Siemens Power Cables & Their Applications

SIEMENS

CABLE

BOOK

POWER

CABLES

&

THEIR APPLICATIONS

PART

1

VOLUME

I

I

Cables

eirApplication

Power

th

and

Part

1

Materials

.

Construction

Criteria

for

Selection

Prniont

Ple n

nin

n

r I vJvvr

Laying and Installation

.

Accessories

Measuring and Testing

Editor: Lothar

Heinhold

3rd

revised

edition.

1990

i

Observations on the German terms

_'Kabel'

and oLeitungen'

and the

VDE

Specifications

' Kabel' and _'Leitungen'

Porrer cables are used for rhe transmission of

elecrri-cal energy

or

as

control

cables

lor

the purpuses

of

measurement,

control and

monitorin-s

in

electric

pouer

installations.

In

German usage. a disrinction

rs made

rraditionally

benr.een

'Kabel'

and

.Leitun-gen'.

'Leituneen' (literally'leads') are

used. generally speaking.

for

wiring in equipment. in u.inng installa-tions and for _{connections to moving or mobile} cquip-ments

and units. The

terrn can

thus

be rranslated as

'insulatcd wires'

or

'l.iring'

or

.flerible

cables'

or'cords'.

'Kabel'

_{(cables) are used principally for power}

rrans-mission and distribution _{in electricity}

supply-aurhori-tv sys[ems.

in

indusrry and in mines etc.

$'ith

the use of modern insulating and sheathin_s

ma-terials rhe _{constructional differences between}

.Kabel'

and 'Leirungen' _{are in many cases no longer}

discern-l ole.

The disrinction _{is therelore observed purelv}

_in

_terms

of

rhe

area

of

applicarion.

as desiribed

in

DIN

lDE

0:98

Part

I

for

pouer

cables

and

part

3 for

s.iring _{and flexible cables, and in the desien specifica_}

tions referred to lherein. e.g.

DIN

VDE

Oij0for

wir-ing and flexible cables and

DIN

VDE

0271

for pVC

insulated cables.

Further

factors

in

the choice between

.Kabel'

and

'Leitungen'

_are

_the

_{equipment Specifications (e.g.}

DIN

VDE

0700), the installation Specifications (e.g.

DIN

VDE

0100)

or

the operating stresses

to

be

ex-pected.

It

can be taken as a rule

of

thumb

that

.Leirungen'

must

not

be

laid

in

the ground, and

that

cables

of

flexible construction

are classified

as

.Leituneen'. even

if

their

rared voltase

is

higher rhan

0.6I

kV

-

e.g.

trailing

cables. This apart, there are also types

of

'Kabel' that

are

nor

inrended

for

laying

in

the

_eround (e.g. halogen-free cables

with

improved

per-formance

_in

_condirions

_{of fire to}

_DIN

_VDE

_0266. or ship

lirin!

cibles to

DfN

VDE

0261).r -

.."

In

the

present

_translation

_the

_ierms

'cable'

an,

'porver _{cable' have been used to include flexible anr_}

u iring cables where there is no risk of confusion.

\-DE

Specifications

_v

From considerations of consistencv in references an,

for greater

clrrity,

the VDE Specificarions applicabl_

to

po$er

cables are eeneralll' quoted

in

accorcancc

rvith the new pracrice as

'DIN

VDE . . .

.'.

This

applies

equalll

ro

rhe older

specificationr

ri

hich

still

_retain

_the

_designarion ,

VDE . . .

'

or

'DIN

57 . .

./VDE

. .

.'

in

their

tirles. Furrhermore

since these specifications are

of

lundamental

signifi-cancc, the practice of quoring rhe date of publication

I

l.l

l.:

J.l

-

3.2 J.J

Constructional

Elements

of

Insulated

Cables

)

1.1

l.l.t

l.

l.l

Elastomers

Thcrmoplastic Elastomers

lTPE).Con-ducting Rubber.Natural R ubber (NR).

Stl rene Butadienc Rubbcr (SBR).Nirrile

Butadiene Rubber (NBR1. Butyl Rubber

( IIR _). E thylene- Pro py lene Rubber (EPR). Silicone Rubber (SiR).Ethl lene Vin;-i Acerrre (EVA)

Thermosetting Polymers

(Duromers) Chemicel Aging

of

Poh nrcrs

Thc Intluence

of

Moisrure on Polyolefi ne Insulating

!larerials

Impregnatcd Paper

Lirerature Referred Protective She:lths

Thermoplastic Sheaths

Elastomer Sheaths

Sheathing Materials for Special Purposes

Conductors

Wiring

Cables Porver Crbles

and Flexible Cables

Insulation Poll mers

Thermoplastics (Plastomers) Copolymers F)uoroplastics.

Polv-r rni

l

Chloridc {PVC) Pohcthylenc tPE)

Cross- Linked Pol.vethylene (XLPE)

l)

l5

l'7 30 J) J_1

ll

l2

IJ

io

?7 3'7 3'l 38 39 39

.ll

4l

::) )t 1 2.) !.) 1t tr.) J to in Secrion 2

-

3.!t 6 t.1 '1 a lvletal Shearh

Protection against Corrosion Cable rvith Lead Sheath

Aluminium-Sheathed Cables

Armour

Concentric Conductors Electrical Screening

Conducting Layers

Metallic _Componen!s

_of

_Electrical

43

41

45 45

Screening

Longitudinally

_Water

proof

_{Screens. 47}46

Insulated Wires

and

Flexible

Cables

8

TJpes of Wires and Cables

3.1

National

and International Standards

8.1.1

VDESpecifications

8.1.2

HarmonizedSrandards

3.1.3

National

Types

8.1.1

IEC

Standards

Selection

of

Flcxible Cables

Clbles

ibr

Fircd

I nsrallations

3.1.1

Fiexible Cablcs

3.1.

-r

FLEXO

Cords

Flcxiblc Ceblcs

lbr \lining

and

Industrv

Halosen-Free SIENOPYR Wiring

rnd

Flexible Ca bles

rritlt

Improvco

Perlormrnce

in thc

Evenr

of

Frrc Core ldentificrrion of Clblcs 3.1 3.1. r

3.i

3.1 t0

ll

lt.l

I

l.:

.+9 .19 .19 .19 54

))

55 56

6:

1l

/)

3l

86 33 89

0t

01 124

t:+

124 124

Application

tnd

Installxtion

of

Cablcs

Rated Voltagc. Opcraring Volrilge Selcction

of

Conductor Cross-Sectional

Area

Power

Cables

lZ

National and Intcrnational Standards

VDE

Specifications

Standards

oI

Other Countries

IEC

and

CENELEC

Standards

Dcfinition

of

Locltions

to

DIN !'DE

0100

Tlpes

of Construction

of

Low- and

High-Voltage Cables General Type Designation Selection

of

Cables 94 94

t2.l

12.2 12.3 100 102

l3

IJ.-t 13.2 t.)..)

