SSN COLLEGE OF ENGINEERING KALAVAKKAM- 603 110 LAB MANUAL EE2259 ELECTRICAL MACHINES – I LABORATORY IV Sem EEE ( D.C Machines & Transformer experiments) Prepared By N.PANDIARAJAN. B.E.,M.Sc(Engg),M.B.A. Associate Professor DEPARTMENT OF ELECTRICAL & ELECTRONICS ENGINEERING
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SSN COLLEGE OF ENGINEERING
KALAVAKKAM- 603 110
LAB MANUAL
EE2259
ELECTRICAL MACHINES – I LABORATORY
IV Sem EEE ( D.C Machines & Transformer experiments)
Prepared By
N.PANDIARAJAN. B.E.,M.Sc(Engg),M.B.A.
Associate Professor
DEPARTMENT OF ELECTRICAL & ELECTRONICS ENGINEERING
2
SSN College of Engineering, Kalavakkam
Department of Electrical and Electronics Engineering
EE2259 – Electrical Machines-1 Laboratory
IV Semester - Electrical and Electronics Engineering
Duration: Dec 2009 to April 2010
INDEX
CYCLE-I
(Fill in the order by which done)
Ex.
No. Date Experiment Name
Page
No
Staff
signature
1.
2.
3.
4.
5.
6.
7.
CYCLE-II
8.
9.
10.
11.
12.
13
14.
3
General Instructions to students for EEE Laboratory courses
SAFETY: 1 You are doing experiments with the help of electrical power. You have to be very
careful. You must clearly know the supply system to your worktable in particular and
the entire laboratory in general.
2 Incase of any wrong observation, you have to IMMEDIATELY SWITCH OFF supply
to the worktable.
3 You have to tuck in your shirts and you have to wear a overcoat.
4 Wearing loose garments in side the lab. is strictly prohibited.
5 You have to wear shoes compulsorily.
ATTENDANCE:
1 Every time you come to the laboratory class, you have to come with your record note
book, observation notebook, calculators etc.
2 You have to attend the lab. at the stroke of the bell in the laboratory.
3 You have to give your attendance. You have to submit your records. You have to show
the day's experiment's circuit diagram and get it signed. You have to occupy the
respective worktable of the machine. Collect required meters etc as per indent slip.
MAKING CONNECTIONS:
1 Start giving connections as per the circuit diagram from one side of the circuit.
2 Series circuits are to be only given first, with the help of power wires.
3 Make parallel connections, namely voltmeters last using silk wires.
4 Terminals of the meters should not be used as junction points. There should not be any
loose connection. Thoroughly check the connections and keep re rheostat positions
suitable for starting. Also keep all meters in such a way to read the readings
conveniently. Call staff to check the connections.
DOING EXPERIMENTS: 1 Start the experiment as per the procedure. First check for the direction of rotation in
case of machines and deflection of meters.
2 If any of the things are wrong, then SWITCH OFF and modify the connections. Inform
to the staff and then START.
OBSERVATION:
1 Enter all readings in the tabulation. Note down the multiplication factor of any meter
immediately. .
2 During load test on motors, the needle of the spring balances may be vibrating.
3 Arrest gently the vibration and take the reading.
4 At the time of over loading, the readings are to be taken quickly.
5 Pour water in the brake drum at the time of loading.
CALCULATION:
1 Calculate all required quantities and enter in the tabulation. Units are VERY, VERY
PORTANT.Draw the necessary graphs. Write the result. Show it to the staff for getting
signature.
RECORD:
1 As the name Implies, it is a record: PERMANENT RECORD for reference. Write
neatly; Draw circuit diagrams neatly and label correctly.
2 Enter readings in the tabulation.
3 UNITS are to be written for various quantities.
4 Draw Graph. Complete the record before you come for next lab class.
5 Bring the record for submission during next lab class.
4
Additional Instructions
Avoid wearing any loose metallic rings, straps or bangles, as they are likely to prove dangerous at times.
Before entering into the laboratory class, you must be well prepared for the experiment that you are going to do on that day.
You must bring the related textbook, which may deal with the relevant experiment.
Get the circuit diagram approved with correct meter & fuse ratings
Get the reading verified. Then inform the technician so that supply to the worktable can be switched off.
You must get the observation note corrected within two days from the date of completion of experiment. Write the answer for all the discussion questions in the observation note. If not, marks for concerned observation will be proportionately reduced.
If you miss any practical class due to unavoidable reasons, intimate the staff in charge and do the missed experiment in the repetition class.
Such of those students who fail to put in a minimum of 75% attendance in the laboratory class will run the risk of not being allowed for the University Practical Examination. They will have to repeat the lab course in subsequent semester after paying prescribed fee.
