Faculty of Engineering and Architecture EECE 502 ... · The magnetic field produced is affected by several factors: • The ratings of the currents passing in the conductors ( typically

Electromagnetic Fields from Power Lines

Faculty of Engineering and Architecture

Department of Electrical and Computer Engineering

EECE 502

Final Year Project

“Electromagnetic Field from Power Lines”

Supervisor: Dr. Farid Chaaban

May 23, 2006

Presented by:

Abu Izzeddin Salma

Berbari Kamal

Obeid Hiba

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Abstract Electromagnetic fields are produced by power transmission lines. Several developments

have taken place in the design of the power lines in order to reduce the electromagnetic

field, such as increasing the distance between the lines and the residences decreasing the

current, shielding, changing the geometry of the conductors through the compaction

method, the phase splitting method as well as the current-phase rearrangement method. It

is important to implement these techniques because many researchers still suspect the

existence of an association between the EMF induced from power lines and health

damages despite all the studies which failed to prove the presence of a causal

relationship.

The main objective of this study is to give a detailed analysis of the magnetic fields

emitted by 220 kV power transmission lines in Lebanon. The paper starts by an overview

on the latest developments in the power line designs, including recent configurations and

the different ways of conductor placements that help in reducing the emitted magnetic

fields and by a review of the basic magnetic field equations that will be used later in the

comparison of theoretical and actual values. A research on major worldwide conducted

studies that discuss the health impact of the high-voltage transmission lines as well as

international guidelines and standards for minimum clearance is carried out.

In the process of performing this study, field measurements are taken on each of the

Zahrani-Saida and Sour-Zahrani power lines, which are 220 kV lines. This field work is

followed by the development of an analytical model of the field estimation through the

implementation of a software program that calculates the magnetic field of these power

transmission lines. Moreover, a finite-element model is implemented using the MagNet

software, which also estimates the magnetic field of the specific power lines. All the

results obtained, either by measurement or using the software program or the finite-

element model are then compared and discussed. This paper is concluded by a set of

guidelines related to power line clearances taking into consideration the current level.

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Table of Contents

Introduction:........................................................................................................................ 5 Electromagnetic Fields: ...................................................................................................... 6

Electric Field:.................................................................................................................. 6 Magnetic Field: ............................................................................................................... 7

Clearance: ......................................................................................................................... 12 Basics of Electromagnetic Field Theory Related to the Power Lines: ............................. 17 Health Effects of Electromagnetic Fields from Power Lines ........................................... 21 Work Done in this Field.................................................................................................... 24 Measurements and Results:............................................................................................... 28

Procedure ...................................................................................................................... 28 Results........................................................................................................................... 28

Finite-Element Analysis.................................................................................................... 30 Calculation of the Magnetic Field using Matlab Software ............................................... 32 Comparison between Field Obtained and Simulated Results ........................................... 32 Guidelines for Minimum Clearance.................................................................................. 33 Mitigation Options ............................................................................................................ 34 Conclusion ........................................................................................................................ 35 References......................................................................................................................... 36 Appendix........................................................................................................................... 38

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Table of Illustrations:

Figures Figure 1: Midspan compaction of an existing line using interphase-insulators without line

structure changes [25]

Figure 2: Space arrangement of the conductors of a power line [17]

Figure 3: Flat, Vertical and Delta Configurations [17]

Figure 4: The Hexagon Line [17]

Figure 5: Typical Flux Lines for Three Conductors and Single Conductor Configuration

Tables:

Table 1: Magnetic Field Reduction Coefficients (MFRC) and Relative Costs [24]

Table 2: Magnetic Fields for different construction types

Table 3: Magnetic fields in different configurations [22]

Table 4: Clearance from the National Electrical Safety Code Handbook [19]

Table 5: Minimum Vertical Ground Clearance for Electrical Safety Consideration [19]

Table 6: The clearance in function of voltage, structure and resulting magnetic fields [19]

Table 7: Relationship between Exposure to Magnetic Fields and Various Types of Cancer

[8]

Table 8: Zahrani-Saida Power Lines Magnetic Fields under 220kV, 311.3A

Table 9: Sour-Zahrani Power Lines Magnetic Fields under 220kV

Table 10: Magnetic Field away from the Sour-Zahrani Line (I=210 A)

Table 11: Actual Load for Sour-Zahrani

Table 14: Comparison between Field Obtained and Simulated Results for the three

conductors’ vertical configuration

Table 13: Guidelines for minimum clearance corresponding to different current levels

using a single conductor and a three-phase vertical configuration power lines

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Introduction: Being an important driving force of the socio-economic developments, the electric power

supply is constantly increasing in modern societies.

At the beginning of the 21st

century, communities and individuals are still facing

problems whenever a new overhead transmission power line has to be installed. The

presumed effects of the electromagnetic fields on the individual health tend to scare

people. Due to this fear protests usually tend to be issued in order to prevent the

installation of these high voltage transmission lines.

One recent event is the case of the connection of the Jamhour distribution station to the

area of Mkalles by installing 220 KV overhead transmission lines near residences and

homes. Residents in Mansourieh, Ain Najm and Ain Saade are calling on the government

to address their safety concerning that particular issue.

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Electromagnetic Fields:

Transmission lines produce electromagnetic fields. These fields are created by electricity

passing through a conductor. These electromagnetic fields are on the one hand dependent

to the distance from the source and on the other hand dependent on the flow of power at

the source. They are composed of two fields: electric field and magnetic field [26, 20].

1-Electric Field: The intensity of the electric field produced depends on the following factors [21]:

• The distance between the conductors and ground.

• The phase spacing if we have two circuits next to each other as well as the

geometric configuration of conductors.

• By the surrounding environment (if we have tall object near by such as trees,

fences etc).

• The transmission centre line tangential distance.

• The point of measurement elevation with respect to ground.

• The line voltage (the actual not the nominal).

The following figure illustrates the electric fields of several transmission lines [24].

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2-Magnetic Field: The magnetic field produced is affected by several factors:

• The ratings of the currents passing in the conductors ( typically lines have average

currents of 700 A, largest line existing supports a current of 4000 A)

• The clearance of the line. We can notice that the maximum fields occur

underneath the conductors and falls rapidly with distance either side.

