Gopi's mcs lab man

1 BTL Institute of Technology EEE Dept.
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15EEL 38 Electrical Machines 1 Laboratory Manual
B T L INSTITUTE OF TECHNOLOGY & MANAGEMENT
No.259/B, Bommasandra Industrial Area, Hosur Road, Bangalore- 560 099
Ph.: 080- 27832379, (EEE Dept.)
A LAB MANUAL ON
ELECTRICAL MACHINES LABORATORY - I
Subject Code: 15EEL38
(As per VTU Syllabus CBCS)
PREPARED BY GOPINATH.B.L
APPROVED BY A G SURESH HOD EEE Dept.

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PREFACE
The significance of the Electrical Machines Lab - I, is renowned in the various
fields of engineering applications. For an Electrical Engineer, it is obligatory to have
the practical ideas about the Electrical Machines. By this perspective we have
introduced a Laboratory manual cum Observation for Electrical Machines Lab-I.
The manual uses the plan, cogent and simple language to explain the
fundamental aspects of Electrical Machines in practical. The manual prepared very
carefully with our level best. It gives all the steps in executing an experiment. And
validation by means of observation, Development of theory/hypotheses, experimental
validation

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Laboratory Safety Rules
Read ALL of the following rules carefully, and remember them while working in the
laboratory.
1. Never hurry. Haste causes many accidents.
2. Always see that power is connected to your equipment through a circuit breaker.
3. Connect the power source last. Disconnect the power source first.
4. Never make wiring changes on live circuits. Work deliberately and care-fully
and check your work as you proceed.
5. Before connecting the power, check your wiring carefully for agreement with
the wiring diagram for an accidental short-circuit and for loose connections.
6. Check out the supply voltage to make sure that is what you expect. For example:
AC or DC, 230V, OR 415V
7. Do not cause short-circuits or high currents arcs. Burn from arcs may be very
severe even at a distance of a few meters. Report all electrical burns to your
instructor. Be careful to keep metallic accessories of apparel or jewelry out of
contact with LIVE CIRCUIT parts and loose articles of clothing out of
moving machinery.
8. When using a multiple range meter always use the high range first to determine
the feasibility of using a lower range.
9. Check the current rating of all rheostats before use. Make sure that no current
overload will occur as the rheostat setting is changed.
10. Check the current rating of all rheostats before use. Make sure that no current
overload will occur as the rheostat setting is changed.
11. Never overload any electrical machinery by more than 125% of the rated voltage
or current for more than a few seconds.
12. Select ratings of a current coil (CC) and potential coil (PC) in a wattmeter
properly before connecting in a test circuit.
13. Do not permit a hot leg of a three phase 415V supply, or of a 230V supply to
come in contact with any grounded objects, as a dangerous short-circuits will
result.

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DO’S & DON’TS IN THE LABORATORY
DO’S:-
1) Proper dress has to be maintained while entering in the Lab. (Boys Tuck in with
apron and shoes, girls with apron)
2) All students should come to the Lab with necessary tools. (Cutting Pliers 6”,
Insulation remover and phase tester)
3) Students should carry observation notes and record completed in all aspects.
4) Correct specifications of the equipment have to be mentioned in the circuit
diagram.
5) Student should be aware of operating equipment.
6) Students should be at their concerned experiment table, unnecessary moment is
restricted.
7) Student should follow the indent procedure to receive and deposit the equipment
from the Lab Store Room.
8) After completing the connections Students should verify the circuits by the Lab
Instructor.
9) The reading must be shown to the Lecturer In-Charge for verification.
10) Students must ensure that all switches are in the OFF position, all the
connections are removed.
11) All patch cords and tools should be placed at their original positions.
DON’Ts:-
1) Don‟t come late to the Lab.
2) Don‟t enter into the Lab with Golden rings, bracelets and bangles.
3) Don‟t make or remove the connections with power ON.
4) Don‟t switch ON the supply without verifying by the Staff Member.
5) Don‟t switch OFF the machine with load.
6) Don‟t leave the lab without the permission of the Lecturer In-Charge.

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INDEX
Sl No Contents Page No
1. PREFACE 2
2. LABORATORY SAFETY RULES 3
3. DO‟S & DON‟TS 4
4. VTU SYLLABUS 5
5. INDEX 6
6. CERTIFICATE 7
7. INTRODUCTION 8
8. INSTRUCTION TO STUDENTS 9
9. LAB CYCLES 10
10.
OPEN CIRCUIT AND SHORT CIRCUIT TESTS ON SINGLE PHASE STEP
UP OR STEP DOWN TRANSFORMER AND PREDETERMINATION OF
(I) EFFICIENCY AND REGULATION
(II) CALCULATION OF PARAMETERS OF EQUIVALENT CIRCUIT
11
11.
SUMPNER‟S TEST ON SIMILAR TRANSFORMERS AND
DETERMINATION OF COMBINED AND INDIVIDUAL
TRANSFORMER EFFICIENCY.
15
12.
PARALLEL OPERATION OF TWO DISSIMILAR SINGLE-PHASE
TRANSFORMERS OF DIFFERENT KVA AND DETERMINATION OF
LOAD SHARING AND ANALYTICAL VERIFICATION GIVEN THE
SHORT CIRCUIT TEST DATA.
18
13.
POLARITY TEST AND CONNECTION OF 3 SINGLE-PHASE
TRANSFORMERS IN STAR – DELTA AND DETERMINATION OF
EFFICIENCY AND REGULATION UNDER BALANCED
RESISTIVE LOAD.
20
14.
COMPARISON OF PERFORMANCE OF 3 SINGLE-PHASE
TRANSFORMERS IN DELTA – DELTA AND V-V (OPEN DELTA)
CONNECTION UNDER LOAD.
23
15.
SCOTT CONNECTION WITH BALANCED AND UNBALANCED
LOADS.
26
16.
SEPARATION OF HYSTERESIS AND EDDY CURRENT LOSSES
IN SINGLE PHASE TRANSFORMER.
29
17.
VOLTAGE REGULATION OF AN ALTERNATOR BY EMF AND
MMF METHODS.
33
18. VOLTAGE REGULATION OF AN ALTERNATOR BY ZPF METHOD. 38
19.
SLIP TEST – MEASUREMENT OF DIRECT AND QUADRATURE
AXIS REACTANCE AND REDETERMINATION OF REGULATION
OF SALIENT POLE SYNCHRONOUS MACHINES.
40
20.
PERFORMANCE OF ASYNCHRONOUS GENERATOR
CONNECTED TO INFINITE BUS, UNDER CONSTANT POWER
AND VARIABLE EXCITATION & VICE - VERSA.
43
21. POWER ANGLE CURVE OF SYNCHRONOUS GENERATOR. 47
22. VIVA QUESTIONS 51
23. SAFETY & COMMON SYMBOLS 53

