OH Transmisssion Lines

8/3/2019 OH Transmisssion Lines

1/97

Univ

ersityo

fSydne

y

SchoolofE

lectrical&Inform

ationEngineering

DrKeithMit

chell

ELEC5

205

-Hig

hVoltage

Engineer

ing


2/97

UnitOverview

An

introductiontothe

practica

l

applicationofthesupplyofelectric

energyoverhighvoltagetra

nsmission

systemstoelectricityusers


3/97

Topics

Covered

inThis

Unit

M

McAlpine:

-

HighVoltage

Engineering

K

Mitchell:

-

OverheadTransmissionLines.

-

Underground

Cables.

-

Switchgear.

-

SwitchyardE

arthing

-

TestingTechniques

-

EnvironmentalImpacts

-

UseofStandards


4/97

TeachingFormat

&Assessment

Format:On

e2-hour

lectureplus3-hour

tutorial/labsessionperweek

Assessment:

Mid-semesterassignment

plusFina

lexam


5/97

ReferenceTextBook

s

PowerSystemAnalysis&

Design-JGlov

er,MSarma,

2nded.

ElectricPo

werEngineeringHandbookE

lectricPower

Generation

,Transmission&Distribution.

LLGrigsbey

(Ed).

CableSystemsforHighan

dEHVoltage

EPeschke&R

vonOlshau

sen,PirelliCab

les

Transmissi

on&DistributionElectricalEn

gineeringC

Bayliss&BHardy

HighVolta

geTestTechniquesDKumud&KFeser

Purcha

seofthesebooksisNOTbeing

recommended,buttheydo

provideusefulad

ditionalbackgroundinformatio

n.

Other

referencesand

materialappea

randareackn

owledgedinth

e


6/97

T

he

Lecturer

D

rKeithM

itchell

WhoamI?

Whatismyb

ackground

?

Contactdeta

ils?

Room

40611-12A

MTues


7/97

E

LEC52

05

-H

igh

Voltage

E

nginee

ring

1.OverheadTrans

missionLines


8/97

Pow

erSyste

mOutlin

e


9/97

Power

SystemC

omponen

ts

Anelectricpowersystemconsis

tsofthreebasic

ele

ments:

On

eormoregen

erators,almo

stuniversally

ofthe

synchronousma

chinetypein

powerstation

scloseto

sourcesofprima

ryenergy

Atransmissionanddistributio

nnetwork,w

hich

transmitspower

inbulkfrom

generationpo

intstoload

centresandthen

stepsthisdownanddistrib

utesitto

ultimatecustomers

Thecustomersw

houseelectr

icenergybywayof

connectingloadstothenetwo

rk.


10/97

TypicalPowerRequirem

ents

Lightbulbs-40to100

Watts;energyefficientbulb15Watts

Vacuumcleaner-600t

o1,000Watts

Electricoven-4.8kW(4,800Watts)

WaterHeater-4.8kW

Avera

gedemand(divers

ified)ofdomesticresidence-4kW

Equiv

alentpeakpowero

fmediummotorcar-100to150kW

WestfieldShoppingtown,Parramatta-30

MW

Clyde

OilRefinery-30

MW

ParramattaCBDload-

150MW

SydneycityCBDload

600MW

Startingpowerof8-car

Tangaracommutertrain-4.5MW;runningpower

about

1.5MW.


11/97

RoleofTransmission

Bulktransmis

sionofmajoramountsofpower

frombase-loadpowerstationstotransmission

su

bstations(andultimatel

ydowntothe

cu

stomer)

Highcapacity

(upto~120

0MW),hencehigh

vo

ltage

M

ustbehighlyreliable,h

encemeshedstructure

withbuilt-inredundancy


12/97

T

ransGrid500kV

and330kVOH

Double-CircuitLines

NotetheuseofV-insulators

onthe

500kVline,toreduceeasem

entsize.

The

wood-polelineinth

ebackground

isa

single-cct132kVline.


13/97

1

32kVTr

ansmissio

nLine(D

ouble-

Circu

it)


14/97

33

kV

Subtran

smission

Linewith11kV

and415V

distribution

underneath


15/97

HVW

ood-

poleSingle

Circuit

Line

Source:Re

f(1)

About220kV.Note

thetransitio

nfrom

bundledtosingle

conductor.

