APPLICATION OF “SCADA” FOR DISTIBUTION TRANSFORMER PROTECTION

CONTENTS:

ABSTRACT 3

CHAPTER 1

1.1 INTRODUCTION 4

1.2 BLOCK DIAGRAM 6

1.3 CIRCUIT ANALYSIS 7

1.3.1 LOAD MONITORING CIRCUIT 7

1.3.2 HIGH VOLTAGE MONITORING CIRCUIT 9

1.3.3 TEMPERATURE SENSENING CIRCUIT 10

1.3.4 ANALOG TO DIGITAL CONVERTER 12

1.3.5 CLOCK GENERATOR 14

1.3.6 DIGITAL DISPLAY 15

1.3.7 F.M TRANSMITTER 16

1.3.8 F.M RECEIVER 17

1.3.9 SIGNAL AMPLIFIER 18

1.3.10. FREQUENCY TO VOLTAGE CONVERTER 20

1.3.11 POWER SUPPLY 21

1

CHAPTER – 2

DETAILS ABOUT WIRELESS COMMUNICATION

2.1. MODEL OF COMMUNICATION SYSTEM 22

2.2 COMMUNICATION CHANNEL 24

2.3. MODULATOR 25

2.4. DEMODULATOR 26

CHAPTER – 3

DETAILS ABOUT MICORCONTROLLER

3.1. DESCRIPTION 27

3.2. CHIP TECHNOLGIES 28

3.3. DESCRIPTION 89C51 MICROCONTROLLER IC 29

3.4. FEATURES 30

3.5. PIN DIAGRAM 31

3.6. BLOCK DIAGRAM 32

3.7. PIN DESCRIPTION 33

CHAPTER-4

4.1 COMPLETE CIRCUIT DIAGRAM WITH LIST OF 39

COMPONENTS

4.2 ADVANTAGES AND APPLICATIONS 40

CONCLUSION 41

REFERENCES

2

ABSTRACT

The aim of the project work is to protect the distribution transformer or

any other power transformer, burning due to the overload, over temperature and

input high voltage. Normally most of the transformers are burning because of

these three reasons; hence by incorporating this type of monitoring and control

circuits, life of the transformer can be increased. In addition to the monitoring

and control, information about these three parameters can be transmitted to the

nearest electrical office where the maintenance staff of the electrical department

can monitor the transformer continuously without going nearer to the

transformer. For this purpose, radio communication is utilized in this project

work, so that, due to what reason the transformer has been failed, at what time,

when the power is resumed etc., can be monitored and this information can be

stored in a computer at the receiving station. With the help of this kind of

system, the maintenance staff of the department can have a continuous vigilance

over the transformer.

3

CHAPTER – 1

1.1. INTRODUCTION

Nowadays, with the advancement of technology, particularly in the

field of computers as well as micro-controllers, all the activities in our day to

day living have become a part of information and we find computers and

micro-controllers at each and every application. Thus, the trend is directing

towards computer based project works. However, in this project work the

basic signal processing of temperature, load current and input high voltage

parameters related to the distribution transformers are monitored with analog

electronics only. For measuring various parameters values, various

transducers are used and the output of these transducers are converted to

control the parameters. The control circuit is designed using micro-controller.

The outputs of all the three parameters are fed to the analog to digital

converter for converting the analog information in to the digital information

and this digital information is fed to micro-controller. The output of the

micro-controller is used to drive the digital display, so that the value of each

parameter can be displayed. In addition to the digital display micro-controller

outputs are also used to drive four relays independently. These relays

energize and de-energizes automatically according to the condition of the

parameter. Out of four relays one relay is treated as common relay and

energizes automatically whenever any parameter exceeds its present value.

This relay contact is used to break the supply to the transformer primary. The

remaining three relays are used for the three different parameters, to transmit

the information about the failured parameter. For example, if the load is

more than the rated load, then immediately the micro-controller energizes one

relay out of these three relays and this relay contact is used to provide supply

to the low frequency oscillator, which produces a perfect square wave of 1

KHz approximately. This low frequency is fed to transmitter as a modulating

4

wave, which is super imposed over the carrier and transmitted as a

modulated wave. Likewise for other two parameters, two different low

frequencies are generated. The idea of generating three different low

frequencies is to identify the failured parameter and to transmit the failured

information.

In the receiver, the received information in the form of low frequency

as a modulated wave is demodulated, amplified and converted into

proportionate DC voltage using frequency to voltage converter. The output of

this F/V converter is again converted into digital pulses, which are essential

for the computer. Here the computer is used at receiving end, where the

receiver is installed; generally the receiving part of the system can be installed

at electrical office.

5

1.2 BLOCK DIAGRAM

6

1.3 CIRCUIT ANALYSIS

The detailed circuit description of the project work APPLICATION OF “SCADA” FOR DISTIBUTION TRANSFORMER PROTECTION” is explained in section wise. For better understanding the total circuit diagram is divided into various sections and each section explanation along with circuit diagram is provided in this chapter.

