IS 7098 part-III

'.'/. ", . IS 7098 ( Part 3 ) : 1993

311Qf~ ~~ ~ q-Tz;fTS:~T{~T~· fcr~m CfTq­~~n:rT ~ ~~ - fcrf~· ..

Indian Standard.

CROSS-LINKED POL YETHYLENE INSULATEDTHERMOPLASTIC SHEATHED CABLES _.

SPECIFICA·TIONPART 3 FOR WORKING VOLTAG.ES FROM 66 kV UP TO AND INCLUDING 220 kV

(First Reprint SEPTEMBER 1996)

UDC 621"315'221'8 : 678'073

o HIS 1993

BUR E A U OF IN D I AN S TAN DAR DSMANAK I3HAVAN, 9 BAHADUR SHAH ZAPAR MARG

NEW DELHI 110002

April 1993 Price GrRP. 7

Power Cables Sectional Committee, ETD 9

FOREWORD

This Indian Standard ( Part 3) was adopted by the Bureau of Indian Standards, after the draftfinalized by the Power Cables Sectional Committee had been approved by the ElectrotechnicalDivision Council.

Other two parts of this series of Indian Standards cover crosslinked polyethylene insulatedthermoplastic sheathed cables of following voltage grades:

Part I For working voltages up to arid including I 100 Y

Part 2 For working volrages from 3'3, kY up to and including 33kY

For the purpose of deciding whether a particular requirement of this standard is complied with, thefinal value, observed or calculated, expressing the result of a test, shall be rounded ofT in accordance

'- .vith IS 2: 1960 'Rules for rounding ofT numerical values (revised)'. The number of significantplaces retained in the rounded off value should be the same as that of the specified value in thisstandard.

IS 70YO \ t'an ~ J, : 17.7J

Indian Standard

CROSS-LINKED POLYET!l.YLENEINSULATEDTHERMOPLASTIC SHEATHED CABLES --

SPECIFICATION 'PART 3 FOR WORKING VOLTAGES FROM 66 kV UP TO AND INCLUDING 220 kV

1 SCOPE

SECTION 1 GENERAL

Table 1 Voltage Grades

1.2 Cables covered under this standard aresuitable for use where the combined ambienttemperature and temperature rise due to I~adresult in conductor temperature not exceeding90·C under normal operation and 2.50·C undershort circuit operation.

3.6 Longitudinally Watertlcbt Cables

Cables to meet the requirements to prevent thepropagation of water along the length of cable.

3.7 Radially Watertight Cable

Cables to meet the requirements to prevent theradial propagation of water.

3.5 Earthed System

An electrical system in which the neutral pointor a mid-point connection is earthed in such amanner that even under fault conditions. the'maximum voltage that can occur between anyconductor and earth does not exceed 80 percent ofnominal system voltage.

3.3 Acceptance Tests

Tests carried out on-samples taken from a lot forthe purpose of acceptance of the let-

3.4 Optional Thts

Special tests. to be carried out. when required. byagreement between the purchaser and thesupplier.

SECTION 2 MATERIALS

.. CONDUCTOR

4.1 The conductors shall be composed of plaincopper wires complying with IS 8130 : [984.

areA

(2 )

38166

64/11076/132

127/220

( I )

66110132220

1.1 This standard (Part 3) covers the require­ments of single core. cross' linked polyethyleneinsulated, unarrnoured or armoured . (with orwithout lead alloy sheath )al1d thermoplasticouter sheathed cables for 3 phase ac earthedsystem for electric supply for the voltage gradesgiven in Table I.

2 REFERENCES

2.1 Indian Standards listed in Annexnecessary adjuncts to this standard.

~s'temVcttage Rated Voltage Highest System'. U ( kV ) Uo/U ( kV ) Vottace

Um( kV)

(3)

72'S12314S24S

C-TERMINOLOGY

3.0 For the purpose of this standard the followingdefinitions in addition to those given in IS [885 .(Part 32) : 1971 shall apply.

5 INSULATION

The insulation shall be of cross-linked poly­ethylene conforming to the requirements ofTable' 2.

3.1 Routine Test

Tests carried out by the manufacturer on allfinished cable lengths to demonstrate integrity ofthe cable.

3.2 Type Tests

Tests required to be made before supply on atype: of cable on a general commercial basis inorder to demonstrate satisfactory performancecharacteristics to meet the intended application.

NOTE - These tests are of such a nature that afterthey have been made. they need not be repeated unlesschanges ale made in the cable materials or designwhich might change the performance characteristics.

6 SCREENING

The screening shall consist of one or more of thefollowing:

a) Non-metallic semi-conducting tape;

b) Nou-metallic semi-conducting compound;and

c) Nou-mag netic metallic tape, wire, strip orsheath.

NO FE - The scrni-conducring tape and the semi­conducting compound ~h811 be suitable COl theo~ratillg temperature (If the cable and cornpaublewith the insulating material.

"f'

15 7098 ( Part 3 ) : 1993

Requirement

12'5 N/sq mm ( Mill )

~OO% ( Mill )

Properly

Table 2 Properties of XLPE Insulation

( Clause 5 )

i) Teus ile slrength before aseing

ii) Elongalion al break before ageing

SI No.

2 Description or material - 0'4 percent Tin. 0'2 percent Antimony.

2

Table :f Cornposltlon of lead Alloy E Sheath

iClause 7.2)

±25Y. ( Max)±25% ( Max I

130±3°C

6h

4% (Max)

200±3°C

15 Minutes20 NIcOli

175';~ ( Max)

15% ( Max)

135±3"C

168 h

8 INNER SHEATH

7.3 Wat.er Blocking Tape/Powdtr

This shall be synthetic non-woven tape/synthetic.powder with suitable water swellable absorbent.The tape/powder can be' either non-conductingor semi-conducting.