Thereare2

earthwires


16/97

Revision:Representatio

nof

TransmissionLines

Bo

thoverheada

ndundergrou

ndcablesare

transmissionlinesintheele

ctricalsense

Distributed(true

)modelalwaysusedinhig

hfrequency

(co

mmunication

s)analysis;onlyinpowersystem

analysisforhigh

voltagesand

verylonglen

gths(>250

km

)

M

ediumlengt

horpimod

elforsub-

transmission/transmissionlinesoverabout

80km

Shortlineswithasimplese

riesRandjX

for

dis

tributionlinesandsub-tran

smissionlines


17/97

True

Representationo

fa

TransmissionLine


18/97

Medium

LengthTransm

ission

Lin

e

R

X

Y

Y


19/97

ShortTransm

issionL

ine

R

X


20/97

TransmissionL

ineModels.

Z=R+jL

/mseriesimpeda

nceperunitlength

y

=G+jc

V/mshuntadmittanceperunitlengt

h

Z=Zl

l=Linelengthinm

eters

Y=yl

V

Z=sinhl

Zc=

z/y

Characteristic

Impedance

Y/2=tanh(l/

2)

Zc

=zym

-1

Propagation

Constant

y

y

y

y

y

z

z

z

z

Shortline

80kmorless

Mediumlengt

hline

80kmto250km

Longline250kmor

more

ZZ

Z

VsVs

Vs

VR

VR

VRI

R

IR I

R

IsIsIs

Y/2

Y/2

Y

/2

Y

/2

TransmissionLines

ComparisonofShort,

Mediu

mandLong

models


21/97

MediumandS

hortLineAp

proximations

Using

ABCDparam

eters

Stan

dardShortLine

piEquivalent

Modelforatransmissionline

VS=A

VR+BIR

IS=CVR+DIR

A,B,C,D

areparametersde

pend

onthetransmissionline

parameter

s:R,L,C,G

TheABCDparametersare

complexn

umbers.

Solvingth

esystemof2

equations:

AD-BC=1


22/97

Med

iumLength

Transmissi

onLineD

etermining

theABCD

Medium-Lengthtransmissionline

nominalpicircuit

Mediumlinelengthfrom80to250km

lcjG

yxl

Y

ZY

Y

C

Z

B

ZY

D

A

ZI

ZY

V

YV

IZ

V

V

YV

I

I

R

R

R

R

R

S

R

R

S

)

( )2

1(

2

1

)21(

)2

( 2

+

=

=

+

= =

+

=

=

+

+

=

+

+

=

+

=


23/97

M

eshedV

sRadial

PowerN

etwork

Arrangements

Majortransmissionlinesservemanycustomersandare

me

shedsub-sy

stemshaveredundantcapa

city

automaticswitching;nolossofsupply

Majortransmissionsubstation

shaveredundant

transformercapacity

Localdistributio

nlinesservefewercustom

erseach

andareradialLocaldistributionsubstationshave

sim

pleswitchgearandnored

undancyma

nualre-

switching;some

lossofsupply


24/97

Reliabilitybase

dDesignand

DeliberateRedundancy

M

odernsystemsgiveoutageratesof~1hour

pe

rcustomerperyear(99

+%availab

ility)

Keytodesign

philosophy

is(Probabilityof

ou

tage)X(numberofcus

tomersaffected)

M

ajortransmissionassets

->morecu

stomers

su

pplied->higherreliabilityrequired


25/97

Mes

hedPow

erSystem


26/97

Ex

ampleof

MeshedNetwork

Integral

Ener

gySub-transmissio

n


27/97

Ring-

MainPo

werSystem


28/97

W

hyOverheadHV

Transm

ission?

Greaterpowercapacitypereasement

(dueto

bu

ndledconductorsandair-cooling)

UG/OHcostr

atiosupto15:1forvoltagesof

30

0kVandabove

EH

Vcableno

tavailableuntilfairlyrecently


29/97

WhyDouble-CircuitO

H?

M

oreefficientuseofspac

e(easementspacefor

EHVOHlinesisverydifficulttoget).