7

1.3.1 LOAD MONITORING CIRCUIT

The current transformer used in this project work is designed for

5Amps i.e., the current flowing through the primary is restricted for 5Amps.

But in practical a higher rating transformer can be used according to the rated

power of the distribution transformer. Most common industrial CT’s have 5 to

10 Amp current outputs and can generate high voltage levels when not

connected to a burden resistor.

The CT used in this project work is nothing but a step-up transformer.

This transformer is designed in 1:50 ratio, so that the voltage developed across

the secondary is 50 times more than the voltage induced at primary. The

voltage induced at primary is proportional to the load current. The CT

secondary when it is open circuited, the voltage developed across the open

terminals may be very high because of the step-up ratio, and therefore, the

secondary winding of the CT should always be connected to a burden resistor.

The secondary AC signal, which is proportional to the current flowing through

the primary, due to transformer action, is rectified with the help of a diode

(Half wave rectification) and then filtered by a filter capacitor. This DC

voltage is a variable voltage, which varies according to the load current. The

variable voltage from the CT secondary is fed to analog to digital converter

for converting the analog information into digital information. The output of

the A/D converter is fed to Micro-controller 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.

The following is the circuit diagram of load sensing circuit.

8

9

In the above circuit, with the help of a 470 resistor connected across the

CT secondary, the ripple can be suppressed and real value can be obtained at

the output of CT. This voltage can be adjusted to the required level, for this

purpose 2K variable resistor is used and the final output taken from midpoint

of the preset. Since it is a prototype module, in this project work for the

demonstration purpose, a small transformer of 230V secondary at 1amp rating

is considered, and it is treated as distribution transformer. This transformer

secondary is used to drive the lamp load through the current transformer

primary. For this purpose two No’s of 230V 200W, 100W AC lamps are used,

one lamp is treated as nominal load and the other one is used to create a fault

i.e., the transformer secondary is designed to drive only one amp load, if the

load is more than one amp then the transformer may burn because of over

load, to protect the transformer burning due to the over load, the output of the

load monitoring circuit is used to drive the relay through the A/D converter

and microcontroller. This relay contact is used to break the supply at the

primary side of the transformer. So that once the transformer is overloaded

automatically primary supply can be disconnected.

1.3.2 HIGH VOLTAGE MONITORING CIRCUIT

The Line voltage sensing circuit used in this project work is capable to

measure up to 250V AC. For this purpose a step down transformer of 6V-0-

6V, 500mA, Center tapped secondary is used for monitoring the line voltage

continuously. In the prototype module, the line voltage can be increased

through the autotransformer, the output of the line voltage sensing circuit is

fed to micro-controller unit through the A/D converter, so that according to

the received digital information form the ADC, the micro-controller energizes

relay. This relay contact is used to break the supply to the feeder cable.

10

The output of the line voltage-sensing transformer is rectified and

filtered for obtaining pure DC voltage. The final output is taken from the

midpoint of 2K variable resistor (Preset), so that the voltage applied to the

A/D converter can be controlled. As the line voltage varies, according to that

output voltage also varies. This variable voltage from the potential

transformer (PT) is applied to the A/D converter. The applied voltage to the

ADC should not exceed more than 5V, so that the output voltage is clamped at

+5V DC, for this purpose, 1W, 5V zener is used. This circuit is designed such

that, the voltage applied to the transformer primary, if it is more than 245V

AC then immediately the microcontroller energizes the relay and breaks the

supply to the primary, by which the transformer can be protected burning due

to the over voltage. Since it is a prototype module, the output of the

transformer is restricted for lower voltages for the demonstration purpose, but

when it is implemented for the real time applications, at that time the output of

the distribution transformer will be around 220V AC, and with the help of this

kind of voltage control circuit, the household electrical gadgets like TV,

Fridge, Tube, Motor etc., can be protected burning due to the over voltage.

The following is the circuit diagram of the High voltage Sensing

1.3.3 TEMPERATURE SENSENING CIRCUIT

In this block, two op-amps are used to form two different stages. The

first stage is configured as differential amplifier and the second stage is

configured as gain amplifier. In the first stage an ‘NPN’ General purpose

11

transistor (SL100) is used as a temperature sensor and this transistor is having

‘TIN’ metal body so that it can absorb the heat properly. This transistor is

connected in feedback loop (input to output). This first stage is designed in

such a way so that, as the transistor body temperature rises, according to the

temperature, the base- emitter or base-collector junction resistance decreases.

This first stage is designed to generate 2mv/0C which is not sufficient for the

calibration. Hence, using 2nd stage this voltage is amplified, and the gain of

the 2nd stage is 10, so that (2x10) 20mv per degree centigrade can be obtained

at the output of the second stage. This variable voltage (according to the

temperature) from the output of second stage is fed to the analog to digital

converter for converting the analog information in to the digital information

and this digital information is fed to the microcontroller for taking the

necessary action.

