Separation of core losses of a single phase transformer
5.
Efficiency of a three phase alternator
31-34
6.
Brake test on three phase induction motor
35-38
7.
Regulation of a three phase alternator by synchronous
impedance & m.m.f methods
V and inverted V curves of a three phase synchronous
motor
Equivalent circuit of a single phase induction motor
39-43
Determination of Xd and Xq of a Salient pole
synchronous machine
Additional Experments
Scott connection of Transformers.
Parallel Operation of Two Single Phase Transformers.
52-55
8.
9.
10.
11.
12.
2
27-30
44-47
48-51
56-60
61-63
Electrical Machines-II Lab Manual
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY
III Year B.Tech EEE ISem
Academic year 2013-2014
L T/P/D C
0 -/3/- 2
(55602) ELECTRICAL MACHINES LAB –II
The following experiments are required to be conducted as compulsory experiments.
1. O.C. & S.C. Tests on single phase transformer.
2. Sumpner's test on a pair of single phase transformers.
3. Brake test on three phase squirrel cage induction motor.
4. No-load & blocked rotor tests on three phase Slip ring Induction motor.
5. Regulation of a three phase alternator by synchronous impedance (EMF & MMF) method.
6. V and inverted V curves of a three - phase Synchronous motor.
7. Equivalent circuit of a single phase induction motor.
8. Determination of Xd and Xq of a salient pole synchronous machine.
In addition to the above experiments, at least any two of the experiments from the
following list are required to be conducted.
1. Parallel Operation of Single Phase Transformers.
2. Separation of core losses of a single phase transformer.
3. Scott connection of Transformers.
4. Regulation of a three phase alternator by ZPF & ASA method.
5. Efficiency of a tree phase alternator.
6. Heat run test on a bank of 3 Nos of single phase delta connected transformers.
7. Measurement of sequence Impedance of a 3phase alternator.
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Electrical Machines-II Lab Manual
Experiments Conducted by the Department:1. O.C. & S.C. Tests on single phase transformer .
2. Sumpner's test on a pair of single phase transformers .
3. No-load & Blocked rotor tests on three phase induction motor
4. Separation of core losses of a single phase transformer
5. Efficiency of a three phase alternator
6. Brake test on three phase induction motor
7. Regulation of a three phase alternator by synchronous impedance & m.m.f methods
8. V and inverted V curves of a three phase synchronous motor
9. Equivalent circuit of a single phase induction motor
10. Determination of Xd and Xq of a Salient pole synchronous machine
Additional Experments
1. Parallel Operation of Two Single Phase Transformers.
2. Measurement of sequence Impedance of a 3phase alternator.
3. Scott connection of Transformers.
4
Electrical Machines-II Lab Manual
FIRST CYCLE EXPERIMENTS:
Experiment No.
1
Experiment Name
OC & SC test on single phase transformer
2
Sumpners’s test on a pair of single phase transformer
3
No-load & Blocked rotor tests on three phase induction motor
4
Separation of core losses of a single phase transformer
5
Efficiency of a three phase alternator
SECOND CYCLE EXPERIMENTS :
Experiment No.
Experiment Name
6
Brake test on three phase induction motor
7
Regulation of a three phase alternator by synchronous impedance & m.m.f
methods
8
V and inverted V curves of a three phase synchronous motor
9
Equivalent circuit of a single phase induction motor
10
Determination of Xd and Xq of a Salient pole synchronous machine
5
Electrical Machines-II Lab Manual
LABORATORY PRACTICE
SAFETY RULES
SAFETY is of paramount importance in the Electrical Engineering Laboratories.
2.Electricity NEVER EXECUSES careless persons. So, exercise enough care and attention
in handling electrical equipment and follow safety practices in the laboratory. (Electricity
is a good servant but a bad master).
3.Avoid direct contact with any voltage source and power line voltages. (Otherwise, any such
contact may subject you to electrical shock)
4.Wear rubber-soled shoes. (To insulate you from earth so that even if you accidentally
contact a live point, current will not flow through your body to earth and hence you will be
protected from electrical shock)
5.Wear laboratory-coat and avoid loose clothing. (Loose clothing may get caught on an
equipment/instrument and this may lead to an accident particularly if the equipment
happens to be a rotating machine)
6.Girl students should have their hair tucked under their coat or have it in a knot.
7.Do not wear any metallic rings, bangles, bracelets, wristwatches and neck chains. (When
you move your hand/body, such conducting items may create a short circuit or may touch a
live point and thereby subject you to electrical shock)
8.Be certain that your hands are dry and that you are not standing on wet floor. (Wet parts of
the body reduce the contact resistance thereby increasing the severity of the shock)
9.Ensure that the power is OFF before you start connecting up the circuit.(Otherwise you will
be touching the live parts in the circuit)
10.Get your circuit diagram approved by the staff member and connect up the circuit strictly
as per the approved circuit diagram.
11.Check power chords for any sign of damage and be certain that the chords use safety
plugs and do not defeat the safety feature of these plugs by using ungrounded plugs.
12.When using connection leads, check for any insulation damage in the leads and avoid
such defective leads.
13.Do not defeat any safety devices such as fuse or circuit breaker by shorting across it.
Safety devices protect YOU and your equipment.
14.Switch on the power to your circuit and equipment only after getting them checked up
and approved by the staff member.
15.Take the measurement with one hand in your pocket. (To avoid shock in case you
accidentally touch two points at different potentials with your two hands)
16.Do not make any change in the connection without the approval of the staff member.
17.In case you notice any abnormal condition in your circuit ( like insulation heating up,
resistor heating up etc ), switch off the power to your circuit immediately and inform the
staff member.
18.Keep hot soldering iron in the holder when not in use.
19.After completing the experiment show your readings to the staff member and switch off
the power to your circuit after getting approval from the staff member.
20.While performing load-tests in the Electrical Machines Laboratory using the brakedrums:Avoid the brake-drum from getting too hot by putting just enough water into the
brake-drum at intervals; use the plastic bottle with a nozzle (available in the laboratory ) to
pour the water.(When the drum gets too hot, it will burn out the braking belts)
Do not stand in front of the brake-drum when the supply to the load-test circuit is switched
off. (Otherwise, the hot water in the brake-drum will splash out on you)
After completing the load-test, suck out the water in the brake-drum using the plastic
bottle with nozzle and then dry off the drum with a sponge which is available in the
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Electrical Machines-II Lab Manual
laboratory.(The water, if allowed to remain in the brake-drum, will corrode it)
21.Determine the correct rating of the fuse/s to be connected in the circuit after
understanding correctly the type of the experiment to be performed: no-load test or fullload test, the maximum current expected in the circuit and accordingly use that fuserating.(While an over-rated fuse will damage the equipment and other instruments like
ammeters and watt-meters in case of over load, an under-rated fuse may not allow one
even to start the experiment)
22. At the time of starting a motor, the ammeter connected in the armature circuit overshoots,
as the starting current is around 5 times the full load rating of the motor. Moving coil
ammeters being very delicate, may get damaged due to high starting current. A switch has
been provided on such meters to disconnect the moving coil of the meter during starting.
