The project is designed to develop a system to detect the synchronization failure of any external supply source to the power grid on sensing the abnormalities in frequency and voltage. There are several power generation units connected to the grid such as hydel, thermal, solar etc to supply power to the load. These generating units need to supply power according to the rules of the grid. These rules involve maintaining a voltage variation within limits and also the frequency. If any deviation from the acceptable limit of the grid it is mandatory that the same feeder should automatically get disconnected from the grid which by effect is termed as islanding. This prevents in large scale brown out or black out of the grid power. So it is preferable to have a system which can warn the grid in advance so that alternate arrangements are kept on standby to avoid complete grid failure.

1. A Technical Report
ON
“DETECTING POWER GRID SYNCHRONISATION FAILURE ON SENSING BAD
VOLTAGE OR FREQUENCY”
Is submitted in the partial fulfillment for the award of the degree of
BACHELOR OF TECHNOLOGY
IN
ELECTRICAL AND ELECTRONICS ENGINEERING
By
A.PRADEEP 11B71A0244
DEPARTMENT OF ELECTRICAL & ELECTRONICS ENGINEERING
SINDHURA COLLEGE OF ENGINEERING & TECHNOLOGY
( Approved by AICTE New Delhi, affiliated to JNTUH.)
Medipally, Godhavarikhani, Ramagundam (M), Karimnagar (D), T.S.
During the academic year 2011-2015.

2. SINDHURA COLLEGE OF ENGINEERING & TECHNOLOGY
(Approved by AICTE New Delhi, affiliated to JNTUH, Hyderabad)
DEPARTMENT OF ELECTRICAL & ELECTRONICS ENGINEERING
CERTIFICATE
This is to certify that the technical report entitled “DETECTING POWER GRID
SYNCHRONISATION FAILURE ON SENSING BAD VOLTAGE OR FREQUENCY”
is submitted in the partial fulfillment for the award of the degree of BACHELOR OF
TECHNOLOGY in ELECTRICAL AND ELECTRONICS ENGINEERING.
By
A.PRADEEP 11B71A0244
Bonafide student of SINDHURA COLLEGE OF ENGINEERING & TECHNOLOGY
During the academic year 2014-2015.
Mr. A.ANIL Mr. J.MADHUKAR REDDY
Seminar Supervisor H.O.D, EEE Dept

3. ACKNOWLEDGEMENT
I am very grateful to Mr. R.Narayan Das, Principal, Sindhura College of
Engineering & Technology for providing the required facilities in the college campus.
I express my sincere thanks to Mr. J.Madhukar Reddy, Associate Professor &
Head of the Department of Electrical and Electronics Engineering for the constant
cooperation and constructing, criticism, throughout the technical seminar.
I express my sincere thanks to our seminar supervisor Mr. A.ANIL, Asst. Professor
for his guidelines and suggestions, which have contributed to complete the technical seminar.
I thankful to the Management and Administration for providing us the necessary
support during the technical seminar.
BY
A.PRADEEP 11B71A0244

4. ABSTRACT
The project is designed to develop a system to detect the synchronization failure of
any external supply source to the power grid on sensing the abnormalities in frequency and
voltage.
There are several power generation units connected to the grid such as hydel, thermal,
solar etc to supply power to the load. These generating units need to supply power according
to the rules of the grid. These rules involve maintaining a voltage variation within limits and
also the frequency. If any deviation from the acceptable limit of the grid it is mandatory that
the same feeder should automatically get disconnected from the grid which by effect is
termed as islanding. This prevents in large scale brown out or black out of the grid power. So
it is preferable to have a system which can warn the grid in advance so that alternate
arrangements are kept on standby to avoid complete grid failure.
This system is based on a microcontroller of 8051 family. The microcontroller
monitors the under/over voltage being derived from a set of comparators. As the frequency of
the mains supply cannot be changed, the project uses a variable frequency generator (555-
timer) for changing the frequency, while a standard variac is used to vary the input voltage to
test the functioning of the project. A lamp load (indicating a predictable blackout, brownout)
being driven from the microcontroller in case of voltage/frequency going out of acceptable
range
Further the project can be enhanced by using power electronic devices to isolate the
grid from the erring supply source by sensing cycle by cycle deviation for more sophisticated
means of detection.