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Department of Electrical and Electronics
Engineering
CERTIFICATE
This is to certify that this book is a bonafide record practical work
done in the Electrical Machines- 1 Laboratory in 3rd
semester
of………yearduring the year….......
Name:-……………………………
Roll. No. :-……………………………
Branch:-……………………………
Date:-……………
Signature of the Staff member

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INTRODUCTION
“A practical approach is probably the best approach to mastering a subject and gaining a clear insight.”
ELECTRICAL MACHINES LABORATORY - I Sub Code: 15EEL38
Practical session covers those practical oriented Electrical AC Machines that are very essential for
the students to solidify their theoretical concepts. This workbook provides a communication bridge between
the theory and practical world of the Electrical Laboratory. The knowledge of these practical are very
essential for the engineering students. All of these practical are arranged on the modern trainer boards.
The program starts with courses of providing in-depth coverage of basic topics related to the field of
electrical machines such as Testing of transformers, rotating machines, ac power Generation. The program
then builds on the knowledge gained by the student through these basic courses to provide training
synchronous generator, and asynchronous generator technologies
This manual, teaches the basic concepts of three-phase transformer banks. Students are introduced to
the different characteristics of Single/three-phase transformer banks. They learn how to connect the
windings of three-phase transformer banks in wye or delta. Students are also determining the voltage,
current, and phase relationships between the primary windings and the secondary windings of three-phase
transformer banks of various configurations. They learn how to ensure proper phase relationships between
the phase windings. Students also verify the theory presented in the manual by performing circuit
measurements and calculations.

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INSTRUCTIONS TO THE STUDENTS
1. WEAR SHOES COMPULSORILY
2. SHIRTS SHOULD BE TUCKED IN
3. GIRLS SHOULD PROTECT THEIR HAIR
4. DO NOT ALLOW CHAINS TO HANG
5. DO NOT LEAN OVER ROTATING MACHINERY
6. ENERGIZE THE CIRCUIT ONLY AFTER GETTING APPROVAL FROM THE FACULTY IN-
CHARGE
7. MAKE SURE THAT THE CORRECT SWITCH HAS BEEN SWITCHED ON/OFF BEFORE/AFTER
THE EXPERIMENT.
MAKING CONNECTIONS
• Make sure that the supply is OFF.
• Meters should be positioned properly.
• Do not connect more than one wire to each terminal of ammeters & voltmeters.
• Make series connections before parallel connections.
• All the connections should be tight.
• Get the connections checked before switching ON.
• Check the position of rheostats, autotransformers, switches before switching ON.
• Never exceed the permissible values of current or voltage.
• While conducting brake test, pour water on the brake drum to avoid overheating.
• Show the readings to the faculty-in-charge before switching off.
ROUGH RECORD
1. Write Name of the experiment with number & date, aim, apparatus required, neat circuit diagram,
tabulations, sample calculations (for one set of readings showing the substitution of the values) and results.
No need to write principle or procedure.
2. Take at least six sets of readings, if possible. Each student in a group should do sample calculations for
different sets.
3. Get signature of the faculty-in-charge after completing the rough record.
FAIR RECORD
1. Write the name of the experiment on the top of the right side in capital letters
2. Experiment Number & date should be written at the top.
3. Each record should contain the following on the right side
• Aim of the experiment
• Apparatus required
• Principle
• Procedure
• Sample Calculation (on the left side if possible; if calculations are too long, write onright side so that no
pages on the right side are left blank) Result (at the end)
4. On left side
• Neat circuit diagram with PEN
• Name plate details/specifications
• Tabulations
• Sample Calculation (on the left side if possible; if calculations are too long, write on the right side so that
no pages on the right side are left blank)
• Graph (draw with PEN if possible; use different colors for different graphs on the same graph sheet).
DO EXPERIMENT TODAY; SUBMIT ROUGH RECORD IN THE NEXT CLASS & FAIR
RECORD IN THE THIRD CLASS.

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ELECTRICAL MACHINES LABORATORY - I Sub Code: 15EEL38
LAB CYCLE-1
1 Open Circuit and Short circuit tests on single phase step up or step down
transformer and predetermination of (i) Efficiency and regulation (ii)
Calculation of parameters of equivalent circuit.
2 Sumpner‟s test on similar transformers and determination of combined and
individual transformer efficiency.
3
Parallel operation of two dissimilar single-phase transformers of different kVA
and determination of load sharing and analytical verification given the Short
circuit test data.
4 Polarity test and connection of 3 single-phase transformers in star – delta and
determination of efficiency and regulation under balanced resistive load.
5 Comparison of performance of 3 single-phase transformers in delta – delta and
Y– Y (open delta) connection under load.
6 Scott connection with balanced and unbalanced loads.
7 Separation of hysteresis and eddy current losses in single phase transformer.
LAB CYCLE-2
8 Voltage regulation of an alternator by EMF and MMF methods.
9 Voltage regulation of an alternator by ZPF method.
10 Slip test – Measurement of direct and quadrature axis reactance and
predetermination of Regulation of salient pole synchronous machines.
11
Performance of synchronous generator connected to infinite bus, under constant
power and variable excitation & vice - versa.
12 Power angle curve of synchronous generator.

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EXPERIMENT NO:-01 DATE:
O.C. TEST S.C. TEST & LOAD TEST ON A SINGLE PHASE TRANSFORMER.
Objective:
To determine the iron losses, copper losses and efficiency of a transformer at any given load.
Apparatus:
Sl. No. Instruments Qty.
1 0-1 Amps Ammeter 01
2 0-5 Amps Ammeter 01
3 0-300 Volts Voltmeter 01
4 0-200 Watts L.P.F. type Wattmeter 01
5 0-3.0 KW U.P.F. type Wattmeter 01
Transformer Ratings:
Power: 1 KVA, Primary/Secondary :230/230 Volts. Max Current Rating : 4.43 Amps.
Circuit Diagram:
Procedure:
FOR O.C. TEST
1) Connect the circuit as shown.
2) Ensure that the dimmerstat Position is at zero.
3) Switch on the single phase AC. Supply.
4) Apply rated voltage of 230V, to the primary side of transformer.
5) Note the ammeter, voltmeter and wattmeter readings.