• The phasing of the conductors such as the conductor spacing, the phase

positioning and the phase balancing affects the magnetic field. For example, for

“untransposed” phasing (where the phases on both sides of the line are in the

same order from top to bottom) we have a magnetic field that decrease with the

inverse square of distance from the line. While for "transposed" phasing (where

the phases on one side are of opposite order to the others on the second side) the

reduction in the magnetic field is inversely proportional to the cube of the

distance [21, 20].

In our report we will be studying the electric and magnetic fields created by high voltage

transmission lines at 50 to 60 Hz (considered as extremely low frequencies ELF).

Extremely high voltage transmission lines operate at or above 345 KV and high voltage

transmission lines operate between 115 KV and 3454 KV. These figures vary according

to each study. These electromagnetic fields can harm the living species in the area. We

are going to introduce some techniques that were developed to limit the effects of these

fields. We are also going to state the health impact of these EMFs on people living in the

vicinity of high voltage transmission lines. Finally, we are going to state some of the

work and studies done in this field.

Magnetic fields can be reduced by taking the following measures or procedures:

1- By setting and increasing the distance between the power lines and the

population. The allowable distance is set by the clearance table. This measure

does not reduce the magnetic fields but helps reducing its effect on humans.

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http://www.emfs.info/source_distance.asp


2- By decreasing the current in a source. This is done by increasing the voltage. This

decrease in current results in reducing the magnetic fields.

3- Shielding the field source or the person that is close to it. This procedure consists

of adding between the power circuit and the right of way edge (ROW) lightly-

insulated overhead conductors. These conductors are cross-connected at each end

in order to form a loop. A voltage is induced by the magnetic field formed by this

loop which in return induces a current flow that creates a magnetic field that

cancels partially the transmission line’s field. We can add a series capacitor in the

shield loop that helps increasing the shielding effect by canceling a part of the

loop reactance which results in an increase in the induced current [23].

4- By doing phase cancellation. Phase cancellation consists of having two equal

fields of opposite direction that cancel each others. This procedure is possible

because we have on the one hand a 60 Hz frequency and by that the fields are

reversing their direction 60 times per second and on the other at all times, the

“hot” and “neutral” lines are 180 degrees out of phase.

5- By implementing new design changes that targets mainly the geometry of the

conductor and the conductor height above the ground such as using one of the

following designs:

• Compaction: this method can be achieved because the field is proportional

to the phase spacing. Compaction consists of reducing the phase distance

of power lines as well as increasing the ground clearance of the outer two

phases. This is done using interphase insulators. This results in reducing P

which results in a decrease in the magnetic field with the square of the

distance. The advantage is that it can be used for existing lines. The

disadvantage on the other hand is that it is not applicable to all line

designs. The structural loading, corona performance and also the line

tensioning should be studied before applying the method. The following

figure illustrates this method [26, 24].

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Figure 1: Midspan compaction of an existing line using interphase-insulators without line structure changes [25]

• Split phase line: we increase n which represents the subphases. This can

be done by the division of the phases of the power line. Phase splitting

lowers the magnetic fields with respect to the cube of the distance [24].

Note: It is effective to apply the compaction design and the phase- current splitting design

only when we have no net current and also when the currents are well balanced. The field

reducing resulting from the compaction has a factor of 2 to 3, while the field reducing

resulting from the phase-current splitting has a factor of 10.

The preceding two designs have some disadvantages. One of them is that the compaction

and splitting procedures are bound by the audible noise produced by the corona. Also in

the splitting method as we increase the number of phases, the cross section increases and

by that the effect of wind and ice loads on the transmission lines [26, 24].

We also have the following transmission lines structures:

• H-frame

• Delta structure which have different substructures such as:

- Tall delta structure

- Short delta structure

- Vertical delta structure

- Horizontal delta structure

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• Flat structure

• Double circuit/ split phase

• Multiphase structure

• Deceased Phase Spacing

• Increased Voltage

• Single circuit steel pole

The schemes of these designs are in the appendix.

These structures reduce the electric and magnetic fields of the transmission lines.

The difference between the strength of the magnetic and/ or the electric fields for each

structure is going to be given in the following tables. These tables vary according to the

rating of the current considered while measuring the fields and also the base case

considered when doing field reduction comparison for the different structures.

The following table gives the reduction factor that each design induces.

Table 1: Magnetic Field Reduction Coefficients (MFRC) and Relative Costs [24]

The following table gives the different magnetic fields value induced by some of the

stated structures. [25]

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Table 2: Magnetic Fields for different construction types

Figure Construction Magnetic Field (µT) Type Distance from Centreline (meter) -13.716 -9.144 0 9.144 13.716

1 H-Frame 4.63 6.94 10.39 6.94 4.63 2 Vertical Delta 1.33 2.00 3.33 2.00 1.29 3 Short Delta 1.26 1.93 3.35 1.93 1.26 4 Tall Delta 1.07 1.53 2.30 1.53 1.07

We can notice from table 2 that the best type as for having the least magnetic field is the

Tall Delta.

Description Cost/Mile

(Thousands) Magnetic Fields (mG) Electric Fields (kV/,) under 40° 200° under 40° 200° A. Best Case 230 – 260 59.6 29.7 1.6 2.6 1.9 0.04230 kV 300 A 125 MW Wooden H Frame 5.8 m spacing B. Vertical Delta 220 – 250 27 11 0.6 1.9 0.7 0.04C. Horizontal Delta 220 – 250 28.9 9.8 0.5 1.6 0.7 0.03D. Decreased Voltage 200 – 230 91.5 34.4 1.9 1 0.6 0.01115 kV 600 A 3.5 m spacing E. Increased Voltage 400 – 500 24.4 18.9 1.2 5.5 5.3 0.1500 kV 138 A 9.1 m spacing steel lattice tower F. Double Circuit/Split Phase 350 – 400 14.5 4.8 0.1 1.7 0.6 0.02150 A /conductor steel pole G. Multiphase 380 – 450 16.7 6.7 0.4 2.5 0.9 0.056-phase line 132 kV 150 A/conductor steel structure H. Singel Circuit Steel Pole 275 – 350 36.2 22.1 1.5 2.7 0.8 0.1Vertical configuration

