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IS 7098-2 (2011): Crosslinked Polyethylene Insulated Thermoplastics Sheathed Cables, Part 2: for Working Voltages from 3.3 kV up to and Including 33 kV [ETD 9: Power Cables]

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IS 7098 (Part 2) : 2011

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Indian Standard CROSSLINKED POLYETHYLENE INSULATED THERMOPLASTIC SHEATHED CABLES SPECIFICATION
PART 2 FOR WORKING VOLTAGES FROM 3.3 kV UP TO AND INCLUDING 33 kV

( Second Revision )

ICS 29.060.20

BIS 2011

BUREAU OF INDIAN STANDARDS

MANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG NEW DELHI 110002

December 2011

Price Group 7

Power Cables Sectional Committee, ETD 09

FOREWORD This Indian Standard (Part 2) (Second Revision) was adopted by the Bureau of Indian Standards, after the draft finalized by the Power Cables Sectional Committee had been approved by the Electrotechnical Division Council. This standard was originally published in 1973 and subsequently revised in 1985. This revision has been undertaken to bring it in line with International practices. The following changes have been incorporated in this revision: a) A special category cables with improved fire performance has been included in this standard. Classification has been given. b) Strippability test for semi conducting insulation screen incorporated. c) In insulation eccentricity and ovality has been included along with test method. d) In outer sheath polyethylene material has been included. e) Test voltages have been enhanced in line with IEC 60502-2. f) Partial discharge test voltage has been increased to 1.73UO from 1.5 UO and sensitivity has been enhanced in line with IEC 60502-2. This standard is one of the series of Indian Standards on cross-linked polyethylene insulated thermoplastic sheathed cables. Other parts in the series are: Part 1 For working voltage up to and including 1 100 V Part 3 For working voltages from 66 kV up to and including 220 kV Particular attention has been drawn to the limitations of the short circuit ratings of the types of cables covered by this standard owing to the absence of the metallic sheath and the possible loss of electrical contacts between the strands of armour as a result of corrosion or presence of compound between them or both. A separate standard about recommended short circuit ratings of these cables is under formulation. Attention is also drawn to the fact that the current ratings of the types of cables covered by this standard are different from those of the paper insulated metal sheathed cables. The correct type of cables should be selected for the system keeping in view whether the system is earth or unearthed.
NOTE It should be realized that in an electric system where an earth fault is not automatically and promptly eliminated the extra stress on the insulation of the cables during the earth faults reduces the life of cables to a certain extent. Therefore if the system is expected to be operated quite often with prolonged earth fault it is advisable to select cables suitable for unearthed system.

In the formulation of this standard assistance has been derived from IEC 60502-2 (2005) Power cables with extruded insulation and their accessories for rated voltages from 1 kV up to 30 kV Part 2: Cables for rated voltages from 6 kV up to 30 kV issued by the International Electrotechnical Commission. For the purpose of deciding whether a particular requirement of this standard is complied with the final value observed or calculated expressing the result of the test shall be rounded off in accordance with IS 2 : 1960 Rules for rounding off numerical values (revised). The number of significant places retained in the rounded off value should be the same as that of the specified value in this standard.

IS 7098 (Part 2) : 2011

Indian Standard CROSSLINKED POLYETHYLENE INSULATED THERMOPLASTIC SHEATHED CABLES SPECIFICATION

PART 2 FOR WORKING VOLTAGES FROM 3.3 kV UP TO AND INCLUDING 33 kV

( Second Revision )
1 SCOPE 1.1 This standard (Part 2) covers the requirements of following categories of crosslinked polyethylene insulated and PVC sheathed or polyethylene sheathed cables for single phase or three phase (earthed or unearthed) systems for electricity supply purposes: a) Types of Cables 1.4 This standard also covers cables with improved fire performance categories C1 and C2 as given in Annex A. For such cables additional requirements have been included, wherever necessary. 2 REFERENCES The following standards contain provisions which, through reference in this text, constitute provisions of this standard. At the time of publication, the editions indicated were valid. All standards are subject to revision and parties to agreements based on this standard are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below: IS No. Title 1885 (Part 32) : Electrotechnical vocabulary: Part 32 1993/IEC 50- Electric cables 461 : 1984 3975 : 1999 Mild steel wires, formed wires and tapes for armouring of cables 4905 : 1968 Methods for random sampling 5831 : 1984 PVC insulation and sheath of electric cables 8130 : 1984 Conductors for insulated electric cables and flexible cords 10418 : 1982 Drums for electric cables 10462 Fictitious calculation method for (Part 1) : 1983 determination of dimensions of protective coverings of cables: Part 1 Elastomeric and thermoplastic insulated cables 10810 Methods of test for cables: (Part 1) : 1984 Annealing test for wires used in conductors (Part 2) : 1984 Tensile test for aluminium wires (Part 3) : 1984 Wrapping test for aluminium wires (Part 5) : 1984 Conductor resistance test (Part 6) : 1984 Thickness of thermoplastic and elastomeric insulation and sheath (Part 7) : 1984 Tensile strength and elongation at break of thermoplastic and elastomeric insulation and sheath 1

1) Single-core unscreened, unarmoured (but non-magnetic metallic tape covered); 2) Single-core screened, unarmoured; 3) Single-core armoured (non-magnetic) screened or unscreened; and 4) Three-core armoured, screened or unscreened. b) Voltage Grade (Uo/U) 1) Earthed systems: 1.9/3.3 kV, 3.8/6.6 kV, 6.35/11 kV, 12.7/22 kV and 19/33 kV. 2) Unearthed system: 3.3/3.3kV and 11/11kV.
NOTES 1 Cables of 6.35/11kV grade (earthed systems) are suitable for use on 6.6/6.6 kV and (unearthed system) also. 2 The cables conforming to this standard may be operated continuously at a power frequency voltage 10 percent higher than rated voltage. 3 Under rule 54 of the Indian Electricity Rules, 1956 in case of high voltage, the permissible variation of declared voltage at the point of commencement of supply is not to vary by more than 6 percent on the higher side or by more than 9 percent on the lower side, 4 Measures taken for achieving longitudinal water tightness shall be as agreed between the purchaser and the supplier.

