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PowerCableHANDBOOK

2011 Edition

Harmonisation of Power DistributionSystems in the Lower Mekong Subregion


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Copyright 2010

International Copper Association Southeast Asia Ltd

All rights reserved. No part of this publication may be reproduced or distributed in any form or by any means, or stored

in a database or retrieval system, without the prior written permission of the publisher.

Printed in Singapore

Underground Power Cable

HANDBOOK


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Foreword

Overhead power lines, a familiar sight in many old cities, are slowly disappearing from city skylines. Anoticeable trend towards underground power cabling is gathering momentum around the world. And

nowhere else is this more evident than in Asia. City after city, professionals involved in city planning

and development, from planners and architects to consultants and engineers, are deciding in favour of

underground power distribution, realising the immense benefits that it offers.

Underground power cable systems offer far reaching benefits. Not only do these systems dramatically

improve the skyline of a city, they also result in better environment, lower power distribution costs,higher reliability and greater protection against hazards associated with overhead power lines. This

trend is a significant development especially for countries in the Lower Mekong Subregion (LMS)

and for the copper industry. Copper cables, due to much higher conductivity and other properties, are

better suited for underground applications. This means reliability and quality of power supply, critical

factors in reducing technical losses in the electricity grids of Utilities in the LMS.

In deciding on the choice of conductor for an underground cabling system, Utilities have to consider

the basic properties of the conductor material - electrical resistivity, tensile strength, melting point and

coefficient of thermal expansion. Other factors to consider include:

Space

Underground cabling puts pressure to keep space requirements for trenches or ducts to the minimum.

Conductivity, resistance and losses of the conductor in relation to its diameter will therefore determine

its space efficiency. Allowable space must also be provided for thermal expansion of the conductor.

Current Carrying Capacity

The higher the conductivity of the material, the higher is the current rating for the same overall

diameter of the conductor.

Ruggedness

Deterioration at cable joints and risk of mechanical damage can be minimised by the hardness of the

conductor material. Its resistance to corrosion can protect joints against water penetration. And


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functional problems due to heating and developing hot spots will be less prone in conductors with the

heating ability to withstand overloads/surges.

Studies and experiences of Utilities have shown that transformers and power cables are the two largest

loss makers in the electricity grid. So, much can be done in these two areas to help reduce significantlosses in the LMS power distribution systems.

I am therefore pleased to note that the development of this underground power cable handbook is a

progression of the power and distribution transformer handbooks. The development and harmonisation

of technical specifications for transformers as well as power cables, in relation to international

standards and best practices, can help to narrow the differences and gaps for LMS Utilities to work

towards further reducing losses in their electricity grids.

Development of handbooks is only an academic exercise. Reduction will only come when the

guidelines and recommendations are followed and implemented by all associated with the design of

the electricity grid, specifying the standards of equipment for procurement and subsequently operating

or maintaining them.

Victor ZhouDirector - China & Southeast Asia

ICA Asia


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Introduction

The Lower Mekong Subregion (LMS)Harmonisation Programme

Being developing countries, their power distribution systems, an essential infrastructure, play a

significant role in the economic development. Energy end-users are dependent on the availability,

reliability, and quality of electricity from the power distribution systems. The level of development

and advancement of power distribution systems has direct impact on the developmental potential and

economic growth, especially in urban cities.

The power distribution systems in the urban areas of these LMS countries, however, do not have the

same level of development. It is widely acknowledged that harmonisation in the development of power

distribution systems can benefit these countries and accelerate their economic growth.

In 2005, six power partners entered into a Memorandum of Understanding (MOU) to share the intent

of working together towards harmonisation of power distribution systems in the following four LMS

countries: Cambodia, Lao PDR, Thailand and Vietnam. The founding partners are:

Electricit du Cambodge (EDC), Cambodia

Electricit du Laos (EDL), Lao PDR

Ho Chi Minh City Power Company (HCMC PC), Vietnam

Hanoi Power Company (HNPC), Vietnam

Metropolitan Electricity Authority (MEA), Thailand

International Copper Association Southeast Asia (ICASEA) [formerly known as Copper

Development Centre Southeast Asia]

Cambodia, Lao Peoples Democratic Republic (Lao PDR), Thailand and

Vietnam have achieved different levels of economic development. These

countries in the Lower Mekong Subregion (LMS) have strong economic

inter-dependence.


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This led to a study of power distribution systems of the power partners in Cambodia, Lao PDR and

Vietnam; and the preparation of a regional cooperation roadmap and action plan.

Building on the success of the first MOU, ICASEA and MEA inked a second MOU to continue their

strategic partnership in conducting further studies and facilitating programmes as outlined in phase 2of the road map and action plan. This impetus is to enable the LMS countries to make further progress

towards harmonisation and the realisation of the objectives as set out in the MOU with all the power

partners.

The study of power distribution systems in the LMS countries under the first MOU had revealed that

there are many differences in the power distribution systems in this region. The objective of this

second MOU was to narrow down the differences in six key areas and enable the LMS countries tomove towards greater harmonization of their power distribution systems.

Joining this Harmonisation Programme in 2009 were:

Danang Power Company (DNPC), Vietnam

HaiPhong Power Company (HPPC), Vietnam

And in 2010,

Provincial Electricity Authority (PEA), Thailand

Central Power Corporation (EVNCPC), Vietnam


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Loss in the Power Distribution System is a common and pressing concern

expressed by Utilities in the LMS. Reducing loss is the priority given

the energy shortage arising from rapid economic growth and high oil

prices.

A Regional Loss Reduction Workshop for LMS Utilities was held in Phnom Penh, Cambodia on 18 &

19 March 2008. It concluded with a consensus to, amongst other areas of collaboration, reduce lossesin the Power Distribution Systems of EDC, EDL, HCMC PC and HNPC by harmonising technical

specifications and developing a best practices handbook for energy efficient equipment based on

international standards.

The views of and input from participating Utilities were crucial in the development of technical

specifications for the harmonisation of power equipment in the LMS. Only with acceptance and

implementation of the technical specifications can LMS Utilities reduce losses associated with

inefficient power equipment. Hence, a 6-member Technical Working Group (TWG) comprising a

senior technical representative from each Utility and ICASEA was formed to participate and contribute

in discussions and meetings.

The objective of this TWG was to start with the development of technical specifications to harmonise

underground power cables in the LMS. This step-by-step approach was to enable the participating

Utilities to review and evaluate the result of this Technical Working Group before collectively moving

to the next step of harmonising other equipment.

This handbook was developed to help LMS Utilities implement low loss power cables. Reduction will

only come when the minimum performance guidelines are followed and implemented by all associated

with the design of the electricity grid, specifying the standards of equipment for procurement and

subsequently operating or maintaining them.

Preface


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Chairman

Mr.Asawin Rajakrom

Director, Electrical Equipment and UG CableInstallation Division

Metropolitan Electricity Authority, Thailand

Electricite Du Cambodge (EDC), Cambodia

Mr. Lim Sisophuon

Deputy Chief, Dispatching Control Centre

Electricite Du Laos (EDL), Lao PeoplesDemocratic Republic

Mr.Bounkheuth Vilayhak

Deputy Chief, Technical Standards Office

Ho Chi Minh City Power Corporation

(HCMC PC), Vietnam

Mr.Nguyen Huu Vinh

Electrical Engineer, Technical Department

Hanoi Power Corporation (HNPC), Vietnam

Mr.Dinh Tien Dung

Expert, Technical Department

Metropolitan Electricity Authority (MEA),

Thailand

Mr. Werawat Buathong

Director, Electrical Engineering Division

Mr. Somchai Homklinkaew

Asst Director, Power System Planning Division

Mr.Preecha Tongkaewkerd

Senior Electrical Engineer, Power System

Planning Division

Ms. Sasianong VacharasikornSenior Electrical Engineer, Research and

Development Dept.