The circuit design consists a basic transducer, which converts

temperature in to equalent voltage. For this, transistor ‘SL100’ is used as a

sensor. The transistor junction (Base & emitter or Base & collector)

characteristics are depends upon the temperature. For a transistor, the

maximum average power that it can dissipate is limited by the temperature

that collector - base junction can with stand. Therefore, maximum allowable

junction temperature should not be exceeded. The average power dissipated in

collector circuit is given by the average of the product of the collector current

and collector base voltage. At any other temperature the de-rating curves are

supplied by the manufacturer to calculate maximum allowable power (Pj).

(Pj) = Tj-Tc

Qj

Where TC is case temperature, Tj is junction temperature and Qj is the

thermal resistance.

The entire circuit design of the temperature sensing circuit is given

below. In the above circuit diagram with the help of 2K preset (variable

resistor) connected at the input of first stage, the initial room temperature

12

corresponding output voltage can be adjusted for the easy calibration. The

output of the second stage is clamped with 5V zener and the same output is

fed to the A/D converter.

For sensing the transformer body temperature, a sensor has to chosen

based on the following requirements.

1. Sensitivity and accuracy

2. Temperature Range

3. Desired life of Sensor

4. Budget

In the prototype module for the simulation purpose, ‘SL100’ NPN

Transistor is used as sensor because semiconductor Temperature sensor are

best suited for embedded applications as they tend to be electrically and

mechanically more delicate than other temperature sensor types.

In the present module, as the resistance property of the transistor cannot

be used directly for interfacing, this transistor is employed as a feedback

element.

1.3.4 ANALOG TO DIGITAL CONVERTER

13

The outputs of the various parameters are fed to A/D converter. The

channel selection depends upon the address selection sent by the Micro-

controller. This ADC is having three address inputs to select one out of eight

channels of the ADC. This ADC 0809 is a successive approx. Analog to

digital converter and the clock rate at which the conversion is fed from the IC

555 timer configured as astable multi-vibrator. The digital output after

conversion is fed to Micro-controller

For ADC to start converting the data after selecting the channel by

sending the address inputs, the start conversion signal is to be sent by Micro-

controller. Then ADC starts converting the analog signals voltage into

corresponding digital data. For Ex: The following table shows the digital data

corresponding to analog input.

After conversion, the ADC generates EOC (End of conversion). This

indicates to Micro-controller that the conversions is completed and take the

digital data corresponding to analog input.

The following is Circuit diagram of A/D Converter along with its clock

generator

14

In the above circuit diagram 555 timer IC is used for generating the

required clock pulses.

1.3.5 CLOCK GENERATOR:

The required clock for the ADC is generated using 555 Timer IC which

is configured as Astable multi-vibrator (Self Oscillator). In this mode of

operation the required frequency can be adjusted using two external

components i.e., resistor and capacitor. Keeping capacitor value constant

where as by varying the value of resistor the frequency can be adjusted from

1Hz to 500 KHz. Here the required frequency is 100 KHz approximately.

In the above circuit diagram 555 timer IC is used for generating the

required clock pulses. Frequency can be adjusted using variable resistor 100K

(Rb). In this circuit, the external capacitor charges through Ra+Rb and

discharges through Rb. Thus the duty cycle may be precisely set by the ratio of

these two resistors. In this mode of operation, the capacitor charges and

15

discharges between 1/3 VCC and 2/3 VCC. As in the triggered mode, the charge

and discharge times, and therefore the frequency are independent of the

supply voltage. Here the timing resistor is now split into two sections, RA and

RB, with the discharge transistor (Pin 7) connected to junction of Ra and Rb.

When the power supply is connected, the timing capacitor C charges towards

2/3 VCC through Ra and Rb. When the Capacitor voltage reaches 2/3 VCC, the

upper comparator triggers the flip-flop and the capacitor starts to discharge

towards ground through Rb. When the discharge reaches 1/3 VCC the lower

comparator is triggered and a new cycle is started. The capacitor is then

periodically charged and discharged between 2/3 VCC and 1/3 VCC

respectively. The output state is high during the charging cycle for a time

period t1, so that

The output state is LOW during the discharge cycle for a time period t2,

given by

t2 = 0.693 RbC

Thus, the total period charge and discharge is

T = t1 + t2

= 0.693 (Ra + 2Rb) C (Seconds)

1.3.6 DIGITAL DISPLAY The following is the Circuit diagram of Digital Display Driven by themicro-controller

16

In the above circuit diagram, four common anode 7-Segment displays

are used for displaying the motor speed. The output of the Micro-controller is

fed to digital display through the latches, for this purpose IC 74573 is used,

this is a octal transparent D-type latches IC. To drive the displays

independently 547 transistors are used. A seven segment LED is a device for

display of numbers and letters. It contains seven LED bars, which can be

turned on by placing the appropriate signals on the appropriate pins.

In order to produce a specific number, we must light the correct

segments of the LED. For example, to display the number 3, we must light

segments a, b, c, d and g. By which we understand that the pattern of lit and

unlit segments can be formed into a binary number.

