PLC Communication Analysis In Nigerian Distribution Network

8/8/2019 PLC Communication Analysis In Nigerian Distribution Network

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PERFORMANCE ANALYSIS OF PLC FOR NARROW AND BROAD

BAND APPLICATIONS IN NIGERIAN DISTRIBUTION NETWORKS

FACILITY

Awalu, S. O. & Aliyu, U. O.

Abubakar Tafawa Balewa University,

Bauchi-Nigeria.

ABSTRACT

Communication over electric power distribution lines (PLC) has wide area of

applications. Areas of application of power line communication include distribution

automation, internet communication, local area networking and industrial control. Designing

and planning an efficient power line communication system over any distribution network

require information on signal transmission characteristics of the network. This paper presents

signal transmission characterization and performance analysis of power line communication

system over some selected distribution networks in Nigeria with respect to frequency bands

of 50-500 kHz and 1-10 MHz for low and high bit rate applications respectively. The

simulation results and field measurements are discussed extensively from the stand points of

signal attenuation in the Nigerian distribution network infrastructure.

I INTRODUCTION

In addition to transmitting power at 50 Hz/60Hz, electric power lines are also used as

communication media for transmitting communication signals. This technology of sending

communication signals through existing electric power networks is known as power line

communication (PLC). The areas of applications of power line communication includes

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distribution automation, industrial control, local area networking, home automation and

internet communications (Selandar,1999; Newbury,1996; Patrick et al,1995). While the

utility companies that operate power systems have a natural interest in the development of

such techniques for control and communication for purposes of distribution automation, the

driving force for others is the benefits of the technology in the context of home automation,

internet communication and industrial control.

Unlike other communication channels, power lines are not designed specifically for

communication purposes as such they present unique technical problems as communication

medium. Generally, the characteristics of power lines which are channels for power line

communication system are time and location dependent. The impedance, noise and

attenuation of power line vary with frequency, time, distance and location (Abraham and

Roy, 1992; Tang et al., 2003). Many electrical devices which are connected to the lines inject

significant noise back into the network. In addition, the variation of electrical loads connected

to the networks creates a timevarying environment altering characteristic impedance of the

line as well as the noise (Cavdar, 2004). These represent the most critical obstacle to a

universal design for power line communication system. Therefore, it is necessary to

investigate into characteristics of power line communication systems from different parts of

the world for the design of standard power line communication system. The aim of this paper

is to investigate the performance of power line communication system in Nigerian

distribution system facilities for narrowband and broadband applications.

The rest of the paper is divided as follows. In Section II, power line communication

signal attenuation of low voltage distribution network based on theoretical models is

described. Section III presents field measurements of signal attenuation of out-door and in-

door low voltage distribution networks., In Section IV, signal attenuation obtained from

theoretical and measurement results have been applied to differential phase shift keying

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(DPSK) channel to determine the performance of power line communication system over the

distribution networks. Section V presents the results and section VI presents results analysis.

II DERIVATION OF SIGNAL ATTENUATION FROM THEORETICAL MODELS

Transmitters in power line communication systems are connected either between two

line conductors or between a conductor and ground. Their signals must pass through

distribution transformers, electric power cables, electrical loads and PLC modems before

reaching the receiver. These elements are responsible for signal attenuation due to their

characteristics combined with power line communication modems. Therefore, to determine

the power line communication signal attenuation, all the network elements mentioned above

and other PLC communication equipments must be considered. The overall PLC signal

attenuation model is obtained by combining the individual component models of distribution

transformer, distribution line, electrical load and PLC modem.

In secondary distribution networks, PLC modems are connected at the secondary port

of the transformer, therefore for circuit analysis, transformer model is referred to the

secondary (Cavdar, 2004). For secondary distribution circuits, lumped series parameter

model have been found to be satisfactory for evaluation of power line communication

(Wasley and Momoh, 1978). Generally transformer-capacitor coupling circuits are used in

power line communication modem mainly because the transformer provides galvanic

isolation from the power line network and acts as a limiter when saturated by high voltage

transients. In such coupling circuits, the capacitor and self-inductance of the transformer form

a series resonance circuit, a high pass filter which remove power frequency signal, its

harmonics and all other spectral components with low frequencies. Figure 1 shows the parsio

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nosious power line communication signal attenuation model developed for a typical 415/240

V distribution network.