1.2 These cables are suitable for use where sum of ambient temperature and temperature rise due to load results in conductor temperature not exceeding 90C under normal operation and 250C under short-circuit conditions. 1.3 Armoured cables up to 11 kV grade specified in this standard are suitable for use in mines also. However, for such cables, additional requirements have been included, wherever necessary (4.1.1, 17.5 and 21.2.1).

IS 7098 (Part 2) : 2011 IS No. (Part 10) : 1984 (Part 11) : 1984 (Part 12) : 1984 (Part 14) : 1984 (Part 15) : 1984 (Part 30) : 1984 (Part 32) : 1984 (Part 33) : 1984 (Part 36) : 1984 (Part 37) : 1984 (Part 38) : 1984 (Part 39) : 1984 (Part 40) : 1984 (Part 41) : 1984 (Part 42) : 1984 Title Loss of mass test Thermal ageing in air Shrinkage test Heat shock test Hot deformation test Hot set test Carbon content test for polyethylene Water absorption test (gravimetric) Dimensions of armouring material Tensile strength and elongation at break of armouring materials Torsion test on galvanized steel wires for armouring Winding test on galvanized steel strips for armouring Uniformity of zinc coating on steel armour Mass of zinc coating on steel armour Resistivity test of armour wires and strips and conductance test of armour (wires/strips) Insulation resistance High voltage test Partial discharge test Impulse test Dielectric power factor test Heating cycle test Bending test Flammability test Oxygen index test Determination of the amount of halogen acid gas evolved during combustion of polymeric materials taken from cables Thermal stability of PVC insulation and sheath Flame retardant test Fire resistance test for bunched cables Measurement of temperature index
have been made they need not be repeated unless changes are made in the cable materials or design which might change the performance characteristics.

3.3 Acceptance Tests Tests carried out on samples taken from a lot for the purpose of acceptance of the lot. 3.4 Optional Tests Special tests to be carried out, when required, by agreement between the purchaser and the supplier. 3.5 Earthed System An electric system which fulfills any of the following conditions: a) Neutral-point or the mid-point connection is earthed in such a manner that, even under fault conditions, the maximum voltage that can occur between any conductor and the earthed does not exceed 80 percent of the nominal system voltage; and b) The neutral-point or the mid-point connection is not earthed but a protective device is installed which automatically cuts out any part of the system which accidentally becomes earthed within a duration of 1 min; or c) In case of ac systems only, the neutral-point is earthed through an arc suppression coil with arrangement for isolation within 1 h of occurrence of the fault for the non-radial field cables and within 8 h for radial cables, provided that the total of such periods in a year does not exceed 125 h. 3.6 Unearthed Systems An electric system which does not fulfill the requirement of the earthed systems (see 3.5). 4 CONDUCTOR 4.1 The conductors shall be composed of plain copper or aluminium wires complying with IS 8130. 4.1.1 Mining cables to be used in gassy mines shall be of copper conductor only. 5 INSULATION The insulation shall be of cross linked polyethylene conforming to the requirement given in Table 1. 6 SCREENING 6.1 The screening shall consist of one or more of the following, as specified: a) Non-metallic semi-conducting tape, b) Non-metallic semi-conducting compound, and c) Non-magnetic metallic tape wire, strip or sheath. 2

(Part 43) : 1984 (Part 45) : 1984 (Part 46) : 1984 (Part 47) : 1984 (Part 48) : 1984 (Part 49) : 1984 (Part 50) : 1984 (Part 53) : 1984 (Part 58) : 1998 (Part 59) : 1988

(Part 60) : 1988 (Part 61) : 1988 (Part 62) : 1993 (Part 64) : 2003

3 TERMINOLOGY For the purpose of this standard, the following definitions in addition to those given in IS 1885 (Part 32) shall apply. 3.1 Routine Test Test made by the manufacturer on all finished cable lengths to demonstrate the integrity of the cable. 3.2 Type Tests Tests required to be made before supply on a general commercial basis a type of cable in order to demonstrate satisfactory performance characteristics to meet the intended application.
NOTE These tests are of such a nature that after they

IS 7098 (Part 2) : 2011

NOTE The semi-conducting tape and semi-conducting compound shall be suitable for the operating temperature of the cable and compatible with the insulating material.

7 FILLERS AND INNER SHEATH 7.1 The fillers and inner sheath shall be of the following: a) Vulcanized or unvulcanized rubber; and b) Thermoplastic materials.
NOTE Vulcanized or unvulcanized rubber or thermoplastic material used for inner sheath shall not be harder than XLPE compounds used for insulation and outer sheath respectively. Fillers and inner sheath materials shall be chosen to be compatible with the temperature rating of the cable and shall have no deleterious effect on any other component of the cable.