This switch should be closed after the motor attains full speed. Moving iron ammeters
and current coils of watt meters are not so delicate and hence these can stand short time
overload due to high starting current. No such switch is therefore provided on these
meters. Moving iron meters are cheaper and more rugged compared to moving coil
meters. Moving iron meters can be used for both a.c. and d.c. measurement. Moving coil
instruments are however more sensitive and more accurate as compared to their moving
iron counterparts and these can be used for d.c. measurements only. Good features of
moving coil instruments are not of much consequence for you as other sources of errors in
the experiments are many times more than those caused by these meters.
23. Some students have been found to damage meters by mishandling in the following ways:
Keeping unnecessary material like books, lab records, unused meters etc. causing meters
to fall down the table.
Putting pressure on the meter (specially glass) while making connections or while talking
or listening somebody.
STUDENTS ARE STRICTLY WARNED THAT FULL COST OF THE METER WILL BE
RECOVERED FROM THE INDIVIDUAL WHO HAS DAMAGED IT IN SUCH A
MANNER.
Copy these rules in your Lab Record. Observe these yourself and help your friends to observe
I have read and understand these rules and procedures. I agree to abide by these rules and
procedures at all times while using these facilities. I understand that failure to follow these
rules and procedures will result in my immediate dismissal from the laboratory and additional
disciplinary action may be taken.
GUIDELINES FOR LABORATORY NOTEBOOK
The laboratory notebook is a record of all work pertaining to the experiment. This record
should be sufficiently complete so that you or anyone else of similar technical
background can duplicate the experiment and data by simply following your laboratory
notebook. Record everything directly into the notebook during the experiment. Do not use
scratch paper for recording data. Do not trust your memory to fill in the details at a later time.
Organization in your notebook is important. Descriptive headings should be used to separate
and identify the various parts of the experiment. Record data in chronological order. A neat,
organized and complete record of an experiment is just as important as the experimental
work.
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Electrical Machines-II Lab Manual
1. Heading:
The experiment identification (number) should be at the top of each page.Your name
and date should be at the top of the first page of each day's experimental work.
2.Object:
A brief but complete statement of what you intend to find out or verify in the
experiment should be at the beginning of each experiment
3.Diagram:
A circuit diagram should be drawn and labeled so that the actual experiment circuitry
could be easily duplicated at any time in the future. Be especially careful to record all
circuit changes made during the experiment.
4.Equipment List:
List those items of equipment which have a direct effect on the accuracy of the data. It
may be necessary later to locate specific items of equipment for rechecks if discrepancies
develop in the results.
5.Procedure:
In general, lengthy explanations of procedures are unnecessary. Be brief. Short
commentaries along side the corresponding data may be used. Keep in mind the fact that the
experiment must be reproducible from the information given in your notebook.
6.Data:
Think carefully about what data is required and prepare suitable
data tables. Record instrument readings directly. Do not use calculated results in place
of direct data; however, calculated results may be recorded in the same table with the direct
data. Data tables should be clearly identified and each data column labeled and headed by the
proper units of measure.
7.Calculations:
Not always necessary but equations and sample calculations are often given to
illustrate the treatment of the experimental data in obtaining the results.
8.Graphs:
Graphs are used to present large amounts of data in a concise visual form. Data to be
presented in graphical form should be plotted in the laboratory so that any questionable
data points can be checked while the experiment is still set up. The grid lines in the notebook
can be used for most graphs. If special graph paper is required, affix the graph
permanently into the notebook. Give all graphs a short descriptive title. Label and scale
the axes. Use units of measure. Label each curve if more than one on a graph.
9.Results:
The results should be presented in a form which makes the interpretation easy. Large
amounts of numerical results are generally presented in graphical form. Tables are
generally used for small amounts of results. Theoretical and experimental results should be
on the same graph or arrange in the same table in a way for easy correlation of these results.
10.Conclusion:
This is your interpretation of the results of the experiment as an engineer. Be brief
and specific. Give reasons for important discrepancies.
8
Electrical Machines-II Lab Manual
EXP.NO. 01
DATE:
1. OC & SC TESTS ON 1- Φ TRANSFORMER
AIM:
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.
NAME PLATE DETAILS:
1Φ - 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
Dimmerstat
9
Range
Quantity
Electrical Machines-II Lab Manual
CIRCUIT DIAGRAM:
CIRCUIT DIAGRAM: OC AND SC TESTS ON A SINGLE PHASE
TRANSFORMER
0-1A,
MI
1A
Ph ●
● || ●
||
||
230/ 0|| 270V
230V,
|| DVariac
1φ,50Hz
|| P
AC
|| S
Supply
|| T
● || ●
N
1
||
A
||
Ph ●
● ||
||
||
||
230V,
||
1φ,50Hz
||
AC
||
Supply
||
N
● ||
||
||
●
M
L
C
V
2KVA
240 / 415 V
•
A
V
0-150V
,MI
O
C
LV
0-10 A
MI
5
A
230/ 0270V
DVariac
300V ,5 A L,
PF
150V,1 0 A,
UPF
M
L
C
V
•
H
V
2KVA
415 /240 V
•
A
V
0-30 V
,MI
P
S
T
●
S
C
H
v
V
V
5
A
LV
•
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 = I0 and power input = P0
Indeed the no-load current, I0 is so small (it is usually 2-6% of the rated current) and R 01 and X 01 are
also small, that V1 can be regarded as = E1 by neglecting the series impedance. This means that for all
practical purposes the power input on no-load equals the core (iron) loss i.e.,
P0 = V1 I0cos0
cos0 = P0 / V1 I0
10
Electrical Machines-II Lab Manual
Iw = I0cos0, I = 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 arrangement and 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 current under short circuit
is as low as 5-8% of the rated voltage. The exciting current under these conditions is
only about 0.1to 0.5% 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)
Z 01= VSC / ISC =  R 012 + X 012
Equivalent resistance, R01= PSC / (ISC)2
Equivalent reactance, X 01 =  Z 012 – R 012
PROCEDURE :
OC TEST :
(1) All the connections are done as per the circuit diagram of OC test
(2) By using 1- variac apply rated voltage to the circuit.
(3) At this rated voltage note down voltmeter, ammeter & wattermeter readings.
(4) From the values we can find R0 and X0
SC TEST :
(1) All the connections are done as per the circuit diagram of SC test
(2) By using 1- variac rated current is made to flow in the circuit.
(3) At this rated current note down voltmeter, ammeter & wattermeter readings.
(4) From this values we can find out R01 & X01
PRECAUTIONS :
(1) Open circuit test is performed on LV side i.e meters are connected LV side and HV side will be
open circuited.
(2) For short circuit test is connect meters on HV side and LV side will be short circuited
(3) Rated voltage and rated current must be maintained in OC test and SC test respectively
11
Electrical Machines-II Lab Manual
(4) All the connections must be tight
TABULAR COLUMNS
Observations:
OC TEST:
Vo
Volts
Io
Amps
Wo
Watts
Isc
Amps
Wsc
Watts
SC TEST:
Vsc
Volts
CALCULATIONS:
Efficiency vs Load
Power factor lagging
%LOAD
0.2
0.4
0.6
25
50
75
12
0.8
1
Electrical Machines-II Lab Manual
100
125
Regulation
Power factor laging
%LOAD
0.2
0.4
0.6
UPF
0.8
Power factor leading
1
0.8
0.6
0.4
25
50
75
100
125
EQUALENT CIRCUIT:
V1 =240V R
R02
X02
E
X0
0
1
MODEL GRAPHS
Regulation
Pf lea
d
leading
Pf lagging
Regulation
13
0.2
Electrical Machines-II Lab Manual
RESULT:
14
Electrical Machines-II Lab Manual
EXP.NO. 02
DATE:
1. SUMPNER’S TEST ON A PAIR OF 1-Ф TRANSFORMER
AIM:
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.