8.1 The inner sheath shall be of PVC compoundor thermoplastic polyethylene compound.

8.2 The PVC compound shall conform to TypeST2 or IS 5831 : 1984.

v) Shrinkage

a) Treatment : Ten-perature

Duration

b) Shrinkage

iii) Ageing in air oven

a) Treatment : Temperature

Duration

h) V:lli:llilln from corrc snonding values before agdn/l.:

Temilc ~lr('''~:lh

Elongarion at brtak

i v) HoI set

:1) Trcarrneut ; Tcruperarure1 ill:~ uru'er loadMecha nica l SUeH

b)· Elongarion under load

c) Pcrrnanenr elongation after coolil'g

Antimony Tin Tellurium Sih"er Copper Bismuth Zinc Total Lead OtherElements

",- ----"--_ ..- . r- ___ A.-__~ ;- ___A ____

Min Max Min Max Max Max MaJ( Max Max Max Min

( I ) ( 2 ) ( 3 ) ( 4 ) ( 5 ) ( 6) ( 7 ) ( 8 ) ( 9 ) ( 10) ( II )

0'15 0'25 0'34 0'45 0'005 0'005 0'06 .0'05 0'002 0'01 Remainder

NOTES

1 Values are ill percentage by weight.

7 MOISTURE BARRIER

7.1 Laminated Tape

This shall be a plastic coaled non-ferrous metaltape longitudinally applied and suitably sealed.

7.2 Lend Alloy Sheath

The metallic sheath shall' be of Lead Alloy Econforming 10 requirements given in Table 3.

NOTE - For special arplicarions other lead alloysmay be used as agreed fl' between the purchaser andthe manufacturer.

.~~----_..~~lSj.~''''';'~'''''''''·~

NOTE - Semi-conducting barrier <:tnrcilarcs wlrhlllilll!>le oV\'rlnl' 11111)' he npplied hetween the conductorIIIHI r:\uudnlclIndllclClr .erreliinG, :olllch barrier larw/tapes when used shall he cnmpntlble with !heir.sulating ruaterinl and suitable for the operallngtemperature of the cable.

IS 7098t\Part 3 ) : 1993

12.2 The minimum thickness of extruded . con- ,ductor screening shall be 0'8 mm,

13 INSULATION

300~'~

300%

a) Tensile strength beforeageing ( M in )

b) Elongation at break ( Min )

- before ageing

-After ageing in air ovenat llO± zoe for 14 days

- "R.3 The Ihermoplaslic polyethylene compeundsh/lll coufunu to Iullowing pruperues:

12'S N/mm 2

c) Hot-deformation test ­lIS ± re for 6 hours

-Max depth of indentation SO%

d) Carbon black content 2'S±0'S%

9 ARMOUR

9.1 The armour shall be of non-magneticmetallic wires.

9.2 The requirements of non-magnerie materialshall be as agreed to between the purchaser andthe supplier.

10 OUTER SHEATH

13.1 The insulation shall be extruded Cross­linked Polyethylene (XLPE) satisfying therequirements of Table 2.

13.2 The average thickness of insulation shall be'riot less than the nominal value (II) specified inTable S.

13.3 The smallest of Ihe measured valuellofthickness of insulation shall not fall below thenominal value ( 11 ) specified in Table 5 by morethan 0'1 II.

Table 5 Nominal Thicknesa.cf XLPE Insulation..II

16

18

Z7

Nominal InsulationThickness. rnrn/'

\'oltaj(c GradeUo/U ( kV )

38/66

64/110

76/13~

127/22010.3 The' thermoplastic polyethylene compound" _shall conform to 8.3.

10.1 The outer sheath may be of PVC compoundor thermoplastic polyethylene compound.

10.2 The PVC compound shall conform to TypeST2 of IS S83 I : 1984.

SECTION 3 CONSTRUCTION

11 CONDUCTOR

14 INSULATION SCREEj~ING

14.1 The insulation screening shall consist (If twoparts, namely. metallic and non-metallic.

11.1 The conductor shall be of stranded circularcompacted construction complying with therequirements of Class 2 of IS 8130 : 1984.

NOTE - Where necessary. segmental construction ispermissible:

14.2 Non-metallic Part ,

14.2.1 The non-metallic part sha II consist of alayer of semi-conducting compound extrudeddirectly over the insulation,

11.2 The smallest nominal conductor c:";oss-sectionfor each voltage grade shall be as per Table 4.

NOTF. - Conductor screening. insulation andinsulation screening shall be extruded in oneopera tion .

Table " Nominal Cross-Section of Conductor

Voltage GradeUo,U (kV)

( I 1

38/6664/11076/13!­

127/220

Smallest Nominal yoss-Sectiol1lt(If Conductor ( sq. mn )

( 2 J

95

150185400

14.2.2 The minimum thickness of extrudedinsulation screening shall be 0'8 111m.

14.2.3 Semi-conducting tape/tapes with suita bleoverlap may be applied over the extrudedinsulation screening. Such barrier tupe/t a peswhen used shall he compatible with the insulatingmaterial and suitable for the operuting tempera­lure of the cable.

12 CONDUCTOR SCREENING14.3 Met a llic Part

12.1 Tile conductor screening shall consist of alayer of semi-conducting compound extruded overthe conductor.

14.3.1 The meta ll ic part of the screening shallconsist of Copper wires/Copper tape( s ) he lica llyapplied over the lead alloy sheath or non-metallicscreening.

