Final Report Plc

ACKNOWLEDGEMENT

The success of this project can be attributed to the help of a number of people. Firstly, we would like to thank our project supervisors, Mr. __________- and Mr. ___________, for their support and technical advice during the course of the project. We are also thankful to Dr. _______________________ for his valuable suggestions.

We are thankful to _____________, ______________, _______________, other lab supervisors, our batch mates and juniors who helped us a lot in implementation phase of our project. A word of thank is also goes to ________________ from Southern Methodist University, Dallas, Texas who helped us in the designing process of coupling.

Warm thanks goes to our family and friends specially ______________ who had provided support during the challenges, and understanding of our many hours spent at University.

ABSTRACT

The communication flow of today is very high. Many applications are

operating at high speed and a fixed connection is often preferred. If the power utilities

could supply communication over the power-line to the costumers it could make a

tremendous break-through in communications. Every household would be connected

at any time and services being provided at real-time. Using the power-line, as a

communication medium could be a very cost-effective way compared to other

systems because it can use the existing infrastructure, the electrical power distribution

network, which is a ubiquitous one. In this report, we investigate the applicability of

power line communications technique to data communications. The investigation is

both theoretical and practical, we detail on all aspects of power line carrier

communications and a working power line link is designed and tested. Topics covered

include feasible applications of power line carrier communications (hereafter referred

to as PLCC), currently available protocols and the impact of international standards.

Chapter One introduces the core technology, critically evaluating its benefits and its

feasibility. It also contains detailed project goals.

The power line channel is discussed with emphasis on noise and disturbances,

attenuation and signal coupling afterward the chapter four deals with the simulation of

power line channel with the help of MATLAB. Currently available protocols and the

regulatory standards governing it are discussed in chapter two. Chapter Three contains

the study we performed on the various digital modulation schemes available, along

with the selection of an optimum method. The issues concerning the design of the

coupling network are also discussed. Lastly, the design, construction and testing of a

working system providing the data transmission on the power line is in the chapter

Five of the report. At last but not least in the chapter six the main work of our project

is detailed. This consists of a study on a recent method of remote detection of the

illegal electricity uses via PLCC, an idea is proposed in this chapter for the Indian

conditions.

Table of contents

Chapter One-Introduction………………………………………………………………6

1.1 Introduction………………………….…………………………………..…….71.2 Benefits……………………………………………………………….……….91.3 The Challenge…………………………………………………………..…….101.4 Project Aims………………………………………………………………….10

Chapter Two-Focus on Power Line Carrier Communications…………………...…11

2.1 Existing PLCC standards…………………………………………………….12 2.1.1 X-10………………………………………………………………………12 2.1.2 CEBus………………………………………………… …………………12 2.1.3 LONWorks……………………..……………………… ………………...13 2.1.4 PLC-1…..………………………………………………… ……………...132.2 Power Line Carrier Challenges………………………………… …………..14 2.2.1 Noise and Disturbances………………………………………… …….... 14 2.2.2 Power line channel impedances and attenuation…………………..…… .162.3 Relevant Regulatory Standards…………………………………….….… ….182.4 Conclusions…………………………………………………………… …….20

Chapter Three-The PLCC Device: Practical Issues……………………………...….21

3.1 Modulation methods…………………….……………………………..….….22 3.1.1 ASK…………….…………………………………………………..……..22 3.1.2 FSK………………..………………………………………………..…….22 3.1.3 PSK………………………….….………………………………..……….243.2 The Coupling Networks………………………………………………..…….25 3.3 The interfacing network………………………………………………..…….273.4 Conclusions……………… ………………………………………………….30

Chapter Four- PLC System Modeling and Simulation………………………………29

4.1 Introduction……………………………………………………………..……304.2 Modeling………………………………………………………………..……304.3 Simulation………………………………….………………….……..………33

Chapter Five- Building and testing a working Power Line Carrier Communication System ……………………………………………..……………………………………35

5.1 From Theory to Practice……………………………………………..………36

5.2 Implementation of the Mod. System…………………….…………..………365.3 The Coupling Network……………………………..……………..…………375.4 Results and outcomes of the implementation……………………………..…38

Chapter Six: Study of an Vital Application………………………...…………………39

6.1Introduction………………………………………………………………..…406.2 System Description…………………………………………………….……406.3 Problem in Indian Scenario……………………………… …………………426.4 Solution to Problem………………………… ………………………………43

References……………………………………………….

………………………………45 Glossary of

terms…………………………………………………………….…………47

Appendix A-Component Selection Calculations………………………………….

….50A-1 FSK Modulation Circuit-XR2206…………………………………………51A-2 FSK Demodulation Circuit-XR2211………………………………………52

Appendix B-Circuit Diagrams………………………………………………….………

53

Appendix C-MATLAB Code for Channel Simulation…………………………....……56

Appendix D-Device Data sheets………………………..…………………………....…59

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CHAPTER ONE: Introduction

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1.1 Introduction: Powerline Communication is the technology that enables

the transmission of data over power line that carries and supplies electric power. PLC

has long history while the concept of broadband data transmission has been recently

developed. Replacing the slow data transmission rate with only one-way

communication, the emerging PLC technology has brought wider bandwidth with

two-way communications.

For a long time, PLC technologies have achieved very limited success in a

certain vertical market. The major applications of PLC Technology have remained

within the boundaries of monitoring & control of load control, low capacity data

communication, various automation system and remote metering system, and low

speed data communication up to 9600bps as well as analog signal transfer.

There are several current technologies that could implement such home

networks:

Radio frequency communication links:

This is certainly a very flexible technique, which allows untethered

device control. However the communication links required are currently too

expensive to be affordable for the average home users.

Phone line networking:

Another viable and high performance system for implementing home

network is the phone line networking. In this case the phone lines in a house are used

as communication channels. But the major limitation in phone line networking is the

number of phone instruments and their particular positions.

Traditional wiring schemes:

Co-axial, unshielded twisted pair wires are of low-cost and high performance.

They are a very practical way of implementing home networking in a new home

under construction. However major building work is required to install traditional

network wiring in an existing building. The alternative being unsightly cables strung

around. Techniques available remain costly, overly limited and difficult to install in a

pre-existing building. PLCC seems to be a correct alternative method, which can

overcome all the drawbacks of the existing techniques and also give a high efficiency.

Brief overview of Power Line Communications origins:

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Power line communications (PLC) has been around since the

1950’s but was never seriously thought of as a communication medium due to its low

speed, low functionality and high development cost. However in recent times, new

modulation techniques supported by technological advances have finally enabled

power line communications to become a realistic and practical means of

communication.

Short History of Power Line Communications:

 The first technique to make use of the power line for control messages was

the method - Ripple Control. This is characterised by the use of low frequencies (100

– 900Hz) giving a low bit rate and a demand on very high transmitter power, often in

the region of several 10kWs. The system provided one-way communication

technology, and among the applications provided was the management of street lights

and load control.

 In the mid 1980’s experiments on higher frequencies were carried out to

analyse the characteristic properties of the electric grid as a medium for data transfer.

Frequencies (in the range of 5 – 500kHz) were tested in which the signal to noise

levels were important topics for measurements as well as the attenuation of the signal

by the grid. These tests were done both in Europe and in the U.S. Scanda (Supervisory

Control and Data Acquisition) technology was developed at this time to carry out

these studies.

 Bi-directional communication was developed in the late 80’s and early 1990’s

and the main difference between these systems and modern systems today is that

much higher frequencies and a substantial reduction of the signal levels are used on

today’s power grid network. Since the 1997 experiment in a school of Manchester

(United Kingdom) utility and technology companies continued to experiment with

higher bandwidth data transfer across the electric grids in Europe and the U.S.

Advances in PLC technology now allows for high speed, broadband communications

over medium and low voltage mediums yielding extraordinary market opportunities.

