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 networ ks 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 easie r. 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 t he 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 cir cuitry 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 ( oC) = Vout * (100

oC/V)…………………….. (19)

Hence, if Vout is 0.84V, then, Temperature = 84oC



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 tr ansmit 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.

http://www.keil.com/support/man/docs/uv3/uv3_creating_apps.htm

http://www.keil.com/support/man/docs/uv3/uv3_debugging.htm



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, curre nt

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