Electric machinery experiment report of Jiangsu university of science and technology
Jiangsu University of Science and Technology
College of Electronic & Information
Electric Machinery
Report
Student name：MD SHAHARIAZ ALAM
Student
ID：192910301121
Data：2021.06.23
Electric machinery experiment report of Jiangsu university of science and technology
THREE-PHASE ALTERNATOR BY OPEN CIRCUIT AND SHORT
CIRCUIT TESTS:
1．Introduction
1.1 The most commonly used machine for generation of electrical power for
commercial purpose is the synchronous generator or alternator. An alternator works
as a generator when its rotor carrying the field system is rotated by a prime-mover
which in this case is DC shunt motor. The terminal voltage of an alternator changes
with load.
1.2 Alternators are by far the most important source of electric energy. Alternators
generate an AC voltage whose frequency depends entirely upon the speed of rotation.
The generated voltage value depends upon the speed, the dc field excitation and the
power factor of the load.
2．Experimental Process
It is performed by driving the alternator at its rated speed and increase the field
excitation till the armature voltage reaches to its rated value. Increase the load on
alternator terminals during this process alternator armature current will increase,
terminal voltage will vary according to the type of the load.
2.1 APPARATUS:1. Ammeter (0-5A) AC-1No; (0-1A) DC-1 No.
2. Voltmeter (0-300V) AC-1 No.
3. Tachometer - 1 No.
4. Rheostats (400. 1.7A) 1No; 1000. 1.2A 1No.
5. Alternator 3 kVA, 4.2A, 1500 RPM, 3
6. D.C. Motor 3 HP, 220V, 1500RPM
7. Connecting wires etc.
2.2 CIRCUIT DIAGRAM:
[A] OPEN CIRCUIT TEST
Electric machinery experiment report of Jiangsu university of science and technology
[B] SHORT CIRCUIT TEST
PROCEDURE:
[A] OPEN CIRCUIT TEST
1) Connect the circuit as shown.
2) Set potential divider to zero output position and motor field rheostat to minimum
value.
3) Switch on dc supply and start the motor.
4) Adjust motor speed to synchronous value by motor field rheostat and note the
meter readings.
5) Increase the field excitation of alternator and note the corresponding readings.
6) Repeat step 5 till 10% above rated terminal voltage of alternator.
7) Maintain constant rotor speed for all readings.
[B] SHORT CIRCUIT TEST
1) Connect the circuit as shown.
2) Star the motor with its field rheostat at minimum resistance position and the
potential divider set to zero output.
3) Adjust the motor speed to synchronous value.
4) Increase the alternator field excitation and note ammeter readings.
5) Repeat step 4for different values of excitations (field current). Take readings up to
rated armature current. Maintain constant speed for all readings
6) Measure the value of armature resistance per phase Ra by multimeter or by
ammeter- voltmeter method.
7) Plot the characteristics and find the synchronous impedance.
Electric machinery experiment report of Jiangsu university of science and technology
PRECAUTIONS:
1)All connections should be perfectly tight and no loose wire should lie on the work
table.
2)Before switching ON the dc supply, ensure that the starter’s moving arm is at it’s
maximum resistance position.
3)Do not switch on the supply, until and unless the connections are checked by the
teacher
4)Avoid error due to parallax while reading the meters.
5)Hold the tachometer with both hands steady and in line with the motor shaft so that
it reads correctly.
6) Ensure that the winding currents do not exceed their rated values.
3. Experimental Results
O.C TEST.
S.C.TEST
Sr. Field
Terminal
No load O/P Field
Terminal
States
No current
voltage Per voltage(E0)
current
voltage Per current(A)
If (Amp) phase Vo
phase Vo
1
3.5 mA
6V
990V
3.55mA
6V
0.3A
2
3.65 mA
11V
400V
3.73mA
13V
0.8A
CALCULATIONS:
Eo = [(V cos + Ia Ra)2 + (V sin  + Ia Xs)2 ]
+ sign is for lagging pf load.
- sign is for leading pf load.
V = rated terminal voltage per phase of alternator
((E0-V)/V) *100
O.C TEST 1 = 16,400
O.C TEST 2 = 3536. 3536
It is performed by driving the alternator at its rated speed and increase the field
excitation till the armature voltage reaches to its rated value. Increase
the load on alternator terminals during this process alternator armature current will
increase, terminal voltage will vary according to the type of the load.