1.2 Benefits

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PLCC integrates the transmission of communication signal and 50/60 Hz

power signal through the same electric power cable. The major benefit is the union of

two important applications on a single system. The data link appears 'transparent' to

the user. Although the devices are connected through the power line, consumers

perceive that there is a “separated” link available for data communications.

Since the existing power lines are used for signal transmission, the initial

heavy cost and investment for setting up a data communications system is avoided.

Setting up such a communications system then involves installation of transmitter

and/or receivers at appropriate points.

Though there are no set standards in PLC all implementations act in the same

manner. PLC is based on the idea that any copper medium will transport any electrical

signal for a certain distance. Basically a radio signal is modulated with the data we

wish to send. This radio signal is then sent down the copper medium (our power lines)

in a band of frequencies not used by for the purposes of supplying electricity and

managing electricity.

The frequencies and encoding schemes used greatly influence both the

efficiency and the speed of the PLC service. Most PLC radio traffic generally occurs

in the same bandwidth roughly 1.6 MHz to 80 MHz. These frequencies are in the MF

Medium Frequency (300KHz-3 MHz), HF High Frequency (3MHz – 30 MHz) and

some of the VHF Very High Frequency (30MHz – 300 MHz) spectrum. Various

encoding schemes have been used for sending the data along the Power Lines these

include:

GMSK

Used with the Single Carrier Version of PLC providing low bandwidths <1

MHz

CDMA

Used with the Single Carrier Version of PLC providing low bandwidths <1

MHz

OFDM

Used with the Multi Carrier version of PLC providing a bandwidth of 45 MHz

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1.3 The Challenge

Since the power line was devised for transmission of power at 50/60 Hz and at

most 400 Hz, the use of this medium for data transmission (especially at high

frequencies) presents some technically challenging problems. It is one of the most

electrically contaminated environments, which makes it very hostile for transmission

of data signals. The channel is characterized by high noise levels and uncertain (or

varying) levels of impedance and attenuation. In addition, the line offers limited

bandwidth in comparison to cable or fiber- optics. Power line networks are usually

made of a variety of conductor types and cross sections joined almost at random.

Therefore a wide variety of characteristic impedances are encountered in the network.

This imposes interesting difficulties in designing the filters for these communication

networks.

1.4 Project aims : The project aims to thoroughly explore the theoretical and

practical aspects of power line carrier communications (PLCC) techniques. To this

end a number of specific goals were proposed at the start of the project.

To gain a detailed knowledge of the challenges faced by PLCC techniques-why

they are not a widespread communications method.

To study thoroughly the wide spread applications of PLCC techniques.

To find a solution of wide spread problem of illegal electricity usage using PLCC

system.

To research and design a working PLCC model for the data transmission.

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CHAPTER 2: FOCUS ON POWER LINE

CARRIER COMMUNICATIONS

Challenges, Current Systems and Modern

Techniques

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2.1 Existing PLCC standards:

Various protocols have been developed for use for communication on power line. They differ in their modulation techniques, channel access mechanisms and the frequency bands they use. A brief overview of the most popular protocols is presented here.

2.1.1 X-10X-10 is one of the oldest power line communication protocols. It uses a form

of amplitude shift keying (ASK) technique for transmission of information. Although it was originally unidirectional (from controller to controlled modules) some bi-directional products have also been implemented. X-10 controllers send their signals over the power line to simple receivers that are used mainly to control lighting and other appliances. A 120 KHz amplitude modulated carrier, 0.5-watt signal, is superimposed into AC power line at zero crossings to minimize the noise interference. Information is coded by way of bursts of high frequency signals.

The standard includes addressing mechanisms to individually identify appliances. The presence of a 120Khz signal burst at zero crossing indicates the transmission of a binary ‘1’, whilst the absence of the 120Khz signal indicates a binary ‘0’. In order to control specific devices, modules are assigned an address, which consists of a house and unit code. A typical X-10 transmission would include a start code, house address, device address, and then function code (such as ON, OFF, etc…). The more the devices on the line, the more frequently they try to send messages, the more likely it is that commands may be lost. So, if a button is pushed to turn on a light, if someone arrives at the front door and the motion sensor sends a signal and if they occur at the same time, these will interfere with each other. Not only will the light fail to turn on, but the motion at the front door will also be missed. The basic limitations of the X-10 protocol are speed, collisions and signal strength

2.1.2 CEBusThe CEBus protocol uses peer-to-peer communication model. To avoid

collisions a carrier sensed multiple access (CSMA) with collision resolution and collision detection is used. The power line physical layer of the CEBus communication protocol is based on spread spectrum technology patented by Intellon Corporation.

Unlike traditional spread spectrum techniques (used in frequency hopping, time hopping or direct sequence), the CEBus power line carrier sweeps through a range of frequencies as it is transmitted. A single sweep covers the frequency band from 100-400 KHz. This frequency sweep is called a chirp. Chirps are used for synchronization, collision resolution and data transmission. Using this chirp technology data rate of about 10 KHz can be obtained. It specifies that a binary digit be represented by how long a frequency burst is applied to the channel. For example, a binary ‘1’ is represented by a 100-microsecond burst, whilst a binary ‘0’ is represented by a 200-microsecond. CEBUS is a commercially owned protocol, and thus attracts registration fees.

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2.1.3 LONWorks:Echelon Corporation is the developer of LONWorks networks. The protocol

provides a set of communication services that allow the applications in a device to send and receive messages over the network without needing to know the topology of the network or the names, addresses, or functions of other devices. All communications consists of one or more packets exchanged between devices. Each packet is a variable number of bytes in length and contains a compact representation of the data required for each of the 7 layers of the OSI model.

The addressing algorithm of this protocol defines how packets are routed from a source device to one or more destination devices. Packets can be addressed to a single device, to any group of devices or to all devices. LONWorks address types include physical, device, group, and broadcast addresses. Every packet transmitted over the network contains the device address of the transmitting device (the source address) and the address of the receiving device (destination address) that can either be a physical, a device, a group or a broadcast address. It is possible for two or more independent LONWorks systems to coexist on the same physical channel, as long as each system has a unique domain ID. Devices in each system respond only to those packets corresponding to their domain ID and do not know about packets addressed with other domain IDs. Each domain in a system using this protocol can have up to 32,835 devices. There can be up to 256 groups in a domain and each group can have any number of devices assigned to it, except that end to end acknowledgement is required. There can be up to 255 subnets in a domain and each subnet may have up to 127 devices.

2.1.4 PLC-1:Metricom is the maker of its own power line communications devices. Unlike

the CEBus standard, its nodes do not have to transmit as well as receive. Metricom’s current main product is the PLC-1, which is a transmitter receiver that includes a set of high-level functions that enable designers to implement high-performance power line communication (PLC) networks. Metricom claims that their chip is easily modifiable to transmit over different medium, although it does not appear that they market any variations. It seems that Metricom has set their product in opposition to the CEBus standard, X10, and LonWorks. (See: www.metricom-corp.com/compare.html, in which Metricom compares PLC-1 to the three preceding products/standards.) In general it appears that Metricom has tried to find what they believe are weak spots in the designs of CEBus, X10, and LonWorks and make a product that fills those spots. PLC-1 is designed to be low-cost with the ability to be used with different protocols and to form systems of a variety of purposes.

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2.2 Power Line Carrier Challenges:Power lines and their associated networks are not designed for communications use. Theyare a hostile environment that makes the accurate propagation of communication signals

difficult. Noise levels are often excessive, and cable attenuation at the frequencies of interest is often very large. Important channel parameters such as impedance and attenuation are time varying in unpredictable ways. The biggest challenges faced in PLC methods are:

2.2.1 Noise and DisturbancesCommon causes of noise on electrical power networks include corona discharge, lightning,

power factor correction banks and circuit breaker operation. On the low voltage network, much of this noise is filtered by medium/low voltage transformers, so the most common interference in low voltage domestic networks can be attributed to the various household devices and office equipment connected to the network. Noise and disturbances on the electrical power network can be generally classified as follows:

(i) Waveshape disturbancesThese include:a. Over-voltages, both persistent (>2 seconds) or surges (<2 seconds).b. Under-voltages, both persistent or surges.c. Outages.d. Frequency variations.e. Harmonic Distortions.

ii) Superimposed disturbancesThese include:a. Persistent oscillations, either coherent or random.b. Transient disturbances, both impulse and damped oscillations.

