DMRC Electrical Standards & Design Wing DMES-T/0018

SPECIFICATIONS FOR 33 kV CABLES FOR ELEVATED AND Draft-1

UNDERGROUND CORRIDOR

DELHI METRO RAIL CORPORATION LIMITED

DMRC ELECTRICAL STANDARDS &

DESIGN WING (DESDW)

SPECIFICATION NO.
DMES- T/0018/ DMRC-E-TR-CABLE-2

SPECIFICATIONS FOR 33 kV CABLES FOR

ELEVATED AND UNDERGROUND CORRIDOR

Issued on:
Date Stage
20thAug 2014 Draft-1

DELHI METRO RAIL CORPORATION LTD.

7th Floor, B-Wing, Metro Bhawan, Fire Brigade Lane,
Barakhamba Road, New Delhi –110 001

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 DMRC Electrical Standards & Design Wing DMES-T/0018

SPECIFICATIONS FOR 33 kV CABLES FOR ELEVATED AND Draft-1

UNDERGROUND CORRIDOR

Previous Record of specification

Stage Date
Draft -1 20/08/2014

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 DMRC Electrical Standards & Design Wing DMES-T/0018

SPECIFICATIONS FOR 33 kV CABLES FOR ELEVATED AND Draft-1

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Contents

1. Detailed description of the equipment and its application in DMRC - MV cables ................. 4
2. Governing Specifications .................................................................................................................... 5
2.1 Standards .........................................................................................................................5
2.2 Abbreviations ...................................................................................................................6
3. Technical Requirement ....................................................................................................................... 6
3.1 ConductingCore ...............................................................................................................6
3.2 Conductor:........................................................................................................................6
3.3 Conductor Screen: ...........................................................................................................7
3.4 Insulation: .........................................................................................................................7
3.5 Insulation Screen:.............................................................................................................7
3.6 Water Barrier: ...................................................................................................................7
3.7 Metallic Screen: ................................................................................................................8
3.8 Inner Sheath: ....................................................................................................................8
3.9 Armouring:........................................................................................................................8
3.10 Short Circuit Ratingof Metallic Sheath/Screen ..................................................................8
3.11 Outer Sheath ....................................................................................................................8
4. Additional Requirement ...................................................................................................................... 9
4.1 Outer Sheath should have following features: ..................................................................9
5. Maintenance & Life ............................................................................................................................10
6. Special Condition ...............................................................................................................................10
7. TESTING..............................................................................................................................................11
8. DATA SHEET - 33 kV CABLES ...................................................................................................12

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SPECIFICATIONS FOR 33 kV CABLES FOR ELEVATED AND Draft-1

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1. DETAILED DESCRIPTION OF THE EQUIPMENT AND ITS APPLICATION IN DMRC -

MEDIUM VOLTAGE CABLES
These specifications are applicable to 33 kV cables in various corridors,
constituting the 33 kV distribution network.

33 kV Cables are required to be used in the Auxiliary Network, for supply of power at
33 kV to various ASSs located at Stations and in the Depot. The Auxiliary Network
consists of duplicate 33 kV feeders, each feeder consisting of 3 Single core cables,
assembled in twisted or cloverleaf pattern. The Cross section of the conducting core
generally used is as follows for various connections:

Conducting Core
 From AMS/RSS to ASS 400 sq. mm Copper
 33 kV Ring Main (Underground section) 400 sq. mm Copper
 33 kV Ring Main (elevated section) 300 sq. mm Aluminum
 From ASS to ASS 300 sq. mm Aluminum
 33 kV CB to Transformer (33 kV/415 V)
95 sq mm Copper
(less than and up to 3 MVA)
 Station ASS Panel to PD ASS 95 sq mm Copper

The electro technical characteristics required to be guaranteed for medium voltage cable
for the above cable sizes, are shown in the technical sheet enclosed as an Annexure
with this specification.