International Copper Association Southeast

Asia (ICASEA)

Mr. Louis Koh

Project Leader, Power Distribution

Mr. Piyadith Lamaisathien

Country Manager, Thailand

MEA Project Support Team

Ms. Sutida Sindhvananda, Project Director,

International Service Business

Ms. Kunlathida Pongchavee, Executive Project

Assistant, International Service Business

Mr. Prawit Chaikaew, Electrical Engineer,

International Service Business

Members of the Technical Working Group for Power Cable:


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Electricit du Cambodge, Cambodia

Mr. Keo Rottanak,Managing Director

Mr. Chan Sodavath,Deputy Managing Director

Electricit du Laos, Lao Peoples Democratic

Republic

Mr. Khammany Inthirath,Managing Director

Mr. Sisavath Thiravong,Deputy Managing

Director

Mr. Boun Oum Syvanpheng,Deputy Managing

Director

Ho Chi Minh City Power Corporation, Vietnam

Mr. Le Van Phuoc,Director

Mr. Tran Khiem Tuan,Deputy Director

Hanoi Power Company, Vietnam

Mr. Tran Duc Hung,Director

Mr. Vu Quang Hung, Vice Director, Technical

Mr. Nguyen Anh Tuan, Vice Director, Business

Metropolitan Electricity Authority, Thailand

Mr. Pornthape Thunyapongchai,Governor

Mr. Danai Chitterapharb,Director, Business

Investment Dept.

International Copper Association Southeast

Asia

Mr. Steven Sim, Chief Executive Officer

Acknowledgements

The harmonisation of power distribution systems in the LMS will

contribute to the expansion of the ASEAN Power Grid. However,

harmonisation requires a robust partnership and sustained effort over

many years.

The harmonisation of technical specifications together with the development of this handbook is

taking the process a step closer towards the realisation of the objectives as set out in the strategicroadmap for the harmonisation of power distribution systems in the LMS.

Strengthening regional cooperation to build the capacity of both technical and functional staff would

not have been possible without the endorsement and support of:


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Table of Contents

Introduction 1

Chapter 1 1

1.1 Introduction 1

1.2 Objective 1

1.3 General Requirements

1.4 Principle Specifications 5

1.5 Existing Requirement for Electricite du Cambodge (EDC), Cambodia 10

1.6 Existing Requirement for Electricite du Laos (EDL), Lao Peoples Democratic Republic 11

1.7 Existing Requirement for Ho Chi Minh City Power Corporation (HCMCPC), Vietnam. 11

1.8 Existing Requirement for Hanoi Power Corporation (HNPC) Vietnam 13

1.9 Additional Requirement for Metropolitan Electricity Authority (MEA), Thailand 14

1.10 Conclusion 16

Chapter2 17

2.1 Introduction 17

2.2 Objective 17

2.3 Documents required for evaluation 17

2.4 Guideline for bid evaluation 22

2.5 Conclusion 24

Chapter 3 25

3.1 Introduction 25

3.2 Objective 25

3.3 Inspection Committee Management 25

3.4 Manufacturing Process Inspection 26

3.5 Factory acceptance tests 29

3.6 Conclusion 32


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Chapter 4 34

4.1 Introduction 34

4.2 Objective 34

4.3 Acceptance Committee Management 34

4.4 Acceptance Process 35

4.5 Conclusion 39

Chapter 5 40

5.1 Introduction 40

5.2 Objective 40

5.3 Ampacity Calculation 405.4 Insulation and Sheath Thickness Calculation 55

5.5 Calculation on Cable Pulling Tension 58

5.6 Conclusion 71

Chapter 6 72

6.1 Introduction 72

6.2 Objective 72

6.3 Types of installation 72

6.4 Cable Laying Procedure 79

6.5 Installation Acceptance Process 88

6.6 Conclusion 89

Chapter 7 90

7.1 Introduction 90

7.2 Objective 90

7.3 Maintenance and Inspection 91

7.4 Field Tests on Cable 98

7.5 Cable Monitoring System 106

7.6 Conclusion 107


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References 108

APPENDIX A : Specification of 8.7/15 kV & 12/20 kV XLPE COPPER CABLE A-1

APPENDIX B : Specification of 69 & 115 kV XLPE COPPER CABLE B-1

Figures

Figure 1 : Cross-section of 69 & 115 kV PE Outer Sheath (Jacket) 10

Figure 2 : Cross-section of 69 & 115 kV PE Outer Sheath (Jacket) 15

Figure 3 : Cross-section of 69 & 115 kV Fire Retardant PVC Outer Sheath (Jacket) 16

Figure 4 : Cable Drawing 21

Figure 5 : Schematic diagram of Extrusion Line 28

Figure 6 : The geometric factor (G) and the Screening Factor 50Figure 7 : Mutual Heating Effect 52

Figure 8 : Direct Burial Installation 73

Figure 9 : Semi-Direct Burial Installation 74

Figure 10 : Concrete Trough Installation 74

Figure 11 : Concrete Encased Installation 75

Figure 12 : Concrete Trench 76

Figure 13 : Horizontal Directional Drilling Construction Layout Crossing the River 77

Figure 14 : Cross Section of Concrete Pipe ID 1 m 78

Figure 15 : Pulling Eye 80

Figure 16 : Pulling Grips 80

Figure 17 : Direct Burial Cable Laying Procedure 82

Figure 18 : Cable Laying for Direct Burial 82

Figure 19 : Cable Laying Procedure for Duct Installation 83

Figure 20 : Test Rod or Dummy 84

Figure 21 : CCTV Camera for Checking Duct 84

Figure 22 : Checking Duct by Using CCTV Camera 84

Figure 23 : Method of Cable Pulling 84

Figure 24 : Cable Laying Procedure for Tunnel Installation 86

Figure 25 : Floor Mounting Rollers 87

Figure 26 : Cable Installation in Tunnel by Caterpillar Method 87

Figure 27 : Megger Test1 kV 88


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Figure 28 : Insulation Testing 88

Figure 29: Murray Loop Bridge Method 95

Figure 30: Cable Fault Waveform Reflections 96

Figure 31 : Tan Test Results (K. Brown IEEE ICC Minutes Spring 2005) 104

Tables

Table 1 : Major characteristics of underground cable 5

Table 2 : Nominal diameters of round armor wires 12

Table 3 : Nominal thickness of armor tapes 12

Table 4: Sample of Proposed Technical Data for High Voltage XLPE Copper Cable 20

Table 5 : Partial Discharge Test 30Table 6: Voltage Test 30

Table 7 : Routine and Special Tests Report 37

Table 8 : Acceptance Tests Report 38

Table 9 : Conductor AC Resistance 43

Table 10 : Dielectric losses of insulation 43

Table 11 : Sheath Resistance of each material 44

Table 12 : Thermal Resistances of each material 49

Table 13 : Nominal Thickness of PVC/B Insulation for Cable Rated Voltages 55

Table 14 : Nominal Thickness of Cross-lined Polyethylene (XLPE) Insulation 55

for Cable Rated Voltages

Table 15 : Nominal Thickness of Ethylene Propylene Rubber (EPR) and Hard 56

Ethylene Propylene Rubber (EPR) Insulation for Cable Rated Voltages

from 6 kV (Um

= 7.2 kV) to 30 kV (Um

= 36 kV)

Table 16 : Maximum Cable Cross-sectional Area as a Percentage of Internal 58

Conduit or Duct Area (Refer to NEC)

Table 17 : Minimum Recommended Bending Radii for Unarmored Power Cables 60

for Cables Rated

Table 18 : Cable Configurations in Conduit 61

Table 19 : Recommended Basic Dynamic Coefficient of Friction, Straight Pulls 63

& Bearing Pressures

Table 20 : Recommended Maximum Pulling Tensions at Pulling Eyes 64

Table 21: Recommended Maximum Pulling Tensions Copper and Aluminum 65

Conductor Single


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Table 22 : Definition of symbols 68

Table 23: Comparison of Different Methods of UG Cable Installation 79

Table 24: Value of Direct Voltage for Jacket Test 88

Table 25 : DC Test Voltage according to IEC 60502-2005 99

Table 26 : AC Test Voltage according to IEC 60840-2004 101

Table 27 : VLF Test Voltage according to IEEE 400.3-2006 102

Table 28: Summary of Different Tests 106

Table 29 : Methods for Monitoring Underground Cable System 107


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Introduction

This is the first ever handbook on underground cables. The objective of this handbook is to serve as

a desk and field compendium for the utilities of Lower Mekong Sub-region (LMS) countries. These

utilities are Electricite du Cambodge (EDC), Cambodia; Electricite du Laos (EDL), Lao Peoples

Democratic Republic; Hanoi Power Corporation (HNPC); Ho Chi Minh City Power Corporation

(HCMCPC), Vietnam; and the Metropolitan Electricity Authority (MEA), Thailand.

