Transformer Protection using PLC

PARAMETER MEASUREMENT AND PROTECTION FOR ELECTRICAL
TRANSFORMERS USING POWER LINE COMMUNICATION
Department of Electrical and Electronics Engineering, GAT 0
CHAPTER 1
INTRODUCTION
1.1 Background of study
Protection against fault in power systems (PS) is very essential and vital
for reliable performance. A power system is said to be faulty when an undesirable
condition occurs in that power system, where the undesirable condition might be
short circuits, overcurrent, overvoltage etc.
The power transformer is one of the most significant equipment in the
electric power system, and transformer protection is an essential part of the general
system protection approach. Transformers are used in a wide variety of
applications, from small distribution transformers serving one or more users to very
large units that are an integral part of the bulk power system (Anderson, 1998,
P.673).
Moreover with the increasing population and their unavoidable
demands, leads to the high increase demands on electrical power. With this increase
in demand of power, the existing systems may become overloaded. The overloading
at the consumer end appears at the transformer terminals which can affect its
efficiency and protection systems. One of the reported damage or tripping of the
distribution transformer is due to thermal overload. To escape the damaging of
transformer due to overloading from consumer end, it involves the control against
overcurrent tripping of distribution transformer. Where the technology of the day
has given the opportunity to use the latest trends, and microprocessor,
microcontrollers are one of the day requirements to apply in the remote protection
of the transformer.

The purpose of power system protection is to detect faults or abnormal
operating conditions and to initiate corrective action. Relays must be able to evaluate a
wide variety of parameters to establish that corrective action is required. Obviously, a
relay cannot prevent the fault. Its primary purpose is to detect the fault and take the
necessary action to minimize the damage to the equipment or to the system. The most
common parameters which reflect the presence of a fault are the voltages and currents at
the terminals of the protected apparatus or at the appropriate zone boundaries.
The Protective relays require reasonably accurate reproduction of the
abnormal and normal conditions in the power system for correct sensing and operation.
This information input from the power systems are usually through Current Transformer
(CT) and Voltage Transformer (VT).
Furthermore, for the past several years fuse, circuit breakers and
electromechanical relays were used for the protection of power systems. The traditional
protective fuses and electrometrical relays present several draw backs.
Alternatively, some researches were conducted on relay which can be
interfaced to microprocessors in order to eradicate the drawbacks of the traditional
protective techniques which led to many improvements in transformer protection in
terms of lower installation and maintenance costs, better reliability, improved
protection and control and faster restoration of outages.
Therefore a proposed solution is chosen to develop a microcontroller based
transformer overload protection prototype because the microprocessors based relays
provides greater flexibility, more adjustable characteristics, increased range of setting,
high accuracy, reduced size, and lower costs, along with many ancillary functions, such
as control logic, event recording, fault location data, remote setting, self-monitoring and
checking, etc.

1.2 Problem statement
An essential concern in transformer protection is the high cost of the
transformer and the relative long outage time that occurs when a large transformer fails.
The proper type of protection can often detect initial faults before they become major,
and thereby prevent major physical damage and long outage times.
Transformers experiences faults which leads to deterioration and acceleration
aging and failure of transformer winding resulting from insulation failures, one of the
causes is the over current. Due to overload and externally applied conditions including
over current and external short circuit causes rise in temperature of both transformer oil
and windings.
Whenever the winding temperature raises and exceeds transformer thermal
limits, the insulation will deteriorate and may fail prematurely. Continuous thermal
overload (over temperature) might weaken the insulation of a transformer and resulting in
rapid transformer loss of life.
Over excitation (an increase in system voltage), internal faults can lead to
deterioration, acceleration aging and fault trips in transformer protection function.
Similarly, transformers must not be subjected to prolong overvoltage. For
maximum efficiency they are operated near the knee of their saturation curve, so at
voltages above 110% of rated, the exciting current becomes very high. Just a few percent
increase in voltage results in a very large increase in current. These large currents can
destroy the unit if they are not reduced promptly.
However engineers and scientist have worked out various ways in which the
transformer can be protected; one of such ways is by using a relay. Therefore in order to
protect the transformer using relay, a control system idea is developed through the use of
microcontroller, hence the name of the project.

1.3 Aim and Objectives
1.3.1 Aim: The aim of this project is to design and implement a microcontroller based
transformer protection system through power line carrier communication.
1.3.2 Objectives
1. To design the current and voltage sensing circuits that will be interfaced
to the microcontroller for monitoring through power line carrier communication.
2. To develop an algorithm and codes to the microcontroller which will work for under
over current, over voltage, under voltage conditions and transmit the parameters to a
personal computer.
3. To analyze and validate the performance of this system using appropriate simulation
software.
4. To protect transformer from faults like short circuit, and measure the parameters like oil
level, fire detect temperature.
1.4 Research scope
The overall aim of the study is to build a microcontroller based transformer
protection with transformer parameters monitoring capabilities. This protection is based
on the transformer parameters fed into the ADC of the microcontroller and monitoring
the transformer parameters through PC. Immediately a fault is detected the
microcontroller taking necessary action through power line carrier communication.
Furthermore, the limitation of the entire project is divided into two. First part of the
project is to design and build the hardware of the entire system. Where a voltage
transformer of 230:160 VAC, current sensor, electromechanical relay, microcontroller,
LCD display, and finally a power supply that can generate 5VDC in order to activate the
relay circuit, the microcontroller and LCD and plcc modems. The second part is the

development of a C language program that will satisfy the protection of the transformer
algorithm.
Correspondingly, the system development will also concentrate on elaborating
and designing a suitable transmitter module using microcontroller based circuit. An AVR
microcontroller was selected for this project because of its universal synchronous
asynchronous receiver and transmitter (USART), inbuilt ADC functionalities etc.
Finally, the highest priority is given to the software design and
implementation in order to develop a suitable algorithm that will promptly interact with
the, microcontroller and the personal computer through power line carrier
communication.

CHAPTER 2
LITERATURE REVIEW AND
THEORETICAL BACKGROUND
2.1 Literature Review
Enormous work has been done on protection of power transformers such as:
overload voltages, over current and external short-circuit etc. Some of those researches
which had been conducted, their setbacks, ambiguities and merits are as discussed in the
subsequent paragraphs.
In 2003 Ali Reza Fereidunian proposed a design which was based on a digital
differential relays for transformer protection using Walsh series and least square
Estimators. The Two estimators were been developed using the Walsh series and least
square algorithms. The transformer internal fault (short circuit) protection function was
the functionality of the differential relay. The performance of the proposed relay was
tested for internal, external faults and inrush current of the transformer. In their project
the digital differential relaying scheme comprised of filter, pre-process, data acquisition
system and a decision maker. The protective relay performs the duty of making decision
about the faulted or non-faulted situations.
The transformer internal faults and the external faults situations were tested on
the designed differential relay, and the results of these test illustrates the efficiency of the
system. Also, it was seen that both estimation algorithms perform their job correctly, but
the Walsh series acts better than least squares algorithm estimation (Ali Reza et al.,
2003).