1.3.7 F.M TRANSMITTER:

The following is the circuit diagram

17

In the above circuit design, the instantaneous frequency of the carrier is

varied directly in accordance with the base band signal by means of a device

known as VCO (Voltage controlled oscillator) one way of implementing such

a device is to use a sinusoidal oscillatory having a relatively high – Q

frequency. Determining net work and to control the oscillator by symmetrical

incremental variation of the reactive components. Thus the tone signal

modulated at 100 MHz carrier.

To understand how radio wave are generated and radiated into space,

consider alternating currents of suitable frequency fed into conductor or wire

of suitable length called the antenna. Fast moving alternating currents produce

a moving electric field around the antenna. This field in turn produces a

magnetic field at right angles to it. This combination of electric and magnetic

fields constitutes the radio wave or electromagnetic wave which is a form of

radiant energy.

1.3.8 F.M RECEIVER

The FM receiver is located at the remote end. The first stage of this

remote end unit is the F.M. Radio Receiver, which is designed with Phillips

IC TEA 5591A. In the circuit diagram an LED indicator is connected at Pin

No.7 of 5591 IC, which glows brightly, if the receiver is tuned perfectly with

the transmitter.

18

The F.M. receiver, which operates at 100 MHz, will have an

intermediate frequency of 10.7 MHz and bandwidth of 200 KHz. This IC

consists of a built in RF amplification circuit. It matches the input impedance

of the antenna. This IC consists of F.M. Detector including amplifier of

modulated signal (RF amplification). Two sections of LC are provided and a

ceramic filter is used to filter the IF of 10.7 MHz the FM demodulator is

basically a frequency to amplitude converter, which converts the frequency

deviation of the incoming carrier into an AF (Audio frequency) amplitude

variation identical to that of modulating signal. In demodulation any change in

amplitude of the signal fed to the FM demodulator is a spurious signal.

Therefore it must be removed, if distortion is to be avoided. A limiter is a

form of clipping device. It is quite possible for the amplitude limiter to be

described to be inadequate to its task, because signal strength variations may

easily take average signal amplitude outside the limiting range. As a result,

further limiting is required. In practice, two amplitude limiters are used in

cascade. This arrangement increases the limiting range satisfactory. To ensure

that the signal fed to the limiter is within its range regardless of input signal

limiting range strength and also to prevent overloading of the amplifier, the

AGC (Automatic Gain Control) is used. Instead of designing a double limiter,

the better performance is obtained by using one limiter and AGC. The

frequency-modulated signal is fed to a tuned circuit whose resonant frequency

is to one side of the center frequency (CF) of the FM signal, the output of this

tuned circuit will have amplitude that depends on the frequency deviation of

the input signal. The following is the circuit diagram of F.M. Receiver.

19

1.3.9 SIGNAL AMPLIFIER

For maximum power output and impedance matching the audio frequency driver transformer is used in the signal amplifier circuit. The design equation of a driver transformer is

Ri = 1 Rl

n2

When n = Ratio of the transformer = N2

N1

Where N1 = Primary winding and N2 = Secondary winding. The following is

the circuit diagram of signal amplifier.

20

The signal, which is detected by the receiver, is further amplified with

the help of above audio amplifier. In this circuit, the input capacitor 0.1 MF

permits complete input power to flow into the base circuit. It also blocks the

DC component to flow into the base circuit. The 330K resistor works as a

biasing resistor. The purpose of this biasing is as follows.

The operating point may then be suitably placed in this region by

proper selection or dc potentials and currents through use of external energy

sources. With a properly selected operating point, the time varying component

of the AC input signal. Say base current in common emitter amplifier, results

in output signal of the same waveform. An improperly selected operating

points results in an output signal, which differs in waveform from the input

signal, such an operative point is unsatisfactory and should be rejected. The

selection of suitable operating point is vital for linear amplification. The 100Ω

and 330KΩ forms as a input resistance of the transformer primary. For

securing maximum transfer of power from the amplifier to the load, the source

impedance should match with the input impedance of the amplifier transferred

to the primary of the transformer. Similarly for maximum transfer of power

from the amplifier to the load, the output impedance of the amplifier is

matched with the load impedance. To get large output the two secondary

21

signals are cascaded and output is taken for further processing. The output of

this signal amplifier is fed to the F/V converter.

1.3.10. FREQUENCY TO VOLTAGE CONVERTER

The output of the signal amplifier is converted into DC voltage in

proportion to the tone frequency, with the help of phase locked loop IC 4046

and Multi-plexer IC 4053. The amplified signal is fed to the in signal (Pin

NO.14) of the device, which is the input of the phase comparator. The other

input of the phase comparator is fed from the internally generated voltage

controlled oscillator (VCO), whose frequency is set with the help of external

capacitor connected between Pin 6 and 7 here PLL is used for

synchronization. The output of the PLL is fed to the Multiplexer. The Signals

of the phase comparator – I and phase comparator – II are fed so that the

output is multi-plexed with the help of IC4053.The output of the F/V

converter is fed to the Analog to digital converter circuit for converting the

Analog information into digital pulses. The circuit design of phase locked

loop with multiplexer and its associated circuitry is shown below.

