ti spc ohe inscom 1070

GOVERNMENT OF INDIA

MINISTRY OF RAILWAYS RESEARCH DESIGNS & STANDARDS ORGANISATION

MANAK NAGAR , LUCKNOW 226 011

SPECIFICATION No. TI/SPC/OHE/INSCOM/1070

TECHNICAL SPECIFICATION FOR SILICONE COMPOSITE INSULATORS FOR 25 kV a.c. 50 Hz SINGLE PHASE OVERHEAD TRACTION LINES

1.0 SCOPE 1.1 This specification covers design, manufacturing, requirements and tests method for Silicone

composite insulators used on single phase overhead electric traction lines having a nominal voltage of 25 kV (line-earth) ac at 50 Hz. The system voltage may, however, go up to 30 kV.

1.2 Reference Specifications: The following IS, IEC, ASTM and other standard specifications

referred in this specification shall be referred while assessing conformity of insulators with these specifications. These shall mean latest revision with amendments issued unless specifically stated otherwise in the specification.

S N Relevant

IS/IEC/ASTM/SPECS. Item description

i IEC: 61109 Composite insulators for a.c. overhead lines with a nominal voltage greater than 1000 V- Definitions, test methods and acceptance criteria

Ii IEC 60507 & IS: 8704 Artificial Pollution tests on high voltage Insulators to be used on a.c. systems.

iii IEC 60575 Thermal mechanical performance tests and mechanical performance test on string insulator units.

iv IEC 60815 & IS: 13134 Guide for the selection of insulators in respect of polluted conditions.

v IEC 60060-1 & IS: 2071 (Part I to III)

Methods of high voltage testing.

vi IS: 14329 Malleable iron castings - Specification vii. ETI/OHE/13(4/84) issued by

RDSO Specification for Hot dip zinc galvanisation of steel masts (rolled and fabricated), tubes and fittings used in 25 kV ac OHE.

viii IEC 60707 Flammability of Solid non-metallic materials when exposed to flame sources

ix IEC 60587 Method for evaluating resistance to tracking and erosion of electrical insulating materials used under severe ambient conditions.

x. IEC 61467 AC Power arc test on insulator sets.

of 23 Specification No.TI/SPC/OHE/INS COM/1070

2

Xi IEC 93 Method of the test for volume resistivity and surface resistivity of solid electrical insulating materials.

Xii ASTM D624 –00 Type B Standard Test Methods for tear strength of rubber and Thermoplastic Elastomers

xiii IEC 243-3 / ASTM D – 149

Methods of test for electric strength of solid insulating materials Part I: Tests at power frequencies.

xiv ASTM D 495 –73 Method for High – Voltage, low – current, Dry Arc Resistance of Solid Electrical insulation,

xv ASTM D 578 –05 Standard specification for glass fiber strands. 2.0 TERMINOLOGY : For the purpose of this specification, the following definitions shall

apply: 2.1. 850 mm creepage distance insulator i.e. 16 mm/kV: These 850 mm creepage distance

insulators shall be used in light polluted zones for stay, Bracket, 9-Tonne, post, operating & sectioning insulators.

2. 2 1050 mm creepage distance insulators i.e. 20 mm/kV: These insulators shall be used in

medium polluted areas where SDD is 0.1 to 0.3 mg/sqcm, for stay, bracket & 9 Tonne insulators only.

2. 3 1600 mm creepage distance insulators i.e. 31 mm/kV: These insulators shall be used in

heavily /very heavily polluted zones, where SDD is more than 0.3 mg/sq.cm and shall be used for stay, bracket & 9-Tonne insulators only.

Note IEC Publication 60815& IS: 13134 prescribe from the point of view of pollution level,

four levels of pollution from light to very heavy pollution. For the purpose of standardization, & in order to avoid multiplicity of types of insulators to suit each type of pollution, at present, only stay arm, bracket tube and 9-tonne insulators shall be used in zones where the pollution level is light, medium and/or heavy.

2.4 Stay arm insulator: The insulator which forms part of the horizontal member, known as

the stay arm of the cantilever assembly from which the traction conductors are suspended, and which insulates that member from the mast or structure to which the cantilever is attached.

2.5 Bracket insulator: The insulator which forms, part of the inclined member, known as the

bracket tube of the cantilever assembly, (from which, the overhead traction conductors are suspended) and which insulates bracket from the mast or structure to which the cantilever is attached.

2.6 9-Tonne Insulator: The insulator is normally, though not exclusively, used as a strain

insulator for anchoring of conductors. It is also used in a vertical position to support 25 kV feeder wire.

2.7 Post Insulator: A post insulator is used for supporting rigidly the live contacts of 25 kV

isolator switches, the 25 kV bus bars at sub-stations/switching stations, the 25 kV bus bars over portals and at such other locations.


3

2.8 Sectioning Insulator: The insulating element of a piece of equipment (called section

insulator assembly) which is used for separating adjacent sections of the overhead traction lines, belonging to different elementary electrical sections, in the normal condition. It provides a continuous smooth (mechanical and electrical) path for passage of the pantograph of electric rolling stock.

2.9 Operating Rod Insulator: The insulator used in the operating rod of a 25 kV isolator

for opening and closing of the isolators.

Note: Metal fittings of all the above insulators shall be checked for the critical dimensions by suitable gauges. The insulators which do not comply with the requirements of the specifications / approved drawings due to defects shall be rejected and destroyed in presence of the inspecting official. The details of rejection i.e. batch number, date of rejection, and quantity shall form part of the type / acceptance reports.

2.10 Creepage Distance: It is the shortest distance along the contours of the external surfaces of the insulating part of the insulator i.e. distance between those parts which normally have the operating voltage between them.