Table 3: Magnetic fields in different configurations [22]

From the previous table we can deduce that increasing the voltage in the transmission

lines results in a lower magnetic field and higher electric field while decreasing the

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voltage in the transmission lines results in a higher magnetic field and lower electric field

[22]. The double- circuit-/split-phase has the higher magnetic field reduction. The two

delta types stated in the table have similar magnetic fields. The split phase line is an

“excellent” method for reducing the magnetic field. Shielding and compaction method

are “good” methods for field reduction. [22]

As a conclusion we can find that the split-circuit configuration results in lower field than

the delta which also results in a lower field than the flat configuration. And that the

horizontal structures generate higher magnetic field than the vertical structure.

Clearance: Because EMF’s are present, the higher the voltage is, the greater distance between the

conductors and the surroundings such as people, traffic and other wires. This distance is

known as the clearance. For safety reasons many tables and ground regulations where set

to specify the clearance for transmission lines with different voltages. These

specifications vary from one source to another and fro one country to another. They also

depend on the design of the lines that supports the conductors.

The following table represents the National Electrical Safety Code Handbook on

clearances with respect to voltage for several areas.

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Voltage Height of Wire (meter)

0 – 750 V 8.2296 751 V – 22 kV 8.5344 Clearance over railroads

22 – 50 kV 8.8392 0 – 750 V 5.4864

751 V – 22 kV 6.096 Clearance over roads, streets, alleys, nonresidential driveways, parking lots, and other areas subject to truck traffic.

22 – 50 kV 6.4008

0 – 300 V 3.6576 751 V – 22 kV 6.096

Clearances over residential driveways, commercial areas not subject to truck traffic 22 – 50 kV 6.4008

0 – 300 V 3.6576 301 – 750 V 4.572

751 V – 22 kV 4.572

Clearances over spaces or ways accessible to pedestrians only

22 – 50 kV 4.8768

0 – 750 V 5.4864

751 V – 22 kV 6.096 Clearances along and

within rights-of-ways 22 – 50 kV 6.4008

Table 4: Clearance from the National Electrical Safety Code Handbook [19]

The minimum vertical ground clearance can also be determined and considered in the

designs of transmission lines. The vertical ground clearance is measured from the lower

point of the conductor to the ground level. The following table gives the values of the

Minimum Vertical Ground Clearance for Electrical Safety Consideration.

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Voltage Level (kV) Minimum Vertical Ground

Clearance (m)

400 7.6

132 6.7

66 6.1

33 6.1

11 6.1

Table 5: Minimum Vertical Ground Clearance for Electrical Safety Consideration [19]

As stated before, for safety reasons the EMF and by that the magnetic field that a person is exposed to should be limited. The following table gives the clearance in function of the voltage, the structure and also the resulting magnetic fields.

magnetic field in µT at distance from centerline

maximum under line

10 m 25 m 50 m 100 m

clearance 7.6 m phasing U load 4.7/4.7 kA

108.422 95.780 38.422 11.697 3.096

largest lines clearance 13 m phasing T load 0.4/0.6 kA

5.783 5.247 2.194 0.578 0.119


54.142 46.300 16.283 4.865 1.278

400 kV

and

275 kV

smaller lines clearance 13 m phasing T load 0.4/0.6 kA

4.971 4.158 1.557 0.400 0.084

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81.942 72.818 22.103 8.148 2.145

typical design used for new lines clearance 13

m phasing T load 0.4/0.6 kA

5.604 4.938 1.979 0.514 0.106

clearance 7 mphasing U load 1.4/1.4 kA

30.445 20.532 5.553 1.528 0.392

largest lines clearance 10 m phasing U load 0.13/0.13

1.848 1.359 0.468 0.138 0.036

clearance 7 mphasing U load 1.2/1.2 kA

24.585 17.217 4.587 1.247 0.318

smaller lines clearance 10 m phasing U load 0.13/0.13 kA

1.731 1.317 0.451 0.132 0.034

clearance 7 msingle circuitload 0.7 kA

12.347 12.347 0.738 0.192 0.048

132 kV

and

66 kV

smallest wood-pole design clearance 10

m single circuitload 0.1 kA

1.764 0.385 0.099 0.027 0.007

clearance 5.5 m phasing U load 1/1 kA

25.686 10.742 2.274 0.594 0.150 Larger lines on steel pylons

clearance 8 mphasing U load 0.1 kA

1.556 0.822 0.214 0.058 0.015

33 kV

smaller lines on wood poles clearance 5.5 14.748 2.961 0.541 0.138 0.035

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Table 6: The clearance in function of voltage, structure and resulting magnetic fields [19]

single circuitload .5 kA clearance 8 msingle circuitload 0.1 kA

1.325 0.471 0.103 0.027 0.007


9.456 7.664 1.490 0.364 0.090 Larger lines on steel pylons

clearance 8 mphasing U load 0.1 kA

1.004 0.942 0.274 0.071 0.018

clearance 5.5 m single circuitload 0.2 kA

3.744 0.668 0.124 0.032 0.008

11 kV

smaller lines on wood poles

clearance 8 msingle circuitload 0.05 kA

0.399 0.134 0.030 0.008 0.002

clearance 5.5 m single circuitload 0.2 kA net 0.01 kA@90

1.227 0.277 0.088 0.041 0.020

400 V Wood pole

clearance 8 msingle circuitload 0.05 kAnet 0.005 kA@90

0.215 0.099 0.041 0.020 0.010

The values obtained in this table were calculated using the EM2D computer program

done by John Swanson. T stands for transposed phases for 275 kV and 400 kV while U

stands for untransposed phases for 132 kV and below. All the fields are calculated at 1 m

above the ground level and the calculations ignore the zero-sequence current. The U

phasing gives the highest field. However, the T phasing give even higher fields but only

when it is close to the centerline at low clearance. 275 kV lines having the same

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constructions as the 400 kV lines the magnetic fields are in principle the same if the two

lines are built to the same minimum clearance.

