160901-Electrical Machines-III
Electrical Engineering
PRACTICAL MANUAL
On
Electrical Machine-III(160901)
AT
Shankersinh Vaghela Bapu Inst. Of Tech.
VASAN,GANDHINAGAR
B.E. Semester 6th (ELECTRICAL ENGINEERING)
Year 2014
BY
Prof. Lokin Joshi , Electrical Department
Prof. Rachana Patel , Electrical Department
Page | 1
Shankersinh Vaghela Bapu Institute of Technology.Vasan
160901-Electrical Machines-III
Electrical Engineering
INDEX
SR.
NO.
NAME OF EXPERIMENT
01
TO FIND THE REGULATION OF ALTERNATOR BY
DIRECT LOADING.
02
TO FIND THE REGULATION OF ALTERNATOR BY
PERFORMING EMF METHOD AND MMF METHOD.
03
TO DETERMINE THE POTIER REACTANCE AND VOLTAGE
REGULATION OF 3 PHASE ALTERNATOR BY ZERO
POWER FACTOR METHOD .
04
TO PLOT V & INVERTED V CURVES OF A
SYNCHRONOUS MOTOR.
05
06
07
08
DATE
PAGE
NO.
SIGN
DETERMINE SHORT CIRCUIT RATIO OF ALTERNATOR
TO STUDY THE SYNCHRONIZATION AND
PARALLEL OPERATION OF ALTERNATOR USING
SYNCROSCOPE.
TUTORIAL -1
TUTORIAL -2
Page | 2
Shankersinh Vaghela Bapu Institute of Technology.Vasan
160901-Electrical Machines-III
Electrical Engineering
Date: …../…../……….
EXPERIMENT NO:-01
AIM:-
TO DETERMINE VOLTAGE REGULATION OF 3 PHASE ALTERNATOR BY DIRECT LOADING
APPARATUS
Sr.no
1
Name of apparatus
Ammeter
2
3
Voltmeter
Rheostat
4
Load
Range
0-5amp.AC
0-1amp.DC
0.300V AC
400 ohms.1.7 Amp
1000 Ohms.1.2 Amp
Qty
01 No.
01 No.
01No
01No
01No
THEORY:
The voltage regulation of an Alternator is defined as the change in terminal voltage from no-load to
load condition expressed as a fraction or percentage of terminal voltage at load condition ; the speed
and excitation conditions remaining same. For Alternator with small power rating, voltage regulation
can be easily determined by direct loading test. In this test alternator is actually loaded by 3 phase load
and for that load, percentage regulation can be determine.this method gives real value of
regulation.But most of the Alternators are manufactured with large power rating , hundreds of kW or
MW, and also with large voltage rating upto 33kV. For Alternators of such power and voltage ratings
conducting load test is not possible. Hence other indirect methods of testing are used and the
performance like voltage regulation then can be predetermined at any desired load currents and power
factors.
NAME PLATE DETAIL
D.C MOTOR
ALTERNATOR
Page | 3
Shankersinh Vaghela Bapu Institute of Technology.Vasan
160901-Electrical Machines-III
Electrical Engineering
CIRCUIT DIAGRAM:
PROCEDURE:
1) Connect the circuit as shown in the diagram.
2)Keep load zero, set field potential divider to zero output voltage position.
3) Keep field resistance of motor to its minimum value.
4) Start the motor with the help of starter.
5) With the field rheostat of motor adjust the speed to synchronous value.
6) Switch on DC supply of field (Alternator) and adjust the potential divider so that the
voltmeter reads rated voltage of the alternator. Note this voltage as no load (E).
7) Increase the load in steps till rated current of alternator and note the different sets
of readings.
8) Keep speed constant during all the readings with the help of motor field rheostat..
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 connection 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.
Page | 4
Shankersinh Vaghela Bapu Institute of Technology.Vasan
160901-Electrical Machines-III
Electrical Engineering
OBSERVATION: E = Terminal voltage at no load =
Sr.
No.
Load current
Terminal voltage
Vt
volts.
% Regulation
CALCULATIONS:
% Regulation =
(
)
× 100
RESULT:
MODEL GRAPH
Page | 5
Shankersinh Vaghela Bapu Institute of Technology.Vasan
160901-Electrical Machines-III
Electrical Engineering
CONCLUSION:
DISCUSSION:
1)
Give the classification of alternator on the basis of rotor and their
application?
2) Mention disadvantages of determining the regulation of alternator by direct
loading?
3) What is hunting in Alternator?