This handbook describes all the important processes -- from procurement to final acceptance --

involved in an underground power cable project. These processes include preparation of specifications,

bidding evaluation, cable manufacturing inspection, contract acceptance, calculations on cable, cable

installation, cable system operation, maintenance and testing.

The handbook refers to the reputable reference books, the latest editions of international and national

standards, and the current specifications of LMS utilities. Specifically, it covers underground cables

with voltage rating from 22 kV (minimum) to 115 kV (maximum) and frequency rating of 50 Hz.

The study of power distribution systems in the LMS countries reveals that there are many differences

in underground cable system practice, hence, to promote the harmonization of the LMS practice, the

common specification for underground cable of the LMS utilities shall be developed for concrete

implementation in the future. The normative technical specification of underground power cable is

then proposed in Appendices A and B for optional application in the LMS underground system.


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Chapter 1

Preparation of National Normative Technical Specification ofUnderground Copper Cable

1.1 Introduction

Underground power cables have different electrical characteristics from overhead lines. These

differences must be taken into consideration during cable system planning, design and operation.

This chapter describes some of the most important requirements that should be considered by utilities

while preparing specifications of underground cables.

1.2 Objective

The objective is to provide general information on how to select, design, install and maintain a cable

system effectively. And also to help cable engineers reduce cost, which tends to increase due to

ineffective use and maintenance of underground cable. The information provided should also enable

utilities to minimize the need for new investments, learn about loss reduction programs and minimize

negative environmental impact.

The secondary objectives include encouraging greater energy efficiency; developing new national

standards; starting cost effective energy saving programs for both utilities and customers; reducing

losses from utility-owned underground cables; and minimizing life cycle costs. Eventually,

these programs would increase system capacity and decrease the cost of investment in constructing

new distribution substations.

1.3 General Requirements

This specification is for power utility companies in the Lower Mekong Sub-region (LMS). An

underground cable shall be installed in a cable tray or in a duct under the ground and also by direct

burial where fault level is up to 25 kA for MV system and 40 kA for HV system.

Site and Service Condition: LMS utilities operate in a tropical climate. The altitude ranges from 0

meter to 1,800 meters above sea level, ambient temperature ranges from 30C to 45C and relative


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humidity measures 84%. The cable shall be suitable for continuous use at conductor temperature of

90C for normal operation and 250C for short-circuit condition.

Reference Standard:The International Electrotechnical Commission (IEC) is the common

reference standard for all LMS utilities as well as for a majority of countries around the world. ForMV underground cables, IEC 60502 series is the key reference. IEC 60840 is the reference for HV

underground cable, and IEC 60228 serves as the reference for conductor. For fire retardant cables, IEC

60332 and ISO 4589 shall be applied. Some utilities also refer to their own national standards, which

are mostly equivalent to IEC except for some addition requirements due to their specific experience

and local conditions.

Test, Inspection and Test Report:There will be three main tests:

Type test: The proposed cable should successfully pass all the type or design tests in accordance with

the reference standards.

In case the fire retardant jacket is required, the following tests shall be included:

The oxygen index of non-metallic sheath material shall be not less than 30 according to ISO

4589 or equivalent.

Testing on completed cable under fire condition according to IEC 60332-3-22 or equivalent.

The testing shall be done by a reputable independent testing agency or an agency acceptable to LMS

utilities.

Cable manufacturers who do not have a type test report for the proposed cable shall alternatively

submit a type test report within the range of type approval as specified in IEC standard.

Routine tests: Routine tests shall be made on each reel of the finished cables in accordance with the

reference standards. At minimum, the following tests shall be included:

a) Measurement of electrical resistance of conductors

b) Partial discharge test

c) High voltage test

Special tests: The special tests shall be made on one length from each manufactured lot of the cables

of the same type and size. But these tests shall be limited to not more than 10% of the number of cable


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lengths in the contract, rounded to the upper unity. Special tests, conducted in accordance with the

reference standards, will at least include the following items:

a) Conductor examination

b) Checking of dimensions including measurement of external diameter c) Electrical test

d) Hot set test for XLPE insulation

Special and routine tests shall be carried out to determine whether the cable complies with the

specifications. For any additional tests required as per the mutual agreement between the purchaser

and the manufacturer, the test method shall be proposed by the manufacturer and approved by the

purchaser before proceeding with the testing.

Type tests help to validate design, raw material, workmanship and quality control during the

manufacturing process. Routine tests, as the name implies, are tests that are routinely performed on

each drum of cable to assure that cables are good quality and made according to required specification

before it leaves the factory. The utility reserves the right to send representatives to witness all

the required tests at the factory.

Routine and Special Test Report: Prior to shipment, the supplier shall submit to the utility six (6)

complete and certified sets of all test reports. The test reports shall include all the data required for

their complete interpretation, e.g., diagrams, methods, instruments, constants and values used in the

tests and the results obtained.

Drawings and Instruction: The supplier shall furnish six (6) sets of documents covering all

the significant details of the underground cable to the utility for approval within a stipulated

timeframe.

To protect mutual interest in cases of delayed or late submission, compensation terms shall be

specified in the contract. Special installation instructions and precautions, characteristic curves,

installation instructions and instruction manuals with the contract number marked thereon -

in the metric system - shall be machine printed or typed and delivered prior with the first

shipment.

Rating and Features:The major characteristics of the underground cable must be properly specified,

such as shown in the following table:


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Type Solid Extruded Dielectric

System voltage level (kV)(MV) 15, 22, 24, 35 kV

(HV) 69, 110, 115 kV

U /U (kV)

(MV) 12.7/22, 12/20, 21/35 kV

(HV) 36, 64 kV

Frequency ( Hz ) 50

Conductor Size (sq.mm.)(MV) 70, 150, 240, 400

(HV) 400, 800, 1000, 1200

Insulation XLPE

Metallic Screen COPPER WIRE

Non Metallic Outer Sheath PVC or PE or fire retardant PVCOperating Temperature (C) 90

Table 1 : Major characteristics of underground cable

1.4 Principle Specifications

The following specifications apply to underground cables for LMS utilities.

1.4.1 Medium Voltage (MV) Cable

The MV underground cable shall be extruded-dielectric XLPE type manufactured by dry

curing process only. The cables shall be installed direct burial, in ducts, trays. The requirement

of each layer shall be as follows.

Conductor:The conductor type shall be plain annealed copper and the construction shall be

compact round concentric lay stranded.

Conductor Screen:The conductor screen is a conducting material by the triple extrusion

with the insulation over the surface of the conductor. The thickness of the conductor screen

for each utility shall be between 0.0635 and 1.0 mm. The extruded conductor screen shall have

resistivity in accordance with the reference standards.

Semi-conductive tape may be applied between conductor and conductor screen.

Insulation:The insulation shall be cross-linked polyethylene (XLPE) and simultaneously

extruded with the semi-conductive conductor screen and insulation screen layer. Electrical,


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mechanical, and other properties shall comply with IEC 60502-2 or equivalent.

The dry curing process is required. Conventional steam or hot water curing processes are

not acceptable.

The average thickness of insulation shall not be less than the nominal value specified in the

reference standards. The minimum thickness shall not fall below the nominal value by more

than 0.1 mm + 10% of the nominal value, i.e.:

tm

tn (0.1+0.1 t

n)

Where, tmis the minimum thickness

tnis the nominal thickness

Insulation Screen:The insulation screen shall consist of a nonmetallic covering directly over

the insulation in combination with metallic screen. Nonmetallic covering having maximum

volume resistivity at rated temperature shall be applied over the insulation in one or more

layers.

Nonmetallic screen may consist of a conducting tape or a layer of conducting compound

having thickness between 0.0635 and 1.0 mm.

Metallic Screen:Metallic screen shall consist of nonmagnetic metal component applied over

the nonmetallic covering. The metallic screen shall be made of copper.

Copper screen shall consist of plain annealed copper flat or round wires applied helically

over the nonmetallic covering. The wires shall be electrically continuous and bonded together

throughout the cable length with copper contact tape. The total cross-sectional area of the screen

and minimum number of wire shall be not less than the specified value in the contract.

Outer Sheath:The properties of outer sheath shall comply with mechanical requirements

specified in IEC 60502-2 or equivalent. It shall also be suitable for use with the cable having

maximum conductor temperature of 90C. The material of outer sheath shall be black PVC

or black PE (ST7).