Basics of Electromagnetic Field Theory Related to the Power Lines: Using applications of Maxwell’s equations, which contain within them most of the

electromagnetic field theory, we can get to specific equations that are specifically related

to the magnetic field generated by the power lines.

Some research papers base their studies on the “multipole expansion of the magnetic

field” to get to the approximate formulae specific to these fields. These formulae are

accurate when the distances from the line are considered large.

Magnetic field calculation using double complex numbers

Let us consider the following space arrangement of the semiconductors of a power line.

Figure 2: Space arrangement of the conductors of a power line [17]

Based on the electromagnetic field theory concepts (mostly Faraday and Maxwell’s

equations), we can calculate the magnetic flux density created by the conductor k as:

( )022

kk x

k

ib eR kRμ

π= ×

Knowing that the magnetic permeability 7104 −×= πμ

If we have several or n conductors, the equation of the magnetic flux density becomes:

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( )02

1 1

ˆ2

n nk x k

kk k k

i e Rb b

Rμπ= =

×= =∑ ∑

In this analysis, the vectors in the xy plane are written as complex numbers such that:

which leads us to get to the following equation for the magnetic flux density:

( )2 Re j tjb B ω= e

where

0

12

nk

k k

i IBR

μπ =

= ∑

The real and imaginary parts of the magnetic flux density can be written as:

,0

12

nk r

Rk k

IiB

Rμπ =

= ∑ ,0

12

nk i

ik k

IiB

Rμπ =

= ∑

Since this analysis is based on the multipole expansion of the magnetic field, we can

arrive to the following translations of the magnetic flux density:

knowing that

Here, M is called the moment and both B and M represents the “elliptical rotating fields”.

Λ is called the magnetic flux density order term.

For single-circuit lines,

considering:

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where

Therefore, we get to

To summarize, for the following three different configurations, the magnetic field can be

estimated as follows.

Figure 3: Flat, Vertical and Delta Configurations [17]

For the flat arrangement we can estimate

12 2 2

04 2 2 4

32 2 cos 2

Is R sBR R R s s

μπ

⎛ ⎞+= ⎜ ⎟− Φ +⎝ ⎠

. On the

other hand, if we consider the vertical arrangement (mostly used in this paper because it

the most widely used in Lebanon), then we can estimate the magnetic field using the

equation

12 2 2

04 2 2 4

32 2 cos 2

Is R sBR R R s s

μπ

⎛ ⎞+= ⎜ + Φ +⎝ ⎠

⎟ . Finally, for the delta configuration, the

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magnetic field can be calculated using the equation 1

2 2 20

6 3 3 6

3 24 2 sin 3

Is R sBR R s s

μπ

⎛ ⎞+= ⎜ ⎟− Φ +⎝ ⎠

. [17]

The configurations mentioned above are the most widely used; however, there are other

configurations that are not included in the above discussion, of which we can mention the

hexagon line. In the following, we are going to calculate the magnetic field in this

configuration.

First, the following drawing shows the hexagon line configuration:

Figure 4: The Hexagon Line [17]

The distance is calculated as:

The moment with λ order is calculated as:

And

Using the multipole expansion, we get:

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or

After replacement, we get

This analysis showed that it is efficient to use the double complex numbers method and

the multipole expansion to get the equations for the magnetic field.

Other techniques such as the efficient current simulation or solving a multi-objective

optimal power flow can be used to determine as well that magnetic fields in power lines.

Health Effects of Electromagnetic Fields from Power Lines Many studies have been conducted all through the past decades in order to find whether

there exists any relationship between the electromagnetic field emanating from power

lines and major impacts on health such as cancer, other diseases and effects of

pacemakers. This hypothesis was first proposed by a researcher in 1979 [5].

It has been proven throughout most of the studies published that no relationship exists

between chronic diseases and the electromagnetic field emanating from power lines.

In fact, a study conducted in June of the year 1999 by the NCR (National Research

Council) stated that it is very unlikely to have a causal relationship between the magnetic

fields and the risk of cancer induction. Also, in the same time the National Institute of

Environmental Health Sciences declared that through experiments in labs, it was proven

that magnetic fields from power lines do not induce any biological changes or mutations.

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In addition to these studies, another experiment held in Canada showed the uncertainty of

having a causal relationship between the magnetic fields developed by the power lines as

well as that around the homes and the risk of having leukemia. We can also mention

other studies that support the same hypothesis such as the study held by the National

Academy of Science, which concluded, after revising a large number of preceding

studies, that it’s very unlikely to have a cause and effect relationship between the two

factors studied. In addition to these publications, another study that we can mention and

that supports the hypothesis stated above was published in April 1995 by the American

Physical Society. Finally, one of the largest studies that were held and which support the

mentioned hypothesis was held by the UKCCS (UK Childhood Cancer Study)

investigators. In this study, these investigators interviewed 3838 cases and 7629 controls

[3]. Throughout this study, the researchers investigated the intensity of the magnetic field

to which the children suffering from leukemia were exposed. The results found in this

study do not show any major association between the magnetic field due to electricity

supply and the risk for childhood leukemia, malignant brain tumors and other childhood

cancer [3]. Also, this study is consistent with others that show that the exposure to more

than 0.2 μT does not increase the risk of suffering from childhood leukemia. However, it

still remains uncertain whether the exposure to higher that 0.4 μT increases the risk or

not. As opposed to these studies that support the inexistence of a relationship between

magnetic fields and developing chronic diseases such as leukemia, in 1997, the National

Cancer Institute concluded that there is little evidence that shows that the proximity to

high-voltage power lines induces acute lymphoblastic leukemia [1]. Another study, which

is considered as one of the most recent and largest studies, and which also, proves the

possibility of having a relationship between childhood leukemia and the proximity to

power lines was held in England, more specifically in the Wales region. In this study

