article rseec 2014 en beiu

8/10/2019 Article RSEEC 2014 en Beiu

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CIGR Regional South-East European Conference - RSEEC 2014 (2ndedition)cto!er "th- 10th2014# $i%isoara &otel 4'# $i%isoara Cit# Ro%ania

ELECTRIC AND MAGNETIC FIELD EXPOSURE DURING LIVE WORKING

h*+ student C+ ,EI'# h*+ .+ G/.'' h*+ + S$/C&E''

h*+ Ileana ,R.'' h*+ C+ $*ER'' h*+ Georgeta ,IC3'

'.ational Research and *eelop%ent Institute for /a!or rotection 5l+ *ara!ont6 ,ucharest#Romania,

''niersit /I$E&.IC of ,ucharest# Electric o7er Engineering *epart%ent#Romania

Su%%arMaintenance of energized high voltage networks are driven by the need to ensure continuity

of supply to users. In this sense, power supply quality standards impose obligations for transmissionoperators during scheduled interruptions, which cannot exceed a certain number of hours. Working

on energized high voltage networks have a number of advantages, both economic, by increasing

reliability indicators and the use of networks and ensure continuity of supply to the users. his

paper aims to present how the worker is affected by electric and magnetic field during work

activities and to compare the results obtained with the exposure limit values !"#$% and the action

level !% of the "uropean 'irective ()*+ +-" on the minimum health and safety requirements

regarding the exposure of workers to the risks arising from physical agents !electromagnetic fields%.

8e7ords#ive working, electric field, magnetic field, "uropean 'irective

cbeiu/protectiamuncii.ro


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1+ I.$R*C$I.#ow frequency electric and magnetic field !-) 0z% is typically associated with high voltage

overhead lines. & person in the vicinity of an overhead power lines can feel an electrostatic

discharge if is touching a conductive ob1ect, phenomenon caused by electrical induction electric

field due to the power line. Many people are concerned about the possible adverse effects on health.

2esearch on the effects of electric and magnetic fields caused by power lines, conducted so far, areinconclusive. It is considered that, so far, results are not sufficiently well defined to decide on a

causal effect between the electric and magnetic field and health. 0owever, international

organizations have issued a number of recommendations regarding exposure to electric and

magnetic fields, considering that exposure levels below recommended limits have no adverse

effects over a long time on workers3 health. he authors aim to analyze the other papers regarding

this matter, and to determine if, in given conditions, the worker is sub1ect to adverse effect of

electromagnetic field.

2+ $&E C/C/$I. 9 E/EC$RIC .* :G.E$IC 9IE/* I.E/EC$RIC/ I.S$//$I.S

2+1 Calculation of %agnetic induction for oerhead lines"lectric currents are sources of magnetic field generated by overhead lines. o determine the

magnetic field at a distance under one meter from the axis of the phase, magnetic induction can be

calculated using &mpere3s law. In this case, the magnetic induction of magnetic field B is

determined only by the nearest conductor 4*5+6.

) )(

IB H

d

= =

Where

I is the electric current passing through the phase conductors7d is the distance from the axis of the conductor !d 8*m%7

9)is magnetic permeability of free space ! :*);< 0 m%.

able I shows the calculated magnetic field values for an overhead line with aluminum5steel

conductors with cross section of *=-+( mm(and diameter of *>.( mm 4


3/8

$a!le I - alues of %agnetic induction for ;!are hand6 %ethod

Ao. $oltage level Ao of sub5conductors

on phase

#ine electric

current

2esultant magnetic

induction

5 4k$6 5 4&6 4m6* **) * B)) *(,-

( (() ( *()) *(,=

+

AoteC he calculation is for theoretical purpose only.

In figure ( is drawn the variation of magnetic induction in relation with the distance between

the conductor and the calculation point, for a single conductor per phase.

Figure 2 -Magnetic induction variation in relation it! calculation "oint di#tance

@igure ( shows the variation of the magnetic field around the path of electric current, with

values of *(.- m on the phase conductor, decreasing to ).( m at a distance of ).- m from it.

@or relatively bigger distance compared with the distance between the phase conductors, the

resulting magnetic field is determined by the contributions of all phases.he intensity of the magnetic field at a point in the vicinity of a three5phase power line can

be assessed, for the case considered, on the basis of the calculation scheme shown in @igure +.

Figure $ - %!e configuration for calculating t!e magnetic field #rengt!