3.0 Basic features: Silicon composite insulator should be manufactured according to

followings: 3.1 Shed and Sheath material: Composite insulator shed & sheath shall be made of HTV

type silicone rubber, having silicon content between 40-50 % by weight and preferably ATH (Alumina Tri hydrate) as filler .The filler should be properly mixed with silicon compound to ensure the uniform distribution of it in the polymer. Proper additives viz vulcanizing agent, coupling agent, softener etc should be used to ensure desired properties of final product. Insulator should be manufactured by injection moulding process. The joint formed due to, the mold parting line of moulding vessel, should be smooth.. Thickness of sheath should be minimum 3mm & shall have excellent Hydrophobic and anti-tracking properties. The strength of bond between FRP rod & sheath shall be more than the tearing strength of the polymer. The material should confirm to the tests specified in this specification. & Should protect against attack of rats/birds/squirrels/other rodents at storage location & on line. Manufacturer should indicate the method of cleaning & solvent to be used for cleaning silicone rubber sheds.

3.2 Core: Core of the composite insulator should be manufactured from Boron free,

Electrically corrosion resistant (ECR) grade glass fiber reinforced epoxy resin rod having at least 70% fibres by weight. Pultrusion process should preferably be adopted to manufacture the FRP rod/core & it should be void free & have high resistance to acid corrosion. The temperature of die and speed of individual fiber movement should be so controlled that, there are no cracks on the center of FRP rod. The core should confirm to the tests specified in the specification.


4

3.3 End FITTINGS 3.3.1 The end fitting shall be made of black heart malleable cast iron conforming to Grade BM:

350 of IS: 14329 or of spherical graphite cast iron to Grade: 400/15 of IS: 1865-1991 or forged steel fittings to BS 970 (Part-II). Approval of the type test of an insulator implies employment of metal fitting of the design approved during type test. Both the metal fittings of one insulator should be of same material.

3.3.2 The metal fittings shall be galvanized after machining. The galvanized surface shall be

smooth. The mass of zinc coating on stay arm insulator hook shall not be applicable to the threaded portion of the hook.

3.3.3 All metal fittings shall be hot-dip galvanised in accordance with specification No.

ETI/OHE/13 (4/84). The minimum weight of zinc coating shall be as follows:

850 mm insulators : 610 g/m2 (min) for all types of metal fittings 1050 mm zone insulators: i) 1000 g/m2 (min) for all types of metal fitting. ii) 750 g/m2 (min) for stay arm insulator hook.

NOTE: The threads of the tapped holes in the metal fittings of stay arm, operating rod and post

insulators shall be cut after galvanisation and protected against corrosion by application of suitable grease. The threads of all other metal fittings shall be cut before galvanisation. All the tapped holes shall be suitable for galvanised bolts and shall conform to IS: 4218 (Part I to VI)- latest.

3.3.4 Tilt of Metal fittings: No tilt of metal fitting is acceptable for all types of insulators. 3.3.5 Threads of metal fittings: Wherever thread cutting is required in the metal fittings, each

insulator shall be checked for the diameter of thread and depth of threaded portion as per the specification/approved drawing using suitable gauges.

3.3.6 The jointing of the metal fittings with the FRP core shall be as per RDSO’s approved

drawings. Which shall neither react chemically with the metal fittings nor cause their fracture/looseness on account of expansion or contraction resulting in loosening of the metal fittings. During the jointing process, care shall be taken to ensure that the FRP core and the metal fittings are properly aligned.

4.0 TESTS: 4.1 DESIGN TESTS: Silicone composite insulators suitability for long-term use for high

voltage applications shall be assessed by design tests. 4.1.1 These tests are carried out to prove conformity with the requirement of the specification

& are intended to prove the suitability of the design, materials and method of manufacture (technology).

4.1.2 The tests on interfaces and connections of metal fittings and the assembled core load – time

test shall be conducted on each type of insulator offered. The test of housing – tracking


5

and erosion test need not be repeated if the material of the sleeve is same for other types of insulators offered. Similarly the test for core material need not be repeated, if the material or glass fibre is same for other types of insulators offered.

The results shall be considered valid for the whole class of insulators having the following characteristics. - Same materials for the core, sheds and same manufacturing process. - Same material of the fittings, the same designs, and the same method of

attachment. - Same or greater layer thickness of the shed material over the core - Same or smaller ratio of all mechanical loads to the smallest core diameter between

fittings. - Same or greater diameter of the core.

4.1.3 The tested composite insulators shall be identified by a drawing giving all the dimensions

with the manufacturing tolerances. The Design tests results should be recorded in a test report. Each test can be performed independently on new test specimens wherever appropriate. The composite insulator of a particular design qualifies only when all insulators or test specimens pass the Design tests as given in the following table. “They shall be repeated whenever the design or the material of the core/sleeve of the insulator is changed/ modified by the manufacturer”. The following tests shall be part of Design tests.

Table - 1

S. No

Description Post Operating rod Sectioning Stay, Bracket & 9 Tonne

1. Tests on interfaces and connections of metal fittings.

a Test specimens and preliminary tests (Clause 5.1.1 of IEC 61109)

b Dry power frequency voltage test (Clause 5.1.2 of IEC 61109).

c Pre stressing (Clause 5.1.3 of IEC 61109) (i) Sudden mechanical load release Test

(Clause 5.1.3.1 of IEC 61109) (ii) Thermal Mechanical Test (Clause 5.1.3.2 of

IEC 61109) (iii) Water immersion test (Clause 5.1.3.3 of

IEC 61109) (d) Verification Test (Clause 5.1.4 of IEC

61109) (i) Visual Examination Test (Clause 5.1.4.1 of

IEC 61109) (ii) Step front impulse voltage test (Clause

5.1.4.2 of IEC 61109)

Three Insulator of each type to be the sequence as given in the IEC 61109.


6

(iii) Dry Power Frequency Voltage Test (Clause 5.1.4.3 of IEC 61109)

2. Assembled Core Load time test. a Test specimens (Clause 5.2.1 of IEC 61109) 06 06 06 06 b Mechanical Load test (i) Determination of the average failing load

of the core of the assembled insulator (Clause 5.2.2.1 of IEC 61109)

03 03 03 03

(ii) Control of the slope of the strength time curve of the insulator (Clause 5. 2.2.2 of IEC 61109)

03 03 03 03

c Test of housing: Tracking and erosion test (Clause 5.3 of

IEC 61109) 02 02 02 02

d Test for the core material (Clause 5.4 of IEC 61109) (i) Dye penetration tests (Clause 5.4.1 of IEC

61109). 10 10 10 10

(ii) Water diffusion (High voltage) test (Clause 5.4.2 of IEC 61109).