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OR S.C. TEST
1) Connect the circuit as shown.
2) Ensure that the dimmerstat position is at „0‟ (zero).
3) Switch on the single phase AC. Supply.
4) Slowly increase the output voltage of the dimmerstat till the ammeter on
primary side shows rated current of 4.35 amp.
5) Note the ammeter, voltmeter & wattmeter readings.
Precautions:
1) All the connections should be perfectly tight.
2) Supply should not be switched ON until& unless the connections are checked by the instructor.
3) Do not bend while taking the readings
4) No loose wires should lie on the work table.
5) Thick wires should be used for current circuit and flexible wires for voltage circuits.
6) The multiplying factor of wattmeter should be correctly used.
Observations:
FOR O.C.TEST (Read on primary side.)
Rated input Voltage
V0
No load current
I0
No load power
W0
230V
FOR S.C. TEST (Read on primary side)
Short circuit voltage
Vsc
Rated primary current
(i.e full load value)
Isc
Short circuit power
Wsc
4.35amp

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Calculations:
FOR O.C. TEST
No load power factor =cos<Do = Wo / (Vo Io) Magnetising
component of Io = Iµ = Io sin<Do amps.
Core loss component of Io = Ic = Io cos<Do amps.
Core loss resistance Ro = Vo/ Ic ohm.
Magnetising reactance Xo = Vo/ Iµ ohms. FOR S.C. TEST
Short circuit power factor cos<Dsc = Wsc/ (Vsc Isc) Short circuit
impedence Zsc =Vsc / Isc Q
Short circuit resistance Rsc = Wsc / Isc2
Q
Short circuit reactance Xsc = --√ Zsc2
-Rsc2
Copper loss in transformer at full load =Wsc watts.
Copper loss in transformer at half full load = Wsc/4 watts.
EFFICIENCIES:
1) At full load and at 0.8 power factor
Full load kVA x103
x cos<D x 100
η =
Full load KVA x103
x cos<D +core loss +copper loss at full load
2) All half full load and U.P.F.
Half load KVA x 103
x cos<D x100
η =
Half load KVA x 103
x cos<D + core loss + copper loss at half load
REGULATIONS:
1) At full load and 0.8 power factor lagging.
Voltage drop = Isc (Rsc cos<D + Xsc sin<D)
% Regulation = Voltage drop x100
Rated primary voltage (Vo)
2) At full load and 0.8 power factor leading.
Voltage drop = Isc (Rsc cos<D – Xsc sin<D)
Voltage drop x100
% Regulation =
3) At full load and U.P.F.
Voltage drop = Isc Rsc cos<D
% Regulation = Voltage drop x100

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Equivalent Circuit:
Draw simplified equivalent circuit showing calculated values of all parameters on it.
Result: - Full load efficiency at 0.8 p.f. =
Full load efficiency at U.P.F. =
Full load regulation at 0.8 lagging p.f. =
Full load regulation at 0.8 leading p.f. = Full load
regulation at U.P.F. =
Ro = ; Xo =
Rsc = ; Xsc =
Viva Questions: -
Q.1. What is the significance of O.C. & S.C. test?
Q.2. Why h.v. winding is kept open during O.C. test and 1.v. winding is shorted during S.C. test in
case of large transformers?
Q.3. In O.C. test, a voltmeter is connected across secondary winding and still it is
called as O.C. test. Why?
Q.4. What will happen if dc supply instead of ac supply is applied to a transformer? Q.5. Which is the
alternate method for finding efficiency and regulation of atransformer other than O.C. & S.C. tests ?
What are their advantages over each other?
Q.6. What is the importance of equivalent circuit?
Q.7. Why regulation of transformer is negative for leading p.f. load?
Q.8. “ The wattmeter reading during O.C. test is considered as core loss while wattmeter reading during
S.C. test is considered as copper loss” Justify

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Sumpner’s Test
Objective : To predetermine the efficiency, regulation and equivalent circuit of a given pair of
identical single - phase transformers by conducting Sumpner's test.
Name plate details of the two identical transformers:
Primary voltage : 230 Volts Secondary voltage: 230 Volts
Primary current : 4.34 Amps Secondary current 4.34 Amps Power
(Burden) : 1 KVA Frequency: 50 Hz.
Apparatus:
Digital voltmeter,0 to 1000Volts 02
Digital ammeter, 0 to l0 Amps 02
wattmeter, 0 to 300 Watts 02
Digital temperature indicator, 0 to 100
Degrees
01
Theory:
The efficiency of a transformer can be predetermined by conducting o.c. and s.c. tests. But the
rise in temperature can be found only by conducting the actual load test. It is difficult io conduct the
actual load test for large transformers. [n case of Sumpner‟s test the efficiency, regulation and rise in
temperature can be obtained with small amount of power consumption.
In Sumpner's test, the two primary windings of the identical transformers are connected in parallel
across the supply and the two secondary‟s are connected in series with their polarities in opposition. One
digital wattmeter (L.P.F. type), one voltmeter and one ammeter are connected
at primary side. One digital wattmeter (U.P.F: type), one voltmeter and one ammeter are connected at
secondary side. If primaries are energized then the voltage across the two secondaries will be zero since
both the transformers are identical transformers.
The power input to the transformers at no-load is indicated by the wattmeter on the primary
side. This power is, equal-to the iron losses of the two transformers. An auto-transformer is connected
in series with the two secondary‟s. A small voltage is injected in the secondary circuit from a separate ac
source. It will circulate a current in the secondary side since the secondary‟s are in opposition, the
secondary current will cause primary current in opposite directions so that the reading of wattmeter on
primary is not affected and it will indicate the iron losses of the two transformers. The auto-transformer is
adjusted till the full load current flows in the secondary side of the transformer. At full load current the
wattmeter on the secondary side indicates the full load copper losses of the two transformers.
Procedure:
* Make all the connections as per the circuit diagram shown in fig .Z.Z.
* Keep the switch 's' open on the secondary side of the transformer.
* Keep the auto-transformer at zero position and disconnect the supply to
the auto transformer.
* Apply the normal voltage of 230Volts to the primary side.
* Check the voltmeter reading across the switch. If it reads zero, it means the secondary‟s are
connected in opposition. If the voltmeter reads twice the secondary rated voltage then the connections
should be reversed on the secondary side.
* lf voltmeter reads zero close the switch .S'.
* Connect the supply to the auto-transformer and energize the secondary circuit and adjust the auto
transformer till the ammeter on the secondary side reads the rated current (4.82A).
* Record the readings of the meters on both the primary and secondary
sides.
* Calculate Req , xeq , regulation and efficiency of the transformer 0.8 pf lag, 0.8pf lead and upf for
full