5. INDEX
S.NO TITLE PAGE NO
1. INTRODUCTION 1
2. EMBEDDED SYSTEMS 2
2.1 What is Embedded System 2
2.2 Characteristics of Embedded System 2
2.3 Applications 3
3. BLOCK DIAGRAM 4
4. HARDWARE REQUIREMENTS 5
4.1 Power Supply Block 5
4.1.1 Transformer 5
4.1.2 Voltage Regulator 7805 6
4.1.3 Rectifier 6
4.1.4 Filter 7
4.2 Microcontroller AT89S52 8
4.3 Liquid Crystal Display 12
4.4 555 Timer 13
4.5 LM358 (Dual Operational Amplifier) 14
4.6 LM339 15
4.7 Relay 15
4.8 Push Buttons 16
4.9 BC 547 16
4.10 LED 17
4.11 1N4007 (Diode) 17
4.12 Resistors 17
4.13 Capacitors 18
5. OPERATIONAL EXPLANATION 19
5.1 Connections 19
5.2 Working 19
5.3 Voltage Sensing Part 20
5.4 Frequency Sensing Part 20
CONCLUSION 22
REFERENCES 23

6. LIST OF FIGURES
FIG.NO FIGURE NAME PAGE NO
3 Block Diagram 4
4.1.1 A Typical Transformer 6
4.1.2 Voltage Regulator 7805 6
4.1.3 Full Bridge Rectifier 7
4.1.4 Capacitive Filter 7
4.2 Pin Diagram of AT89S52 9
4.3 LCD Display 13
4.4(a) 555 Timer IC 13
4.4(b) 555 Timer Pin Diagram 14
4.6 LM 339 15
4.7 Relay 15
4.8 Push Buttons 16
4.9 BC 547 Transistor 16
4.10 Symbol of LED 17
4.11 1N4007 diodes 17
4.12 Resistors 18
4.13 Capacitors 18

7. 1. INTRODUCTION
This project presents the development of a microcontroller based islanding detection
for grid connected inverter with under/over voltage and under/over frequency islanding
detection. The system is based on a microcontroller from Atmel 8051 family. The
microcontroller monitors the under/over voltage derived from a set of comparators and
under/over frequency from by the interrupt program for the utility grid and the processed
value of voltage and frequency for turning ON/OFF the relay between a grid connected
inverter and the utility grid. The project would alternatively use a variable frequency
generator representing the inverter using 555-timer for changing the frequency while a
standard variac shall be used to vary the input voltage for achieving the test conditions by a
lamp load being driven from the microcontroller output as stated above. The microcontroller
used in the project is of 8051 family which is of 8 bit. The power supply consists of a step
down transformer 230/12V, which steps down the voltage to 12V AC. This is converted to
DC using a Bridge rectifier. The ripples are removed using a capacitive filter and it is then
regulated to +5V using a voltage regulator 7805 which is required for the operation of the
microcontroller and other components.

8. 2. EMBEDDED SYSTEMS
2.1 What is embedded system?
An Embedded System is a combination of computer hardware and software, and
perhaps additional mechanical or other parts, designed to perform a specific function. An
embedded system is a microcontroller-based, software driven, reliable, real-time control
system, autonomous, or human or network interactive, operating on diverse physical
variables and in diverse environments and sold into a competitive and cost conscious market.
An embedded system is not a computer system that is used primarily for processing,
not a software system on PC or UNIX, not a traditional business or scientific application.
High-end embedded & lower end embedded systems. High-end embedded system - Generally
32, 64 Bit Controllers used with OS. Examples Personal Digital Assistant and Mobile phones
etc .Lower end embedded systems - Generally 8,16 Bit Controllers used with an minimal
operating systems and hardware layout designed for the specific purpose.
2.2 Characteristics of Embedded System:
• An embedded system is any computer system hidden inside a product other than a
computer.
• They will encounter a number of difficulties when writing embedded system software
in addition to those we encounter when we write applications.
– Throughput – Our system may need to handle a lot of data in a short period of
time.
– Response–Our system may need to react to events quickly.
– Testability–Setting up equipment to test embedded software can be difficult.
– Debugability–Without a screen or a keyboard, finding out what the software is
doing wrong (other than not working) is a troublesome problem.
– Reliability – embedded systems must be able to handle any situation without
human intervention.
– Memory space – Memory is limited on embedded systems, and you must
make the software and the data fit into whatever memory exists.
– Program installation – you will need special tools to get your software into
embedded systems.