NAME PLATE DETAILS:
1Φ - TRANSFORMERs
T/F-1
T/F
Rated power
LV side
Rated voltage
Rated current
Frequency
APPARATURS REQUIRED:
15
HV side
T/F-2
HV side
LV side
Electrical Machines-II Lab Manual
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
Dimmerstat
Range
Quantity
THEORY:Without conducting any actual loading test is the Sumpner’s test which can only
be conducted simultaneously on two identical transformers. In conducting the Sumpner’s test
the primaries of the two transformers are connected in parallel across the rated voltage
supply(V1), while the two secondaries are connected in phase opposition. As per the
superposition theorem, if V2 source is assumed shorted, the two transformers appear in opencircuit to source V1 as their secondries are in phase opposition and therefore no current can
flow in them. The current drawn from source V1 is thus 2I0 (twice the no-load current of each
transformer) and power is 2P0 (= 2Pi , twice the core loss of each transformer). When V1 is
regarded as shorted, the transformers are series-connected across V2 and are short-circuited
on the side of primaries. Therefore, the impedance seen at V2 is 2Z and whenV2 is adjusted to
circulate full-load current (Ifl), the power fed in is 2Pc (twice the full-load copper-loss of each
transformer). Thus in the Sumpner’s test while the transformers are not supplying any load,
full iron-loss occurs in their core and full copper-loss occurs in their windings; net power
input to the transformers being(2Po+2Pc).The heat run test could , therefore, be conducted on
the two transformers, while only losses are supplied.
For each trans former the results are
Voltage =V1 , Current = I0 /2 , Core losses = P0 /2
Voltage =Vsc /2 , Current = Isc , Copper losses = Psc /2
P0 = Pi (iron-loss)
P0 = V1 I0cos0
cos0 = P0 / V1 I0
16
Electrical Machines-II Lab Manual
Iw = I0cos0, I = I0sin0
R0 = V1/ Iw , X0 = V1 / I.
Vsc =Voltage, Isc = Current , Psc = Power (Copper loss)
Z 01= V sc / ISC =  R 012 + X 012
2
Equivalent resistance, R01= Psc / (ISC)2
2
Equivalent reactance, X 01 =  Z 012 – R 012
CIRCUIT DIAGRAM:
● || ●
||
||
0|| 230/
270V
230V,
|| DVariac
1φ,50Hz
|| P
AC
|| S
Supply
|| T
● || ●
N
1A
||
||
5A
||
● || ●
Ph ●
||
||
|| D
230V,
230/0-270V
|| P Variac
1φ,50Hz
|| S
AC
|| T
Supply
||
● || ●
N
||
||
300V,10A,LPF
0-1A,MI
1A
Ph ●
M
L
C
V
A
0-300V,MI
V
240 V
150V,10A,UPF
0-10A,MI
M
L
A
C
V
V
0150V,MI
● || ●
0
||
D ||
P ||
S || V
T ||
||
||
● || ●
||
0
240V
2KVA
240/415
V •
415 V
415 V
0-600V,MI
PROCEDURE :
||
NAME PLATE
(1) Connections are done as per the circuit diagram.
DETAILS:
(2) By using the variac rated voltage is 240V is made to apply across the low voltage side
of the transformer.
17
Electrical Machines-II Lab Manual
(3) Before closing the DPST switch the reading of the voltmeter connected across DPST
switch must be zero.
(4) By using the variac in H.V side rated current is made to flow in the circuit.
(5) At this instant note down all the meter readings.
(6) By using above tabulated readings the efficiency and regulation of the transformers
are calculated.
RECAITIONS:
1) The Dimmer stat should be kept at minimum O/P position initially.
2) The Dimmer stat should be varied slowly & uniformly.
TABULAR COLUMNS
Observations:
Primary Side:
Vo
Volts
2Io
Amps
2Wo
Watts
Isc
Amps
2Wsc
Watts
Secondary Side:
2Vsc
Volts
CALCULATIONS:
Efficiency vs Load
Power factor lagging
18
Electrical Machines-II Lab Manual
%LOAD
0.2
0.4
0.6
0.8
1
25
50
75
100
125
Regulation:
Power factor laging
UPF
Power factor leading
%LOAD
25
50
75
100
125
EQUALENT CIRCUIT:
V1 =240V R
R02
X02
E
X0
0
1
MODEL GRAPHS
Regulation
19
Electrical Machines-II Lab Manual
RESULT:
20
Electrical Machines-II Lab Manual
DATE:
EXP.NO.3
NO LOAD AND BLOCKED ROTOR TEST ON 3- PHASE INDUCTION MOTOR
AIM:
To conduct the no load & blocked rotor test on 3- phase induction motor
& to draw the equivalent circuit of 3- phase squirrel cage induction motor.
NAME PLATE DETAILS:
Parameters
Induction Motor
Rated Power
Rated Voltage
Rated Current
Rated Speed
APPARATUS REQUIRED:
S.No
Name of apparatus
Type
1.
Ammeter
MI
2.
Voltmeter
MI
3.
Wattmeter
EDM
21
Range
Qty.
Electrical Machines-II Lab Manual
4.
Tachometer
5.
Connecting Wires
digital
THEORY :
A 3-phase induction motor consists of stator, rotor & other associated parts. In the stator
,a 3- phase winding (provided) are displaced in space by 120. A3- phase current is fed to the
winding so that a resultant rotating magnetic flux is generated. The rotor starts rotating due to
the induction effect produced due the relative velocity between the rotor
Winding & the rotating flux.
As a general rule, conversion of electrical energy to mechanical energy takes place in to the
rotating part on electrical motor. In DC motors, electrical power is conduct directly to the
armature, i.e, rotating part through brushes and commutator. Hence, in this sense, a DC motor
can be called as 'conduction motor'.
However, in AC motors, rotor does not receive power by conduction but by induction in
exactly the same way as secondary of a two winding T/F receives its power from the primary.
So, these motors are known as Induction motors. In fact an induction motor can be taken as
rotating T/F, i.e, one in which primary winding is stationary and but the secondary is free.
The starting torque of the Induction motor can be increase by improving its p.f by adding
external resistance in the rotor circuit from the stator connected rheostat, the rheostat resist
ance being progressively cut out as the motor gathers speed. Addition of external resistance
increases the rotor impedance and so reduces the rotor current. At first, the effect of improved
p.f predominates the current decreasing effect of impedance. So, starting torque is increased.
At time of starting, external resistance is kept at maximum resistance position and after a
certain time, the effect of increased impedance predominates the effect of improved p.f and
so the torque starts decreasing. By this during running period the rotor resistance being
progressively cut-out as the motor attains its speed. In this way, it is possible to get good
starting torque as well as good running torque.
CIRCUIT DIAGRAM:
22
Electrical Machines-II Lab Manual
PROCEDURE :
NO LOAD TEST :
(1).