3

IS 7098 ( Part 3 ) : 1993

14.3.2 The diameter of copper wire in the screen.ing shall not be lessthan 0'8 mrn. The perpend i­cular gap between two adjacent wires shall notbe more than 4'0 rnrn, The nominal thickness ()fcopper tape shall be not less than 0'1 mm. Theminimum thickness shall not fall below thenominal value by more than 10%.

14.3.3 A bindertape of copper shall be appliedover the wire screen. The nominal thickness ofthe tape shall be not less than 0'1 mm. Theminimum thickness shall not fall below thenominal value by more than 10%,

16 lNNER SHEATH

16.1 For armoured cables the extruded innersheath shall be applied over the moisture barrieror the metallic screen,

16,2 The thickness of inner sheath at any pointshall not be less than the minimum value specifiedin Table 7.

Table 7 Thickness or Inner Sheath

')Fictilious diameter calculated as described in Annex B.

------""""'------Over Up to and

Including

')Calculated DiameterUnder Inner Sheath

mOl

09.-0 -1'11-2

I'Z

/'3

1'41'5

1'6)"6

"7I'S

1'92-0

2'02')

2'2

Minimum Thickness ofInner Sheath

mm

4045

5055

6065707580859095

100

105) 10115

404550556065707580859095

100105110) 15

15.2 MetallicSheath

15.1 The Moisture Barrier shall be ·provided asgiven below:

a) Water blocking tape/powder shall besuitably applied; and

b) Laminate tape shall be applied longitudin­ally with overlap and sealed;

OR -

Metallic sheath of lead alloy 'E' shall beapplied by extrusion.

NOTE - Where Lr ad A 1I0y Sheath is provided overthe non-rncra llic part of the insulation screening asmoisture barrier. it shall form the metallic part of thescreening.

15 MOlSTURE BARRIER

15.2.1 This shall consist of extruded metallicsheath of lead alloy E as per 7.2.

15.2.2 Thickness of sheath shall not fall belowthe value specified in Table 6,

Table 6 Thickness of Metallic Sheath

')Calculated Diameter UnderMetallic Sheath

mlllr--------."A...--~---__.._

Over Up (0 andIncluding

Minimum Thickness ofMetallic Sheath

mm

I7 ARMOUR

17.1 Armour. when specified. shall co~sist ofnon-magnetic metallic wires helically a pplied overthe inner sheath.

Table 8 Dimensions of Armour Round Wires

17.2 The dimensions of armour wires shall be asspecified in Table 8.

'>Calculated DiameterUnder ° Armour

mOl,--- -----"'--------...

Above Up to andIncluding

40 1'9",_.

40 45 2045 45 2'(50 55 2'255 60 2' )

60 65 2'4

65 70 2'570 75 2'675 80 2'780 85 2885 90 2890 95 2'995 100 )'0

100 105 ), I

105 110 ) 2

110 115 ).)

40

55

70

40

55

70

Nominal Diameter ofRound Wire

mm

20

2' 50

)°15

4°00

')Fictitious diameter calculated as described in Annex B, ')Fictilious diameter calculated as described in Annex B.

4 ..

17:J The R rmnur wires shn II he applied AI closelya, possible.

17.4 The directi'm of lay of armour shall be lefthand.

17.5 Joints in the armour wires shall be made bywelding and surface irregularities shall be remov­ed. A joint in any wire shall be at least 300 mmfrom the nearest joint in any other armour wirein the completed cable.

IS 7098 ( Part 3 ) : 1993

11.3.1 ArmO/lutJ Ci,Mn

The thicknesx of outer sheath· at any point for~ured cables shall not be less than theminimum value specified in col S 'of Table 9.

18.4 The outer sheath shall be coated with asuitable conducting material.

Table 9 Thickness of Outer Shuth

(ClauuJ 18.3.1 and 18.3.2 )

mill

Minimumof Outer

Sheath forArmoured

Cable

ThiekneSi of OuterShearh for

Unarmourc:dCablc:s'

".----:--.-.......---.-~Nominal Minimum

JIll II rnm

Above: Up 10 andIncludin,

t I ) ( 2 I ( 3 I ( 4 I « $ )

40' 2'4 1'72 "7240 4S 2'6 "88 I'SS

4$ $0 2"8 2'0-4 2'04

.50 55 )'0 2'20 2'20

55 60 )2 2'rs 2'J660 65 )'4 2'52 2'5265 70 )·ti 2'1\1l 2'611

70 75 )'ll 2'84 2'84

75 4'0 3'0 3'0

mm

l>Calculartd DiameterUnder Outer

Shuth

".---_ ...... __ ._-a) over the moisture barrier or metallic screen

unarmoured cables. and

b) over the armour for armoured cables..

NO IE - A binder rape may be applied under theouter sheath.

18.1 The outer sheath shall be applied byextrusion. It shall be applied:

18 OUTER SHEATH

18.2 The colour of outer 'heath shall be Black.C'

-- 18.3 Thickness of Outer Sheath

18.3.1 Unarmoured Cables

The thickness of outer sheath of unarmouredcables determined by taking the: average of anumber of measurements shall not be less thanthe nominal value specified in col 3 ofTable 9 and the smallest of the measured valuesshall be not less than the minimum value specifiedin col 4 ofTahle 9. '>Ficriliou, l1illme:lcr ca tcutared IU described in Annex B.

SECTION 4 TESTS

19 CLASSIFICATION OF TESTS

19.1 Type Tests

The following shall constitute the type tests: ...

;..l~-

~'-...-~

Test

a) Tests on conductor:

i) Annealing test ( for copper)

ii) Resistance test

b) Physical test on insulation:

i) Test for thickness and dimensions ofinsular ion

ii) Tensile strength and elongation at break

iii) Thermal ageing in air oven

iv) HoI set testv) Shrinkage test

vi) Void and contaminants lest

c) Resistivity test for semi-conducting layers

d) Test for concentric metallic screen:i) Test for concentric copper wire

ii) Test for coucen [ric copper ta pe

Rr/o/Requirements ..