9. – Power consumption – Portable systems must run on battery power, and the
software in these systems must conserve power.
– Processor hogs – computing that requires large amounts of CPU time can
complicate the response problem.
– Cost – Reducing the cost of the hardware is a concern in many embedded
system projects; software often operates on hardware that is barely adequate
for the job.
• Embedded systems have a microprocessor/ microcontroller and a memory. Some
have a serial port or a network connection. They usually do not have keyboards,
screens or disk drives.
2.3 APPLICATIONS:
1) Military and aerospace embedded software applications
2) Communication Applications
3) Industrial automation and process control software
4) Mastering the complexity of applications.
5) Reduction of product design time.
6) Real time processing of ever increasing amounts of data.
7) Intelligent, autonomous sensors.

10. 3. BLOCK DIAGRAM
Fig 3:Block Diagram

11. 4. HARDWARE REQUIREMENTS
 HARDWARE COMPONENTS:
1. POWER SUPPLY BLOCK
2. MICROCONTROLLER (AT89S52/AT89C51)
3. LIQUID CRYSTAL DISPLAY
4. 555 TIMER
5. LM358
6. LM339
7. RELAYS
8. PUSH BUTTONS
9. BC547
10. LED
11. IN4007
12. RESISTORS
13. CAPACITORS
4.1 PowerSupply Block:
4.1.1 Transformer:
Transformers convert AC electricity from one voltage to another with a little loss of
power. Step-up transformers increase voltage, step-down transformers reduce voltage. Most
power supplies use a step-down transformer to reduce the dangerously high voltage to a safer
low voltage. In this we are considering a 230/12V transformer.
Fig 4.1.1: A Typical Transformer

12. 4.1.2 Voltage Regulator 7805:
The LM78XX/LM78XXA series of three-terminal positive regulators are available in
the TO-220/D-PAK package and with several fixed output voltages, making them useful in a
Wide range of applications. Each type employs internal current limiting, thermal shutdown
and safe operating area protection, making it essentially indestructible. If adequate heat
sinking is provided, they can deliver over 1A output Current. Although designed primarily as
fixed voltage regulators, these devices can be used with external components to obtain
adjustable voltages and currents.
Fig 4.1.2: Voltage Regulator 7805
4.1.3 Rectifier:
A rectifier is an electrical device that converts alternating current (AC), which
periodically reverses direction, to direct current (DC), current that flows in only one
direction, a process known as rectification. The output from the transformer is fed to the
rectifier. It converts A.C. into pulsating D.C. The rectifier may be a half wave or a full wave
rectifier. In this project, a bridge rectifier is used because of its merits like good stability and
full wave rectification.
Fig 4.1.3: Full Bridge Rectifier

13. 4.1.4 Filter:
Fig 4.1.4: Capacitive Filter
Capacitive filter removes the ripples from the output of rectifier and smoothens the
D.C. Output received from this filter is constant until the mains voltage and load is
maintained constant. However, if either of the two is varied, D.C. voltage received at this
point changes. Therefore a regulator is applied at the output stage. This filter is also used in
circuits where the power-supply ripple frequency is not critical and can be relatively high.
4.2 Microcontroller AT89S52:
The AT89S52 is a low-power, high-performance CMOS 8-bit microcontroller with
8K bytes of in-system programmable Flash memory. The device is manufactured using
Atmel’s high-density non volatile memory technology and is compatible with the industry
standard 80C51 instruction set and pin out. The on-chip Flash allows the program memory to
be reprogrammed in-system or by a conventional non volatile memory programmer. By
combining a versatile 8-bit CPU with in-system programmable Flash on a monolithic chip,
the Atmel AT89S52 is a powerful microcontroller which provides a highly-flexible and cost-
effective solution to many embedded control applications.
 Features:
• Compatible with MCS®-51 Products
• 8K Bytes of In-System Programmable (ISP) Flash Memory
• Endurance: 10,000 Write/Erase Cycles
• 4.0V to 5.5V Operating Range
• Fully Static Operation: 0 Hz to 33 MHz