Waveshape disturbances are usually of little effect on PLC systems. Transceivers are usually robust enough to cope with minor over-voltage and under-voltage disturbances. Naturally, in the case of (i)(c), total line outages will make information transmission impossible. Yet the outage of a piece of distant equipment will not effect the performance of a domestic PLC system. Harmonic disturbances can be a major source of disturbance, yet these occur at frequencies below those designated for PLC communications by statutory authorities.

Frequency variations can cause major problems in PLC systems, as many simple systemsrely on the mains carrier (50Hz sine wave) for synchronization between transmitter and

receiver. Frequency variation in this wave will cause transmission error. Modern systems overcome this obstacle by avoiding reliance on the mains carrier for synchronization.

On the medium voltage network, class (ii) noise is attributed to large factories with extensive plant or machinery, and industrial users with poorly filtered appliances. On the low voltage network, a number of household appliances are most often responsible for superimposed disturbances. Vines et al further categorise type (ii) noise as:

A. Noise having line components synchronous with the power system frequency;B. Noise with a smooth spectrum;C. Single event impulse noise, and;D. Non synchronous noise.

A. Noise having line components synchronous with power system frequency.

The usual source of this noise (hereafter called Type A noise) are triacs or silicon controlled rectifiers (SCR’s), found domestically, for example, in light dimmers or photocopiers. The spectrum of this noise consists of a series of harmonics of the mains frequency (50Hz).

There are three ways to combat this kind of noise: [1]· As the frequency spectrum of class A noise is regular, successful communicationmay be possible with modulation schemes that avoid, or have nulls, at thesefrequencies.· Filter these noise components out using accurate notch filtering.· Considering the time domain representation of class A noise, a noise pulse can be

expected at equal intervals. Using fairly simple time division multiplexing schemes and error correction, unwanted effects can be minimized.

B) Noise with a smooth spectrum.Noise with a smooth spectrum (hereafter called type B noise) is generally caused by

universal motors. A result of the commutation process in motor powered appliances such as blenders and vacuum cleaners, this noise has a flat spectrum in the frequency ranges used by PLC systems. Thus it can be modeled as band limited white noise. A characteristic of many of the appliances that contain universal motors is that they are often used for a short period of time. Thus, PLC systems that do not have to function in real time can avoid this noise by operating at a time when the noise is absent. Conversely, real time systems must be able to cope with type B noise.

C) Single event impulse noise.Single event impulse noise (type C noise) is primarily due to switching phenomena

lightning, the closing of contacts, etc. Type C noise disturbs the whole frequency band for a short amount of time, and is often modeled as an impulse disturbance due to the relatively short times involved. Experience with impulse noise in other communications environments shows that type C noise can be overcome by error correcting codes.

D) Non synchronous noise.Non synchronous noise (type D noise) is characterized by periodic components that occur

at frequencies other than harmonics of the mains frequency. Major sources of type D noise include television and computer monitors. The scanning and synchronization signals in such appliances cause noise components at known frequencies- for example, interference from a PAL system television set is at 15734kHz and associated harmonics. Different standards of television and computer scanning have different radiated noise components. The solution to minimizing such interference is to avoid data transmission at 15734kHz and associated harmonics, and to use a modulation scheme that is frequency diverse, thus avoiding potential type D noise at any unforeseen frequencies.

So far a qualitative description of noise on the low voltage network has been given. Quantitative values of noise for various common appliances can be found in Table 2.1. With an understanding of the noise inherent on domestic power networks, various suggestions can be made for the development of a PLC communications system:

· Appropriate error correcting codes should be implemented to cope with noise types A, B and C.

· To avoid type D noise, television line frequency and harmonics should be avoided when modulating the signal onto the channel- no signal information should be transmitted at these frequencies.

· Some kind of frequency diversity (for example frequency hopping) should be implemented to cope with interference at unknown frequencies.

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Table 2.1. Measured amplitude and duration characteristics of noise from common household appliances.

2.2.2 Power Line Channel Impedances and Attenuation.

The characteristic impedance of an unloaded power cable can be obtained by a standarddistributed parameter model, and given by

At the frequencies of interest for PLC communications, this approximates to

where L and C are the line impedance and capacitance per length. Malack and

Engstrom[22] list the characteristic impedance of the cables used for power transmission as ranging from 70-100 Ohms.

Unfortunately, a uniform distributed line is not a suitable model for PLC communications, since the power line has a number of loads (appliances) of differing impedances connected to it for variable amounts of time. Thus, it can be seen that the channel impedance is a strongly fluctuating variable that is difficult to predict. Measured impedance models of common electric apparatus are presented in Table 2.2. As can be seen, impedance values vary greatly. As mentioned, the overall impedance of the low voltage network results from a parallel connection of all the network’s loads, so the small impedances will play a dominant role in determining overall impedance. Overall network impedances are obviously very difficult to predict. Schaap [5] quotes figures of 0.1-2for low voltage networks. Dostert [21] claims a power line impedance of 2-150, whilst Malack and Engstrom [22] list results of 0-80. Clearly, channel impedance is very low. This presents significant challenges when designing a coupling network for PLC communications. Maximum power transfer theory states that the transmitter and channel impedance must be matched for maximum power transfer. With strongly varying channel impedance, this is very difficult. The PLCC system designer must suffice with designing a transmitter and receiver with sufficiently low output/input impedance (respectively) to approximately match channel impedance

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in the majority of expected situations. See the model section of this report for more information on this area.

Table 2.2, Impedance models for common electric apparatus.

Communications signal attenuation in the power line environment is high. Straightforward channel attenuation combines with impedance mismatching problems to give very large attenuation levels. Schaap[5] lists attenuation levels of 100dB/km over the low voltage network. Obviously, over distances of even hundreds of meters, repeaters may be required, but remain unnecessary for intra-building use.

2.3 Regulatory Standards for Power Line Carrier Communications.

Various standards exist that provide regulations on the operating specifications of PLC systems. The standards were designed with consideration for such things as providing for maximum multiple-user efficiency, and avoiding interference with ripple control systems such as street lighting, off-peak water system control and other PLC devices. CENELEC, the E.E.C’s electrical standardization body, provide the most rigorous standard of all those on PLC communications, and gives the specification to which most devices are designed to meet.

CENELEC’s standard EN50065 “Low voltage mains signaling” gives regulations on key parameters such as frequency range, signal power and so on. The standard allows for PLC communication systems to operate in the frequency band 3- 148.5kHz, avoiding interference with ripple control systems at the lower boundary, and interference with long wave (LW) and medium wave (MW) radio broadcasts by posting the upper boundary. CENELEC then divide this band into further categories:

The band from 3-95kHz, or A-Band, is allocated for electrical utility use, for such things as automated meter reading and customer load control.

The range from 95-148.5kHz, comprising the B, C, and D bands is reserved for end-user applications. These three bands are primarily differentiated by regulations in protocols for each band. B band, from 95-125kHz requires no use of access protocol for establishing communications. Thus, it is possible for two systems to transmit simultaneously on the B band,

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and therefore messages to collide. This band is designed for use in applications such as baby-monitors and intercoms.

The C band, from 125-140kHz requires an access protocol to be used by devices transmitting at this range. This protocol is aimed at making simultaneous transmission of messages highly improbable. Thus, different systems may cohabit, but only one transmitter can operate at any one time. Specifications are given for access protocol frequencies, and so on. Applications for devices operating in this band would be such things as intra-building computer communications.