Avoid wearing any loose metallic rings, straps or bangles, as they are likely to prove dangerous at times.
Girls should put their plait inside their overcoat
Acquire a good knowledge of the surrounding of your worktable. Know where the various live points are situated in your table.
In case of any unwanted things happening, immediately switch off the mains in the worktable. The same must be done when there is a power break during the experiment being carried out.
Avoid carrying too many instruments at the same time.
Avoid using water hydrant for electrical fires.
5
How to fix rating? 1.GENERAL:
1 We have to fix meters and provide fuse for the experiment. Identify the correct
machine/transformer on which experiment is to be conducted. Notedown the complete
NAMEPLATE DETAILS including Name of the company, Serial No, etc of the
machine / transformer in your observation notebook.
2 MOVING COIL METERS are to be used for measuring dc quantities.
3 MOVING IRON METERS are to be used for measuring ac quantities.
2. LOAD EXPERIMENTS:
1 In this case, we have to load upto 125% of rated capacity. By seeing the Nameplate
details, ammeters, voltmeters can be selected. It may be MC or MI meters. Normally
rated voltages are to be measured (0-300V) MC for dc and (0-300V) MI for single
phase ac and (0-600V) MI voltmeters for 3 phase ac may be used.
2 Power measurement using wattmeters must be carefully done. Under load conditions,
powerfactor will be high; henceUPF wattmeters may be used, with suitable voltage and
current level.
3 Under no-load conditions, Power factor will be poor; hence LPF wattmeters with
correct voltage and current levels may be selected.
4 In the case of transformers, kVA rating will be known from the Name plate details. For
eg: 1 KVA; 200/100V 1 phase ac transformer has the rated current in the primary ,
Ip = 200 =5A;
and In the Secondary, Is = 100 =10A;
• Hence ammeters for Primary and Secondary in this case may be (0- 5A)MI and (0-
10A)MI respectively are used when load experiments are conducted.
3. NO LOAD EXPERIMENTS:
• Voltmeters may be selected suitably. Since there is no load, the ammeter may be of
lower range. Normally, no-load current will be around 10% and 15% of rated current in
the case of machines and transformers respectively. According to the no-load current
value arrived, appropriate ammeter may be used.
4. LOAD:
There is no difficulty in the case of motors, because mechanical (brake down) loads may be
employed.But in the case of generators and transformers, power rating and voltage level of the
loads are to be specified. Normally water loads, resistive loads and lamp loads are available.
By seeing the nameplate of the machine, the voltage and power of the load is to be specified. .
5. FUSE: Fuse is an important element in an electric circuit. It is a protective element. Fuse is to be
provided in order to protect machines and meters. Fuse rating in any case should not exceed
rated current of the machines in the case of load experiments and not exceed the ammeter
range in the case of no-load experiments.
6
Duties of a student
1. Attend the classes regularly. Class may be missed only under exceptional
circumstances beyond one’s control.
2. Take class notes in separate notebook for each subject.
3. Write down all that written by the teacher on the board. In addition write down some
points told by the teacher orally. This will keep your attention focussed towards the
subject and will help you to appreciate the teacher’s lecture better.
4. Refer your class notes while reading from a book.
5. Purchase at least one textbook written by a standard author or as suggested by your
teacher or as prescribed by the University. Cheap books, books having large number of
solved problems etc. can be additional source material, but these cannot substitute a
textbook. Cost of a book is much lower than the cost of marks and knowledge.
6. Take the unit tests seriously by giving your best performance. Your performance in
tests will be an indicator towards your future performance in the university
examinations.
7. Do a lot of writing work at home. Writing is remembering. Remembering through
writing is faster than remembering through reading. In addition writing will help you to
remember the spellings, improve your grammar and writing speed. Formulae and their
derivations can be learned through writing only. Solve a large number of unsolved and
also solved problems independently.
8. Take your studies seriously. Get very good marks in the University examinations
because these are a must for a good placement. As only brilliant students are admitted
in this college, a little hard work may lead you to get University Ranks. Getting a
University Rank will be an achievement that will deliver you fruits for the lifetime in
several different ways. This is MUST for good placement also.
9. Do not hesitate to consult your teacher in case of any difficulty in understanding any
topic. Do not accumulate your doubts.
Basic duties to be completed to get the permission to do the experiment 1) All the members in the groups have to go through the experiment and
Complete the given circuit diagram(s) with fuse rating, instrument ratings,
Apparatus required tables and all other required things.
2) Each student has to answer the following questions compulsorily.
i) What is the aim of the exercise?
ii) What is the procedure to do the exercise?
iii) What are the precations?
iv) Two or three qtns given at each exercise.