ReliabilityofOHHVline

sishighco

mpared

po

tsamelengthoflowervoltageline.A

do

uble-circuitoutageisveryrare.


30/97

Conductors

Used

inHV

Transm

ission

Source:R

ef(1)


31/97

Typic

alASCR

Conductor

Source:ref(1).Theh

igher-resistance

steelinnercoreandskineffect

forcecurrentmainlyin

totheAlouterlayers.

Straigh

tAlisusedins

ub-transmission

anddistributionlines

Strandingaddsabout1

5%toresistance

Skineffectcanaddup

to30%forlargeconductors.


32/97

Resistan

ceofOH

Transm

ission

Lines

Fo

rmulas:

Rdc=l/A

hot=cold*(Thot+Tref)/(Tcold+Tref)

Rac=Rdc*Fs

kin*Fstrand


33/97

ResistanceStra

ndingFactor


34/97

LandC

ofTransmission

Lines

r

D

=

GMR

GMD

x

L

ln.10

2

7

.

ln

2

=

GMR

GMD

C

Equalspacing,GMD=D

Singlewire,GMR=rforL

GMR=rfor

C

n


35/97

InternalFlux

Linkage

Consideruniformcurrentdensity.Atinternaldistancex,thelinkedcurrentI(x)=

I(x/r)2,withthefieldintensity

H(x).Theinductanc

eisconstantregardle

ssofradiusr.

Atinternaldistancex,

H(x)=I(x)/2x


36/97

Flu

xLinkageBetwe

en2Conductors

12=2x10-7.I.ln(D

2/D1)


37/97

SelfandMutualL

for2W

ires

Consid

erfluxlinkagesbetw

eenconductorxan

dconductory,(bothinternaland

externallinkages)andthenrepeatprocessfrolinkagesbetweencondu

ctory

andconductorx,andsum.


38/97

SelfGM

R(r)

ofConductors

Simplifiesind

uctancecalcsbyincorp

orating

effectofinternalflux

Is

radiusofeq

uivalenthollowconduc

tor

r

=r.exp(1/4)whererisradiusofsm

ooth

co

nductor

Ty

picalvalues:Al/Cu0.7

26(7-strand

)to0.779

(solidconductor);ACSR0.68(6-strand)to

0.81(54strand

)


39/97

ExtendedforBalanced3-Phase

Considerthefluxlink

ageswithaphase,duetoi)itself,

ii)bphaseandiii)cphase,thens

umup.Note:c

urrents

balancedinallphasesandsumtozer

o.

Duetosymmetry,the

sameresultswillapplytothe

other

twophases.

a=

2x10-7.I.ln(D/r)


40/97

FluxLinkageM

Conductors

Consider

fluxlinkagesfromallMconductorsandpointP,thenmovePtoinfinity,

atthesam

etimesettingsumofcurrentstozero(balancedsystem).


41/97

ExtendedforN

Conduc

tors

This

systemhasNforw

ardandMreturnc

onductors,sharing

atot

alcurrentI.Dkmrepresentsthedistancefromconductorkand

cond

uctorm;Dkkrepresentstheselfinductanceofconductork.


42/97

E

xtended

forBund

ledConductors

Ex

tendinggen

eralformul

afrompreviousslide,

thefluxlinkagewithcom

positeconductorxis

an

dhencethe

inductance

is


43/97

C

oncepto

fGMR

Usinggeneralform

ulaforNconductorsdeve

loped

previously,thereisatermforth

eselfGMDamong

allconductorsand

themselves.Thisisdefinesasthe

GMR

(geometricmeanradius).

Form

ula:

(prov

eastutorialexercise)

DetermineGMRs

for2-,3-and

4-wirebundles


44/97

Advantage

sofBun

dledConductors

Increasedrating-lessweightthanan

equivalent

singleconductor

Le

ssskineffectlosses

Reducedserie

sL-improvespower

transmissionc

apacity

Reduceselectricfieldstre

ngtharound

co

nductors-reducescoro

na

Se

etutorialexercise


45/97

Transpo

sitionof

Conductors

(un

equalSp

acing)

Reallinesarerarelygeometricallyarranged.Theune

qualspacingcausesunbalanced

inductances.Solvedbyrotatingconductorsabouteve

rykmorsotoaverageoutspacings.