Table 1 Properties of XLPE Insulation (Clause 5)

Sl No. (1) Property (2) Requirements (3) 12.5 N/mm, Min 200 percent, Min 135 3 C 7 day 25 percent, Max 25 percent, Max

i) Tensile strength ii) Elongation at break iii) Ageing in air oven: a) Treatment (Temperature Duration) b) Tensile strength variation c) Elongation variation iv) Hot set test a) Treatment: 1) Temperature 2) Time under load 3) Mechinical stress b) Elongation under load c) Permanent elongation (set) after cooling v) Shrinkage: a) Treatment (Temperature Duration): b) Shrinkage vi) Water absorption (Gravimetric): a) Treatment (Temperature Duration) b) Water absorbed

8 ARMOURING 8.1 Armouring shall be of the following:

200 3 C 15 min 20 N/cm 175 percent, Max 15 percent, Max

a) Galvanized round steel wire, and b) Galvanized formed wires, or c) Any metallic non-magnetic wire/strip. 8.2 The galvanized steel wires/strip shall comply with the requirements of IS 3975. The requirements of nonmagnetic material shall be as agreed to between the purchaser and the supplier. 9 OUTER SHEATH The outer sheath shall be of polyvinyl chloride (PVC) or polyethylene conforming to the requirements of Type ST 2 of IS 5831 or Table 3 respectively.
NOTE For Category C1 and C2 PVC Type ST 2 with suitable additives to be used to meet the requirements of 19.1.3 and 19.2.2 .

130 3 C 1h 4 percent, Max 85 2 C 14 days 1 mg/cm, Max 1 1014 cm, Min 1 1012 cm, Min

vii) Volume resitivity a) at 27 C b) at 90 C

6.1.1 Non-metallic Semiconducting Compound The material shall be bonded or strippable type conforming to the requirements given in Table 2. Unless otherwise specified it shall be bonded type. Table 2 Properties of Extruded Semiconducting Screen
Sl No . (1) i) Property (2) Strippability test for strippable semiconducting insulation screen Requirements (3) Force required to remove semiconducting screen from insulation without damaging shall be not less than 4 N or greater than 45 N before and after ageing when test as per Method of Test as per Annex B Method of Test as per Annex E

10 CONDUCTOR 10.1 The conductor shall be of stranded construction, size 25 mm2 and above complying with Class 2 of IS 8130. 10.2 In case of 1.9/3.3kV cables, a protective barrier may be applied between the conductor and insulation at the discretion of the manufacturer such barrier, when used shall be compatible with insulating material and suitable for the operating temperature of the cable. 11 CONDUCTOR SCREENING 11.1 All cables rated above 1.9/3.3 kV shall be provided with conductor screening. Conductor screening shall be provided over the conductor by extrusion of semiconducting compound or a combination of nonmetallic semi conducting tape and extrusion of semi conducting compound. 12 INSULATION 12.1 The conductor (with protective barrier or screen, where applied) shall be provided with cross linked polyethylene insulation applied by extrusion. 3

ii)

Resistivity test for semiconducting screen: a) Conductor screen 1000 m, Max 500 m, Max b) Core screen

6.1.2 Non-magnetic Metallic Tape for Single Core Unscreened and Unarmoured Cables Requirements for this tape shall be as agreed to between the purchaser and the manufacturer.

IS 7098 (Part 2) : 2011 Table 3 Properties of Thermoplastic Polyethylene Sheath (Clause 9)

Sl No. (1) i) Property (2) Without aging a) Tensile strength (N/mm) b) Elongation at break Ageing in air oven: a) Treatment Temperature Duration b) Elongation at break Carbon black content Hot deformation test 110 2 C for 6 h Maximum depth of indentation Requirements (3) 12.5 N/mm, Min 300 percent, Min 110 2 C 7 days 300 percent, Min 2.5 0.5 percent

12.5 Application of Insulation The insulation shall be so applied that it fits closely on the conductor (or conductor screening or barrier if any) and it shall be possible to remove it without damaging the conductor. 13 INSULATION SCREENING 13.1 All cables rated above 1.9/3.3 kV shall be provided with insulation screening. 13.2 The insulation screening shall consist of two parts; namely, metallic and non-metallic. 13.3 Non-metallic part shall be applied directly over the insulation of each core and shall consist of either extruded semi-conducting compound or a combination of semi-conducting tape and extruded semi-conducting compound. The test method for strippability test for strippable semi-conducting insulation screen is given in Annex B. Semiconducting water swell-able tapes if used shall be as agreed between the purchaser and the supplier. 13.4 Metallic part shall consist of either tape, or braid, or concentric serving of wires or a combination of wires and tapes or a sheath shall be non-magnetic and shall be applied over the non-metallic part. For single-core armoured cables, the armouring may constitute the metallic part of the screening.

ii)

iii) iv)

50 percent

12.2 Thickness of Insulation The average thickness of insulation shall be not less than the nominal value (ti) specified in Table 4 12.3 Tolerance on Thickness of Insulation The smallest of measured values of thickness of insulation shall not fall below the nominal value (ti) specified in Table 4 by more than 0.1 mm + 0.1 ti. 12.4 Eccentricity and Ovality Eccentricity of insulation shall not exceed 15 percent when tested as per Annex A.