and

Accessories

Power Cables for Special Applicatiom

14.1

Cable wirh Elastomer Insulation

14.2

Shipboard Power Cable

1.1.2.2 Application and Installation

1.1.3

Halogen-Free Cables

with

Improved

Characteristics in the Case of Fire

1.1.3.1 Testing Performance under Conditions

of

Fire

Spread of Fire.Corrosivity of

Combus-rion Gases. Smoke Density. Insulation Retention under Conditions

of

Fire

Construction and Characteristics L:r1ing end I nsralla rion

Cables

for

Mine

Shafts

and

Galleries

R ivcr and Sea Crbles

Airport

Cablcs

Cable ',vith Polymer Insulation and Lead Sheath

I nsulated Overhead Line _Cables

l5

High- and Extra-High-\roltage Cables

Cable

with

Polymcr Insulation Lo*.Pressure Oil-Filled Cable wirh

Leld

or

Aluminium Sheath

Thermally

Stable Cable

in

Stcel Pipe

High-Pressure Oil-Filled Cable

lnternai Gas-Prcssu re Crble

External Gas-Pressure Cablc (Pressure

Cable) 125 l:)

ll5

l+,_).J t.1.4 14.5 1r.6 11.7

1{8

1i.1 1 5.2 1 5.3 l i.3.1 15.1.2 15.3.3 1E 18.1 18.2

l:8

129

1i0

lJl 131 t.)! lJ+ I J+ 1i5 138 1i8 139 139

Planning

of

Cable

Installations

16

Guide

for

Planning of Cable Installations

17

Cable Rated Voltages

17.1

.Allocation

_of

Cable

Rated

Voltages

17.2

Rated Lightning Impulse Withstand

Voltage

17.3

Voltage Stresses

in

the Event

of

Earth

Fault

t4l

t+o l+o '| .11 147 150 150 152

t52

157 159

Current-Carrving Capacity in Normal

Operation

Terms, Definitions

and

Regulations Operating Conditions and Design Tables

18.2.1

Operating Conditions

forlnstallations

in Ground

18.2.2

Operating Conditions, Installation

in

air

18.2.3

Project Design Tables

Load Capacity Installed in Ground/Air.

Rating Factors for Installation in Ground,

lor

Differing

Air

Temperatures and for Groups in Air

18.2.4

Use

of

Tables

18.3

Calculation

of

Load Capacity

18.4

ThermalResistances

18.4.1

Thermal Resistance

of

the Cable

18.4.2

Thermal Rcsistance

of

Air

Horizontal I nstallation . Vertical

Installa-tion . _{Atmospheric Pressure. .\mbicnt}

Temperature. Solar Radiarion. Arr;r

n-ge-nrent of Cables

18.4.3

Thermal Resistance

of

the

Soil

.

lgi

Temperature Field of a Cable.Definition

of Soil-Thermal Resistance . _{Daily Load}

Curve and Characteristic Diameter 'Dry-ing-Out of the Soil and Boundary

Iso-rherm

_d.

Fictitious Soil-Thermal

Resis-tance 7"j and ?"j".Load

Capacirv v

18.-1..:l Grouping

in

the

Ground

.

107

Fictitious Additional Thennal Rcsistanccs

AIj

and

AIi-

duc to Grouping.Loud

Ca-pacity. Extension of the

Dn

.\rea.Cur-rent-C:rrrying Cupacity

ol

Dissimilar

Ca b les

18.-1.5 Installation

in

Ducts and

Pipcs

.

l1-i

-Thernral Resisrances

I{

and ?'i.Load Capacity for an Installarion of Pipes in

Ground or

Air

or in Ducts Banks

18.4.6

Soil-Thermal-Resisrivity

_{. ll}

{J

Cable in thc Ground. Phi'sical and

Ther-mal Characteristics of Soil. Influcnce

of

Moisture Content.Msasurins. Basic

Quantities for Calculation Bedding Matc-rial.Sand.Gravel Mixtures. Sand-Ccmcnt

Mixtures Calculation

of

Loud Caplcity

Installation

in

Channcls and Tunncls

.

?-10

Unventilatcd Channels and

Tunncls

_.,.0

Arransemcnt

of

Cablcs in

Tunncls .

133

-Channcls

u'ith

Forced

Venrilation

.

215

Load Capacity

of

a Cablc for

Short-Time and Intermittcnt

Operatron

.

239

-General

.

239

Calculation

with

Minimum Time Value 239

Adiabatic Heat

Rise

.

241

_

Root-Mean-Square Value of

Current

241

Short-Time

Operation

.

242

Intermittent

Operation

.

243

_{_}

Symbols Used in Formulae in Section

l8

245

Literature Referred

to in

Section

18.

.

250

180

l8t

184 18.1 186 18.5 1 8.5.1 18.5.2 18.5.3 18.6 18.6.1 18.6.2 18.6.3 18.6.4 18.6.5 18.6.6 18.7 18.8 19 19.1 19.2 19.2.1 Short-Circuit Conditions General

Temperature Rise

of

Conductor under

Line-To-Earth Short Circuit

Conductor and Sheat Currents under

Line-To-Earth Short Circuit

Load Capacity under Line-To-Earth

1<1 -1<'l

257

/J9

I

i

l9.i

l9.l.

t

19.1.3

Short-Circuit

Thcrntal Rating

Guidc

tbr

Projcct

Dcsrgn

.

"

'

Pcrlornrrncc undcr Short'CircuiL Condi-rions Short-Circuit Dut).' Short-Circuit

Crplcity

ol' Conductor. Scrccns- Shclths

end.\rmour

Criculutions of

Short-Circuit Capacity

..\dirbltic

und Non-

\rlilbrrtic

Tcmpcrl-rurc Risc ivtethod Tcmperature Rise dur-ing Short-Circuit

Thermo-N{echanic;rl Forccs and

Erpansion

Gcnerll

EtTcct of Thermal Explnsion in

Crblcs Mounting ot' Singlc-Core Cables

Accessones

\fechanical

Short-Circuit

C"p".iry

.

.

Elecrromlgnetic Forccs

Eilccr

of

Electromagnctic Forccs

Line-To-Elrth.

Linc-To-Line und Balanced

Thrcc-Phlsc Short Circuit

\lulti-Corc

Crrblc

Tcnsilc Force

fi

Surlucc Prcssure

fi'

Clble

Construction Erperience and

Calcuhtion Quantities

Firing

Elements

Single-Core Cables and Fixing

\[cthods

Bcnding Stress Surluce Prcssure

fi

Srrcssing ol' C)amps

lnd

Binders

.\cccssories

Sl mbols used

in

Formulae

in

Scction l9

Litcrature

Rcfcrrcd

to in

Section

l9

Resistance and Resistance per Unit

Lcngth

of

Conductor

Resistance

per

Unit

Length

on

d.c. Resistance pcr

Unit

Lcngth on a.c.

Currcnt

Reiatcd Losses

Inductance and lnductance per Unit

Length

Inductance per

Unit

Length

of

a

Conductor System

Single-Core Cables

Earthed

at

Both Ends

Arrangement

of

Cables

Earthing

from

Either One

or

Both

Ends

of Metal

Sheath

or

Screen

Cross-Bonding

of

the Sheaths,

Transposition

of

the Cables

Multi-Core

Cables

Sequence Impedance and Zero-Sequence Impedance per

Unit

Length

Literature

Referred

to in

Section 21

r65

l6J

185

.

292 296 19'7

.

_r05 r v.+.1

l9.l.,l

19.5 19.6 20 19.3.+ 19..r 19..1. I 20. r 20.2 20.1 ir

-l.t

i.2

21.2.1 21.2.2 21.2.3 11 1,1

tt

? 21.4

i00

.

_-ili

.

ll6

.

319

.

i20

J-U

.

320

.

321

.

3?2

.

322

.

32f

.

322 - J-:O

.

328

.

328

.

329 329

.

JJU

27

Clp:rcitlnce

:tnd C:lpacitancc per

Lnit

Lcngth

.

-ri l

ll.l

ccncnrl

.lil

ll.l

Operating Capacitance per

Unit

Lcngth

Ci

l-l1

:1.-.1

Clpacitivc Currcnt

/i

and Earth'Fault

Currcnt

,fi

of

a

Cable

.

li't

ll.+

Dielcctric

Losses

.

il6

23

InsulationResistance,Insulation Resistrnce per

Unit

Length

rnd

Leakage )) I

21

Determination

of

Voltage

Drop

.