If the fire retardant outer sheath is specified in the contract, the sheath shall be black flame

retardant PVC. The oxygen index of outer sheath material shall be not less than 30 as measured


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according to ISO 4589 or equivalent. A certified test report from the raw material manufacturer

or an accepted reputable independent institution shall be submitted for approval. The f lame

retardant outer sheath shall be able to stop flame propagation along vertical or horizontal cable

ways and delay damage to cables. Test on completed cable under fire condition according to

IEC 60332-3-22 or equivalent shall be done by reputable independent testing institution or at

the factory test station witnessed by utilitys representative. The test report shall be submitted

before shipment. Fire retardant is used only in confined area such as substation building or

tunnel.

Marking: The outer sheath shall be marked on the surface with, at minimum, cable

description, manufacturers name or symbol, and date of manufacturing. The details of the

marking shall be specified in the contract. Continuous marking on the sheath along the whole

cable length shall also be provided at 1 meter interval.

Cable End Sealing: Immediately after the factory test, the cable inner end shall be covered

with an end cap, and the cable outer end shall be connected to a moisture-proof pulling eye of

sufficient strength. Cable rib shall be removed before sealing. The material of cable end sealing

shall be a metal cap or a heat shrinkable cap.

1.4.2 High Voltage (HV) Cable

The HV underground cable shall be extruded-dielectric XLPE type, manufactured by dry curing

process only. The cables shall be installed by direct burial in ducts or in trays where they are

immersed in the water all the time. The detailed requirements for each layer are as follows:

Conductor:The conductor type shall be plain annealed copper. The construction shall be

compact round concentric lay stranded or compact segmental stranded for cross-section area

less than 1,000 mm. It will be compact segmental stranded for cross-section area 1,000 mm

and above.

Conductor Screen: The conductor screen shall be semi-conductive cross-linked polyethylene.

The conductor screen is a conducting material by the triple extrusion with the insulation over

the surface of the conductor. The thickness of the conductor screen for each utility shall be

between 0.8 to 1.5 mm. The extruded conductor screen shall have resistivity in accordance

with the reference standards.


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Semi-conductive tape may be applied between conductor and conductor screen.

Insulation:The insulation shall be cross-linked polyethylene (XLPE) simultaneously extruded

with the semi-conductive conductor screen and insulation screen layer. Mechanical, electrical

and other properties shall comply with IEC 60840 or equivalent.

The dry curing process is required. Conventional steam or hot water curing processes are

not acceptable.

The minimum thickness of the insulation shall not be less than 90 per cent of the nominal value

specified, and additionally it should satisfy:

Where, maximum thickness and minimum thickness are the measured values at one and the

same cross-section of the insulation.

Insulation Screen: The conductor screen shall be semi-conductive cross-linked polyethylene.

The conductor screen is a conducting material applied by triple extrusion with the insulation

over the surface of the conductor. The thickness of the conductor screen for each utility shall

be between 0.8 to 1.5 mm. The extruded conductor screen shall have resistivity in accordance

with the reference standards.

Synthetic Water Blocking Layer:A semi-conductive, non-biodegradable water blocking

layer shall be provided under the metallic screen to provide a continuous longitudinal

watertight barrier throughout the cable length.

This layer shall be compatible with other cable materials and shall not corrode adjacent metal

layers during heat aging of the cable.

Metallic Screen (Grounding Screen): The metallic screen shall be a concentric layer of

copper wires, which is electrically continuous and bonded together throughout the cable length

with copper contact tape. The total cross-sectional area and minimum number of wires of the

metallic screen shall not be less than the value specified in the contract.

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Synthetic Water Blocking and Cushioning Tape: A non-conductive, non-biodegradable

water blocking tape shall be applied over the metallic screen to provide a continuous

longitudinal watertight barrier throughout the cable length. The tape shall have sufficient

thickness to perform well as a thermal stress relief layer and to provide for cushioning and

bedding.

The tape shall be compatible with other cable materials and shall not corrode adjacent metal

layers during heat aging of the cable.

Radial Water Barrier:As a protection against formation of water trees in the insulation, a

traverse water barrier consisting of laminated aluminum tape coated on both sides with an

ethylene acrylic acid adhesive co-polymer or polyethylene shall be incorporated under the non-metallic sheath. The average thickness of aluminum tape shall not be less than 0.19 mm.

Outer Sheath: The outer sheath shall be PVC or compound black polyethylene (PE) ST7. It

should be suitable for use with the cable having maximum conductor temperature of 90C and

130C under normal and emergency condition respectively. The mechanical properties shall

be in accordance with reference standard.

If the fire retardant outer sheath is specified in the contract, the sheath shall be black flame

retardant PVC. The oxygen index of outer sheath material shall be not less than 30 as measured

according to ISO 4589 or equivalent. A certified test report from the raw material manufacturer

or an accepted reputable independent institution, shall be submitted for approval. The flame

retardant outer sheath shall be able to stop flame propagation along vertical or horizontal cable

ways and delay damage to cables. Test on completed cable under fire condition according to

IEC 60332-3-22 or equivalent shall be done by reputable independent testing institution or at

the factory test station witnessed by utilitys representative, the test report shall be submitted

before shipment. Fire retardant is used only in confined area such as substation building or

tunnel.

Additional requirement for 69 & 115 kV PE outer sheath for the purpose of electrical

protection and ease of pulling, the sheath shall be ribbed type having crest width and depth of

approximately 2.5 mm and the center to center distance between crests shall be approx. 7 mm,

except for length marking. The crest width shall be approximately 10 mm. See Figure 1.


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Marking:Manufacturers name or trade name, year of manufacturing and contract number

shall be provided at appropriate interval throughout the cable length. This will be done on

the outer longitudinal water blocking or on the outer sheath by inserting identification tape

between radial water barrier layer and outer longitudinal water blocking layer.

Cable End Sealing:Immediately after the factory test, the cable inner end shall be covered

with an end cap, and the cable outer end shall be connected to a moisture-proof pulling eye of

sufficient strength. Cable rib shall be removed before sealing. The material of cable end sealing

shall be a metal cap or a heat shrinkable cap.

1.5 Existing Requirement for Electricite` du Cambodge

(EDC), Cambodia

The additional specifications for MV underground cables required by Cambodias EDC utility are

as follows:

Metallic screen shall be copper tape. The minimum thickness shall not be less than 0.2 mm.

For 3 cores cable only, the cables shall include an armor layer, which will be double tape type.

Water blocking is required by using swelling material in conductor strand.

HV underground cable specification is not currently employed.

Figure 1 : Cross-section of 69 & 115 kV PE Outer Sheath (Jacket)

FOR LENGTH MARKING

10 mm (APPROX.)

2.5 mm (APPROX.)

7mm(APPR

OX.)


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1.6 Existing Requirement for Electricite` du Laos (EDL),

Lao Peoples Democratic \ Republic

The existing specification for MV underground cables required by EDL utility is as follows:

Metallic screen shall be copper tape.

HV underground cable specification is not currently employed.

1.7 Existing Requirement for Ho Chi Minh City Power

Corporation (HCMCPC), Vietnam.

The existing specifications required by HCMCPC utility are as follows:

1.7.1 MV underground cables

The metallic screen shall be double copper tape having maximum thickness of 0.127 mm

and minimum width of 12.5 mm.

Inner covering and fillers are required for multi-cores cables. The cables shall have an

inner covering over the laid-up cores. The inner coverings and fillers shall be of suitable

materials. An open helix of suitable tape is permitted as a binder before applying an

extruded inner covering. The material used for inner coverings and fillers shall be suitable

for the operating temperature of the cable and compatible with the insulating material.

The thickness of extruded inner coverings shall be specified in accordance with the

reference standards.

The cables shall have separation sheath. When the metal screen and armor are made

of different metals, these shall be separated by an impervious extruded sheath. This

may be instead of, or in addition to, an inner covering. The separation sheath shall be

thermoplastic compound (PVC, PE or similar materials) or vulcanized elastomeric

compound (polyethylene or similar materials). The quality of the material used for

the separation sheath shall be suitable for the operating temperature of the cable. The

nominal thickness of this sheath, rounded to the nearest 0.1 mm, shall be derived from

the formula:

Ts= 0.02D + 0.6 mm


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Where: D is the fictitious diameter under the sheath. The smallest nominal thickness

shall be 1.2 mm. The minimum thickness at any point shall not fall below 80% of the

nominal value by more than 0.2 mm.