Table 4 Nominal Thickness of Insulation (Clauses 12.2 and 12.3)

Sl No. Nominal Area of Conductor 1.9/3.3 kV and 3.3/3.3 kV Single Core Armoured Cables mm (3) 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.6 2.8 3.0 3.3 3.5 Single Core Unarmoured and Three Core Cables mm (4) 2.2 2.2 2.2 2.2 2.2 2.2 2.2 2.2 2.2 2.2 2.2 2.4 2.6 2.8 3.0 Nominal Thickness of Insulation (tI) 3.8/6.6 kV 6.35/11 kV 11/11 kV 12.7/22 kV 19/33kV

mm2 (1) i) ii) iii) iv) v) vi) vii) viii) ix) x) xi) xii) xiii) xiv) xv) (2) 25 35 50 70 95 120 150 185 240 300 400 500 630 800 10000.

mm (5) 2.8 2.8 2.8 2.8 2.8 2.8 2.8 2.8 2.8 3.0 3.3 3.5 3.5 3.5 3.6

mm (6) 3.6 3.6 3.6 3.6 3.6 3.6 3.6 3.6 3.6 3.6 3.6 3.6 3.6 3.6 3.6

mm (7) 5.5 5.5 5.5 5.5 5.5 5.5 5.5 5.5 5.5 5.5 5.5 5.5 5.5 5.5 5.5

mm (8) 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0

mm (9) 8.8 8.8 8.8 8.8 8.8 8.8 8.8 8.8 8.8 8.8 8.8 8.8 8.8 8.8 8.8

IS 7098 (Part 2) : 2011 14 CORE IDENTIFICATION 14.1 Core identification for three core cables shall be as follows: Table 5 Thickness of Inner Sheath (Clause 16.3) All dimensions in millimetres.
Sl No. Calculated Diameter Over Laid Up Cores, Ref to IS 10462 (Part 1) Over (1) i) ii) iii) iv) v) (2) 25 35 45 55 Up to and Including (3) 25 35 45 55 Thickness of Inner Sheath Min

Voltage Grade kV 1.9/3.3 and 3.3/3.3

Method of Identification a) Different colouring of XLPE insulation, or b) Coloured strips applied on the cores, or c) By numerals (1, 2, 3,) either by applying numbered strips or by printing on the cores.
NOTE It is permissible to apply the strips above the insulation screen

(4) 0.3 0.4 0.5 0.6 0.7

3.8/6.6, 6.35/11, 11/11, 12.7/22 and 19/33 kV

a) Coloured strips applied on the cores, or b) By numerals (1, 2, 3) either by applying numbered strips or by printing on the cores

protective barrier or non-metallic part of insulation screening, if any in case of single core cables or over inner sheath in case of screened and armoured single core cables and over inner sheath in case of three cores cables. 17.1.1 The armour wires/formed wires shall be applied as closely as practicable. 17.1.2 The direction of lay of armour shall be left hand for double wires/formed wires armoured cable this requirement shall apply to the inner layer of wires/ formed wires the outer layer shall, except in special cases be applied in the reverse direction to the inner layer, and there shall be a separator of suitable nonhygroscopic material: such as plastic tape bituminized Hessian cotton tape, rubber proofed tape between the inner and outer layers of armoured wires/formed wires. 17.1.3 A binder tape may be applied over the armour. 17.2 Types of Armour Where the calculated diameter below armouring does not exceed 13 mm, the armour shall consist of galvanized round steel wires. The armour of cables having calculated diameter below armouring greater than 13 mm shall consist of either galvanized round steel wires or galvanized formed wires. 17.2.1 In case of single-core cables for ac system, the armouring shall be of non-magnetic material. 17.3 Dimensions The dimension of galvanized steel wire or formed wires shall be as specified in Table 6. 17.4 Joints The joints in armour wires or formed wires shall be made by brazing or welding and the surface irregularities shall be removed. A joint in any wires/ formed wires shall be at least 300 mm from the nearest 5

14.1.1 For identification by using coloured strips, red, yellow and blue colours respectively shall be used to identify phase conductors. 15 LAYING UP OF CORES 15.1 In three core cables, the cores shall be laid together with a suitable right hand lay. Where necessary the interstices shall be filled with non-hygroscopic material. 16 INNER SHEATH (COMMON COVERING) 16.1 The laid up cores shall be provided with inner sheath applied either by extrusion or by wrapping. It shall be ensured that the shape is as circular as possible. 16.2 The inner sheath shall be so applied that it fits closely on the laid up cores and it shall be possible to remove it without damage to the insulation. 16.2.1 In case of single core cables where there are both metallic screening and armouring there shall be extruded inner sheath between them. 16.3 Thickness of Inner Sheath The thickness of inner sheath (common covering) shall be as given in Table 5 single core cables except those specified on 15.2.1 shall have no inner sheath. 16.3.1 When one or more layers of binder tapes are applied over the laid up cores, the thickness of the tapes shall not be construed as a part of the inner sheath. 17 ARMOURING 17.1 Application Armouring shall be applied over the insulation or