Page | 6
Shankersinh Vaghela Bapu Institute of Technology.Vasan
160901-Electrical Machines-III
Electrical Engineering
Date: …../…../……….
EXPERIMENT NO:-02
AIM: TO FIND REGULATION OF A THREE-PHASE ALTERNATOR BY EMF AND MMF METHOD
APPARATUS REQUIRED:Sr.no
1
2
3
Name of apparatus
Ammeter
Voltmeter
rheostat
Range
0-5amp.AC
0-1amp.DC
0.300V AC
400 ohms.1.7 Amp
1000 Ohms.1.2 Amp
Qty
01 No.
01 No.
01No
01No
01No
THEORY:
A synchronous machine is an ac machine whose speed under steady-state conditions is proportional to
the frequency of the current in its armature. Nearly, all the generators in power stations are
synchronous machines.
Some of the important performance characteristics of the alternator are;


The open circuit characteristic (the open-circuit voltage vs. the field current).
The short circuit characteristic (the armature short circuit current vs. the field current).
To determine the performance characteristics of the synchronous generator some tests are performed
such as the open circuit and the short circuit tests. Then, the equivalent circuit of the alternator is
determined. The compounding curves are important curves as they give clear idea about the required
field control range to regulate the alternator voltage.
NAME PLATE DETAIL
D.C MOTOR
ALTERNATOR
Page | 7
Shankersinh Vaghela Bapu Institute of Technology.Vasan
160901-Electrical Machines-III
Electrical Engineering
CIRCUIT DIAGRAM:
Page | 8
Shankersinh Vaghela Bapu Institute of Technology.Vasan
160901-Electrical Machines-III
Electrical Engineering
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) keep TPST switch
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 4 for 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.
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
faculty 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.
Page | 9
Shankersinh Vaghela Bapu Institute of Technology.Vasan
160901-Electrical Machines-III
Electrical Engineering
OBSERVATIONS:
Rotor speed = -------------------- RPM (constant)
Alternator armature resistance per phase Ra=------------Ohm
Sr.
No
O.C TEST
Field urrent
Terminal voltage
I (Amp)
Per phase (Vo)
Sr.
No.
S.C TEST
Field
f current
(IF)
Short circuit
current(Isc)
DETERMINATION OF STATOR ARMATURE RESISTANCE(Ra)
SR.NO
V(Volt)
I(amp)
Rdc(Ω)
Page | 10
Shankersinh Vaghela Bapu Institute of Technology.Vasan
160901-Electrical Machines-III
Electrical Engineering
CALCULATIONS:
(i)
EMF Method:
OA
Vo1
Synchronous impedance
Zs = ---------= ----------for field current Isc1.
OB
Isc1
Isc1 is selected over the linear part of OCC, generally it corresponds to rated armature current.
Synchronous reactance, Xs = √ (Zs2 - Ra2)
Calculate the excitation emf Eo and voltage regulation for full-load and
1. 0.8 lagging p.f.
2. Unity power factor
3. 0.8 leading p.f.
Eo = √[(V cosØ+ Ia Ra)2 + (V sin Ø+ Ia Xs)2]
+ sign is for lagging pf load.
- sign is for leading pf load.
V = rated terminal voltage per phase of alternator
% Voltage Regulation= (Eo-V) / V x 100
(ii)
MMF Method:
From the OC and SC characteristics determined from OC and SC tests the field currents If1 and If2
are determined to give rated voltage V on no-load (neglecting armature resistance drop) and cause
short-circuit current, equal to full load current, on short-circuit. If1 gives full load rated voltage and If2
gives demagnetizing ampere-turns at full load.
Total field current If is:
=
(
) +(
) ±
(
Where,
+ sign is for lagging pf load.
- sign is for leading pf load.
− )
Read E0 (No load phase voltage from OCC curvecorresponding to total field current If
%
=
(
− )
×
Page | 11
Shankersinh Vaghela Bapu Institute of Technology.Vasan
160901-Electrical Machines-III
Electrical Engineering
RESULT:
EMF Method:
Regulation of alternator at full load is found to be,
At unity pf
= -------------At 0.8 lagging = ---------------At
0.8 leading = -------------Synchronous Impedance varies for different values of excitation.
MMF Method:
Regulation of alternator at full load is found to be,
At unity pf
= -------------At 0.8 lagging = ---------------At
0.8 leading = -------------MODEL GRAPH:
CONCLUSION:
Page | 12
Shankersinh Vaghela Bapu Institute of Technology.Vasan
160901-Electrical Machines-III
Electrical Engineering
DISCUSSION:
1.