For multi-cores cables, the cables shall consist of armor layer. The armor shall be flat orround wire (galvanized Fe, Pb-coated Fe, Al or Al alloy) or double tape (Fe., galvanized

Fe, Al or Al alloy).

Fictitious diameter under the armor [mm] Nominal diameter of armor

wire [mm]Above Up to and including

15 0.8

15 25 1.625 35 2.0

35 60 2.5

60 3.15

Table 2 : Nominal diameters of round armor wires

The dimension of round armor wires shall not fall below the nominal value by more than 5%.

Flat armor wires: For fictitious diameters under the armor greater than 15 mm, the nominal

thickness of the flat steel wire shall be 0.8 mm. The dimension of flat armor wires shall not fall

below the nominal value by more than 8%.

Table 3 : Nominal thickness of armor tapes

Fictitious diameter under the armor [mm] Nominal thickness of tape [mm]

Above Up to and includingSteel or galvanized

steel

Aluminum or

aluminum alloy

30 0.2 0.5

30 70 0.5 0.5

70 - 0.8 0.8

The dimension of armor tapes shall not fall below the nominal value by more than 10%.


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1.7.2 HV underground cables

The metallic screen (sheath) shall be of aluminum laminated or corrugated aluminum and

complying with the following requirements:

a. Laminated aluminum

The metallic screen shall consist of laminated aluminum. This screen shall be a combination of

a copper wire and a layer of aluminum tape.

The cross-section of the copper screen shall have sufficient area to withstand the thermal and

dynamic effect of a single-phase to ground short circuit current of 31.5 kA for 3 seconds. The

bidder shall submit the calculation for determining the cross-sectional area of the copper wirescreen.

b. Corrugated aluminum sheath

The metal sheath shall consist of a tube of corrugated aluminum. The thickness of the corrugated

aluminum sheath shall be sufficient to withstand the thermal and dynamic effect of a single-

phase to ground short circuit current of 31.5 kA for 3 seconds.

The bidder shall submit the calculations for determining the sheath thickness.

The sheath shall be designed and manufactured as a homogeneous construction with the following

characteristics: uniform thickness, close fitting, seamless and free from defects, porosity and

inter-crystalline fracture. The sheath corrugation shall be of annular ring or helix construction

designed to minimize the ingress of moisture even when the serving is damaged.

1.8 Existing Requirement for Hanoi Power Corporation(HNPC) Vietnam

The existing specifications of MV and HV Underground Cable required by HNPC utility

are as follows: Metallic screen shall be copper wires. The total cross-sectional area of the

copper wires screen shall be specified in the contract.

For multi-cores cable, the cables shall consist of armor layer. The armor shall be steel tape

type.


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Swelling material in conductor strand, longitudinal water blocking over copper wire screen

and radial water blocking below outer sheath are required.

1.9 Additional Requirement for Metropolitan Electricity

Authority (MEA), Thailand

In addition to 1.4 Principle specifications, the following specifications should be employed to enhance

safety, reliability, performance and maintenance:

1.9.1 MV underground cables

The tension necessary to remove an extruded insulation screen from cable at room

temperature shall not be less than 13.3 N.

Copper wire screen will consist of plain annealed copper fate or round wires applied

helically over the nonmetallic covering. The wires shall be electrically continuous and

bonded together throughout the cable length with copper contact tape. The total cross-

sectional area of the screen and minimum number of wire shall be not less than the

specified value in the contract.

If PVC fire retardant outer sheath is specified in the contract, the sheath shall be black,

flame retardant PVC. The oxygen index of outer sheath material shall be not less than

30 as measured according to ISO 4589 or equivalent. A certified test report from the

raw material manufacturer or a reputable independent institution, which is acceptable

to MEA, shall be submitted for approval. The flame retardant outer sheath shall be able

to stop f lame propagation along vertical or horizontal cable ways and delay damage to

cables. Test on completed cable under fire condition according to IEC 60332-3-22 or

equivalent shall be done by reputable independent testing institution or at the factory

test station witnessed by MEAs representative. The test report shall be submitted before

shipment.

1.9.2 HV underground cables.

If a fire retardant outer sheath is specified in the contract, the sheath shall be black, flame

retardant, and made of PVC. The oxygen index of non-metallic sheath material shall

be not less than 30 as measured according to ISO 4589 or equivalent. A certified test


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report from the raw material manufacturer or a reputable independent institution, which

is acceptable to MEA, shall be submitted for approval. The flame retardant non-metallic

sheath shall be able to stop flame propagation along vertical or horizontal cable ways and

delay damage to cables. Testing on the completed cable under fire condition according to

IEC 60332-3-22 or equivalent shall be done by a reputable independent testing institution

or at the factory (to be witnessed by MEAs representative). And the test report shall be

submitted before shipment.

Additional requirement for 69 & 115 kV PE outer sheath for MEA: The sheath shall be

ribbed type having crest width and depth of approximately 2.5 mm and the center to

center distance between crests shall be approx. 7 mm, except for length marking. The

crest width shall be approximately 10 mm. See Figure 2.

Figure 2 : Cross-section of 69 & 115 kV PE Outer Sheath (Jacket)

Additional requirement for 69 & 115 kV fire retardant PVC sheathed for MEA: The

sheath shall be ribbed type having crest width and depth of approx. 2.5 mm and the

center to center distance between crests shall be approx. 7 mm. The crest width at the

quarters shall be approximately 5 mm, and the crest width for length marking shall be

approximately 10 mm. See Figure 3.

FOR LENGTH MARKING

10 mm (APPROX.)

2.5 mm (APPROX.)

7mm(A

PPROX.)


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Figure 3 : Cross-section of 69 & 115 kV Fire Retardant PVC Outer Sheath (Jacket)

1.10 Conclusion

From this chapter cable engineers can learn the specifications of other power utilities and compare

them with their own specifications. This will enable them to know the advantages and disadvantages

of different types of cable design and improve their specifications. The cable constructions for each

power utility may be different because of its unique installation requirements. It is recommended that

power utilities review their specifications for the cable insulation material from the point of view of

the cost as well as the losses. However, in order to promote the harmonization of the LMS practice,

the common specification for underground cable of the LMS utilities shall be developed for concrete

implementation in the future. The normative technical specification of underground power cable is

then proposed in Appendices A and B for optional application in the LMS underground system.

FOR LENGTH MARKING

10 mm (APPROX.)

7mm(A

PPROX.)

2.5 mm (APPROX.)

5mm

(APPROX.)


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Bidding Evaluation

2.1 Introduction

Bidding evaluation is one of the most important processes to ensure that a utility gets good quality

cables on time. And to support bid evaluation, utilities must instruct suppliers to submit all the

necessary documents. Inefficient documents may lead to poor quality of cables. The specification

should clearly specify the necessary documents required to be submitted by the suppliers. Suppliers

should fill-in all tables and forms as required in the bid documents.

2.2 Objective

The objective of this chapter is to guide and assist the utilities to learn about documents, data and tables

required for evaluation. If a bidding document is complete, its evaluation will be easy and efficient. If

not, more documents will be requested and submitted in a limited period, otherwise the bid shall not

be considered. Only underground cables shall be discussed in this chapter.

2.3 Documents Required for Evaluation

Usually, there are five main documents required for evaluation: (i) type test report, (ii) proposed

technical data, (iii) deviation form, (iv) detail drawing and (v) reference list of supply. Additional

documents or samples may be required depending on special requirements of each utility.

Bids should be evaluated by an Evaluation Committee whose members are selected from related

departments. It is important not to get bids evaluated by only a single person or department.

The requirements and instructions for evaluating each of the above-mentioned five bid documents

are as follow.

2.3.1 Type test report

The proposed cables should pass all the type tests according to the reference standard specified

in the specifications. The tests shall be conducted by a reputable independent testing agency

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acceptable to the utility. All test reports shall be submitted with the offer otherwise such offer

will not be considered.

Cable manufacturers who do not have type test reports of the proposed cables can submit a

type test report of the cable with the range of type approval specified in reference standard forconsideration or bigger sizes of conductor but same ratings and construction design.

In the case of fire retardant cable, the test for vertical flame spread of vertically-mounted bunched

cables can be carried out after the award of contract but before shipment or else the right will be

reserved to purchase from the second lowest bidder with penalty to compensate for the balance

in order to keep delivery schedule.

2.3.2 Proposed technical data

Proposed technical data is important for bid evaluation as it provides information for the

Evaluation Committee to assess whether the proposed cables conform to the specifications.

