microprocessor based system of automatic synchronizer full report
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22-01-2010, 07:22 AM

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The manual method of
synchronization demands a skilled operator and the method is suitable
for no load operation or normal frequency condition. under emergency
condition such as lowering of frequency or synchronizing of large
machines a very fast action is needed, which may not be possible for a
human operator. Thus there is a need of autosynchroniser in a power
station or in an industrial establishment where generator are employed.
This paper describes a microprocessor based set up for synchronizing a
three phase alternator to a busbar. Also existing methods of
synchronization are mentioned.

It is well known that electrical load on
a power system or an industrial establishment, is never constant but it
varies. To meet the requirement of variable load , economically and
also for assuring continuity of supply the number of generating units
connected to a system busbar are varied suitably . The connection of an
incoming alternator to system bus, ie; synchronization requires
fulfillment of the condition like the same phase sequence equality of
voltages and frequency between the incoming machine and frequency
between the in coming machine and busbar. In order to order to overcome
the 9 technical drawbacks of the conventional synchronization methods
we can introduce a microprocessor based system.

a Synchronizing Lamp

The operation of connecting an
alternator parallel with another alternator or with a common busbar is
known as synchronizing for proper synchronization of alternators the
following three conditions must be satisfied

1.The terminal voltage of incoming machine must be the same as the
busbar voltage.
2.the speed of the incoming machine must be same such that the
frequency is equal to the busbar frequency.
3. The phase of the alternator voltage must be identical to the busbar
It means that the switch must be closed at the instant
the two voltages are in correct phase.
Condition 1 can be checked with the help of voltmeter,
frequency is adjusted by varying the prime mover speed. In the dark
lamp method the lamps are connected across the alternator and busbar
terminal. If the phase sequence is different, the lamps will brighten
in a cyclic manner correct phase sequence is indicated by simultaneous
darkening brightening of lamps. The switch is closed in the middle of
the dark period.once synchronized properly, the two alternators
continues to run in synchronism.

b sychroscope

The armature of the sychroscope will align
itself so that the axis of windings are R and F are inclined at an
angle equal to phase displacement between V and Vâ„¢. If there any
difference between the frequencies of V and Vâ„¢ a pointer attached to
the armature shaft will rotate at slip speed, and the direction of of
its rotation will indicate whether the incoming machine is running
above or below synchronism. At synchronism, the pointer will remain
stationary, but it must be brought to the particular position which
indicates zero phase displacement between V and Vâ„¢ before the main
switch of the incoming generator is closed.

Synchronization by means of manually operated
switching served well enough when the individual generators were
relatively small, but with the growth of system capacity, it becomes
necessary to use automatic devices to ensure the closing of the main
switch of the incoming machine at the proper instant.

The scheme introduced here is for the complete
automation of synchronization i.e.; the adjustment of magnitude of
voltage and frequency of incoming alternator is done automatically.
When all the requirements of synchronization are satisfied, closing of
the main switch of the incoming machine is done by the automatic

The auto synchronizer has been developed to
carry out the following tasks related to the synchronization such as

I To check if the phase sequence of incoming machine
is correct or otherwise, in case of wrong phase sequence, to terminate
the further steps in the process and also to indicate corrective
II To check if frequency of incoming machine is equal to
that of busbar and to adjust it to a value nearly equal to the busbar
III To check machine voltage is equal to that of busbar
and to adjust it to a value nearly equal to the busbar voltage and
IV After ascertaining the fulfillment of the above
condition, to give closing signal to the circuit breaker so that the
breaker will close the exact inphase instant.

In addition, the auto synchronizer has been designed so that the
alternator is started with in minimum voltage and minimum frequency

The hardware has been designed to fulfill all the
requirements of the synchronizing process.
Block diagram of auto synchronizer setup is shown in fig (1)
A microprocessor trainer kit is used as a controller for the setup.
Also the figure showing the auto synchronizer setup consist of

a Frequency control unit
b Voltage control unit
c Potential transformer unit
d Signal conditioning card
e Display card and
f Circuit breaker with the switching circuit.
5.1 Frequency Controlling Unit

The frequency of an alternator can be changed
by varying the speed of the prime mover which is a DC shunt motor in
this case .A rheostat is provided in the field circuit of the motor for
this purpose The frequency controlling unit is a lead screw arrangement
driven by a stepper motor attached to the variable point on the
rheostat the stepper motor (SM1) is controlled by an 8085
microprocessor system through a driver circuit.
5.2 Voltage Controlling Unit