(2).
(3).
(4).
Connections are given as per the circuit diagram.
Precautions are observed and motor is started on the no load.
Autotransformer is varied to have rated voltage applied.
The meter readings are then tabulated.
BLOCKED ROTOR TEST :
(1). Connections are given as per circuit diagram.
23
Electrical Machines-II Lab Manual
(2). Precautions are observed and motor is started on full load or blocked rotor position.
(3). Autotransformer is varied to have rated current flowing in motor.
(4). The meter readings are then tabulated.
PRECAUTIONS :
NO LOAD TEST:
(1).
(2).
(3).
Initially TPST switch is kept open.
Autotransformer must be kept at minimum potential position.
The machine must be started at no load.
BLOCKED ROTOR TEST:
(1). Initially the TPST switch is kept open.
(2). Autotransformer must be kept at minimum potential position.
(3). The machine should be started on full load.
FORMULA USED:
FOR NO LOAD TEST:
Wsc = √3 Vo IoCOSФ watts
Iw = Io cosФ amps
Ro= V0/ Iw Ω
Xo= Vo/Iu Ω
FOR BLOCKED ROTOR TEST:
Wsc =3I2*Ro watts
Ro1 = Wsc/3(Isc)2 Ω
Zo1 = Vsc/Isc Ω
Xo1 = √Zo1^2-Ro1^2 Ω
TABULAR COLUMNS:
NO LOAD TEST:
Voltage
Voc
Current
Ioc
Volts
Amps
Wattmeter
readings (W1)
Wattmeter Toyal
readings
Power
(W2)
Wo
(W1-W2)
Voc= open circuit voltage
24
cosΦo=
Wo/
(3 Voc
Ioc)
Φo=
Electrical Machines-II Lab Manual
Ioc = open circuit current
BLOCKED ROTOR TEST:
Voltage
Vsc
Current
Isc
Volts
Wattmeter
readings (W1)
Wattmeter Toyal Power
readings
Wsc
(W2)
(W1-W2)
Amps
cosΦo=
Wsc/
( 3Vsc
Isc)
Φsc=
Vsc = short circuit voltage
Isc = short circuit current
GRAPH:
RESULT: Hence by conducting the no load & blocked rotor test of 3- phase induction
motor
EXP.NO. 04
DATE:
SEPERATION OF CORE LOSSES 1- TRANSFORMER
AIM : To separate hysteresis and eddy current losses of a given 1- transformer.
NAME PLATE DETAILS:
DC Motor
Alternator
Rated Power
Rated voltage
25
Transformer
Electrical Machines-II Lab Manual
Rated current
Rated speed
Rated field current
APPARATUS REQUIRED:
SL.NO
Name of the Apparatus
Type
1
Ammeter
MC
2
Voltmeter
MI
3
Wattmeter
EDM
4
Rheostat
Wire wound
5
Potential Divider
Wire wound
6
Tachometer
Range
Quantity
Digital
THEORY :Hysteresis and eddy current losses are called iron loss and take place in core of the
transformer .
Hysteresis loss is given by = Wh = KBmox1.6 f = Af
Eddy current loss also depends on the frequency f and is given by
We = KB2mox f2 t2 =Bf2
B max = Maximum flux density weber / m2
F = frequency cycles/ seconds
t = thickness of stamping
The iron loss will be expressed by
W i = Af +B f2
W i/ f = A + B f ,
y =mx+c
This is equation of straight line y = m x + c, when y = w i / f , c = A , and m = B
and x = f.
Eddy current and Hysteresis loss can be separated when A and B are found.
The variable frequency supply is obtained from an alternator when frequency can be
varied.
CIRCUIT DIAGRAM:
3 Pt starter
+
●
220V ,DC
Supply
● || ●
||
||
||
||
||
|| D
|| P
|| S
|| T
10 A
•
L A F
● ● ●
18Ω/12A
Z
M
145Ω
2.8A
360Ω
1.2A
A
R
X
26
145 Ω
2.8A
B
Y
Electrical Machines-II Lab Manual
PROCEDURE :
(1) Connections are done as per the circuit diagram.
(2) Initially rheostat in the armature circuit of motor is kept at maximum position, the
rheostat in the field circuit of motor is kept at minimum position and the rheostats in the
field circuit (potential divider)of the alternator are kept so that minimum voltage is
applied to the field circuit of the alternator.
(3) Start the motor with the help of 3-point starter
(4) Bring the speed of the motor to the rated speed by using the rheostats of the motor.
(5) By increasing the excitation of alternator using the potential divider bring the voltage of
the alternator to the rated voltage.
(6) Apply the rated voltage to the high voltage side of the transformer by closing the DPDT
switch.
(7) Note down all the meter readings and speed.
(8) Alternator is made to run at different speeds below the rated speed and adjust the voltage
of the alternator, so that v / f ratio is constant.
(9) At each and every speed, note down the readings of voltmeter, ammeter, wattmeter and
the speed of the motor.
(10) Perform the experiment up to 80% of the rated speed and graphs are drawn between
27
Electrical Machines-II Lab Manual
(i) Wi / f Vs f
TABULAR FORM :
S.no
Voltage
(V)
(ii) losses Vs f
Wattmeter
reading (W)
Speed
(rpm)
f = PN / 120
V/f
Wi / f
1
2
3
4
5
6
7
8
9
10
11
12
MODEL GRAPH
W/f
A
PRECAUTIONS :
f
(1) Care must be taken about the v / f value constant so that the flux density is maintained
constant.
(2) The rheostat in the field circuit of motor should be minimum position, the rheostat in the
armature circuit of motor should be maximum position and potential divider of alternator
should give voltage to the alternator at the time of starting.
28
Electrical Machines-II Lab Manual
RESULT : Separate hysteresis and eddy current losses of a given 1- transformer are
obtained as follows:
Eddy current losses=
Hysteresis losses =
Total Core losses
=
EXP.NO. 05
DATE:
5. EFFICIENCY OF A THREE PHASE ALTERNATOR
Aim:-To conduct a suitable test on the given alternator and to determine the efficiency of a
three phase alternator.
Name Plate Details:Serial Number
1
2
3
Parameters
Rated Voltage
Rated Current
Rated Speed
DC Shunt Motor
29
Alternator
Electrical Machines-II Lab Manual
4
5
Rated Power
Rated Field Current
ApparatusRequired:Serial Number
1
2
3
4
5
6
Item
Voltmeter
Ammeter
Rheostat
Tachometer
Potential Divider
Connecting
Wires
Type
MI&MC
MI&MC
Wire wound
Digital
wirewound
Range
Quantity
Theory:Just as in case of generator the input to the alternator is not readily measured .The
direct measurement of efficiency of actual loading is accompanied by different difficulties of
providing the necessary power and finding suitable load .Efficiency is therefore determined
by measuring the losses of the machinery .The losses in alternator are as follows :a) Electrical Losses: - This includes field loss, armature winding loss, and brush contact
loss. The copper loss in the field circuit is obtained by adding If2Rf loss of field
winding and the electrical loss of field rheostat or more simply by multiplying the
excitation voltage by current. This loss is constant for any given voltage and power
30
Electrical Machines-II Lab Manual
factor but varies with to. The maintenance of rated voltage at low lagging power factor
needs comparatively large field current and gives the maximum field loss.
