Date: 10-12 September 2012 Venue: Shah Alam Convention · PDF file•Cable Constructions ... • 1926 Pressurised oil filled type for voltages upto 66 kv (Emanueli) ... (XLPE) insulation

Venue: Shah Alam Convention Centre

Date: 10-12 September 2012

Hosted by: Organized by:

Electric Cables, by design

Presented By

Lokman A. Dahlan

Technical Advisor

Organized by:


Contents

• Brief History on Cables

• Basic Design Principles

• Cable Constructions

• Common Design Options

• Cable Standards

• Tests on Cables

• Quality Assurance

• Special Topics


Brief History on Cables

• 1880 Gutta Percha used as insulation

followed by natural rubber & bitumen

• 1890 Paper insulation introduced (Ferranti)

• 1914 Screening developed to increase voltage levels upto 33kv (Hochstadter)

• 1926 Pressurised oil filled type for voltages upto

66 kv (Emanueli)

• 1930s PVC insulation introduced (Germany)

• 1933 BS 480 published for PILC type


Brief History on Cables (Cont.)

• 1943 First 132 kv oil pressured cable installed

• 1949 Introduction of mass-impregnated non-draining

compound for PILC cables

• 1950s PVC increased use for LV cables, thermosetting

(XLPE) insulation was under trials. Aluminium

conductors increasingly accepted as an economic

alternative to copper.

• 1954 First 275kv oil filled cable installed

• 1961 100kv DC link installed between France/England



• 1969 First 400kv oil filled cable installed • 1970 Metrication of British Standards • 1970s IEC 502 for extruded solid dielectric insulated cables upto 33kv was published. Thermosets, mainly XLPE were increasingly used upto 33kv. Trial installations were conducted for XLPE at higher transmission voltages. • 1980s Rapid development in process extrusion and cross-linking of polymerics



• 1990s XLPE widely used at LV/MV and increasingly

accepted at higher voltages.

Material type, cleanliness, handling and processing methods are becoming concerns of manufacturers & customers.

Qualification and test requirements are constantly reviewed to meet higher expectations for quality and reliability of supply.


What Cable ?

• Aerial, underground, submarine,

• AC, DC, distribution, transmission

• Aluminium, Copper

• PILC, PVC, XLPE, Bare

• LV, MV, HV, EHV, 11kV etc.

• Screened, Belted, Armoured


Design Requirements

• Satisfies power needs

• Flexible

• Reliable

• Has long life

• Minimal maintenance

• Economic


Basic Design Elements

• CONDUCTOR

- determines base current ratings

• INSULATION

- determines voltage / stress levels

• PROTECTION

- determines installation conditions


Conductor Metals

Metals VR @ 20oC

(.mm2/km)

Density

(gm/cm3)

Mass

(kg/km)

Price

(US$/kg)

Total

(US$/km)

Silver 16.4 10.5 172.2 169.6 29,205

Copper 17.2 8.89 152.9 1.667 254.9

Gold 24.4 19.3 470.9 8336 3,925,590

Aluminium 28.3 2.70 76.4 1.44 110

Tin 124.0 7.29 904.0 5.245 4741.5

Lead 214.0 11.4 2440 0.309 754


Aluminium & Copper Conductors

• Copper

– Highly Conductive

– Good Mechanical Properties

– Relatively Easy to Process

– Usually Annealed

• Aluminium

– 60% conductance of copper at same size

– Half the weight of copper at the same conductance


Insulation Types

• Common types

– PVC (Polyvinyl Chloride)

– PE (Polyethylene)

– XLPE (Cross linked PE)

– Rubber (EPR,EVA)

– PILC (Paper insulated Lead Covered)


Insulation Type - PVC

• PVC resins with plasticizers, stabilizers, fillers & additives

• Applied by extrusion process

• Continuous operation at 70oC

• Good dielectric & thermal properties

• Operable up to 3.3kV only


Insulation Type - XLPE

• Polyethylene resins with minor additives

• Applied by special chemically heat treated “vulcanized” extrusion process

• Continuous operation at 90oC

• Excellent dielectric, thermal and mechanical properties

• Widespread use at medium voltages

• Operable at EHV

• Sensitive to voids and moisture


Protection

• Cables need to be mechanically protected against external damage & installed environments

• PRIMARY – by the insulation

• SECONDARY

• double insulation and/or sheaths • armour or reinforcement when exposed to potential

damage (direct in ground) • barriers to prevent ingression of moisture, oils,

solvents etc.