Normally, the standard provides guidelines for the technical data required to be filled up in the

inquiry and order section. Any other additional requirements for technical data should also be

provided in this section.

Bidders are requested to fill in all the blank spaces in the technical proposal data form and return

with the bid. Failure to submit the form or incomplete forms may render the bid invalid and

constitute a sufficient case for bid rejection.

The sample of technical proposal data form is shown in Table 4.

2.3.3 Deviation form

Bidders must clearly indicate all deviations from the specifications fill in the Deviation Form

and attach it with the bid. If there is no deviation stated in the Deviation Form, the characteristics

of the proposed cables shall be considered to be in complete compliance with specifications.

However, if the delivered cable is found not in compliance with the specification, it will be

rejected.


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2.3.4 Drawing

The drawing of the proposed cables is also important for bid evaluation. It should show all

important details of the proposed cables, including cable construction, dimension, material, etc.

All information shall be in English or the countrys official language, machine printed or typed.

Information on drawing shall be in engineering lettering. All measurements and quantities shall

be expressed in the units of metric system. If they are expressed in other unit systems, the metric

equivalent shall also be indicated.

Figure 4 shows a sample of detailed drawing of a cable.

2.3.5 Reference list of supply and field experience

A reference list of bidders supply and field experience shall also be taken into consideration when

evaluating bids. Bidders should attach a reference list of supply and field experience in the same

design of cables as proposed with the quotation.

A reference list of previous supply projects is particularly important for evaluation in case the

cable(s) offered are of new manufacturers. This is to ensure that the manufacturer is qualified for

supplying cables as per the specifications and associated standards.


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db k f d d bl |

Material Code 204-6500

Manufacturer ABC

Country THAILAND

Applied standard, publication number and year IEC 60840

Rated voltage 115 kV

Outline drawing number (to be attached) HVMAC-O5-155

Conrm to attach type test reports of the cable with similar design(yes or no)

YES

Conrm to attach the detail of water penetration test (yes or no) YES

Copper conductor

Applied standard, publication number and year IEC 60228

Volume conductivity at 20C, minimum IACS 100 %

Number of wires 53 (minimum)

Number of layers 4

Wire diameter (with tolerance) 4.47 1% mm

Conductor temper (anneal, hard-drawn, etc.) ANNEALED

Material Code 204-6500

Lay ratio of the outer layer 10

Direction of lay of the outer layer LEFT- HAND

Nominal cross-sectional area 788 mm2

Stranding (concentric, compress or compact) COMPACT

Overall diameter 34 mm

Tolerance of overall diameter 1%

Weight 14,000 kg/km

Maximum dc resistance at 20C 0.221/km

Conductor screen

Material SEMI-CONDUCTIVE

Volume resistivity, maximum

At room temperature, .........C 1*104.cm

At 90C 1*105.cm

Thickness

Average 1.5 mm

Minimum 1.2 mm

Table 4: Sample of Proposed Technical Data for High Voltage XLPE Copper Cable


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Figure 4 : Cable Drawing


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2.4 Guideline for Bid Evaluation

The bid evaluation process is very important. All bids shall be scrutinized by the Evaluation Committee.

Only those bids which are complete in terms of data and information shall be evaluated. This process

takes a lot of time. It is recommended to make a request for more information in a limited period. sothat it will not delay the delivery schedule and the whole project. Usually, bids are evaluated based on

the following criteria and priorities.

2.4.1 Type Test report

As the top priority, type test report should be assessed first. The proposed cable should pass all the

type tests according to the reference standard as specified in the specifications. Otherwise, the bid

shall be rejected immediately, and there is no need to review other documents.

Manufacturers may not usually have the type test report for cables of the same size, design and

rating as the proposed cables. There is, however, no need to do type test for all sizes and ratings

of the cables and in such a case, the type test report of an identical cable may be acceptable on the

following conditions.

Once the type tests on cable(s) of specific cross-section(s), rated voltage and construction have

been successfully performed and cleared/passed, the same type approval shall be considered

valid for cables of other cross-sections, rated voltages and constructions as long as all of the

following conditions are met:

The voltage group is not higher than that of the tested cable(s).1.

The conductor cross-section is not larger than that of the tested cable(s).2.

The cable has the same or similar construction to that of the tested cable(s).3.

The calculated nominal electrical stress at cable conductor screen does not exceed the4.

electrical stress at cable conductor screen of the tested cable(s) by more than 10%.

The calculated nominal electrical stress at cable insulation screen does not exceed the5.

electrical stress at cable insulation screen of the tested cable(s).

The type test on cables of different voltage ratings and conductor cross-sectional areas are required

if these cables are of different materials and/or have been produced using different manufacturing

processes.


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Repetition of ageing test on pieces of a complete cable to check the compatibility of materials may

be required in the following condition: The combination of materials applied over the screened

core is different from that of the cable on which the type tests have been successfully carried

out.

2.4.2 Proposed technical data

After the type test report has been scrutinized and found in compliance with the specifications,

the next step is to review the proposed technical data provided by the supplier.

This data is also important because it provides the key details of the proposed cable, that are cable

construction, physical & electrical characteristics, materials applied and packing details.

If the proposed technical data is not in compliance with the specifications, the bid will be rejected

unless explanation is given in a deviation form. In case, some of proposed technical data has not

been asked or specified clearly in the specifications, it could be accepted, provided that it does not

have implications on the installation, rating and life time of the cable.

2.4.3 Deviation form

The Deviation Form clearly describes the characteristics of the proposed cable that are different

from the specifications. If there are any major deviations, the proposed cable shall be rejected.

In the event of minor deviations, the decision shall be made based on certain key factors, such as

effect on installation, rating and life span of the cable.

2.4.4 Drawings

Drawings are required to allow the committee members understand the detailed construction and

characteristics of the proposed cable.

Drawings containing all information required shall be attached with the bid. Drawings and

the proposed technical data should be evaluated together. If there are any major deviations, the

proposed cable shall be rejected. In the event of minor deviation(s), the related departments shall

be consulted and the decision shall be made based on the likely impact on installation, capacity

and life span of the cable.


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2.4.5 Reference list of supply and field experience

Sometimes, one supplier offers two options of cables, one from a reputable manufacturer and

the other from an inexperienced manufacturer whose price is lower than that of the former

manufacturer. In this case, a reference list of supply field experience is needed. Some utilitiesmay make a trip to visit the factory of the new manufacturers to make sure they are qualified.

If necessary, it is recommended that utilities make a special requirement for reference list of

supply field experience of the proposed cable manufacturer in their specification; for example, a

specific number and year of supply of the proposed cable(s) to other countries. Another solution

to purchase from the new manufacturer is called trial contract which the utility can specify in

the tenders condition to purchase not more than 10% of the tender quantity and to purchase the

balanced quantity from the fully comply tenders condition bidder.

2.5 Conclusion

The bid evaluation process and documents required of each LMS utility may be similar. However,

it takes a lot of time to get through the process. To complete the evaluation process in a short period

of time, all required documents and data to be included in the bid shall be clearly specified in the

specifications. Also, the Evaluation Committee shall be represented by qualified personnel.

It is also recommended to perform separate evaluation if proposed cables have different construction

characteristics and/or made of different materials.


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Cable Manufacturing Inspection

3.1 Introduction

After the procurement contract for underground cables is signed, several processes need to be verified

to ensure that cables comply with the specifications and conditions specified in the contract. Drawings

shall be provided for approval.

If necessary, the test method shall be, by the agreement between the purchaser and the manufacturer,

proposed by the manufacturer and approved by the utility. Representatives from the utility, who are

appointed based on experience in various aspects, such as specification handling, installation, testing,

maintenance and purchasing, shall inspect the production of cables at the factory.

3.2 Objective

The inspection of cable manufacturing processes is required to ensure all processes run according to

contractual requirements. If any processes are found not conforming to the reference standard and

specifications, the Inspection Committee shall reserve the right to suspend the production and resolve

all issues before restarting the production line.

This chapter describes the cable manufacturing processes and testing, which includes partial discharge

test and high voltage test. A diligent inspection of cable manufacturing processes is fundamental to

ensuring satisfactory quality of cables and operating life of at least 25 years.

3.3 Inspection Committee Management

Each utility may have different practices and regulations depending on their own policies. This proven

practice is very useful as it can prevent introduction of poor cables in the service. It also has a track record

of success in a utility that is responsible for distributing electricity in capital and other main cities.