What is armature reaction effect?
2.
What are the advantage and disadvantage of estimating the voltage regulation of an
alternator by EMF method?
3.
When is the regulation negative and why?
4.
Why is EMF method called Pessimistic method?
5.
Why is MMF method called Optimistic method?
Page | 13
Shankersinh Vaghela Bapu Institute of Technology.Vasan
160901-Electrical Machines-III
Electrical Engineering
Date: …../…../……….
EXPERIMENT NO:-03
AIM: TO DETERMINE THE POTIER REACTANCE AND VOLTAGE REGULATION OF 3 PHASE
ALTERNATOR BY ZERO POWER FACTOR METHOD .
APPARATUS
Sr.no
1
Name of apparatus
Ammeter
2
3
Voltmeter
rheostat
Range
0-5amp.AC
0-1amp.DC
0.300V AC
400 ohms.1.7 Amp
1000 Ohms.1.2 Amp
Qty
01 No.
01 No.
01No
01No
01No
THEORY: This method is based on the separation of armature leakage drop and the armature reaction
effects Hence it gives more accurate results. It makes use of (i) Open circuit characteristics and
(ii) zero power factor were also called wattless load characteristic. It is the curve of terminal
volts against excitation which the armature is delivering full load at zero power factors.
By using the two characteristics the potier triangle can be found out. From the potier triangle
the armature reaction mmf and armature leakage reactance or the Potier reactance can be
determined by combining these two values the total Voltage induced E0 can be calculated.
The synchronous machine is run at rated synchronous speed by a primemover. A purely
inductive load is connected across the armature terminals and the field current is increased till
full load armature current is flowing. The load is then carried in steps and field current is
adjusted to maintain full load armature current.The armature terminal voltage and field current
are recorded at each step to get point “A” short circuit the output terminal of alternator. Vary
the excitation to get rated current flowing through armature.
NAME PLATE DETAIL
D.C MOTOR
ALTERNATOR
Page | 14
Shankersinh Vaghela Bapu Institute of Technology.Vasan
160901-Electrical Machines-III
Electrical Engineering
CIRCUIT DIAGRAM:-
PROCEDURE:
TO PLOT OCC
 Plot the characteristics between open circuit voltage and field current .
TO PLOT ZPF
 Connect the circuit diagram as shown in figure.
 Start the motor and run it at synchronous speed.
 Vary the inductive load in steps and adjust the field current to a value till full load armature
current is flowing.
 Every time note down the field current and the terminal voltage of alternator.
SHORT CIRCUIT TEST







Connect the circuit as shown.
Star the motor with its field rheostat at minimum resistance position
and the
potential divider set to zero output.
Adjust the motor speed to synchronous value.
Increase the alternator field excitation and note ammeter readings.
Repeat step 4 for different values of excitations (field current). Take readings up to rated
armature current. Maintain constant speed for all readings
Measure the value of armature resistance per phase Ra by multimeter or by ammetervoltmeter method.
Plot the characteristics and find the synchronous impedance.
Page | 15
Shankersinh Vaghela Bapu Institute of Technology.Vasan
160901-Electrical Machines-III
Electrical Engineering
TO GET STARTING POINT OF ZPF
(i) Connect the circuit diagram as shown in figure.
(ii) Start the motor and run it at synchronous speed.
(iii) Vary the field excitation to get rated current flowing through
armature. Note down this value of field current.
A) OCC:
Sr.No
Voltage
Field Current IF
Armature
current(IA)
Field Current IF
B) SCC:
Sr.No
C) ZPF:
Sr.No
Voltage
Field Current
RESULTS:
Sr.no
CosØ
sinØ
Field
Current
(If)
Voltage
(E0)
% Reg
Page | 16
Shankersinh Vaghela Bapu Institute of Technology.Vasan
160901-Electrical Machines-III
Electrical Engineering
MODEL GRAPH
CONCLUSION:
DISCUSSION QUESTIONS:1. What is additional effect taken in to account using potier reactance?
2. What are advantages of ZPF method?
3. What is necessity for predetermination of Voltage regulation?
Page | 17
Shankersinh Vaghela Bapu Institute of Technology.Vasan
160901-Electrical Machines-III
Electrical Engineering
Date: …../…../……….
EXPERIMENT NO:-04
AIM: TO PLOT V & INVERTED V CURVES OF A SYNCHRONOUS MOTOR.