IS 7098 (Part 2) : 2011 Table 6 Dimensions of Armour Round Wires and Formed Wires (Clause 17.3) All dimensions in millimetres.
Sl Calculated Diameter Nominal Nominal Diameter No. Under Armour Thickness of of Round Wire [IS 10462 (Part 1)] Steel Strip Over (1) i) ii) b) c) d) e) f) 13 25 40 55 70 (2) For all diameter in excess of 13 or 13 25 40 55 70 Up to and Including (3)

formed wires in armour by required number of tinned copper wires/formed wires is permissible. 18 OUTER SHEATH 18.1 The outer sheath shall be applied by extrusion. It shall be applied: a) Over the non-magnetic metallic tape covering. The insulation or over The nonmagnetic metallic part of insulation screening in case of un-armoured single core cables, and b) Over the armouring in case of armoured cables. 18.2 Colour of outer sheath shall be black or any other colour as agreed to between the purchaser and the supplier. 18.3 Thickness of Outer Sheath 18.3.1 Unarmoured Cables The thickness of outer sheath of unarmoured cables determined by taking the average of a number of measurements shall be not less than the nominal value specified in col 3 of Table 7 and the smallest of the measured values shall not fall below the nominal value specified in col 4 of Table 7. 18.3.2 Armoured Cables The thickness of outer sheath shall not be less than the minimum value specified in col 5 of Table 7.

(4) 0.8 0.8 0.8 1.4 1.4 1.4

(5) 1.4 1.6 2.0 2.5 3.15 4.0

NOTE (i) and (ii) indicate two methods of practice in the application of armouring.

joint in any other armoured wire/formed wires in the completed cable. 17.5 Resistance In case of cable for use in mines the resistance of armoured shall be not exceed that of conductor as specified in IS 8130 by more than 33 percent. To satisfy this, substitution of the galvanized steel wires/

Table 7 Thickness of Outer Sheath (Clauses 18.3.1 and 18.3.2) All dimensions in millimetres.
Sl No. Calculated Diameter Under the Outer Sheath [IS 1S462 (Part 1)] Over (1) i) ii) iii) iv) v) vi) vii) viii) ix) x) xi) xii) (2) 15 25 35 40 45 50 55 60 65 70 75 Up to and Including (3) 15 25 35 40 45 50 55 60 65 70 75 Thickness of Outer Sheath for Unarmoured Cables Nominal (t s ) (4) 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 Minimum (5) 1.24 1.4 1.56 1.72 1.88 2.04 2.2 2.36 2.52 2.68 2.84 3.0 (6) 1.24 1.4 1.56 1.72 1.88 2.04 2.2 2.36 2.52 2.68 2.84 3.0 Minimum Thickness of Outer Sheath for Armoured Cables

IS 7098 (Part 2) : 2011 19 CLASSIFICATION OF TESTS 19.1 Type Tests The following shall constitute type tests: 19.1.1 Test (viii), (x), (xii) and (xiii), are applicable only to screened cables. 19.1.2 With the exception and provision of 19.1.1 the following tests on screened cable shall be performed

Sl No. (1) i)

Test (2) Test on conductor: a) Annealing test (for copper) b) Tensile test (for aluminium) c) Wrapping test (for aluminium) d) Resistance test Test for armouring wires/formed wires

For Requirements, Ref to (3) IS 8130 IS 8130 IS 8130 IS 8130 Clause 7, Table 6 and IS 3975

Method of Test, Ref to IS 10810 (4) 1 2 3 5 36-42

ii) iii)

iv) v)

Physical test for insulation: a) Tensile strength and elongation at break Table 1 b) Ageing in air oven Table 1 c) Degree of cross linking d) Hot set test Table 1 e) Shrinkage test Table 1 f) Water absorption test (gravimetric) Table 1 Test for thickness of insulation Clause 11, Tables 4, 5 and (eccentricity) and sheath 7 and Annex A Test on extruded semi conducting screens a) Test for strippability of semiconducting strippable insulation screen (when applicable) Table 2 and Annex B

7 11 30 12 33 6

vi)

b) Volume resistivity Physical test for outer sheath: a) Tensile strength and elongation at break b) Ageing in air oven c) Shrinkage test d) Hot deformation e) Loss of mass in air oven f) Heat shock g) Thermal stability h) Carbon black content of polythene sheath Thermal ageing test for complete cable Partial discharge test Bending test Dielectric power factor test: a) As a function of voltage b) As a function of temperature Insulation resistance (volume resistivity) test Heat cycle test Impulse withstand test High voltage test Flammability test for PVC sheathed cables

Table 2 and Annex E IS 5831 or Table 3 IS 5831 or Table 3 IS 5831 IS 5831 or Table 3 IS 5831 IS 5831 IS 5831 Table 3 7 11 12 15 10 14 60 32 or any other thermo analytic method (by thermo gravimetric analysis) see 19.9 46 50 48

vii) viii) ix) x)

19.9 19.2 19.3 19.4

xi) xii) xiii) xiv) xv)

Table 1 19.5 19.6 19.7 19.8

7

43 49 47 45 53

IS 7098 (Part 2) : 2011 successively on the same test sample of completed cable not less than 10 m in length between the test accessories: a) b) c) d) e) Partial discharge test, Bending test followed by partial discharge test, Dielectric power factor as a function of voltage, Dielectric power factor as a function of temperature, Heating cycle test followed by dielectric power factor as a function of voltage and partial discharge tests, f) Impulse withstand test, and g) High voltage test. 19.1.2.1 If a sample fails in test (vii) one more sample shall be taken for this test preceded by tests (ii) and (v). 19.1.3 The following shall constitute additional type test for the cables with improved fire performance as per the Categories given in Annex C.