1.3.11 POWER SUPPLY

22

The required DC levels are derived from the mains supply for this

purpose a step-down transformer of 12V-0-12V center tapped secondary

transformer is used. The current rating of the transformer is 750 ma at

secondary. The secondary is rectified and filtered to generate 12V smooth DC

which is un-regulated voltage and which is required to drive the buzzer and

relay. With help of positive voltage regulators, a constant voltage source of

+5V and +9V are derived, for this purpose 7805 and 7809 3Pin Voltage

regulators are used so that, though the mains supply varies from 170V to

250V, the output DC levels remains constant. The following is the circuit

diagram of power supply.

CHAPTER – 2

23

2. DETAILS ABOUT WIRELESS COMMUNICATION

2.1. Model of a communication system:

The overall purpose of the communication system is to transfer

information from one point to in space and time, called the source to another

point, the user destination. As a rule, the message produced by a source is not

electrical. Hence an input transducer is required for converting the message to

a time varying electrical quantity called a message signal. At the destination

point another transducer converts the electrical waveform to the appropriate

message.

The information source and the destination point are usually separated

in space. The channel provides the electrical connection between the

information source and the user. The channel can have many different forms

such as a microwave radio link over free space a pair of wires, or an optical

fiber. Regardless of its type the channel degrades the transmitted single in a

number of ways. The degradation is a result of signal distortion due to

imperfect response of the channel and due to undesirable electrical signals

(noise) and interference. Noise and signal distortion are two basic problems of

electrical communication. The transmitter and the receiver in a

communication system are carefully designed to avoid signal distortion and

minimize the effects of noise at the receiver so that a faithful reproduction of

the message emitted by the source is possible.

The transmitter couples the input message signal to the channel. While

it may sometimes be possible to couple the input transducer directly to the

channel, it is often necessary to process and modify the input signal for

efficient transmission over the channel. Signal processing operations

performed by the transmitter include amplification, filtering, and modulation.

The most important of these operations is modulation a process designed to

match the properties of the transmitted signal to the channel through the use of

a carrier wave.

24

Modulation is the systematic variation of some attribute of a carrier

waveform such as the amplitude, phase, or frequency in accordance with a

function of the message signal. Despite the multitude of modulation

techniques, it is possible to identify two basic types of modulation: the

continuous carrier wave (CW) modulation and the pulse modulation. In

continuous wave (CW) carrier modulation the carrier waveform is continuous

(usually a sinusoidal waveform), and a parameter of the waveform is changed

in proportional to the message signal. In pulse modulation the carrier

waveform is a pulse waveform (often a rectangular pulse waveform), and a

parameter of the pulse waveform is changed in proportional to the message

signal. In both cases the carrier attribute can be changed in continuous or

discrete fashion. Discrete pulse (digital) modulation is a discrete process and

is best suited for messages that are discrete in nature such as the output of a

teletypewriter.

Modulation is used in communication systems for matching signal

characteristics to channel characteristics, for reducing noise and interference,

for simultaneously transmitting several signals over a single channel, and for

overcoming some equipment limitations. A considerable portion of this article

is devoted to the study of how modulation schemes are designed to achieve

the above tasks..

The main function of the receiver is extract the input message signal

from the degraded version of the transmitted signal coming from the channel.

The receiver performs this function through the process of demodulation, the

reverse of the transmitter’s modulation process. Because of the presence of

noise and other signal degradations, the receiver cannot recover the message

signal perfectly. In addition to demodulation, the receiver usually provides

amplification and filtering.

Based on the type of modulation scheme used and the nature of the

output of the information source, we can divide communication systems into

three categories:

25

1. Analog communication systems designed to transmit analog

information using analog modulation methods

2. Digital communication systems designed for transmitting digital

information using digital modulation schemes and

3. Hybrid systems that use digital modulation schemes for transmitting

sampled and quantized values of an analog message signal.

Other ways of categorizing communication systems include the

classification based on the frequency of the carrier and the nature or the

communication channel

2.2. Communication Channel

The Communication channel provides the electrical connection between

the source and the destination. The channel may be a pair of wires or a

telephone link or free space over which the information bearing signal is

radiated. Due to physical limitations, communication channels have only

finite bandwidth (B HZ), and the information bearing signal often suffers

amplitude and phase distortion as it travels over the channel. In addition to the

distortion, the signal power also decreases due to the attenuation of the

channel. Furthermore, the signal is corrupted by unwanted, unpredictable

electrical signals referred to as noise. While some of the degrading effects of

the of the channel can be removed or compensated for, the effects of noise

cannot be completely removed. From this point of view, the primary objective

of a communication system design should be to suppress the bad effects of the

noise as much as possible.