The elevated corridor ASSs shall be supplied from a 33 kV cables Network, which shall
consist of two cables (cable 1 and cable 2) normally independent from one another. The
network is divided into loops, as necessary, as shown in the relevant ‘Auxiliary Power
Supply scheme’. The 33 kV distribution cables in the elevated sections shall be laid inside
cable path/channels provided on the viaduct along the tracks. Current rating for cables
shall be determined taking into consideration the following installation methods as
applicable:

 In the tunnels
 In cast –in pipes
 Trenches
 On brackets
 Ducts
And on the following as per design data:
 temperature correction
 thermal resistivity
 laying depth
 cable distance
 cable grouping factor etc
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2. GOVERNING SPECIFICATIONS

The 33 kV Cables shall conform to IEC 60502 and shall be of 18/30 kV (36 kV). The cables
shall be of dry-insulated, radial-field cable, based on proven technology. They shall be
constituted by assembly of three single core cables in twisted or cloverleaf pattern, annealed
circular stranded Copper conductor or stranded Al Conductor for the cables as specified.
The cable shall be XLPE insulated with semi-conducting screen over conducting core. The
cable shall also be Tape armoured. It shall conform to IEC 60502 Part 2 latest for
construction and for testing.

2.1 Standards

The 33 kV Cables shall satisfy the following requirements and shall also comply with
standards in force when the cables are manufactured, particularly which are in the
following table (Unless otherwise stipulated in the specifications, the latest version of the
following Standards shall be applicable): -

Standard # Description
Power cables with extruded insulation and their accessories for rated
voltages from 1 kV (Um = 1,2 kV) up to 30 kV (Um = 36 kV) –
IEC 60502
Part 2: Cables for rated voltages from 6 kV (Um = 7,2 kV) up to 30 kV
(Um = 36 kV)"
IEC 60228 Conductors of insulated cables
Power cables with extruded insulation and their accessories for rated
IEC 60840 voltages above 30 kV (Um = 36 kV) up to 150 kV (Um = 170 kV) - Test
methods and requirements
Part 1 : Tests on electric and optical fibre cables under fire conditions
IEC 60332
Part 3 : Tests on electric cables under fire conditions
Electric and optical fibre cables - Test methods for non-metallic
IEC 60811
materials
Test on gases evolved during combustion of materials from cables -
IEC 60754
Part 1: Determination of the halogen acid gas content
ASTM D Standard Test Method for Density of Smoke from the Burning or
2843 Decomposition of Plastics

ASTM
Standard
D Test Method for Measuring the Minimum Oxygen Concentration to
2863 Support Candle-Like Combustion of Plastics (Oxygen Index)

IS 7098 Cross linked polyethylene insulated thermoplastic sheathed cables,

Part 2 Part 2: for working voltages from 3.3 KV up to & Including 33 KV.

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2.2 Abbreviations
 IEC – International Electro technical Council
 ASTM - American Society for Testing and Materials
 AMS – Auxiliary Main Substation
 ASS – Auxiliary Sub Station
 RSS – Receiving Sub Station
 XLPE – Cross Linked Poly Ethylene
 FRLS – Fire Retardant Low Smoke
 FRLSZH – Fir Retardant Low Smoke Zero Halogen
 CB – Circuit Breaker
 PD – Property Development
 IS – Indian Standard

3. TECHNICAL REQUIREMENT
The cables shall be insulated with chemically cross-linked polyethylene (XLPE), with
semi-conducting screen over a copper conducting core, insulating envelope
AIuminium Tape armouring and suitable protective sheath.

 operating voltage: 33 kV rms between phases,

 specified voltage: 18/30 kV rms (according to IEC 60502)
 Conductors as specified

The Contractor shall calculate and inform current rating to verify cross-sectional area of
33 kV cables, according to the latest arrangement of the ASSs along each 33 kV cable.

All cables whether Fire Retardant Low Smoke (FRLS) to be used in elevated sections or
Fire Retardant Low Smoke Zero Halogen (FRLSZH) to be used in the Underground
Sections shall conform to IEC 60502 or equivalent. The cables, in addition, shall be non-
fire propagating, non-toxic and low-smoke producing type.

The various constructional features required for the 33 kV cables are as under:

3.1 Conducting Core

The conducting core shall be made of bare annealed copper or aluminium, as the case
may be according to Class 2 as per publication IEC 60228; Latest Version.