14. • Three-level Program Memory Lock
• 256 x 8-bit Internal RAM
• 32 Programmable I/O Lines
• Three 16-bit Timer/Counters
• Eight Interrupt Sources
• Full Duplex UART Serial Channel
• Low-power Idle and Power-down Modes
• Interrupt Recovery from Power-down Mode
• Watchdog Timer
• Dual Data Pointer
• Power-off Flag
• Fast Programming Time
• Flexible ISP Programming (Byte and Page Mode)
• Green (Pb/Halide-free) Packaging Option
 Pin Configurations of AT89S52
Fig 4.2: Pin Diagram of AT89S52
 Pin Description:
 VCC:
Supply voltage.
 GND:

15. Ground
 Port 0:
Port 0 is an 8-bit open drain bidirectional I/O port. As an output port, each pin can
sink eight TTL inputs. When 1s are written to port 0 pins, the pins can be used as high-
impedance inputs. Port 0 can also be configured to be the multiplexed low-order address/data
bus during accesses to external program and data memory. In this mode, P0 has internal pull-
ups. Port 0 also receives the code bytes during Flash programming and outputs the code bytes
during program verification. External pull-ups are required during program verification.
 Port 1:
Port 1 is an 8-bit bidirectional I/O port with internal pull-ups. The Port 1 output
buffers can sink/source four TTL inputs. When 1s are written to Port 1 pins, they are pulled
high by the internal pull-ups and can be used as inputs. As inputs, Port 1 pins that are
externally being pulled low will source current (IIL) because of the internal pull-ups. In
addition, P1.0 and P1.1 can be configured to be the timer/counter 2 external count input
(P1.0/T2) and the timer/counter 2 trigger input (P1.1/T2EX).
 Port 2:
Port 2 is an 8-bit bidirectional I/O port with internal pull-ups. The Port 2 output
buffers can sink/source four TTL inputs. When 1s are written to Port 2 pins, they are pulled
high by the internal pull-ups and can be used as inputs. As inputs, Port 2 pins that are
externally being pulled low will source current (IIL) because of the internal pull-ups. Port 2
emits the high-order address byte during fetches from external program memory and during
accesses to external data memory that uses 16-bit addresses (MOVX @ DPTR). In this
application, Port 2 uses strong internal pull-ups when emitting 1s. During accesses to external
data memory that uses 8-bit addresses (MOVX @ RI), Port 2 emits the contents of the P2
Special Function Register.
 Port 3:
Port 3 is an 8-bit bidirectional I/O port with internal pull-ups. The Port 3 output
buffers can sink/source four TTL inputs. When 1s are written to Port 3 pins, they are pulled
high by the internal pull-ups and can be used as inputs. As inputs, Port 3 pins that are
externally being pulled low will source current (IIL) because of the pull-ups.

16.  RST:
Reset input. A high on this pin for two machine cycles while the oscillator is running
resets the device. This pin drives high for 98 oscillator periods after the Watchdog times out.
The DISRTO bit in SFR AUXR (address 8EH) can be used to disable this feature. In the
default state of bit DISRTO, the RESET HIGH out feature is enabled.
 ALE/PROG:
Address Latch Enable (ALE) is an output pulse for latching the low byte of the
address during accesses to external memory. This pin is also the program pulse input (PROG)
during Flash programming.
In normal operation, ALE is emitted at a constant rate of 1/6 the oscillator frequency
and may be used for external timing or clocking purposes. Note, however, that one ALE
pulse is skipped during each access to external data memory.
 PSEN:
Program Store Enable (PSEN) is the read strobe to external program memory. When
the AT89S52 is executing code from external program memory, PSEN is activated twice
each machine cycle, except that two PSEN activations are skipped during each access to
external data memory.
 EA/VPP:
External Access Enable. EA must be strapped to GND in order to enable the device to
fetch code from external program memory locations starting at 0000H up to FFFFH. Note,
however, that if lock bit 1 is programmed, EA will be internally latched on reset. EA should
be strapped to VCC for internal program executions. This pin also receives the 12-volt
programming enable voltage (VPP) during Flash programming.
 XTAL1:
Input to the inverting oscillator amplifier and input to the internal clock operating
circuit.
 XTAL2:
Output from the inverting oscillator amplifier