RS

VS

Lt Ct LrCrL R

ZL

Req

Leq

VO

Figure 1: PLC Overall Model for Low Voltage Distribution Network

Where Ct and Cr are modem capacitances at the transmitter and receiver sides

respectively, Req and Leq are equivalent circuit elements of the distribution transformer, Vs is

the transmitted signal, V0 is the received signal, Rs is the source resistance and R and L are

the lumped parameter of a given distribution network

Taking Laplace transforms of the equations describing the model in figure 1 resulted

in the equations:

.(1)

.(2)

.(3)

From equations 1, 2 and 3, the transfer function of the PLC model is obtained to be:

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.(4)

Where

From the typical values of the system parameters, the poles of the system are in the

left side of the s-plane indicating the stability of the system. Using the transfer function, the

signal attenuation can be obtained as:

.(5)

III FIELD MEASUREMENTS OF SIGNAL TRANSMISSION ATTENUATION

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Although the distribution network topology and electric wires are known, it is not

adequate to rely on signal attenuation obtained by direct calculation since detail information

on the load is not available. Hence, there is the need for field measurement. In this study,

Signal transmission measurements were carried out in two categories as follows:

- In building signal transmission attenuation measurement

- Out-door signal transmission attenuation measurement

A MEASUREMENT SETUP

The measurements have been carried out with an oscilloscope and function

generators. The oscilloscope is PHYWE 11448.98 2 channels. Two types of function

generators used are 2 MHz and 150 MHz bandwidth types. In order to protect the sensitive

equipments from damaging by the 50Hz main power, passive high pass filters have been

used. Figures 2, 3, and 4 shows the schematic diagram of the measurement setup, photograph

of measurement set-up at the transmitter side and photograph of measurement set-up at the

receiver side respectively

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FunctionGenerator

CouplingCircuit

CouplingCircuit

OscilloscopeChannel

Figure 2: A schematic diagram of the measurement setup

Figure 3: Photograph of measurement set-up at the transmitter side

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Figure 4: Photograph of measurement set-up at the receiver side

B IN-BUILDING SIGNAL ATTENUATION MEASUREMENT

In-building signal strength measurement is important for the design of home

automation and internet access in homes and offices via power lines. Two sets of

measurements were carried out for this purpose. Measurement in the frequency range of 50-

500kHz for low data rate applications and measurement in the frequency range of 1-10MHz

for high data rate applications respectively. For this purpose intensive measurements were

carried out in thirty homes in Bauchi metropolitan of north eastern Nigeria over a period of

six months. In these experiments a function generator was used to produce the high frequency

signal which is coupled into the power line through a high pass filter. At a distant location,

the signal was coupled out through a high pass filter and measured with an oscilloscope. The

access points were reached with the help of connection wires whose effects and that of the

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filters were considered. To obtain the signal attenuation between the two access points, the

received signals were normalized to the transmitted signal level. For each set of

measurement, the means of the signal attenuation and their standard deviations were

determined and plotted as a function of frequency.

C OUT-DOOR SIGNAL ATTENUATION MEASUREMENT

Outdoor signal attenuation measurement is important for the purpose of applications

such as remote meter reading, remote control of home appliances, local area networking and

internet access via power lines. Here also measurements were done in the frequency range of

50-500 kHz and 1-10 MHz for low and high bit rate applications respectively. To determine

the outdoor signal attenuation, extensive measurements of signal strength were carried out in

low voltage distribution networks in Bauchi, north-eastern Nigeria over a period of six

months. The distribution network of the area is over head 415V/240V three phase four wire

low voltage network. High frequency signals were coupled into the power line through a high

pass filter at the transformer and received at various at various remote location in the

network. The means of the signal attenuation and their standard deviations in the frequency

range of 50-500 kHz and 1-10 MHz were determined and plotted as functions of frequency.

IV PERFORMANCE OF POWER LINE COMMUNICATION WITH DPSK

MODULATION

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By PLC performance, we mean whether receivers in the power line communication

system will be able to correctly interpret the messages sent to them. The crucial factors are

the signal and noise levels at the receivers. Several indices may be constructed to measure the

performance of a communication system among which is the bit error probability, Pe. The

modulation schemes often used for power line communication are PSK, OFSK and Spread

Spectrum among which PSK has the best bandwidth efficiency (Proakis, 1995 and Cavdar,

2004). In modern communication bandwidth is limited and precious resource which makes

bandwidth efficiency essential. The bit error probability Pe for coherent DPSK as derived by