IS 8 130 : 1984

IS 8130: 1984

Tables 5, 19, 16

Table 2Table 2fable 2

Table 2

Under consideration

20.2.4

20.4, Note

20.4

. ReI forTnt Melhod Jl

Part IPart 5

Part 6

~)art 7

Part IIPart 30Part 12

'41. ;Annex C

20.320.4

')Reference 10 various pa r t s uf IS 10810 ser ies , retevantclauses of this standard,

5

IS 7098 ( Part 3 ) : 1993

Test

e) Thickness of metallic sheath

f) Tests for armouring material:

i) Dimensions

ii) Tensile strength and elongation at break

iii) Wrapping test

iv) Resistivity test

Ref 0/Requirements

20.5

20.6

Under consideration

Under consideration

Under consideration

RefforTest Method')

Part 34

Part 36

Part 37

Part 3

Part 42

g) Physical tests for outer sheath:

I) Measurement of thickness

2) PVC sheath

i) Tensile strength and elongation at break

ii) Thermal ageing in air oven

iii) Loss of mass

iv) Heat shock test

v) Hot deformation test

vi) Shrinkage test

vii) Thermal stability

Table 9

IS 5831

IS 5831

IS 5831

IS 5831

IS 5831

IS 5831

IS 5831

19~4

1984

19114

191n

1984

1984

1984

Part 6

Part 7

Part II·

Part 10

Part 14

Part IS

Part 12

IS 5831 1984

3) PEsheath

i) Carbon black content

ii) Tensile strength and elongation atbreak before and after ageing

iii) Hot-deformation

h) Flammability test ( for PVC outersheathed cables only)

j) Water tightness test

k) i) Thcrmnlngciug on complete I-,able sample

ii) Tensile strength and clongauo n at breakfor insulation and outer sheath

iii) Resistivity test for semi-conducting layer

m) Bending test followed by P.O. test

. n) Dielectric power factor and capacitancemeasurement at ambient temperature

p) Dielectric power factor measurement atelevated temperature

q) Load cycle test followed by P.D.measurement

t) Impulse withstand test followed by HV test

NOTES

Nominal value:2'5% ± 0'5% .

8.3

8.3

207

20.8.3

20,9. I .

Table 2 andIS 583 I: 1984

20.2

20.11.1

20.12. 20.18

20.13

20.14.1

20.15.1

Part 32

Part 7

Part 15

Part 53

20.8

20.9

Part 7

20.2

20.11

20.12. 20. [8Part 48

20.13

2.0.14

20.15

1 Ile Ior e Ll'1I111;C/ll"CmClll of t h c c lcctr icc l ty r-c te s t s f'Cd" 'n' to 'q ' compliance of 19.5 shalf be cnvured,

2 After co mp lc t ion of c lc ct r ic.rl type test, from 'n' to 'r ', the shcurh and any urrnour ingor ta p es shall be removedIrom the sample for phy s rca! i nvpccuon of the shield a nd t h e insulation screen. 1 he observation should notreveal br ok cn wilu/larc in ihc shie.d and no damages shall have occurred on the insula lion screen causingdiscontinuity.

')Rcfelencc to various pans of IS 10810 scr ic s. relevant clauses of thi! standard.

6

I~ 7098 ( Part 3 ) : 1993

20.2 Resistivity Test for Semi-conducting Layer

211.2.1 Thc resistivity test for extruded semi­conducting layers applied over the conductor andover the insulation shall be: determined bymeasurements on test pieces taken from the core.

20.8.2 Radial Water Tightness Test

Under consideration.

20,8.3 There shall be no water leak from the endsof the sample.

20.2.2 The procedure for measurement shall beill accordance with Annex C.

ZO-.2.3 The measureme nts shall be made at atemperature within ± 2°C of the rated maximumnorma I ope rat ing cond nctor tempera I.ure.

20.9 Thermal A~eing Tests on Compl_ Cable

This lest sha l! be carried out to check that theinsulation, Ron-melallic sheath and extruded semi­conducting layers over the conductor and insula­tion are not liable to deteriorate in operation dueto contact with their components in the cable.

20.8 Watcr Tightness Test

NO IT - The r.:si~li viry of the copper \\ ire/tape nt20·C shall not exceed O'17116 ohm "'01' PCI mctrc cablelength.

20.6 Dimensions 'of Armour

The dimensions of non-magnetic armour shall notbe less than the specified nominal values.

20.7 Flammability Tcst

Period of burning afterremoval of the flame shallnot exceed 60 seconds and the unaffected( uncharted ) portion from the lower edge of thetop clamp shall be at least 50 rnrn.

500 ohm IIIii) Insulation screen:

20.9.1 The test results l"ortensile strength andelongation at break shall comply with the valuesof insulation and sheath after ageing as given inTable 2 for insulation and IS 5831 : 1984 forPVC outer sheath and 8.3 for thermoplasticpolyethylene outer sheath.

The resistivity of the extruded semi-conductinglayers shall be determined on the test pieces fromthe aged cable sample in accordance withAnnex C.

The maximum Ie,.! of the Partial Dischargemagnitude at 1'5 Uo shall not exceed 5 pC fortype test and 10 pC for routine test.

The resistivity of semi-conducting screen layersmeasured as per Annex B shall not exceed thefollowing values:

i) Conductor screen: 000 ohm m

20.10 Partial Discharge Test

The partial discharge test shall be carried out inaccordance with IS 10810 (Part 46): 1984,except for the test voltages and durations.