APPARATUS:Sr.no
1
Name of apparatus
Ammeter
2
3
Voltmeter
rheostat
4
Power factor meter
Range
0-10amp.AC
0-2amp.DC
0.600V AC, 0-300V DC
400 ohms.1.7 Amp
1000 Ohms.1.2 Amp
600V, 10A
Qty
01 No.
01 No.
01No
01No
01No
01No
THEORY:If the armature current is plotted versus field current for several power levels, the regulating plots
are the motor V-curves shown in Figure. The points marked a, b, and c on the upper curve
correspond to the operating conditions (underexitation, normal exaitation, and overexaitation) the
lagging power factor operation is electrically equivalent to an inductor and the leading power factor
operation is electrically equivalent to a capacitor. Leading power factor operation referred to as
synchronous condenser or synchronous capacitor operation. Typically, the synchronous machine Vcurves are provided by the manufacturer so that the user can determine the resulting operation
under a given set of conditions.
Page | 18
Shankersinh Vaghela Bapu Institute of Technology.Vasan
160901-Electrical Machines-III
Electrical Engineering
NAME PLATE DETAIL
SYNCHRONOUS MOTOR
CIRCUIT DIAGRAM:
PROCEDURE:1) Make the connections as shown in circuit diagram.
2) Adjust the field rheostat of DC generator at maximum position, the potential divider at zero
output position and the load at off condition.
3) Switch on the 3-ph. supply, start the synchronous motor and let it run at its rated speed.
4) Switch on the DC supply and adjust the generator field current to a suitable value so that it
generates rated voltage.
Page | 19
Shankersinh Vaghela Bapu Institute of Technology.Vasan
160901-Electrical Machines-III
Electrical Engineering
5) Increase the alternator field current and note down corresponding power factor and armature
current covering a range from low lagging to low leading power factor through a unity power
factor. Note that armature current is minimum when the p.f. in unity.
6) Repeat step No.5 for some constant load on the Generator.
OBSERVATIONS:[A] AT NO LOAD
Sr.No
If
Power factor
Ia
Sr.No
If
Power factor
Ia
[B] AT LOAD
GRAPH: Plot the curves between
(i) Armature current (Ia) vs field current (If)
(ii) Power factor (cosØ) vs field current (If)
MODEL GRAPH:
Page | 20
Shankersinh Vaghela Bapu Institute of Technology.Vasan
160901-Electrical Machines-III
Electrical Engineering
CONCLUSION:
DISCUSSION:
Page | 21
Shankersinh Vaghela Bapu Institute of Technology.Vasan
160901-Electrical Machines-III
Electrical Engineering
Date: …../…../……….
EXPERIMENT NO:-05
AIM: TO FIND SHORT CIRCUIT RATION (SCR) OF ALTERNATOR
APPARATUS REQUIRED
Sr.no
1
Name of apparatus
Ammeter
2
3
Voltmeter
rheostat
Range
0-5amp.AC
0-1amp.DC
0.300V AC
400 ohms.1.7 Amp
1000 Ohms.1.2 Amp
Qty
01 No.
01 No.
01No
01No
01No
THEORY:
The ratio of the field current required to generate rated voltage on open circuit required to
circulate rated armature current during short circuit is termed as short-circuit ratio (SCR). The
short-circuit ratio is also the reciprocal of the per unit value of the saturated synchronous
reactance. The short-circuit ratio of a generator is a measure of the transient stability of the unit,
with higher ratio providing greater stability. For lower value of SCR, the value of Xs is more hence
the drop IaXs is more. Hence the machine requires large change in field current for small change in
load, to keep terminal voltage costant.
NAME PLATE DETAIL
D.C MOTOR
ALTERNATOR
Page | 22
Shankersinh Vaghela Bapu Institute of Technology.Vasan
160901-Electrical Machines-III
Electrical Engineering
CIRCUIT DIAGRAM:-
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) keep TPST switch
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.
Page | 23
Shankersinh Vaghela Bapu Institute of Technology.Vasan
160901-Electrical Machines-III
Electrical Engineering
5) Repeat step 4 for 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.
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
faculty 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.
OBSERVATIONS:
Rotor speed = -------------------- RPM (constant)
Alternator armature resistance per phase Ra=------------Ohm
O.C TEST
S.C TEST
Sr.
Field
Sr.
f current
Field urrent
Terminal voltage
No.
(IF)
No
I (Amp)
Per phase (Vo)
Short circuit
current(Isc)
GRAPH: Plot the readings to draw following graphs. Use same graph paper for both curves.