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Procedure: 1) Make the connections as shown in circuit diagram.
2) Keep switches S2 & S3 open and the dimmerstats at zero position.
3) Switch ON the supply and check the correctness of polarities of the two transformers.
If V2 = 0 then polarities of connected transformers are correct i.e. connections are back to back
and emf induced in secondary‟s are in phase opposition but if V2 = 2xKxV1, then secondary
emf‟s are in phase, in that case change the polarities of any one secondary winding.
4) Note down the readings of V1, I1 and W1
5) Now close switch S and increase dimmerstat output voltage gradually so that full
load current flows through secondary windings.
6) Note down V2 , I2 and W2. While doing so , the values shown by V1, I1 and W1 should not
deviate from their earlier readings.
Observation Table:
SR.
No.
Primary
voltage
V1
Primary
current
I2
Primary
power
Iron loss W1
Secondary
voltage
V2
Secondary
Current
I2
Secondary
power
Cu. Loss W2
Calculations:
Iron loss per transformer Wi = W1 / 2
Copper loss per transformer Wcu = W2 / 2

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Out put Power
% Efficiency = ------------------------------ x 100
Output Power + Losses
kVA x Cos <D
% lJ = ------------------------------------------------ x 100
kVA x Cos <D + Iron loss + Cu. Loss
With the help of above equation, calculate efficiency at
1. Full load , UPF
2. Half full load and 0.8 p.f. lagging.
Results: It is found that,
i) % Efficiency at F.L. & unity power factor =
ii) % Efficiency at half full load & 0.8 power factor (lag.) =
Viva Questions:
1. What is the condition to be satisfied by the two transformers to be tested using this method?
2. What is the main advantage of this test?
3. Other than losses and efficiency, what else can be determined from this test?
4. How are the full load conditions simulated?
5. How are the losses separated?

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EXPERIMENT NO:- 03 DATE:
Parallel Operation Of Two Single Phase Transformers
AIM:-
To operate the given two 2KVA,and 1 KVA 230/230 V single phase Transformers in parallel and
study the load sharing between them when supplying resistive load .
NAME PLATE DETAILS:
1Φ - TRANSFORMERs
T/F T/F-1 T/F-2
HV side LV side HV side LV side
Rated power
Rated voltage
Rated current
Frequency
APPARATURS REQUIRED:
SL.
NO
Name of the
Apparatus
Type Range Quantity
1 Ammeter MI
2 Ammeter MI
3 Voltmeter MI
4 Voltmeter MI
5 Wattmeter EDM(LPF)
6 Wattmeter EDM(UPF)
7 Dimmerstat
THEORY
Transformers may be connected in parallel to supply currents greater than rated for each transformer. Two
requirements must be satisfied:
1) The windings to be connected in parallel must have identical output ratings;
2) The windings to be connected in parallel must have identical polarities.
Severe damage may be made to circuitry if these requirements are not satisfied , KVA Ratings may vary.
Two transformers with different kVA‟s, same percent impedances, are connected to one common bus. In this
situation, the current division causes each transformer to carry its rated load. There will be no circulating
currents because the voltages (turn ratios) are the same.
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.

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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
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

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EXPERIMENT NO:- 04 DATE:
STAR-DELTA CONNECTION POLARITY TEST AND STAR-DELTA CONNECTION
Aim: To test the polarity of three single phase transformers and to determine the Efficiency and Regulation
for Star-Delta connection for balanced and Unbalanced loading (UPF)
Apparatus Required:
Sl.
No.
Particulars Ranges Quantity
1
Ammeter (MI) 0-2.5/5 A
0-10 A
2
2
2 Wattmeter
(UPF)
500V, 1 / 2 A
250V,2.5 A
2
2
3 Voltmeter (MI)
0-500 V
0-250 V
2
2
4
Digital
Multimeter
-- 1
Procedure for 3 phase Transformer Connection:
* Polarity Testing:
1) Connections are made as shown in the circuit diagrams(1).
2) Keeping load switches open and auto transformer at zero position, the supply switch is closed.
3) A small voltage (say 50 v) is applied to the primary by gradually varying single phase auto-transformer and the
reading of digital multimeter is noted down.
4) The single phase auto-transformer is brought back to its initial zero output position and the supply switch is
opened
5) Connections are made as shown in the circuit diagram(2).
6) Above procedure is repeated.
Three 1-Phase Transformer Connection ( Star-Delta)
1) Connections are made as shown in the Circuit diagram(3)
2) Keeping the load minimum and the 3-phase auto-transformer at zero output voltage position supply switch is
closed.
3) Rated voltage is applied by gradually varying the 3-phase auto-transformer.
4) Gradually the load is applied and at each step all the meter readings are noted down.
5) Load is applied until the rated current of transformer reached.
Gradually the load is decreased, 3-phase auto-transformer is brought back to its initial zero output voltage position
and the supply switch is opened.

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CIRCUIT DIAGRAM

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Observation Table:
No-load secondary voltage E2 = ---------- Volts
Sr.No. I1Amp V1 Volts W1 Watts I 2 Amp V2 Volts W2 Watts % Reg % lJ
1
2
3
4
5
Calculations:
O/ Power W2
% η = -------------------- x 100
I/P power W1
No load voltage (E2) – voltage at load (V2)
% Reg = ---------------------------------------------------------- x 100
No load voltage (E2)
Graph: Plot the graph output Power Vs efficiency.
Precautions:
1) All the connection should be perfectly tight.
2) Supply should not be switched ON unstill & unless the connection are checked by the teacher.
3) Do not bend while taking the readings.
4) No loose wire should lie on the work-table.
5) Thick wire should be used for current circuit and flexible wires for voltage circuits.
6) The multiplying factor of wattmeter should be correctly noted.
Result: The % efficiency & regulation of transformer at full load condition is found as follows.
Percentage efficiency = ------------------%
Percentage regulation = ------------------%
Conclusion: Transformer efficiency initially increases as the load on transformer is increased.
After maximum efficiency if we increase the load further, the efficiency of transformer reduces.
Also terminal voltage reduces as the load is increased
Viva Questions:
1. What is the condition for max efficiency?
2. What is the condition for zero voltage regulation?
3. Which is the other method of finding efficiency and regulation?
4. Draw phasor diagram of transformer at full load and 0.5 p.f. lagging.
5. Draw phasor diagram of transformer at full load and 0.5 p.f. leading.