Furthermore in 2007 S.M. Bashi et al, designed and built a microcontroller
based syste for power transformer protection. The system includes facilities for
discrimination between internal fault current and magnetizing inrush current, differential
protection, over current protection has been included.
The performances of the proposed system have been examined and from the
experimental readings and observation, it was understood that the proposed system
monitors and controls the transformer when there is any fault ( Bashi et al 2007).
In 2010 V. Thiyagarajan and T.G. Palanivel proposed an innovative design to
develop a system based on microcontroller that was used for monitoring the current of a
distribution transformer in a substation and to protect the system from the rise in current
due to overloading. The protection of the distribution transformer was accomplished by
shutting down the entire unit with the aid of radio frequency communication.
The performance of the proposed system had been examined with three
various types of loading which had been added to the transformer. From the experimental
observations it was understood that, the proposed system monitors and controls the
transformer in an efficient manner. Whenever an over current was sensed by the system
while monitoring the transformer, it directs the main station to shut down the transformer
and thus it guards the unit from any serious damages (Thiyagarajan et al 2010).
In June 2006 Atthapol Ngaopitakkul and Anantawat presented an algorithm
based on a combination of discrete wavelet transformer and neural networks for detection
and classification of internal faults in a two winding three-phase transformer. The fault
conditions of the transformer are simulated using ATP/EMTP in order to obtain current
signals. The training process for the neural network and fault diagnosis decision are
implemented using MATLAB.
It was found that the proposed method gave a satisfactory accuracy and can
be useful in a development of a modern differential relay for transformer protection

scheme (Ngaopitakkul et al, 2006).
Larner et al presented a paper that attempts to review the concept of a fuse
application on high voltage Power transformers. The practical connecting of a power
transformer directly to a transmission line through fuse was discussed and was found that
the fuse presents several problems in the protection. One of the stated problem that a fuse
is that it cannot detect a fault current resulting from turn-to turn faults within the
protected transformer which can be well below the load current rating of the transformer
(Larner et al 1959).
In 2010 Mazouz et al conducted a new approach research for transformer
differential protection that ensures security for external faults, inrush and over-excitation
conditions and provided dependability for internal faults. The approach uses
programmable logic controllers (PLCs) to realize transformer differential protection.
It was concluded that the PLCs gave the protection circuits more flexibility
and makes their integration with other protection and control circuits easier. And also
found that the differential protection using PLCs provided high sensitivity for internal
faults and high stability for external faults and magnetizing inrush currents (Mazouz et al
2010).
Finally in 2000 Vaccaro et al proposed a neural diagnostic system for
transformer thermal overload protection. The research was conducted because the IEEE
power system relaying committee were lacking inaccuracy in the prediction of maximum
winding hot-spot temperature of a power transformer in the presence of overload
conditions. The proposed method was based on a radial basis function network (RBFN)
which taking in to account the load current, the top oil temperature rise over the ambient
temperature and other meteorological parameters, permits recognition of the hot-spot
temperature pattern.
The radial basis function network (RBFN) based algorithm was designed and
trained, in order to estimate the winding hot-spot transformer temperature

from knowledge of the experimental top oil temperature, weather conditions and load
current data obtained from a laboratory prototype mineral-oil-immersed transformer.
Finally, the RBFN-based algorithm for the identification of the dynamic
thermal overload in power transformers have been developed and was found that the
accuracy was improved compared with the results obtained from the IEEE power system
relay committee (Vaccaro et al 2000).
From the above review, it is finally concluded that researches done on the
transformer protection have some weaknesses; therefore by using the proposed method,
which is by using microcontroller based approach, the protection will be enhanced to a
better protection because the application of microcontroller in protecting transformer
against overcurrent and over voltage is speedily growing.
2.2 Theoretical Background
From the reviewed journals, based on S.M. Bashi work, this project plan to
design, analyse and implement the hardware of the system. Correspondingly, it is
understood that the topic of research is an advanced area of power systems protection
engineering which is normally being explored by power engineers. The purpose of the
system design is to solve complex and eradicate the problems encountered using the local
protection techniques such as fuse, circuit breakers etc.
The project is based on microcontroller transformer protection with PC based
transformer parameters monitoring capabilities. This protection is focused on the
transformer parameters feed into the ADC of the microcontroller and monitoring the
transformer voltage, current and temperature through personal computer through power
line carrier communication. The voltage transformer will be connected across a variable
AC input source using an autotransformer which can be varied from 0-250VAC. The
output of the transformer (secondary) will beconnected to electric bulbs which will serve
as loads. The load current will be monitored by connecting a current sensor in series

between the load and the secondary side of the transformer.
The transformer voltage will be monitored through rectifying a step down
230-12VAC transformer to a pure 5VDC and then feed to the microcontroller ADC pin
for voltage monitoring. The input of the step down transformer will be connected to
autotransformer and the output will be perfectly rectified to a pure 5VAC.
Whenever the input voltage is varied, the microcontroller shows the value of
the voltage on an LCD and also on the PC through power line carrier communication. As
input voltage is varied above 230VAC, the microcontroller detects an over voltage fault
and it sends a trip signal to the voltage protective relay for protecting the transformer and
the load connected.
Similarly, the microcontroller monitor’s the load current and temperature of
transformer and displays the values on LCD and on the PC. Whenever loads are added to
the secondary side of the transformer, the current at the secondary side rise. As the load
current exceeds the rated current rating of the transformer, the temperature of the
secondary winding rises, therefore the microcontroller will send a trip signal to the
overcurrent protective relay, thereby protecting the transformer from burning.
`

CHAPTER 3
SYSTEM DESIGN
3.1 Overview
Transmitter:-
RECEIVER:-
Fig 3.1: Block diagram of the system
ARM
MICROCONTROLLER
(LPC2148)ADC
Transformer
(230-12V)
VOLTAGE
MEASURING
CIRCUIT
ALCD
FIRE
Detector
TEMPERATUE
SENSOR
OIL Level
LOAD
PLCC
Modem
Relay
Main
supply
Current
sensor
DC
Adaptor
Power supply
12V,5V
230v Electric
Mains
PLC Modem Computer

The primary of the 230:160VAC transformer is connected to a variable AC input
voltage (autotransformer), and the output is connected to a load which is usually
electrical appliances such as bulbs, electric heater etc.
At the primary side of the 230:160VAC transformer, a step down 230-12VAC
transformer is rectified to a pure 5VDC and feed into the ADC pin of the microcontroller
for monitoring the voltage of the transformer.
At the secondary side of the transformer, a current sensor is connected in
series between the load and the transformer secondary terminal for sensing, the load
current, output of the current sensor is then feed to the microcontroller ADC pin for
monitoring.
The LCD is used to display the transformer voltage, current and temperature,
similarly the personal computer is used to display the transformer parameters for
monitoring purpose through power line carrier communication.
While monitoring the transformer parameters, whenever the load current
exceeds the transformer rated current, the microcontroller detects an overcurrent faults
and it sends a trip signal to the overcurrent relay, thereby protecting the transformer from
blowing off.
Moreover, when the autotransformer secondary is varied above the specific
limit, the microcontroller detects an overvoltage faults and it sends a trip signal to the
overvoltage protective relay, thereby protecting the transformer and the loads from
blowing off.
Moreover , when short circuit occur then the signal from microntroller send to
the relay ,the relay trip and the load disconnected and the fault is displayed on the LCD
display and through power line carrier communication on the computer.
Similarly, for fire detector ,oil level detector ,temperature sensor if the fault
had occurred then sensor will detect the and the signal is send to microcontroller then