Averagefluxlinkagesarethenth

eaverageofthelogs

(seeformulaabove)

-thiscreatesa

geometricm

eandistanceorGM

D=3D1.D2.D3


46/97

Effe

ctof

Earthin

LineSeries

Impe

dance

Earthreturncurrentscanbereplaced

withequivalentconductorsunderthe

surfacecarryingthenegativecurrent

oftheoverhead

conductor(Carsons

equations).

Dkk=Dkkm(GMRsthesame)

Dkk=658.5(

/f)m

Rk=9.869x10-7f/m

InAustralia,f=

50hz

Imagesofthe3

phaseandN

O/Hneutrals

3phases(a,b,c

)

andNO/H

neutrals(n1-nN)


47/97

Complete

Equ

ivCct

fo

rall

Conductors

andImages

Note:Onlyphaseconductors

havedrivingvoltages(phase

volts);theneutralshaveno

drivingvoltag

es


48/97

Deter

mination

ofPhaseand

Sequence

Imped

ances(1)

Reference:Glo

ver&Sarma

(Ref1),pp176

-182.

Equationsfora

systemof3

phasesandNO

/Hneutrals.

Theimpedance

matrixisoften

referredtoasth

eprimitive

matrix.

TheRk,resistanceofthe

earthimageofconductork,is

givenbythepreviousslide.


49/97

Deter

mination

ofPhaseand

Sequence

Imped

ances(2)

Reference:Glo

ver&Sarma

(Ref1),pp176

-182.

Theprimitiveimpedance

matrixissimplifiedby

partitioningand

transformation

intoaphase

matrix,ZP(Kronreduction)


50/97

Deter

mination

ofPhaseand

Sequence

Imped

ances(3)

Reference:Glo

ver&Sarma

(Ref1),pp176

-182.

ThephasematrixZPcanbe

convertedintoasequence

matrixZSforanalysisby

symmetricalco

mponents,

whichisnorma

llyeasier.

OnlyworksifZ

Pis

symmetrical.T

hisis

approximatelytrueforaline

withtransposed

conductors.


51/97

Deter

mination

ofPhaseand

Sequence

Imped

ances(4)

Reference:Glo

ver&Sarma

(Ref1),pp176

-182.

IfZPisassumedsymmetrical

(by,egtakinga

veraged

values),thenth

e

transformation

intothe

sequencematrixZSisalot

easier.

Refertotutoria

lexample.

Therearealsocomputer

programsthatd

othese

calculationsforyou.


52/97

ElecField

andPotentialDiff-

S

ingleWire

Consideracylinderwitharadial

electricfield.

GuasssLawis

thenapplied.

Foralengthlandacircularpath

ofradiusx,

.E

(x).2x.l=q.l,for

chargeofqperunitlength.

ThusE(x)=q/2xV/m

Note:thefield

is>0onlyoutside

thecharge.

Refertutorialexercise,andshow

thatV12=(q/2

).ln(D2/D1)


53/97

ExtendedforM

Conductors

Extendthepreviousslideto

determinethepotentialdifference

betweenconductorskandi,due

toa

chargeqmonconductorm.Thus

,

Vki,m=(qm

/2).ln(Dim/Dkm)

Now,sum

theeffectofallm

conductors.


54/97

Capacitanceof2

-WireSystem

D

r

Apply

thepreviousslideto

caseofM=2,radiu

srandspacingD.

Considerpotentialdifferen

cebetweenconducto

rs1and2duetocha

rge+qon

condu

ctor1,andthenaddthepotentialdifferencebetweenconductors2and1,

dueto

charge-qonconduc

tor2.Thus,

V12=

(1/2)[q.ln(D12/D11-q.ln(D22/D21)]

V12=

(1/).q.ln(D/r),as

D12/D21=D;D11/D22=r.(wheredidthe2goto?)

ThusC=q/V=

/ln(D/r)Note:forcapacitance,user,notr.W

hy?

Capac

itanceperphaseton

eutralC=2

/ln(D/r)F/m.Whythe2?

Refer

tutorialexercise.