The D band (140-148.5kHz) is similar to the A band in that it requires no access protocol, and thus message collision is possible. CENELEC EN50065 also specifies interference immunity requirements for PLC communication systems, both for immunity to interference from other PLC systems, and interference from system noise. Again, the standard is split up into utility and end-user categories. Test methods for determining such immunity are given. Lastly, EN50065 specifies such things as communication protocols (in line with OSI2 layers 1 {physical layer} and layer 2 {data link layer}), equipment impedance (avoiding excessive signal attenuation due to multiple PLC devices of low impedance on one network), and filter specifications for carrier removal, etc. CENELEC specifies the maximum transmitted power from a PLC device should not exceed 500 mW.

Other statutory authorities list similar specifications. In Europe, Deustche Bundespost specifies one channel of 30-146 kHz. In America and Japan, only MW or AM broadcasts need be considered. These start at 535 kHz, with intermediate frequencies of typically 455 kHz. Thus, American PLC communication systems often operate in the band 100-450 kHz. Part 15 of the American FCC’s Rules and Regulations lists PLC communications systems as “Restricted Radiation Devices”, and as such there are very few applicable regulations on them, nor do they require licensing or registration.

Figure 2(a): CENELEC frequency band allocation

Figure 1(b): FCC frequency band allocation

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2.4 Chapter Two ConclusionsMany challenges are faced by power line carrier communications. The power line was

never intended for communications purposes, and challenges such as strong interference, varying attenuation and impedance have limited current PLC devices to simple home-automation use. However, with careful thought many modern communications techniques, such as spread-spectrum methods, Orthogonal Frequency Division Multiplexing(OFDM), CDMA etc. can be applied to overcome these challenges. Lastly, the PLCC system designer is limited in the bandwidth available for communications not by physical properties of the power line, but by regulatory standards imposed by governing bodies. Aside from these challenges, a number of unique issues exist when trying to communicate across a power line, a medium never intended for communications use. These issues are covered in Chapter Three.

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CHAPTER THREE : The PLCC Device - Practical

Issues

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3.1 Modulation Methods:Various choices of modulation methods are available for digital transmission, including

Digital Amplitude Modulation, Quadrature Amplitude Modulation, Phase Shift Keying and Frequency Shift Keying. Due to the often severe attenuation characteristics of the PLC channel, the best modulation options for PLC communications are Frequency Shift Keying and Phase Shift Keying, both schemes being robust yet simple. More complex proprietary PLCC modulation schemes are being developed, but these remain beyond the scope of this project.

3.1.1 Amplitude Shift keying:In the ASK modulation scheme the carrier wave is directly multiplied by the digital signal

using balanced modulators or like. Mathematically, the modulated carrier signal can be given as:

Where, A = amplitudewo = carrier frequencyb(t)= unipolar digital data

This implies that the carrier frequency is present when data is at high logic level and there is no carrier at all when the data is at logic low level.

3.1.2 Frequency Shift Keying.Frequency shift keying (FSK) modulation is a form of FM modulation where the frequency

of the carrier wave is varied by the binary input stream. As the binary input signal changes from a logic 0 to a logic 1, and vice-versa, the FSK output shifts between two frequencies: a mark or logic 1 frequency and a space, or logic 0 frequency. An FSK waveform is shown in figure 3.1.

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The general expression for a binary FSK signal is:

where: v(t) = binary FSK waveformVc = peak unmodulated carrier amplitudewc = radian carrier frequencyvm(t) = binary digital modulating signal

∆w = change in radian output frequencyWe see that the carrier amplitude, Vc, remains constant with modulation, however the

output carrier radian frequency shifts by an amount 2 w . This frequency shift is proportional to the amplitude and polarity of the binary input signal. In addition, the rate at which the carrier frequency shifts is equal to the bit rate of the binary input signal.

3.1.3 Phase shift keying.Phase shift keying (PSK) modulation is a form of phase modulation where the phase of the

carrier wave is varied by the binary input stream. With binary phase shift keying two output phases are possible, carrier frequency remaining constant. One output phase represents logic 1 and the other logic 0. As the digital input signal changes state, the phase of the output carrier shifts between two angles that are 180 degrees out of phase. Such a waveform is shown in figure 3.2.

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Mathematically, phase shift keying is represented as:

where a is the fundamental frequency of the binary modulating signal, and c is the

frequency of the unmodulated carrier. Higher bandwidth PSK schemes exist, where the binary stream is represented by up to 16 different phase variations, but these systems were deemed unsuitable due to complexities in their implementation.

It is a difficult problem to determine which modulation scheme, FSK or PSK is more suitable to power line carrier applications. In deciding between the advantages and disadvantages of each scheme, the PLCC designer must continuously keep in mind the hostile environment of PLC communications.

3.2 The Coupling Network

There are a number of ways to couple a communications onto the electrical power network.Two main categories exist:

In the case of differential mode coupling, the line, or active wire, is used as one terminal, and the neutral wire as the second terminal. In cases where a neutral line is not present (high voltage networks), the ground line acts as the second terminal.

In common mode coupling, the line (active) wire and neutral wires are used together, forming one terminal, and the ground wire serves as the second terminal. The reader may think this coupling mode impossible, due to the connection of neutral and ground wires at the transformer. In practice, the inductance between points of coupling and the short-circuit point is large enough to allow signal transmission. However, problems exist in using common mode coupling in the presence of earth leakage protection devices, and certain countries do not allow common mode coupling because of the perceived dangers to customers.

Considering the physical implementation of the coupling, two methods are possible:The first method is capacitive coupling. A capacitor is responsible for the actual

coupling.Alternatively, inductive coupling may be used. An inductor is used to couple the

communications signal onto the power network. Inductive coupling provides a physical separation between power network and communications network, making it safer to install.

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Another challenge in designing a power line coupling network is obtaining a suitable frequency response of the coupler. In the receive direction, it is desired that the coupling device possess a band-pass characteristic, blocking 50Hz mains voltages, and passing signals at the carrier frequency. In the transmit direction we wish for the coupler to possess high-pass properties, passing the communications signal unattenuated. Such a network should also be impedance matched to the power line for maximum power transfer. Meeting all these requirements concurrently becomes very difficult. The ultimate coupler network design becomes a compromise between the different characteristics for receive and transmit direction, plus impedance.

Focusing on using an inductive coupling method (for safety reasons), the most common coupler topology is shown in figure 3.5.

This method is based on two principles:1. A value of Ceq that has sufficient impedance to block the 50 Hz power frequency.2. Resonance between the coupling capacitor Ceq and the primary winding inductance L1 to

give suitable low characteristic impedance. The shortcomings of this topology involve use of the iron-core transformer. The effective inductance of this core is difficult to measure, and can change in a non-linear fashion, altering the characteristics of the coupling network. Roy and Abraham [2] list an alternate coupler topology, given in figure 3.6.

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Here, a large coupling capacitance (Ceq=0.5uF) is used to couple the signal onto the transmission line. Giving a low transceiver input impedance, the major drawback of this approach is that it results in significant carrier frequency loss (quoted as up to 20dB). Given the significant losses faced using the second coupler topology.

For the prototypic implementation of the system we are trying to establish simplex communication between two data communication equipments. Thus we need two couplers of different frequency responses, one in the transmit direction and the other in the receive direction. At the receiver side the coupling device should posses a band pass characteristic, blocking the 50 Hz mains voltage and passing signal at the carrier frequency. At the transmitter side, the coupler should posses high pass properties, passing the communication signal un-attenuated. The coupler should also be impedance matched to the power line for maximum power transfer.

3.3 Interfacing Network: Interfacing network is there to link the computer parallel port with the PLCC network as to

send information to the particular home device. As we are implementing our project in the context of home automation application of PLCC technique. The parallel port program is written in C using graphics as to made it attractive. Program sends the data on the output pin of the 25 pin RS232 connector in the form of ‘0’ and ‘1’. Some specifications of RS 232 interface are given below.