the relay trip and the load disconnected and the fault is displayed on the LCD display and
through power line carrier communication on the computer.
3.2 Component details
Based on the various reviews conducted on transformer protection and the
above block diagram which was conceived out of those literature reviews conducted,
numbers of components are required in developing the protection system.
3.2.1 Microcontroller
The microcontroller is required to serve the purpose monitoring the
transformer information such as temperature, voltage and current through the LCD
display, personal computer and triggering the relay when there is any fault. Modern
power networks require faster, more accurate and reliable protective schemes.
Microcontroller-based protective schemes are capable of fulfilling these
requirements. They are superior to electromagnetic and static relays. These schemes have
more flexibility due to their programmable approach when compared with the static
relays which have hardwired circuitry.
Therefore in order to achieve this task the The LPC2141/42/44/46/48
microcontrollers are based on a 16-bit/32-bit ARM7TDMI-S CPU with real-time
emulation and embedded trace support, that combine microcontroller with embedded high
speed flash memory ranging from 32 kB to 512 kB. A 128-bit wide memory interface and
a unique accelerator architecture enable 32-bit code execution at the maximum clock rate.
For critical code size applications, the alternative 16-bit Thumb mode reduces
code by more than 30 % with minimal performance penalty.
Due to their tiny size and low power consumption, LPC2141/42/44/46/48 are ideal
for applications where miniaturization is a key requirement, such as access control and
point-of-sale. Serial communications interfaces ranging from a USB 2.0 Full-speed

device, multiple UARTs, SPI, SSP to I2C-bus and on-chip SRAM of 8 kB up to 40 kB,
make these devices very well suited for communication gateways and protocol converters,
soft modems, voice recognition and low end imaging, providing both large buffer size and
high processing power. Various 32-bit timers, single or dual 10-bit. ADC(s), 10-bit DAC,
PWM channels and 45 fast GPIO lines with up to nine edge or level sensitive external
interrupt pins make these microcontrollers suitable for industrial control and medical
systems.
Fig 3.2: ARM microcontroller(LPC2148)

Fig 3.3: ARM pin diagram

ARM MICROCONTROLLER FEATURES:
• 16-bit/32-bit ARM7TDMI-S microcontroller in a tiny LQFP64 package.
• 8 kB to 40 kB of on-chip static RAM and 32 kB to 512 kB of on-chip flash.
• memory. 128-bit wide interface/accelerator enables high-speed 60 MHz operation.
• In-System Programming/In-Application Programming (ISP/IAP) via on-chip boot.
• loader software. Single flash sector or full chip erase in 400 ms and programming of
256 bytes in 1 ms.
• Embedded ICE RT and Embedded Trace interfaces offer real-time debugging with the
on-chip Real Monitor software and high-speed tracing of instruction execution.
• USB 2.0 Full-speed compliant device controller with 2 kB of endpoint RAM. In
addition, the LPC2146/48 provides 8 kB of on-chip RAM accessible to USB by
DMA.
• One or two (LPC2141/42 vs. LPC2144/46/48) 10-bit ADCs provide a total of
6/14 analog inputs,with conversion times as low as 2.44 μs per channel.
• Single 10-bit DAC provides variable analog output (LPC2142/44/46/48 only).

3.2.2 POWER LINE CARRIER COMMUNICATION MODEM
Fig 3.4: Power line carrier communication modem
URQ-1120F + is a 9-pin single row of small volume high-performance the zero carrier data
transceiver module. Is designed for 220V AC, strong interference, strong attenuation, long-
range requirements of the environment, the reliable transmission of data and high cost of

specially designed and developed carrier module. Suitable for meter reading, street lighting,
smart home, fire, building control and other applications that require power lines to transmit
data.
URQ-1120E + / K + is also a single row 9-pin small footprint and high performance
carrier data transceiver module. DSP processing module further improve anti-jamming
capability, designed specifically for the 0V-220V AC-DC, power outages, and no power
environment (such as pipes and the earth, a signal line and the earth, two signal on the basis of
the URQ-11200E line, 12V AC and DC power cord, etc.), the reliable transmission of data and
the high cost of the specially designed and developed carrier module. Suitable for industrial
control, railway, intelligent, smart home, building control and the need for carrier data transfer
applications. The URQ-1120F + carrier rate is 100BPS the highest carrier rate URQ-1120E +
400BPS highest carrier rate the URQ-1120K + 2400BPS.
First, the performance of the URQ-1120 Integrated URQ-1120 module, and peripheral
circuits of the carrier plate, without the rest of the coupling element, directly connected to a
220V AC use. Dimensions 53 × 38 × 17 mm (L × D × H), single row pin leads (see below) 1,2
pin 220V AC power direction (1 foot, 2 feet spacing 2X0.1 inch) 2 feet, 3 feet spacing of 1.1
inches, 0.1 inches spacing between the rest of the foot.
Operating frequency 120 ~ 135KHZ, interface baud rate of 9600bps. A start bit, 8 data
bits, one stop bit Temperature range: -25 ℃ ~ +70 ℃ Humidity ≤ 90%
A continuous transmission ≥ 253 bytes in length, the byte length from 1 to 253 defined by the
user, the module does not send redundant data.
Receiver sensitivity ≤ 1mV
module receives the noise data.
Receive data or 9600BPS asynchronous mode, the format of a start bit, 8 data bits, 1 stop bit
format, sent from the TX, but about to be sent every 0.09 seconds. In custom mode equivalent.
Custom work mode: the user define the transmission of data in accordance with the company, a
transmission of data is defined as follows:
The first byte: To transmit a number of bytes 0-250 (excluding the first byte)

The second byte to the first n +1 bytes: byte data the user needs to be transmitted
Note: when the module has not transmitted a data does not receive the next frame data.
Receive data and transmit data equivalent.
If sent to the RX side output in other modules TX: 02 AE 87 02 AE 87
02 is a byte length, and this indicates that the following two bytes of data.
If sent to the RX side: 0,901,020,304,050,607 08 09
Output in the other module TX 08 09 0,901,020,304,050,607
09 is a byte length, which means that there are nine bytes of data behind.
The largest byte length to 253.
If sent to the RX side: FD 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E ... FD
In other modules TX output FD 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E ... FD
The valid data can be to the 253.
URQ-1120 series modules distinction:
URQ-1120F + is specifically for AC 220V/110V 50HZ/60HZ strong interference design based
on the exchange of zero transmission scheme carrier module, mains above transmission effect,
transmission distance. To transfer data in the case of AC power, the carrier rate is
50HZ/100BPS, 60HZ/120BPS our by optimization nine BIT can send a byte.
3.2.3.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.