The armature copper loss in the stator winding is determined on
the basis of armature resistance whether the ohm or the effective resistance should be
used depends on the treatment of stray load loss.
The electrical loss at the brush contacts between brushes and slip
ring is usually quite small and is often neglected.
b) Core Loss: - Due to the eddy currents and hysteresis caused by the flux resulting
from the combined rotor and stator field such losses occur in the pole face and
armature teeth and core. This loss is assumed to be independent of load but varies
with excitation, if the excitation is factor then this loss changes also. It is equal to the
difference of power required to drive the alternator with and without the field excited.
c) Friction and Winding Loss: - It includes ventilation loss (power requirement to
include the cooling air) and loss due to bearing and brush friction. Since the speed is
constant so this loss for particular machine remains constant .It is equal to the
mechanical power required to drive the alternator at rated speed with no excitation.
d) Load or Stray Power Loss: - Loss is due to armature leakage flux which causes eddy
current and hysteresis loss in the iron surrounding the armature conductors in addition
core loss caused by distortion of the magnetic field under load conditions. It may
however be included in the efficiency calculation by using the effective value of R
instead of the dc R.
Procedure:i.
Couple the dc motor and alternator, run the dc motor above at the rated speed
(Synchronous speed of alternator). For the dc motor record terminal voltage Vo,
armature current Ia ,
For known value of armature circuit resistance Ra
V1I1 = friction and wind age loss of motor +friction and wind age loss of alternator
+ core loss
+ Ia2Ra...
2
V1I1=Fwm +Fwa +core + Ia Ra.
X
ii.
iii.
iv.
X=V1I1-Ia12Ra
Fw=W1=0.35X
Couple the alternator mechanically with dc motor, run the dc motor again at Ns
with alternator field unexcited .Record V2I2 values
V2I2=X + W2 + Ia22Ra
W2 = V2I2-(X+Ia22Ra)
Field core loss is equal to the product of voltage applied to field winding and
normal field current.
W3=IfVf
Run the dc motor at rated speed, perform three- phase Symmetrical short circuit
test on alternator with short circuit current equal to the rated current of alternator
Record V3, I3 values.
V3I3=X +W4 +Ia32Ra
31
Electrical Machines-II Lab Manual
W4=V3I3-(X + Ia32Ra)
Total Loss=W1+W2+W3+W4
Efficiency =
𝐾𝑉𝐴 𝑟𝑎𝑡𝑖𝑛𝑔 𝑋 𝑝𝑜𝑤𝑒𝑟 𝑓𝑎𝑐𝑡𝑜𝑟
𝐾𝑉𝐴 𝑟𝑎𝑡𝑖𝑛𝑔 𝑋 𝑝𝑜𝑤𝑒𝑟 𝑓𝑎𝑐𝑡𝑜𝑟 + 𝑡𝑜𝑡𝑎𝑙 𝑙𝑜𝑠𝑠𝑠
Output =KVA rating X power factor
For maximum efficiency
Output = xscosφ
X=
𝑊1+𝑊2 +𝑊3
𝑊4
Total Loss=2x2W4
𝑜𝑢𝑡𝑝𝑢𝑡
Maximum Efficiency =𝑂𝑢𝑡𝑝𝑢𝑡 +𝑇𝑜𝑡𝑎𝑙
Observation:V1=
V2=
VF=
V3=
𝑙𝑜𝑠𝑠
I1=
I2=
IF=
I3=
Ia1=
Ia2=
Ra=
Ia3=
Calculation:V1=
I1=
Ia1=
R a=
X=V1I1-Ia12Ra
Fw=W1=0.35X
V2I2=X + W2 + Ia22Ra
W2 = V2I2-(X+Ia22Ra)
W3=IfVf
V3I3=X +W4 +Ia32Ra
W4=V3I3-(X + Ia32Ra)
Total Loss=W1+W2+W3+W4
Efficiency =
𝐾𝑉𝐴 𝑟𝑎𝑡𝑖𝑛𝑔 𝑋 𝑝𝑜𝑤𝑒𝑟 𝑓𝑎𝑐𝑡𝑜𝑟
𝐾𝑉𝐴 𝑟𝑎𝑡𝑖𝑛𝑔 𝑋 𝑝𝑜𝑤𝑒𝑟 𝑓𝑎𝑐𝑡𝑜𝑟 + 𝑡𝑜𝑡𝑎𝑙 𝑙𝑜𝑠𝑠𝑠
Output =KVA rating X power factor
For maximum efficiency
Output = xscosφ
X=
𝑊1+𝑊2 +𝑊3
𝑊4
32
Electrical Machines-II Lab Manual
Total Loss=2x2W4
𝑜𝑢𝑡𝑝𝑢𝑡
Maximum Efficiency =𝑂𝑢𝑡𝑝𝑢𝑡 +𝑇𝑜𝑡𝑎𝑙
𝑙𝑜𝑠𝑠
Result: - Suitable test is conducted and
The efficiency of three phase alternator is
Maximum Efficiency of three phase alternator is
at full load
EXP.NO. 6
DATE:
BRAKE TEST ON 3–Φ SQUIRREL CAGE INDUCTION MOTOR
AIM:
To draw the performance characteristics of 3-phase squirrel cage induction motor by
conducting load test.
NAME PLATE DETAILS:
Parameters
Induction Motor
Rated Power
Rated Voltage
Rated Current
Rated Speed
APPARATUS REQUIRED:
S.No
Name of apparatus
Type
1.
Ammeter
MI
2.
Voltmeter
MI
33
Range
Qty.
Electrical Machines-II Lab Manual
3.
Wattmeter
EDM
4.
Tachometer
digital
5.
Connecting Wires
THEORY:
A 3-phase induction motor consists of stator and rotor with the other associated parts. In the
stator, a 3-phase winding is provided. The windings of the three phase are displaced in space
by 120º.A 3-phase current is fed to the 3-phase winding. These windings produce a resultant
magnetic flux and it rotates in space like a solid magnetic poles being rotated magnetically.
CIRCUIT DIAGRAM:
PROCEDURE:
1.Connections are given as per circuit diagram.
2.3-Ф induction motor is started with DOL starter.
3. If the pointer of one of the wattmeter readings reverses, interchange the current coil
terminals and
take the reading as negative.
4.The no load readings are taken.
34
Electrical Machines-II Lab Manual
5. The motor is loaded step by step till we get the rated current and the readings of the
voltmeter,
ammeter, wattmeters, spring balance are noted.
PRECAUTIONS:
1.TPST switch is kept open initially.
2.There must be no load when starting the load.
FORMULAE USED:
1)
2)
3)
4)
5)
% slip= (Ns-N/Ns)*100
Input Power = (W1+W2)watts
Output Power = 2∏NT/60 watts
Torque = 9.81*(S1-S2)*R N-m
% efficiency = (o/p power/i/p power)* 100
OBSERVATIONS:
S.NO
Line
Voltage
volts
Input
Current
Amps
Wattmeter Reading
W1*4
W2*2
watts
S1
Spring Control
S2
Speed
watts
1
2
3
4
5
6
CALCULATIONS:
Speed
S1- S2
T
(S1S2)9.81
Out put
power
Input
power
2𝜋NT/60
W1+ W2
35
Slip
Ns − 𝑁
Ns
Power
factor
𝑖/𝑝
3𝑉𝐼
ɳ
Electrical Machines-II Lab Manual
GRAPHS:
1)
2)
3)
4)
Output Power vs Efficiency
Output Power vs Torque
Output Power vs Speed
Output Power vs %s
36
Electrical Machines-II Lab Manual
RESULT: Hence the load test on Squirrel cage Induction motor is performed and
performance characteristics are drawn.