Category (1) 01 C1

Test (2) No additional test a) Oxygen index b) Flame retardance test on single cables c) Flame retardance test on bunched cables d) Temperature index a) Oxygen index b) Flame retardance test on single cables c) Flame retardance test on bunched cables d) Smoke density test (on sheathing material) e) Test for halogen acid gas evolution f) Temperature index

For Requirement, Ref to Clause (3) 20.10 20.11 20.12 20.15 20.10 20.11 20.12 20.14 20.13 20.15

Methods of Test, Ref to IS 10810 (4) 58 61 62 64 58 61 62 under preparation 59 64

C2

NOTES 1 For Category C1 tests (a) and (d) are to be performed on sample taken from the outer sheath, as applicable and prepared in the manner given in the relevant test methods . 2 For Category C2 test (a) , (e), and (f) are to be performed on samples taken from outer sheath , as applicable and prepared in the manner given in relevant test methods .

19.2 Acceptance Tests The following shall constitute acceptance tests: a) b) c) d) e) Annealing tests (for copper), Tensile test (for aluminium), Wrapping test (for aluminium), Conductor resistance tests, Test for thickness of insulation (eccentricity) and sheath, f) Hot set test for insulation, g) Tensile strength and elongation at break test for insulation and outer sheath, h) Partial discharge test (for screened cables only), j) High voltage test, k) Insulation resistance (volume resistivity) test, and m) Test for cross linking for extruded semiconducting screen.
NOTE Partial discharge test shall be carried out on full drum length.

19.2.1 A recommended sampling plan for acceptance test is given in Annex D. 19.2.2 The following shall constitute additional acceptance tests for cables with improved fire performance as per the categories given in Annex C. Category 01 C1 No a) b) c) a) b) c) d) e) Test additional test Oxygen index Flame retardance test on single cable Flame retardance on bunched cables Oxygen index Flame retardance test on single cable Flame retardance test on bunched cables Test for halogen acid gas evolution Test for smoke density

C2

19.3 Routine Tests The following shall constitute routine tests: a) 8 Conductor resistance test,

IS 7098 (Part 2) : 2011 b) Partial discharge test (for screened cables only), c) High voltage test, and d) Resistance test for armour (for mining cables) in accordance with IS 10810 (Part 42) and 17.5.
NOTE Partial discharge test shall be carried out on full drum length.

The heating cycle shall be of atleast 8 h duration. The conductor temperature shall be maintained within the stated temperature limits for atleast 2 h of each heating period. This shall be followed by atleast 3 h of natural cooling in air to a conductor temperature within 10 K of ambient temperature.
NOTES 1 The cycle shall be carried out 20 times. 2 After twentieth cycle, the sample shall be subjected to dielectric power factor as a function of voltage (20.4.1) and partial discharge test (see 20.2).

19.4 Optional Test Cold impact test for outer sheath (see IS 5831).

20.6 Impulse Withstand Test 20 DETAILS OF TESTS 20.1 General Unless otherwise stated in this standard, the test shall be carried out in accordance with appropriate part of IS 10810, taking into account additional information given in this standard. 20.2 Partial Discharge Test The partial discharge magnitude at test voltage equal to 1.73 Uo shall not exceed 10 pC for routine tests/ acceptance tests and 5pC for Type Tests. 20.3 Bending Test The diameter of the test cylinder shall be 20D 5 percent where D is the overall diameter of the completed cable. After completing the bending operations, the test sample shall be subjected to partial discharge measurement and shall comply with the requirements given in 20.2. 20.4 Dielectric Power Factor Test 20.4.1 tan as a Function of Voltage The measured value of tan at U o shall not exceed 0.004 and the increment of tan between 0.5 Uo and 2 Uo shall not be more than 0.002. 20.4.2 tan as a Function of Temperature The measured value of tan shall not exceed 0.004 at ambient temperature and 0.008 at 5 C to 10 C above the maximum conductor temperature in normal operation. 20.5 Heating Cycle Test The sample, which has been subjected to previous tests shall be laid out on the floor of the test room and heated by passing a current through the conductor, until the conductor reaches a steady temperature of 5C to 10 C above the maximum conductor temperature in normal operation. For three core cables, the heating current shall be passed through all conductors. 9 Impulse voltage level shall be as given below:

Rated voltage, 3.8/6.6 6.35/11 11/11 12.7/22 19/33 kV Impulse volt60 75 95 125 170 age, kV
No breakdown of insulation shall occur during the test. The temperature of the conductor shall be at 5 C to 10 C above the maximum conductor temperature in normal operation. 20.7 High Voltage Test 20.7.1 Type/Acceptance Test The cable shall withstand without breakdown an ac voltage equal to 4 Uo when applied to the sample between conductor and screen/metallic tape/armour (and between conductors in case of unscreened cable). the voltage shall be gradually increased to the specified value and maintained for a period of 4 h. If while testing, interruption occurs during the 4 h period the test shall be prolonged to the same extent. If the interruption period exceeds 30 min, the tests shall be repeated. 20.7.2 Routine Test The cables shall withstand without any failure, the test voltages given below, when applied for a period of five minutes for each test connection:

Voltage Grade kV

Test Voltage Between Conductor and Screen/Armour kV (rms) Between Conductor kV (rms) 10