Protection

• Cables need to be electrically protected against damage to adjacent cables, connecting equipment and for safety of users against electrical hazards

• PRIMARY – by the insulation & sheaths

• SECONDARY

- by conductive layer(s) for the safe transfer of leakage currents, to be appropriately sized to meet system ratings and/or suitable grounding or bonding methods against leakages, transients and lightning


Protection from Pest Attack

Method Features

Mixing termite repellent in surrounding earth

Environmental problem

Coating oversheath with termite repellent

Difficult to apply Health problem

Aldrin & Dieldrin Effective but use is however banned in many countries

Mixing termite repellent into cable sheaths Copper naphthanate,

Cypermethrin Alternative to Aldrin & Dieldrin, reasonably effective

Polyethylene Sheath Slows down attack

Common metal sheaths Slows down attack

Tape armour Good protection from large insects and rodents

Nylon Sheath Resistant to termites, but difficult to manufacture




SINGLE CORE XLPE CABLE (Foil Laminate)

Conductor Conductor

Screen

XLPE

Insulation Insulation

Screen Semi-conducting

Water swellable

tape

Copper Wire

Screen

Copper Equalising

Tape

Semi-con Water

Swellable Tape

Laminated Metal

Tape

Oversheath

THREE CORE XLPE CABLE (Lead Sheathed)

Conductor

Conductor

Screen

XLPE

Insulation

Insulation

Screen

Copper Tape

Screen

Binder Tape

Fillers

Separation

Sheath

Lead Sheath

Bedding

sheath

Armour Wires

Oversheath

Preferred for waterlogged

environments


Voltage rating LV MV HV

Application Home & indoor

Others (industrial, distribution & transmission)

Conductor

Copper Copper or Aluminium

Single or Multicores Single core

Circular Circular or

Sector Circular

Flexible or fixed

Fixed Class II

Conductor screen N/A Required

Insulation PVC, Rubber, XLPE XLPE

Colourable Natural

Insulation screen N/A Required

Metallic screen N/A Required

Moisture barrier N/A Optional Required

Fillers For Multicores N/A

Armour N/A Optional

Jacketing Optional Required

Cable Constructions


Cable Construction

• Conductors

– Copper conductors are commonly used for home & light industrial applications

– Aluminium conductors are optionally used by utilities for distribution & transmission

– BS 6360/IEC 60228 of varying Class depending on usage

– Single wire “solid” type for small conductors or Stranded Class 5 for flexible installations

– Stranded Class II for fixed installations

– Sector shaped for LV 50-500sqmm multi-cores

– Circular stranded can be compacted

– Circular segmental for 1000sqmm and above


Cable Construction

• Conductor Screen (MV/HV)

– semi-conductive

– thermosetting

– extruded type only

– thickness not normally specified


Cable Construction

• PVC & LV XLPE Insulation – thickness as stipulated in standards – Consistent in thickness and finish – Colourable

• MV/HV XLPE Insulation – thickness stipulated in standards, specified by

customer or proven design – Natural and clean – triple extruded with adjacent screens (one step

preferred) – handling and processing more critical at higher

voltages


Cable Construction

• Insulation Screen (MV/HV)

– semi-conductive

– thermosetting

– extruded types (thermosetting) preferred

– thickness not normally specified

– strippable for MV cables only


Cable Construction - XLPE

• Metallic Screen (MV/HV)

– applied immediately over or in electrical

contact with insulation screen

– non-corrosive metals preferred, in the form of (copper) tapes, wires or (lead) sheath

– can be sized accordingly to meet specified

earth fault rating



• Fillers (For Multicores)

– applied when combining individual cores together to fill interstices between cores

– suitable materials in the form of strings, twines, pre-formed or extruded fillers

– completely removable

– overall binder tape applied to maintain circular construction (except extruded type)



• Bedding (For Armoured Cable)

– also known as inner or separation sheath

– usually extruded (PVC or Pe)

– tapes may be applied instead of or in addition to extruded sheath

– thickness as specified or calculated from Standards



• Armour

– for multicores, a layer of steel wire or double layer of steel tape normally applied

– galvanised steel to reduce corrosion

– for single core cables, non-magnetic materials applied (i.e. aluminium)

– wire armour can provide additional path for short circuit currents

– armour dimensions specified by standards


Cable Construction

• Outer Covering(s)

– also known as over/outer sheath or Jacket

– extruded sheath or compounded fibrous tapes or twines

– preferably black for extruded sheaths

– thickness specified in standards or higher

– may consists of several layers for multiple functions


Common Design Options

- Swellable yarns, compounds, powders applied

strategically in conductor for water blocking

- Semi-con tapes applied over conductor, in

addition to extruded screen

- Extruded metallic sheath (preferred) or foil

laminate applied as radial moisture barrier

- Swellable tapes applied between extruded layers

as transverse (longitudinal) moisture barrier


Common Design Options

– Double layer of wire armour for additional protection (e.g. submarine type)

– Application of tinned copper wires between

wire armour to increase fault rating

– Anti - Termite protection using additives, steel

armour tapes, brass tapes, nylon sheath

– Conductive (graphite) layer applied on oversheath for periodic sheath integrity test