Fig 3.5: A typical transformer
The input coil is called the primary and the output coil is called the secondary. There is no
electrical connection between the two coils; instead they are linked by an alternating magnetic
field created in the soft-iron core of the transformer. The two lines in the middle of the circuit
symbol represent the core. Transformers waste very little power so the power out is (almost)
equal to the power in. Note that as voltage is stepped down and current is stepped up.
The ratio of the number of turns on each coil, called the turn’s ratio, determines the
ratio of the voltages. A step-down transformer has a large number of turns on its primary
(input) coil which is connected to the high voltage mains supply, and a small number of turns
on its secondary (output) coil to give a low output voltage.
TURNS RATIO = (Vp / Vs) = ( Np / Ns )
Where,
Vp = primary (input) voltage.
Vs = secondary (output) voltage.
Np = number of turns on primary coil.
Ns = number of turns on secondary coil.
Ip = primary (input) current.
Is = secondary (output) current.
Ideal power equation

Fig 3.6: The ideal transformer as a circuit element
If the secondary coil is attached to a load that allows current to flow, electrical power is
transmitted from the primary circuit to the secondary circuit. Ideally, the transformer is
perfectly efficient; all the incoming energy is transformed from the primary circuit to the
magnetic field and into the secondary circuit. If this condition is met, the incoming electric
power must equal the outgoing power:
Giving the ideal transformer equation
Transformers normally have high efficiency, so this formula is a reasonable approximation. If
the voltage is increased, then the current is decreased by the same factor. The impedance in one
circuit is transformed by the square of the turn’s ratio. For example, if an impedance Zs is
attached across the terminals of the secondary coil, it appears to the primary circuit to have an
impedance of (Np/Ns)2Zs. This relationship is reciprocal, so that the impedance Zp of the
primary circuit appears to the secondary to be (Ns/Np)2Zp.

3.2.4 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. Rectifiers have many uses including as components of power
supplies and as detectors of radio signals. Rectifiers may be made of solid K es, vacuum tube
diodes, mercury arc valves, and other components. 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. In positive half cycleonly two diodes( 1 set of parallel diodes) will
conduct, in negative half cycle remaining two diodes will conduct and they will conduct only
in forward bias only.
Fig 3.7: Circuit diagram and waveform for bridge rectifier
3.2.4.1 Over voltage protection circuit
The over voltage and under voltage protection circuit is capable of measuring
and monitoring voltage from 200 to 250VAC. In this project the voltage can be increased

or decreased by using the autotransformer and the output of the voltage monitoring
circuit is fed to ADC converter, whenever the voltage is varied to 200VAC, the
microcontroller will detect under voltage fault and whenever the voltage is varied to
250VAC, the microcontroller detects over voltage fault, consequently the microcontroller
sends a trip signal to the relay, and the relays cuts the primary of the transformer from the
AC mains, thereby protecting the transformer.
Fig 3.8: Over voltage sensing circuit
In Figure 3.8, a step down transformer of 230-12VAC was used and was
rectified to a pure dc using the capacitor and then adjusted to voltage within 5VAC using
the potentiometer in order to be fed the analogue signal into the ADC without burning the
ADC converter.
Whenever the primary voltage of the transformer is adjusted, the secondary
voltage also changes, and based on the microcontroller program, the input voltage can be
monitor, displayed and the transformer can be protected from any over voltage fault.

From equation 3, the VAC is the RMS transformer voltage and the 0.7V is the
voltage drop across the rectifier. As there are two diodes conducting for each half cycle,
therefore there will be two rectifier voltage drops.
3.2.5 RESISTOR
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, that is, in
accordance with Ohm's law:
V = IR
Resistors are used as part of electrical networks and electronic circuits. They are extremely
commonplace in most electronic equipment. Practical resistors can be made of various
compounds and films, as well as resistance wire (wire made of a high-resistivity alloy, such as
nickel/chrome).
The primary characteristics of resistors are their resistance and the power they can
dissipate. Other characteristics include temperature coefficient, noise, and inductance. Less
well-known is critical resistance, the value below which power dissipation limits the maximum
permitted current flow, and above which the limit is applied voltage. Critical resistance
depends upon the materials constituting the resistor as well as its physical dimensions; it's
determined by design. Resistors can be integrated into hybrid and printed circuits, as well as
integrated circuits. Size, and position of leads (or terminals) are relevant to equipment
designers; resistors must be physically large enough not to overheat when dissipating their
power.

Fig 3.9: Various types of resistor
A resistor is a two-terminal passive HYPERLINK
"http://en.wikipedia.org/wiki/Electronic_component"electronicHYPERLINK
"http://en.wikipedia.org/wiki/Electronic_component" 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. The reciprocal of the
constant of proportionality is known as the resistance R, since, with a given voltage V, a larger
value of R further "resists" the flow of current I as given by Ohm's law:
Resistors are common elements of electrical networks and electronic circuits and are
ubiquitous in most electronic equipment. Practical resistors can be made of various compounds
and films, as well as resistance wire (wire made of a high-resistivity alloy, such as nickel-
chrome). Resistors are also implemented within integrated circuits, particularly analog devices,
and can also be integrated into hybrid and printed circuits.
The electrical functionality of a resistor is specified by its resistance: common
commercial resistors are manufactured over a range of more than 9 orders of magnitude. When
specifying that resistance in an electronic design, the required precision of the resistance may
require attention to the manufacturing tolerance of the chosen resistor, according to its specific

application. The temperature coefficient of the resistance may also be of concern in some
precision applications. Practical resistors are also specified as having a maximum power rating
which must exceed the anticipated power dissipation of that resistor in a particular circuit: this
is mainly of concern in power electronics applications. Resistors with higher power ratings are
physically larger and may require heat sinking. In a high voltage circuit, attention must
sometimes be paid to the rated maximum working voltage of the resistor.
The series inductance of a practical resistor causes its behavior to depart from ohms
law; this specification can be important in some high-frequency applications for smaller values
of resistance. In a low-noise amplifier or pre-amp the noise characteristics of a resistor may be
an issue. The unwanted inductance, excess noise, and temperature coefficient are mainly
dependent on the technology used in manufacturing the resistor. They are not normally
specified individually for a particular family of resistors manufactured using a particular
technology. A family of discrete resistors is also characterized according to its form factor, that
is, the size of the device and position of its leads (or terminals) which is relevant in the
practical manufacturing of circuits using them.
3.2.6 CAPACITOR
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.
An ideal capacitor is characterized by a single constant value, capacitance, which is
measured in farads. This is the ratio of the electric charge on each conductor to the potential

difference between them. In practice, the dielectric between the plates passes a small amount of
leakage current. The conductors and leads introduce an equivalent series resistance and the
dielectric has an electric field strength limit resulting in a breakdown voltage.
The properties of capacitors in a circuit may determine the resonant frequency and
quality factor of a resonant circuit, power dissipation and operating frequency in a digital logic
circuit, energy capacity in a high-power system, and many other important aspects.
Fig 3.10: Various types of capacitors
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.
Capacitors are widely used in electronic circuits for blocking direct current while
allowing alternating current to pass, in filter networks, for smoothing the output of power
supplies, in the resonant circuits that tune radios to particular frequencies and for many other
purposes.
A capacitor is a passive component consisting of a pair of conductors separated by a
dielectric (insulator). When there is a potential difference (voltage) across the conductors, a

static electric field develops in the dielectric that stores energy and produces a mechanical
force between the conductors. An ideal capacitor is characterized by a single constant value,
capacitance, measured in farads. This is the ratio of the electric charge on each conductor to the
potential difference between them.
The capacitance is greatest when there is a narrow separation between large areas of
conductor, hence capacitor conductors are often called "plates", referring to an early means of
construction. In practice the dielectric between the plates passes a small amount of leakage
current and also has an electric field strength limit, resulting in a breakdown voltage, while the
conductors and leads introduce an undesired inductance and resistance.