Shanmungam (1979) is:

)exp(2/12

2

br

A

eP =

(6)

Where A = amplitude of the received signal and rb = bit rate

Selandar (1999) showed that for DPSK, the bandwidth is given as;

bMLog

rW2

3= ... (7)

Where M = number of signal alternatives

For binary PSK, M = 2

W = 3rb ... (8)

V PRESENTATION OF FIELD MEASUREMENTS AND SIMULATION RESULTS

In order to determine the actual signal attenuation of the low voltage distribution

networks, field measurements were carried out over indoor and outdoor distribution

networks. Average indoor and outdoor signal attenuations in the frequency bands of 50-500

kHz and 1-10 MHz are presented in figures 5 and 6. The corresponding standard deviation of

signal attenuation for indoor and outdoor distribution networks in the frequency bands 50-

500 kHz and 1-10 MHz are presented in figures 7 and 8. From the results, the attenuation is

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frequency selective. To obtain the signal attenuation from theoretical models, the model in

Figure 1 was simulated for some distribution networks in north eastern Nigeria in the Matlab

environment in the frequency range of 10 z-500 kHz and 1-10 MHz with Rs = 1 , Ct = Cr =

1 F and Lt = Lr = 10-5 H. The distribution network is an over head 415V/240V three phase

four wire low voltage network. The model parameters for the distribution network are:

equivalent secondary impedance of the distribution transformer is 0.01 - 0.2 and the line

inductance and resistance are 0.001 mH/m and 0.001 /m respectively. These parameters

were calculated from the data collected from the electric power utility distribution company.

The variation of signal attenuation with frequency, load and distance are shown in figures 9-

14.

To determine performance of power line communication system over electric power

distribution networks in Nigeria, attenuation obtained from field measurements and

simulation of theoretical models were applied to equation (6). Abraham and Roy (1992) and

Selandar (1999) measured noise power spectral density of distribution networks in the

frequency range of 0-500kHz. They reported noise power spectral density to be between

-110dB and -158dB. Dostert (1998) and Selandar (1999) measured noise power spectral

density of distribution networks to be between -120dB and -160dB in the frequency range of

1-16MHz. To represent the worst case, the maximum value of the noise power and the signal

attenuation obtained from both the theoretical models and field measurements were used.

Figures 15-20 showed the variation of bit error probability with frequency, load impedance

and line length.

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14

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

10 110 210 310 410

Attenuation(dB)

f (kHz)

Figure 9: Variation of signal attenuation with frequency for different values of load impedance and line lenght of1000m

ZL=0.1 ohm ZL=1 ohm ZL=10 ohm ZL=20 ohm

-100

-80

-60

-40

-20

0 2 4 6 8 10 12 14 16 18 20

Attenuation(dB)

load impedance (ohm)

Fig ure 10 : Variation o f signal attenuation with load impedance for various frequencies and line lenght of1000m

f=200 kHz f=250kHz f=300kHz f="350kHz"

f=400kHz f=450kHz f=500kHz


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15

-140

-120

-100

-80

-60

-40

-20

0

100 200 300 400 500 600 700 800 900 1000

Attenuation(dB)

Distance (m)

Figure 8 : Variation of signal attenuation with d istance for various combination of frequenccies and loadimpedance

f=2.5MHz,ZL=O.1ohm f=2.5MHz,ZL=1ohm f=5MHz,ZL=0.1ohm

f=5MHz,ZL=1ohm f=7.5MHz,ZL=0.1ohm f=7.5MHz,ZL=1ohm

f=10MHz,ZL=0.1ohm f=10MHz,ZL=1ohm

-140

-120

-100

-80

-60

-40

-20

0

1 2 3 4 5 6 7 8 9 10

Attenuatio

n(dB)

f (MHz)

Fig ure 12 : Variation o f signal attenuation with with frequency for various load impedance and a linelenght of 1000m

ZL=0.1 ohm ZL=1ohm ZL=10ohm


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16

-130

-120

-110

-100

-90

-80

-70

-60

-50

-40

0 2 4 6 8 10

Attenuation(dB)

Load im pedance (ohm)

Figure 13 : Variation of signal attenuation wi th load impedance for various frequencies and li nelengh t of 1000m

f=2MHz f=4MHz f=6MHz f=8MHz f=10MHz

-140

-120

-100

-80

-60

-40

-20

0

100 200 300 400 500 600 700 800 900 1000

Attenuation(dB)