06 06 06 06

4.2 TYPE TESTS 4.2.1 These tests are carried out to prove conformity with the requirement of the specification

& are intended to prove the general quality and design of a given type of insulator. “They shall be repeated whenever the design or the material of the core/sleeve of the insulator is changed/modified by the manufacturer or as per instructions issued by RDSO”. Vendors should keep the material ready for specimen preparation in presence of RDSO official. The following tests shall be part of type test

Table - 2

S. No

Item description Post Operating rod

Sectioning Stay/ BT/ 9-Tonne (for each type of

insulator) 1.0 Visual examination 2.0 Verification of dimensions

03 03 03 03

3.0 Mechanical failing load test (Tensile, Eccentric loading in case of sectioning insulator, bending, (Torsion in case of Post insulator, & Mechanical Performance Test –03 insulators for each test.

09 09 09 09

4.0 Galvanisation test. 03* 03* 03* 03* 5.0 Mechanical load time test (Clause 6.4 of

IEC 61109) 03 03 03 03

6.0 Analysis of material properties. a) Housing material (Silicon compound) (i) Silicon content by weight 01 01 01 01 (ii) Ultimate Elongation % 01 01 01 01


7

(iii) Tear strength 01 01 01 01 (iv) DC Volume resistivity 01 01 01 01 (v) Resistance to weathering & UV 01 01 01 01 (vi) Limiting oxygen Index test/flammability. 01 01 01 01 (vii) Arc Resistance 01 01 01 01 (viii) Specific gravity 01 01 01 01 (ix) Dielectric strength in kV/mm 01 01 01 01 (x) Hardness (Shore A) 01 01 01 01 (xi) Tensile strength 01 01 01 01 b) Core Material (i) Verification of dimensions 01 01 01 01 (ii) Dye penetration test. 10 10 10 10 (iii) Percentage of glass content. 01 01 01 01 (iv) Hardness 01 01 01 01 (v) Flexural strength 01 01 01 01 (vi) Water absorption 01 01 01 01 (vii) Water diffusion test 06 06 06 06 (viii) Brittle fracture resistance test. 01 01 01 01 7.0 Visible discharge test 03 03 03 03 8.0 Dry lightning impulse withstand voltage

test (Clause 6.1 of IEC 61109) 03 03 03 03

9.0 Wet Power Frequency test (Clause 6.2 of IEC 61109)

10.0 Wet Power Frequency max withstand voltage test

03 03 03 03

NOTE: (i) The galvanization test shall be conducted on each type of insulator, on 3 samples of metal fittings of the insulators broken in the mechanical load test and mechanical performance test. This test shall be conducted on 3 samples of the hook in case of stay arm insulator.

(ii) All the tests at 6.0(a) & (b) above shall not be repeated for each type of insulator offered at a time for type testing, if the same material has been used.

4.2.2 ACCEPTANCE CRITERIA FOR DESIGN/TYPE TESTS 4.2.2.1 A single batch of insulators and test specimens manufactured and offered for design

tests in accordance with Clause: 4.1 should pass all the type tests as stipulated above. 4.2.2.2 The bulk manufacturing of the insulator shall be taken up, only after approval of the

original tracings of drawings, incorporating changes, if any, necessitated during the type tests and clear written approval of the results of the tests on the prototype is communicated by the Purchaser/Director General (TI), Research Designs and Standards Organisation to the manufacturer,

4.2.2.3 The manufacturer shall stick with the same materials properties and process of

manufacture as adopted for the prototype. In no circumstances, shall materials with other than those adopted in the design/drawings and/or during the manufacture of prototype be used for bulk manufacture on the plea that they had been obtained prior to the approval of the prototype.


8

4.2.2.4 Notwithstanding approval having been accorded to manufacture for supply of the

insulators, on the basis of the results of the type tests, RDSO can conduct tests including destructive tests at any time during the process of bulk manufacture-without prior advice to the manufacturer. All facilities shall be made available to conduct such test- without any charges.

4.2.2.5 The prototype approval shall be accorded for a period of two years only as per RDSO

policy for all the directorates. The approval of QAP shall also be valid till the expiry of the prototype approval. Whenever renewal of the approval of prototype is sought, the manufacturer, for approval of RDSO, shall submit the QAP in case there is any change in the design features. In addition, a mandatory quality audit shall be done minimum twice a year for checking quality of the manufacturing process.”

4.2.2.6 Prior to giving a call to the Director General (Traction Installation) Research Designs and

Standards Organization, Lucknow for testing of the prototype (at least 15 days in advance), manufacturer shall submit a detailed test schedule consisting of schematic circuit diagrams for each of the tests and the number of days required to complete all the tests at one stretch. Prior to that, it should be ensured that, prototype sample is ready in each and every respect. Once the schedule is approved, the tests shall invariably be done accordingly. However, during the process of type testing or even later, RDSO reserves the right to conduct any additional test (s), besides those specified herein, on any insulator so as to test the insulator to his satisfaction or for gaining additional information and knowledge.

4.2.2.7 In case any dispute or disagreement arises between the manufacturer and

representative of the Director General (Traction Installation) Research Designs and Standards Organization, Lucknow during the process of testing as regards the procedure for type tests and/or the interpretation and acceptability of the results of type test, it shall be brought to the notice of the Director General (Traction Installation) Research Designs and Standards Organization, as the case may be, whose decision shall be final and binding.

4.2.2.8 The insulator shall be visually examined to see that it is free from physical distortion of

shape, chalking (flouring), crazing and that the sleeve is free from cracks or any other defect likely to be prejudicial to satisfactory performance in service.

4.2.2.9 The metal fittings shall be smooth without any excrescence. Before accepting the lot for

type test, the purchaser shall check all the insulators for the defects and 10% of the lot of insulators shall be checked for these defects in case of “acceptance tests”).

4.3 ROUTINE TESTS: These tests are for the purpose of eliminating insulators

with manufacturing defects. They are conducted on every insulator offered for acceptance.