One of the ways in which the effects of noise can be minimized is to

increase the signal power. However, signal power cannot be increased beyond

certain levels because of nonlinear effects that become dominant as the signal

amplitude is increased. For this reason the signal-to-noise power ratio (S/N),

which can be maintained at the output of a communication channel, is an

important parameter of the system. Other important parameters of the channel

26

are the usable bandwidth (B), amplitude an phase response, and the statistical

properties of the noise.

2.3. Modulator

The modulator accepts a bit stream as its input and converts it to an

electrical waveform suitable for transmission over the communication

channel. Modulation is one of the most powerful tools in the hands of a

communication systems designer. It can be effectively used to minimize the

effects of channel noise, to match the frequency spectrum of the transmitted

signal with channel characteristics, to provide the capability to multiplex

many signals, and to overcome some equipment limitations.

The important parameters of the modulator are the types of waveforms

used, the duration of the waveforms, the power level, and the bandwidth used.

The modulator accomplishes the task of minimizing the effects of channel

noise by the use of large signal power and bandwidth, and by the use of

waveforms that last for longer durations. While the use of increasingly large

amounts of signal power and bandwidth to combat the effects of noise is an

obvious method, these parameters cannot be increased indefinitely because of

equipment and channel limitations. The use of waveforms of longer time

duration to minimize the effects of channel noise is based on the well-known

statistical law of large numbers. The law of large numbers states that while

the outcome of a single random experiment may fluctuate wildly, the overall

result of many repetitions of a random experiment can be predicted accurately.

In data communications, this principle can be used to advantage by making

the duration of signaling waveforms long. By averaging over longer

durations of time, the effects of noise can be minimized.

To illustrate the above principle, assume that the input to the modulator

consists of 0’s and 1’s occurring at a rate of 1 bit/sec. The modulator can

assign waveforms once every second. Notice that the information contained in

the input bit is now contained in the frequency of the output waveform. To

employ waveforms of longer duration, the modulator can assign waveforms

27

once every four seconds. The number of distinct waveforms the modulator has

to generate (hence the number of waveforms the demodulator has to detect)

increases exponentially as the duration of the waveforms increases. This leads

to an increase in equipment complexity and hence the duration cannot be

increased indefinitely. The number of waveforms used in commercial digital

modulators available at the present time ranges from 2 to 16.

2.4. Demodulator

Modulation is a reversible process, and the demodulator accomplishes

the extraction of the message from the information bearing waveform

produced by the modulator. For a given type of modulation, the most

important parameter of the demodulator is the method of demodulation. There

are a variety of techniques available for demodulating a given modulated

waveform: the actual procedure used determines the equipment complexity

needed and the accuracy of demodulation. Given the type and duration of

waveforms used by the modulator, the power level at the modulator, he

physical and noise characteristics of the channel, and the type of

demodulation, we can derive unique relationship between data rate, power

bandwidth requirements, and the probability of incorrectly decoding a

message bit. A considerable portion of this text is devoted to the derivation of

these important relationships and their use in system design.

CHAPTER – 3

28

DETAILS ABOUT MICORCONTROLLER

3.1. DESCRIPTION

The micro-controller is a chip, which has a computer processor with all

its support functions, memory (both program storage and RAM), and I/O built

in to the device. These built in functions minimize the need for external

circuits and devices to be designed in the final applications

Most micro-controllers do not require a substantial amount of time to

learn how to efficiently program them, although many of them have quirks

which you will have to understand before you attempt to develop your first

application.

Along with micro-controllers getting faster, smaller and more power

efficient they are also getting more and more features. Often, the first version

of microcontroller will just have memory and simple digital I/O, but as the

device family matures, more and more part numbers with varying features will

be available

With all the 8051 manufacturer’s products taken into account, there are

over two hundred different 8051 part numbers, each with different features

and capabilities. For most applications, we will be able to find a device within

the family that meets our specifications with a minimum of external devices,

or an external but which will make attaching external devices easier, both in

terms of wiring and programming.

For many micro-controllers, programmers can be built very cheaply, or

even built in to the final application circuit eliminating the need for a separate

circuit. Also simplifying this requirement is the availability of micro-

controllers with SRAM and EEPROM for control store, which will allow

program development without having to remove the micro-controller from the

application circuit.

3.2. CHIP TECHNOLOGIES

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Microcontrollers, like all other electronic products, are growing smaller,

running faster, requiring less power, and are cheaper. This is primarily due to

improvements in the manufacturing process and technologies used (and not

the adoption of different computer architectures). Virtually all

microcontrollers built today use CMOS (complementary metal oxide

semiconductor) logic technology to provide the computing functions and

electronic interfaces. CMOS is a push-pull technology in which a PMOS and

NMOS transistor are paired together. The following is the circuit diagram of

push-pull configuration

When the input signal is low, the PMOS transistor will be conducting

and the NMOS transistor will be ‘off’. This means that the switch (or

transistor) at Vcc will be ‘ON’, providing Vcc at the signal out. If a high

voltage is input to the gate, then the PMOS transistor will be turned off and

the NMOS transistor will be turned on, pulling the output line to ground.