EXP.NO. 7
DATE:
REGULATION OF 3–Φ ALTERNATOR BY SYNCHRONOUS IMPEDANCE
AND MMF METHODS
AIM:
To predetermine the regulation of 3-phase alternator by EMF and MMF methods and
also draw the vector diagrams.
NAME PLATE DETAILS:
Parameters
DC Shunt Motor
Alternator
Rated Power
Rated Voltage
Rated Current
Rated Speed
Rated field current
APPARATURS REQUIRED:
SL.NO
1
Name of the Apparatus
Type
Ammeter
MC
37
Range
Quantity
Electrical Machines-II Lab Manual
2
Ammeter
MI
4
Voltmeter
MI
5
Rheostat
6
Potential Divider
7
Tachometer
Wire
wound
Wire
wound
Digital
THEORY:
The regulation of a 3-phase alternator may be predetermined by conducting the Open
Circuit (OC) and the Sort Circuit (SC) tests. The methods employed for determination of
regulation are EMF or synchronous impedance method, MMF or Ampere Turns method and
the ZPF or Potier triangle method. In this experiment, the EMF and MMF methods are used.
The OC and SC graphs are plotted from the two tests. The synchronous impedance is found
from the OC test. The regulation is then determined at different power factors by calculations
using vector diagrams. The EMF method is also called pessimistic method as the value of
regulation obtained is much more than the actual value. The MMF method is also called
optimistic method as the value of regulation obtained is much less than the actual value. In
the MMF method the armature leakage reactance is treated as an additional armature reaction.
In both methods the OC and SC test data are utilized.
CIRCUIT DIAGRAM:
38
Electrical Machines-II Lab Manual
PROCEDURE: (FOR BOTH EMF AND MMF METHODS)
1.
2.
3.
4.
Note down the name plate details of the motor and alternator.
Connections are made as per the circuit diagram.
Switch ON the supply by closing the DPST switch.
Using the Three point starter, start the motor to run at the synchronous speed by
adjusting the motor field rheostat.
5. Conduct Open Circuit test by varying the potential divider for various values of field
current and tabulate the corresponding Open Circuit Voltage readings.
6. Conduct Short Circuit test by closing the TPST switch and adjust the potential divider
to set the rated armature current and tabulate the corresponding field current.
7. The Stator resistance per phase is determined by connecting any one phase stator
winding of the alternator as per the circuit diagram using MC voltmeter and ammeter
of suitable ranges.
PROCEDURE TO DRAW GRAPH FOR EMF METHOD:
1. Draw the Open Circuit Characteristic curve (Generated Voltage per phase VS
Field current).
2. Draw the Short Circuit Characteristics curve (Short circuit current VS Field
current)
3. From the graph find the open circuit voltage per phase (E1 (ph) for the rated short
circuit current (Isc).
4. By using respective formulae find the Zs, Xs, Eo and percentage regulation.
PROCEDURE TO DRAW GRAPH FOR MMF METHOD:
39
Electrical Machines-II Lab Manual
1. Draw the Open Circuit Characteristic curve (Generated Voltage per phase VS
Field current).
2. Draw the Short Circuit Characteristics curve (Short circuit current VS Field
current)
3. Draw the line OL to represent
PRECAUTIONS:
(i)
The motor field rheostat should be kept in the minimum resistance position.
(ii)
The alternator field potential divider should be kept in the minimum voltage
position.
(iii) Initially all switches are in open position.
FORMULAE:
1. Armature Resistance Ra =
Ω
2. Synchronous Impedance Zs = O.C. voltage
S.C. current
3. Synchronous Reactance Xs = √ Zs2 – Ra2
4. Open circuit voltage for lagging p.f = √(VcosΦ + IaRa)2 + (VsinΦ + IaXs)2
5. Open circuit voltage for leading p.f. = √(VcosΦ + IaRa)2 + (VsinΦ – IaXs)2
6. Open circuit voltage for unity p.f =
√(V + IaRa)2 + ( IaXs)2
7. Percentage regulation = (Eo – V)/V
TABULAR COLUMNS
OPEN CIRCUIT TEST:
Field Current (If)
S.No.
Amps
Open Circuit Line
Voltage (VoL)
Volts
Open circuit Phase
Voltage (Voph)
Volts
1
2
3
4
5
6
7
8
9
10
11
SHORT CIRCUIT TEST:
S.No.
Field Current (If)
Amps
Short Circuit Current (120%
to 150% of rated current)
(ISC)
Amps
40
Electrical Machines-II Lab Manual
1
MODEL GRAPH:
RESULT:
Thus the regulation of 3-phase alternator has been predetermined by the EMF and
MMF methods.
41
Electrical Machines-II Lab Manual
EXP.NO. 8
DATE:
V AND INVERTED V CURVESOF 3–Φ SYNCHRONOUS MOTOR
AIM
To draw the V and inverted V curves of a 3 phase Synchronous Motor.
NAME PLATE DETAILS:
Parameters
Synchronous Motor
Rated Power
Rated Voltage
Rated Current
Rated Speed
APPARATUS REQUIRED:
S.no
Name of
Apparatus
Range
Type
42
Quantity
Electrical Machines-II Lab Manual
1
2
3
4
5
6
Ammeter
Voltmeter
Wattmeter
Rheostat
Tachometer
Connecting
Wires
MI
MI
EDM
Wire Wound
Digital
THEORY:
The variation of field current effects the power factor at which the synchro- nous motor
operates. For a syn motor, the armature current phasor is given by Ia=V-E where V is the
applied voltage .From the above equation it is clear that the magnitude and phase angle of
phasor Ia
depends upon the value of DC excitation. When the syn. Motor is operated at constant load
with variable field excitation, it is observed that:
a) When the excitation is low, the armature current is lag in nature & the magnitude is
comparatively high.
b) If the excitation is gradually increased, the magnitude of Ia is gradually decreasing and the
angle of lag is gradually reduced.
c) At one particular excitation, the magnitude of Ia corresponding to that load in minimum
and vector will be in phase with V vector.
d) If the excitation is further increased, the magnitude of Ia again gradually increased and Ia
,vector goes to leading state and the angle of load is also gradually increased.
CIRCUIT DIAGRAM:
43
Electrical Machines-II Lab Manual
PROCEDURE:
(1) Note down the name plate details of the motor.
(2) Connections are made as per the circuit diagram..
(3) Close the TPST switch.
(4) By adjusting the autotransformer from the minimum position to the maximum
position the rated supply is given to motor. The motor starts as an induction
motor.
(5) In order to give the excitation to the field for making it to run as the synchronous
motor, close the DPST switch.
(6) By varying the field rheostat note down the excitation current, armature current
and the power factor for various values of excitation.
(7) The same process has to be repeated for loaded condition.