Once frequency of alternator is fixed ,or
adjusted ,its voltage is controlled by variation of excitation current.
This excitation current is varied by providing a rheostat in the field
circuit of the alternator. The automatic variation of excitation
current is obtained by lead screw and stepper motor(SM2) arrangement
similar to the one used for frequency control.
5.3 Potential Transformer Unit
This unit consist of a bank of four shell type
transformer(P.Ts).Fig.(2) shows the connection diagram. Out of the four
transformers thee are used for stepping down three phase voltages of
alternator and the remaining one is used for stepping down the voltage
of the phase R of the bus bar. The potential transformers connected to
the phase R of the bus bar and the phase R of the alternator are
having two secondaries. Hence one secondary is used for voltage
measurement and the other is used for frequency measurement .The
potential transformers connected to the Y and B phases have only one
secondary each
5.3 Signal Conditioning Card
It is subdivided into (i) signal conditioning card and (ii) ADC
The signal conditioning subunit consists of for
identical circuits each of which comprises of a zero crossing detector
(ZSD)(for ralt,yalt,balt and rbus) two rectifier and filter circuits
for ralt2 and rbus2 and an inphase sequence detector and an inphase
instant detector as shown in fig.(1).

The ZSD converts sinusoidal output of potential transformer secondary
to rectangular signal Fig.3 shows the ZSD output waveforms these square
waves are fed to microprocessor system for measurement of frequency and
phase sequence detection using developed software

The rectifier and filter circuits converts the AC signal of
ralt2 and rbus2 to DC signal compatible for ADC 0809.These are used for
the voltage measurements of the alternator and the bus.
Inphase instant detector circuit is used for
detecting the inphase instant of signals ralt1and rbus1 which is
the correct instant for synchronization.
The ADC subunit consists of ADC0809 interfaced
with 8085-microprocessor system. The clock required for this ADC is
derived from a frequency divider circuit made up of three 7490 counter
ICs. The clock available on microprocessor kit of 1.7 MHz, which is
divided by further factors 5,10,10. Therefore out of three available
outputs, 340KHz and 3.4KHz outputs are used respectively for the ADC
8255. The digital output corresponding to the alternator and busbar
voltages are obtained using separate channels for alternator and busbar
5.5 Display Card
Display card has been provided for indication of
messages during alternator synchronization process It uses four seven
“segment LED displays to represent the three inphase synchronization
conditions and circuit breaker position. Also the kit display is used
for displaying messages such as ËœHALTâ„¢,â„¢DONEâ„¢etc.
5.6 Circuit Breaker With Switching Circuit

The circuit breaker used as a synchronizing
switch is in the form of a direct on line starter .In order to operate
the circuit breaker, its operating coil is connected to 230 V d.c
Supply through electromagnetic relay. The relay is activated at proper
instant by the microprocessor so that the circuit breaker is closed
at the correct inphase instant.
The main program performs the following functions.
1. Phase sequence detection
2. Alternator frequency measurement and its adjustment
3. Alternator voltage measurement and its adjustment, and
4. Synchronizing at zero phase difference condition

The following subroutines are developed and called in the main program
1 IN PHASE : The subroutines checks the in phase instant of
Ralt and Rbus
where Ralt refers to the phase R of
the incoming alternator and
Rbus1 refers that of the bus
2 LSW : This subroutines checks if the limit
switch is closed or not
3 SM : Rotates the stepper motor either in
clockwise or anticlockwise
4 KCLOSE : Checks the closure of the key to be handled by
the operator
5 PSEQ : Checks the phase sequence of the
6 FRQ : Measures the frequency of the alternator
or bus bar
7 VOLM : Measures the voltage of the alternator or
bus bar
8 CMPHD : Compares the contents of HL register pair
with the contents of DE pair

9 SUBDH : Subtract the contents of DE pair from
contents of HL pair
10 In addition the following monitor subroutines are used whenever
required :
a. CRLF clears the display
b OUT MSG displays the given message on the
c delay provides delay in the program
d DONE Displays the message ËœDONEâ„¢
Fig (4) shows flowchart of the main program for autosynchronising
setup. The status of the limit switches LS1and LS2 are checked . These
are provided with the field circuit rheostats of exciter and driving
motor. Accordingly the stepper motor are rotated in appropriate
directions to obtain initial positions respectively of field rheostat
(Rf) and exciter rheostat (Rex) . ht emessage ËœSTARTâ„¢ is displayed
indicating operator to start the DC motor (prime mover). When the
operator sees the prompt, he switches ËœONâ„¢ the DC motor of the
alternator. Once the alternator is started, it develops some voltage at
some frequency, following sequence of events will take place
1 Detection of phase sequence
2 Frequency measurement and control
3 Voltage measurement and control
4 Synchronizing