Note: Every insulator shall pass the routine tests as given below. The manufacturer shall

conduct the tests. The Purchaser shall have the right to witness routine tests. The


9

manufacturer shall maintain the detailed record of the number of insulators tested, number rejected and other essential data for the purpose of examination.

4.3.1 Routine Visual Examination: The visual examination shall be conducted as per clause:

8.2 of IEC 61109. 4.3.2 Routine Mechanical Load Test: All insulators except for sectioning insulator shall be

subjected to axial tensile load of 70% of the value specified in TABLE-5 for one minute. In case of sectioning insulator, the tensile load shall be applied 80 mm eccentric as indicated in Fig. If any insulator cracks or its metal fittings loosen or deform or crack, it shall be rejected. Every insulator passing the routine mechanical load test shall be affixed with a clear label or stamp on the end fitting indicating that it has passed routine mechanical load test.

4.4 ACCEPTANCE TESTS: 4.4.1 These tests are for the purpose of verifying the mechanical characteristics as well as the

required properties of the FRP and sleeve material of insulator and other characteristics as considered necessary, to ensure quality of manufacturing and the material used. The following tests including tests specified in IEC 61109 & some additional tests, shall constitute part of acceptance tests to be conducted on the insulators selected in random from the lot offered for acceptance.

Table -3 S N Name of the test Clause of the spec. Qty 1. Visual examination IEC 61109 100% of sample

size 2. Verification of dimensions RDSO approved drg. 3 Nos. 3. Verification of the specified

mechanical load Clause 7.4 of IEC 61109 33% of sample

size 4 Bending load test 33% of sample

size 5 Mechanical performance test IEC 575 33% of sample

size 6. Dry power frequency withstand

voltage test IS-2071 (at 100Kv(rms)) for one minute.

5% of offered quantity

7. Galvanization test. ETI/OHE/13 (4/84) 3 Nos.

8. Analysis of material properties (Housing material) ***

a Hardness (Shore A) ASTM D 2240

b Specific gravity ASTM D 792

3 No

*** Tests to be conducted on the specimen prepared according to standards indicated. NOTE:- i) While conducting the bending test, mechanical performance test and tensile test, the

load shall be increased until the failing load is reached and its value recorded.


10

ii) The visual examination shall be conducted on 10% of the lot offered, thereafter,

other acceptance tests shall be conducted on the randomly selected samples from the lot offered for acceptance tests. If any failure occurs in the visual examination, a further quantity of 20% of the lot shall be visually examined. If any insulator fails in the retest, the entire lot shall be rejected.

iii) Further the dry power frequency voltage withstand test shall be conducted on at

least 5% of the offered quantity at 100 kV (r.m.s.) for one minute in vertical position of the insulator as per IS: 2071 latest/IEC- 61109.

4.4.2 In case of stay arm each insulator shall be checked for the diameter of transverse holes,

distance between the transverse holes, distance of these holes from the ends of metal fittings, using suitable gauges. In case of bracket insulator, each insulator shall be checked for the machining of the hole as per the relevant drawing using suitable gauges and U bolts.

4.4.3 The sample size shall be 1.5% of the quantity offered subject to a minimum of 6 picked up

at random in accordance with the above sample size and shall be equally distributed for tensile, bending & mechanical performance tests.

4.4.4 Each hook shall be checked for eyehole gap, diameter of thread and length of the threaded

portion as per drawing using suitable “Go and No Go gauges”. The measurement of specified pitch of the threads of stay arm insulator hook and hook side metal fitting shall be checked on 20% quantity of each lot.

4.4.5 The following shall form part of the acceptance test report.

• A certificate by the Inspecting official in regard to the effect that he has checked the records of the routine tests conducted by the manufacturer and found in line with the test results submitted to inspecting officials.

• A statement from the manufacturer, countersigned by the Inspecting Official, showing the rejection rate of insulators in the routine tests conducted by the manufacturer for each lot offered.

• The following documents shall be provided by the manufacturer at the time of type/acceptance test for Silicon compound & FRP rod.

1) Name and trade mark of manufacturer. 2) Product data sheet/Test certificate.

Any other information required by the purchaser. 4.5 UFormation lot of insulatorsU: All the insulators of the same type and design manufactured

under identical conditions of production shall be offered for acceptance. A lot may consist of the whole or part of the quantity ordered.

4.6 UBatch of InsulatorsU: A batch of insulators shall be the complete number of insulators

manufactured from one type of silicon rubber/FRP rod procured in one stretch for the


11

purpose of conducting prescribed type tests, during the process of inspection and testing of prototype. The required number of test specimens for the purpose has to be manufactured.

5.0 DRAWINGS AND THEIR APPROVAL 5.1 The supplier shall submit three prints each of the following drawings showing all the details

in scale 1:1, separately for each type of insulator (in the proforma for the drawing enclosed) as per Railway Standards in sizes of 210mmx297mm or any integral multiple thereof for approval for the purpose of prototype test only.

• Assembly drawing of the insulator. • FRP Core drawing. • Metal fittings drawings.

5.2.1 The drawings approved for the prototype tests only shall be modified, if need be, as a result of changes necessitated during testing or as desired by RDSO. The modification shall be first got approved and then incorporated in drawing duly signed by the representative of Director General (Traction Installation) Research Designs and Standards Organization, Lucknow. If there is no modification at all, the drawings approved for prototype tests shall be treated as final.

6.0 ESSENTIAL REQUIREMENTS: 6.1 The insulators shall conform to essential dimensions shown in fig. 1 to 9 for

interchangeability. The method of fixing of the metal fittings to the FRP core shall be as per RDSO’s approved drawings.

6.2 It shall cover the entire dimensional parameters characterizing of the insulator profile &

shall generally conform to IEC Publication 60815-1986& IS: 13134. 7.0 UMarking: EUach insulator shall be legibly and indelibly marked during moulding. The marking

on the sheath of the core should be with 4/5mm figures while that on sheds shall be with 6mm figures to show the following:

a) Name or trade mark of the manufacturer (on the core at the time of moulding) b) Month and year of manufacture on sheds by screen-printing, which should not get

wiped out during the life of the insulator.