31000 cases of cancer diagnosis were counted relatively to the distance to 275 and 400

kV overhead power lines in addition to a “small fraction of 132 kV lines”. In this study,

the researchers measured the distance from the residences of children having leukemia,

central nervous system disease and other diagnosis to power lines. These distances were

divided into categories (less than 49 meters, between 50 and 99 meters, between 100 and

199 meters until we have greater than 600 meters). Next, the relative for each disease was

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calculated using conditional logistic regression taking as a reference the category of

distances greater than 600 meters. The relative risk is the “incidence of cancer in a group

of ‘exposed’ people divided by the incidence of cancer in a group of ‘unexposed’ people”

[8]. In order to check for the existence of an association between the disease and the

proximity to the overhead power lines, the relative risks were analyzed. If the relative risk

is, at any distance, less than one, then they could conclude that no association can be

made between the particular disease and the electromagnetic field. This study concluded

that we can have an association only between childhood leukemia and the proximity to

power lines; however they could not find any trend in this relationship. As a conclusion

in this study, we can say that there is still no proof of the existence of a causal

relationship between leukemia and electromagnetic field emanating from power lines [2].

Note that the studies were mostly focused on childhood leukemia as the disease that

could possibly be induced from living close to power lines, however, other types of

cancer can be studied as well leukemia as the following table suggests.

Type of Cancer Number of Studies Median RR Range of RR's

childhood leukemia 20+ 1.20 0.80-1.90

childhood brain cancer 10+ 1.20 0.80-1.70

childhood lymphoma 8 1.80 0.80-4.00

all childhood cancer 7 1.30 0.90-1.60

adult leukemia 6 1.15 0.85-1.65

adult brain cancer 5 0.95 0.70-1.30

all adult cancer 8 1.10 0.80-1.35

Table 7: Relationship between Exposure to Magnetic Fields and Various Types of Cancer

[8]

Similarly to cancer, electromagnetic fields are suspected to cause damages with respect to

people having cardiac pacemakers. First, it is important to mention that the cardiac

pacemakers monitor the electric activity of the heart [6]. It has been proven that if the

pacemaker is subjected to a strong electric or magnetic field, then it can “malfunction, be

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reprogrammed or be turned off completely” [6], which has very harmful effects on

human health. Some research showed that high-voltage power lines could be harmful to

pacemakers and the safest distance to separate people having pacemakers and these

power lines should be of 7.62 meters (25 feet) [6]. On the other hand, some research

such as that conducted by the American College of Cardiology state that it is unlikely for

magnetic fields to have inference with the function of the cardiac pacemakers [7].

However, this is still not determined. Throughout an experiment conducted by the

mentioned college, three out of 245 people having cardiac pacemakers and exposed to

high-density magnetic fields had problems with the device. Therefore, the conclusion that

the researchers ended up with is that there exists a very low interference of the magnetic

with the cardiac pacemakers’ function [d, g]. Finally, we should mention that the Health

Physics Society, through its research stated that strong ELF could interfere with the

cardiac pacemakers [9].

Although we have mentioned that some researchers have set the value of 0.2 to 0.4 µT (2

to 4 mG) as maximum allowable values for the magnetic that do not harm the human

health, it is the worth to mention that the World Health Organization (WHO) has set other

values. In fact, according to the WHO researchers the maximum allowable magnetic field

exposure is 100 µT (1000 mG) [28].

To sum up, many researches are still taking place in order to find a causal relationship

between health and proximity to power lines; however, this association is still not found,

whether talking about cancer or about medical devices such as pacemakers.

Work Done in this Field Many of what was published concerning the electromagnetic field emanating from power

lines was held by the EPRI (Electric Power Research Institute). This work is mainly

concerned with the means of reducing the magnetic field emanating from power lines of

115 to 500kV. This work is published in three handbooks. The first handbook discusses

several ways for reducing the exposure to magnetic fields such as shielding, changing

habits as well as changing the structure of the lines so as to have a lower magnetic field

emanating from them. In the second handbook, we find an evaluation of different new

designs that can help in reducing the magnetic fields from power lines. We also find in

this handbook tables that help engineers study the performance of specific line designs

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for power lines of 115 to 500 kV (as previously mentioned), taking into consideration the

different magnetic field reduction techniques and the variations in parameters (“electrical

and mechanical characteristics, construction and maintenance criteria, costs,

configuration and aesthetics” [10]). Note that the different magnetic field reduction

techniques, such as compaction, phase splitting and are mentioned in previous

discussions. In addition to these techniques, the EPRI Journal also talks about shielding,

or cancellation loops. In the handbooks of the EPRI Journal, in addition to the techniques

of the reducing the magnetic field due to power lines, we also find an implementation of

software that help find the performance of the power lines.

On the other hand, work related to the reduction or measurement of magnetic fields

emanating from power lines has also been conducted in a symposium for EMF

engineering, covering however, some common as well as other aspects of this topic. In

fact, this symposium focused on the guidelines for magnetic field measurement, the

personal and general exposure as well as the field management [11].

In this study, we find mentioned what is called the RAPID (Research and Public

Information Dissemination) Risk Assessment Program, which helped in further work on

the EMF effects through eight projects. These projects provided guidelines for the

measurement of the “field source” [11] as well as the “environment-specific magnetic

field” [11]. They also provided guidelines for the measurement of the personal exposure

to magnetic (such as how to plan and design a study). The fifth project of the RAPID is to

develop a database where the EMF measured information can be stored. Three databases

are already available on the internet. Another RAPID project was to conduct a survey that

gathers information about the personal exposure to electromagnetic fields for around a

thousand people [11] which lead to conclusions concerning the mean and standard

deviation (0.9 mG and 2.7 respectively), the activities that could increase or decrease the

personal exposure (work and going to bed respectively), gender and age differences as

well as sizes and mobility of residences differences [11]. The seventh project was focused

on the prediction of the personal exposure to the electromagnetic fields taking into

account the time and activity patterns [11]. Finally, the last project discussed and

evaluated the different techniques of reducing the magnetic field such as matching the

current-carrying conductors with the return conductors [11], reducing the distance

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between the opposing current pairs, splitting the currents (or phases), decreasing the

distance from the source and decreasing the currents. Most of these techniques were

thoroughly discussed earlier in our paper. To wrap everything about the RAPID Risk

Assessment Program up, we can conclude that this program focuses on implementing

technologies for the measurement and characterization of the magnetic field, gathering

information about the human exposure to these fields and the type of activities that could

lead to the increase of this exposure, implement techniques to manage these fields and

reduce their impact publish the information gathered.