@or the case of a +5phase system, the horizontal and vertical components can be determined

by the following relations 4*6C

+


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( ) ( ) ( ) ( )

+ +

( ( ( (

* *

7( (

i i&total 'total

i i i i

' ' & &I IH H

& & ' ' & & ' '

= =

+ +

uur uur

Where&iand'iare the coordinates of phase iand&and'are the coordinates of the point of

measurement.

he phase angle between totalH and 'totalH can be determined from the relationC

tan'total

&total

H

H= uur

@or the case of a **)k$ overhead line, considering one circuit grounded and one circuit

energized and symmetric load on all + phases of B)) &, and the geometric characteristics of the

column d*D -.+ m, d(D


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*

n

) i i)

i

( * "=

= iD *, (, ...n,)D *, (, ...nor in matrix form 4*6C

[ ] [ ] [ ]( P *=

in whichC[ ]( is the column matrix of potential conductors !n H *%[ ]* is column matrix of tasks !n H *%[ ]P is square matrix of potential coefficients !n H n%

o calculate the potential coefficients pi1, it is used the method of images. erms of matrix

4E6 can be calculated with the following relations 4(,+6C

5 p115 own potential coefficient

)

(*ln

(

)

))

)

!"

r

=

5 pi15 mutual coefficient of potentialI

)

*ln

(i)

i)

+ i)"

+=

Where

) >

*

< > *)

=

[@m], and the other quantities are explained in figure -.

Figure - eometrical "arameter# needed to calculate t!e coefficient# of "otential

o determine the electric field strength at the point E( !@ig.


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( )( )

( )

,tan , ).*(

,

'

0

/ ' '

/ ' = = ur

2+< $he electric field induced in the !od of 7or=ers in po7er stationshrough high voltage substations can pass electrical currents of thousands of amperes,

which can cause a considerably magnetic field on site and in the immediate vicinity. With theincreasing demand for energy, were built many such power stations near cities.

& worker on a high5voltage substation is sub1ected, during his activities, to the

electromagnetic field generated by the voltage level of the substation and electrical current going

through the substation.

In the following, it was examined the case of a worker during verification of presence of

voltage, using a voltage detector. 'uring operation, the worker handles with both hands a side of the

detector, and the other end is in contact with the active part of the system 4B6. he power path is

formed from the electrical system, to earth, passing through the voltage detector and the workerJs

body that is in contact with the ground. he resistance of the detector !i% must be large enough so

that to limit the electrical current passing through the body of the worker to non5hazardous values

!see @igure B%. he resistance of the detector is between +)) and +))) MK, depending on whether it

is wet and dirty or dry and cleans 4:6.

Figure 3 - or5er c!ec5ing t!e a6#ence of voltage in a 110 5( #u6#tation 789

he calculation is based on the finite element method 4:6 and quasistatic electromagnetic

field approximations. sing Maxwell3s equations and introducing the concepts of vector potentialA

with the property that : B = , and the electric scalar potential e , the electric field can be written

asC

e/ grad ) : =

aking into account the quasistatic assumptionsC

ediv grad ) div : =

and)

ediv grad =

Where complex permittivity is defined as)

= +

), with permittivity )r = , ! r is

relative permittivity and ) permittivity of free space% and is effective conductivity.

If all dielectric materials satisfy the condition


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Figure 8 - Bod "o#ture# of or5er and "o##i6le !and gri"

he body resistance !6% during the operation of a voltage detector is derived based on the

conducted current. In the case wheniis +)) MK, the potential presents at the detector handle is

found to be *.> $, *.= $ and *.* $, respectively for posture * to +. &t these potentials, the peak

2ML values of the induced electric fields in various parts of the body are plotted in able II 4:6.

$a!le II - ,od i%pedance and electric field induced in arious organs for Ri> 6.

Figure ; - %!e relation#!i" 6eteen /


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C.C/SI.&nalyzing the results obtained with regulated values covered by " 'irective ()*++-"

is found that the resulting values for the electric and magnetic field that are sub1ect workers are not

exceeded.

,IGR&4*6 leb 'rNgan !coordinator%,;0igh voltage engineeringO, $olume III, 2omanian &cademy Eublishing

0ouse Fucharest, ())+

4(6 imotin &., 0ortopan $., Ifrim &., Ereda M., P#essons of electrical heoryO, 'idactic and Eedagogic

Eublishing 0ouse, Fucharest, *>:)4+6 Mocanu ?.I ., P"lectromagnetic field theoryO, "'E, *>:)

4#, Ehys. Med. Fiol. vol.--, no. (, pp (+5+=, Uanuary, ()*).

4=6 P" 'irective no ()*++-" on the minimum health and safety requirements regarding the

exposure of workers to the risks arising from physical agents !electromagnetic fields%O

4>6www.emfs.info

=
http://www.emfs.info/http://www.emfs.info/http://www.emfs.info/

article rseec 2014 en beiu

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