-1'+0

ll.l

General

.

i40

l-+.1

Short Cable

Runs

.

-1-10

l+.i

Long Cable

Runs

.

ll0

25

Economic

Optimization

of

Cable

Size

i'll

l-i.l

S;-mbols used

in

Formulae in

Section

25

i47

15.:

Lircrature

Relerred

to in

Section

25

.

i-17

26

Interference

of

Porver Cables nith

Control

ud

-f elecommunication

Crbles

l'19

16.l

lnductivc

lntcrtcrcncc

.

-151

16.1.1

\lutual

Inductancc

.

]51

16.1.1

Inducing

Currcnts

.

-lil

16.l.i

Current

Rcduction Fcctor

of

the

Intlucncing Powcr

Cable

.

i52

16.1.-l

Voltagc Reduction Factor

of

the

lnl'lucnccd Telccommunication Cable

.

355

16.1-5

Rcduction Factors

of

Compensating

Conductors

.

357

26).

Noise Voltage

in

Symmetrical

Circuits

358

16.3

Ohmic

Intert'crence

.

i58

26.1

Inductive and Ohmic

Interference .

359

l6.j

Details Required

for

Planning

.

i59

:6.6

Crlculated

Example

.

160

Z7

Design and Calculation

of

Distribution

Systems

.362

27.1 Introduction

.

362

27

.Z

Determination

of

Power Requirement

as a Basis

for

Planning

27

.?..1

Load Requirement

of

Dwellings

27

-2.2

Load Requirements

of

Special

JOJ 363 365 JOO 366 JOO JO/ 27.2.3 27.3 27.3.t z't.3.2 Consumers

Total

Load

Planning

of Distribution

Systems

General

17.3.3

Low-Voltage

Systems

_.-'

'^^'

Ststcm Configuratron and lypes

ol

up-ciation

in

the Public Supply Extension

of

a Low-Voltage System Systems of

Build-ings lndustrial SupPly Systems Location

oisubstations Component Parts

of

the

Lo$.Voltage SYstem

17.i.-1 \f

edium-Voltage SYsrems

Public S upply' Expansion of the

Medium-voltage System' Distribution Systems tn

Large Buildings lndustrial Supply

Sys-tems Standby Power Supply Component

Parts of the Medium-Voltage System

Charge Current Compensation and Star Point Treatment The Superimposed

High-Voltage SYstem

368

1? 1 I

! | .+.)

Svstem Calculation

Calculation

ol

a Lorv-Voltage S1'stem

Inlestigations of Protective Measures

Asainst Excessive Touch Voltage

27.4.,1

In" estigation

of

Short-Circuit

Protection and Discrimination

17.+.5

Computer-Aided Systenr Calculation

27.5

Literature Referred

to

in

Section 27

Laying

and

Installation

28

Cable ldentification

Marking

28.1

Manufacturers,VDE-Marking

28.2

Colours

of

Outer Sheaths and

i81 )61

t8i

Basics

i75

385 189

..395

..395

Prolective Coverings

?8.3

Core Identification

for

Power Cables

up

to

Uql

U:0.6/ I

kV

28.4

Core Identification

for

Cables

for

Rated Voltages Exceeding

L:o,U _=0.611 kV

Lal ing the Cables

Transporting

Preparation

for

LaYing the Cable Differences

in

Level

of

the Cable Route

Laying

of

Cables

in

the Ground

Cable Route

Laying

of

the Cables

Laying

of

Cables Indoors

Cables on Walls, Ceilings

or

Racks '

Cable Tunnels and Ducts Cable Clamps

Types

of

Clamps

Arrangements and Dimensions

Installation Guide

Preparation

of

Cable Ends

39'7 398 399 399 400 29 )9.1 29.2 29.3 29.4 29.4.1 29.4.1 29.5 29.5.1 29.5.2 29.6 29.6.1 29.6.1 30 30.1 401 401 401 403 408 408 408 410 415 415 30.2 JU. J 31 Jl.t i1.2 32 )J.l 31.2

il.3

i2.4

-r_:.+,I -:1 _{.i 1} 32..1.3 J-,+,+ 32.4.5 12.4.6

rl-)

Jtr J).-: 35.3 36 J O.1 JO. J JO.+ Jb. ) JO.O 37 38 416 418 410 420 ,11i .124

Earthine

of Metallic

Sheaths and

Coverings

Conductor Jointing

Repair of Damage to Outer Sheath

Outer Sheath

of

Polyvinylchloride

lPVC) and PolyethYlene tPE)

Jute Servines on Cables s'ith Lead

Sheath

Cable Accessories

Fundament::l Objectit es

Requirements

Stress Control

Fundamental PrinciPles

for

the

Construction and Installation

of

Acccssones

Compound

Filling

Tc'chnique

Cast-Resin Techniques Shrink-On Technique Lapping Tcchnique Push-On Technrque Plug Tcchniquc

in

Section

32

.

137 r J't

tl7

lt9

4ll

+J{ 135 437 .138

33

Cable Plan

Measuring and Testing

of

Power

lnstallations

34

Elcctrical l'Ieasurements in thc Cablc Installation, as Installed

Literaturc Referred to

Voltage Tests General

Testing

with

d.c. Voltage Tesring rvith a.c. Voltage Locating Faults

Preliminary Measurements

Location Measurements bY the

Conventional Method

Locating

of

Faults by Pulse Reflection

Method

Preparation

of

Fa

Through

ult

Point by

Bum-Locating Using

Audio

FrequencY

Testing

of

ThermoPlastic Shealhs

Construction and Resistance

of

Conductors Conversion Table 439 440 443

M7_

449 450

452

-454 457 458

iuonstrucilonal

I

ElgtllgtILS

ul

ll

l5ulclLE\l

vc|utso

-

₁

_Conductors

The conductors

in

wiring

cables and

flerible

cables

consis! norvada.vs of copper (Cu). The use of

alumin-ium

(Al),

as well as copper, is also common in power cables.

The

cross-sectional area

of

the conductor ls

quoted brsically

not Js

the geonterritul

but

as the

electrical!1' eJfectiL'e cross'sectional

area.

i.e

the

cross-scctiontl

rrcl

as

dctermined

by

e

rcsistance

, -rasurement.

In

the

international standard

tor

copper. IEC 28

'lnternational

Stendard

ot'

Resis(ilnce

tor

Copper'.

n

_{standrrd value}

_for

_the

_resistivity

_at

_?0'C

.-

given

as

g,o=$=g.0l7l1l

Omm:im

The temperature coefficienI

e:o at

]0'C

for

this copper

is

rro:3.93

x

10-riK.

This

value increases

or

de'

creases approximatcly

in

proportion

to

thc

conduc-tivity.

Investigations have

sho$n

that

the

product

of

the temperature coefficient and the resistivity rvith

different

conductivities

is

neariy

constant

a!

0.6776

x

10-a O mm'?/m K.

Similar

relationships

exist

for

aluminium.

In

this

case,

IEC

1

11

'Resistivity

of

Commercial

Hard

Drawn Aluminium

Conductor

Wire'

gives

the

re-sistivity

at a

temperature

of

20

"C

as azo:0.028264 Q mm2/m and the temperature coeffi-cient as

e.o:4.93

x 10-

r/K.

This coefficient is

pro--ortional to

the degree

of

purity

of

the aluminium.

z{d

decreases

with

increasing

impurity

in

the same

.y

as the

electrical

conductivity.