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AIM:
Comparison Performance of 3 Single-Phase Transformers in Delta – Delta and V - V (Open Delta)
Connection Under Load.
Open-Delta or V-V Connection (Theory)
If one of the transformers of a Δ-Δ is removed and 3- phase supply is connected to the primaries as
shown in Fig: A1 then 3 equal 3-phase vol t ages w i l l b e availableat the secondaryterminals on no-
load.
It is employed:
1. When the three phase load is too small to warrant the installation of full three-phase transformer bank.
2. When one of the transformers in a Δ-Δ bank is disabled, so that service is continued although at reduced
capacity, till the faculty transformer is repaired or a new one is sustained.
3. When it is anticipated that in future the load will increasenecessitatingthe closing of open delta.
Δ-Δ capacity = Δ 3VL.IL= Δ 3VL.( Δ 3IS)=3VLIS
In Fig: A2 it is obvious that when Δ-Δ bank becomes V-V bank, the secondary line current IL becomes
equal to the secondary phase current IS.
V-V capacity = 3VL.IL=3VL.IS (Since line current and phase current are equal)
It means that the capacity of V-V transformer is 57.7 %( or 1/3 times) of the capacity of -conn,
The disadvantages of V-V connection are:
1. The average power factor at which the V-bank operates is less than that of the load. his power
factor is actually 86.6 of the balanced load power factor.
2. Secondary terminal voltages tend to become unbalanced to a great extent when the load is
increased, this happens even when the load is perfectly balanced.
Fig A1 Fig A2

``
Observation Table Δ-Δ for Balanced Load:
1
2
3
4
5

``
Observation Table V – V for Balanced Load:
1
2
3
4
5
Calculations:
O/ Power W2
% η = -------------------- x 100
I/P power W1
No load voltage (E2) – voltage at load (V2)
% Reg = ---------------------------------------------------------- x 100
No load voltage (E2)
CONCLUSION
You set up a three phase transformer in the open ∆ configuration and observed that it supplies a 3phase
load with voltages and currents in the proper phase relationships. You also demonstrated that load power
must be reduced by 57.7% (1/√3) to avoid exceeding the current rating of the phase windings

``
EXPERIMENT NO: 06 DATE:
SCOTT CONNECTION
AIM : To convert three phase system to two phase system with the help of scott Connection
NAME PLATE DETAILS:
T/F T/F-1 T/F-2
HV side LV side HV side LV side
Rated power
Rated voltage
Rated current
Frequency
APPARATURS REQUIRED:
SL.
NO
Name of the
Apparatus
Type Range Quantity
1 Ammeter MI
2 Ammeter MI
3 Voltmeter MI
4 Voltmeter MI
7 Dimmer stat --
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
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.)
Theory: It should cover the following.
1. Explanation and mathematical proof of how a balanced two-phase supply can be obtained by using Scott

``
connection.
2. Phasor diagram illustrating the phase quadrature between the secondary voltages of the two transformers.
Procedure:
1. Connect the circuit as shown.
2. Use 86.6% tapping for teaser transformer and 50% tapping for main transformer.
3. Keep both loads zero
4. Switch on the 3-ph. supply and take the readings.
5. Vary the loads as per given in observation table and take the readings
Observation Table:
[A] FOR BALANCED LOAD
S.
No.
Load condition Teaser transformer Main transformer
I1T I2T V1T I1M I2M V1M V2M
1.
2.
No load
1kW load on
both
transformers
[B] FOR UNBALANCED LOAD
S.
No.
Load condition Teaser transformer Main transformer
I1T I2T V1T I1M I2M V1M V2M
1.
2.
1kW load on
Teaser
transformer
1kW load on
Main
transformer

``
Calculations:
Conclusion:
The 3 – Phase to two phase conversion was verified. i.e. 3 – phase system can be converted in to two
phase system using Scott-connections.
Viva Questions:
1) Is it possible to obtain a 3- phase a.c. supply from 2 – phase a.c. supply by using Scott-connection ?
2) Where dose the Scott-connection find its use?
3) If the two transformers used in Scott. Connection are identical, then how many primary turns of the teaser
transformer are actually used?
4) What is the ratio of number of turns on the primaries of teaser transformer in case of Scott-connection?
5) Are the two transformers connected for Scott-connection coupled magnetically?
6) Do you know any other method of conversion of 3-phese a.c. supply from 2-phese a.c. supply?

``
EXPERIMENT NO: 07 DATE:
SEPARATION OF EDDY CURRENT AND HYSTERESIS LOSSES
Aim:To separate the eddy current loss and hysteresis loss from the iron loss of single phase transformer.
APPARATUS REQUIRED:
S. No. Name of the Apparatus Range Type Quantity
1 Rheostat 1250Ω , 0.8A Wire Wound 2
2 Wattmeter 300 V, 5A LPF 1
3 Ammeter (0-2) A MC 1
4 Voltmeter (0-300) V MI 1
5 Connecting Wires 2.5sq.mm Copper Few
PRECAUTIONS:
1. The motor field rheostat should be kept at minimum resistance position.
2. The alternator field rheostat should be kept at maximum resistance position.
PROCEDURE:
1. Connections are given as per the circuit diagram.
2. Supply is given by closing the DPST switch.
3. The DC motor is started by using the 3 point starter and brought to rated speed by adjusting its field rheostat.
4. By varying the alternator filed rheostat gradually the rated primary voltage is applied to the transformer.
5. The frequency is varied by varying the motor field rheostat and the readings of frequency are noted and
the speed is also measured by using the tachometer.
6. The above procedure is repeated for different frequencies and the readings are tabulated.
7. The motor is switched off by opening the DPST switch after bringing all the rheostats to the initial position

``
TABULAR COLUMN:
Sl.No. Speed
N (rpm)
Frequency
f (Hz)
Voltage
V (Volts)
Wattmeter
reading
Watts
Iron loss
Wi (Watts)
Wi / f
Joules
FORMULAE USED:
1. Frequency, f =(P*NS) / 120 in Hz P = No.. of Poles & Ns = Synchronous speed in rpm.
2. Hysteresis Loss Wh = A * f in Watts A = Constant (obtained from graph)
3. Eddy Current Loss We = B * f2 in Watts B = Constant (slope of the tangent drawn to the curve)
4. Iron Loss Wi = Wh + We in Watts Wi / f = A + (B * f)
Here the Constant A is distance from the origin to the point where the line cuts the Y- axis in the graph
between Wi / f and frequency f. The Constant B is Δ(Wi / f ) / Δf
B = y/x
RESULT:
Thus separation of eddy current and hysteresis loss from the iron loss on a single-phase transformer is
conducted.
y
x
A
Wi/f
Frequency f