4. Questions and Reflections
1. Why OCC looks like B-H curve?
2. Why SCC is a straight line?
3. What is armature reaction effect?
4. What are the causes of voltage drop?
Electric machinery experiment report of Jiangsu university of science and technology
LOAD CHARACTERISTICS OF AN ALTERNATOR LAB REPORT:
Introduction:
output current with speed of the alternator. If the speed of the alternator is decreased
then the output current of the alternator also decreased. efficiency with the speed of
the alternator. current drop with increasing alternator temperature.
PURPOSE:
To discover the effect of differing power factor loads on the terminal voltage of an
detonator.
BRIEFING:
If there is no load on an alternator, its terminal voltage depends solely on speed and
field current. However, load current flows through the an nature coils making terminal
voltage depend on the nature of the load. In this experiment we will maintain a
constant speed and a a constant field current while loading the alternator with a unity,
leading, and lagging loads. There are three reasons why terminal voltage is different
from that generated. First is armature resistance. Second is armature reaction. Third is
Armature reactance. With a resistive (unity power factor) load, then is the voltage drop
due to the Armature coil's resistance. This IR drop increases as the load increases. Also
there is the inductance of the Armature coil. This IXL increases as the load increases.
Armature reaction is the effect that the magnetic field of the armature has on the main
rotor field. It weakens the main field reducing the generated voltage. It, too, acts like
a voltage drop, increasing as the load increases. When the load is inductive (lagging
power factor) all three elements are still present. However, the load current is already
lagging terminal voltage. This doesn't change the IR drop but it does increase the
effects of armature reactance and armature reaction. With a capacitive (leading power
factor) load, there is a completely different situation. you still have the IR drop due to
resistance, but the D(r, adds to the generated voltage instead of subtracting from it.
From Lenz's law we know that inductive reactance tends to oppose whatever causes
it. Its cause in the alternator is the load current. The load current, however, leads the
generated voltage. If the angle of lead is great enough, the coil's back-voltage (which
is where inductive reactance comes from) makes the terminal voltage larger than the
generated voltage. A::nature reaction helps too. Instead of weakening the main field,
it strengthens it. Therefore, with a leading power factor load, terminal voltage
increases as the load increases. Voltage regulation (V.R.) is the ratio between the total
drop in voltage and the full load voltage. The equation is:
Upon successful completion of this experiment, the student will be able to:
1. Explain why loading has an effect on terminal voltage.
2. Differentiate between unit5r, lagging, and leading power factor loads.
MACHINES REQUIRED:
DM-IOOA DC Machine operating as a motor SM-1OO-3A Synchronous Machine
Electric machinery experiment report of Jiangsu university of science and technology
operating as a generator.
POWER REQUIRED:
0-125 volt variable DC, 5 amps 0-125 volt variable DC, 1 amp
METERS REQUIRED:
O-3O0 volt AC voltmeter
ADDITIONAL MATERIAL REQUIRED:
MGB-IOODG Bedplate
SLA- 1OOD Strobe-Tachometer
RLC-100 Resistance/Reactance Load
PROGRAM PLAN:
Step 1. Place the two machines on the bedplate. Couple and clamp the machines
securely. Install guards
Step 2. Connect the DC machine as a self excited shunt motor as shown in Figure 5-1.
Do not turn the power on yet.
Step 3. Have someone check your connections to be sure they are correct.
Step 4. Tum on the main AC circuit breaker; the 0-125V.DC circuit breaker and the
motor.
Step 5. Tum on the excitation (150V.DC) supply and the alternator switch and increase
its output until the alternator terminal voltage is 208 volts (T2 to TB).
Step 6. Turn on 4 resistance load steps.
Step 7. Re-adjust the excitation supply until the alternator's terminal voltage is exactly
208 volts.
Step 8. Turn OFF the alternator switch.
TEST RESULTS:
FULL LOAD VOLTS
208
208
208
UNITY
LAGGING
LEADING
NO LOAD VOLT
VOLTAGE BEGUI-ATIO
DE-BRIEFING:
1. From the data recorded in TABLE l compute the voltage regulation of this alternator
when connected to a unity power factor load.
2. From the data recorded in TABLE 1 compute the voltage regulation of this alternator
when connected to a lagging power factor load.
Electric machinery experiment report of Jiangsu university of science and technology
Synchronous Motor Lab Report:
Introduction:
The purpose of this experiment was to observe synchronous generator behavior, and
perform
Open Circuit Test and Short Circuit Test on it.
The purpose of this experiment was to observe synchronous generator behavior, and
perform
Open Circuit Test and Short Circuit Test on it.
The purpose of this experiment was to observe synchronous generator behavior, and
perform
Open Circuit Test and Short Circuit Test on it.