Here again, the

product

of

resistivity and temperature coefficient

re-mains approximately constant,

in

rhis

case

at

.139

x

10

-a

f)

mm27m

K.

The temperature dependence

ofthe

resistivity is given

in

general by

Qc.:

Qr,[l + a3,(3,

_-

9,)]

Thus : for copper, (1.0) for aluminium.

Qr:Q:o*

1.1

x

10-r(9-20)

Q

mm:im

(1 2)

rvith the tempcrature J) expressed in "C.

ln

the planning

of

cable installations. horvever. in vierv

of

the

unavoidable uncertaincies

in

the given

intbrmation.

it

is

quite

sut'ficient

to

calculate rvith

the

conventional temperature

coefficients

lsee

page 310): for copper.

1:o:393xl0-17K

7.o

:126

x

l0-r;K

1

On:-1-:234

5

6

[or aluminium. 1:o

:4

03

x

10- ri

K

zo :4.38

x

10 - 31K I O _o

::-:2)8

K

6(|

In

general. 1 aJ _{= ---:}

l/N.

VOf O for copper,

254.5

1000

n,o=R"ri#frx:,

ottm

To

convert

a

measured conductor resistance

to

the

reference conditions

of

20 "C and 1000 m length, the

following

expressions

are

applicable, according to rEC 228, 1966: (1.3) (1 4) (1.5) (1.6) ( 1.7) (1.8) 11

q"=g.o*0.68

x

10-a(3-20)

O

mm2/m

(1.1)

I

Conductors

lor

aluminium,

R:o = Ra

-

#L

₂₄₈₊₃

,.

lloo

97t

-

{ t.9)

I

s here

i]

conductor temperature (oC)

R,

measured conductor resislance at

3'C

(Q)

1

length of cable (m)

R.o

conductor resistance at

l0'C

(Q,'km)

To permit the economicai construction oIcables rrirh

a small numbcr of rvire

-eauges. the conduclor desiqn

has been siightly altered

in

accordance

uith

IEC

ll8

(for

_details see IEC

ll8.

1966) and rhe resisrancc

de-termined

lccording

ro Ihc e\pression

minium for

conductors

in

wiring cables

for

fixcd

in-stallations. These types. also mentioned

in

the ncu

IEC

specification, have not, however, been gencrall. accepted so far.

The minimum number and the diameter of the wirc

and

the resistance

of

the conductor are

laid

dowr

in

IEC 228 and

DIN

VDE

0295 (see _also pages

45i

to

457). Cables used abroad embody conductors

ir

accordance

wirh the

rcspectile

national

specifica

tions.

in

the case rhar rhesc differ from IEC.

If

the conductors are insulated rvirh a material $ hicL

provokes an adverse chemical reacrion s,ith the

cop-per. a metallic protective laver round rhe coppcr $ irc

is

necessary. e.g.

of

tin or

some other barrier (scr

page 27).

l.I

Wiring

Cables

and Flexible

Cables Tlpes of Conductor

For flcxible and

uiring

cablcs in the Federal Republic

of

Germany.

rvith

fcw

cxceprions.

circular

copper

conductors

arc

uscd. Thcsc are aimed

at

two

arear

of application:

For

Fi.rc/

lnstullut iorr

The cables are subjcct

to

nrechanical stresses due to bending

only during

installation. Accordingiy, solid conductors are preferably uscd up to

cross-sectional-area

of

10

mm:

and

_{strandcd conductors}

i'

-\vc

l0

mm2

For the Connection o-f ll'lobile Equipnrcnl

These cables. since they have to be flexible. embody_

fine-stranded conductors for all cross-sectional areas.

Where a particularly high degree of flexibility is

nec-essary, e.g.

in

the leads

to

welding-electrode holders,_

Fig.

l.t

Multiple stranded, circular fl exible conductor (1.10)

\\ here

.1

resisrivity at

20'C

for

copper.

.4

₌

l'1 .211 Qmmr; km

lor

aluminium, ,1

:)8.264

f)mm?,,km

n

number of wires

in

the conductor

d

diameter

of

individual wires (mm)

K

factor to allow

for

the cffects

of

manulacruring

processes:

K,

for u,ire diameter and surface trcatment

K.

for conductor stranding

K.

for core stranding

Because of improved manufacturing techniqucs.

par-trcularll

lhe compaction of stranded circular and sec-tor-shaped conductors,

the

basic principles shich had underlain the establishmcnt

of

conductor

resis-tances had lost something

in validity.

so that a revi-sion

of

the existing

IEC

and

VDE

specifications

be-came necessary.

In

particular

the differences

in

rhe

resistance values

lor

solid and stranded conductors.

and

for

single- and

multicore

cables,

in

the former

ranges were no longer applicable.

It

was thus possible

in

the

1978

edition

of

iEC

228

to

achieve greater consistency

of

resistance value

and a

reduction in the number

of

conductor classifications

from

six to

four.

In

1980

this

international

agreemenl. rras

incorporated

_{into the}

standards

for

power cables,

u'ires,

and

wiring

cables

and

flexible

cables

(DIN

VDE 0295). The new values are raken

inlo

ac-count in the tables and planning sheets in the presenr

book.

As

well

as plain aluminium conductors, the use has

been

tried

in

some

countries

of

nickel-olated or

tinned aluminium, and the so-called coppei-clad alu-IJ

.\.:o _{= ---; /\ I A: At !Z Llll}

1l'ft rl'

Tinscl cond uctor Tinscl strxnds

Fig,

1.2

Tinse I conductor

Fllt

coppcr wire

Thrcad oi svnthetic Ilbres

Fie.

1.3

Construction of tinsel strund

--\e

conductor strands are madc up

ot'c

number. ilp-opriate to the cross-sectionul urer of the conductor.

oi errra

tlnc

substrands (multiple srrunded. circular

tlerible

conductors.

Fig.

l.l).

For

very llexible con-nccting cords

of

vcry small cross-scctional arcir. c.g.

0. 1

mmr

lbr

clcctric shavcrs. tinscl conductors ( Figs.

l.L

and

l.i):tre

uscd.

IIultiple

strunded

cirtulur

_JIe.rible <'onluttors (Fig. 1.1) consist

of

strands whose

individual

rvircs are

themselves stranded

or

bunched. The

ability

of

the

conductor

to

wirhstand mechanical stresses and its

fle.ribility

depcnd

particularly

on

rhc stranding ar-rangement. as

well

as

on

the

quality

and diamctcr

of

the wires. The shorter the lay

of

the strands and

substrands, the greater the

flexibility

and the ability

r

withstand

bending.

The

srrands

may

be

laid

in

ne

same

direction

in all

layers (uniform-lay

strand-.,rg) or the direction may alternate from layer to la,'-er

(reversed-lay _{stranding). Conducrors}

_with

uniform-lay stranding are preferred in llexible cables for hoists

'

,ecause

of

their

better runnins

behaviour

rvhen

changing direction over rollers.

Tinsel conductors

(Fig.

1.2) are made up

ofa

number

of _{tinsel threads stranded rogether. Each thread (Fig.}

1.3) consists

_of

a textile core with a helical wire strip

(copper _{strip 0.1 ro 0.3 mm wide and 0.01 to 0.02 mm}

thick).

Coppcr Conductors

.

Solid

conductors

lrc

prctcrrcd up

to

l(r

mm-

cross-scctional srea. strondcd conductors

lbr

25

rnm:

and

J boVc.

Givcn

lnd

adcquatc

lbility

to rvithstand bcnding. thc conductors should have a space

tlctor

rvhich. togeth-er

with

rhe chosen conductor scction. results in good

utilization

of

the

cross-sectional urea

of

the

cable.