55/97

Extended

forBalanced3-Phase

Balanced3-wiresystem,ra

diusr,spacingD

Extendthe

2-wiresystemtoa

balanced3-wiresystem(orusethe

Mconductorscase).Consider

potentialdifferenceonconductor1

duetochargesonconductors2and

3.Notethatthechargesandelectric

fieldcontributionshavetobe

considered

asphasors.

Resultis:C

=2

/ln(D/r)F/m

(phaseton

eutral).

Refertotutorialexercise.


56/97

Capacitanc

eofBun

dledConductors

Considera3-phsystemwithatwin-conductorbundle.

Thereisachargeof

q/2oneach

conductor.

Thepotentialdifferencebetweensayconductorsaand

bcanbedetermined

asbeforeby

consideringallchargesonallconductors.

ThecapacitancecanbeshowntobeC=2

/ln(GMD

/GMRc)

F/m.

TheconductorGMDisthesameaswithinductanceca

lcs.However,GMR

cusesthe

conductorradiusr,notr.Why?

Refertutorialexercise.


57/97

EffectofEarthonElecField

Theearthisaconductingplaneandeffectstheelectricfield.Theeffe

ctisthesameifall

conduc

torswerereplacedb

yimageconductorsundertheearthssurface.Eachimage

conduc

torhasthesameradiusandisthesamedistancebelowground

asitscorresponding

realconductorisaboveearth.Notethattheseim

ageconductorsared

ifferentfromthe

imageconductorsusedwith

inductancecalculations..


58/97

E

ffectofEarthon

Capacitance-2

WireSystem

Considerthe2-wiresystemshow

n,ofconductorsxandyandtheirrespectiveimage

conductorsxandy.Ifconductorxhasachargeof+q,thenywillhavea

chargeof-q.

Imagecond

uctorshavereversec

hargesieimagexhascharge-qandimag

eyachargeof+q.

Thevoltage

differencebetweenconductorsxandy,Vxy,canbedetermine

dbyconsidering

theelectricfieldcontributionsfromallconductorsinc

ludingimages.

TheresultisVxy=(q/)[ln(D/r)-ln(Hxy/Hxx)]andthuscapacitance

Cxy=/[ln

(D/r)-ln(Hxy/Hxx)]

F/m.Theeffectis

minimalexceptforh

orizontal

arrangemen

tsclosetoearth.Re

fertutorialexercise.

x

y

x

y

Earthplan

e

D

Hxx

Hxy


59/97

Determ

inationofPhase

and

SequenceCapacitances

(1)

Considerno

wageneralsystem,of3phase

conductorsa,b,c;Noverheadneutralsn1..

nN;andtheirrespectiveearthim

ages.

Forconductork,thethepotentia

l

differenceV

kkbetweenitanditsimage

conductork

,duetoallmconductors,isthe

sumofeffectsofallconductorsandtheir

images.

Thus,Vkkisgivenby-


60/97

Determination

ofPh

aseand

Seq

uence

Capacitances

(2)

ReferGlover&

Sarma

(ref1),pp194-197.


61/97

Determination

ofPh

aseand

Seq

uence

Capacitances

(3)

ReferGlover&

Sarma

(ref1),pp194-197.

Theprocedure

is

similartotheline

inductances,creatinga

potentialmatrixP


62/97

Determination

ofPh

aseand

Seq

uence

Capacitances

(4)

ReferGlover&Sarma

(ref1),pp194

-197.

Asbefore,thismatrix

istransformed

intoa

phasecapacita

nce

matrixCPand

thence

intoasequenc

ematrix

CS.


63/97

Determination

ofPh

aseand

Seq

uence

Capacitances

(5)

ReferGlover&Sarma

(ref1),pp194

-197.

Again,thepha

se

capacitancem

atrix

mustbesymm

etrical

toenableitseasy

conversionint

othe

sequencematr

ixand

useinsymmetrical

componentsanalysis.


64/97

Determin

ingSequ

enceImpedances

Asa

llHVtransmissionlinesaretra

nsposed,thenw

ecan

aver

agephaseimpedancematricesandconvertinto

sequence

impedances.

Fortransmissionlin

esandcables,n

egativesequenc

eimpedance

Z2=

positivesequenceimpedanceZ

1.