– Fire or Flame retardant tapes or sheaths


Property PVC Polyethylene LSOH

Tensile (N/sqmm) 15 25 10

Elongation 150% 300% 100%

Density 1.3 - 1.5 0.91 - 0.96 1.4 - 1.6

Physical Soft and flexible Hard and rigid Semi-hard and rigid

Abrasion Resistance Poor Excellent Acceptable

Hot indentation Acceptable Excellent Good

Impact Resistance (thick slab) Good Poor Poor

Stress cracking Resistant Variable (dependent on

molecular weight i.e.

density)

Variable (dependent on base

compound and mix)

Moisture Absorbs moisture with

prolonged contact

Negligible absorption Absorbs and retains moisture

within a short time

Vapour permeability Reasonably permeable Resistant Permeable

High temp. performance Increased ageing at higher

temps.

Improved thermal & ageing

performance

Generally stable

Low temp. performance Brittle at sub zero Stable at sub zero Generally stable

Resistance to chemicals Good Excellent Poor

Fire Performance Flame retardant, emits toxic

fumes & smoke

Low OI, burns without

toxic fumes

Flame retardant, low smoke &

no toxic fumes

Processability Readily extrudable Extrudable Extrudable with special tools

Compound Compounded with

additives and fillers

Homogeneous Highly filled base compound

with additives and fillers

InstallationConditions :

Direct in Ground - Dry Excellent Excellent Good

Direct in Ground - Wet Good (short term only) Excellent Not Recommended

Exposure to UV light Resistant Good (require UV resistant

additives)

Variable (dependent on base

compound and mix)


Cable Standards

International

• IEC 60227, IEC 60502, IEC 60840

National

• MS, BS, AS/NZS, JIS, VDE

Associations

• AEIC, ASTM, UL, EEMUA


Cable Standards - International

• IEC 60227 Polyvinyl Chloride insulated cables 450/750V

• IEC 60502 Cables with extruded insulation 1-33kV

• IEC 60055 Paper Insulated 1-33kV • IEC 60840 Tests for cables with extruded

insulation >33 - 150kV • IEC 60811 Common test methods for

cable insulation and sheaths • IEC 60287 Calculation of Current Rating


Cable Standards - National

• BS 6480 Paper Insulated 1-33kV

• BS 5467 Polymeric cables 1-3.3kV

• BS 6622 Polymeric cables 6.6-33kV

• AS 1429-1 Polymeric cables 3.3-33kV

• AS 1429-2 Polymeric cables >33-132kV

• VDE 0272 XLPE cables 1kV

• VDE 0273 XLPE cables 10-30kV


Cable Standards by Associations

• AEIC CS5 XLPE cables 5-46kV

• AEIC CS7 XLPE cables 69-138kV

• ICEA S66-524 XLPE cables for transmission & distribution of energy

• IEEE 575 Application & Calculation for sheath bonding methods

• ESI 09-16 Test Methods for XLPE cables 66-132kV


Publications & Reports

• Neher/McGrath Calculation of load capabilities of cable systems

• ERA 69-30 Current ratings to BS 6480

• CIGRE (1986) Transients & Cyclic Loads

• BICC C55/4 Engineering Recommendation for Insulated Sheath Systems


wire drawing

WD1, WD2,

WD3

Stranding

ST1,ST2,ST3,

ST4

XLPE

insulation

TM2,CV1,CV2

Curing/

degassing

Core screen

SC1,SC2,LP5

Lay up

LU1,LU2,LU3

Bedding

QX1,QX2,QX3

Armouring

AR1,AR3,AR4,

AR5

Sheathing

QX1,QX2,QX3

Testing

XT1,XT2

Delivery

RL1,RL2

Lead sheath

LS1,LS2

drawing of aluminum/copper

wire rod to smaller diameter

twisting of wires together and the

formation of a compact strand

conductor

screen,insulation core

screen

the crosslinking of the product using

heat and moisture. to provide

mechanical strength and resistance to

high temperature

copper tape,

copper wires

to screen individual cores and improve

electrical performance

fillers, tapes2 or more cores twisted together to form

a circular cable

PE, PVCapplied for cables used

in oil and gas industry

steel, aluminum wires,

steel tapes

covering of the cable which provide

some electrical protection

PE, PVC

partial

discharge,

resistance

final covering for further protection

cable

inspection

FLOW CHART FOR MANUFACTURE OF XLPE CABLES


Cable Tests & Inspection

• ROUTINE TESTS - final inspection on all completed cables according to standards

• SAMPLE TESTS - special tests on selected samples as required by customer

• TYPE TESTS - comprehensive test regime on a cable type to demonstrate the ability of manufacturer to meet the requirements


Routine Tests – Conductor Resistance

• Confirm (electrical) size of conductor

• Accurate measurement by a suitable resistance bridge, corrected to 20oC

• Corrected measurement per kilometre shall not exceed the maximum ohm/km value in the standard for conductor type and size


Routine Tests – Voltage Withstand

• Determine ability of cable insulation to withstand a fixed voltage of higher rating.