The measurement of the magnetic field and implementation of new techniques that

enhance the reduction of the exposure to this field, when induced by the power lines,

have been the concern of many engineers for the past years; this lead to the publication of

many studies and development research in this area, such as the CAI, or the

Commonwealth Associates Inc. These associates work on the measurement of the

magnetic field under high voltage and distribution power lines [13]. Calculations are also

done by them to observe the changes in the magnetic field due to changes in the power

lines and the substations [13]. These changes, similarly to all what was mentioned in the

previous discussions, include the rearrangement of the phases in the power lines, provide

an equilibrium in the phase and circuit loadings, changing the structure of the line

designs, switching from single-phase to three-phase distribution, increasing the voltages

and finally using cancellation or shielding loops [13]. After studying all the parameters

that could determine whether the particular magnetic field reduction technique can be

implemented or not, the CAI also performs a cost analysis to check for the feasibility of

the EMF reduction technique due to cost considerations. Finally, the CAI reports all the

analysis done concerning the electromagnetic field considerations [13].

The Enertech Consultants also researched and worked on the different techniques of the

EMF mitigation or reduction. In their publications, these consultants discuss the general

ways of reducing the magnetic field and focus on the shielding technique. In this

research, we find different steps that are involved in the process of reducing the

electromagnetic field. This process starts by identifying the source of the magnetic field

[14] (in our report the power lines). Next, the Enertech develops computer programs that

can help test the various magnetic field reduction techniques and then choose the best,

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taking into account the different parameters involved among which we find the cost

factor. In the next step, they include the installation of the equipment needed for the

magnetic field reduction. Finally, the measurements are taken again to check if the

magnetic field reduction took place and was effective or not [14].

Other type of work and studies was conducted in the field of electromagnetic fields

emanating from power lines. Many software designs were implemented helping in the

calculations and estimation of the magnetic field depending on sets of parameters and

different equations such as Laplace/Poisson equations that provide boundary-condition

problems. One of the computer programs implemented was based on linear boundary and

domain element approach, which ends up with “matrix equations” [12] and determines

the electromagnetic field coefficients. This technique is called the “Method of Windows”

[12]. Using this method, the user can manage a large number of elements in the matrices

since it differs from all other techniques in the fact that it does not reduce the arrays into

“manageable size elements” [12] but rather it takes “manageable size of array format”

[12] and uses it to fill a “multipaned window” [12] so that each piece of the window is

formed of a manageable set of elements [12]. Using the finite-element and boundary-

conditions techniques has been implemented and widely used in the calculation and

estimation of the electromagnetic fields induced from power lines, overhead and

underground; however, our main concern in this report is the magnetic field related to

overhead power lines. Other software designs are use the finite-element techniques are

being implemented in order to measure and calculate the magnetic field and its effects

using elementary parameters.

In this project a MagNet simulation is performed and a Matlab software is implemented

in order to estimate the magnetic field under power transmission lines. The results of both

these simulations are then compared to field measurements to prove their reliability.

Finally, these software programs are used to deduce tables for the minimum clearance

according to the current level.

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Measurements and Results:

Procedure Since the study is concerned with the electromagnetic fields emanating from high-voltage

power lines, measurements of the magnetic field under different 220kV power

transmission lines in the country were taken. EDL provided us with the different

parameters relative to the two power lines Sour-Zahrani, and Zahrani-Saida, the main

parameters being the height of the conductors above ground, their material, their lengths,

the distances between the conductors, the distance between the two circuits and the

maximum current passing through the conductors. In order to get the exact values of the

current passing through these conductors at the specific instances, coordination with the

Sour and the Zahrani power plants was established. The different maps and tables

provided by EDL are found in the appendix.

The procedure of performing the measurements consisted of starting from the first pole,

and measuring at different specific distances, using a three-dimensional Gaussmeter, the

magnetic field. Note that we chose these distances because the maps that we were given

to us by the EDL provided the exact height of the conductors at these specific locations.

The next part of the field work was to stand directly under the line and take

measurements and moving perpendicularly to the line at specific distances.

Note that the two power lines differ in the fact the Zahrani – Saida power line is a double

circuit power line whereas the Sour – Zahrani can be considered as a single circuit power

line since one of the terns does not function.

Results The following tables show the different heights from the lowest conductor to ground, the

different distances to pole #1 where we took the values of the magnetic field using the

Gaussmeter.

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Height (m) 26 24 21 21 24.5 28 30.4 25 26.6 31.7 Distance Corresponding to pole 1 (m)

0 40 80 120 160 240 280 320 360 392.4

Magnetic Field Measured (mG)

8.6 9.9 8.1 6.8 6.3 4.6 4.3 5.7 5 4.4

Table 8: Zahrani-Saida Power Lines Magnetic Fields under 220kV, 311.3A

In order to perform our MagNet and Matlab simulations, we used the information relative

to the three heights 26m, 21m and 31.7m.

Height (m) 25.7 22.2 19 18 17 19.7 18.5 22.2 27.2 31.7 Distance Corresponding to pole 1 (m)

0 40 80 120 160 200 240 280 320 347

Magnetic Field Measured (mG)

4.4 6.3 9.7 9.1 10.1 9 7.6 5.4 4 3.6

Table 9: Sour-Zahrani Power Lines Magnetic Fields under 220kV

For our simulation, we used the information relative to the three heights 22.2m, 17m and

31.7m.