Positivesequenceim

pedances(LandC)canberea

dily

calculatedbytheno

rmalmethod,ig

noringearthforLandonly

consideringearthfo

rCwithhorizontalconductora

rrangements

reasonablyclosetotheground.

Zero

sequenceimpe

dancesZ0howe

verrequiretheconsideration

ofallconductorsandtheirearthimages,forbothR,LandCand

matrixtransformation.


65/97

ThermalRatingsofO

H

TransmissionLines

Thermalratingo

foverheadlinesdependso

n(i)the

ma

ximumallow

ableconducto

rtemperature,beforeit

anneals(softens)andfallsdown,and(ii)th

emaximum

sag

permissible,

beforethelin

esgettooclo

setolines

underneath,structure,humans,etc

Thefirstfactori

softenreferredtoasampacity

Theampacityof

alinedependsonambient

tem

perature,wind,solarradia

tionandcond

uctor

surfacecondition.


66/97

MainFactorsAffectingR

atings

Eq

uations:


67/97

R

atingEquation


68/97

TypicalRatin

gs

ofOHLines

Availablefromconductormanufactu

rers.


69/97

ShortT

ermand

RealTime

Ratin

gs

Itw

illtakealittlewhilefora

coldconductortoreach

wo

rkingtempfo

llowingastepincreaseincurrent.

Thisallowstheapplicationof

short-time,emergency

ratingstooverheadlines.

Usualemergencyratingisabout10minutes.

Iflineratingsareconstrained

bysag,often

are-

ten

sioningand/o

rliftingconductorshigher

offthe

gro

undwillallowanincreasedrating.


70/97

InsulatorsU

sedonO

HTrans

mission

Lines

StandardC

levis

Disk

LongRod

Insulators


71/97

In

sulatorM

aterials

To

ughenedGlass(Clevis

disks)

Po

rcelain(Cle

visdisks,cabletermina

ting

structures,transformerbu

shings,CTs

Ep

oxy(posto

rstand-offinsulators)


72/97

Advantages

of

Stand-

off

Insulators

Source:Ref(1).Theuseofstand-off

insulatorsreduc

esconductorswing,

enablingtheuse

oflargerconductors

andincreasedvo

ltages,aswithlessswing,

conductorcleara

ncescanbemaintained.

Inthisexample,

theMVAratinghasbeen

increasedbyabo

utafactorof3times.


73/97

Typic

alHV

Line

Design

Param

eters

Source:Ref(3)


74/97

Lightnin

g&SwitchingSurges

Lightningisafastwavefront(fewmicrosec)

Sw

itchingcause

sslowwav

efronts(few

milliseconds)

Insulatorscanw

ithstandhigh

erlevelsoffastsurges

Lightningsurgestendtobefixed,duetoth

elightning

processitself,in

dependentof

linevoltage

Sw

itchingsurge

scanbeashighas2xline

volts

Lightningmore

ofaproblem

3

00kV


75/97

Lig

htningS

urges

Typical1/50Lightnin

gsurge(travellingwave)

Lightnin

g(directstroke,induce

d,earthpotentialrise)

Switching(suddenenergisation

)


76/97

Lightnin

gMitiga

tionMethods


77/97

L

ightning

Ground

FlashD

ensity

Where-

GFD=groundflashdensity,

strokes/km2/yr

TD=thunder-daylevel=35/yearinSydneyregion

TH=thunderhours/year


78/97

LightningStrok

eIncidence

Where-

Ns=no

ofstrokesper100kmofline/year

h=heig

htofconductorabov

eearth

GFD=groundflashdensity


79/97

LightningI

nductive

Overvoltageon

Tower

Where-

l=lengthofline

h=heightofconductoraboveearth

r=conductorradius


80/97

LightningOutage

sonShielded

Line

s

Source:Ref2


81/97

Lightning

Outages

onUnsh

ielded

Line

s

Source:Ref2


82/97

Earth

WireShieldAngle

The30d

egangle

hasbeen

determin

edfrom

experien

ce


83/97

TransmissionLin

eSIL(orBIL)

Th

eSIL(standardinsulatio

nlevel)ofan

OH

transmissionlinevarieswithlinenominalvoltage

De

terminedbypeakvalueof

standard1.2x50surge

SetbyASandIEC(alsoIEEEetc)standards.For

example(IEC)-

36

kVline:

70

kV170kV

245kVline:46

0kV1050kV

525kVline:1175kV1550k

V

(sh

ort-timepowerfreq/lightningimpulsew

ithstands)


84/97

Ty

picalClearances

Th

eSILdeterminesclearance

sinair

De

terminedbysafety,maxelectricfieldlevels

SetbyASandIECstandards.