The lest voltage shall be gradually increased10 ('75 times the rated voltage, maintaiued for 10seconds and then slowly reduced to \'5 times therated voltage and Partial Discharge magnitudemeasured.

Three pieces of complete cable about 200 mrnlong shall be suspended vertically and substanti-'ally in the centre of the oven at least 20 mm awayfrom each other and shall not occupy more than2 percent of the volume of the oven. The pieces'of cable shall be kept in the oven at the temper­ature of 10 :i- 2"C above the rated maximumnormal operating conductor temperature of thecable for a, c: uration of 168 h.

The lest pieces of insulation and sheath from theaged pieces of cable shall. be prepared and sub­jected to tensile strength and elongation at break.

I 000 ohm-metre

500 ohm-metre

not exceed the20.2.4 The r esjst ivjty shall[ollowing:

i) Conductor screen:

ii) Core screen:

20.4 Test of Concentric Screen of Copper Tape

On a lest piece with a length at least I metre, alllayers over the screen including shenth areremoved. All parts of the screen are unwoundand straightened. The electrical resistance of thetape shall be measured.

20.3 Test for Concentric Copper Wire

On a test piece With a length of at least I metre,all layers over the copper wire shall be removed.Copper wires numbering 10% or 5 whichever ismore, shall he straightened, and the electricalrcsisrance measured as per relevant test method.

While measuring the resistance of the concentriccopper wires, all the wires are connected tC'Jelherat both ends of the test piece. '

20.5 Measurement of Thickness of Mctailic Sheath

This lest shall be applicable if the cable has ametallic sheath [as per 10810 (Part 34): 1984].

.Minimum thickness shall not fall below 'thespecified value in Table 6.

;:-

(,-

c

20.8.1 Longitudinal Water Tightness Test

This test shall be carried out as specified InAnnex D.

20.11 Bending Test

The bending test shall be carried out as perIS 108.10 ( Part 50) : 1984.

8

19.1.( The le.I~-frol1l (n) 10 (r) shnll he performedsuccessively Oil the surue leU sltlllple of completecable 1101 less than lt) metres in length bel weenthe cable accessories.

19.1.2 Special Provision

Tests at (p) and (q) may be carried out ondifferent samples.

(9.2 Acceptance Tests

19.2.1 The following shall constitute acceptancerests:

a) Conductor resistance test

b) Annealing test

c) Test for dimensions of insulation

d) Hot set test for insulation

e) Void and contaminunts test

o Test for thickness of metallic sheath

g) Test for thickness of outer sheath

h) Partial discharge test

j) High voltage lest (as per 20.17)

k) Measurement of capacitance ( as per 20.18)

NOTE - Partial discharge test shall be carried out onfull drum length.

19.3 Routine Test

19.3.1 The following shall be carried out asroutine test:

a) Conductor resistance lest

b) Partial discharge test

c) High voltage test

19.4 Optional Test

Cold impact test shall constitute Hie optional test.

19.5 Check on Insularion Thickness Defore theElectrical Type Tests

The average value 01 the insulation thickness shallbe measured at both ends of (he sample (as perPart 6 of IS IO~IO). If the average of the twomeasurements of the insulation thickness is:

-not more than 10% over the declarednominal val~e for the cable, the test voltagesas specified In re lcv.mt clauses of t h is specifi­cation shall be used.

-more than lO~~ but not more than IS"%, overthe declared nominal value for the cable, thetest voltages as specified In relevant clauses orthis spccifica t io n shall be increased to give anclcct r ica l fielJ stress at the co nd uct or screenwhich will be the ssm e value as with nominalinsulation th ick ncss and specified test voltage.-more than 15/~ OVer the declared nominalvalue (or the cablcs another test surnp le shallbe chosen.

7

IS 7098 ( Part 3 ) : 1993

20 METHOD OF TESTS

20.1 Void and (;onlamillanl. Tnt (or Illlul.Uon

20.1.1. Preparation of test sample and determin­ation of voids and contaminates.

Five centimetres of the sample shall be cuthelically or in some other convenient manner toproduce thin samples of the insulation. Wafers( or the turns of the helix) shall be approxirnetely0'6 mm thick. The cutting blade shall be sharpand sha l! produce II sample with very smooth cutsurfaces. The sample shall be kept clean andshall be handled carefully to prevent scratchingthe sample surface.

The entire specimen shall be, viewed by transmit­ted light f(ir detcrmination of voids, contaminantsand translucent materials in the insulation.

A contaminant is any solid or liquid materialwhich is opaque or 110t homogenous cross linkedpolyethylene insulation. including opaque ordiscoloured, translucent material of more than0'127 rnm in its radial 'vector projection.

The entire area of 20 consecutive wafers (orequivalent turns of the helical sample) shall beexamined with a minimum of 15 power rnagnifi­cation, including any areas which appear suspectduring the above examination by transmittinglight. .

A tabulation of numbers and sizes shall be madewith a minimum of 15 power magnification of:

i) All voids. 5 j.Lm in greatest dimensions andlarger

ii) All contaminants. 5 j.Lm in greatest dimen­sions and larger

iii) Discoloured, translucent material of morethan 5 p.m. This tabulation shall berecorded and reported,

The largest void, the largest contaminant and thelargest translucent material shall be marked byencircling and must be subsequently measured ona micrometer microscope of· minimum of 40power magnification.

The number of voids. contaminants and translu­cents per unit length of insulation shall becalculated from the tabulation.