8.0 Packaging: The insulators shall be securely packed first with thick polythene bag and it should be kept inside 7 ply (140-120-120-120-120-120-140) cardboard box having 75 mm thickness thermocol at both the ends of box. Appropriate hole to support the metal fitting should be made in the thermocol. Care shall be taken to ensure that sheds of the entire four insulator should not touch each other and from the walls of the box. It shall be ensured that there is no damage to sheds during loading & transportation. Not more than four insulators shall be packed in a box, so as to facilitate manual loading and unloading. The manufacturer shall provide instructions regarding handling & storage to be taken during transportation & at site along with the supplies.


12

9.0 STANDARD ATMOSPHERIC CONDITIONS

Electrical tests shall, however, be carried out under conditions obtaining at the time of the tests. The barometric pressure, air temperature and humidity at the time of tests shall be recorded for the purpose of calculating the corrections to test voltage in accordance with Appendix B.

10.0 REQUIREMENTS OF ELECTRICAL & MECHANICAL PARAMETERS 10.1 Voltages for High voltage tests: The values of voltages at Standard Atmospheric

Conditions for the various high voltage tests on the insulators shall be as given in TABLE-4. TABLE-4

VALUES OF VOLTAGES FOR HIGH VOLTAGE TESTS

Wet Power frequency withstand voltage test

Dry lightning impulse withstand voltage test

Type of insulator

Visible discharge test KV (rms)

Insulator vertical kV (rms)

Insulator horizontal kV (rms)

Positive wave kV (peak)

Negative wave kV (peak)

1 2 3 4 5 6 Stay arm 35 100 125 240 260

Bracket tube 35 100 125 240 260 9-tonne 35 100 125 240 260

Operating rod 35 100 125 240 260 Post 35 100 - 240 260

Sectioning 35 - 125 240 260 Note: These values apply to all standard, polluted and heavily polluted zone insulators. 10.2 Minimum Mechanical Failing Loads and Bending and Torsional Moments: The minimum

mechanical failing loads and bending and torsional moments shall be in accordance with TABLE-5.

TABLE-5 MINIMUM MECHANICAL FAILING LOADS, BENDING AND TORSIONAL MOMENTS.

Type of insulator

Tension (kgf)

Tension with 80mm eccentricity of load

(kgf)

Bending moment (kgf.m)

Torsional moment (kgf.m)

1 2 3 4 5 Stay arm 7000 - 200 -

Bracket tube 7000 - 200 - 9-tonne 11000 - 210 -

Operating rod 2200 - 70 - Post 6000 - 370 550

Sectioning - 5000 - -


13

11.0 After Sales Service. 11.1 The manufacturer shall make necessary arrangements for closely monitoring the

performance of the insulators through periodical visits to the offices of the consignees to whom, the insulators have been dispatched for interaction with the operating and maintenance personnel of the Indian Railways.

11.2 The manufacturer shall respond promptly and in a workman-like manner to any call given by

Indian Railways for any assistance by way of attending to failures, investigation into the causes of the failures including tests, to be done and such other items with a view to seeing that the insulator serves the purpose for which it is intended.

12.0 This specification supersedes the earlier Specification No. TI/SPC/OHE/INSCOM/0991

issued on 03.05.2005.

☺☺☺☺☺☺☺☺☺


14

APPENDIX “A” DETAIL DESCRIPTION OF TESTS

1.1 Tests on interfaces & connections of metal fittings. 1.1.1 Test specimens and preliminary tests: Three Insulators assembled on the

production line shall be tested. The insulation length (metal to metal spacing shall not be less than 800 mm. Both metal fittings shall be the same as on standard production insulators. The metal fittings shall be assembled so that the insulating part from the fitting to the closest shed shall be identical to that of the production line insulator. The insulators shall be examined visually and it shall be checked that the dimensions conform to the drawing. They shall then be subjected to the mechanical routine test according to 8.3 of IEC E 1109.

1.1.2 Dry Power Frequency Voltage Test: On the three specimens, the dry power

frequency flashover voltage shall be determined, by averaging five flashover voltages on each specimen. The average flashover voltage shall be corrected to normal standard atmospheric conditions as mentioned in IEC 60-1/Appendix `B’ (attached). The flashover voltage shall be obtained by increasing the voltage linearly from zero within 1 min.

1.1.3 Pre stressing: The tests shall be carried out on the three specimens in the sequence

as indicated below. 1.1.4 Sudden load release test: The three insulators shall be mounted in the testing

equipment. The temperature inside the chamber shall be set to -20o C to - 25oC . Every test specimen is subjected to five sudden load releases from a tensile load amounting to 30% of the specified mechanical load.

1.1.5 Thermal Mechanical Test: This test shall be done on three insulators in

accordance with Clause5.1.3.2 of IEC 61109. 1.1.6 Water immersion test: The three insulators subjected to Thermal

Mechanical test as per clause 1.1.5 shall be kept immersed in a vessel, in boiling deionized water with 0.1% by weight of Na Cl. for 42 hours. After completion of 42 hours, the samples should be left in the vessel until the water cools down to about 50o C and maintained at this temperature in the equipment till verification test start in the following sequence.

1.1.7 Verification tests: The time interval between the following tests i.e. visual

examination, steep front impulse voltage test and dry power frequency voltage test shall be such that the verification tests are completed within 48 hours.

1.1.8 Visual Examination: The housing of each specimen is inspected visually. No

cracks/damage are permissible.


15

1.1.9 Steep front impulse voltage test: The test specimens are to be fitted with sharp edged electrodes (consisting of clips e.g. made of a copper strip approximately 20 mm wide and less than 1 mm thick). These electrodes are fitted firmly around the housing between sheds so positioned to form sections of about 500 mm or smaller. The voltage shall be applied to the original metal fittings in case of insulators with an insulation length smaller than or equal to 500 mm.

An impulse voltage with a steepness of at least 1000 kV/µs shall be applied between two neighboring electrodes or between the metal fitting and the neighboring electrode respectively. Each section is to be stressed with 25 impulses of positive and 25 impulses of negative polarity. Each impulse shall cause external flashover between the electrodes & no puncture shall occur. The electrodes used to form sections shall be removed.