52

kVline:

0.17m(powerfreq)/0.7m(surges)

245kVline:0.69m/2.0m

765kVline:2.3

m/5.6m


85/97

Atmospheric

Pollution

Dust,plantpollens,industrialparticles,salt(nearco

ast)get

coatedonoutsideof

insulators

Whendamp(eginlightrain),thesearesemi-conductors

Caus

epartialdischargesandeventuallyflash-over

PDs

causeaudibleandelectricalnoi

se

Skirtdesignoninsulatorsincrease

strackingpath

length

Artif

icialrainteston

insulatorsets

Creepagedistances16-31mm/peakkV(basedonpo

llution

class

ification)


86/97

IECHVEquipmentC

reepageDistances

Ref:AS6

0044.1


87/97

OtherO

HLineDesignIssues

Fla

sh-overpathinairmustbe

longenough

to

extinguishpowe

rfrequencyarc

Sag-tensionofconductors-notexceedtensilestrength

(whencold)ors

agexcessively(groundclearance)

wh

enhot.

Mid-spancondu

ctorclearances(allowfors

wing)

Clearancestostructures,grou

ndhighenoughfor

surgesandsafeworking.


88/97

Ageing&FailureMechanisms

M

echanicalFailure

(P

orcelain)Insulator(glazeandporce

lain)

pu

nch-through


89/97

ElectricalCorona

OnsetFormula

Whe

re-

Eciscriticalelectricalfie

ld

aisconductorradius

mis

is


90/97

Au

dible

Noise(AN)

Coronas

Source:Ref2


91/97

Rad

io

Interference

(RI)

Coro

nas


92/97

ElectricFieldStrength

on

Conduc

tors

Refertutorialexercise

Singleconductor

Averageofn

conductors

Q=C

V


93/97

ElectricFieldStrengthatEarth

Refertutorialexercise


94/97

EnvironmentalImpactsofHVOH

Line

s

Aesthetics-th

eyrebig!

El

ectromagneticinterferencewithele

ctronic

eq

uipment(50

hzinduction,coronan

oise)

Lo

wfrequenc

yelectroma

gneticradia

tion

(healthconcerns)


95/97

MagneticFieldUnderOH

TransmissionLine

Calculatehorizo

ntalandverticalcomponen

tsof

ma

gneticfluxdensityatacho

senpoint,basedon

dis

tancetoeach

phaseconduc

tor

Ad

deffectsofall3phases(th

esearephaso

rs)

ResultantHand

Vcomponentsarealsophasors

Squareandadd,

converttoanewphasoran

dtakesqrt

Refertutorialex

ample.Field

ishighestdirectlyunder

the

lines(ordire

ctlyabove,in

thecaseofU

Gcables).


96/97

PowerFrequencyEM

R

ReportbyKarolin

skaInstitute(Sweden)inearly

1970ssuggested

apossiblelow

-levellinkbetween

pow

erfrequencymagneticfieldsandchildho

od

leuk

aemia

Noeffectnotedbyelectricfields

Late

rreportsinU

KandUSsee

medtosuppo

rtthe

earlierreport

Late

ststudieshav

enotprovenanydirectlink.If

present,itseemsveryweak.

Thereishowever,moreofaconcernwithRFfields

near

thehead-he

nceworriesw

ithmobileph

oneuse.


97/97

OHLineT

esting&

Comm

Des

ignchecks,etcforstructures

Cur

rentinjectionte

st(forimpedances,earthres

Insulatortests(doneoninsulatorse

ts)-

-

Powervoltage

withstand

)

-

Fastandslo

wsurgetest)valuessetb

-

Artificialrain(pollutiontest)

-

Powerarctest

)

-

RIstrengthtest

)

-

Coronaonsettest

)asagr

eedwithsup

Documents

OH Transmisssion Lines