``
REGULATION OF ALTERNATOR BY EMF AND MMF METHODS
Aim:
To pre-determine the voltage regulation of an alternator by using EMF and MMF methods.
Apparatus Required:
Precautions:
1. The Motor field rheostat must be kept at the minimum resistance position at the time of starting.
2. The generator field rheostat must be kept at the maximum resistance position.
3. Three point starter should be kept at the off position initially.
Procedure:
Open Circuit Test:
1. Give the connections as per the circuit diagram.
2. Close the DPST switch on the supply side.
3. The speed of DC motor is adjusted to rated speed by using the motor field rheostat.
4. Keeping the TPST switch open on alternator side vary the alternator field current in convenient steps till
rated field current of alternator.
5. Note the corresponding values of alternator field current and alternator voltage.
6. Bring the alternator field rheostat to the original position.

``
Short Circuit Test:
1. The same circuit is used.
2. The rotor TPST switch is closed.
3. The field current of the alternator is slowly increased from zero to the rated current of the alternator by
adjusting the field rheostat of the alternator.
4. The field current corresponding to the rated current of the alternator is alone noted in tabular column.
5. Reduce the field current of the alternator to zero.
6. Now open all the switches.
Armature resistance test:
1. Connections are made as per the circuit diagram.
2. The control resistance is initially kept at either maximum resistance or open position.
3. Observing the precautions the DPST switch is closed
4. The readings of ammeter and voltmeter are noted.
5. The ratio of V
a
to I
a
gives the value of armature resistance (R
a
).
Circuit diagram:

``
Regulation of alternator by EMF and MMF method

``
Model calculation:
HOW TO DRAW THE GRAPH FOR EMF METHOD:
i) Draw the open circuit characteristics curve (V vs. If).
ii) Draw the short circuit characteristics curve (short circuit current Vs If).
iii) From the graph find the open circuit voltage per phase ( E1(ph)) for the rated short circuit current ( Isc).
iv) By using respective formulae find the Zs, Xs, Eo and percentage regulation.
HOW TO DRAW THE GRAPH FOR MMF METHOD:
i) Draw the open circuit characteristics curve (V vs. If).
ii) Draw the short circuit characteristics curve (short circuit current Vs If).
iii) Draw the line OL to represent If, which gives the rated generated voltage (V).
iv) Draw the line LA at an angle (90 +or –Ф) to represent If which gives the rated full load current (Isc) on short
circuit. {(90+Ф) for lagging power factor and (90-Ф) for leading power factor.
v) Join the points O and A and find the field current (if) by measuring the distance OA that gives the open circuit
voltage (Eo) from the open circuit characteristics.
vi) Find the percentage regulation by using suitable formula.
VIVA QUESTIONS:
1) What are synchronous machines?
The machines generating ac emf are called alternating or synchronous generators. While the machine accepting input
from ac supply to produce mechanical output are called synchronous motors. Both these machines work at a specific
constant speed called synchronous speed and hence in general called synchronous machines.
2) Define voltage regulation. Name two methods used to determine voltage regulation of alternators.
%Reg = E-Vrated / Vrated *100 Where E = No load voltage Vrated = Rated voltage
Two methods to determine voltage regulation:
i) EMF method
ii) MMF method
3) What are the two types of alternators?
i) Non salient pole alternator
ii) Salient pole alternator.
4) State the principle of alternator.
When the rotor is rotated by the prime mover, the stator windings or conductors are cut by the magnetic flux hence an
emf is induced in the stator conductors. (Faraday‟s law of electromagnetic induction).

``
5) Is EMF method an accurate method?
No, it is not an accurate method because the value of synchronous impedance found is always more than the original
value.
6) Write the emf equation of an alternator.
E = 4.44f ФTKcKd volts
Where, f = frequency in hertz
Ф = flux per pole
T = Number of turns in stator windings
Kc = Pitch factor
Kd = Distribution factor
4) What is known as Armature reaction?
The effect of armature flux on main flux is called as armature reaction.
5) What is meant by synchronous reactance?
Synchronous reactance Xs = Xl + Xa
Xl = leakage reactance
Xa = Armature reactance
7) Can a DC generator be converted into an alternator? How?
Yes, by providing two collector rings on end of the armature and connecting these two rings to two points in the
armature windings 180 degree apart.
8) What is the other name for EMF and MMF method?
The other name for EMF method is called as Synchronous impedance method and MMF method is called as Ampere
turn method.
EMF method – Pessimistic method
MMF method – Optimistic method

``
Aim:- To find the regulation of 3Φ Alternator by ZPF & ASA Method, comparing the values obtained by two
methods
Name plate details:-
Apparatus
:- S.No
Name of
the Item
Type Range Qty
1
2
3
4
5
6
Procedure:-
O.C Test:-
1) Give all connections as per the circuit diagram.
2) switch-ON the supply & by varying the starter, prime mover Speed is adjusted to rated.
3) Now keeping the field current at zero, note the induced emf in Armature duo to residual Magnetism.
4) By slowly varying the potential divider, field current is increased & corresponding emf Induced is noted up to
above 20% of rated voltage.
SC Test:
2) switch-ON the supply & by varying the starter, prime mover
Speed is adjusted to rated.
3) By slowly varying the potential divider, field current is increased
& corresponding short Circuit current is noted up to rated value. To find armature resistance (Ra):
Give the connections as per diagram and by slowly varying the
Rheostat, note the values of ammeter & voltmeter up to some value and average them.