1.1.10 Dry Power Frequency Voltage Test: The test is to be conducted as per clause 5.1.4.3 of IEC 61109. 1.2 Assembled Core load time test: 1.2.1 Test specimens: Six insulators made on the production line shall be tested. These

insulators shall be examined visually and checked whether the major/critical dimensions confirm with the relevant drawing.

1.2.2 Mechanical load Test: This test is to be performed in two parts at ambient

temperature. 1.2.3 Determination of the average failing load of the core of the assembled insulator:

Three of the specimens shall be subjected to tensile load. The tensile load shall be increased rapidly but smoothly from zero to 75% of the expected mechanical failing load and then gradually to be increased in a time between 30 seconds to 90 seconds until breakage of the core or complete pull out occurs. Any test leading eventually to a failure of the couplings shall be ignored. The average of the three failing load shall be calculated.

1.2.4 Control of the slope of the strength time curve of the insulator:

The remaining three specimens shall be subjected to a tensile load, which shall be increased rapidly but smoothly from zero to 70% of the average failing load, as calculated in clause 1.2.3 and then maintained at this value for 96 hours. Without failure.

1.3. Tracking & erosion test. :

1000 hrs test: This shall be part of design test & shall be carried out as per clause 5.3 of IEC 61109 – 1992 (3) with amendment –1-1995-04. The test is regarded as passed, if no more than three over current trip-outs occur for each specimen tested, if no tracking occurs, if erosion does not reach the glass fiber core and if no sheds are punctured. The core shall not be visible & shall maintain hydrophobicity. There should not be any crazing, chalking, cutting etc.


16

5000 hrs test: 1000 hour test should be further carried out for 5000 hrs to check the tracking and erosion property for 1600mm creepage distance insulator & shall be a part of design test

Note: (i) The test of housing – Tracking & erosion test need not to be repeated, if the material of the sleeve is same for other types of insulator offered. Similarly, the test for core material need not be repeated for other type of insulators, if the material for glass fibre is same for other types of insulators offered.

(ii) Several interruptions of the test for inspection purposes each of these not exceeding 15

min are permissible; interruption periods will not be counted in the test duration.

1.4 Test for the core material: To check the performance of core material against water penetration, the following test shall be carried out.

1.4.1 Dye Penetration Test: Ten samples shall be cut from a production line insulator

making the cut at 90o C to the axis of the core with a diamond coated circular saw blade under running cold water. The length of the samples shall be 10 mm +/- 0.5 mm. The cut surfaces shall be smoothened by means of fine abrasive cloth (Grain size 180). The cut surfaces shall be clean and parallel.

The specimens are placed (fibers vertical) on a layer of steel or glass balls of same

diameter (1 mm to 2 mm) in a glass vessel. A dye, 1% alcohol solution of fuchsin (1 gm fuchsin in 100 gm ethanol) is poured into the vessel, its level being 2 mm to 3 mm higher than the level of the balls. The dye can rise by capillarity through the core. The time taken for the dye to rise through the specimens shall be measured. The time taken for the dye to rise through the specimens shall be longer than 15 minutes.

1.4.2 Water diffusion Test: Six samples shall be cut from a production line insulator, making

the cut at 90o to the axis of the core with a diamond-coated circular saw blade under running cold water. The length of the sample shall be 30 mm +/- 0.5 mm. The cut surfaces shall be smoothed by means of fine abrasive cloth (Grain size 180). The cut surface shall be cleaned & parallel. The surfaces of the specimens’ material shall be cleaned with isopropyl – alcohol and filter paper immediately before boiling. The specimen of only one core will be boiled in a glass container for 100 h+/- 0.5 hour in deionized water with 0.1% by weight of NaCl. After boiling, the specimens shall be removed from the glass container and placed in another glass container filled with tap water at ambient temperature for at least 15 min. All the six specimens will be subjected to a voltage test by putting between the electrodes in accordance with clause 5.4.2.3 of IEC 61109 within the next 3 hours after the removal of the specimens from the boiling container. During the test, no puncture or surface flashover shall occur. The current during the whole test shall not exceed 1 milli Amp(r.m.s).

1.5 Visual examination:

The insulator shall be visually examined to see that it is free form physical distortion of shape and the surface is free from cracks, chalking, crazing or any other defect likely. The visual defects shall not exceed the limits permissible for the appropriate class of insulator


17

as specified in IEC: 61109 to be prejudicial to satisfactory performance in service. The metal fittings shall be smooth without any excrescence.

1.6 Verification of dimensions: The dimensions of the insulator shall be verified to see that

they are in accordance with the approved drawings. Unless otherwise specified, a tolerance of +/- (0-03 d+0-3) mm shall be permissible on any dimension of the housing only, ‘d’ being the dimension in mm.

1.7 Galvanisation test: The uniformity, adherence and mass of zinc coating shall be tested

in accordance with specification No.ETI/OHE/13 (4/84) and the results of the tests shall meet the requirements specified. The mass of zinc coating shall be as specified in clause 3.3.3. of the specification.

1.8 Mechanical Load Time test: This test shall be performed on three specimens picked up

from production line or three core samples with metal fittings at ambient temperature to confirm the specified mechanical load (SML) of the insulator after the application of a tensile load of 70% of SML & this load maintained for 96 hours. Each specimen shall have a length between metal fittings of at least 10 times the core diameter. Test shall be performed in accordance with clause 6.4.2 of IEC 61109.During /after the test no failure (breakage or complete pull out of the core or fracture of the metal fittings) occurs.

1.9 Analysis of material properties 1.9.1 Housing material: The following tests shall be conducted on housing material according to

the specifications.