After the contract is signed, an Inspection Committee should be approved by the top management. The

committee members will be selected from the related departments, such as:

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Electrical Engineering Department: The department responsible for specification or term of

reference (TOR).

Installation and Construction Department: The department with field experience in installation

and construction of the cables and their accessories.

Testing Division or Maintenance Department: The departments with experience in testing and

preventive maintenance of cables.

Purchasing or Contract Department: The department that controls all the related documents --

quotation, technical and commercial condition agreement and the approval drawings.

All engineers and technicians represented in the production Inspection Committee will be given theapproval drawings and the related correspondence for their references before they go witnessing the

cable production line and testing.

The supplier shall provide free access to the production facilities and shall satisfy the representatives

that the material and equipment are in accordance with the specifications and the contract.

In the event of a disagreement or dispute, for example, if either the contract details are not clear or the

supplier would like an exception to be made, the issues should be discussed with the top management.

The meeting with the top management should keep the interests of the utility as the main focal point

while deciding on such disputed matters. This should be considered as a standard practice.

3.4 Manufacturing Process Inspection

This section describes manufacturing process of extruded-dielectric cables, which are used nowadays.

Once the production of cables starts, the Manufacturing Inspection Committee will be requested to

visit the factory and inspect the production line of cables. This is to make sure that manufacturing is

according to the specifications in the contract.

The manufacturing process begins by making copper wires and then stranding the conductor. Stranding

is performed using the conventional method regardless of whether the conductor is concentric, round,

compressed, compact, or segmental, and with or without strand blocking. The stranded conductor is

reeled onto a drum, which is placed into its position on the extrusion line. Then the drum becomes the

payoff reel or the first subsystem in a series of subsystems that comprise the extrusion process.


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Other subsystems (not all required for all insulation types) are:

Accumulator: Provides in-line conductor time for changing reels and welding the conductor for

continuous extruder operation.

Conductor preheating: It shortens the curing time by 20-60% depending on conductor size,

consequently increasing the line speed and plant production.

Compound Handling Subsystem; Stores, dries, and feeds the compound into the extruders and,

in some cases, incorporates in-line inspection.

Extruder: The polymer materials are supplied mixed with additives and cross-linking catalysts,

and are heated to a plastic state. The extruder screw compresses the material and forces itthrough a fine mesh screen into the crosshead through which the conductor travels.

Crosshead: In a true-triple extrusion process, one crosshead contains the extruder for the

insulation and the two semiconducting layers. The three layers are formed onto the conductor

simultaneously through their respective dies. This special process will prevent the impurity such

as moisture, dust or any pollution particles from penetrating the insulation layer

Vulcanizing Tube: It provides the pressure and temperature required for the cross-linking process

used for XLPE and EPR (Ethylene Propylene Rubber) insulations.

Cooling Tubes: It provide a carefully controlled cooling zone following the cross-linking process

for XLPE or EPR.

Traction Units: The capstan and caterpillar maintain the proper line tension required for catenary

vulcanizing lines.

Control Unit: It monitors and controls the temperature and pressure, and provides synchronized

operation between the line speed and the extruder screw speed.

Take-Up: This final step reels completed cable core onto a drum and hauls the drum away for

subsequent processes in cable assembly.


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Figure 5 : Schematic Diagram of Extrusion Line

Of the three insulation types, only PE doesnt require curing tube since there is no cross-linking of the

polymer. After the insulation and extrusion of the two semi-conducting layers onto the conductor, the

line passes through a controlled cooling chamber (frequently a closed, pressurized tube) before being

reeled on a take-up drum.

Dry-Cure Systems: The radiant dry-cure system, as opposed to the steam-cure system, features

independent control of pressure and temperature. This system uses an inert gas, such as nitrogen, as

the pressurizing medium. Pressure prevents the premature release of the volatile curing agents. The

temperature is maintained by an electrically heated curing tube. Heat is transferred from the tube to

the cable by radiation.

In the gas-cure system, both pressure and temperature are provided by a high-pressure, nitrogen

circulating system. This system circulates nitrogen through a curing tube, then through a heat

exchanger and finally back to the curing tube. In the long-land die-curing system, the extruder die is

50-66 ft (15-20 m) long and the required temperature and pressure are maintained within the die, which

serves as the curing tube. Because the die is full and under high pressure, there is little opportunity for

gravity to pull the extruder off the center.

Copper Wire Making Process

Conductor Making Process

Extrusion Line

Cleaning

Cleaning

Drawing Reducing

Stranding 1 Stranding 2 Stranding 3 Tractive

Dio

monitor

Preheat Corss Head

for 3 layer

extrusion

Cooling Monitor Electrotechnical

monitor

Compound

Pay off

Pay off

Pay off

Take up

(Conductor)

Take up

(Copper wire)

Length

Counter

Take up


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Cooling:Opinions vary as to which is the best method of cooling. Some manufactures believe

that even the driest cables have some residual moisture that cannot be reduced. They claim that the

moisture is not from the cooling water, but rather is a by-product of the curing process. Others claim

that water cooling shocks the insulation and sets up mechanical stresses which, in turn, intensify the

shrink-back phenomenon. Dry-cooling methods use gas or silicone-oil circulating systems. It is in the

cooling system that cables release volatile by-products of cross-linking, which must be carried away.

The cable continues to de-gas for about three weeks.

Without de-gassing, cable outer sheath may swell when subject to high temperature in tropical climate

of LMS, then the manufacturer or contractor should take response to release all generated gas by

pumping machine until the cable resume as standard specification requirement before installation.

Hermetic Sealing:The industry practice is that if the cable is to be installed in a wet environment

where moisture ingress through the jacket is probable, the cable should be hermetically sealed. This is

to prevent moisture ingress and initiated treeing under voltage stress. The types of hermetic sealing in

common use are lead sheath, corrugated aluminum or copper sheath, and metal laminates.

3.5 Factory Acceptance Tests

When the production is finished, the cable is ready to undergo routine and special tests required

by the customer -- the utility. The routine and special tests witnessed by the Inspection Committee

are called Factory Acceptance Tests or FAT. The Inspection Committee will witness at least the

following tests.

Testing Procedure

Routine tests

Partial discharge test:1. The partial discharge test shall be carried out in accordance with

IEC 60885-3, except that the sensitivity as defined in IEC 60885-3 shall be 10 pC or less.

The test voltage shall be raised gradually to hold at 1.75 Uo for 10s and then slowly reduced

to 1.5 Uo. The magnitude of the discharge at 1.5 Uo shall not exceed 10 pC. Values of the test

voltage for the standard rated voltages are given below.


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Voltage test:2. The voltage test shall be made at ambient temperature using an alternating

test voltage at power frequency. The test voltage -- between the conductor and metallic

screen/sheath -- shall be raised gradually to the specified value and held there for 30

minutes. The test voltage shall be 2.5 Uo. There will be no breakdown of the insulation.

The voltage test values are shown below.

Rated voltage U

kV22 - 24 45 - 47 60 - 69 110 - 115 132 - 138 150 - 161

Rated voltage Uo

kV12 26 36 64 76 87

Test voltage 2.5 Uo

kV30 65 90 160 190 218

Rated voltage U

kV22 - 24 45 - 47 60 - 69 110 - 115 132 - 138 150 - 161

Rated voltage Uo

kV12 26 36 64 76 87

First raised voltage 1.75

Uo kV

21 45.5 63 112 133 152.3

Test voltage 1.5 Uo

kV18 39 54 96 114 131

Electrical test on non-metallic sheath3.

If required in contract, the non-metallic sheath shall be subject to the routine electrical test

as specified in IEC 60229.

Special tests

Special tests shall be done on the cables for about 10% of total drums.

1. Construction and dimension check: Construction and dimension of each layer shall be

checked. The test method shall be in accordance with clause 8 of IEC 60811-1-1.

Table 6: Voltage Test

Table 5 Partial Discharge Test


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Requirement for insulation

The lowest measured thickness at any point shall not fall below 90% of the nominal

thickness:

Tmin 0.9 Tn

Additionally: (Tmax

- Tmin

)/ Tmax

0.15

Where Tmax

: The maximum thickness (mm)

Tmin

: The minimum thickness (mm)

Tn : The nominal thickness (mm)

Note: Tmaxand Tminare measured at the same cross-section of the sample. Thickness ofthe semi-conducting screen on the conductor and over the insulation shall not be included

in the thickness of the insulation.