3.2 Conductor:
The conductor shall be formed from annealed circular stranded Copper conductor (or
stranded Aluminum Conductor as the case may be) complied with IEC latest publications
60228. The conductor shall be compact circular stranded.

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3.3 Conductor Screen:

The conductor screen to be provided as per Clause 7.1 IEC 60502-2:2005 or equivalent
clause in latest version of IEC 60502-2. The conductor screen shall consist of suitable
thickness and volume resistivity. It shall be easily removable from conductor during
jointing. Nominal thickness of conductor screen shall be 0.7mm.

3.4 Insulation:

The Insulation shall be XLPE complying with IEC 60502 and IEC 60811. The
insulation shall have a higher degree of Cross- Linking, free from contaminants and air
voids, heat resistant and shall be applied by the extrusion process.

The XLPE insulation shall be suitable for use on power cable in wet and dry locations at
conductor temperature as per IEC 60502-2.For this purpose, short circuit current in
conductor is to be considered as 7 kA.

The conductor with screening shall be provided with cross-linked polyethylene (XLPE)
insulation applied by extrusion. The nominal thickness of insulation shall not be less than
8 mm as per IEC 60502-2 and subject to tolerance as per IEC – 60840, clause 10.6.2.
Alternatively higher thickness of insulation as per IS 7098 with specified eccentricity in
IS 7098 will also be accepted.

The insulation compound shall be of high quality, and shall be heat, moisture, ozone and
corona resistant. XLPE compound should be from reputed manufacturer e.g. Borealis
Sweden or NUC Japan or equivalent with satisfactory service experience of more than 5
years. The Insulation shall be applied by triple extrusion and vulcanized using dry curing
process to form a compact homogenous body free from micro voids and
contaminants.

3.5 Insulation Screen:

The Insulation screening shall be applied direct upon the insulation as per IEC 60502-2.
The screen shall be tightly fitted to the insulation to exclude all air voids and still it could be
easily stripped on site. Semiconducting compound should be from a reputed
manufacturere.g. Borealis, Sweden or NUC Japan or equivalent with satisfactory service
experience of more than 5 years. Nominal thickness of insulation screen shall be 0.7mm.

The conductor screen, insulation & insulation screen shall be extruded in a single process
(triple extrusion).

3.6 Water Barrier:

Longitudinal:

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The water barrier shall be semi-conducting water swellable tape to be applied over the
extruded insulation screening to block and prevent moisture propagation in a
longitudinal direction. The semi-conducting tape shall be suitable for the operating
temperature of the cable and compatible with the insulation.

3.7 Metallic Screen:

The metallic screen shall be plain copper round wire and copper tape applied helically
over the semi-conductor bedding tape(s). An annealed plain copper binder tape shall be
applied in the form of an open helix, over the copper wire screen. The area of the copper
wire /copper tape should be able to withstand specified earth fault current (minimum 1 kA
for 3 sec). Bidder to submit the calculations giving details of the area of copper wire/
copper tape screen.

The three-phase short-circuit current capacity of metallic screen is to be considered, 1 kA

(for the cables to be fed by substations where Neutral Grounding Resistor (NGR) is
installed).

The sheath shall be impervious to moisture, reasonably close fitting and free from defects
and impurities such as oxide, which give rise to failure under working conditions.

3.8 Inner Sheath:

A polypropylene tape shall be applied over the metallic screen. For FRLSZH cables an
inner layer of FRLSZH tape shall be applied over metallic screen followed by
Polyethylene laminated Aluminium tape.

3.9 Armouring:

Double Tape Aluminium armouring should be applied over the inner sheath and the
thickness of the same should be as per IEC 60502.

3.10 Short Circuit Rating of Metallic Sheath/Screen

The area of copper wires/copper tape shall be designed to meet the requirement of the
system short circuit rating of 1 kA for 3 Seconds.

3.11 Outer Sheath

The outer sheath to be provided as per IEC 60502-2.