1. I f versus Vo (from OC test)
f
2. I versus Isc (from SC test)
CALCULATIONS:
SCR=
XS =
Page | 24
Shankersinh Vaghela Bapu Institute of Technology.Vasan
160901-Electrical Machines-III
Electrical Engineering
RESULT:
SCR =---------------XS =------------------MODEL GRAPH:
CONCLUSION:
DISCUSSION:
Page | 25
Shankersinh Vaghela Bapu Institute of Technology.Vasan
160901-Electrical Machines-III
Electrical Engineering
Date: …../…../……….
EXPERIMENT NO:-06
AIM:- TO STUDY THE SYNCHRONIZATION AND PARALLEL OPERATION OF
TWO ALTERNATOR USING SYNCHROSCOPE.
APPARATUS:Sr.no
1
2
3
4
2
3
Name of apparatus
AC Ammeter
AC Voltmeter
DC Voltmeter
DC Ammeter
rheostat
Synchroscope
Range
0-10 Amp
0-500V
0-200V
0-1 Amp
400 ohms.1.7 Amp
Qty
6 No
6 No
2 No.
2 No
2 No
1 Nos.
THEORY:To connect two alternators in parallel, the two alternators must be synchronized. The
synchronization process must be performed also when connecting an alternator to the grid. The
purpose of synchronization is to ensure that at the moment of closing the circuit breaker (closing
the 3-pole single throw switch to connect the alternator to the grid in this experiment), the
voltages across the three phases of the breaker are as close to zero as possible and remain so
after the switch is closed. To ensure that, the following conditions must be metch:
1- The generated voltage of two alternator must be approximately equal.
2- The frequency of the two generated voltages must be equal.
3- The phase sequence of the two generated voltages must be the same.
4- The phase of the generated voltages relative to some reference must be very close to the
phase of other alternator.
These conditions can be understood by considering the voltage of one line of the alternator-1,
va1, to be connected to one line of the alternator-2, va2. Suppose
Va1 = va1(t) = Vma1 sin (ωa1t + φa1)
_____(1)
Va2 = va2(t) = Vma2 sin (ωa2t + φa2)
_____(2)
The voltage across the switch is Va1-Va2. It is obvious that for this voltage to be close to zero
and remains close to zero, the above four conditions must be met. In short, the above two
voltage waveforms must be on top of each other if seen on the oscilloscope. The voltage Va1Page | 26
Shankersinh Vaghela Bapu Institute of Technology.Vasan
160901-Electrical Machines-III
Electrical Engineering
Va2 can be seen by applying this voltage to a light bulb. The brightness of the bulb is an
indication of the voltage across it. When the light bulb is totally dark, the voltage across it is
zero.
NAME PLATE DETAIL:D.C MOTOR
ALTERNATOR
CIRCUIT DIAGRAM:-
Page | 27
Shankersinh Vaghela Bapu Institute of Technology.Vasan
160901-Electrical Machines-III
Electrical Engineering
PROCEDURE:1)
2)
3)
4)
5)
6)
7)
8)
9)
10)
Connect the circuit as shown in the diagram.
Keep all the switches in open position and put on the DC supply.
Start the DC motor-1 and bring the speed very near to synchronous speed of the
alternator.
Gradually increase the DC excitation field supply and adjust alternator output voltage
to rated voltage.
Now repeat step-3 & 4 for Motor-Alternator set-2.
Check whether all the conditions for synchronization are satisfied.
Now set the switch for synchroscope and observe the rotation of needle. When the
needle comes to zero, the phase difference is minimum.
Only at an instant when needle is at zero position, close switch to synchronize both
alternator to bus.
Connect balanced load.
Note all the line voltage and current reading for both alternator.
OBSERVATIONS:
Alternator-1
Field
Current
IF (Amp)
Line voltage
(VA) Volt
Alternator-2
Line
Current
IA
(Amp)
Field
Current
IF (Amp)
Line
voltage
(VA) Volt
Line Current
IA (Amp)
Without load
With Load
RESULTS:-
Page | 28
Shankersinh Vaghela Bapu Institute of Technology.Vasan
160901-Electrical Machines-III
Electrical Engineering
CONCLUSION:-
DISCUSSION QUESTIONS:1)
What are the conditions of synchronization of two alternators?
2)
What are the possible effects of wrong synchronization?
3)
What are the different methods for synchronization?
5)
6)
7)
After synchronizing what is the effect of changing the excitation of the alternators.
Why the incoming m/c in parallel operation is operated at slightly higher speed then the
synchronous speed during synchronization.
In parallel operation of generator, for which condition circulating current develop
even no load on the machine.
Page | 29
Shankersinh Vaghela Bapu Institute of Technology.Vasan