Comparative review of analogue and digital Synchroscope in India used for synchronization of power alternators during parallel operation

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 09 Issue: 11 | Nov 2022 www.irjet.net p-ISSN: 2395-0072
© 2022, IRJET | Impact Factor value: 7.529 | ISO 9001:2008 Certified Journal | Page 625
Comparative review of analogue and digital Synchroscope in India used
for synchronization of power alternators during parallel operation.
Mr. Akash Holmukhe1, Prof. Bhushan Save2, Mr. Anuj Kap³, Mr. Lalit Sonar4
1,3,4B.E. Student, Electrical engineering, VIVA Institute of Technology, Maharashtra, India
²Assistant Prof & HOD, Dept. of Electrical Engineering, VIVA Institute of Technology, Maharashtra, India.
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Abstract - Synchroscope is an important device used in
the process of synchronization of alternators at generating
stations. Synchronization of alternators is important to
connect the two or more alternators in parallel. There are
commonly three methods used for synchronization i.e. Three
Dark Lamps method, the Two Bright One Dark method, and
Synchroscope Method. Where the synchroscope method is
frequently used for better accuracy. Synchroscope used for
this process is an electro-mechanical and analog type and
requires manual operation and other measuring devices
also. So, we tend to use the digital synchroscope. This single
device shows all parameters on the display and also gives
the option for automatic operation. It is reliable, easy to use,
easy to monitor, and cost-effective.
Key Words: synchronization, digital synchroscope,
parallel operation, alternators, synchroscope.
1. INTRODUCTION
Nowadays due to the high-power demand, the parallel
operation of two or more alternators are the need in the
electrical power system to achieve the demand. Also, there
are more advantages of using the parallel operation of
alternators like a reliable, flexible, expandable, cost-
effective and providing good quality and continuity of
power to the consumers. For this parallel operation, we
need to synchronize the alternators. If proper
synchronization is not done, then the alternator can be
damaged. The methods used for synchronization of
alternators are three dark lamps, two bright one dark
lamp, and the synchroscope method used for
synchronization. Where the synchroscope method is used
frequently nowadays. At a time of synchronization, we
have to match parameters such as a voltage, frequency,
phase sequence, and phase angle of an incoming alternator
and running alternator or bus bar, where we have to use a
separate measuring instrument like voltmeter, frequency
meter, phase sequence meter, and synchroscope to
monitor the individual parameter for performing the
parallel operation, which increase the cost of the system
and synchroscope used in this method is analogue type
highly sensitive, less accuracy, required more power to
run. Now that the world is becoming digital, we should
prepare the digital system for parallel operation. This
paper accentuates the digital type synchroscope. It will be
more accurate, less sensitive, and lightweight. Which will
show all required parameters on the single screen, so no
need to use individual instruments for measuring
purposes. This will automatically reduce the cost of the
system and also reduce the complexity of the system. The
relay terminals are also provided which gives the option to
the operator for automatic or manual operation of
synchronization. While the system is set to automatic
operation, the relay gives the signal to the circuit breaker
to close the circuit, and if there is any mismatch condition
in parameters the circuit breaker will open. So, the use of
this device increases the accuracy and easy operation of
the synchronization of alternators.
In a power station one or more alternators are connected
in parallel. This parallel operation is important for
reliability in a parallel system if a single alternator fails or
is taken out for maintenance the others will keep the
system active and maintain continuity. Also, the
requirement of the load may vary throughout the day. So,
to meet the demand of load more alternators can be
added. Efficiency can also be maintained if alternators
operate at their load rating.
Alternators operating in parallel can give a bigger load
than a single alternator. So more alternators in the system
can increase the capacity of the system.
1.1CONDITION FOR SYNCHRONIZATION
At the time of the synchronization process, we have to
make sure that four parameters align between the
alternators.
1. Phase sequence: the three phases of an incoming
alternator and running alternator must have the same
phase sequence.
2. The voltage magnitude: The voltage of both
alternators must be equal.
3. The frequency: The frequency of both alternators
is also equal because unequal frequency can create an
unstable flow of energy and this instability may lead to
damage to the equipment.
4. Phase angle: The phase angle of an incoming
alternator and running alternator must be zero.

2.SYNCHRONIZATION METHOD FOR PARALLEL
OPERATION OF ALTERNATORS
2.1 Three dark lamp method
Fig 1- Three dark lamp method
Three lamps and one voltmeter are used to check the
conditions for paralleling operation of the incoming
alternator and running alternator. The figure1 shows the
three-dark lamp method. Generally, this method is used
for low-power machines.
The incoming alternator is started and brought up to its
rated speed. Then the field current is adjusted to make the
incoming alternator voltage equal to the running
alternator or bus bar voltage. If the phase sequence is
proper then the lamp will be dark and bright at the same
time. Lambs will flicker at an equal rate if the frequencies
are different. So, the frequency is adjusted until the lamps
stop flickering or flicker at a slow rate. After satisfying all
conditions the synchronizing switch or circuit breaker is
closed in middle of the lamps dark period.
2.2 Two bright one dark lamp method
Fig 2- Three bright lamp method
In this method two Lamps are cross-connected between
two phases and one is connected between the
corresponding phase that is R is connected to R', Y is
connected to B', and B is connected to Y' as shown in the
figure 2.
The synchronizing switch will be closed when the straight
lamp is dark and the other two cross-connected lamps
bright equally. If phase sequences are incorrect then all
lamps will be dark. Also, the voltmeter is connected across
the straight connected lamp since lamb can be dark at
certain low voltage. So, when the voltmeter shows the zero
reading then only synchronizing switch will close.
2.3Three bright lamp method
Fig 3- Two bright one dark lamp method
Similarly in this method, three lamps are used only the
connections are different. It is connected across the phases
that R is connected to Y', Y is connected to B', and B is
connected to R' as shown in fig. Identification of conditions
for parallel operation is the same as the previous method
only the different synchronizing switch is closed in a
middle of a bright period of the lamp. The advantage of
this method is the brightest point is easier to identify than
the middle of the dark period.
2.4 Synchroscope method
 What is a synchroscope?
It is an instrument that indicates the two
alternating currents of alternators are in exact
phase relation in parallel connection. It shows the
phase angle between the machines and also
defines the operating speed (slow or fast) of the
incoming alternator.