1.9/3.3 3.8/6.6 6.35/11 11/11 12.7/22 19/33

10 13 21 35 42 63

IS 7098 (Part 2) : 2011 20.8 Flammability Test for PVC Sheathed Cables Period of burning after removal of the flame shall not exceed 60 s and the unaffected (uncharred) portion from the lower edge of the top clamp shall be at least 50 mm. 20.9 Thermal Ageing Test for Complete Cable This test shall be carried out to check that the insulation, non-metallic sheath and extruded semiconducting layer over the conductor and insulation are not liable to deteriorate in operation due to contact with other components in the cable. Three pieces of complete cable about 200 mm long shall be suspended vertically and substantially in the center of the oven at least 20 mm away from each other and shall not occupy more than 2 percent of the volume of the oven. The pieces of cables shall be kept in the oven at the temperature of 10 2C above the rated maximum normal operating conductor temperature of the cable for duration of 168 h. The test piece of insulation and sheath from the aged piece of the cable shall be prepared and subjected to tensile strength and elongation at break. The resistivity of the extruded semi-conducting layers shall be determined on the test piece from the aged cable sample in accordance with Annex E. The resistivity of semi conducting screen layers measured as per Annex E shall not exceed the following values: a) Conductor screen b) Insulation screen : : 1 000 . m 500 . m reached a height exceeding 2.5 m above the bottom edge of the burner, measured at the front and rear of the cable assembly.
NOTE Requirements for this test are split in 3 categories that is A, B and C as described in IS 10810 (Part 62). For the purpose of this standard, category B and C test method shall be used. In the absence of any special requirements for method B, method C shall be used for both categories C1 and C2.

20.13 Test for Halogen Acid Gas Evolution The level of HCl evolved shall not exceed 20 percent by weight. 20.14 Test for Smoke Density Smoke density rating shall be 60 maximum. 20.15 Test for Temperature Index The extrapolated values of temperature at which oxygen index is 21 shall be minimum 250C. 21 IDENTIFICATION 21.1 Manufacturers Identification The manufacturer shall be identified throughout the length of cable by manufacturers name or trade-mark and the voltage grade and year of manufacture indented, printed or embossed or by means of a tape bearing this information. the indentation, printing or embossing shall be done only on the outer sheath. For manufacturers name, if none of these methods is employed or if the purchaser so desires, colour identification threads in accordance with a scheme to be approved by the Indian Standard insulation shall be employed. 21.2 Cable Identification 21.2.1 In case of cables intended for use in mines, the word Mining shall be indented, printed or embossed on the outer sheath throughout the length of the cable. 21.2.2 The special cables with improved fire performance for Category C1 and C2 shall be identified by indenting, embossing or printing the appropriate legend on the outer sheath throughout the cable length in addition to the existing marking requirements. Type of Cable a) Improved fire performance or Category C1 b) Improved fire performance or Category C2 21.3 Cable Code The following code shall be used for designating the cable: 10 Legend FR FR-LSH

20.9.1 The test results for the tensile strength and elongation at break shall comply with the values of insulation and sheath after ageing as given in Table 1 for insulation and IS 5831 for PVC outer sheath and Table 3 for thermoplastic polyethylene outer sheath. 20.10 Oxygen Index Test The test on samples of outer sheath shall be done at 27 2C or ambient. The oxygen index shall not be less than 29. 20.11 Flame Retardance Test on Single Cables (for overall diameter 35 mm) After the test, there should be no visible damages on the test specimen within 300 mm from its upper end. Mark from fixing devices, soot or changing of the colour are not considered damages. 20.12 Flame Retardance Test on Bunched Cables After burning has ceased, the cables should be wiped clean and charred or affected portion should not have

IS 7098 (Part 2) : 2011 Sl No. Constitute Code Letter i) Aluminium conductor A ii) XLPE insulation 2X iii) Steel round wire armour W iv) Non-magnetic round wire armour Wa v) Steel strip armour F vi) Non-magnetic strip armour Fa vii) Double steel round wire armour WW viii) Double steel strip armour FF ix) PVC outer sheath Y x) Polyethylene outer sheath 2Y
NOTE No code letter for conductor is required when the conductor material is copper.

b) c) d) e) f) g) h)

Manufacturers name or trade-mark; Type of cable and voltage grade; Number of cores; Nominal cross-sectional area of conductor; Cable code; Length of cable on the drum; Number of lengths on the drum (if more than one); j) Direction of rotation of drum (by means of an arrow); k) Gross mass; m) Country of manufacture; and n) Year of manufacture. 22.2.1 BIS Certification Marking The cable (drum or label) may also be marked with the Standard Mark. 22.2.1.1 The use of the Standard Mark is governed by the provisions of the Bureau of Indian Standards Act, 1986 and the Rules and Regulations made there under. The details of conditions under which the Iicence for the use of the Standard Mark may be granted to manufacturers or producers maybe obtained from the Bureau of Indian Standards.

22 PACKING AND MARKING 22.1 The cable shall be wound on a drum either wooden (see IS 10418) or steel and packed. The ends of the cable shall be sealed by of non-hygroscopic sealing material. 22.2 The cable shall carry the following information either stenciled on the drum or contained in a label attached to it: a) Reference to this Indian Standard, for example, see IS 7098 (Part 2);

ANNEX A (Clauses 1.4 and 12.4)

TEST METHODS FOR ECCENTRICITY AND OVALITY A-1 TEST METHOD FOR ECCENTRICITY The eccentricity of the insulation shall be checked as follows: Percent eccentricity = A-2 TEST METHOD FOR OVALITY The ovality of the core shall be checked as follows: Percent ovality =

t Max t Min 100 t Max

dcore Max dcore Min 100 dcore Max

where t stands for the thickness of insulation. 11

where d stands for the diameter of the core.