S.No. Test Reference Spec. Specified value. 1 Resistance to tracking & erosion IEC: 60587 Min. 4.5 2 Tear strength (KN/m) ASTM D 624-B Min. 12 3 Volume resistively IEC 60093

Min. 1x10 13

4 Resistance to weathering & UV ASTM G53-96 No crack is to be observed in the test duration of 96 hours.

5 Arc Resistance ASTM-495-1973 >200 sec. 6 Specific gravity ASTM D 792 1.52 to 1.58 7 Dielectric strength in kV/mm ASTM D 149/IEC

60243 17.5

8 Hardness (Shore A) ASTM D 2204 68 ± 7 9 Ultimate elongation ASTM D 412 Min 100 10 Tensile strength ASTM D 412 Min. 40 kg/sqcm 11. Limiting oxygen Index ASTM D 2863 40% min.

1.9.2 Core Material: The following specified values should be achieved in the tests conducted on

specimens


18

S.No. Test Reference Spec. Specified value. 1 Verification of dimensions As per approved drawing. As per approved

drawing. 2 Bending tests As per RDSO

Spec.No.ETI/OHE/15(9/91) 210 kgfm (min)

3 Dye penetration test. IEC61109 (Clause 5.4.1) No dye penetration for 15 minutes (min)

4 Percentage of glass content.

ASTM D2584 70% (min.)

5 Hardness test (Bacol) ASTM D2583 50 min 6 Water absorption IEC 61109, ASTM D 570 0.1 % max. 7 Specific gravity ASTM D 792 1.9 to 2.1 8 Brittle fracture resistance

test. As per procedure given in Para 1.15

Shall withstand

1.10 Mechanical failing load tests: These tests shall comprise tensile, bending, eccentric

loading and torsion tests. 1.10.1 Tensile load test: This test shall be done on all the insulators except the sectioning

insulator. The load shall be applied to the insulator in line with its axis. It shall be increased at a rate agreed to between the manufacturer and the purchaser to 70% of the specified minimum tensile failing load. It shall be maintained at this value for one minute and then raised at the same rate until separation or breakage of metal fittings or total breakage of the insulator occurs. The separation or any permanent deformation in the insulator and its components shall not occur before the load reaches the minimum tensile failing load specified in TABLE-5.

1.10.2 Bending tests: This test shall be done on all the insulators except the sectioning insulator. One end of the insulator shall be rigidly fixed in a suitable fixture so as not to cause the failure of the metal fitting of this end during the test, which is for the composite shell only. The load shall be applied to the other end of the insulator in line with the diameter and in a direction perpendicular to the axis of the insulator and shall be increased at a rate agreed to between the manufacturer and the purchaser to 70% of the specified minimum failing bending moment, taking into account the distance between the top of the fixture and the point at which the load is applied. It shall be maintained at this value for one minute and then raised at the same rate until the total breakage of the insulator metal fittings or separation occurs. The failing bending moment shall be calculated by multiplying the value of the load in kgf and the distance from the point of application of load to the point of breakage in m and this value shall be not less than the minimum bending moment specified in TABLE-5.

1.10.3 Mechanical Performance Test: This test shall be done on all the insulators in accordance

with Clause 4 of IEC Publication 575. The insulators shall be subjected to a tensile load (eccentric tensile load in the case of sectioning insulator) equal to 70% of the specified minimum failing load and immediately removed. This shall be done 4 times in quick succession. Thereafter the insulator shall be subjected to the tensile test (eccentric


19

tensile tests in the case of sectioning insulator) in accordance with Clause 1.10.1. The separation or breakage of the metal fittings or the total breakage of the insulator or any permanent deformation in the insulator and its components shall occur not below the specified minimum failing load specified in TABLE-5. In case of the sectioning insulator, the line of application of the load shall be 80mm away from and parallel to the longitudinal axis of the insulator.

Note: (1) The choice of the end to be fixed rigidly shall be left to the manufacturer. (2) The recommended rates of increase of load in the tensile and bending tests as per IEC

are: Tensile test: 200 to 300 kgf/s Bending test: 15 to 30 kfg/s 1.10.4 Eccentric loading test: This test shall be done only on the sectioning insulator. The load

shall be applied by means of suitable jigs such that the line of application of the load is 80 mm away from and parallel to the longitudinal axis of the insulator. Care shall be taken to ensure that during the test, the jigs do not move and the distance of the load from the centerline of the insulator does not become less than 80 mm. The load shall be increased at a rate agreed to between the manufacturer and the purchaser to 70% of the specified minimum eccentric tensile failing load. It shall be maintained at this value for one minute and then raised at the same rate until separation or breakage of metal fittings or total breakage of the insulator occurs. The separation of metal fittings or total breakage of the insulator or any permanent deformation in the insulator and its components shall not occur before the load reaches the minimum eccentric tensile failing load specified in TABLE-5

1.10.5 Torsion test: This test shall be done only on the post insulator. The insulator shall be

subjected to a torsional load of the lever arm used for imparting the torsion, the load corresponding to the minimum torsional failing moment shall be calculated and 70% of the value of load so calculated shall be gradually applied at the end of the lever arm and maintained at that value for one minute. The load shall then be raised at the same rate till breakage of the insulator shell takes place. The moment shall be calculated with torsional the load at which the insulator breaks by multiplying the load and the lever arm length and that breakage shall occur at torsional moment not less than the minimum specified in TABLE-5.

1.11. Analysis of material properties (Type & acceptance): the tests for material

properties shall confirm to table: 2 & the test for acceptance tests shall confirm to table: 3.

1.12 Visible discharge test: The room in which the test is to be done shall be darkened

completely and a period of at least five minutes shall be allowed for the observer to become accustomed to the darkness. A power frequency voltage of the value specified in TABLE-4 shall be applied in accordance with the procedure laid down in Appendix ‘C’ and maintained at that value for five minutes. During this period, there shall be no signs of visible corona. The voltage shall then be raised gradually and the value at which corona first appears shall be recorded. The voltage shall then be reduced gradually, and the value at which the corona just disappears shall also be recorded.


20

1.13 Dry lightning impulse withstand voltage test: The insulator shall be tested dry under the conditions described in Appendix “C”. The impulse generator shall be adjusted to apply a standard 1.2/50 wave at the specified impulse withstand voltage adjusted for the atmospheric conditions at the time of test. Fifteen such voltage waves shall be applied to the insulator. If there is no flashover or puncture, the insulator shall be deemed to have passed the test. However, two flashovers on the external insulation are permissible. The insulator shall pass the impulse withstand voltage test with voltages of both positive and negative polarity. The insulators shall not be damaged by these tests, but slight marks on the surface of the metal fitting shall be permissible. The original oscillograms recorded during the test shall form part of the type test report.