Accordingly, where possible, compacted circular

con-ductors.

or.

if

the cable construction permits. com-pacted sector-shaped conductors. are used. The space

flctor

defines the percentage of the geometrical

cross-sectional

area

of

a

conductor

that

is

occupied by

the

individual

wires. The construction

of

single-core

cable

and

three-core separately-leaded

(S.L.)

cable

rcquircs the use

of

circular conductors.

Aluminium Conductors

DIN

VDE

0295 pcrmits the use of circular solid and

stranded

aluminium

conductors

lionr

25

nrmr

up-rvlrds

lnd

scctor-shapcd conductors

Irom

50 mm: upwrrds.

Solid conductors ure prcterrcd in cables rvith pol.v''nrer

insulation and sector-shlped conductors in the rangc

of

cross-sectional urcas

tiom

50

to

185 mnrr. Single-corc cablcs

normally

have strandcd circular

conduc-tors: solid conductors are usuirlly uscd only in laid-up single-corc cablcs

in

cases

of

high thermal loading. because

of

thc

problems

of

thcrm:rl expansion (see

page 192).

If cables

with

polymcr insulation and aluminium pro-tcctive

(P)

or

ncutral (PEN)

conductors are

laid

in

the ground

or in

an

agrcssive atmosphere.

in

the

evcnt

of

damagc

to

the

sheath and

thc

insulation

these conductors may be open-circuited in the course

of time through corrosion. The possibiiity of damage

must

therefore

be

taken

into

account. rvhen such

cables are installed.

by

the selection

of

appropriate protecuve measures.

llilliken

Conductors

For

high-power

transmission

with

conductor

cross-sectional areas

of

1200 mm2

or

more. special mea-sures are necessary

to

keep additional losses due to

skir

effect

within

tolerable limits. To this end, either

the

individual

conductor stlands are provided

with

an

insulating

layer (e.g. enamel) and so laid-up that

l

Conductors

\ormal

lay-up

Lou -loss conductor for oil-lillcd

cables (

\liiliken

conductor)

Fig.

l..l

Construction of multi-core circu

Fig. 1.5

Construction of sector shaped conductors

Fig. 1.6

Model of a flexible superconducting cable core.

Constructed of aluminium wires each with a lhin coaring of Niobium laid-up over a PE carrying tube.

Above this an insulation of polymeric plastic

loil

is

applied followed b1r the concentric retum conductor

their position

within

the cross-section of the

conduc-tor

changes periodically along the lenght

of

rhe

con-ductor,

or

the conductors are made up

of

separate

stranded, sector-shaped elements which are rrrapped

in

conducting

paper

(Fig.

1.4). This

latter type

is

also known as the milliken conductor.

Single-core oil-filled cables require a hollorv

conduc-tor,

rvhile external-gas-pressure pipe

llpe

cables

re-quire oval conductors.

Superconductors

The most suitable conductor materials for

supercon-ducting

cables are

pure niobium

and niobium-tin.

those critical

temperatures are around 9.5

K

..

_.

18.4

K

respecrively. Since the current

llorls onhlin

a

very

thin

surface layer (0.1gm). lhere is

no

need

for

the u,hole conductor

to

consist

ol

this rclatively expensive superconducting material.

It

is

sufficicnt

if

a

thin

layer (10

to

100 pm) is dcposited on a carricr

naterial,

e.g. high-purity copper or aluminium. The

carrier

metals

must be so

disposed

that

they

are

not traversed by rhe magnetic field of the conductor,

and the generation of eddy-current losses is avoided

(Fig.

1.6).

The development of superconducting cables is as yet

in

rhe early stages, although 110 kV cables capable

of

transmitting

2500

MVA

have already been

pro-duced

for

experimental purposes. Compacted Circular holloq conouclof lar conductors Solid shaped conductor shaped conductor.

and a profiled PE rape as proleclive layer

t-@

Oval conductor

x1<s.

,/.n

fl/$'

ffi

Stranded tl

--l

For

the

insulariorl

of

rviring

cables

and

llexible

cables. s-vnthetic nraterials

and

naturll

rubber are

used. and

for

porver cables. as rvell as these'

tmpreg-nated paper.

As

a

result

of

the development which

has

taien

place

in

recent years. these materials can

be produced rvith various electrical- thermal and

me-chanical properties according

to

their intended

pur-pose.

It

is

thus

possible

to

manufacture cables

lbr

specific requirements and tields of application.

2.1

Pol-vmers

A

poll-mer is

I

macromolecule composed

oi

r

hrqe number

of

basic units. the monomers.

If

tlte

mlcro-molecule

is

s-"-nthesized

using

onl."-

one

kind

of

rD{,pomer. the producr is a homopolymcr.

If

the

po-i-

.er chains are made

up

of nro

diffcrent

tvpes

of

monomer.

the

result

is a

copoll-mer. and

of

three

different t)-Pes a terpolYmer'

\lost

of

the

important

insulating matcrials are today produced s).'nthetically. Only in the case of clastomers

rre partly

narural products

still

oi

technical signil-i-cance.

Technically important

polymers are classified

(Tl-ble 3.1.1 .rccording

to

their physical properties as

tr

thermoplastics (Plastomers),

F

elastomers and

tr

thermosetringpolymers(duromers).

The

polymers

principally

used

in

cabie engineering are listed

in

Table 2.2.

It

is rvorth

noting

that

materials rvhich

do

not fit

lnto rhls clussification

oi

thermoplastics. elastomerics

and

thermosetting materials

are

finding increasing

application

in

cable engineering. These include the cross-linked polyolefines (e.g. cross-linked polyethl-l-ene), rvhich behave as elastomers above the criticel

melting

point.

as

manifested

particularly

in

the

heat-pressure characteristics

:lt

iligh

letnperatures

(Fig.2.1).

Also

in

this crteeorv ure the so-cllled thermophstic

elastomers

rvith their

chdracterislic thermoplastic

behlviour

at

processing temperatures

and

elasto-meric

cltlrlctcristics

ltt

thc

temperatures

at

r''hich thev are used.

Trblc

2.1

Technically important polymers chssilied according to thcir physical properties Polymers

^r,,rtu,ior,ill

Sy.'ntheti, mate rials

lrstomers Thermoplaslic (Plastomers) Thermosetting pol,vmers (Duromers)

Highly molecular materials which

after

cross-linking (vulcanizing) develop elastic characteristics i.e.

a large reversible elongation in

re-sPonse to low tensile stress

Macromolecular materials lvhich

are. at higher temperatures.

Plas-tically formable and are

teversl-bly

plastifiable, i.e. theY harden

on

cooling

but

become

Plastifi-able when reheated

Polymers

which

harden when

heated above a critical

temPera-ture and are no longer reversiblY

formable.