Those who are unable to meet out the above requirement, need not be allowed to
do the exercise.
.
7
SSN COLLEGE OF ENGINEERING
DEPARTMENT OF ELECTRICAL & ELECTRONICS ENGINEERING
LABORATORY PRACTICE
SAFETY RULES
1 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.
8
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
brake-drums:
(i) 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)
(ii) 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)
(iii) 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 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 full-load test, the maximum current expected in the circuit and
accordingly use that fuse-rating.(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 wattmeters
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.
21. Moving iron meters can be used for both a.c. and d.c. measurement.
22. Moving coil instruments are however more sensitive and more accurate as compared
9
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:
i. Keeping unnecessary material like books, lab records, unused meters etc.
causing meters to fall down the table.
ii. Putting pressure on the meter (specially glass) while making connections or
while talking or listening somebody.
iii. Switching on the circuit without getting the connections checked by the staff.
STUDENTS ARE STRICTLY WARNED THAT FULL COST OF THE METER WILL
BE RECOVERED FROM THE INDIVIDUAL WHO HAS DAMAGED IT IN SUCH A
MANNER.
10
SSN College of Engineering, Kalavakkam
Department of Electrical and Electronics Engineering
EE2259 – Electrical Machines-1 Laboratory
IV Semester - Electrical and Electronics Engineering
INDEX
Ex.
No. Experiment Name
Page
No
1. O.C.C & Load Characteristics of D.C Separately
Excited Shunt Generator.
11
2. O.C.C & Load Characteristics of D.C Self Excited
Shunt Generator. 19
3. Load Test on D.C. Compound Generator
27
4. Load test on D.C. Shunt Motor 33
5. Speed Control of D.C.Shunt Motor 39
6. Load Test on D.C Series Motor 43
7. Load Test on D.C. Compound Motor 49
8. Load Test on Single Phase Transformer 55
9. OC , SC tests on Single Phase Transformer 61
10. Swinburne’s Test 69
11. Sumner’s Test 73
12. Hopkinson’s Test 79
13 Separation Of Losses In Single Phase Transformer 85
11
Ex.No: Date:
1. Open Circuit Characteristics (O.C.C) &
Load Characteristics of D.C Separately Excited Shunt Generator. (P.325 & 333 of text book)
AIM: I. To determine the no load magnetization or open circuit characteristic separately
excited dc shunt generator, compare it with self excited one, and hence
a. To deduce the O.C.C. for various speed, 1000 and 1250 rpm.
b. To determine the critical field resistance and critical speed.
II. To determine the external and internal (load) characteristics of the separately excited
DC shunt generator by actually loading the machine.
APPARA TUS REQUIRED:
S.No Name of the apparatus Range Type Quantity
1
2
3
4
5
6
7
8
THEORY: (i) O.C.C
In any D.C generator generated emf is d1rectly proportional to the exciting field current
i.e. flux. O.C.C shows the relation between the no-load generated emf in the armature, 'Eo'
and the field or exciting current 'If’ at a given fixed speed.
It should be noted that OCC for a higher speed would be above this curve and for a
lower speed, would be below it.
(ii) Load Charactristics:
Let us consider a dc generator giving it’s rated no load voltage 'Eo' for a certain
constant field current. If there were no armature reaction and armature voltage drop, then this
voltage would have remained constant as shown in modal graph by the dotted horizontal line I.
But when the generator is loaded, the voltage falls due to these two causes, thereby
giving slightly drooping characteristics. If we subtract from Eo the value of voltage drops due
to armature reaction for different loads, then we get the value of E, the emf actually induced
in the armature under load conditions. Curve II is plotted in this way and is known as the
INTERNAL CHARACTERISTIC.
If we subtract from E the armature drop laRa, we get terminal voltage V. The reverse
procedure may also be adopted to obtain Internal characteristic (ie) adding laRa to V. Curve III
represents the EXTERNAL CHARACTERISTIC.
Comparison of self and separately excited generator gen characteristics: Since the field current depends on terminal voltage in self excited generator, it’s load
characteristics would be more drooping than the other one. In O.C.C. there is no much
Load Characteristics of D.C Self Excited Shunt Generator.
(P.325 to 337 of text book) AIM: I. To determine the no load magnetization or open circuit characteristic self
excited dc shunt generator and hence,
a. To deduce the O.C.C. for various speed, 1000 and 1250 rpm.
c. To determine the critical field resistance and critical speed.
II. To determine the external and internal (load) characteristics of the self excited
DC shunt generator by actually loading the machine.