During a state transition, a very small amount of current will flow through the

transistors. As the frequency of operation increases, current will flow more

often in a given period of time (put another way, the charge transferred per

unit time, which is defined as “current”, will increase). This increased current

flow will result in increased power consumption by the device. Therefore, a

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CMOS device should be driven at the slowest possible speed, to minimize

power consumption.

An important point with all logic families is understanding the

switching point of the input signal. For CMOS devices, this is typically

1.4Volts to one half of Vcc. However, it can be at different levels for different

devices. Before using any device, it is important to understand what the input

threshold level is. CMOS can interface directly with most positive logic

technologies, although we must be careful of low voltage logic, to make sure

that a high can be differentiated from a low in all circumstances.

3.3. DESCRIPTION 89C51 Micro controller IC

The AT89C51 is a low-power, high-performance CMOS 8-bit

microcomputer with 4K bytes of Flash programmable and erasable read only

memory (PEROM). The device is manufactured using Atmel’s high-density

nonvolatile memory technology and is compatible with the industry-standard

MCS-51 instruction set and pin out. The on-chip Flash allows the program

memory to be reprogrammed in-system or by a conventional nonvolatile

memory programmer. By combining a versatile 8-bit CPU with Flash on a

monolithic chip, the Atmel AT89C51 is a powerful microcomputer which

provides a highly-flexible and cost-effective solution to many embedded

control applications.

The AT89C51 provides the following standard features: 4Kbytes of

Flash, 128 bytes of RAM, 32 I/O lines, two 16-bit timer/counters, five vector

two-level interrupt architecture, a full duplex serial port, on-chip oscillator and

clock circuitry. In addition, the AT89C51 is designed with static logic for

operation down to zero frequency and supports two software selectable power

saving modes. The Idle Mode stops the CPU while allowing the RAM,

timer/counters, serial port and interrupt system to continue functioning.

The Power-down Mode saves the RAM contents but freezes the

oscillator disabling all other chip functions until the next hardware reset.

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3.4. Features

• 4K Bytes of In-System Reprogrammable Flash Memory– Endurance 1,000

Write/Erase Cycles

• Fully Static Operation: 0 Hz to 24 MHz

• Three-level Program Memory Lock

• 128 x 8-bit Internal RAM

• 32 Programmable I/O Lines

• Two 16-bit Timer/Counters

• Six Interrupt Sources

• Programmable Serial Channel

• Low-power Idle and Power-down Modes

3.5. Pin diagram

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3.6. BLOCK DIAGRAM

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3.7. Pin Description

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VCC Supply voltage.

GND Ground.

Port 0Port 0 is an 8-bit open-drain bi-directional I/O port. As an output port,

each pin can sink eight TTL inputs. When 1s are written to port 0 pins, the

pins can be used as high impedance inputs.

Port 0 may also be configured to be the multiplexed low order

address/data bus during accesses to external program and data memory. In this

mode P0 has internal pull ups.

Port 0 also receives the code bytes during Flash programming, and

outputs the code bytes during program verification. External pull-ups are

required during program verification.

Port 1Port 1 is an 8-bit bi-directional I/O port with internal pull-ups. The Port

1 output buffers can sink/source four TTL inputs. When 1s are written to Port

1 pins they are pulled high by the internal pull-ups and can be used as inputs.

As inputs, Port 1 pins that are externally being pulled low will source current

(IIL) because of the internal pull-ups.

Port 1 also receives the low-order address bytes during Flash

programming and verification.

Port 2Port 2 is an 8-bit bi-directional I/O port with internal pull-ups. The Port

2 output buffers can sink/source four TTL inputs. When 1s are written to Port

2 pins they are pulled high by the internal pull-ups and can be used as inputs.

As inputs, Port 2 pins that are externally being pulled low will source current

(IIL) because of the internal pull-ups.

Port 2 emits the high-order address byte during fetches from external

program memory and during accesses to external data memories that use 16-

bit addresses (MOVX @ DPTR). In this application, it uses strong internal

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pull-ups when emitting 1s. During accesses to external data memory that uses

8-bit addresses (MOVX @ RI), Port 2 emits the contents of the P2 Special

Function Register.

Port 2 also receives the high-order address bits and some control signals

during Flash programming and verification.

Port 3Port 3 is an 8-bit bi-directional I/O port with internal pull-ups The Port

3 output buffers can sink/source four TTL inputs. When 1s are written to Port

3 pins they are pulled high by the internal pull-ups and can be used as inputs.

As inputs, Port 3 pins that are externally being pulled low will source current

(IIL) because of the pull-ups.

Port 3 also serves the functions of various special features of the

AT89C51 as listed below:

Port Pin Alternate Functions

P3.0 RXD (serial input port)

P3.1 TXD (serial output port)

P3.2 INT0 (external interrupt 0)

P3.3 INT1 (external interrupt 1)

P3.4 T0 (timer 0 external input)

P3.5 T1 (timer 1 external input)

P3.6 WR (external data memory write strobe)

P3.7 RD (external data memory read strobe)

Port 3 also receives some control signals for Flash programming and

verification.