3.2.7 Current sensor
+
Fig 3.11: Current sensor
The protection of the transformer against over current is concerned with the
detection and measurement of fault, where the measurement can be dangerous and indeed
impossible to measure if the actual load and fault currents are very large. A professional
way of avoiding these difficulties is to use the current sensor. Therefore in the block
diagram, current transformer is used to measure the load current.
The current sensor ACS756 was used because the current sensor ICs provides
economical and precise solution for AC or DC current sensing in industrial, automotive,
commercial, and communication systems. The device package allows for implementation
by the customer. Typical applications include motor control, load detection and
management, power supplies and overcurrent fault protection. The current sensor is
capable of measuring up to 50A.The monitored current values are displayed on the LCD
display and as soon the voltage transformer is overloaded the current transformer sends
the information through the ADC and the microcontroller energizes the relay, thereby
protecting the transformer.

3.2.7.1 Overcurrent protection circuit
An ammeter cannot be used in measuring the load current in this project
because an analogue signal most be fed into the ADC of the microcontroller for
monitoring the load current. A current sensor was found to be the suitable current sensing
device for this purpose. The current sensor used can measure up to 50A. The BB-
ACS756 comes with one set of dean-T connector and a 3 ways right angle pin header.
The ACS756 is power up with 5VDC and gives out voltage to indicate the direction and
current value.
The output of the current sensor is fed to Micro-controller ADC unit for
taking the necessary action. The current flowing through the CT primary can be
measured, for this purpose, digital display is provided at the output of the Micro-
controller Chip.

Fig 3.12: Shows the circuit diagram of the current sensing circuit
3.2.8 RELAY
Fig 3.13: A typical 8 pin 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. The first relays were used in long distance telegraph circuits,

repeating the signal coming in from one circuit and re-transmitting it to another. Relays
were used extensively in telephone exchanges and early computers to perform logical
operations.
A type of relay that can handle the high power required to directly control an
electric motor or other loads is called a contactor. Solid-state relays control power circuits
with no moving parts, instead using a semiconductor device to perform switching. Relays
with calibrated operating characteristics and sometimes multiple operating coils are used to
protect electrical circuits from overload or faults; in modern electric power systems these
functions are performed by digital instruments still called "protective relays".
The relay is an electrically controllable switch widely used in industrial
controls, automobiles, and appliances. It allows the isolation of two separate sections of a
system with two different voltage sources. For example, a +5V system can be isolated
from a 120V system by placing a relay in between them. One such relay is called an
electromechanical or electromagnetic relay EMR as shown in figure 3.13. The EMRs
have three components: the coil, spring and contacts. In Figure 3.13, a digital +5V can
control a 230Vac lamp without any physical contact between them. When current flows
through the coil, a magnetic field is created around the coil (the coil is energized), which
causes the armature to be attracted to the coil. The armature’s contact acts like a
switch and closes or opens the circuit.
The relay serves as the protective device of the entire system. The relay
receives trip signal from the microcontroller and thereby cutting the transformer primary
from the input ac source hence protecting the transformer.

3.2.8.1 Relay Driver Circuit
Microcontroller pins lack sufficient current to drive a relay. While the 6volts
relay’s coil needs around 12mA to be energized, the current is obtained by the V/R
expression. For example, if the coil is 6VDC and the coil resistance is 500Ω, a minimum
of 12mA (6V/500Ω = 12mA) is need to energize the relay while the microcontroller’s pin
can provide a maximum of 1-2mA current, therefore a transistor was used as relay driver
which is placed between the microcontroller and the relay as shown in figure 3.13.
Fig 3.14: 1230V A Clamp switched ON using microcontroller based relay

3.2.8.2 Transistor used as Driver
The transistor is used as the driver and the basic function of the driver
circuit is to provide the necessary current to energize the relay coil. The Resistor
R1 is used to set the base current for the transistor, the value of R1 should be such
that when input voltage is applied to the transistor, it is driven into saturation i.e. it
is fully turned ON and the Relay is energized. It’s important that the transistor is
driven into saturation so that the voltage drop across the transistor is minimum
thereby dissipating very little power.
The protection diode in the circuit is used to protect the transistor from
the reverse current generated from the coil of the relay during the switch off time.

3.2.9 VOLTAGE REGULATOR
Fig 3.15: Voltage regulator (LM317)
The LM317PS 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 shut down 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.

TABLE 3.1: ELECTRICAL CHARACTERISTICS OF LM317PS

3.2.10 LIQUID CRYSTAL DISPLAY
In recent years the LCD is finding widespread use replacing LEDs
This is due to following reasons
• The declining prices of LCDs
• The ability to display numbers, characters and graphics. This is in contrast to LEDs,
which are limited to numbers and few characters.
• Incorporation of a refreshing controller in to LCD, there by relieving the CPU of the
task of refreshing the LCD. In contrast LCD must be refreshed by CPU to keep
displaying the data.
Fig 3.16: LCD display
 Even limited to character based modules, there is still a wide variety of shapes and
sizes available.
 This section deals with the character based LCD module which use Hitachi HD44780
controller chip. These modules are not quite as advanced as the latest generation, full
size, full color, back lit types used in today’s laptop computers, but far from being
“phased out”, Character based LCDs, are still used extensively in commercial and
industrial equipment ,particularly where display requirements are reasonably simple.

Table 3.2: LCD pin Description
Pin Symbol I/O Description
1 Vss - Ground
2 Vcc - +5V Power Supply
3 Vee - Power Supply to contrast
4 RS I RS = 0 to select command
register
5 R/W I RS = 1 to select data register
6 EN I/O Enable
7 to 14 D0 to D8 I/O 8 bit data bus
3.2.10.1 CONNECTIONS
A 14 pin access is provided having 8 data lines,3 control lines and 3 power lines. The
connections are laid out in one of two common configurations, either two row of seven pins, or
a single row of 14 pins.
On most displays, the pins are numbered on the LCD’s PCB, but if not, it is quite
easy to locate pin1.Since this pin is connected to ground, it often has a thicker PCB track
connected to it and it is generally connected to the metal work at some point. The block
diagram of an LCD module with all the pin details is shown in Table 3.2.
The function of each of the connections is shown in table 1.Pin 1 and 2 are the power supply
lines, Vss and Vdd. The Vdd pin should be connected to positive supply and Vss to 0V supply
or ground. Although the LCD module data sheets specify a 5VDC supply.
Supplies of 6V and 4-5V both work well, and even 3V is sufficient for some modules.Pin 3 is a
control pin ,Vee , which is used to alter the contrast of the display. Ideally, this pin should be
connected to a variable voltage supply.