(8) Later the motor is switched off and the graph is drawn.
PRECAUTION:
(1) The Potential barrier should be in maximum position.
(2) The motor should be started without load.
(3) Initially TPST switch is in open position.
OBSERVATION TABLE:
44
Electrical Machines-II Lab Manual
S.NO
IF
V
Ia
W1
W2
Amps
Volts
Amps
Watts
Watts
1
2
3
4
5
6
7
Power Factor:
CosΦ=(W/ 3 VLIL)
Where
IL= Ia+ IF
MODEL GRAPHS:
45
W
W1+ W2
Watts
COSΦ=
W/( 𝟑 VL
IL )
Electrical Machines-II Lab Manual
The graph is drawn for(1) Armature current Vs Excitation current.
(2) Power factor Vs Excitation current.
RESULT: The determination of V and inverted V curves of three phase synchronous motor
was obtained.
EXP.NO.09
DATE:
46
Electrical Machines-II Lab Manual
EQUIVALENT CIURCUIT AND PRE-DETERMINATION OF PERFORMANCE
CHARACTERISTICS OF 1Ф INDUCTION MOTOR
AIM:
To draw the performance characteristics of a single phase induction motor by
conducting the no-load and blocked rotor test.
NAME PLATE DETAILS:
1Ф -Induction Motor
Parameter
Rated Power
Rated Voltage
Rated Current
Rated Speed
APPARATUS REQUIRED:
S.No
1
Name of
Apparatus
Voltmeter
2
Ammeter
3
Wattmeter
4
Connecting
wires
Range
Type
Qty.
MI
MI
MI
MI
UPF EDM
LPF EDM
THEORY:
A 1-Ф induction motor consists of stator,rotor and other associated parts.In the rotor of a
single phase winding is provided.The windings of a 1- Ф winding(provided) are displaced in
space by 120º.A single phase current is fed to the windings so that a resultant rotating
magnetic flux is generated.The rotor starts rotating due to the induction effect produced due
to the relative velocity between the rotor winding and the rotating flux.
CIRCUIT DIAGRAM:
47
Electrical Machines-II Lab Manual
PROCEDURE:
NO LOAD TEST:
1. Connections are given as per the circuit diagram.
2. Precautions are observed and the motor is started at no load.
3. Autotransformer is varied to have a rated voltage applied.
BLOCKED ROTOR TEST:
1.
2.
3.
4.
Connections are given as per the circuit diagram.
Precautions are observed and motor is started on full load or blocked rotor position.
Autotransformer is varied to have rated current flowing in motor.
Meter readings are the noted.
PRECAUTIONS:
48
Electrical Machines-II Lab Manual
NO LOAD TEST:



Initially TPST Switch is kept open.
Autotransformer is kept at minimum potential position.
The machines must be started on no load.
BLOCKED ROTOR TEST:



Initially the TPST Switch is kept open.
Autotransformer is kept at minimum potential position.
The machine must be started at full load(blocked rotor).
Reff = 1.5*Rdc
FORMULAE:
NO LOAD TEST:





cos Ф = Wo/VoIo
Iw = Io cosФ
Im = Io sin Ф
Ro = Vo/Iw
Xo = Vo/Im
BLOCKED ROTOR TEST:
Zsc = Vsc/Isc Ω
Rsc = Wsc/Isc2 Ω
Xsc = √(Zsc2 – Rsc2) Ω
TABULAR COLUMNS
NO LOAD TEST:
S.No.
Vo(volts)
Io(amps)
Wo(watts)
1
BLOCKED ROTOR TEST:
49
Electrical Machines-II Lab Manual
S.No.
Vsc(volts)
Isc(amps)
Wsc(watts)
1
EQUALENT CIRCUIT:
RESULT: Thus the pre-determination of Equivalent circuit parameters and
efficiency of 1-phase induction motor was obtained as follows
EXP.NO.10
DATE:
50
Electrical Machines-II Lab Manual
SLIP TEST ON 3–Φ ALTERNATOR
AIM:To measure Direct Axis (Xd) and Quadeature Axis (Xq) synchronous reactance of
Synchronous machine by performing SLIP Test.
NAME PLATE DETAILS:
PARAMETERS
DC Shunt Motor
Alternator
Rated Power
Rated Voltage
Rated Current
Rated Speed
Rated field current
APPARATUS REQUIRED:
S.no
Name of
Apparatus
1
Ammeter
2
Voltmeter
3
Variac
4
Rheostat
5
Tachometer
6
Connecting
Wires
Range
Type
Quantity
MI
MI
Wire Wound
Digital
THEORY:
In a salient pole alternator, the reactance of magnetic circuit along is along its quad stator
axis. The alternator is driven by auxiliary prime mover at a speed slightly less than the
synchronous speed under these conditions. The armature current is when the armature current
mmf is in line with the field poles. The reactance by the magnetic field current is minimum.
The ratio of maximum voltage to minimum current gives the direct axis impedance and the
ratio of minimum voltage to maximum current gives the armature axis impedance.
The values of Xd & Xq are determined by conducting the slip-test. The syn. machine is
driven by a separate prime mover at a speed slightly different from synchronous speed. The
field winding is left open and positive sequence balanced voltages of reduced magnitude
(around 25% of the rated value) and of rated frequency and impressed across the armature
terminals. Here, the relative velocity b/w the field poles and the rotating armature mmf wave
is equal to the difference b/w syn. speed and the rotor speed i.e, the slip speed . When the
rotor is along the d-axis, then it has a position of min reluctance, min flux linkage and max
flux produced links with the winding.then Xd = (max. armature terminal voltage/ph) / (min.
armature current/ph)As the current is small then Vt
will be high as drop will be small.When the rotor is along q-axis, then it is max, then the flux
linkage would be max.Then The min flux produced links with winding. So max emf. Xq =
(min. armature terminal voltage/ph) / (max. armature current/ph)
CIRCUIT DIAGRAM:
51
Electrical Machines-II Lab Manual
PROCEDURE:
52
Electrical Machines-II Lab Manual
1.
2.
3.
4.
5.
6.
7.
8.
Note down the name plate details of motor and alternator.
Connections are made as per the circuit diagram.
Give the supply by closing the DPST switch.
Using the three point starter, start the motor to run at the synchronous speed by
varying the motor field rheostat at the same time check whether the alternator field
has been opened or not.
Apply 20% to 30% of the rated voltage to the armature of the alternator by adjusting
the autotransformer.
To obtain the slip and the maximum oscillation of pointers the speed is reduced
slightly lesser than the synchronous speed.
Maximum current, minimum current, maximum voltage and minimum voltage are
noted.
Find out the direct and quadrature axis impedances.
PRECAUTIONS:
1. The motor field rheostat should be kept in minimum.
2. The direction of the rotation due to prime mover and the alternator on the motor
should be the same.
3. Initially all the switches are kept open.
TABULAR COLUMNS
To find the Direct Axis and Quadrature axis impedances:
S.NO
Vmax
Vmin
Imax
Imin
1
OPEN CIRCUIT TEST:
Field Current (If)
S.No.
Amps
Open Circuit Line
Voltage (VoL)
Volts
1
SHORT CIRCUIT TEST:
53
Open circuit Phase
Voltage (Voph)
Volts
Electrical Machines-II Lab Manual
S.No.