RST

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Reset input. A high on this pin for two machine cycles while the

oscillator is running resets the device.

ALE/PROG

Address Latch Enable output pulse for latching the low byte of the

address during accesses to external memory. This pin is also the program

pulse input (PROG) during Flash programming.

In normal operation ALE is emitted at a constant rate of 1/6 the

oscillator frequency, and may be used for external timing or clocking

purposes. Note, however, that one ALE pulse is skipped during each access to

external Data Memory.

If desired, ALE operation can be disabled by setting bit 0 of SFR

location 8EH. With the bit set, ALE is active only during a MOVX or MOVC

instruction. Otherwise, the pin is weakly pulled high. Setting the ALE-disable

bit has no effect if the microcontroller is in external execution mode.

PSEN

Program Store Enable is the read strobe to external program memory.

When the AT89C51 is executing code from external program memory,

PSEN is activated twice each machine cycle, except that two PSEN

activations are skipped during each access to external data memory.

EA/VPP

External Access Enable. EA must be strapped to GND in order to

enable the device to fetch code from external program memory locations

starting at 0000H up to FFFFH. Note, however, that if lock bit 1 is

programmed, EA will be internally latched on reset.

EA should be strapped to VCC for internal program executions.

This pin also receives the 12-volt programming enable voltage (VPP)

during Flash programming, for parts that require 12-volt VPP.

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XTAL1

Input to the inverting oscillator amplifier and input to the internal clock

operating circuit.

XTAL2

Output from the inverting oscillator amplifier.

Oscillator Characteristics

XTAL1 and XTAL2 are the input and output, respectively, of an

inverting amplifier which can be configured for use as an on-chip oscillator,

as shown in Figure 1. Either a quartz crystal or ceramic resonator may be

used. To drive the device from an external clock source, XTAL2 should be

left unconnected while XTAL1 is driven as shown in Figure 2.There are no

requirements on the duty cycle of the external clock signal, since the input to

the internal clocking circuitry is through a divide-by-two flip-flop, but

minimum and maximum voltage high and low time specifications must be

observed.

Idle ModeIn idle mode, the CPU puts itself to sleep while all the on chip

peripherals remain active. The mode is invoked by software. The content of

the on-chip RAM and all the special functions registers remain unchanged

during this mode. The idle mode can be terminated by any enabled interrupt or

by a hardware reset.

It should be noted that when idle is terminated by a hard ware reset, the

device normally resumes program execution, from where it left off, up to two

machine cycles before the internal reset algorithm takes control. On-chip

hardware inhibits access to internal RAM in this event, but access to the port

pins is not inhibited. To eliminate the possibility of an unexpected write to a

port pin when Idle is terminated by reset, the instruction following the one that

invokes Idle should not be one that writes to a port pin or to external memory.

Figure 1. Oscillator Connections

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Note: C1, C2 = 30 pF ± 10 pF for Crystals = 40 pF ± 10 pF for Ceramic Resonators

Figure 2. External Clock Drive Configuration

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CHAPTER-4

4.1 COMPLETE CIRCUIT DIAGRAM WITH LIST OF COMPONENTS

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4.2 ADVANTAGES AND APPLICATIONS

Advantages:

Can avoid cable intervention. Can avoid manual intervention. Can send the data from one place to other place by minor

modifications. Can monitor the system and the signal from remote

places through some modifications.

Applications:

In substations. In corporate and government power generation plants. In supervisory and control applications. In industrial monitoring stations.

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CONCLUSION

This project titled “SCADA IMPLEMENTED OVER POWER

TRANSFORMER WITH REMOTE MONITORING SYSTEM” is a simulation model, by using Microcontroller ATMEL 89C51.

The Distribution Transformers failures are effectively protected against overload, over temperature and over voltage.

The parameters of the transformer are continuously monitored and transmitted to the nearest nearest electrical office for the necessary actions.

Wireless communication systems are used for transmitting and receiving the data from the transformer and the nearest electrical office by using RF communication.

In this project the over voltage, temperature and over load are monitored in signal system. The project is fully automated and require no manual interface.

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REFERENCES

Text Books:

(1) Linear Integrated Circuits –By: D. Roy Choudhury, Shail Jain

(2) Power Electronics - By: SEN

(3) Relays and their applications - By: M.C.SHARMA

(4) Op-Amps Hand Book - By: MALVIND

(5) Mechanical and Industrial Measurements - By: R.K. Jain

(6) Computer Controlled System - By: Karl J.ASTROM

(7) Programming and Customizing the 8051 Micro-controller

- By: Myke Predko

(8) The concepts and Features of Micro-controllers - By: Raj Kamal

(9) C++ an Introduction to Programming -

By: JESSE LIBERTY. JIM KEOGH

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