Pin 4 is the (RS)register select line. When this line is low, data bytes transferred to the display
are treated as commands and data bytes read from the display indicate its status.By setting the
RS line high, character data can be transferred to and from the module.Pin 5 is read/write line.
this line is pulled low in order to write commands or character data to the module, or pulled
high to read character data or status information from its registers.
Table 3.3: Pin description
3.2.11 Power Supply design
3.2.11.1 Power supply theory
The power supply circuit design is one of the important parts of this project,
without a power supply the electronic devices such as microcontroller, relay, alarm, LCD
etc. display will not function. Similarly a wrong power supply design will lead to the
damaging of the electronic devices used in this project.
The main power supplies needed for this project is 5VDC in order to power on
the relay and other electronic devices such as microcontroller etc. The design is done
using a transformer, bridge rectifiers, filter capacitor and a voltage regulator.Figure 3.17
shows the sequential process of designing a constant DC power supply.

230 V, 50 Hz
Ac
Transformer
20:1
Bridge
Rectifier
Filter Regulator
LM78**
Fig 3.17: Transformer power supply
In Figure 3.17 the input voltage is obtained the main 230VAC outlet and then
connected to the transformer. A step down transformer is used in stepping the 230VAC to
a 12VAC.The 12VAC serves as an input voltage to the bridge rectifier which is basically
for diodes connected where two diodes are in forward biased and the other two are in
reversed biased for each half cycles. The bridge rectifier is used in converting the 12VAC
into a dc voltage.
The filter capacitor serves as a smoother to smooth the dc voltage from the
bridge rectifier and the LM317PS is the voltage regulators which purposely stabilizes the
output voltages to 6VDC and 5VDC.

3.2.12 Temperature sensing unit
The LM35 was chosen to be the temperature sensing device in this project.
The LM35 series are precision integrated-circuit temperature sensors, whose output
voltage is linearly proportional to the Celsius (Centigrade) temperature. The LM35 thus
has an advantage over linear temperature sensors calibrated in degree Kelvin, as the user
is not required to subtract a large constant voltage from its output to obtain convenient
Centigrade scaling with a rated operating temperature range of over -55° to +150°C
Fig 3.18: Temperature sensor
These sensors use a solid-state technique to determine the temperature. That is
to say, they don’t use mercury (like old thermometers), bimetallic strips (like in some
home thermometers or stoves), nor do they use thermistors (temperature sensitive
resistors). Instead, they use the fact as temperature increases, the voltage across a diode
increases at a known rate.

Similarly, the LM35 is chosen over thermocouples because it can measure
temperature more accurately than a using a thermistor. The sensor circuitry is sealed and
not subject to oxidation, etc. The LM35 generates a higher output voltage than
thermocouples and may not require that the output voltage be amplified. Figure 3.19
shows an LM35 sensor interfaced with the AMR microcontroller.
Fig 3.19: LM35 sensor interfaced with the ARM microcontroller
The output voltage of the LM35 varies linearly with temperature. Therefore to
calculate the temperature, a general equation is shown below which is used to convert the
output voltage to temperature.
Temperature ( o
C) = Vout * (100 o
C/V)…………………….. (19)
Hence, if Vout is 0.84V, then, Temperature = 84o
C

3.2.13FIRE DETECTOR
Fig 3.20: Fire detector
Fire detector used for detection of fire , the flame sensor is very sensitive to IR
wavelength at 760nm-1100nm light. AO, Analog output, real-time output voltage signal
on the thermal resistance. DO ,digital output, when the temperature reaches a certain
threshold , the output high and low signal threshold adjustable via potentiometer, with
3mm install screw hole , can be powered by DC 3-3.5V and comes with connecting cable
{20cm}.

3.2.14 BUZZER ALARM
Fig 3.21: Buzzer alarm
A Buzzer alarm is an audio signaling device, which may be mechanical,
electromechanical , or piezoelectric .Typical uses of buzzers and beepers include alarm
devices , timers and confirmation of user input such as a mouse click or keystroke ,
specification : Max. voltage 30V. Rated voltage :12V
Max current rating :3.5mA , min sound pressure level :85db, frequency :2800/-500hz ,
future can be use in communication , household applinance , toys etc.

3.2.15 Transmitter
Description
The transmitter section consists of the MAX232 IC and plcc modem the
Microcontroller pin. The microcontroller is interfaced to the computer using MAX232
through RS232 serial communication. RS232 (recommended standard 232) supports both
synchronous and asynchronous transmissions and its user data is send as a time of bits.
MAX232 is an integrated chip that converts convert Transistor–transistor logic (TTL) to
RS232 and RS232 to TTL voltage levels compatible with digital logic circuit such as the
microcontroller. The serial data sends from the microcontroller is then fed to the PC
through RS232 for monitoring purpose.
3.2.15.1 Interfacing Microcontroller and MAX232 with serial port
(DB9)
Max232 is an integrated circuit that has a dual driver/receiver and typically
converts signals from an RS-232 serial port to signals suitable for use in TTL compatible
digital logic circuits such as the microcontroller. The serial data sends from the PC
through RS232 gets converted to parallel data and is fed to the AVR microcontroller and
conversely. When a TTL level is fed to Max232 IC, it converts TTL logic 1 to between -
3VDC and -15VDC, and converts TTL logic 0 to between +3VDC to +15VDC and
conversely when converting from RS232 to TTL. The table below clarifies the RS232
transmission voltages at a certain logic state are opposite from RS232 control line
voltages at the same logic state.

Table 3.4: RS232 Line Type and Logic Level
Rs232 line type and logic
level
Rs232 voltage TTL voltage to/from MAX
232
Data transmission (Rx/Tx)
logic 0
3V to +15V 0V
Data transmission (Rx/Tx)
logic 1
-3V to 15V 5V
Control-signal
(RTS/CTS/DTR) logic 0
-3V to 15V 5V
Control-signal
(RTS/CTS/DTR) logic 1
+3V to +15V 0V
Fig 3.22: Microcontroller with Max232 interface with RS23 Interface

3.2.15.2 Interfacing serial (DB9) with PC
Currently, most PC’s have a 9 pin connector on either the side or back of
the computer. From Table 3.3 it is seen that the PC can send data (bytes) to the
transmit pin (i.e. pin 2) and receive data (bytes) from the receive pin (i.e. pin 3. The
Serial port (DB9) rs232 (recommended Standard 232) is much more than just a
connector to PC because it converts data from parallel to serial and changes the
electrical representation of the data. If the connector on the PC has female pins,
therefore the mating cable needs to have a male pin connector to terminate in a DB9
connector and conversely. Data bits flow in parallel from the PC because it uses many
wires at the same time to transmit whereas serial flow in a stream of bits from the serial
connector because it transmit or receive over a single wire. The serial port create such
a flow by converting the parallel data to serial on the transmit pin (i.e. pin 2) and
conversely. The serial port has a built -in computer chip called USART used in
translating data between parallel and serial forms.
Table 3.5: Pin assignments (DB9 PC signal set)
Pin 1 Input DCD Data Carrier Detect
Pin 2 Input RXD Received Data
Pin 3 Output TXD Transmitted Data
Pin 4 Output DTR Data Terminal Ready
Pin 5 Nil Nil Signal ground
Pin 6 Input DSR Data Set Ready
Pin 7 Output RTS Request To Send
Pin 8 Input CTS Clear To Send
Pin 9 Input RI Ring Indicator
3.3 SOFTWARE DESIGN OVERVIEW