Distance from middle (m) 5 10 15 20

Magnetic field (mG) 9.7 8.1 6.4 5.1

Table 10: Magnetic Field away from the Sour-Zahrani Line (I=210 A) Noting that, in Sour – Zahrani we were able to get the values of different power components passing by each of the 3 phases R, S, and T:

I

(A)

V

(KV)

P

(MW)

Q

(MVAR) cosθ

R 214.1 218.2 24.2 12 0.88

S 208.6 218.7 23.3 12.3 0.88

T 217.5 217 23.5 13.3 0.88

Table 11: Actual Load for Sour-Zahrani

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Finite-Element Analysis The finite-element method is a technique which provides solutions to differential

equations. The main concept behind this technique is the division of a complicated

domain, where the differential equations are difficult to solve into smaller, less

complicated sub-domains. After solving the problem in each sub-region, all the solutions

found are then assembled [27]. Using the MagNet software, which is an application of the

finite-element method, we performed our simulation considering one conductor as well as

three conductors in the vertical configuration.

In the process of modeling the power lines, we start by having a scheme of the

conductors, as they are spaced in the case studied. This is done by drawing a rectangle,

our environment as well as three circles inside this rectangle; these circles are a

representation of the three conductors. Using the data provided to us by EDL and the

power plants mentioned earlier, we set the distances between the conductors, the cross-

section of the conductors and the height from the ground to the first conductor

(clearance). Next, we provide the material type of the model components setting Air for

the gaps and Aluminum for the conductors. Finally, we consider the conductor as a

current-carrying coil and thus specify the value of the current passing through it.

Knowing that the currents in three-phase systems are sinusoidal and that in balanced

systems (as we assumed our system to be) the phase angle difference between the three

conductors is 120°, we performed our simulation at different instances.

The following are the values of the currents at the different instances considered:

I1=150.897, I2=-0, I3= - 150.897

I1= 150.897, I2=150.897, I3= -301.793

I1= 0, I2=301.793, I3= -301.793

I1= 298.84, I2=-185.89, I3= -112.95

I1= 286.4726, I2=-225.452, I3= -61.0211

I1= 289.19, I2=-219.33, I3= -69.859

I1= 288.3139, I2=-221.394, I3= -66.9197

I1= 287.41, I2=-223.43, I3= -63.974

I1= 279.13, I2=-238.93, I3= -40.199

I1= 150.1635, I2=-301.792, I3= 150.6284

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I1= 271.7486, I2=-249.557, I3= -22.1915

I1= 269.0691, I2=-252.901, I3= -16.168

I1= 267.6889, I2=-254.535, I3= -13.1536

I1= 266.2819, I2=-256.144, I3= -10.138

We performed the simulation using these values and by trial and error we found the

specific magnetic field corresponding to the desired height.

At the end, and in order to perform the simulation, the option “Solve” is chosen, taking

into account only the magnetic field (B-Smoothed). Finally, to get the values of the

different magnetic field, we used the option “probe” taking the specific distances that we

had in the maps.

We then obtained the graphs of the magnetic flux shown in figure 5 respectively:

Figure 5: Typical Flux Lines for Three Conductors and Single Conductor Configuration

As we can see from the graphs obtained by the MagNet simulation and that are shown in

the preceding figure, the magnetic fields emitted, as defined by their property, are

concentric. The figure representing the 3 conductors shows the cancellation between the

magnetic fields emitted by each conductor at a specific instance. This results in obtaining

two sets of concentric fields instead of three.

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Calculation of the Magnetic Field using Matlab Software The equations of the magnetic field described previously were implemented using

Matlab. The data provided by EDL, during the time the measurements were performed,

were used to solve the equations in order to obtain the magnetic field emanating from the

specific configuration conductors.

The values obtained using the Matlab program are found in Table 12.

Comparison between Field Obtained and Simulated Results The values obtained from the field measurements, the MagNet software as well as the

Matlab software are presented in Table 13.

Height (m) 31.7 22.3 17

Magnetic Field Obtained from Field Work in Sour-Zahrani (mG) 3.6 6.3 10.1

Simulated Magnetic Field (mG) 3.57 6.14 10.22

Magnetic Field Obtained Using the Software (mG) 3.58 6.45

Table 12: Comparison between Field Obtained and Simulated Results for the three conductors’ vertical configuration

9.93

As we can notice from Table 5, the values of the magnetic fields obtained are very close,

which shows the accuracy and reliability of the software designs. Therefore, these

designs can be used in order to obtain the minimum clearance corresponding to different

current levels so that the magnetic fields are always equal to 3 mG, which, according to

different studies, is a value that does not harm the human being as stated before.

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Guidelines for Minimum Clearance Current

level (A)

Anticipated field

(mG)

Minimum Clearance for

one conductor (m)

Minimum Clearance for 3

conductors (m)

100 3 29.01 6.55

150 3 35.58 8.92

200 3 39.88 10.93

250 3 44.51 12.70

300 3 47.17 14.30

Table 13: Guidelines for minimum clearance corresponding to different current levels using a single conductor and a three-phase vertical configuration power lines

The table above presents the minimum allowable clearance of the different configuration

of overhead transmission lines, taking a limit of 3 mG for the allowable magnetic field as

previously defined. We can conclude from this table that the clearance for a single

conductor should be much greater than that of a three phase vertical configuration. This

could be explained by the fact that for the three conductors, the magnetic fields emitted

by each conductor cancel each others to a certain extent and thus reduce the total

magnetic field.

However, the currents studied in this paper cannot be considered as the maximum that

could flow in the conductors. Therefore, we studied the worst case scenario, which occurs

during the time this maximum current flows in the conductors.

As we previously mentioned World Health Organization (WHO) has set a much higher

limit for the maximum allowable magnetic field; hence, we used the standards of the

minimum clearance set by this organization and calculated using the Matlab software the

magnetic field corresponding to the specific clearances at the rated voltages found in

Lebanon, using values of the maximum currents that can pass through the conductors.

The results are found in table 15.

Note that the values of the maximum currents were provided to us by EDL through tables

that can are present in the appendix.