The Parallel Port is the most commonly used port for interfacing home made projects. This port will allow the input of up to 9 bits or the output of 12 bits at any one given time, thus requiring minimal external circuitry to implement many simpler tasks. The port is composed of 4 control lines, 5 status lines and 8 data lines. It's found commonly on the back of your PC as a D-Type 25 Pin female connector. There may also be a D-Type 25 pin male connector. This will be a serial RS-232 port and thus, is a totally incompatible port. Newer Parallel Port’s are standardized under the IEEE 1284 standard first released in 1994.

This standard defines 5 modes of operation which are as follows,1. Compatibility Mode.2. Nibble Mode. 3. Byte Mode. 4. EPP Mode (Enhanced Parallel Port).5. ECP Mode (Extended Capabilities Port).

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The aim was to design new drivers and devices which were compatible with each other and also backwards compatible with the Standard Parallel Port (SPP). Compatibility, Nibble & Byte modes use just the standard hardware available on the original Parallel Port cards while EPP & ECP modes require additional hardware which can run at faster speeds, while still being downwards compatible with the Standard Parallel Port.

Compatibility mode or "Centronics Mode" as it is commonly known, can only send data in the forward direction at a typical speed of 50 kbytes per second but can be as high as 150+ kbytes a second. In order to receive data, you must change the mode to either Nibble or Byte mode.

Nibble mode can input a nibble (4 bits) in the reverse direction. E.g. from device to computer.

Byte mode uses the Parallel's bi-directional feature (found only on some cards) to input a byte (8 bits) of data in the reverse direction.

Extended and Enhanced Parallel Ports use additional hardware to generate and manage handshaking. To output a byte to a printer (or anything in that matter) using compatibility mode, the software must.

1. Write the byte to the Data Port.2. Check to see is the printer is busy. If the printer is busy, it will not accept any data, thus

any data which is written will be lost.3. Take the Strobe (Pin 1) low. This tells the printer that there is the correct data on the

data lines. (Pins 2-9)4. Put the strobe high again after waiting approximately 5 microseconds after putting the

strobe low. (Step 3)This limits the speed at which the port can run at. The EPP & ECP ports get around this by

letting the hardware check to see if the printer is busy and generate a strobe and /or appropriate handshaking. This means only one I/O instruction need to be performed, thus increasing the speed. These ports can output at around 1-2 megabytes per second. The ECP port also has the advantage of using DMA channels and FIFO buffers, thus data can be shifted around without using I/O instructions.

We are using the Compatibility or Centronics mode in our project as we have to send information only from computer to the home appliance or device. Here in our project we use only one device to make ‘on’ or ‘off’ using the computer panel.

Hardware PropertiesOn the next page is a table of the "Pin Outs" of the D-Type 25 Pin connector. The D-Type

25 pin connector is the most common connector found on the Parallel Port of the computer, while the Centronics Connector is commonly found on printers. The IEEE 1284 standard however specifies 3 different connectors for use with the Parallel Port. The first one, 1284 Type A is the D-Type 25 connector found on the back of most computers.

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3.4 Chapter Three ConclusionsIn designing any communications system a number of decisions exist as to modulation

methods, channel and so on. Power line carrier communications has a number of its own unique issues to be considered. After comprehensive computer simulation, it was found that Frequency Shift Keying is the most suitable modulation scheme in an environment of unpredictable phase shift. The coupling network used to couple a signal onto the power line is the result of an unhappy compromise between desired impedances and frequency responses, and the main problem was aroused in the implementation of this system. We had opted for the design on the basis of a paper [12] comprising of bidirectional impedance adapting 1:7 ratio transformers. Lastly, the interfacing network is based on the parallel port of computer. Chapeter Four details the modeling and simulation of a typical PLCC system. Chapter Five details how all these theory suggestions specially related to the coupling network were implemented in a working power line carrier communications system.

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CHAPTER FOUR:PLC System Modeling and

Simulation

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4.1 Introduction: As stated before that the PLCC channel has a time varying impedance and so the total losses associated with the channel are also time varying. This study is an analysis and presentation of the data obtained from power network analysis based on ABCD parameters. MATLAB simulation is also done later on to obtain the impedance dependence of the losses. The overall transfer function of a typical PLC system is shown in the fig 4.1. In the PLC system given in Fig. 4.1, the host unit will send instructions through the power line to the appropriate target unit at the designed time. The target units receive instructions from the host unit through the power line and, if appropriate, the target units then perform the designed command. In one PLC system, each host unit will be able to store profiles for up to many target units.

Fig.4.1: Principal Block Diagram of PLCC system

4.2 Modeling of PLC Channel:

The main elements in PLC system are distribution transformer, power line, and the electrical loads at homes or offices. These elements cause the degradation on the system performance due to their characteristics combined with PLC modems. Therefore, to obtain the PLC system performance, overall power network elements described above and other PLC communications equipment must be considered together. PLC modems are connected at the secondary port of the distribution transformer; therefore, for circuit analysis, transformer equivalent circuit is referred to secondary. In the approximate equivalent circuit referred to secondary, n represents the turns ratio of the transformer, Req and Xeq are equivalent resistance and inductive reactance, respectively, and can be written as

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where Rs and Rp are the dc resistances of secondary and primary coils, respectively, and Xls and Xlp define the inductive reactance’s of both coils of transformers [40]. Generally for transmission lines less than 50 miles long, the equivalent circuit can be represented as lumped series impedance parameters, such as serial resistance R and inductive reactance XL [15].Fig. 4.2 shows the overall equivalent circuit of long distance applications of PLC system using distribution transformer, line, load, and the coupling capacitors. In Fig. 4.2, C1 and C2 are modem coupling capacitances, R1 and L1 are the equivalent circuit elements of the distribution transformer, R2 and L2 and are the elements of the line equivalent. T or ABCD parameters can be calculated for equivalent circuit shown in Fig. 4.2.

Fig. 4.2 : Overall equivalent circuit of the PLC system for long distance applications

The ABCD parameters as calculated using the above shown PLC system model are given below,

System overall Transfer Function in term of ABCD parameters can be given as,

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……………………………..…………..(i)The overall transfer function in terms of standard polynomial form is as follows,

...............................................................................(ii)

Where the coefficients of the Polynomial are given as

With an expression for the voltage transfer function Av(s) it is possible to calculate the total loss introduced on inserting the circuit under consideration between the generator(or source) and load. The Power loss of overall network between input and output ports can be calculated as follows:

................................................................................(iii)

So the modeling of a typical long distance PLCC system is done and the next passage describes the simulation part.

4.3 Simulation of PLCC Channel:

Using the transfer function of the overall system from equation (i), the amplitude response can be calculated. Transfer function Av(s) has no poles in the right semi region of the s- domain, so system is absolute stable in all frequencies which is shown in the fig. 4.3 by the bode plot drawn using MATLAB.

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Fig 4.3: Bode Plot of Transfer function Av(s)

Using the ABCD parameters and the equation (ii) and (iii) the simulation of complete model is done with the help of MATLAB and the resulting graphs shows the variations in the loss L(dB) with respect to the carrier frequency and the load impedances at a 1000 m line. For given equivalent network in fig 4.2, the approximate values are in the following [15].

Rs = 2-4 ΩC1 = C2 = 1 µFL1 = 0.5 mHR1 = 0.02 ΩR2 = 0.001 Ω/m (here taken as 1 Ω for 1000 m length)L2 = 0.001 mH/m (here taken as 1 mH for 1000 m length)

Fig 4.4 depicts the result of the above mentioned simulation in this fig the system power losses are plotted against communication frequencies for various load impedances. The MATLAB codes for the simulation and bode plot are given in the appendix.

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Fig. 4.4 : Power Loss versus Frequency for various load impedances

Following is a summary of results obtained from the above simulation1) Carrier frequency is an important parameter for the path loss and its effects are shown in

the fig.4.4. Path losses increase with the increase in the carrier frequency.2) Load impedance seems to be the most significant negative effect in the system. Fig.4.4

shows that the system losses increase with a decrease in the load impedance.