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SPECIFICATIONS FOR 33 kV CABLES FOR ELEVATED AND Draft-1

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4. ADDITIONAL REQUIREMENT

Cables laid on viaduct & ramps shall be exposed to sun, therefore such cables shall be
capable of withstanding ultraviolet radiation. They shall be black in colour with
identification for Red, Yellow & Blue phases which can be clearly seen without
efforts throughout the run.

4.1 Outer Sheath should have following features:

A. Cables laid in elevated sections shall be exposed to sun. The outer sheath shall
be extruded in black colour with UV Protection, FRLS PVC conforming to the
requirement of IEC specifications and extruded continuously. Such cables shall
have phase identification after interval of 10 meters. Colour coding shall be done
at manufacturer’s works. The details of compound used for outer sheath shall be
submitted.
B. For Underground cables the outer sheath shall be extruded Red/ Yellow/
Blue colour halogen free flame retardant polyolefin conforming to the
requirement of IEC specifications and extruded continuously. Outer sheath
shall be treated with Anti Termite/ Anti pest/ Anti rodent & corrosion Resistant
Compound. The sheath shall be resistant to water, ultraviolet radiation, fungus
attacks, conforming to the requirement of IEC specifications and extruded
continuously. The details of compound used for outer sheath shall be submitted.

4.2 The Contractor shall confirm the cross section of the cables in as regard to:
- the route installation,
- the thermal conditions in service,
- the climatic conditions,
- the energy and currents flowing through these cables, taking into account the
worst electrical conditions,
- operation under permissible overload conditions,
- operation under permissible overload conditions when all 33 kV distribution are
supplied by only one transformer, and on only one 33 kV cable.

4.3 The protective sheath shall carry the indications listed below, in letters and digits at
least 6 mm high:

- Designation of ownership,
- Nature and cross-sectional area of conductors,
- Specified cable voltage,
- phase numbering,
- Manufacturer’s name
- Length of cable shall be marked at 1 m interval.
- Year and month of manufacturing

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4.4 The cable shall be manufactured by a company having ISO accreditation for quality.
4.5 The manufacturing process of XLPE cable shall consist of conductor screen,
insulation & insulation screen which shall be extruded in a single process. (Triple
extrusion) and cross linked by a standard Process of dry curing technology to
ensure homogeneity and absence of micro voids. The cables shall be manufactured
by “Dry Curing” Process.

4.6 The Contractor shall provide trefoil clamps of non – metallic sturdy type at every
5 meters with cable ties at every meter.

4.7 The Employer may decide to visit the works of cable manufacturer to verify the
manufacturing process mentioned.

4.8 The Bidder along with the Bid, shall submit the details regarding cable construction,
bill of material the manufacturing process proposed to be adopted for the
manufacturing of 33 kV cables to be used in the project, along with Quality control
measures adopted by the Manufacturer, to ensure :-

 The values and tolerances are strictly as per IEC.

 The cable manufacturer exercises strict quality control measures, including stage
inspections, routine inspections etc. to ensure conformity to standards.

Periodical inspections of the Manufacturer works, manufacturing processes, Internal

Quality control records of the manufacturer etc shall be carried out by the User
(DMRC/Nominated agency), to ensure compliance to Quality standards.

5. MAINTENANCE & LIFE

The cable should be designed for maintenance free service of minimum 35 years for all
types of installation & under prescribed environmental conditions.

6. SPECIAL CONDITION

6.1 All type of Cables to be used in Underground Sections shall be Fire Retardant
Low Smoke Zero halogen Type (FRLSZH) and cables to be used in elevated and
at grade sections shall be FRLS Type. Cables from AMS to ASS shall also be FRLS
type excluding portion laid in underground section (station and tunnel) which shall be
FRLSZH type. The interconnections between the elevated & underground section shall
be dealt accordingly with minimum number of joints.
6.2 The manufacturer shall have laid down in-house selection process of the raw material
used and shall submit all details, if equivalent raw material (as referred in clause 3.4, 3.5
above) is used whenever specified.