``
Z.P.F Test:-
2) Verify the connections by the instructor.
2) switch-ON the supply & Start the motor with the 3-pont starter, Adjust the rated speed of prime mover by
varying the field rheostat.
3) Gradually increasing the field excitation bring the alternator voltage to rated value
4) Switch on the inductive load and adjust, so that the full load current will flow through the ammeter. In mean
time rated voltage must be maintained.
PROCEDURE TO DRAW THE POTIER TRIANGLE: (ZPF METHOD)
1. Draw the open circuit characteristics curve (Generated voltage per phase Vs field current).
2. Mark the point A at X axis, which is obtained from short circuit test with full load armature current.
3. From the ZPF test, mark the point B for the field current to the corresponding rated armature current and the rated
voltage.
4. Draw the ZPF curve which is passing through the point A and B in such a way parallel to the open circuit
characteristic curve.
5. Draw the tangent for the OCC from the origin (Air gap line).
6. Draw the line BC from B towards Y axis which is parallel and equal to OA.
7. Draw the parallel line for the tangent from c to the OCC curve.
8. Join the point B and D also draws a perpendicular line DE to BC.
DE = Armature leakage reactance drop
BC=Armature reaction excitation
Graph: 1) A graph is drawn b/w If and V which is known as OC curve, by taking If on X-axis and V on Y-axis.
2) A graph is drawn b/w If and ISC which is known as SC curve, by Taking If on X-axis and ISCV on Y-axis.

``
SLIP TEST ON 3-PHASE SALIENT POLE SYNCHRONOUS MACHINE
AIM:
i) To conduct the slip test on 3-phase salient pole synchronous machine
ii) To determine the direct axis and quadrature axis synchronous reactances
iii) To predetermine the voltage regulation at different loads and power factors and
APPARATUS:
S.No. Name of the apparatus Type Range Quantity
1. Voltmeter MI (0-500V) 2
2. MI (0-300V) 1
3 MC (0-30V) 1
4. Ammeter MI (0-10A) 1
5. MC (0-10A) 1
6. Rheostat Wire Wound 9Ω 8.5A 1
7. Tachometer 1
PRINCIPLE:
The direct and quadrature axis reactances can be measured by slip test. The machine is driven by a dc motor at a speed
slightly less or slightly more than synchronous speed. The field winding is kept open circuited and a low voltage 3
phase supply (about 25% of the rated voltage) is applied to the armature terminals. The direction of rotation should be
same as the direction of rotating field. If this condition is fulfilled, a small ac voltage would be indicated by the
voltmeter across the field winding. The relative velocity between armature mmf and field poles is equal to slip speed
i.e. difference between synchronous speed and rotor speed. The stator mmf moves slowly past the field poles at slip
speed. This would cause the armature current to vary cyclicallyat twice the slip frequency. When the peak of the
armature mmf is in line with the fieldpoles, the reluctance offered by the magnetic circuit is minimum, the armature
current,required for the establishment of constant air-gap flux, will be minimum. Constantapplied voltage minus the
minimum impedance voltage drop (armature current being minimum) in the leads and 3-phase variac gives maximum
armature-terminal voltage.The ratio of maximum armature terminal voltage per phase to minimum armature current
per phase gives Zsd. After one quarter of slip cycle, the peak of armature mmf is in line with q-axis and the reluctance
offered by the magnetic circuit is maximum. The armature current, required for the establishment of constant air-gap
flux, will be maximum and the armature terminal voltage will be minimum. The ratio of minimum armature terminal
voltage per phase to maximum armature current per phase gives Zsq.
When the armature mmf is in line with field poles, the armature flux linkage with field winding is maximum and rate
of change of this flux linkage is zero, so that induced voltage across the field winding is zero. On the other hand,
when armature mmf is in line with q-axis, the flux linkage with field winding is minimum and rate of change of this
flux linkage is maximum, so that induced voltage across the field winding is maximum.
.

``
PROCEDURE:
SLIP TEST
Make the connections as shown in figure.
Precautions : i) Keep the autotransformer at minimum voltage position
ii) Keep DPST, TPST and SPST switches open
iii) Keep dc motor field rheostat at minimum resistance position Switch on the d.c. supply by closing the
DPST switch. Using the three point starter, start the motor. Run the motor at synchronous speed by varying the motor
field rheostat. Close the TPST switch. By adjusting the autotransformer, apply 20% to 30% of the rated voltage to the
armature of the synchronous machine. Make sure that the direction of rotation of the prime mover and the direction of
rotation of the magnetic field produced in the armature are the same by closing the SPST switch. If the voltmeter
reading across the alternator field winding is very small, both the directions are correct. If the voltmeter reading is
high, interchange the two lines of 3 phase supply after switching off the 3 phase supply. SPST switch is kept open.
The speed is slightly reduced/increased from synchronous speed, so that slip is increased and the voltmeter and
ammeter readings are oscillating. The maximum and minimum readings of voltmeter and ammeter are noted. The
above said procedure can be repeated with two more different autotransformer settings. (During slip test, it would be
observed that swing of the ammeter pointer is very wide, whereas the voltmeter has only small swing because of the
low impedance voltage drop in the leads and 3-phase autotransformer).

``
2. Explain the working principle of self excited induction generator.
If the rotor of the machine is driven by its prime-mover, the presence of residual flux causes a small emf to get
induced in the stator windings at a frequency proportional to the rotor speed. This voltage impresses over the 3-phase
capacitor gives rise to leading current drawn by the capacitor which is equivalent to lagging current supplied to the
generator. The flux set up by this current assists the initial residual flux. Hence the net flux will increase causing the
voltage to build up further. The steady state voltage induced on no load is given by the intersection of magnetization
characteristic of the machine and capacitance V-A characteristic. The frequency generated is slightly less than that
corresponding to the speed of rotation. The terminal voltage of the generator increases with the capacitance, but its
magnitude is limited by saturation in the iron. If the capacitance is insufficient, the generator voltage will not build
up. The capacitor bank must be able to supply at least as much reactive power as the machine normally absorbs when
operating as a motor.
3. In case of a line-excited induction generator, how the slip is affecting the
active power delivered?
The active power delivered to the line is directly proportional to the slip above synchronous speed. Thus, a higher
prime-mover speed produces a greater electrical output.
4. What you mean by single phasing?
Single phasing is a fault condition in which a 3 phase motor is operating with one line open (due to blowing of a fuse
in one phase). Although the 3 phase motor will not start with one line open, if the motor is running when single
phasing occurs, it will continue to run as long as the shaft load is less than 80% rated load and the remaining
single phase voltage is normal; rotation of the rotor produces a quadrature field that maintains the rotation.
.5. Draw the torque-slip characteristics of an induction
machine