APPARA TUS REQUIRED:
S.No Name of the apparatus Range Type Quantity
1
2
3
4
5
6
7
8
THEORY: (i) O.C.C & (ii) Load Charactristics:
Refer the expiment “separately excited shunt generator”
Comparison of self and separately excited generator gen characteristics: Since the field current depends on terminal voltage in self excited generator, it’s load
characteristics would be more drooping than the other one. In O.C.C. there is no much
appreciable difference between the two types.
Range fixing:
The current drawn by the shunt motor on no-load is 15 to 20% of full load current.
The current drawn by the shunt motor on load must not exceed 120% of full load
current.
Motor Field circuit rheostat rating is _____ Ω ; ____ A (the current rating should be
slightly higher than the rated current)
Generator load Current IL = _______ A
∴ The range of ammeter AL is (0- )A
The rated field current is _____ A
∴ The range of ammeter Af is (0- )A
Generator Field circuit rheostat rating is _____ Ω ; ____ A (the current rating should
be slightly higher than the rated current and ohmic value should be as high as possible).
Rated voltage of Generator V = _______ Volts
∴ The range of voltmeter V is (0-
20
Load Test:
Speed: .............. RPM; No load voltage: ............. volts
Sl.
No.
Terminal
voltage
Load current
IL If Ia =IL + If Eg = V + IaRa
Model Graphs:
Draw Rc line, such that it is tangent to the initial portion of O.C.C. at rated speed and
passes through origin.
The value of critical field resistance, Rc = the slope of Rc line
Critical speed, Nc = speedRatedNhereNAC
BCRR −× ;
Rsh Line
E0
If
Rc line
O.C.C. Line
V, Eg
IL, Ia
V vs IL
Eg vs Ia
C
B
A
21
PROCEDURE:
O.C.C.Test:
1. Connections are given as shown in the circuit diagram.
2. After the connections are checked, Keeping R1 minimum resistance position and R2 in
maximum resistance position, the supply switch is closed.
3. The motor is started with the help of a dc 3 point starter.
4. The field rheostat R1 of the motor is adjusted to make it run at the rated speed.
Keeping the SPST switch open, Emf generated due to residual magnetism is noted
from voltmeter. (when .field current is zero.)
5. Then SPST switch is closed. By varying the field rheostat R2 in the generator side,
different values of generated emf Eo and field current If are noted from voltmeter and
ammeter and tabulated.
Load Test:
1. Keeping the generator side DPST open, the field rheostat in the generator side is
adjusted for the rated voltage of the generator which is seen in the voltmeter.
2. Now the DPST switch is closed and the resistive load is put up on the generator step by
step. The terminal voltage, armature and load current values are noted down for each
step from the respective meters.
3. Note that while taking each set of readings, the field current is maintained constant as
that for rated voltage [because due to heating, shunt field resistance is increased]
Measurement of Ra and Rsh : 1. Connections are given as shown in the circuit diagram.
2. Keep the resistances in maximum position and close the supply switch and take
Minimum three readings.
22
Measurement of Rsh of Generator :
Measurement of Ra for Generator:
Observation:
A + -
V
+
-
A
A
A
3
P
+
-
220 V
D.C
Z
ZZ
A + -
V G +
-
A
AA
D
P
S
T
S
+
-
RPS
Measurement of Ra:
Sl.
No.
V
(Volts)
I
(Amps)
Ra = V/I
(Ohms)
Measurement of Rsh:
Sl.
No.
V
(Volts)
I
(Amps)
Rsh = V/I
(Ohms)
23
Model Calculation:
O.C.C
E0 ∝ N
So, for different speeds, O.C.C. can be deduced from the O.C.C.at rated speed.
N1 = E1
N2 E2
Load test:
For separate excitation Ia = IL
For self excitation Ia = IL + If
So, induced emf on load, Eg = V + IaRa
GRAPH: Open circuit characteristic is drawn by taking field current 'If' along x axis and generated
voltage Eo along y axis.
To find critical field resistance: From the origin a tangent is drawn to OCC at the linear
portion. The slope of the tangent will give the critical field resistance.
Calculate E0 at different speeds and draw O.C.C. for diff speeds in a separate graph.
External characteristic is drawn taking load current 'IL' along x axis and terminal voltage
'V' along yaxis.
Internal characteristic is drawn by adding laRa drop to external characteristic curve, 'la'
along x axis and 'E' along y axis.
24
25
Result:
QUESTIONS:
1. What is the principle of operation of DC generator?
2. Where the field winding is placed in DC generator? Why?
3. List out the factors involved in voltage build up of a DC shunt generator.
4. Explain briefly the function of a commutator in a DC machine. Can commutator action
be performed by a solid state device.
5. Define and explain critical field circuit resistance and critical speed of DC shunt
generator.
6. What is armature reaction?
7. What is internal & external characteristics of DC shunt generator?
8. What are the applications of DC shunt generator?