The purpose of this experiment was to observe synchronous generator behavior, and
perform
Open Circuit Test and Short Circuit Test on it.
Synchronous motor is the type of motor in which the rotating speed of rotor is same
as the rotating speed of magnetic field. In other words, rotor rotates at
the synchronous speed unlike Induction Motor, which we have discussed
in Introduction to Induction Motor.
Objective:
Three-phase synchronous machines account for a high percentage of this country’s
power generation. Understanding the machine’s behavior and determining its
equivalent network and performance characteristics are of prime importance to a
power engineer. This experiment studies the characteristics of doubly-excited
synchronous motors and generators. Specific tests are run to determine equivalent
circuit parameters, torque, and power factor control. This lab shows that system design
considerations must include frequency, speed, power factor, and voltage. Also
illustrated are important machine design parameters including linear versus non-linear
magnetic characteristics and efficiency.
Theory:
A synchronous motor is one in which the rotor normally rotates at the same speed as
the revolving field in the machine. The principle of operation of a synchronous motor
can be understood by considering the stator windings to be connected to a threephase alternating-current supply. Here we use some mechanical means which initially
rotates the rotor in the same direction as the magnetic field to speed very close to
synchronous speed. On achieving synchronous speed, magnetic locking occurs, and
the synchronous motor continues to rotate even after removal of external mechanical
means. The synchronous motor has the special property of maintaining a constant
running speed under all conditions of load up to full load. This constant running speed
Electric machinery experiment report of Jiangsu university of science and technology
can be maintained even under variable line voltage conditions. It is, therefore, a useful
motor in applications where the running speed must be accurately known and
unvarying. It should be noted that, if a synchronous motor is severely overloaded, its
operation (speed) will suddenly lose its synchronous properties and the motor will
come to a halt. The synchronous speed of the motor used in this experiment is 1800
rpm. The synchronous motor gets its name from the term synchronous speed, which
is the natural speed of the rotating magnetic field of the stator. As you have learned,
this natural speed of rotation is controlled strictly by the number of pole pairs and the
frequency of the applied power. Like the induction motor, the synchronous motor
makes use of the rotating magnetic field. Unlike the induction motor, however, the
torque developed does not depend on the induction currents in the rotor. Briefly, the
principle of operation of the synchronous motor is as follows: a multiphase source of
AC is applied to the stator windings and a rotating magnetic field is produced. A direct
current is applied to the rotor windings and a fixed magnetic field is produced. The
motor is constructed such that these two magnetic fields react upon each other
causing the rotor to rotate at the same speed
as the rotating magnetic field. If a load is applied to the rotor shaft, the rotor will
momentarily fall behind the rotating field but will continue to rotate at the same
synchronous speed. The falling behind is analogous to the rotor being tied to the
rotating field with a rubber band. Heavier loads will cause stretching of the band so
the rotor position lags the stator field but the rotor continues at the same speed. If the
load is made too large, the rotor will pull out of synchronism with the rotating field
and, as a result, will no longer rotate at the same speed. The motor is then said to be
overloaded. The synchronous motor is not a self-starting motor. The rotor is heavy and,
from a dead stop, it is not possible to bring the rotor into magnetic lock with the
rotating magnetic field. For this reason, all synchronous motor has some kind of
starting device. A simple starter is another motor which brings the rotor up to
approximately 90 percent of its synchronous speed. The starting motor is then
disconnected and the rotor locks in step with the rotating field. The more commonly
used starting method is to have the rotor include a squirrel cage induction winding.
This induction winding brings the rotor almost to its synchronous speed as an
induction motor. The squirrel cage is also useful even after the motor has attained
synchronous speed, because it tends to dampen rotor oscillations caused by sudden
changes in loading. Your synchronous motor/generator module contains a squirrel
cage type rotor. The positive reactive power is needed to create the magnetic field in
an alternating current motor.
Electric machinery experiment report of Jiangsu university of science and technology
Equipment’s:
Power Supply, DAI, Synchronous motor (8241), Electrodynamometer
(8960), Tachometer, Timing belt.
BACKGROUND INFORMATION:
The three-phase synchronous machine, illustrated in Figure 1, is literally a DC
machine turned inside-out. The armature, excited by alternating current, is wound in
the stator of the machine, and the direct current field is wound on the rotor of the
machine. Electrical power is transferred to the rotor through stator mounted brushes
that contact rotor mounted slip rings. The rotating field that is necessary for
continuous torque development is accomplished by the AC utility supply.