20.1.2 The insulation of the completed cable shallbe free from:

a) Any void larger than 76 P.Ill. The numberof voids larger than 5 p.m shall nOI exceed2 per cubic ern of insulation.

b) Any contaminants (opaque material ormaterial that is not homogenous withinsulation) larger than 127 p.m in itsgreatest dimensions. The number of.c on t aminn nt s of sizes between 51-'m a n d127 j-'m shall nol exceed I per cubic ern ofinsulation.

c) Any translucent mate r ia l that is larger thanI' 27 nun in Its radial vector projecuon.

\

20.16.1 Insulation Thickness

IS 7098 ( Part J ) : 1993 .

0/ ' . tmax - tmin/0 Eccentricity = X 100

tmax

impulse Test Voltage(kV)'

325

550

650

/050

Rated VoltageUo/U{kV)

38/66

64/110

76/132

127/220

where d stands for the diameter of the core.

The /. ovatiry 'hall not be more than 5% .. 9

20.16.3 Testfor Ovality

The ovality of the core shall be checked asfollows:

where I stands forthethickncss of insulation.

The % eccentricity shall not be more than /5%.

% OvaJity = dcor. max - d core min X 100dcor. max

20.16.2 Test for Eccentricity

The eccentricity of the insulation shall be checkedas follows:

The average thickness of insulation shall be notJess than the specified nominal value ( Ii).

20.16 Test for Dimensions of Insulation

Following tests shall be carried out.

20.14.1 There shall be no breakdown during thetest and after the final cycle, the sample shall besubjected to and shall comply with the require­ments of partial discharge test in accordancewith 20.10.

20.15.1 After the impulse test, the cable sampleshall be subjected to power frequency AC voltagetest as per Part 45 of IS 10810 at 2'S times therated voltage for 15 minutes at room temperatureand no breakdown of the insulation shall occur.

20.15 Impulse Voltage Test Followcd by HighVoltage Test

The cable shall withstand without failure 10positive and /0 negative voltage impulses at con­ductor temperature not less than WOC and morethan IS'C above the maximum rated temperatureof the conductor of the appropriate valuespecified. below:

The cycle of heating and cooling shall be carr!cdout 20 times at least 5 cycles per week. Duringthe entire period oftest a voltage of 2 Uo shall beapplied to the sample.

20.11.1 On completion of this test. the cable shallbe subjected to the Partial Discharge test asin 20.10 and shall comply with the requirementsspecified therein.

20.12 Dlelectric Power Factor and CapacitanceMeasurementsThis test shall be carried out as per IS IOglO( Part 48 ) : 1lJ84 at rated voltage and at ambienttemperature.

The power factor at rated voltage shall not exceed10 x 10-'.

20.12.1 The capacitance ofthe test sample shallbe measured between conductor and metallicscreen and shall not exceed the nominal valuedeclared by the manufacturer by more than 8percent.

20.13 Dielectric Power Factor Measurement atElevated Temperature

The sample shall be heated by passing currentthrough the conductor until the conductorreaches a steady temperature not less than 100 eand not greater than 15°C above the maximumrated temperature of the conductor in normaloperation.

The dielectric power factor shall be' measured asper IS 10810 ( Part 48 ): 1984 at ratedvollageat the temperature specified above.. The measuredvalue of dielectric power factor shall not exceed10 x 10-'.

20.14 Load Cycle Test Followed bj P.O.Measurement

The sample shall be laid on the floor of the testroom in a U bend having the diameter specifiedin 20.11.

The sample shall be heated by passing currentthrough the conductor so that the conductorreaches a steady temperature not less than 10'Cand not more than 15°C above the maximumrated temperature of the insulation in normaloperation.

The-beating current not less than the rater.current shall be applied for at least 8 hours andshall be followed by at least 16 h of naturalcooling, Th~ conductor shall attain the specifiedtemperature lor the la st two hours of each healingcycle.

The diameter or 'the test cylinder shall not begreater than:

i) 2S ( d:+ D) + S~ for cables with leadsheath or with longitudinally applied mttalfoil; and

ii) 20 ( d + D ) + S% for others,

whereD = measured external diameter or the

. cable in mm, and

d = measured diameter of the conductorin rnrn.

9

-;

ii .

.IS 7098 ( Part 3 ): 1993

20.17 High Voltage Test· (as Routine andAcceptance Tests)

The cable shall withstand without any failure thepower frequency AC voltage of 2'5 times therated voltage for 30 minutes betweenconductorand metallic screen at the room temperature,when it is under routine test. For acceptance

lest the voltage shall be 3 times rated voltage for4 hours.

20.18 Measurement of Capacitance

Capacitance shall be measured bel ween conductorand metallic screen. The measured value shallnot exceed the nominal value declared by themanufacturer by more than 8/;;.

ANNEX A .( Clause 2.1 )

LIST OF REFERRED INDIAN STANDARDS

IS No.

1885(Part 32): 1971

583 t : 1984

8130: 1984

10810

Part

Part 3

Part 5

Part 6

Part 7

Title

Electrotechnical vocabulary:Part 32 Cables, conductorsand accessories for electricitysupptyPVC insulation and sheath ofelectric cablesConductors for insulatedelectric cables and flexiblecords

Methods or test for cables:

Annealing test for wires usedin conductorsWrapping test for aluminiumwires

Conductor resistance test

Thickness for thermoplasticand elnstomcric insulationand sheathTensile strength and elonga­tion at break of thermoplasticand clastomcric insulation andsheath

IS No.