• Upto 33kv : 3.5 Uo for 5 minutes

• Above 33kv : 2.5 Uo for 30 minutes

• Pass criteria: No breakdown of insulation


Routine Tests – MV/HV Partial Discharge

• Detection of discharges caused by “defects” in the cable insulation at a fixed voltage level

• Upto 33kV : 1.73 Uo

• Above 33kv : 1.5 Uo

• Pass criteria : 10 pC maximum


Sample Tests

• Hot set test (XLPE)

• Thickness and Diameters

• Overall construction

• Capacitance

• DC sheath test (graphited sheaths)

• Bending test

• Flame retardant test

• Water penetration test (water-blocked designs)


Special Sample Tests

• Material Tests

– Tensile and elongation

– Ageing test (insulation and sheaths)

– Galvanising tests (zinc coating, adhesion)

– Oxygen index (PVC and special sheaths)

– Shrinkage tests (PE)


Type Tests – Electrical (MV/HV)

• Partial discharge

• Bending & partial discharge

• Tan delta measurement

• Heat cycle test

• Impulse (lightning) test

• 4hr Voltage withstand


Type Tests – Non-Electrical

• Dimensional checks

• Mechanical test

• Ageing test

• Compatibility test

• Special properties (hot set, screen resistivity, strippability, heat shock, loss of mass, shrinkage etc.)

• Flame propagation, water penetration test (as designed)


Type Tests - definition

• “Tests made before supplying on a general commercial basis, a type of cable covered by this standard, in order to demonstrate satisfactory performance characteristics to meet the intended application. NOTE. These tests are of such a nature that, after they have been made, they need not be repeated, unless changes are made in the cable materials or design or manufacturing process which might change the

performance characteristics.” (IEC 60502-2 : 2005 Clause 3.2.3)


Quality Assurance

• Verification on design & construction

• In-coming material tests

• In-process control & inspection

• Final tests & inspection

• Documented system

• Internal quality audit

• External Registrar or Customer Audits


Special Topics

• Short circuit ratings

• Water-treeing in cables

• Moisture barrier

• Conductor ratings (ampacity)


Short Circuit Ratings

• Symmetrical faults

– On phase conductors

– Determined by conductor size and temperature rating of insulation

• Asymmetrical faults

– On external metallic coverings

– Dependant on effective area of metallic coverings and their respective temperature limits


Short Circuit Ratings - Asymmetrical

• Copper Tape (not for high currents)

• Copper Wires

• Lead Sheath

• Aluminium Sheath

• Armour Wires

– Unreliable in the event of corrosion

In the event of a fault a low resistance return path

to earth is required.


Critical Issues for HV XLPE Cables

• “SuperClean” insulation

• High grade bonded screens

• Special extrusion control

• Strict material handling methods

• Moisture barrier is essential

• Well proven construction


Water Treeing in Cables

• Formation of “tree-like” structures in polyolefins such as PE and XLPE.

• Reduces the breakdown strength of insulation resulting in “electrical trees”

• Degrades with time, electrical stress, frequency and water pressure

• “Bow ties” within insulation due to voids and contaminants

• “Vented trees” from screen interface protrusions and imperfections


Water Treeing - Structures


“Vented Tree”


Moisture Barrier - Radial

• Extruded Lead Sheath (preferred)

• Extruded Aluminium Sheath

• Metallic Foil Laminate (most economical but least effective)

A radial moisture barrier is required to prevent

the initial ingress of moisture into the cable


Moisture Barrier - Longitudinal

• Using tapes and yarns loaded with swellable material or “solid” compounds

• Strategically positioned underneath and between extruded layers, within metal screens, armour or conductor

In the event of damage to the radial moisture barrier

longitudinal water blocking is essential


Cable Current Ratings

• Temperature

• Cable Design

• Installation Conditions

• Neighbouring Cables

Important factors affecting ratings


Circuit Analogy – Heat Transfer

Temperature Difference

Conductor

Insulation

Metal Sheath

Armour

Bedding Protective Finish

Soil

Cable Surface

Ground Surface


Current Rating Calculations

• Base calculations to IEC 60287 Series

• Including other applicable guidelines & publications i.e. CIGRE reports, papers by Neher/McGrath, Jackson etc.

• Calculation programs available from cable companies or external sources

Documents

Date: 10-12 September 2012 Venue: Shah Alam Convention · PDF file•Cable Constructions ... • 1926 Pressurised oil filled type for voltages upto 66 kv (Emanueli) ... (XLPE) insulation