Figure 1: Cross-sections of synchronous machines.
As shown in Figure 1, the rotor can be of either the salient-pole type or the cylindrical
(non-salient-pole) type.
Electric machinery experiment report of Jiangsu university of science and technology
Figure 2: Mutual and leakage fluxes of synchronous machines.
Figure 2 shows the assumed current direction for phase a of the stator winding.
Fc F max  cos(t + 120º) cos( + 120º)
The total MMF due to the armature currents is the sum of the individual MMF’s. Thus
Figure 3: Steady-state torque-angle characteristic of a cylindrical rotor synchronous
machine
As the rotor moves within the stator, the field induces voltage in the armature winding
of the machine. This voltage is called the generated voltage in a generator and the back
EMF in a motor
Electric machinery experiment report of Jiangsu university of science and technology
Figure 4: Time history of three-phase induced voltages for generator
If the machine is supporting a load (armature current not equal to zero), then there is
a rotating magnetic field created by the armature. The armature field tends to reduce
the net flux in the machine air gap, which in turn causes a reduced voltage. This
process is called armature reaction.
We now have enough information to develop equivalent circuit models for the
synchronous machine. The models are shown in Figure
Where
Ef = no-load generated voltage
Er = generated voltage including armature reaction
I a = armature current
X = inductance to account for armature reaction
X = armature leakage inductance
X s = synchronous reactance
Ra = per-phase armature resistance
Vt = per-phase terminal voltage
THE TEST SET-UP: The machines used for this experiment are four-poles, three-phase, wound-rotor
induction motors, but they work quite well as doubly-excited synchronous machines.
The stators are rated for 120V line-to-line and are wye-connected which is 69.3V lineto-neutral. Both the stator and the rotor windings are rated for 1.5 amperes, but they
will handle 2.5 amperes for short periods of time. The motor being tested operates at
the same speed of the dynamometer. The motor is started as an induction machine by
short-circuiting the rotor windings. After acceleration, the short-circuit is removed and
DC current is applied to the rotor field. The DC field causes the motor to “jump” into
synchronism, where it remains until it becomes overloaded.
Electric machinery experiment report of Jiangsu university of science and technology
SUGGESTED PROCEDURE:
1. Connect the circuitry shown in Fig. This set-up is used to test the synchronous
machine as a motor.
2. Open Circuit Characteristic.
Increase the dynamometer voltage until the generator is running at 1800 RPM. Keep
the speed constant for these tests. With the generator unloaded, measure and record
the RMS line-to-neutral phase voltage as the field current is slowly increased.
3. Short Circuit Characteristic
Increase the dynamometer voltage until the generator is running at 1800 RPM. Slowly
increase the field current until the phase current is 1.3 p.u. (1.95 A). Measure and
record the RMS phase current and the field current in Table 4 for several points. This
data is used to plot the short-circuit characteristic.
Experiment result:
Open Circuit Characteristic: For several points, record the field current and the
terminal voltage in Table 3. This data is used to plot the open-circuit characteristic
(OCC). Return the field current to zero.
Ifield
0.0A
Varm
0.5A
1.0A
1.5A
76.2V
RPM
1800
1800
1800
1800
1800
Short Circuit Characteristic: Measure and record the RMS phase current and the field
current in Table 1 for several points. This data is used to plot the short-circuit
characteristic.
Ifield
Iphase
0.5A
RPM
1800
1.0A
1.5A
1.95A
1800
1800
1800
Finding Armature Resistance: Connect one of the synchronous machine armature
phases to the regulated DC supply. Increase the source current to 0.5 amperes. Record
Electric machinery experiment report of Jiangsu university of science and technology
the voltage and current. This ratio of voltage to current is used to find the armature
resistance. Remember this is a DC resistance measurement, but we need an AC
resistance so include the skin effect of 1.2 in your calculations of 1.2(Rdc) = Rac.
Iarm
Varm
DC arm resistance AC arm resistance
Calculated
Calculated
0.5A
76.2v
700 ohm
1009 ohm
Thinking Question And answer
1. What does hunting of synchronous motor mean?
When the load applied to the synchronous motor is suddenly increased or decreased,
the rotor oscillates about its synchronous position with respect to the stator field. This
action is called hunting.
3. What is synchronous condenser?
An over-excited synchronous motor under no load, used for the improvement of
power factor is called as synchronous condenser because, like a capacitor it takes a
leading current.
7. What are the two types of 3-phase induction motor?
a. Squirrel cage induction motor. b. Slip ring induction motor.
Preview report and Operation score：
Teacher’s Signature：