17.  Oscillator Characteristics
XTAL1 and XTAL2 are the input and output, respectively, of an inverting amplifier
which can be configured for use as an on-chip oscillator, as shown in Figure 1. Either a
quartz crystal or ceramic resonator may be used. To drive the device from an external clock
source, XTAL2 should be left unconnected while XTAL1 is driven as shown in Figure 6.2.
There are no requirements on the duty cycle of the external clock signal, since the input to the
internal clocking circuitry is through a divide-by-two flip-flop, but minimum and maximum
voltage high and low time specifications must be observed.
 Idle Mode
In idle mode, the CPU puts itself to sleep while all the on chip peripherals remain
active. The mode is invoked by software. The content of the on-chip RAM and all the special
functions registers remain unchanged during this mode. The idle mode can be terminated by
any enabled interrupt or by a hardware reset.
 Power down Mode
In the power down mode the oscillator is stopped, and the instruction that invokes
power down is the last instruction executed. The on-chip RAM and Special Function
Registers retain their values until the power down mode is terminated. The only exit from
power down is a hardware reset. Reset redefines the SFRs but does not change the on-chip
RAM. The reset should not be activated before VCC is restored to its normal operating level
and must be held active long enough to allow the oscillator to restart and stabilize.
4.3 Liquid CrystalDisplay:
Liquid crystal display (LCD) has material which combines the properties of both
liquid and crystals. They have a temperature range within which the molecules are almost as
mobile as they would be in a liquid, but are grouped together in an order form similar to a
crystal.
Fig 4.3: LCD Display

18. For an 8-bit data bus, the display requires a +5V supply plus 11 I/O lines. For a 4-bit
data bus it only requires the supply lines plus seven extra lines. When the LCD display is not
enabled, data lines are tri-state which means they are in a state of high impedance (as though
they are disconnected) and this means they do not interfere with the operation of the
microcontroller when the display is not being addressed.
4.4 555 Timer:
The 555 Timer IC is an integrated circuit (chip) implementing a variety of timer and
multi vibrator applications. The IC was designed by Hans R. Camenzind in 1970 and brought
to market in 1971 by Signetics (later acquired by Philips). The original name was the SE555
(metal can)/NE555 (plastic DIP) and the part was described as "The IC Time Machine".
Fig 4.4(a): 555 Timer IC
 Usage
The connection of the pins is as follows:
Pin Name Purpose
1 GND Ground, low level (0 V)
2 TRIG OUT rises, and interval starts, when this input falls below 1/3 VCC.
3 OUT This output is driven to +VCC or GND.
4 RESET A timing interval may be interrupted by driving this input to GND.
5 CTRL "Control" access to the internal voltage divider (by default, 2/3 VCC).
6 THR The interval ends when the voltage at THR is greater than at CTRL.
7 DIS Open collector output; may discharge a capacitor between intervals.
8 V+, VCC Positive supply voltage is usually between 3 and 15 V.

19. Fig 4.4(b): 555 Timer Pin Diagram
 555 Basics
The 555 timer IC is a simple 8 pin DIL package IC. It can:
 be used as a monostable
 be used as an astable
 source or sink 100mA
 use supply voltages of 5v to 15v disrupt the power supply - use a decoupling
capacitor!
4.5 LM358 (Dual OperationalAmplifier):
The LM358 series consists of two independent, high gain; internally frequency
compensated operational amplifiers which were designed specifically to operate from a single
power supply over a wide range of voltages. Operation from split power supplies is also
possible and the low power supply current drain is independent of the magnitude of the
power supply voltage.
4.6 LM339:
These comparators are designed for use in level detection, low level sensing and memory
applications in consumer automotive and industrial electronic applications.
Fig 4.6: LM 339
The LM339 consists of four independent precision voltage comparators, with an
offset voltage Specification as low as 20㎷ max for each comparator, which were designed