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7. TESTING

7.1 All type tests to be conducted as per IEC 60502-2 The 33 kV cable shall comply
with following Test Standards in addition to test standards of IEC 60502:

a. IEC 60332 Part 1 and 3, category A, test on single and bunched cables under fire
condition.
b. Limiting Oxygen Index at least 30 tested as per ASTM D-2863.
c. Temperature index of minimum 250 deg C as per IS 7098 (Part-2).
d. Smoke density Test (on sheathing material), when tested in accordance to ASTM D-
2843, maximum smoke density rating shall be 60 as per IS 7098 Part – 2. This will
be applicable for FRLS Cable.
e. All Insulation is to be moisture and heat resistant, with temperature rating
appropriate to the application conditions and in no case lower than 90 deg C.

f. In addition to the above FRLSZH cables used in U/G section shall also comply
with following test standards :-

 Determination of the amount of halogen Acid Gases as per IEC 60754 Part 1
(Maximum HCL gas shall not exceed 0.5%) and IEC 60754 Part –II
 Smoke density Test (on sheathing material), when tested in accordance to ASTM
D-2843, maximum smoke density rating shall be 30 as per IS 7098 Part – 2. This
will be applicable for FRLSZH Cable.

7.2 The user may ask repetition of the following type tests –
- Bending Test
- Tan δ measurement for cables
- Impulse test followed by a voltage test for 4 hrs.

7.3 The manufacturer shall not change the Bill of Material used in the manufacturing of samples
for routine and Type testing as repeated above and in cables intended to supply against
the contract

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8. DATA SHEET - 33 KV CABLES

S. No. Description Unit Values

1 Manufacturer

2 Cable Size Sq mm 400 300 95

Aluminium/ Copper/
Copper/XLPE
3 Cable type XLPE/PVC XLPE/PVC

4 Voltage Grade (U0/U (U2) kV 18/30 (36) 18/30 (36) 18/30 (36)

5 Reference Standard IEC 60502 IEC 60502 IEC 60502

No. and cross sectional 3 x1C x 400 sq 3 x1C x 300 sq 3 x1C x 95 sq

6 area of conductor mm mm mm

7 Conductor Material Copper Aluminium Copper

Circular Circular Circular

8 Shape compact compact compact
stranded stranded stranded

Class 2/ IEC Class 2/ IEC Class 2/ IEC

9 Class/Standard 60228 60228 60228

Nominal Diameter of
mm * * *
10 Conductor

Extruded semi- Extruded semi- Extruded semi-

Conductor Screen conducting conducting conducting
11 materials com'd com'd com'd

Nominal thickness of
mm * * *
12 conductor screen

13 Insulation material XLPE XLPE XLPE

Nominal thickness of
mm * * *
14 insulation

Nominal diameter over

mm * * *
15 insulation

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Extruded semi- Extruded semi- Extruded semi-

Insulation screen material conducting conducting conducting
16 (Non-metallic) com'd com'd com'd

Nominal thickness of
mm * * *
17 insulation screen

18 Nominal thickness of tape mm * * *

19 No. and Diameter of wires No. /mm * * *

20 Cross sectional area Sq mm * * *

Flame retardant Flame retardant

21 Outer sheath material Flame retardant polyvinyl polyvinyl
chloride chloride

22 Nominal thickness of outer mm * * *

sheath

Nominal overall diameter

23 mm * * *
(± 2mm)

24 Minimum bending radius mm * * *

Max. D. C. Conductor
Ω/km * * *
25 resistance at 20oC

Star reactance per phase

Ω/km * * *
26 at 50 Hz

27 Capacitance per phase µF/km * * *

Charging current per

A/km * * *
28 phase at U0, 50 Hz

29 Max. Current rating in air A * * *

Max. Current rating in

A * * *
30 Ground

Max. Conductor
31 temperature on 90 90 90
continuous

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Max. conductor
32 temperature in short 250 250 250
circuit

Max. short Circuit current

33 * * *
rating

t = 0.1 sec kA * * *

t = 0.2 sec kA * * *

t = 0.5 sec kA * * *

t = 1.0 sec kA * * *

Length marking: Length shall be marked with number at one meter intervals on the sheath.

*Bidder to furnish the data

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