IS 7098 (Part 2) : 2011

ANNEX B (Clause 13.3)

STRIPPABILITY TEST FOR STRIPPABLE SEMICONDUCTING INSULATION SCREEN B-1 This test shall be carried out when extruded semiconducting insulation screen is strippable. The test shall be performed three times on both unaged and aged samples, using either three separate pieces of cable or one piece of cable at three positions around the circumstance, spaced at approximately 120C Core lengths of atleast 250 mm shall be taken from the cable to be tested, before and after being aged according to 20.9. Two cuts shall be made in the extruded semiconducting insulation screen of each sample, longitudinally from end to end and radially down to the insulation, the cuts being (10 1) mm apart and parallel to each other. After removing approximately 50 mm length of the 10 mm strip by pulling it in a direction parallel to the core (that is, a stripping angle of approximately 180C), the core shall be mounted vertically in a tensile machine with one end of the core held in one grip and the 10 mm strip in the other. The force to separate the 10 mm strip from the insulation, removing a length of atleast 100 mm, shall be measured at a stripping angle of approximately 180 C. Using a pulling speed of 250 50 mm/min. The test shall be carried out at a temperature of 27 5 C. For unaged and aged samples, the stripping force values shall be continuously recorded. The insulation surface shall not be damaged and no trace of the semiconducting screen shall remain on the insulation.

ANNEX C (Clauses 19.1.3 and 19.2.2)

CATEGORIES OF CABLES WITH IMPROVED FIRE PERFORMANCE

Category 01

Environment Description Cables in open areas

Type

Cable Description Flame retardant, single cable self extinguishing, does not propagate fire Flame retardant, does not propagate fire even when installed in groups in vertical ducts Flame retardant cables with reduced halogen evolution and smoke

C1

Cables in constrained area

FR

C2

Cables in constrained area with limited human activities and/or presence of sophisticated system

FR-LSH

ANNEX D (Clause 19.2.1)

SAMPLING OF CABLES D-1 LOT D-1.1 In any consignment the cables of the same size manufactured under essentially similar conditions of production shall be grouped together to constitute a lot. 12 D-2 SCALE OF SAMPLING D-2.1 Samples shall be taken and tested from each lot for ascertaining the conformity of the lot of the standard.

IS 7098 (Part 2) : 2011 D-2.2 The number of samples to be selected shall be as given below: order to ensure the randomness of selection, procedure given in IS 4905 may be followed. D-3 NUMBER OF TESTS AND CRITERION FOR CONFORMITY D-3.1 From each of the drums selected, suitable lengths of test samples shall be taken. These test samples shall be subjected to each of the acceptance tests (see 19.2). A test sample is called defective if it fails in any one of the acceptance tests. If the number of defectives is less than or equal to the corresponding permissible number given in D-2.2, the lot shall be declared as conforming to the requirements of acceptance tests otherwise not.

Sl No. of Drums No. of Drums to Permissible No. in a Lot be taken as No. of Sample Defective (1) i) ii) iii) iv) v) (2) Up to 25 26 to 50 51 to 100 101 to 300 301 and above (3) 3 5 8 13 20 (4) 0 0 0 1 1

D-2.2.1 These samples shall be taken at random. In

ANNEX E (Clause 20.9)

METHOD OF MEASURING RESISTIVITY OF SEMICONDUCTING SCREEN E-1 Each test piece shall be prepared from a 150 mm sample of complete cable. The conductor screen test piece shall be prepared by cutting a sample of core in half longitudinally and removing the conductor and separator, if any. The insulation screen test piece shall be prepared by removing all the covering from the sample of the core. The procedure for determining the volume resistivity of screen shall be as follows: Four silver plated electrodes A, B, C and D (see Fig. 1) shall be applied to the semi-conducting surfaces. The potential electrodes B and C shall be 50 mm apart and the two current electrodes A and D shall be each placed at least 25 mm beyond the potential electrodes. Connection shall be made to the electrodes by means of suitable clips. In making connections to the conductor screen electrodes, it shall be ensured that the clips are insulated from the insulation screen on the outer surface of the test sample. The assembly shall be placed in an above preheated to the specified temperature and, after an interval of at least 30 min, the resistance between the electrodes shall be measured by means of circuit, the power of which shall not exceed 100 mW. After the electrical measurements, the diameters over the conductor screen and insulation screen and the thicknesses of the conductor screen and insulation 13 screen shall be measured at ambient temperature, each being the average of six measurements made on the sample shown in Fig. 1. The volume resistivity in m shall be calculated as follows: a) Conductor screen

rc =
where

Rc p ( Dc Tc ) Tc 2 Lc

c = volume resistivity, in m; Rc = measured resistance, in ; Dc = outer diameter over the conductor screen, in m; Lc = distance between potential electrodes, in m; and Tc = average thickness of conductor screen, in m. b) Insulation screen

i =
where i

Ri ( Di + Ti ) Ti Li

= volume resistivity, in m;

IS 7098 (Part 2) : 2011 R i = measured resistance, in ; Di = outer diameter over the insulation screen, in m; Li Ti = distance between potential electrodes, in m; and = average thickness of insulation screen, in m.

B, C = Potential electrodes A, D = Current electrodes

All dimensions in millimetres.

FIG. 1

14

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