Chapter Four Conclusion:In the chapter four the entire modeling and simulation of the PLCC long distance system was done and the simulation shows that load impedance generally varies with time; hence, PLC is basically a time varying channel.

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CHAPTER FIVE:Building and Testing a Working

Power Line Carrier Communication System

5.1 Practical GoalsThe original goals for this project were “Software and hardware implementation of a PLCC system to demonstrate the potential for use in control of electrical appliances- e.g.“home automation”; with a possible extension: “If the above is successful, investigate extension of the scheme to a level where it can be used for transmission of data between computers (albeit at a low baud rate)”.After progressing through the research and theory stages of the project into initial implementation stages, we had faced various problems in the implementation. To this end, the practical implementation component has focused on building a serial link between the appliances and computer. To implement the serial link we designed one set of modulator and demodulator as well as a RS 232 line driver using MAX232 IC.

5.2 Theory into Practice

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The theory section of this report suggests a number of modern communications methods and techniques that lend themselves to reliable performance of a power line carrier communications device in a hostile channel. Modulation and coupling methods were all suggested that are practical to implement and give suitable performance.Practical aspects of each consideration are detailed below.

5.2.1 Implementation of the FSK Modulation and Demodulation System:The implementation stage began with the construction of the FSK modulator and demodulator.

FSK ModulatorIn our final working circuit FSK modulation is performed by the application of a Voltage Controlled Oscillator (VCO). A voltage-controlled oscillator produces an AC waveform, output frequency directly proportional to the DC input voltage. By using the binary waveform as an input to the VCO, we can vary the frequency of the output sinusoid, giving FSK modulation.The integrated circuit employed for this purpose is the EXAR device XR-2206. The XR-2206 is a monolithic function generator IC capable of producing high quality sinusoid of high-stability and accuracy. Frequency of operation can be selected externally over a range of 0.01Hz to more than 1MHz. The circuit is ideally suited for communications, and function generator applications requiring sinusoidal tone, AM, FM, or FSK generation. The system is designed to operate at a mark ’1’ frequency of 30 KHz and a space ‘0’ frequency of 15 KHz. Testing of this circuit was done using a square wave input stream (representing a constantly varying 0-1-0 binary waveform). The mark and space frequencies were confirmed along with general speed and stability. The circuit diagram of the XR-2206 IC is shown in circuit Figure. The component selection equations are shown later.

FSK DemodulatorThe integrated circuit employed for this purpose is the EXAR device XR-2211. The XR-2211 is a monolithic phase-locked loop (PLL) system especially designed for data communications applications. It is particularly suited for FSK modem applications. It operates over a wide frequency range of 0.01Hz to 300 kHz.

The circuit for this revised design is shown in circuit Figures and the calculations of the biasing components are included later in this report in Appendix ATesting the FSK demodulation section involved passing an FSK input into the demodulator, and tuning the phase locked loop parameters until a stable binary output was obtained. Specifically, a square wave was passed into the FSK modulator section, producing an FSK output. This output was passed directly to the demodulator section, and the demodulator output compared to the overall input. Initially, demodulated output did not represent system input particularly well. We found that for reliable performance of the demodulation section, considerable time was required tuning various phase locked loop parameters, such as center frequency and damping coefficients. Eventually, reliable performance was obtained, and we were able to input a square wave into the communications system, with the output observed as a stable square wave of identical frequency.

5.3 Coupling network:

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The coupler employs an inductive coupling of the signal to the power line using differential mode coupling. Since we were not able to obtain a readymade transformer, which could serve our needs we had to hand wound our own transformer.

Design of Bidirectional Impedance Matching Transformer:If the modem input impedance cannot be designed to equal the power line impedance, it is absolutely necessary to equalize the impedance levels by using a step up transformer. A transformer is a powerful impedance transforming device, as any impedance is reflected by the square of the winding ratio[12]. If a transformer is used to equalize the terminating impedances on either side, another advantage results such as:The coupling network can now be used as a bidirectional coupler with the same filter characteristics from both sides.

1. Frequency Specifications: the bidirectional coupler will be designed for the CENELEC B, C and D Bands roughly from 90-150 kHz. Thus 90 kHz would be the worst case frequency for core consideration and 150 kHz would be the frequency where copper losses would be a maximum.

2. Impedance Levels/Winding Ratio: Although the power line access impedance fluctuates between 0.2 to 2 ohms and more, it has been decided that a one ohm power line impedance value satisfies various trade offs. It is also assumed that a 50 ohm modem impedance needs to be adapted to the 1 ohm impedance of the power line. This can be done using a 1:7 transformer. The 50 ohm modem impedance appears as (1/7)^2 * 50 approximately equal to 1 on the power line side, whereas the one ohm power line impedance appears as (7/1)^2*1 approximately equal to 49 ohm on the modem side.

3. Core: An E20 core was chosen manufactured Mn Zn Ferrite material. This core set hass the following properties core cross sectional area Ae=31.2 mm^2 , flux path length le=42.8mm.

4. Skin Effect: the optimum strand diameter is typically chosen between δ and 2 δ depending on the proximity effect and other design factors. For copper at a temperature of 50* C, the penetration depth δ at a certain frequency f is

δ = 0.0699 / f^(1/2) if the relative permeability of copper is assumed as 1 and symbol σ represent the conductivity. Equation yields a δ of 0.18 mm for the 150 kHz. The optimum strand diameter is taken as 0.36 mm for this design. The closest (lower) gauge available at the time of construction was a 0.25 mm diameter copper wire with a cross sectional area of 0.049 mm^2.

5. Number of Strands: the number of insulated strands necessary to obtain a litz wire bundle with sufficient cross sectional area can now be calculated as approximately 12 strands for the power line side and two strands for the modem side.

6. Number of Turns: A typical window fill factor is 0.5, and it is thus expected that only 8 power line side turns and therefore 56 modem side turns would fit on to the transformers bobbin.

Construction of the transformer:

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Here we have used a small HF E core shell type transformer on which 8 number of primary and 56 number of secondary turns are wound. The wire used for the turns is made of the 0.25 mm diameter wire wrapped to made up the strands. Primary wire is made up of the 12 wire strands and the secondary wire is made up of the 2 wire strands. · If we want 12V peak-to-peak signal on the power line, we need to get (slightly above) 12V signal on the "secondary" of the transformer (it is called the secondary, because it's not the one connected to mains).· The ferrite core and large capacitor take care of preventing the mains voltage from melting the primary wire.

5.4 Results and Outcomes of the Practical ImplementationThe implementation of bidirectional impedance adapting coupling network, modulator circuit and the interfacing circuit has been successful. A system has been built and tested that transmits data from the computer successfully after modulating it.

Chapter Six: Study of a Vital Application

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6.1 Introduction :

In this chapter the details of study carried by us in the field of a new scheme for the detection of the illegal use of the electricity in the Indian scene. The idea of this study was came into our mind after reading a paper [16] written by Cavdar. This paper contains a proposal for the remote detection of the illegal electricity usage. The following chapter contains the description of the system suggested by the Cavdar and the correction made by us for the Indian conditions.

6.2 System Description:

The system is based on the Automated Meter Reading (AMR) which is a system used for the remote reading of the electric consumer meters. Automatic kilowatt-hour (kWh) meter reading has become a necessity for most energy suppliers as deregulation, freer customer choice and open market competition occur in the energy supply sector. Visual inspection of meters is time consuming and labor-intensive. Automatic meter reading (AMR) was first tested 30 years ago when trials were conducted by AT&T in cooperation with a group of utilities and Westinghouse. The modern era of AMR began in 1985, when several major full-scale projects were implemented. In India the AMR technique is yet to be introduced and may take some time due to the weak financial condition of the State Electricity Boards, which are responsible for the distribution of the electrical energy. Power line communication can provide the channel for AMR data transmission without use of any extra cabling. AMR also have a potential for providing a system to detect the illegal electricity usage

Remote Detection of Illegal Electricity Usage:

(a) Methods of Theft:

This study presents the methods used for the theft of electricity. Following methods are used by subscribers and non subscribers for the theft of electricity.