``
EXPERIMENT NO. 11
SYNCHRONIZATION OF ALTERNATOR TO INFINITE BUS AND DETERMINATION OF
PERFORMANCE UNDER CONSTANT POWER AND VARIABLE EXCITATION & VICE-VERSA.
Aim
To operate the Alternator on
Infinite Bus.
Constant Power and Variable Excitation.
Variable Excitation and Constant Power.
Apparatus Required
Sl.No. Particulars Range Type Quantity
01 Voltmeter 0 – 500 V MI 01
02 Ammeters
0-1/2A
0-5/10A
M
C
MI
01
01
03 Rheostats
0-750Ω,1.2A
0-38Ω,8.5A
-
-
02
01
04 Watt meters
10/20A,
0 – 600 V
LP
F
02
05 Tachometer - - 01
Procedure
a. Operation on Infinite Bus Bar
1. Connections are made as shown in the circuit diagram (4.a)
2. Keeping the rheostat R1 in the field circuit of motor in cut-out position, the rheostat R2 in the
armature circuit of motor and the rheostat R3 in the field circuit of alternator in cut-in positions,
the bus bar switch (S2) and synchronizing switch (S3) in open positions, the supply switch (S1)
is closed.
3. The motor is brought to the synchronous speed of the alternator by gradually
cutting out the rheostat R2 and cutting in the rheostat R1, if necessary.
By gradually cutting out the rheostat R3, the alternator voltage is built-up to the bus bar
voltage.
4. Now, bus bar switch (S2) is closed, and the phase sequence is verified. For correct phase
sequence, all the lamps will flicker simultaneously. Otherwise, they flicker
alternately. If they flicker alternatively, the bus bar voltage switch is opened and any two
terminals of the bus bar supply are interchanged.
5. Repeat step number 2, 3 and 4.
6. By varying the rheostats R1, R2 and R3 the dark period of the lamps are obtained.
7. When all the lamps are in dark condition, the synchronization switch S3 is closed and now the
alternator is connected in parallel with the bus bar.
8. Switches (S3) and (S2) are opened; all the rheostats are brought back to their
respective initial positions, and supply switch (S1) is opened.

``

``
b. Constant Power - Variable Excitation Operation
1. Connections are made as shown in the circuit diagram (4.b)
2. Follow the procedure steps 2, 3.
3. By gradually cutting out the rheostat R3, the alternator voltage is built-up to its rated voltage.
4. Apply load gradually.
5. Vary generator excitation (R3) to keep wattmeter readings constant (Total Power).
6. Tabulate the readings.
7. Bring back the load to zero, reduce the excitation to a normal value and all rheostats are brought
back to respective initial positions & supply switch (S1) is opened.
c. Constant Excitation - Variable Power Operation
1. Connections are made as shown in the circuit diagram (4.b)
2. Follow the procedure steps 2, 3.
3. By gradually cutting out the rheostat R3, the alternator voltage is built-up to its rated voltage.
4. Apply load in steps & note down all meter readings (Excitation should be constant by
adjusting the speed of the Motor).
5. Bring back the load to zero, reduce the excitation to a normal value and all rheostats are brought
back to respective initial positions & supply switch (S1) is opened.
Tabular Column
1. Constant Power - Variable Excitation Operation
Sl.
No.
If
(A)
Power
(W1+W2)
Speed
(RPM)
Voltage
(V)
I
L
(A)

``
2. Constant Excitation - Variable Power Operation
Sl.
No.
If
(A)
Power
(W1+W2)
Speed
(RPM)
Voltage
(V)
I
L
(A)

``
POWER ANGLE CURVE OF 3-PHASE SALIENT POLE SYNCHRONOUS MACHINE
APPARATUS:
S.No. Name of the apparatus Type Range Quantity
1. Voltmeter MI (0-500V) 2
2. MI (0-300V) 1
3 MC (0-30V) 1
4. Ammeter MI (0-10A) 1
5. MC (0-10A) 1
6. Rheostat Wire Wound 9Ω 8.5A 1
7. Tachometer 1

``

``
VIVA QUESTIONS

``

``
VIVA QUESTIONS GENERAL
1. What is a Generator?
A Generator is a machine which converts Mechanical Energy into Electrical Energy.
2. On which principle a Generator works?
Generator works on Faradays laws of “Electro Magnetic Induction ”
3. What are Faradays laws of Electro Magnetic Induction?
First Law: Whenever a conductor cuts magnetic flux an E.M.F is induced in that conductor.
Second Law: The magnitude of the induced e.m.f. is equal to the rate of change of flux linkage.
4. What are the two main parts of an AC Generator?
1. Stator
2. Rotor
5. What is the main difference between an AC Generator and DC Generator?
In an AC Generator the field is rotating and the armature is stationary whereas in DC Generator the field is stationary and the
armature is rotating.
6. What are the advantages of stationary armature and rotating field in an AC Generator?
1. It is easy to take output from the stationary armature.
2. It is easier to insulate stationary armature for higher voltage.
3. Low voltage excitation supply can be easily supplied to the rotor through slip rings.
7. What is the relation between the frequency, pole and speed of a Generator?
F = PN/120 Hz
Where P is the No.of Poles
N is the Speed in RPM.
8. In a Generator with 2 pole, and speed 3000 rpm, what is the frequency of the induced emf ?
F = PN/120
= 2 x 3000/120
= 50 Hz.
9. What is the connection of winding in a stator?
Double star connection.
10. What is the efficiency of a Generator?
98.55%
11. What is the coolant used to cool stator winding?
Demineralized water distilled water
12. What is the coolant used to cool rotor winding?
Hydrogen.

``
13. What are the advantages of Hydrogen gas as coolant over others?
1. Density is 1/14 of air.
2. Windage loss is low.
3. Low noise.
4. Heat transfer co efficient is 1.5 times higher than air.
5. Thermal conductivity is 7 times higher than air.
14. What are the losses in a Generator?
1. Stator copper
2. Stator iron
3. Rotor copper
4. Windage loss
5. Stray loss
6. Friction loss
15. What is Short Circuit Ratio (SCR) of a Generator?
It is the ratio of the field current required to produce rated voltage on open circuit to the field current required to circulate rated
current on short circuit.
16. What is the value of SCR in a 210 MW Turbo alternator?
SCR = 0.49
17.What are the disadvantages of Low Power Factor?
Low Power Factor Disadvantages: In AC circuits, power consumed depends on the power factor. Thus the power factor plays an
important role in AC circuits. For instant, we know that; Power in a Three Phase AC Circuit = P = √3 V x I CosФ And Current in
a Three Phase AC Circuits = I = P / (3 V x CosФ) I ∝1 /CosФ…. (1) Also, Power in a Single Phase AC Circuits = P = V x
I CosФ And Current in a Three phase AC Circuits = I = P / (V x CosФ) I ∝ 1/CosФ……… (2)
it is clear from both equations (1) an (2) that...

``

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