Field Current (If)
Short Circuit Current (120% to
150% of rated current) (ISC)
Amps
Amps
1
FORMULAE USED:
1. Rac=1.6Rac Ω
2. Zd = Vmax/Imin Ω
3. Zq = Vmin/Imax Ω
4. Xd = √Zd2 – Rd2
Ω
5. Xq = √Zq2 – Rd2 Ω
6. Id = Ia sinФ amps
7. Iq = Ia cos Ф amps
8. %Reg = (Eo-V/V)*100
Where,
Zd = direct axis impedance in Ω
Zq = quadrate axis impedance in Ω
Xd = direct axis reactance in Ω
Xq = quadrate axis reactance in Ω
Id = direct axis current in amps
Ia = quadrate axis current in amps
RESULT: Hence by performing slip test we find the values of Xd= and Xq= .
ADDITIONAL EXPERIMENT NO:-1
DATE:
54
Electrical Machines-II Lab Manual
SCOTTCONNECTION
AIM : To convert three phase system to two phase system with the help of scott
Connection
NAME PLATE DETAILS:
Rated power
Rated voltage
Rated current
Frequency
APPARATURS REQUIRED:
SL.NO
Name of the Apparatus
1
Ammeter
2
Ammeter
3
Voltmeter
4
Voltmeter
5
Wattmeter
6
Wattmeter
7
Dimmerstat
Type
Range
Quantity
THEORY :Phase conversion from three to two phase is needed in special cases, such as in
supplying 2-phase electric arc furnaces.
The concept of 3/2-phase conversion follows from the voltage phasor diagram of
balanced 3-phase supply shown in Fig 1. If the point M midway VBC could be located , then
VAM leads VBC by 90o. A 2-phase supply could thus be obtained by means of transformers;
one connected across AM, called the teaser transformer and the other connected across the
lines B and C. since VAM= (3/2) VBC , the transformer primaries must have  3 N1/2 (teaser)
and N1 turns; this would mean equal voltage/turn in each transformer. A balanced 2-phase
supply could then be easily obtained by having both secondaries with equal number of turns,
N2. The point M is located midway on the primary of the transformer connected across the
lines B and C. The connection of two such transformers, known as the Scott connection, is
55
Electrical Machines-II Lab Manual
shown in Fig. 1(a), while the phasor diagram of the 2-phase supply on the secondary side is
shown in Fig. 1(c).
The neutral point on the 3-phase side, if required, could be located at the point N
which divides the primary winding of the tertiary in the ratio 1 : 2 (refer Fig.)
A
Teaser Transformer
_
IA
a2


_
Ia
+
3 N1 / 2
N

_
IA
B
C

N1 / 2
_
Ic
a1

_
IA / 2
_
IB
b2 / Ib
 
1(a)
+
_
Va
N2
_
Ib
_
_
IA / 2
_
IBC
M

N1 / 2
N2
 b1
_
Vb
_
A
_
Va
N
C
M
_
Vb
B
(b)
(c)
LOAD ANALYSIS:56
Electrical Machines-II Lab Manual
If the secondary load currents are IA and IB , the currents can be
the 3-phase side fig.1(a).
easily found on
_
_
IA = (2N2 / 3N1) x Ia = (2 Ia / 3) (for N1 / N2 = 1)
_
_
_
IBC = N2 / N1 Ib = Ib (for N1 / N2 = 1)
_
_
_
IB = IBC - IA / 2
_
_
_
Ic = - IBC - IA / 2
The corresponding phasor diagram for balanced secondary side load of unity power
factor is drawn in fig. (2) from which it is obvious that the currents drawn from the 3phase system are balanced and cophasal with the star voltages. The phasor diagram for the
case of an unbalanced 2-phase load is drawn in fig (3)
A
Va
IA = 23
Ia
IBC =1
- IBC
- IA / 2 = 1 / 3
- IA / 2
C
Ic
B
IB = 1 + 1/ 3 = 2 / 3
A
1
1
Va
- IBC
Vb
Ib
Ia
Fig.(2)
- IA / 2
IA
IC
a
b
C
Vb
B
IB
IBC
IA / 2
Fig.(3)
Ib
57
Electrical Machines-II Lab Manual
Teaser
Transformer
2 KVA,415 / 240
CIRCUIT DIAGRAM:
SCOTT CONNECTION
● ||
||
||
||
415V, 3-,
||
50Hz,
||
AC Supply
||
||
||
●
● ||
Y
||
||
||
415V, 3-,
||
50Hz,
AC Supply
||
R
B
●
●
●
||
||
●
10
A
●
0 – 300
V,MI
V
0–600
V,MI
T
P
S
T
●
24
0
86.6
%
V
10
A
0 – 600
V,MI
●
V
0
0

●
●
41
5
50
%
0 – 300
V,MI
0
10
A
24
0
0
Main
Transformer
2 KVA
415 /
240 V
PROCEDURE :
58
V
Electrical Machines-II Lab Manual
(1) Connections are done as per the circuit diagram.
(2) By using 3- auto transformer apply different voltages to the circuit.
(3) Note down the all the meter readings.
(4) Observe different meter readings.
TABULAR FORM :
S.NO
VRY
in
volts
3 -  SUPPLY
VYB
in volts
2 -  SUPPLY
VBR
in volts
VPh in volts VPh in volts
VL in volts
RESULT:
ADDITIONAL EXPERIMENT NO:-2
DATE:
59
Electrical Machines-II Lab Manual
Parallel Operation Of Two Single Phase Transformers
AIM:To operate the given two 2KVA, 230/110V single phase Transformers in parallel and stud y
the
load sharing between them when supplying resistive load .
NAME PLATE 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
Dimmerstat
THEORY:
60
Range
Quantity
Electrical Machines-II Lab Manual
PROCEDURE :a) Make connections as for circuit diagram, keep the load switch and switch S open .
b) Switch on the mains , see the volt meter reading of V1 , if this reading is 460V(double
the secondary voltage of both the machines) then switch of and inter change the
connections of secondary of any transformer . if reads zero then the switch S can be
closed , this way the polarities can be checked since wrong polarity will short circuit
the transformers if operated in parallel .
c) Close switch S and then close the load switch.
d) For various values of load current , record terminal voltage ,current in two secondary’s
, power supply by the two transformers and the total power,(do not exceed 10 A for
total current)
e) Switch of load and switch of main.
f) Determine the equivalent reactance’s and resistance’s of both transformers referred
to HV winding by SC test
61
Electrical Machines-II Lab Manual
CAULATIONS :-For a given load current IL at an angle ф the current and power
supply by each
transformer can be found out by the following formula
IA= (IL)X{(ZB)/(ZA+ZB)}
IB = (IL)X{(ZA)/(ZA+ZB)}
If S is the load KVA, then the KVA shared by the transformers can be found out by
SA= (S)X{(ZB)/(ZA+ZB)}
SB = (S)X{(ZA)/(ZA+ZB)}
Check the result obtained with the Theoretical calculations .
RESULTS:a) With the help of phasor diagram verify if IA = IB= I.
b) Check if the load shared is proportional to the KVA capacities of the respective
transformers
c) From the results state if RA /XA =RB /XB
62