20. specifically to operate from a single power supply over a wide range of voltages. Operation
from split power supplies is also possible and the low power supply current drain is
independent of the magnitude of the power supply voltage. These comparators also have a
unique characteristic in that the input common-mode voltage range includes ground, even
though they are operated from a single power supply voltage.
4.7 Relay:
A relay is an electrically operated switch. Many relays use an electromagnet to operate
a switching mechanism mechanically, but other operating principles are also used. Relays are
used where it is necessary to control a circuit by a low-power signal (with complete electrical
isolation between control and controlled circuits), or where several circuits must be
controlled by one signal.
Fig 4.7: Relay
A relay is an electrically operated switch. Current flowing through the coil of the
relay creates a magnetic field which attracts a lever and changes the switch contacts
4.8 Push Buttons:
Fig 4.8: Push Buttons
A push-button (also spelled pushbutton) or simply button is a simple switch
mechanism for controlling some aspect of a machine or a process. Buttons are typically made
out of hard material, usually plastic or metal. The surface is usually flat or shaped to
accommodate the human finger or hand, so as to be easily depressed or pushed.

21. 4.9 BC547:
The BC547 transistor is an NPN Epitaxial Silicon Transistor. The BC547 transistor is
a general-purpose transistor in small plastic packages. It is used in general-purpose switching
and amplification BC847/BC547 series 45 V, 100 mA NPN general-purpose transistors.
Fig 4.9: BC 547 Transistor
4.10 LED:
A light-emitting diode (LED) is a semiconductor light source. LEDs are used as
indicator lamps in many devices, and are increasingly used for lighting. When a light-
emitting diode is forward biased (switched on), electrons are able to recombine with holes
within the device, releasing energy in the form of photons.
Fig 4.10: symbol of LED
4.11 1N4007 (Diode):
Diodes are used to convert AC into DC these are used as half wave rectifier or full wave
rectifier. Three points must he kept in mind while using any type of diode.
1. Maximum forward current capacity
2. Maximum reverse voltage capacity
3. Maximum forward voltage capacity

22. Fig 4.11: 1N4007 diodes
4.12 Resistors:
A resistor is a two-terminal electronic component designed to oppose an electric
current by producing a voltage drop between its terminals in proportion to the current i.e, in
accordance with Ohm's law:
V = IR
Fig 4.12: Resistors
A resistor is a two-terminal passive electronic component which implements electrical
resistance as a circuit element. When a voltage V is applied across the terminals of a resistor, a current
I will flow through the resistor in direct proportion to that voltage.
4.13 Capacitors:
A capacitor or condenser is a passive electronic component consisting of a pair of
conductors separated by a dielectric. When a voltage potential difference exists between the
conductors, an electric field is present in the dielectric. This field stores energy and produces
a mechanical force between the plates. The effect is greatest between wide, flat, parallel,
narrowly separated conductors.
A capacitor (formerly known as condenser) is a device for storing electric charge. The
forms of practical capacitors vary widely, but all contain at least two conductors separated by
a non-conductor. Capacitors used as parts of electrical systems, for example, consist of metal
foils separated by a layer of insulating film.