(1) Direct hook up from the overhead transmission line: this is the only method which can be used by both a subscriber and a non subscriber of the SEB. In this method a wire is used to directly connect the overhead transmission line without using or bypassing the energy meter. This is the most common method of the theft in India and is locally known as “Katiya” connection.

(2) Using the mechanical objects: A subscriber can use some mechanical objects to prevent

the revolution of a meter, so that disk speed is reduced and the recorded energy is also reduced.

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(3) Using a fixed magnet: A subscriber can use a fixed magnet to change the electromagnetic field of the current coils. As is well known, the recorded energy is proportional to electromagnetic field.

(4) Using the external phase before meter terminals: This method gives subscribers free energy without any record. This method is different from the first one as in this the external phase in not taken from the pole directly.

(5) Switching the energy cables at the meter connector box: In this way, the current does not pass through the current coil of the meter, so the meter does not record the energy consumption.

Although all of the methods explained above may be valid for electromechanical meters, only the (1), (4) and (5) methods are valid for digital meters. Therefore, this problem should be solved by electronics and control techniques.

(b) Detection System:

The proposed control system of Cavdar for the detection of illegal electricity usage is shown in Fig. 5.1. PLC signaling is only valid over the low voltage 220 VAC power lines. The system should be applied to every low-voltage distribution network. The system given in Fig. 5.1 belongs to only one distribution transformer network and should be repeated for every distribution network. Although the proposed system can be used uniquely, it is better to use it with automatic meter reading system. If the AMR system will be used in any network, the host PLC unit and a PLC modem for every subscriber should be contained in this system.

Fig.5.1: System Block Diagram proposed by Cavdar

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In Fig. 5.1, the host PLC unit and other PLC modems are named PLC1A,…,PLCNA and are used for AMR. These units provide communication with each other and send the recorded data in kilowatt-hour meters to the PLC unit. In order to detect illegal usage of electrical energy, a PLC modem and an energy meter chip for every subscriber are added to an existing AMR system. As given in Fig. 5.1, PLC1B,…, PLCNB and energy meter chips belong to the detector. The detector PLCs and energy meters must be placed at the connection point between distribution main lines and subscriber’s line. Since this connection point is usually in the air or at underground, it is not suitable for anyone to access, such that its control is easy.

6.3 Problem in Indian Scenario:

The major consideration in this study was the problem related to the direct hook up or ‘Katiya’ method as given in the above passage system depicting this problem in a colony structure is shown in the fig. 1.

In this situation the subscriber A as shown in figure can easily get a illegal access using the hook up method from the line and both the PLC chip energy meter and elctromechanical PLC meter as suggested by Cavdar [5] both get cheated. The fig.2. makes the situation clearer.

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Thus the subscriber 2 gets successes in the theft of electricity without any trouble. As neither of meter reads any unit due to the phase bypass done by the subscriber. Similarly there are a number of non subscribers also present there who also contribute in this wrong deed. In this manner we have to develop another approach to solve the above problem. 6.4 Solution:

A scheme having a provision of a distributed area type of system in which the subscribers between two poles can be taken as a area comprising of approximately 20-30 homes at most. An area energy meter will be installed at one of the pole and that particular area energy meter will be based on the PLCC technique. This particular area energy meter will be able to receive instruction from the remote host PLC technique and to send the data on request from the host PLC unit.

A host PLC unit will generate a specific code during reading operation; this code will work as an identifier for the receiver distributed area energy meters. The receiving area energy meter

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after sensing a signal in the channel compare its specific code with its own code, if this code matches with the incoming code than receiving transmits its reading through PLC channel. So finally the host PLC receives the reading information.

The reading from all the meters from an area is compared in the host PLC unit with the reading from that particular areas energy meter. By this method we can get the information regarding the default area and will than confiscate this area easily. This scheme saves the cost of individual energy chip meter as only one area energy meter is to be places at one pole of suitably divided area.

References

[1] Hendrik C Ferreira and Olaf Hooijen, “Power Line Communications: An Overview”, Transactions of the S.A Institute of Electrical Engineers, September 1995

[2] K. C. Abraham and S. Roy, “A Novel High-Speed PLC Communication Modem”, IEEE transactions on Power Delivery, Vol. 7, No. 4, October 1992.

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[3] personal.vsnl.com/lathish,a site discussing current trends and problems in DPLCC.[4] D.M. Monticelli and M.E. Wright, “A Carrier Current Transceiver IC for DataTransmission Over the AC Power Lines.”, IEEE Journal of Solid-State Circuits, Vol SC-

17, No.6, December 1982.[5] L Schaap, “The ROBCOM System”, Proceedings of the Workshop on Communications

over Power Lines, AJ Han Vinck, O Hooijen, Eds, Essen, ISBN 9074249-05-1, Germany, May 25, 1994, Part V.

[6] J Newbury, “Communication Requirements and Standards for Low Voltage Mains Signalling”, IEEE Transactions on Power Delivery, Vol 13, No. 1, January 1998.

[7] J Newbury, “Power Communication Developments and International Standards”, IEEE Transactions on Power Delivery, Vol 12, No. 2, April 1997.

[8] M. Karl and K. Dostert, “Selection of an Optimal Modulation Scheme for Digital Communications over Low Voltage Power Lines”, IEEE, 1996.[9] M. Karl and K. Dostert, “Selection of an Optimal Modulation Scheme for DigitalCommunications over Low Voltage Power Lines”, IEEE, 1996.

[10] D. Raphaeli and E. Bassin, “A Comparison between OFDM, Single Carrier, and Spread Spectrum for High Data Rate PLC”.

[11] Nortel Communications Pty Ltd. web site, http://www.nortel.com [12] Petrus A. Janse van Rensburg and Hendrik C. Ferraria, “ Design of a Bidirectional

Impedance Adapting Coupling Circuit for Low Voltage Power Line Communications” IEEE transactions on Power Delivery, vol. 20 no. I, January 2005.

[13] J. A. Malack and J. R. Engstrom, “RF Impedance of United States and European Power Lines”, IEEE Transactions on Electromagnetic Compatibility, vol. EMC-18, no. 1, February 1976, pp. 36-38.

[14] J. Onunga and R. W. Donaldson, “Distribution line communications using CSMA access control with priority acknowledgments”, IEEE Transactions on Power Delivery, vol. 4, no. 2, April 1989, pp 878-881.

[15] L.M. Faulkenberry and W. Coffer, Electrical Power Distribution and Transmission. Englewood Cliffs NJ: Prentice Hall, 1996.

[16] I. Hakki Cavdar, “ Remote Detection of Illegal Electricity Usage Via Power Line Communication” IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 19, NO. 4, OCTOBER 2004

[17] T. Waldeck and K. Dostert, “Comparison of Modulation Schemes with Frequency Agility for Application in Power Link Communications Systems”, IEEE Transactions on Power Delivery, 1996, Vol 7, No. 4, pp821-825.

[18] G Kelly, “Home Automation: Past, Present & Future”, Electronics Australia, February 1997.

[19] Principles of communication systems-Taub and Schilling McGraw hill international editions

[20] PLCCS: A Power Line Carrier Communications System, Professor Joseph Picone, Mississippi State University

[21] K. M. Dostert, “Frequency-hopping spread-spectrum modulation for digitalcommunications over electrical power lines”, IEEE Journal on Selected Areas inCommunications, vol 9, no 3, May 1990, pp700-710.

[22] J. A. Malack and J. R. Engstrom, “RF Impedance of United States and European Power Lines”, IEEE Transactions on Electromagnetic Compatibility, vol. EMC-18, no. 1, February 1976, pp. 36-38.