In

this condition these

materials

are

normallY

cross-linked

2lnsulation

Table

2.2

Summary of the most important polymers used in the manufacture of cables

Thermoplastics (Plastomers) Cross-linked Thermo-plastics Thermoplastic Elastomers Elastomers Duroplastic (Duromers) Pol.vvinl lchloride Polyethl lene Ethylene Vinyl-Acetate Copoll mer

(v.{

< 30%) PVC PE EVA Ethylene-.Acrl,late-Copolymer, e.g.: Erhl'lene-Ethyl-Acrylate EEA Elh)'lene-Butyl-Acrylate EBA

Poll'propylene

PP

Poll'amide

P.A Eth.vlen e-Tetrafl

uoro-eth) lene

Copoiymer

ETFE

Ter rr fl rnropthr'lene- Hexafluoropropylcnc-Copoll'mer ( Fluorinated Ethylene

Propllene)

FEP Cross-linked Poly-ethylene XLPE Cross-linked Ethylene Copolymer Blends

of

Polyfines and Natural Rubber I nree btocK -' Polymer Styrene- Alkylene-styrene Thermoplastic Polyurethane (PUR) and Poll,ester Natural

Rubber

NR Buryl Rubber (lsoprene Isobutylene

Rubber)

llR

Styrene- Butadien

Rubber

SBR

N itri lc- Bu tad ien

Rubber Ethylene-Propylene

Rubber

EPR

_"

Ethylcnc-Propylenc Dienc Monomer Rubber Polychloroprenc Chlorsulphonyl Polycthy Ienc Chlorinated Poly-cthylenc Silicone Rubber Epichlorohydrin Rubber Ethylene-Vinyl-Acetatc-Copolymer

(vA

>

l0%)

EVA NBR EPD M CR CSM CM SiK ECO Epoxy

Resin

EP Pol)'ure-tha ne

Resin

PLPI

l _{The gencral} tcrm for EPR and EPDM is EPR

:'tslockpollmcr:acopol)mcruhosachainiscomposcdofaltcrnatingscqucnccsofjdcnticalmonomcrunits

Fig. 2.1

Heat-pressure characteristics of polyolefi nes.

Heat-pressure test to

DIN

VDE 0472

Test sample: conductor 1.5 mmr with insulation

0.8 mm thick, Test duration: 4 h

Determination of load using the formula:

F:0.6.y'2-D-6-6'

F

Load

in

N

D

Diameter of core in mm

d

lvlean wall thickness of insulation in rnm

70 80

90 llvA conren >30%

lo

120 150

140

"c

150 Temperar!re Ll

-lndenr deprh 10 LDPE PVC (70r) I

..1"')

I

,t

.1:":^::y-,r.i

,/-

XIPE minenl

filled I

,,r/

EPR I {cross-linked]r

4:

I

<;

EVA' I (cross.linked)

2.1.1 Thermoplastics ( Plastome rs)

Thermoplastics are madc

up

of

linear

or

branchcd macromolcculcs. and unlike the elastomers and thcr-mosetting pol;-mers

hlvc

rcvcrsible forming

charlc-teristics.

Thc

combinltion of

propertics

of

thcmo-plastics are dctcrmincd by their structural

tnd

molec-ular

arrangcment.

Thc

thermopiastic polyethylene

(PE)

has

the

simplest

structure

oi all

plastics

trls. i.i

t.

Fig.

2.2

Structural torm

of

Poll.'ethelene _{PE)

In

the so-called high-pressure polymerization of

eth-$ne.

_'.ne''l chein molecules

with

liltcral JIkyl

groups ilre

bv redicll

initiation {LDPE

-

los-Densitv

PO. Ionic

polr mcriz:rLion

lt

lorv prcssurc.

on

thc

othcr hxnd. lcads to lincar. very lirtie brlnched chains

(HDPE

_-

ffigh-Dcnsity

Pfl.

Thc less branchcd the

chain molecules

of

a

polyeth-vlene are. the greater

is its possible cr-vstallinity. With increesing

crystallin-ity,

melting

temperature, tcnsile strength. Youn-g's

modulus (stiffness), hardness and resistancc

to

sol-vents increase.

while

impact strength. rcsistancc to stress

crackins and

transparenc.v decrease.

Like

ail thermoplastics, the polyolcfines

_-

as

in

the case

of

e.g. polyethylene

and

polypropyiene

_-

also consist

of

a

mixture

of

macromolecules

of

dilferent

sizes.

and

it

is

possible

to

control

the

mean molecular weight and the molecular weight distribution

within

tain Iimits through the choice of suitable polymeri-zation conditions.

. the technical data sheets of the raw material manu-facturers, instead

of

the mean molecular rveight, the

It

florv

indexr)(for

polyolefines)

or

the so-called

K

value

(for

polyvinyl chloride, PVC) is quoted (see

page 18).

The mean molecular weight and the molecular weight

distribution

have

a

considerable effect

on

the

me-chanical properties. Thus, as a rule, tensile strength, elongation at _{tear and (notched) impact strength}

in-

::--"

The rncl!-llow index tMFI) is thc quanrity of matcrial in g uhich undcr

iO lr""""r:r"" is exrruded rhrough a givc'l sizcd jcr in a pcriod of

creasc rvith incrcasing chain lcngth. as :rlso thc

viscos-ity

oi

the

plasticized material.

It

should

be

borne

in

mind.

however.

that with

incre:rsing mclting

vis-cosity the rnaterial becomcs more

difficuit

to rvork.

The

molecuiar chains (polyethylcnc. polvvinl-l

chlo-ridet

rcsulting

from

the synthcsizing

rclctions.

c.g.

the polymcrization

of

suitable monomers (ethylene.

vinyl

chloride) are tormed by atomic forces (primary

bonds). The cohesion

of

the molecular chains is due

to secondary forces.

In

the polyolefines, for erample,

the dispersion

or

vxn

der Waal forces predominate.

In

this case the forces of attraction betrveen the

mole-cules

are

unpolarized.

In

plastics

rvith

polarized groups. besides the dispersion forces. dipole

orienta-tion

furces betrveen the chains are also eifective (e.9.

in

PVC).

Strong

forces

of

attraction

betrveen the chain molecules are also represented by the hydro,een

bridges. as.

for

example.

in

poly-amides.

poll-ure-thancs

:lnd

iluoroplastics.

With

sy-mmetrical struc-tures the thermoplastics bonded by dispersion. dipole

or

hy-drogen

bonds tend

towards

crvs(rllization. The_"- are thcn hard and tough.

lnd

of high strength.

and the sotjening range is smail.

To

the

e\tent

that

the

macromolecular structure

is

asymmetrical (e.g.

in

PVC).

thc

tendencv

ro

crystallization

is

reduced

and the sollening ranse extended.

Arvareness of thcse rclationships norv makcs

it

possi-ble

to

manul'acture plastics tailored ro their

applica-tion

requirements.

In

addition

to

standard

thermo-plastic PVC and PE. thermoplastics and elastomers

produced

by

specifically directed copoll-merization

of

ethylenes

rvith

other

copolymerable monomers

har e assumed significancc in cable engineering.

Copolvmers

The thermoplastic copolymers most frequentlv used

in

cable engineering are based on ethvlene and are

produced

by

copolymerization

with vinvl

acetate

(EVA

copolymer)

or

with alkyl

acrylates (EEA and

EBA copolymers). EVA copolymers with a vinyl

ace-tate content

up

to

30%

contain methylene units in crysralline formation and are therefore workable as

thermoplastics.

With a

further

increase

in

the vinyl

acetate

(VA)

content the product becomes rubbery. Polyethylenes and the ethylene copolymers, such as e.g.

EVA,

are

of

special significance

in

cable

engi-neering because these thermoplastics can be

cross-HH

tl

HH

rl

2lnsulation

tl

ll

ll

:

tl

:

il

ll

il

il

-co-cH

3

Fig.2.3

Structural form of EVA

)inked b1' means of orsanic peroxides

or

high-energy

radiation.

Cross-linking

increases

the

thermome-chanical

stability

_-

i.e.. rvith

a

temperature loading

beyond

the

crystallite melting

point

of

the

cross-linked thermoplastics the material no longer exhibits

themroplastic.

but

rather thcrmoelastic characteris-tlcs.