Part 10

Pa rt II

Part 12Panf4

Part 15Part 30

Part 32

Part 34

Part 36

Part 37

Part 42

Part 53

Title

Loss of mass test

Thermal ageing in air

Sh rinkage testHeat shock testHot deformation test

Hot set testCarbon content test forpolyethylene

Measurement of thickness ofmetallic sheath

Dimensions of armouringmaterial

Tensile strength and elonga­tion at break of arrnouringmaterials

Resistivity test of armourwires and strips and cond uc­.tance test of armour (wireslstri ps )

Flammability test

ANNEX B(Clauses 15.2.2,16.2, IT2amI18.4)·

FICTLTIOUSCALCULATION l\lETHOD FOR DETERI\IINATlON OFDIMENSIONS OF PROTECTIVE COVERINGS

n-r GENERAL

B-l.l The thickness of cable covering such assheaths and armour, has been related to cablediameters by means of 'step tables'. This so me­times causes problems. The calculated diametersare not ncccssar ily the same as the actual valuesachieved in theproduction, In border line casesqueries can arise, if the thickness of a coverifl~docs not correspond to the actual diamete~because the cal~ulaled diameter is sli~htly

ditfercnt. Vu riat ion In conductor d imcnsio nsbetween munufuct ur crs C;IUSC d itfercnce in C:1I­

cu l.ucd d ia mct crs and may, therefore, lead tovariation in the thick ness of covering used 011 thcsame basic dcsjgu of cable. -

13-1.2 To minimize these difficulties, the fictitiouscalculation method was invented. The idea isto ignore the shape and degree of compactness ofconductors and 10 calculate fictitious diametersfrom Formulue based on the cross-sectional areaor conductors and Tnsulation thickness. Thick­nesses of sheath and other coverings arc thenrelated to fictitious diameters by tables. Themethod of calculating fictitious diameters isprecisely specified and there is no ambiguityabout the thicknesses of covering to be used,which arc independent of differences in manu-f.ict ur ing practices. This standardizes cabledesigns, thicknesses being precalculated andspecified for each size or cable.

10

Ie

B-1.3 The fictitious calculation is used only todetermine dimension5 of sheaths and cable cove­rinas. It is not a replacement for the calculationof-nornml diameters required for practicalpurposes. which should he calculated separately.

B-2 METHOD

B-2.1 The fotlowing fictitious method of cal­culating . thicknesses of various coverings in acable has been adopted to ;nsure that anydifference which can arise in independent calcula­tions. for example. due to the assu-option ofconductor dimensions and the unavoidabledifferences between calculation and actualachieved diameters, arc eliminated,

fl-2.2 Holding strips and counter-helix are nottaken into account in this calculation methodunless their thickness is greater than 0'3 mrn.

B-2.3 The cilculatcd value of, fictitious 'diameterat each stage shall be rounded off to one signifi­cant place of decimal, that is. 0'\ rnm, beforeproceeding to next step, The rounding ofT shallbe done III accordance with IS 2 : \960,

B-3 CALCULATIONS

8-3.1 Conductor

The fictitious diurnerer (elL) of a conductor fnreach cross sectional area shall be taken fromTable 10 irrespective orshare or compactness ofcond lIC[Or.

Table 10 Fictitious Diameter of Conductor (ill

Nurninnl Cruss- d, Ni.miuut Cross- d.t,Sccrinnal Area or Sectiouat Area uf

Conductor Conductornll11 1 Inl11 mrn? nun

I'~ 11'0 6JO 21\'.'

120 12·4 1100 ~I'9

150 I."~ ~ I 000 35'71115 I5'J I 200 39'1

~-lll . \7'5 I 600 ~}'l

300 19'5 2000 50 J

400 22-6 2500 56'4

;00 25'2

B-3.2 Cores

The fictitious diameter De (mm) of a core IS

given by:

o; = elL t 211 + 30 ( mrn), where

II is the nouun al thickness of msulatio n( mm ).

1"0 i E - llJ Ill':l is ulluw cd fv. scuu-couducuuglayers.

U-3.3 Metal Sheath

1 he increase in fictitious diameter due til metalsheath shall be twice t he m in unum thick ucss ~'

mctul sheath ( 1m ),

I 1

IS 7098 ( Part 3 ) : 1993

B-3 ..$ Copper Screen

The increase in fictitious diameter due to copperscreen ( I, ) i~ given in Tn ble II.

Table ,.1 Increase in DiameterDue to Copper Screen

NominA\ Cross- Increase in Nominal Cruss Increase inSectional Ar(':! Diameter Sectional Area Diameter

f\r Copper or CopperScreen Screenmrn! mill nllnz mmI' ,~ 0'5, 50 1'72'5 0·5 70 2'0.. 05 95 2'"Ii (I' 5 120 2'1

10 O'S 150 301(, \'\ HIS 4'025 1'2 240 5'035 1'01 300 6'0

If t,e cross-section of the copper screen liesbetween two of the values given in the tableabove. then the increase in diameter is that givenill the table above, then the increase in diameteris that given for the higher of the two cross­sections.

Area of copper screen sha ll : be calculated asunder:

i) Conceutric copper wire:

11 1T d 'Copper screen area = 4- sq nun

where. II is the number of copper wiles and cIis the nominal diameter. of each wire in mm.

iiI Copper tapes:

Copper screen area = II W T sq mm

where11 is the number of copper tapers).

lI'is the nominal width of copper tapein mrn,

T is the nominal thickness of each coppert ape ill nun.

twu1 F -'\n rncreu..c in ticuuou-, dlalll·~I.:r of cor eDc shall h= tukcn inlo account as per A·J.J and A-J.-lor both, a, the case ni.ry b r , d:renuing upon whetherruc ta llic pari of in-uiatiou screen of cable has mctu lsheath.copper scrctlll or buih.