23. Fig 4.13: Capacitors

24. 5. OPERATIONAL EXPLANATION
Synchronization failure of an alternate supply source connected to the grid is detected
by this system. The failure can be either under/over voltage or under/over frequency. The
project uses a 8051 family microcontroller to perform this operation. This mechanism is
popularly known as islanding of grid connected source.
5.1 Connections:
The output of power supply which is 5v is connected to the 40th pin. Pin 0.0, pin 0.2
of port 0 of microcontroller are connected to 1st LM339, 2nd LM339 & Relay. Pin 2.0 to pin
2.7 of port 2 of microcontroller are connected to data lines of LCD. Read, Write & Enable
pins of LCD are given to pin 3.5, pin 3.6, pin 3.7 of port 3 of microcontroller. Pin 3.4 of port
3 of microcontroller is connected to side switch.
5.2 Voltage Sensing Part:
The microcontroller is connected to the zero voltage sensing circuit to ensure the
frequency of the supply is at normal frequency of 50Hz. A VARIAC is used to get variable
voltage.
Initially both the presets are adjusted such that both the output pins of the OP-AMP
IC are at normal low and normal high level. The VARIAC is adjusted so as to get the input
AC voltage more than the normal value. Now the normally high pin of the OPAMP IC will
go low, giving an interruption pulse to the pin of the microcontroller. The microcontroller
accordingly sends a high logic pulse to switch on the relay driver, which in turn energizes the
relay and the lamp glows as it gets the AC power supply. Similarly when the VARIAC is
adjusted so as to get input AC voltage less than the normal value, at some point, the normally
low pin of the OPAMP IC goes high and the microcontroller on receiving this interruption,
sends a high logic signal to the relay driver to switch on the relay and hence the lamp which
starts glowing.
5.3 Frequency Sensing Part:

25. The VARIAC is adjusted such that the AC input voltage is at its normal value. The
microcontroller pin is connected to the output of the timer through a PNP transistor. The
timer works in astable mode to produce signals at frequencies which can be adjusted using
the variable frequency. This output is connected to the internal timer of the microcontroller
which accordingly calculates the frequency of the pulses and when the frequency of the
pulses goes beyond the normal frequency or less than the normal frequency, the relay driver
is triggered, which in turn energizes the relay and the AC supply is given to the lamp which
starts to glow.
5.4 Working:
Islanding of grid is basically to manage two parameters. One parameter is voltage and
other parameter is frequency. Since we cannot change the frequency we have taken a 555
timer in a free running astable mode, the frequency of which can be varied by R. We know
that by the R & C combination, the multi-vibrator mode of the 555 timer output can be
generated at different frequencies. This output is given to the MC pin 3.0 of port 3 of MC
which has the provision of changing the frequency 46Hz – 54Hz by varying R as explained
above through selector slide switch. So, the MC will get the changed frequency at pin 3.0 of
port 3. We also have provision of feeding the direct frequency at pin 3.0 of port 3 by the
selector slide switch since we are not sure of the direct frequency and it could be somewhere
always near 50Hz it is difficult to test it. This is the reason why we use a 555 timer for giving
precisely 52Hz or 50 KHz or 49 KHz which has to be tested by the program. In the program
it is so written that if the output from 555 timer which is fed to the MC goes to below 48 Hz
or above 52Hz the corresponding outputs of MC will go high , which will result in switching
“ON or OFF” a load to indicate that the islanding has taken place. (Frequency related).
As far as the voltage is concerned we have taken 2 comparators. Both the comparators
are given to i.e., one for inverting input and other for non-inverting input which are given at a
particular voltage. Initially they are so set that the output of these two comparators going to
MC pin 0.1 and pin 0.2 of port 2 remain high for low voltage and for the high voltage it is
held low. So, when the input voltage changes at R8 which is a rectified voltage which is
coming from the DC voltage, when the input voltage changes i.e., if it goes high, (it given a
high command) and if it goes low (it gives a low command) to the microcontroller. That is
how the low-high, high-low commands are handled by microcontroller then the program
takes ones.

26. CONCLUSION
The project is designed to develop a system to detect the synchronization failure of
any external supply source to the power grid on sensing the abnormalities in frequency and
voltage.
There are several power generation units connected to the grid such as hydel, thermal,
solar etc to supply power to the load. These generating units need to supply power according
to the rules of the grid. These rules involve maintaining a voltage variation within limits and
also the frequency. If any deviation from the acceptable limit of the grid it is mandatory that
the same feeder should automatically get disconnected from the grid which by effect is
termed as islanding. This prevents in large scale brown out or black out of the grid power. So
it is preferable to have a system which can warn the grid in advance so that alternate
arrangements are kept on standby to avoid complete grid failure.

27. REFERENCES
 www.atmel.com
 www.beyondlogic.org
 www.wikipedia.org
 www.howstuffworks.com
 www.alldatasheets.com
 www.Scribd.com