Fluoroplastics

Fluoroplastics are characterized

by

an

outsrandint combination of properties. such as good thcrmal sta-bilit.v, excellent electrical characteristics and high rc-sistance to chemical attack and flame rcsistance. Thc

best known fluoropol-vmers

in

cable engineering are

the thermoplasrically workable copolymers

of

ethyl-ene

and

tetrafluoroethylene

(ETFE) and

of

tetra-fluoroethylene

and

hexafluoropropylene

(FEP)

(Fie. 2.a).

The

various mechanical propcrties

of

the polymers

(e.g. tensile strenglh, extension, elasticity

and

cold resistance). the various resistances

to

external

influ-ences (e.g. acids, aikalies.

oil)

and their electrical and

lhcrmal characteristics determine the areas

of

appli-cation of the cables in s hich they are used for

insula-don and sheathine.

rEF

Fig.2.4

Structural form

of

ETFE and FEP

18

Polyvinyl Chloride (PVC)

Among rhe insulating materials used

for

flexible anr

wiring

cables, plastic compounds based on polyvinr chloride (PVC) have assumed particular significance The starring material, the vinyl chloride, is nowadal

produced

mainly

by

the

chlorination

of

eth-vlen.

(Fig. 2.5).

It

can be converted

to

polyvinylchlorid.

by

the

emulsion

(E-PVC),

suspension (S-PVC) o:

mass pol),merization (M-PVC) method.

Fig.

2.5

Structural form

of

PVL

For

insulating and sheathing mixtures

in

cable engi

necring, PVC obtained

by

the suspension method i

usually

used. These types

of

PVC,

offered

by

th

chemical

industry as

S-PVC. are distinguished b'

thcir

grain structure and

K

value. The

K

value. ac

cording

to

Fikentscher

(DIN53726),

characterize

the

mean molecular weight

of

the PVC. The grai:

structurc is significant

from

the

point of

view

of

th

processing

of

the compound.

For

the manufactur.

of soft

PVC compounds

for

the cable

industrl'.

a;

S-PVC

uith

porous

grain

(plasticizer sorption) an(

a

K

value of about 70 has bccome generally acceptcd

PVC

and additives

like

plasticizers, mineral fillers

antioxidants. coulering pigment a.s.o. are preparel

in

a mixing and gelling process, under heat,

to

pro duce the working compound.

The compound, usually

in

granular

form,

is pressec

onto

the conductor as insulation,

or

onto

the cori

as a sheath, by means of extruders.

Pure

PVC

resulting

from

polymerization

is

unsuit-able

for

use as an insulating and sheathing materia

for

flexible and

wiring

cables, because

at

its servic

temperature

it

is hard and brittle, and also thermali' unstable.

It

is only through the incorporation

of

ad

ditives that the

mechanical/thermal

and

electricr characteristics necessary

in

such materials, togerhe:

with

good processing properties, are obtained.

n I

n

I

c-I H

ii-i-i+

ll

it

Y-r

CF3Jy T I I

-tt

rr

lli

n,

il

ll'

:

ll

, :

lli

It;

i

ti

: ^1r l

tr

I

i-i-r-i+

r

I

-+-L

I

I

---l--L

The most import:rnt additivcs arc:

P las tici:ers

The plasticizcrs

normllly

usecl are cstcrs

ol'or3lnic

acids.

such

as DOP

(Di-1-crhyiherylphthaiate) or

DIDP

( Di-isodecy-lphthalatc). Estcrs of lzelnin or

sc-bacic acid

tre

used

for

compounds

rvith

especillly

good

cold

resistance,

while

those

for

higher servtce

temperxtures contain

trimellith

ccid esters or poll

es-ter plcsticizers.

Stabili:ers

These confer thermal and thermal oxidization

stabili-ty

on

rhe PVC compound during processing and in

service. Principally used as stabilizers are

leld

salts

such as basic lead sulphate

or

lead

phthalate

Anti-oxidunts

tre

necesslry

in

addition.

to

prevent.

ibr

c.

,rplc. dcterioration of the plasticizcr through

ori-datlon.

Fillcr s

-f

_{;e are used}

_to

_{obtain a specitied combination}

of

char:rcteristics.

In

addition thev contribute to reduce

thc cost. The most uscd

llllcrs for

PVC compounds

lrc

culcium carbonate and kaolin.

Lubric tut ts

Thcse improve the

workebility

Stclrltcs

urc usually

used.

P ROTO D U R Flexible antl

lYiritg

Cables

Cables

with

PVC

insulation manufactured

by

Sie-mens arc

known

by

the trade name PROTODUR'

They can be laid without special precautions in

ambi-cnt

temperatures

above

_{-5'C. If}

the

cables are

colder than this, they must be carefully warmed

be-,

e installation. Flexible and wiring cables are

gener-ally

of

smaller diameter than porver cables' and are

therefore subject

to

lower stresses

in

installation. so that

with

careful handling they can be laid at lorver

.'

lperatures. For countries such as Norway. Srveden

or

Finland. PVC compounds are available which

af-ford

the necessary bending capability down

to

low

temperatures.

For

installations

with

especially stringent

require-ments as to burning behaviour, compounds for cables

have been _{developed which satisfy the bunched} cable

burning

_{test, Test Category}

_3,

_of

_DIN

VDE 0472,

Pari _{804, lead}

_to

_{a lower emission}

_of

_{smoke and} gas

and

do

not

release hydrogen chloride (see pages 79

and 125).

Pol-veth-'.'lene (PE)

-Polyethylenc is a macromolcculur hydrocarbon rvith

a

structurc

sirnilar

to

thut

of

thc

parat'fins

(tbr

thc

structural tbrnrula see page

l7).

This

matcrial. rvith its excellcnt dielcctric properties. is used

ls

an insulat-ing matcrial in porver cable enginecring in both

non-cross-linked (thermoplastic

PE)

and

cross-linked

(XLPE) form.

The

power cables produced

by

Sie-mens

with

thcrmoplastic polyethylene insulation are

knorvn by the protected

trlde

name

PROTOTHEN'Y

and those

with

cross-linked polyethelene insulation

by

the trade

name

PROTOTHEN-X.

Of

the

wide range of ty'pes of polyethelene offered by the chemical

industry,

only

specially prepared, purified and stabi' lized tlpes

rrc

uscd in cablc cngincering.

Because

both

thermoplastic

and

cross-linked

poil-ethelene

lre

sensitive

to

ionization dischargcs.

it

is

necessar-v-

ior

clbles

rvith

r:rtcd

voltages

from

L 6, L = 3.5 6

kV

upwards

to

incorporlre conducting

la-vers over and under the insulation. The inner lal er usually consists

ol

a weakly conducting

alkyl

copo' l1,mer. Various mcthods rvere tbrmerly used

to

pro-vide the outer conducting laYer:

>

grlphitizing

or conducting lacqucr

or

I

conduct-ing adhesivc rvith weakly conductconduct-ing tape applied

to

it:

tr

cxtruded conducting luyers. lvhich serc either ap-plied in a scparxte process or extruded in the sante

process

with

the insulation.

j I

t

i I !r 't :

r

' : I

I

Conducltng co[]pounds Conduclor Insulalinq compound

T

T

T

I

T

T

T

T

I

T

I I

I

1

-!-I

Fig.2.6

Schematic arrangement of triple extrusion

2Insulation

L

According

to the new

specifications of

DIN VDE

02731 .

.87,

only

outer

conducting layers extruded rvith and bonded

to

the insulation are per-mitted.

The

extruded conducting layers are

very

thin,

and

so

firmly

bonded

to

the insulation

that

they can be separated

from

it

only with a scraper'

In

some

coun-rries conducting layers are used whose adhesion is

somervhat lower, so that

-

if

necessary after scoring

rvith

a

tool

-

they can be stripped

by

hand (cables

rvith

strippable conducting layers). Because

of

the

force required in the stripping operation' such laycrs are made somewhat thicker.