Ds... ~ Dc + 2 1m + I~ l mm )

U-3.S Inner Sheath

The fictitious diameter over the inner sheath ( Ds)is given by:

D. = S8C; ~ 2 1M ( nun )where rM is the minimum thick ness or innersheath ill mill.

13-3.6 Armour

Tile fictitious diameter over the armour (DA ) isgiven by:

f) 1\ -, f). " 2 tI t-; ( Illlll )

where d-; i\ lite nominal diameter or armourwire ill III Ill.

IS 7098 ( Part 3 ) : 1993

ANNEX C( Clause 20.2.2 )

METHOD OF MEASURING RE5ISTlVITY OF SEMI-CONDUCTING SCREEN

where

R = resistance in ohms,D = .diameter over.the insulation in metres,T = average thickness of screen in metres,

andL = distance between potential electrodes

in metres.

C-3.4 After the electrical measurements, thediameter over the conductor screen and insulationand the thickness of' the conductor screen andinsula tion screen shall be measured optically eachbeing the averag~ of six measurements.

C-3.S The volume resistivity in ohm-metres sl'lallthen be calculated as follows:

, RX'IT(D-T)xTi) Conductor Screen = 2L

where

R = resistance in ohms,

D = diameter over the conductor screen inmetres,

T= average thickness of screen in metres,and

L = distance between potential electrodesin metres.

C-l Test pieces shall be prepared from 150 mmlengths of completed cable.

C-2 The conductor screen test piece shall beprepared by cutting a sample of core in halflongitudinally and removing the conductor( Fig. I ). The insulation screen test pieces shallbe prepared by removing all the coverings from asample of core ( Fig. I ).

C-3 The procedure for determining the specificresistivity of the screens shall be as fo llows.

C-3.1 Four silver painted electrodes' A, B, C andD ( Fig. I ) shall be applied to the semi-conduct­ing surfaces. The two potential electrodes, 8 andC shall be each placed at least 25 mm beyondthe potential electrodes.

C-3.2 Connections shall be made to the electrodesby means of suitable clips. In making connectionsto the conductor screen electrodes' it shall beensured that the clips are insulated from theinsulation screen on the outer surface of the testsample.

C-3.3 The assembly shall be placed in an ovenpreheated to 90° ± 2°C and after an interval of30 minutes, ·the resistance between the electrodesshall be measured by means of a circuit, thepower of which shall not exceed 100 rnilliwatts.

ii) Insulation ScreenR 'IT ( D+T) .x T

L

ANNEX DClause 20.8.1 )

METHOD FOR TEST FOR LONGITUDINAL WATER TIGHTNESS

0-1 GENERAL

0-1.1 This test is intended to be applicable tocables which are designed and constructed tomeet the requirement of preventing the longitudi­nal propagation of water along the cable in caseof accidental damages to the outer sheath of thecable.

0-2 TEST SAMPLE

0-2.1 A six metre long piece of a complete cableis subjected to bending test as per 20.11. Threemetres of this cable is cut for water t ight ne ss test.All coverings over the moisture barrier shall beremoved. This test piece is straightened andplaced horizontally. An annular ring of 50 mrnwidth is cut in the middle of the sample so that

thesemi-conducting layer over the insulation isexposed for testing the longitudinal watertightness of the cable.

D-2.2 Suitable arrangements shall be made as In

Fig. 2 for allowing the relevant interstices to beexposed to water pressure of I m height.

0-2.3 The assembly for maintaining the waterpressure shall be suitably mounted on the outersheath without causing any mechanical stress onit. Normal tap water at ambient temperatureshall be used in the pressure head. The con­ductor ends shall be fitted with connections forcirculation of suitable current through the con­ductor. Arrangements for the temperaturemeasurements at the conductor shall be made.

12

0.3 TEST PROCEDURE

The test assemblY as shown in Fig. 2 shall befilled with normal tap water at ambient temper­ature and kept for a period of 24 h. The cableshall then be subjected to heating cycles. Theheating period shall be 8 h followed by 15 h

IS "098 ( Part 3) : 1993

of natural cooling. During heating periodsuitable current shall be passed through the con­~tor, so that the conductor temperature israised to a value between 9S·C and IOS·C. Thespecified conductor temperature shall be attainedduring first two hours of the heating period.

B, C - potential electrodesA, D - current electrodes

All dimensiorrs in millirnetres.

FIG. I PRePARATION OF SAMPLe fOR MEASUREMENT Of THe VOLUME RESISTlVITYOI' THECONDUCTOR AND INSULATION SCREENS.

50mm

50m 3000mm

All dimensions in millimetres.

FIG. 2 ARRANGEMENT fOR W~~'TIGIITNESS TEST

13

50mm

.\ ··r~,Bureau or Indian Standards

illS is a statutory institution established under the Bureau of Indian Standards Act, 1986 to promoteharmonious development of the activities of standardization. marking and quality certification of goodsand attending to connected matters in the country.

Copyright ".

BIS has the copyright of all its publications. No part of these publications may be reproduced in any formwithout the prior permission in writing of BIS. This docs not preclude the free usc, in the course ofimplementing the standard. of necessary details, such as symbols and sizes, type or grade designations.Enquiries relating to copyright be addressed to the Director (P-ublications), BIS.

Review of Indian Strindards

Amendments are issued to standards as the need arises on-the basis of comments. Standards are alsoreviewed periodically; a standard along with amendments is reaffirmed when such review indicates thatno changes arc needed. if the review indicates that changes are needed. it is taken up for revision. Usersof Indian Standards should ascertain that they arc in possession of the latest amendments or edition byreferring to the latest issue of 'BIS Handbook' and 'Standards Monthly Additions'.

This Indian Standard has been developed from Doc: No. ETD 9 ( 2872)

Amendments Iss ued Since Publication

o

Amend No.

Hcadq uartcrs:

Date of Issue

BUREAU OF INDIAN STANDARDS

Text Affected

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