Fig 4- Synchroscope
 Working principle
The synchroscope consists of a stator, two phases, and a
rotor. A Two-phase supply is provided by the alternators.
These two phases are synchronized together then the
third phase is automatically synchronized. The supply
from the running alternator is given to the stator of the
synchroscope and the incoming alternator supplies the
rotor of the synchroscope. The phase shift between the
supply gives a difference between the frequencies. When
the frequency of the alternator is different the device
starts operating to get the desired parameters. When the
status and rotor frequencies are the same, the rotor stops
rotating and remains stationary. If the supply frequency is
having a large difference the rotor rotates at a higher
speed and when the difference is minimum the rotor
speed is reduced. When the frequency and phase angles
are zero the pointer stop rotating and points towards the
zero position. Then two systems are ready to connect
safely.
3.TYPES OF SYNCHROSCOPES
1.Electrodynamic type
2.Moving iron type
3. Electronic synchroscope
4. Digital synchroscope
1. Electrodynamic type
Fig 4- Electrodynamic type
This type of scope is also called a Weston type of
synchroscope which includes an electrodynamic device
and three limb type transformers. The winding on one
limb is connected with a running alternator or busbar and
another outer limb winding is connected to the incoming
alternator and the central limb is connected to the lamp.
The outer limbs produce two fluxes, flowing through
central lines. This flux induces on emf in central limb
winding. When the voltage of both alternators is in phase,
the two fluxes in the central limb are added and induced
emf in the central limb and the lamp glows with maximum
brightness. when voltages are 180 out of phase flux is zero
and no emf induced and thus the lamp does not glow. If
the frequency of both alternators is different, the lamp will
flicker. But it will not indicate whether the alternator is
slow or fast. So, an electrodynamic instrument is provided.
Disadvantages
 This instrument has a low torque/weight ratio
and so low sensitivity.
 Frictional losses are there, also expensive than the
moving iron type synchroscope.
 The power consumption of this instrument is
high.
 Screening of moments against the stray magnetic
field is essential.

2. Moving iron type
Moving iron type synchronous scope consists of a
fixed coil of two parts. Also, there are two iron
cylinders mounted on the spindle and separated by
spacers. The cylinders are excited by two pressure
coils and connected to two phases of the incoming
alternator. The pointer is attached with the spindle
and moves over a dial marked fast and slow.
Fig 5- Moving iron type
Disadvantages
 This instrument suffers from error due to
frequency change hysteresis and stray losses.
 Its scale is non uniform so accurate reading is not
possible.
 Also, the reading of instruments is affected by
temperature variation.
3. Electrotonic Synchroscope
Fig 6- Electrotonic Synchroscope
The operation of this device is the same as the above
synchroscope instead of moving the pointer there is an
incorporated circle of LEDs is used. This led is glowing
sequentially in a clockwise or anticlockwise direction at a
variable speed which indicates the difference in
frequencies of an incoming and running alternator. Waves
synchronization is done the 'SYNC' led will glow. This
device is based on electronic components so, no moving
parts are there. Also, power consumption and losses are
low. The LEDs is it is easily visible to the operator in dark
places.
4. Digital synchroscope
This synchroscope is based on a microcontroller, therefore
there are no moving parts involved in it. This device shows
the actual value of voltage, frequency, and phase angle
difference on a single display in numerical form which
reduces error and increases accuracy. So, there is no need
to use separate instruments for measuring voltage, and
frequency parameters which also reduces the cost of the
system. Digital type also gives the option to the operator
to make the process automatic. There are no friction or
iron losses because of an electronic-based device the
power consumption of this device is also very less.
Fig 7- Digital Synchroscope
4. CONCLUSIONS
As we know the world is going towards digital things and
automation. Synchroscope is the most important part of
the synchronization process. The Digital synchroscope has
many spectacular features that can replace conventional
technologies. Provide a high accuracy level and are easy to
handle and monitor.

REFERENCES
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Khan.R , Mohan Raj.D, “Embedded Design in
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Journal of Engineering & Technology,2018.
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Conference (PPFIC), 2016.
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[6] I. Ahmad. Abo Dabowsa, the Islamic University of Gaza,
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[7] Ashfaq Hussain, Dhanpat Rai & Co. (Pvt) Ltd., Electric
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Comparative review of analogue and digital Synchroscope in India used for synchronization of power alternators during parallel operation

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Comparative review of analogue and digital Synchroscope in India used for synchronization of power alternators during parallel operation