To ensure operational reiiability in medium' and

high-voltage

porver cables.

it

is

particularly important'

apart

from

using high-purity material and observing

appropriate

cleanliness

in

the

nranulacturing

pro-cesscs. that thc insulation and the conducting layers

should be free

of

bubbles, and

that

therc should be

good adhesion bctwecn the conducting laycr and the

insulation. According

to DiN

VDE

0273

this

must be checked on every manufactured length by means

of an ionization test.

In

comparison

with

high

polymers

with

polarized structures, such as PVC. high polymcrs with unpolar-iscd structures, such as PE and

XLPE'

are

character-ized

by

outstanding electrical charactcristics. They

have, horvever, poor adhesion properties

in

relation

to

other

materials, e.g. moulding compounds. This characteristic has

to

be

takcn

into

account

in

the design of accessories.

For

the lorv-voltage range a polycthylenc insulation

compound has

been successfully developed which bonds

s'ell

to

accessory materials

and

thus ensures

the water-tightness of joints.

PROTOTHEN.Y

It

is

not

usual

to

use thermoplastic polyethylene

in

power

cables

for

lJolIJ=0.611

kV,

because

of

the

high

conductor temperatures

to

be expected under

short-circuit

conditions.

For

higber

rated voltages'

while

it

offers advantages

in

comparison

with

PVC

and

paper insulation because

of its

satisfactory

di-electdc properties,

it

has declined

in

significance as

power cable insulation, beceuse of its poor

heat/pres-iure

characteristics

(Fig.2.1),

in

comparison

with

cross-linked polyethylene, and has been omitted

from

the new specification VDE

DIN

0273/..87.

Cross-Linked Polyethylene (XLPE)

PROTOTHEN.X

The linear

chain molecules

of

the polyethylene are

knirted by the cross-linking

into

a three-dimensional network. There is thus obtained from the

thermoplas-tic

a material

uhich

at temperatures above the

crls-tallite mclting point

cxhibits elastomcric propcrties

By

this

mcans the dirnensional

stability

under heat

and the

mechanical properties are

improved As

it

result, conductor temperltures

up

to

90 oC can be

pcrmitted

in

normal opcralion

and up

to

250 "C under short-circuit conditio ns.

There are thrce

principal

methods

for

cross-linking

poll'cthylenc insulation matcrials :

Cross-linking bY Pcro.x idcs

Organic radical componcnts. in particular spccilic or-ganic pcroxidcs. are incorporated. Thesc dccomposc

at

temperaturcs above

thc

cxtruding

lemperaturc'

into

highly rcactive radicals. These radicals interlink

rhe

initially

isolated polymer chains

in

the

thermo-plastic

in

such

a

rvay

that

i]

spxce

netuork

results

(Fig. 2.7).

Formerly,

polyethylcne cable insulation 'o'as

cross-linkcd mainly

by

'continuous vulcanization

in

a

steam tube', in the so-called

CV!)method

(Fig.2.8)'

In

this methoti the polycthylcne. mixcd u

ith

the pcr-oxide as a cross-linking

initiator.

is pressed onto thc conductor. by means of an extruder, at about 130 "C

(below the temperature at rvhich the pcroxide dccom-poses).

Follouing

this.

in

the same process, the

insu-iated

core

is

passed

through

a

tube, about

125 m

long,

Iilled with

saturated steam

at

high

pressure'

At

a pressure

of

16

to

22 bar and

a

temperature ol

aboui

200

to

220

"C,

the

organic peroxide

decom-poses

into

reactive primary radicals, which effect the

cross-linking.

The crosslinking

process

is

followed immediately

by

a cooling stage. This must similarll take place under pressure

in

tubes 25

to

50

m

long' to

privent

the formation of bubbles in the wlcanizec

maierial through the

presence

of

gaseous products

of

the peroxide reaction'

An

alternatives

to

this

'classical' crossJinking pro cess, methods have been developed

in

which gase'

or

liquids, e.g. silicone

oil or

molten salrs (salt bath cross-linking) are used as media for the heat transfer

:

L

L

Ui

li

ll

ll

I

1

n

t0

I' _{Cv: continuouJ nrlcanisation}

Peroxide Primary radical

f".

?"'

R-?-o-o-f

_-R

CH,

CH.

cH.

t--R-9-9'

+

I CH" +

Lr|.

I

R-c-oH +

cH4 I CH.

-

cH2-CH2-cH2-cH2-

cHr-cHr-cHz-cHr--

cH2-cH

_a

-cHz-cH2-O

-

CHz-CH

-CH2-CH2-CH. o

cH.

t-R-C:O

Po

Barliial combination during

network formalion

Fig.2.7

Cross-linking

of

Polyethylene by organrc perortdcs

Cooling

l0ne

Tube length approx 125 m

I

t

-t

I

T

T

I

I

T

I

I

'f t

T

I Polymer radrcal I I

i

Cross linked Pol'Tethylene

+

I

+ unit

I."

-

cH,-tH-cH2-cH2--

cH2-cH-cH2-cH2

-lnterml enl drive unil

b

Tension conlrcl

tit

or

I

Y

I I

2Insulation

Compared

to

vulcanisalion

with

steam, these meth-ods

permit

crossJinking

at

higher temperatures and

lower pressures.

Cross-linking by Electron Beants

The polymer

chains

are crosslinked directly

by means

of

high-energy electron beams,

without

thc necessity

for

the heating stage which is essential

with

peroxides.

It

will

be clear

from

consideration

of

the reaction sequence in the cross-linking of polyethylene

by

electron

irradiation, as illustrated

in

simplified

form in

Fig.2.9,

that

in

this case also gaseous

reac-rion products are formed (mainly hydrogen).

Cross-linking

by

Siloxane Bridges

Polyolefines

can

also be cross-linked

by

means

of

siloxane bridges, u hcreby suitable alkoxysilancs are

radically grafted into the poll,mer chains. In the

pres-ence

of

moisture and a condcnsation catalt st.

hvdro-lysis takes place

to

form

silanol

groups,

which

then

condense

to

the

interlinking

siloxane bonds

(Fig. 2.10).

Because

the

grafted silane can contain

up

to

three reactive alkoxy groups, this offers the possibility that

bundled

linking

locations can be formed.

Although

as

regards

the

chemical structure

of

the

cross-linking bridges the cross-linked polymer matrix

appears

to

be quite different

from

those produced

by the methods previously described, a combination

of

characteristics is nevertheless obtaincd which es-sentially corresponds

to

that

of

the crosslinked PE

produced by the classical methods.

Like

all

polyolefines,

crosslinked

polyethylene is

subject

to a

time and tenrperature-dependent oxida-tive decomposition, and it. has to be protected against

this by

the

addition

of

anti-oxidants, so that

il

can

uithstand

continuous service

at

90

_"C

over

a

lonq period

of

time (see page 27).

Polyethylene

"-

CH

z-CHz-CH2-C

H,

-*CHz-CHz-CHr-CH.^^,

t

leo

I Y

-CHz-CH-CH2-CHr^

a

,

*cHz-cHz-cH2-cH.^,

J

lao

l-

_I Y

*

C

Hz-CH-CH2-CH.^,.,

a a

-,

CHz-CH-CH2-CH"-I Y

*

CH:-FH-CH2-CH,

^-I

^^,CHz-CH-CH2-CH"-,

Formation of polymer radicals

H.

+

H.*

l Eadical combination during nework lormarion

1)

Cross.linked Polyethylene Fig. 2.9 Cross-linking of Polyethylene by electron beams