Distance (m)

Fig ure 14: Variation of signal attenuation with distance for various combination offrequenccies and load impedance

f=2.5MHz,ZL=O.1ohm f=2.5MHz,ZL=1ohm


f=7.5MHz,ZL=0.1ohm f=7.5MHz,ZL=1ohm



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17

0

0.1

0.2

0.3

0.4

0.5

0.6

10 90 170 250 330 410 490

Biterrorprobability

f(kHz)

Figure 15: Effect of frequency on bit error probability for various loads and line

lenght of 1000 m

ZL=0.1 ohm ZL=1 ohm

ZL=10 ohm ZL=20 ohm

0

0.05

0. 1

0.15

0. 2

0.25

0. 3

0.35

0. 4

0.45

0. 5

0 2 4 6 8 10 12 14 16 18 20

Biterrorprobabity

L o a d i m p e d a n c e (o h

Figure 16: Effect of load im pedance on error probability f frequencies and line lenght of 1000 m

f =200 k H z f=250 k H z f =300 k H z

f =350 k H z f=400 k H z f = 450 k H z

f=500 kHz


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19

0.47

0.475

0.48

0.485

0.49

0.495

0.5

0.505

0 1 2 3 4 5 6 7 8 9 10

Biterrorprobability

Load imp edance (ohm

Fig ure 19: Effect of load imped ance on bit error probability for various frequency and line lenght

f=2 MHz f=4 MHz f=6 MHz

f=8 MHz f=10 MHz

0.4

0.41

0.42

0.43

0.44

0.45

0.46

0.47

0.48

0.49

0.5

100 400 700 1000

Biterrorprobability

Distance (m)

Figure 2 0:Ef fect of distance on bit error probability for various combination frequency and load for line lengh t of 10

f= 2.5 MHz,ZL=0.1 ohm f=2. 5 M Hz, ZL=1 ohm

f=5 MHz,ZL=0.1 ohm f=5 MHz,ZL=1 ohm

f= 7.5 MHz,ZL=0.1 ohm f=7. 5 M Hz, ZL=1 ohm

f=10 MHz,ZL=0.1 ohm f=10 MHz,ZL=1 ohm


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VI DISCUSSION OF RESULTS

Figures 5-8 shows the mean and standard deviation of signal attenuation obtained in

the field measurements in the frequency bands of 50-500 kHz and 1-10 MHz for indoor and

outdoor distribution networks. As shown in figures 5 and 6 the signal attenuation is

frequency selective. In the frequency band of 50-500 kHz, the attenuation generally decreases

with frequency while in the frequency band of 1-10 MHz, the attenuation increases with

frequency. Similar behavior was reported by Dostert (1998), Tang et al (2003) and Selandar

(1999). The in-door signal attenuation varies between -29.12 to -6.02 dB and -28.79 to -7.23

dB in the frequency range of 50-500 kHz and 1- 10 MHz respectively. For the out-door case,

the signal attenuation was found to vary between -32.04 to -9.12 dB and -36.1 to -9.51 dB in

the frequency range of 50-500 kHz and 1-10 MHz respectively.

Figures 9-14 showed the variation of simulated signal attenuation with frequency,

load impedance and line for a typical distribution network in the frequency bands of 10-500

kHz and 1-10 MHz. The results showed that the signal strength depends on frequency, load

impedance and line length. At high frequency, low load impedance and long distance, the

received signal level is low which put restrictions on frequency and line length for power line

communication. Variation of bit error probability with frequency, load impedance, and line

length are shown in figures 15-20. From the results, there will be communication problems

with 116 dB V signal amplitude for low load impedance distribution networks. However,

field measurements results showed that distribution networks in Nigeria are characterized

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with high load impedance. This resulted in bit error probability nearly equal to zero for the

worst case for signal amplitude of 116 dB V.

VII CONCLUSION

To design an efficient power line communication system over distribution networks,

signal transmission characterization is essential. In this work signal transmission

characterization of in-door and out-door power line distribution networks is presented for low

and high bit rate power line communication system. It was observed that the signal

attenuation varies with frequency for both in-door and out-door distribution networks hence

they are frequency selective. The results obtained in this study indicated that power line

communication system can be applied in Nigeria distribution networks with signal amplitude

of 116 dB V.

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Newbury, J (1996). Communications Field Trials for Total Utility Metering. IEEE

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PLC Communication Analysis In Nigerian Distribution Network

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