Requirement for the non-metallic sheath

The lowest measured thickness shall not fall below 85 % of the nominal thickness by

more than 0.1 mm.

Tmin 0.85 Tn- 0.1

Where Tmin

: The minimum thickness (mm)

Tn : The nominal thickness (mm)

2. Conductor resistance test: The complete cable length, or a sample thereof, shall be

placed in a test room, which shall be maintained at a reasonably constant temperature

for at least 12 hours before the test. In case of a doubt that the conductor temperature is

not the same as the room temperature, the resistance shall be measured after the cable

has been in the test room for 24 hours. Alternatively, the resistance can be measured on

a sample of conductor conditioned for at least 1 hour in a temperature-controlled liquid

bath. The D.C. resistance of the conductor shall be corrected to a temperature of 20C and

1 km length in accordance with the formulae and factors given in IEC 60228. The D.C.

resistance of each conductor at 20C shall not exceed the appropriate maximum value

specified in IEC 60228, if applicable.


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For example, the maximum D.C. resistance of conductor at 20C for stranded copper

conductor size 70, 150, 240, 400, 800, 1000 and 1200 mm 2are 0.268, 0.124, 0.0754,

0.0470, 0.0221, 0.0176 and 0.0151 /km respectively.

3. Hot set test of insulation: The test piece shall be suspended in an oven and weightsattached to the bottom jaws to exert a force as specified in the applicable standard. After

15 min in the oven at the specified temperature, the distance between the marker lines

shall be measured and the percentage elongation shall be calculated. If the oven does

not have a window and the oven door has to be opened to make the measurement, the

measurement shall be made not more than 30 seconds after opening the door. In case of

a dispute, the test shall be carried out in an oven with a window and the measurement

made without opening the door.

The tensile force shall then be removed from the test piece (by cutting the test piece at

the lower grip), and the cable piece shall be left to recover for 5 minutes at the specified

temperature. The test piece shall then be removed from the oven and allowed to cool

slowly to the ambient temperature, after which, the distance between the marker-lines

shall be measured again.

For the evaluation of results, the median value of the elongation -- derived after 15

minutes at the specified temperature with the weight attached -- shall not exceed the

value specified in the standard. And the median value of the distance between the marker

lines -- after removing test piece from the oven and allowing it to get cool -- should not

increase compared to the value before inserting the piece in the oven by more than the

percentage specified in the standard.

4. Capacitance test: The capacitance shall be measured between conductor and metallic

screen/sheath. The measured value shall not exceed (usually by more than 8%) the

nominal value declared by the manufacturer.

3.6 Conclusion

Usually, utilities have their own inspection committee teams to inspect the production line, and witness

routine and special tests at the factory. In case the factory is located outside the country, utility may

send a representative of the Inspection Committee to the factory or hire a third party inspector.


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Some utilities may have their own inspection forms or special documents to process the comments

and some corrections during the inspection, such as witness tests, material and construction check,

discussion, etc. In case of no inspection form, it is necessary for inspection committee to investigate

the production process and quality control before signing in every document which is usually prepared

by the factory and make a request for a copy for their reference and every comment to the factory

should be sent in official paper.


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Contract Acceptance

4.1 Introduction

The purchasing contract includes all commercial conditions and technical requirements. After

the contract is signed, contract acceptance has to be done to ensure that the quality of the cables

complies with the contract requirements. This process is also important for utilities to ensure cables

are delivered as per the contractual delivery period. The contract acceptance becomes a problem when

the delivered cables do not conform to the contract requirements, such as construction, physical and

electrical characteristics, or when the cables are damaged during transportation. All such problems

shall be settled before cables are accepted.

4.2 Objective

Usually, the contract acceptance is done by an Acceptance Committee and not by one person or a

department. The contract acceptance process and procedure may be different for each utility. The

objective of this chapter is to share the experience in preventing and solving problems faced during

contract acceptance process. Various scenarios have been explained as a guide to solving problem.

4.3 Acceptance Committee Management

This follows the same procedure as mentioned for the Production Inspection Committee in Chapter 3.

The Acceptance Committee should be approved by the upper management after the contract is signed.

The members will be selected from the related departments, such as: Maintenance Department which

is responsible for cable maintenance and repair.

Installation and Construction Department that has field experience in installation and construction

of the cables and their accessories.

Testing Division which is experienced in testing and preventive maintenance of cables.

Purchasing or Contract Department that deals with all the related document like quotation,

technical and commercial agreement, and approval drawings.

Chapter 4


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All engineers and technicians who are members of the Acceptance Committee will be given the

approval drawings and the related correspondence for their reference. They will use these documents

during sampling of the delivered cables for testing. The supplier shall submit the routine test report

and special report of all cables to the utility before the shipment of the cables. After that the routine

tests and special reports will be sent to the Acceptance Committee for approval.

In the event of a disagreement or dispute, for example, if the contract details are not clear or the

supplier would like an exception to be made, the issue should be presented at a meeting with the

top management. During discussions on the dispute, the meeting participants should address the

disadvantages and advantages to the utility as the main focal point. This convention should be

considered as a standard practice.

4.4 Acceptance Process

Practically, the contract acceptance process comprises three steps. The first step is visual inspection.

The second step is routine and special reports verification and the third is acceptance test or

sampling test by utility. Routine and special reports and acceptance test report shall be reviewed

by the Acceptance Committee. The detailed specification with approval drawings shall be used as a

reference. Here is a practical guideline for contract acceptance process.

The delivered cables shall be accepted provided that all three following conditions are met:

4.4.1 Visual Inspection

After the delivery of cables, the Acceptance Committee will conduct a visual inspection

at the site to check the quantity of the cables (according to the invoice of the supplier)

and any damages that may have occurred during transportation. If any damaged cable is

found, the Committee will ask the supplier to replace it with a new one.

During visual inspection, the Committee will also randomly select the quantity of cables

as stated in the contract for acceptance tests by utility itself. The quantity typically does

not exceed 3 meters per drum and not in exceed of 3 drums due to the constraints of cost,

time and laboratory capacity.


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4.4.2 Routine and Special Tests Verification

The routine and special tests shall be carried out in order to determine whether the cable

complies with the specification. The specification includes the required tests. The routine

and special test reports shall be submitted to the utility before shipment. If the test resultof any cable does not comply with the specification, the cable shall be rejected. Samples

of routine and special tests report are shown in Table 7.

As minimum, the following acceptance tests should be done at the utilitys laboratory.

Special tests

a) Construction and dimension check

b) Conductor resistance test

c) Hot set test of insulation

d) Capacitance test

Routine test

a) Partial discharge test

b) Voltage test

c) Electrical test on non-metallic sheath


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Routine and Special Tests Report

Customer: Drum No.:

Cable Type: 115 kV XLPE Copper cable, 800 mm2 Sample Condition:

Contract No.: Ambient Temp.:

Reference Standard: Manufacturer:

Test Items Unit Specification Test Results

Routine testsPartial discharge test at 96 kV1.AC. High Voltage Test at 160 kV for 30 minutes2.Electrical test on non-metallic sheath at 15 kV3.

pC--

10 (Max)No breakdownNo breakdown

0.5No breakdownNo breakdown

Special tests1. Conductor examination & check of dimensions

- Material- Design type- Number of wires- Diameter of conductor

2. Separator tape

- Material

3. Conductor screen

- Material- Average thickness- Minimum thickness

4. Insulation

- Material- Average thickness- Minimum thickness- Diameter over insulation

5. Hot set test

- Elongation under load- Elongation after cooling

6. Insulation screen

- Material- Average thickness- Minimum thickness

7. Synthetic water blocking tape

- Material- Thickness- Width

-

--mm

-

-mmmm

-mmmmmm

%%

mmmm

-mm

Plain annealed copper

Compact circular strand53 (Min)34.0 1%

Semi-conductive tape

Semi-conductive XLPE1.51.2

XLPE16

14.469-72

175 (Max)15 (Max)


Semi-conductive0.4540

Plain annealed copper

Compact circular strand6133.9

Semi-conductive tape


XLPE16.916.270

750.8


Semi-conductive0.4540

4.4.3 Acceptance Tests

It is recommended that even though the supplier performs the entire routine and special

tests on the cables, the utility should also perform sample tests for its own v

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