The software design plays a very important role in the working of the entire
system; the system will not operate without the software. An algorithm needs to be
developed to enable the ARM controllers read the input and respond accordingly. The
programming language selected for this project is the C program. The C program will
enable communication between the transformer, microcontroller and PC through
power line carrier communication with other different interfaces in the system. With
the software programed into it, microcontrollers acts as brain of the whole transformer
protection and transmit its parameters for monitoring its conditions through power line
carrier communication. It will send the transformer information through PC through
power line carrier communication via the RS232 serial port.
3.3.1 INTRODUCTION TO KEIL µVISION3
The µVision3 IDE is a Windows based software development platform that
combines a robust editor, project manager, and make facility. µVision3 integrates all
tools including the C compiler, macro assembler, linker/locator, and HEX file
generator. The µVision3 IDE offers numerous features and advantages that help you
quickly and successfully develop embedded applications. They are easy to use and are
guaranteed to help you achieve your design goals.
FEATURES
• The µVision3 Simulator is the only debugger that completely simulates all on-chip
peripherals.
• Simulation capabilities may be expanded using the Advanced Simulation Interface
(AGSI).
• µVision3 incorporates project manager, editor, and debugger in a single environment.
• The µVision3 Device Database automatically configures the development tools for the
target microcontroller.

• The µVision3 IDE integrates additional third-party tools like VCS, CASE, and
FLASH/Device Programming.
• The ULINK USB-JTAG Adapter supports both Debugging and Flash programming
with configurable algorithm files.
• Identical Target Debugger and Simulator User Interface.
• The Code Coverage feature of the µVision3 Simulator provides statistical analysis of
your program's execution.
The µVision3 screen provides you with a menu bar for command entry, a tool bar where you
can rapidly select command buttons, and windows for source files, dialog boxes, and
information displays. µVision3 lets you simultaneously open and view multiple source files.
µVision3 has two operating modes:
• Build Mode: Allows you to translate all the application files and to generate executable
programs. The features of the Build Mode are described under Creating Applications.
• Debug Mode: Provides you with a powerful debugger for testing your application. The
Debug Mode is described in Testing Programs.
In both operating modes you may use the source editor of µVision3 to modify your
source code. The Debug mode adds additional windows and stores an own screen layout. The
following picture shows a typical configuration of µVision3 in the Debug Mode.
3.3.2 EMBEDDED C:
When designing software for a smaller embedded system with the 8051, it is very
common place to develop the entire product using assembly code. With many projects, this is a
feasible approach since the amount of code that must be generated is typically less than 8
kilobytes and is relatively simple in nature. If a hardware engineer is tasked with designing
both the hardware and the software, he or she will frequently be tempted to write the software
in assembly language.

The trouble with projects done with assembly code can is that they can be difficult to
read and maintain, especially if they are not well commented. Additionally, the amount of code
reusable from a typical assembly language project is usually very low. Use of a higher-level
language like C can directly address these issues. A program written in C is easier to read than
an assembly program.
Since a C program possesses greater structure, it is easier to understand and maintain.
Because of its modularity, a C program can better lend itself to reuse of code from project to
project. The division of code into functions will force better structure of the software and lead
to functions that can be taken from one project and used in another, thus reducing overall
development time. A high order language such as C allows a developer to write code, which
resembles a human’s thought process more closely than does the equivalent assembly code.
[25]The developer can focus more time on designing the algorithms of the system rather than
having to concentrate on their individual implementation. This will greatly reduce development
time and lower debugging time since the code is more understandable.
By using a language like C, the programmer does not have to be intimately familiar
with the architecture of the processor. This means that someone new to a given processor can
get a project up and running quicker, since the internals and organization of the target
processor do not have to be learned. Additionally, code developed in C will be more portable
to other systems than code developed in assembly. Many target processors have C compilers
available, which support ANSI C.

3.3.3 Flow chart of the entire system
The flowchart gives a diagram representation of the program algorithm. The
system flowchart is designed as shown below:
Fig 3.23: Flowchart description of the system
The flowchart above shows the initial description of the system program code.
The first thing the program will do is to initialize and read the ADC and the USART pins,
then sends the transformer parameters which are fed to the ADC to the personal computer
system using the UART1_Write command, then to the LCD display. The microcontroller
ADC will continuously capturing the transformer parameters, as soon as the transformer
secondary current is greater than 1A, it sends a trip signal to the overcurrent relay, and it
cuts off the load that leads to the overcurrent, thereby protecting the transformer from
burning. Same process goes to the over voltage protection, it will check whether the

transformer input voltage is greater than 230Vac, if so, it sends a trip signal to
overvoltage relay, thereby protecting the transformer.

CHAPTER 4
HARDWARE AND SOFTWARE DESIGN
AND IMPLEMENTATION
4.1 Schematic diagram
As designed in chapter 3, the circuit section consists of ARM microcontroller ,plcc
modem, step down transformer circuit for voltage sensing, current sensing circuit, relay
circuits, a temperature sensor ,oil level detector, fire detector, RS232 and the masx232
circuit, buzzer alarm.
The step down transformer used is a 230VAC to 12VAC transformer and is used
for the purpose of sensing the input voltage to the main transformer with a voltage rating
of 230VAC to 160VAC. The step down transformer is been rectified and filtered to a
pure dc which goes directly to the microcontroller ADC for monitoring the input voltage.
For the purpose of current sensing, a current transformer was used for that purpose. It
went through rectification and filtering process then directly connected to the
microcontroller ADC for monitoring the load current.
The microcontrollers send the monitored parameters to LCD display and also
transmit them to a personal computer. The transmission to personal computer was made
possible by interfacing the microcontroller with the computer using MAX232 through
RS232 serial communication. RS232 (recommended standard 232) supports both
synchronous and asynchronous transmission and its user data is send as a time series of
bits.
While monitoring the parameters, whenever a fault occurs which might be high
voltage or over current, the microcontroller sends a trip signal to the relay and thereby
protecting the transformer from burning.

Fig 4.1 Schematic diagram

4.2. Soldering
After the drilling process, there comes the soldering process. Soldering attentions
need to be taken into consideration when laying out the board. Hand soldering is the
traditional method basically used for prototypes and small production stuffs. Major
impacts when laying out the board include suitable access for the iron, and thermal relief
for pads.
4.3 Electrical Testing and Troubleshooting
After soldering, finished PCB has to go through comprehensive checks for
electrical continuity test and shorts that might occur at time of soldering. This is achieved
by using the multimeter continuity check mode. It checks that the continuity of the tracks
if matches each other; if not a troubleshooting session has to take place in order to trace
and rectify the problem.