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Rated Voltage

Clearance (m)

Maximum Current Magnetic Field (mG)

Single conductor 3 phase vertical configuration

s = 4.55 m

s = 2.47 m

s = 1.06 m

s = 0.76 m

220 kV 4.5 550 A 244.44 86.65 87.81 612 A 272 96.42 97.71

680 A 302.22 107.13 108.56 880 A 391.11 138.64 140.49 1760 A 782.22 277.27 280.99

150 kV 4 480 A 240 66.55 550 A 275 76.25 1100 A 550 152.50

66 kV 3.5 75 A 50 10.62 120 A 80 16.99 221 A 147.33 31.28 272 A 181.33 38.50 343 A 228.67 48.55 372 A 248 52.66 433 A 288.67 61.30 550 A 366.67 77.86 570 A 380 80.69

700 A 466.67 99.09Table 15: Values of the Magnetic Field using WHO Standards and Maximum Currents

It is important to note that for a specific rated voltage we do not have one value for the

maximum current that can flow in the conductors because the tables provided to us by

EDL include all the power transmission lines in Lebanon that have 220 kV, 150 kV and

66 kV as rated voltages and each of these lines has a different value of the maximum

current that can flow. Therefore we categorized these current values and studied each

case separately. In addition to that, the 220 kV lines may have phase spacing equal to 4.5

m or 2.47 m, which lead us to calculate the magnetic field in both cases.

Mitigation OptionsWe have already mentioned the different techniques of reducing the magnetic fields. One

of these mitigation techniques is the phase cancellation approach.

We can compare the values of the magnetic field obtained using the MagNet software for

the single conductor configuration and the three conductors configuration. The values

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obtained respectively were: 14.83 mG and 4.59 mG. These results prove one of the stated

methods used for reducing the magnetic field which is the phase cancellation approach.

ConclusionThis final year project starts with a research on the electromagnetic fields and the

different mitigation techniques. It also discusses the different equations that allow us to

calculate the magnetic fields as well as the health effects of the emf.

Values of the magnetic field are obtained through field work measurements as well as

finite-element method simulation (using MagNet and Matlab softwares), for a single

conductor, three conductors in different configurations as well as for a double typical

circuit. The closeness between the results shows the reliability of the software programs.

The work is concluded by a set of guidelines related to power line clearances, taking into

account the current level.

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References [1] PNM Team. Electric and Magnetic Fields. PNM (www.pnm.com) [2] Draper G. (June 2005) Childhood cancer in relation to distance from high voltage power lines in England and Wales: a case-control study. BMJ Volume 330. p 1… 5. [3] UKCCS. (December 1999) Exposure to power-frequency magnetic fields and the risk of childhood cancer. The Lancet Volume 354. p 1925 … 1931. [4] Trigano, A. (March 2005) Clinical study of interference with cardiac pacemakers by a magnetic field at power lines frequencies. Publimed. [5] Health concerns of power frequency electric and magnetic fields. BC Center for Disease Control. [6] Rodgers, E. (July 2005) How do I avoid electrical interference with my pacemaker? [7] (March 2005) Pacemakers not usually affected by power lines. Journal of the American College of Cardiology. [8] Moulder, J. (July 2005) Electromagnetic fields and human health. Medical College of Wisconsin. [9] Classic, K. (February 2005) Extremely low frequency radiation / power lines. Health Physics Society. [10] Lordan,R. (July-August 1996) Handbooks for reducing transmission line fields. EPRI Journal. [11] Gailey, P. (April 1998) Symposium: introduction and context. EMF Engineering Review Symposium. P 1-1 … 1-8 [12] Perambur, S. (January 1991) PC applications measure EMFs induced by power lines. IEEE Computer Applications in Power. P 43…46 [13] Shafer, D. {2004} Evaluation of electric and magnetic fields {EMF}. Systems Studies and TRANSMISSION 2000. p 3 [14] EMF mitigation and shielding. Enertech Consultants. [15] Olsen, R. (July 1995) Development and validation of software for predicting ELF magnetic fields near power lines. IEEE Transactions on Power Delivery, Volume 10, no 3. p 1525 … 1534

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http://www.pnm.com/


[17] Filippopoulos, G. Accurate formulae of power line magnetic fields. Department of Electrical and Computer Engineering, University of Patras, Greece. P 83 … 94 [18] Abdel Salam, M.(1999) Calculation of magnetic fields from electric power transmission lines. Electric Power Systems Research 49. P 99 … 105 [19] (January 2005) Tables of calculated magnetic fields produced by overhead lines in operation in the UK. Electric and Magnetic Fields. (www.emfs.info/Source_mag_fld_table.asp) [20] Azzuhri, S. (2004) Power transmission line magnetic fields: a survey on 120 kV overhead power transmission lines in Malaysia. University of Malaya, Kuala Lumpur. P 421 … 424 [21] (March 2005) Group public position statement electric and magnetic fields. National Grid. P 1 … 3 [22] (1993) EMF reduction and mitigation research. EMF-Link. [23] Walling, R. (January 1993) Series-capacitor compensated shield scheme for enhanced mitigation of transmission line magnetic fields. IEEE Transactions on Power Delivery Volume 8 No 1. P 461 … 468 [24] Rashkes, V. (April 1998) Magnetic field reduction methods: efficiency and cost. IEEE Transactions on Power Delivery Volume 13 No 2. P 552 … 559 [25] Brewer, H. (January 1993) EMF task force. ESEERCO. P 1 …4 [26] Johnson, G. Field-management technologies. Power Research Engineering. P 13-1 … 13-12 [27]Cook R.D, Malkus D.S, and Plesha M. E., Concepts and Applications of Finite Element Analysis, 3rd Ed., John [28] http://www.who.int/peh-emf/about/WhatisEMF/en/index4.html

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http://www.emfs.info/Source_mag_fld_table.asp

Electromagnetic Field from Power Lines

Appendix I- Electric and Magnetic Fields:

[26] II- Structures of different configurations: The following table displays the magnetic field strength of each construction type.

Figure 1: H-Frame design [25] Figure 2: Vertical Delta structure [25]

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Electromagnetic Field from Power Lines

Figure 3: Short Delta Structure [25] Figure 4: Tall Delta Structure [25]

Figure 5: Different transmission lines configurations [22]

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Documents

Faculty of Engineering and Architecture EECE 502 ... · The magnetic field produced is affected by several factors: • The ratings of the currents passing in the conductors ( typically