Before alternator is connected to the busbar first of
all we have to ensure that the phase sequence of the incoming
alternator is the same as that of the busbar. The program checks the
ZCD outputs corresponding to Ralt and Yalt phases for their low to high
transitions and count corresponding to time T1 as shown in fig (8) is
obtained using subroutine ËœPSEQâ„¢. Similarly the ZCD outputs
corresponding to Ralt and Balt are measured or checked for their zero
to one transition and count corresponding to time T2 is obtained. To
check the phase sequence ,T1 and T2 are compared . When T1 is greater
than T2, the phase sequence is not correct. This condition is indicated
by ËœNâ„¢ and the display of message ËœHALTâ„¢ will be there and the program
execution is stopped on the other hand, if T1 is less than T2, the
phase sequence is ËœOKâ„¢ or correct and is indicated by ËœOâ„¢. There after
the program control is transferred to frequency measurement and control
The subroutine FRQ written for frequency measurement of
bus 0or alternator checks their respective ZCD outputs for low to high
In software, the register HL(for busbar signal) or DE
(for alternator signal) initialized with zero components are
incremented till the ZCD outputs are in a high to low transition . This
count in HL is equivalent to the time period corresponding to the half
cycle of alternator signal . The counts obtained inHL and DE pairs are
compared. If the count in HL is less than that of DE , it indicates
that alternator frequency is less than the busbar frequency. The
difference in frequency is checked and if the difference is greater
than allowed difference (0.1Hz), then the stepper motor (SM2) is
rotated to bring the difference with in the limit, and ËœFEâ„¢ is
displayed when this condition is achieved.
On the other hand, if the count in the HL pair is
greater than that in DE, alternator frequency is high and is indicated
by ËœFHâ„¢. The stepper motor (SM2) is rotated in reverse direction to
bring the difference in frequency within limit till ËœFEâ„¢ is displayed.
The digital output corresponding to the alternator and bus
voltages are obtained by the following method. The busbar output and
the incoming alternator output are first stepped down in the same ratio
using P.T unit . These step-down transformer signals are fed to the
rectifier and filter circuits. The output from it is given to ADC
through separate channels. ADC output ie; the digital outputs are
compared and the difference of these is obtained. When the difference
is less than the allowed difference,(1%) the ËœVEâ„¢ is displayed and the
program execution is continued.
When the difference is greater than allowed difference,
either ËœVHâ„¢or ËœVLâ„¢ is displayed to indicate high or low voltage of
alternator respectively. The stepper motor (SM1) is rotated in
appropriate direction to bring the difference with in the limit till
ËœVEâ„¢ is displayed.

After satisfying all these condition, the time (Ti)
between consecutive inphase instants of Rus and Ralt (obtained from
inphase instant detector ) is measured using 8253 in mode ˜0™. The time
interval (Ti-To) where T0 is operating time of switching circuits , is
The closure of circuit breaker is achieved by
sensing next inphase instant with delay of (Ti-T0) wich will enable to
switch on the circuit exactly at the next inphase instant.
The phase sequence has been checked by using developed prototype. When
phase sequence is R.Y.B the auto Ëœsynchroniserâ„¢ gives a prompt to the
operator by displaying ËœOâ„¢ (ie inphase sequence OK). For the improper
phase sequence, ie R.B.Y., the auto synchronizer displays Ëœnâ„¢(NOT OK)
and ËœHalt instruction gets executed to stop entire operation.
The frequency of incoming machine which depends on the speed of the
alternator, ie prime mover(dc shunt motor)is measured and adjusted to
bring the difference in frequency with in the tolerance limit.
To achieve the equality of voltages, the exciter voltage or circuit
resistance was adjusted by auto synchronizer. After obtaining proper
phase sequence, equality of frequency and voltage, the auto
synchronizer has to carry out synchronization
The microprocessor based system of automatic
synchronizer can be used more effectively compared to conventional
methods of synchronization such as dark lamp method, bright lamp method
and synchronization using synchronoscope this because of the fact that
the conventional, method calls for of the operator and accuracy is less
and it depends on the sense of correct judgment of the operator.
Moreover the microprocessor based alternator synchronizer is user
friendly and requires less maintenance. It also exploits the advantage
of superior performance of the microprocessor like accuracy speed and

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02-09-2010, 08:50 PM

i am a final year student of BE(Electrical Engg.) from University of Pune .i want full report of microprocessor based system of automatic synchronizer of alternator which are connected in parallel to the bus..........
i also wants to complete design (such as circuit diagram, different equipement which is need for this project and implimentation,)procedure...........
Amruta Jamdade
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02-01-2011, 12:59 PM

cam you please send me full circuit @programming detail for Microprocessor Based Alternator Synchronisation. please
Amruta Jamdade
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Posts: 2
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02-01-2011, 01:05 PM

can you please send me full circuit diagram & programming details & hardware detail on Hardik
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02-01-2011, 03:15 PM

kindly send me circuit diagram and its programing,
I want to do this project and implimentation
seminar surveyer
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03-01-2011, 09:59 AM

there is a related thread on microprocessor based system of automatic synchronizer. please go through the following thread.

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Posts: 1
Joined: Sep 2010
14-03-2011, 12:35 PM

i am B.E. ELECT. final year student.
i searched in net, i did not find anything.
so please give me full specification of this project and implimentation.

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