4.4 Project prototype
Fig 4.2: Project prototype
The system prototype has been developed with all the features of a
microcontroller based transformer protection as named to be the project title. The
loads are connected to the transformer secondary, and a current sensor is connected in
series with load for real time current monitoring. Based on the real time current
monitored values, the microcontroller takes decision over the relay whether to cut off
or not. The step transformer connected to the input voltage is used for high voltage
monitoring, based on the monitored voltage values; the microcontroller takes
decision over the relay. The AVR microcontroller board contains all the sub
circuits on-board including the high voltage sensing circuit, the liquid crystal display
(LCD) for monitored values display, LED’s for indication, temperature sensor, relays
for protection purposes and finally the MAX 232 and RS232 for transmitting the
transformer parameters to PC.
It can be seen from the prototype developed that all the features of a
microcontroller based transformer protection were provided and well defined. The input

AC voltage was given through the autotransformer, the loads were connected at the
output of the transformer and the transformer parameters are monitored in personal
computer. The AVR microcontroller has on it all the sub-circuits for the transformer
protection including the liquid crystal display (LCD) for voltage, current and temperature
display of the transformer, relay driving circuits, high voltage sensing circuits, current
sensor and the transmitter circuit for real time transmission of transformer information to
personal computer.
Finally, the Proteus simulation software made it easy to test, and troubleshoot the
hardware and the program which saved much of the time and reduced cost of the project.
Therefore, it can be concluded that the hardware and software implementation were
positively achieved.

CHAPTER 5
RESULTS AND DISCUSSION
In order to verify the performance of the proposed microcontroller based
transformer protection system via power line carrier communication (PLCC), a hardware
prototype was implemented with an AMR microcontroller ARM7TDMI-S with a 16MHz
crystal oscillator. During this test, an transformer was used for the input voltage of the
transformer in order to note the voltage. Bulbs were used as loads to create the over
current fault and the over load current is shown in ADC value. Voltage and current
sensing circuits were designed for sensing the transformer voltage and current , fire
detector are used to detect the fire in around the transformer, and a oil level sensor is used
to detect the oil level of the oil transformer and regular temperature is detected by the
temperature sensing unit (LM317) and short circuit test is done by shorting the pin of
microcontroller and ground . The validity of this project prototype is verified through this
test system.

CHAPTER 6
CONCLUSION AND FUTURE RECOMMENDATION
6.1 Conclusion
In this project, the transformer protection using a microcontroller is proposed. For
transformer voltage and current sensing, a current sensing circuit and voltage sensing
circuits were designed and the results have been verified with proteus simulation.
Hardware with an AVR microcontroller was implemented to verify the proposed
technique and the performance of the real time hardware was compared with the proteus
computer simulation. Through the transformer current analysis, we can see that the
current of the transformer rises as load increases, whenever the load current goes above
the transformer rated current, the microcontroller detects an overcurrent and it sends
a trip signal to over current relay thereby protecting the transformer from burning. As
the load current goes below the rated current of the transformer, the microcontroller
detects normal there by sending an on signal to the overcurrent relay.
Moreover, through the transformer voltage analysis, we can see that the voltage
of the transformer rises as the input voltage of the transformer is increased through
varying an autotransformer. Whenever the input voltage goes above the transformer rated
voltage (230VAC), the microcontroller detects an overvoltage and it sends a trip signal to
over voltage relay thereby protecting the transformer from burning.
The results indicate that the microcontroller based transformer protection achieves

numerous advantages over the existing systems in use: 1) fast response, 2) better
isolation, 3) accurate detection of the fault.
Finally, the practical results matched with the simulation perfectly, therefore the
aim and objectives of the project were all achieved successfully and project is said to be
industrious and fully automated with no manual interface required.
6.2 Future Recommendations
Any work and investigation on transformer protection is very advantageous and
challenging. Based on the present time, it can be observed that the world’s population is
increasing rapidly. Therefore demands on electricity will be high and these will lead to
demands of highly sophisticated protection devices, which will be incorporated in
transformer protection schemes.
Based on the work done in this project which protecting transformer using
microcontroller, some improvements need to be made in the future work. It was noticed
that use of current sensor prevent the protection from high performance application
because the current sensor needs some amount of time to sense the load current and
transfer the signal to the microcontroller ADC. Correspondingly, a current transformer
can be used instead of current sensor, switching semiconductor device such as thyristor
can be used instead of relay, highly advanced microcontroller such as 16bit PIC
microcontroller or a digital signal processor can be used for high speed analogue to
digital (ADC) conversion of the transformer voltage and current.

REFERENCES
REFERENCES BOOKS
[1]Badri ram and D N Vishwakarma (1995) power system protection and switch gear New
Delhi: Tata Mc Graw hill.
[2]Frank D. Petruzella (2010) Electric motors and control systems 1st
ed. New York:
McGraw-Hill.
[3]J. Lewis Blackburn , Thomas J. Domin (2006). Protective Relaying Principles and
Applications . 3rd ed. United States of America: CRC press.
[4]Leonard L. Grigsby (2007).The Electric Power Engineering Handbook. 2nd ed. United
States of America: CRC press.
[5]P. M. Anderson (1998). Power system protection. New York: John Wiley & Sons, Inc.
P.673.
[6]Smarajit Ghosh, (2007). Electrric Machines 1st
Edn. India: Dorling Kindersley.
REFERENCES PAPERS
[1]A Review of Transformer Protection by Using PLC System,
International Journal of Digital Application & Contemporary research Website: www.ijdacr.com
(Volume 3, Issue 2, September 2014), Satya Kumar Beher, Ravi Masand.
[2] Rohan Perera & Bogdan Kasztenny, “Application Considerations When Protecting Lines
With Tapped and In-Line Transformers”, previously presented at 2014 Texas A&M
Conference for Protective Relay Engineers, © 2014 IEEE – All rights reserved. 20140210,
TP6575-01.
[3] V.Thiyagarajan & T.G. Palanivel, “An Efficient Monitoring Of Substations Using
Microcontroller Based Monitoring System”, IJRRAS 4 (1), July 2010.
[4] Mallikarjun Sarsamba, Dr. Raju Yanamshetty & Prashant Sangulagi, “ The Load
Monitoring and Protection on Electricity Power lines using GSM Network”, International

Journal of Advanced Research in Computer Science and Software Engineering, Volume 3,
Issue 9, September 2013 ISSN: 2277 128X.
[5] Kipp Yule, Duane Brock, and Jim Purdy, “Accountability and Evaluation of Aggregate
Effects of Through Faults on Power Transformers”, Unclassified Open Source.
[6] Ravi Masand, Prof. S.P Shukla, ”Fault Diagnosis of Induction Motor Using PLC”,
International Journal of Advanced Research in Electrical, Electronics and Instrumentation
Engineering, Volume-II, Issue-12, pp. no.- 2320-3765,December 2013.

APENDIX I
COMPONENTS REQUIRED
SL.NO COMPONENTS NUMBERS COST
01 Arm microcontroller 1 2000
02 PLC modems 2 3000*2=6000
03 Microcontroller board 1 500
04 Adaptor 2 250*2=500
05 Fire sensor 1 150
06 LCD Display 1 250
07 LCD Board 1 150
08 Buzzar alarm 1 20
09 Voltage regulator(LM317) 1 300
10 USB to UART 1 350
11 Current sensor 1 600
12 Transformer(1A , 15-0-15V) 1 600
13 Relay (15 &12 V) 1 250
14 Bulbs holders 2 20*2=40
15 Temperature sensor 1 120
16 Wire Plugs 4 10*4=40
17 Transistor(BC547) 1 10
18 Bridge rectifier & filter 1 50
19 PCB Board 1 150
20 DC jack 1 10
21 Others charges included 4000
TOTAL COST 16090

Transformer Protection using PLC

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