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Glossary of Terms

AC Alternating Current. Electrical power transmission method where the current and voltage waveforms vary periodically about the zero-crossing mark. In the context of this project refers to the 240V mains power voltage.Amplitude Modulation (AM)

A modulation technique where an input waveform is used to modulate the amplitude of the carrier waveform.ASCII

American Standard Code for Information Interchange. A widely used representation of letters, numbers, special characters and control characters in binary form.Baud Rate

The measure of data transmission speed for communication systems. More specifically, the number of signal pulses per second- in common usage, the number of bits per second.Bit Error Rate (BER)

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The fraction of received bits that are in error, usually expressed as a negative power of ten. For example a BER of 10e-6 would mean that one bit in every million is incorrect. A common measure of a communication system/scheme’s effectiveness.Byte

A group of eight bits.Carrier

A single frequency signal whose characteristics are varied in a time dependant way to transmit information.Channel

The medium over which a communications signal is passed. In radio communications the channel is air (more correctly, radio waves), in power line carrier communications the channel is the power line.CEBus

Consumer Electronics Bus. A home-networking standard. See theory section for details.CENELEC

European Economic Community standards body.Coupling Network/Device

An electrical circuit which connects two other circuits, often with different characteristics, together. In this project, coupling network refers to the circuit which connects the communications system to the power line.DCE

Data Communications Equipment. A class of communications equipment specified in the standard RS-232C. A modem is typically referred to as DCE. A DCE must be connected to Data Terminal Equipment (DTE), it cannot be connected to another DCE.Demodulation

The reverse process of modulation. See modulation.

FSKFrequency Shift Keying, a modulation technique where a “1” is represented by one

transmitted frequency and “0” another.Impedance

A measure of an electrical circuit’s response to alternating currents, analogous to resistance for direct currents.Impulse Noise

An unwanted electrical signal of very short time duration.IC

Integrated Circuit. A complex electronics circuit that has been constructed on one single silicon chip. Greatly simplifies the construction of electronic devices by minimising the number of discreet components used.Jamming

Disrupting the operation of electrical systems by generating electromagnetic energy that interferes with desired signals.LED

Light Emitting Diode. Used as an indicator on electronics equipment.LSB

Least Significant Bit.Mark Frequency

The frequency that represents a binary “1” in FSK modulation schemes.Modulation

Varying some characteristics of a signal in a time dependant way to transmit information.

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OSI (ISO-OSI)International Standards Organisation- Open System Interconnect. A general model of data

communications systems that segregates functionality into seven layers: physical, link, network, transport, session, presentation and application.Outage

Refers to when the power supply to an individual dwelling fails or is disconnected.Overvoltage

In the context of this project, the case where the mains voltage at a power point is greater than the system standard. (In India 240-250 Volts.)Packet

A block of information of limited length, typically consisting of a header and data section. In packet communications, a message is broken up into different packets which are transmitted and verified separately.PLC Power Line Carrier. See PLCC.PLCC

Power Line Carrier Communications. A communications technique where electrical power distribution lines are used to carry communications information.PLL

Phase locked loop. See circuit theory textbook!

ProtocolThe agreed-upon procedures that govern communications on a network.

PSKPhase Shift Keying, a modulation technique where the change between a “1” and a “0” is

represented by changing the phase of a carrier signal.RS-232C

An Electronic Institute of American (EIA) standard that governs digital serial communications. It specifies signal functions, voltage levels, and pin-assignments.Signal to Noise Ratio (SNR)

The ratio of signal strength to noise level in a communications system.Space Frequency

The frequency that represents a binary “0” in FSK modulation schemes.Spread Spectrum

An electronic communications technique where the signal is deliberately spread over a wide range of frequencies, rather than being confined to a narrow frequency band.Undervoltage

In the context of this project, the case where the mains voltage at a power point is less than the system standard. (In India 240-250 Volts.)White Noise

Random electrical signals spread uniformly in frequency throughout the spectrum.X-10

A home-automation standard. See theory section for details.

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Appendix A-Component Selection Calculations

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A-1: XR-2206 CalculationsFrom the data sheet it is known that,

For our system we need, f1 = 100 kHz f2 = 50 kHz 50 kHz = 1/(R1*C)

Hence R1*C=1/50*10^3 So R1 = 10 K

Similarly R2 = 5 K

The resistance values are obtained by choosing a value of 2000 pF for the capacitor C.Choosing standard values of the resistances, we have

R1 = 10 K R2 = 5 K C = 2000 pF

Which gives f1 = 100 kHz f2 = 50 kHz

A-2: XR-2211 CalculationsThe VCO free-running frequency is chosen to be at the center of the mark and space frequencies of the FSK signal.

- Equation for the free running frequency of the VCO.

fo = (f1+f2)/2fo = (100+50)/2fo = 75 kHz

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For optimum temperature stability o R must be in the frequency range of 10K to 100K Choosing Ro = 60 K

Co = 221 pF R1 = Ro* [ fo/f1-f2]

R1 = 90 K This is achieved by connecting a fixed resistance of 85K and a pot of 5K .

C1 = Co/4C1= 0.55 pF.

This is achieved by connecting four 202 pF in series with 3 pF in parallel.The coupling capacitor is chosen as Cc = 1.0 mf.The load resistance is taken as Rl= 1. 5K.The damping factor of the PLL is chosen at x=0.5 .The choice of the above values is made per the recommendations given in the data sheets of these IC’s.

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Appendix B-Circuit Diagrams

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Figure 1 : FSK Modulator Circuit

Figure 2: FSK Demodulator

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Figure 3: RS 232 Driver Circuit

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Appendix C- MATLAB Code for PLCC Channel Simulation

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%Program for the simulation of the the PLCC system%Inputs are the System parameters from reference [15]%Output is a Plot for the total losses against communication carrier frequencies% for various values of the line impedances

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%Pauri 01/04/05%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

clfclearceq= 0.000005;z1=[0.1 1 10 50 100] l1=0.0005;l2=0.01; % L2 for 1000 meter lengthr=3; % Rs is taken as 3 r1=0.02;r2=0.001*1000; % R2 for 1000 meter length

for a=1:5z=z1(a)i=1;for f=50*10^3:10*10^3:200*10^3; % frequency range declared

b(i)=f;w=2*pi*f; a2=z*ceq*l1;a1=z*ceq*r1;a0=0;b3=ceq*l1*l2;b2=z*ceq*l1+ceq*(r*l1+r*l2+r2*l1+r1*l2);b1=l1+l2+ceq*(r1*r2+z*r1+r*r1+r*r2+r*z);b0=z+r1+r2;av=((a0-a2*w^2)+j*a1*w)/(b0-b2*w^2+j*(b1*w-b3*w^3)); % Av declaredbv=1/(av);cv=abs(bv);dv=cv^2;l(a,i)=10*log10((dv*z)/4*r); % Loss formulai=i+1;

end;end;plot(b,l(1,:),'r',b,l(2,:),'k',b,l(3,:),'y',b,l(4,:),'k',b,l(5,:),'r')axis([ (50*10^3) (200*10^3) 45 95]);grid on;xlabel('f[Hz]');ylabel('loss[db]');

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%Program for the Bode plot of the Av(s)%to observe the stability of the system taking load impedance as 1 ohm%Pauri 01/04/05%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

clfclearceq= 0.000005; % Values as per the

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z=1; % reference[15] L1=0.0005;L2=0.01;R1=0.02;R2=0.001*1000;NUM=[ceq*L1 ceq*R1 1];DEN=[ceq*L1 ceq*R1 0];A=tf(NUM,DEN); % A ParameterNUM1=[ceq*L1*L2 (R2*ceq*L1+ceq*R1*L2) (ceq*R1*R2+L1*L2) (R1+R2)];%BDEN1=[ceq*L1 ceq*R1 0];B=tf(NUM1,DEN1); % B ParameterNUM2=[1];%CDEN2=[L1 R1];C=tf(NUM2,DEN2); % C ParameterNUM3=[(L1+L2) (R1+R2)];%DDEN3=[ceq*L1 ceq*R1 0];D=tf(NUM3,DEN3); % D ParameterAv=z/(A*z+B+3*C*z+3*D); % Transfer function AvBode(Av)

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