1.14 Wet Power frequency withstand voltage test and wet power frequency maximum

voltage test. The insulator shall be arranged as described in Appendix “C” and exposed for at least 1 minute before application of voltage and throughout the test the artificial rain produced in accordance with Clause 3.3 of IS:2071 (Part-I). The test voltage to be applied to the insulator shall be the specified wet power conditions at the time of test. A voltage of about 75% of the test voltage so determined shall be applied and then increased gradually to reach the test voltage shall be maintained at this value for 1 minute. The insulator shall not flashover or punctures while the test voltage is applied.

The test shall then be repeated at successively higher voltage in step of 2.5 kV or 5

kV until the insulator is unable to withstand the applied voltage for a period of 1 minute. The voltage, corrected as described in Appendix “B”, of the test immediately preceding the last test shall be taken as the maximum wet power frequency withstand voltage.

1.15 Brittle fracture: 1.15.1 Brittle fracture results due to exposure of mechanically stressed Glass fiber in the rod, to

an acidic medium & thereby leads to stress corrosion cracking. Factors that plays a role in brittle fracture failure are, the quality of bonding between Glass fibers and the resin matrix, poor quality of glass resin interface i.e. containing voids or an uneven resin distribution etc. Protection of glass fibers is key to improved brittle fracture resistance at the microscopic level.

1.15.2 This test should be conducted on bare FRP rod. The rod should be crimped with metal

fitting & load to the tune of 80% of SML should be applied for 96 hours. To check the influence of stress in the end fittings & FRP rod and evaluation of brittleness of FRP rods, FRP rod at the middle is fully dipped in 1 N HNO3 and under 80% SML Tensile load for 96 hours as shown in fig – A below

Metal fitting Metal fitting FRP Rod

80% SML Tensile Load 1n HNO3


21

1.15.3 The sample is considered as pass if the rod does not indicate any sign of crack on its

surface during & after 96-hour duration. 2.0 The schedule for number of insulators and specimens to be subjected for each test

mentioned above shall be got approved from Director General/TI, RDSO, Manak Nagar, Lucknow – 226 011.

☺☺☺☺☺☺☺☺☺☺☺


22

APPENDIX “B”

CORRECTION OF TEST VOLTAGES FOR ATMOSPHERIC CONDITIONS A - 1. GENERAL: Variation in barometric pressure and humidity of the atmosphere cause

variation in the electric strength of the air and hence in the flashover voltage of an insulator exposed to atmosphere.

A-2. CORRECTION FACTORS: When the atmospheric conditions around an insulator during test differ from the reference conditions, adjustment are required to be made to certain of the test voltages by the application of the following correction factors in accordance with TABLE-A-1 at the end of this Appendix.

a) Correction factor (d) for air density: D = 0.289 p (d lies between 0.95 and 1.05) 273 + t

When P = atmospheric pressure in mbar, and t = temperature in oC For a wider range of density and for higher accuracy, the factor k shall be used instead of

factor d. The values of factor k corresponding to various values of factor d are given below: d K

0.70 0.72 0.75 0.77 0.80 0.82 0.85 0.86 0.90 0.91 0.95 0.95 1.00 1.00 1.05 1.05 1.10 1.09 1.15 1.13

b) Correction factor (h) for humidity: Figure: A-1 attached gives the values of absolute humidity value for wet and dry bulb temperatures (when the velocity of air over the wet bulb exceeds 3 m/s) for the standard atmospheric pressure of 1013 mbar. For better accuracy, a correction should be applied to the absolute humidity value obtained from Figure: A-1 for any deviation of ambient atmospheric pressure from the standard value of 1013 mbar. This correction is obtained from figure: A-2 as follows: -

Locate the point corresponding to the deviation of ambient atmospheric pressure from 1013 mbar on the left hand side of Figure: A-2B and join it with the right hand side top corner by a straight line. Then locate the point on the curve in Figure: A- 2A corresponding to the observed value of the difference of dry and wet bulb temperatures. Drawn a vertical line through this point to intersect the straight line drawn in Figure: A-2B. Read the correction to be applied to humidity from the right hand side of Figure: A-2B corresponding to the point of intersection. The correction is positive for a positive deviation and negative for negative deviation from the standard atmospheric pressure. For the corrected value of absolute humidity thus obtained, the correction factor (h) of TABLE A-1 shall be determined from Figure: A-3.

TABLE A-1 CORRECTION OF VOLTAGES FOR ATMOSPHERIC CONDITIONS

TYPE OF TEST ADJUSTMENT REQUIRED. Dry lightning impulse withstand voltage Voltage applied shall be the appropriate value specified in TABLE- 4

multiplied by k and divided by h. Wet power frequency withstand voltage Voltage applied shall be the appropriate value specified in TABLE- 4

multiplied by k. Wet power frequency maximum withstand voltage

Measured voltage shall be divided by k.


23

APPENDIX “C”

HIGH VOLTAGE TESTS.

B-1. ARRANGEMENT OF INSULATOR. B-1-0 GENERAL – The insulator shall be clean and dry and in thermal equilibrium with its

surroundings. B-1.1 Insulators tested in vertical position: B-1.1.1 The insulators shall be hung vertically from an earthed support by means of a wire rope

or metal rod. The distance between the top of the insulator metal fittings and the point of support shall be not less than 1 m. At the lower end of the insulator shall be attached, if required, a metallic rod of weight adequate to ensure that the insulator remains in vertical position during test.

B-1.1.2 No object shall be nearer to the axis of the insulator than 1 m or 1.5 times the length of

the insulator whichever is the greater. B-1.1.3 The test voltage shall be applied between the metal rod at the bottom of the insulator

and the earthed point of suspension. B-1.2 Insulators tested in horizontal position: B-1.2.1 The insulator shall be anchored by means of a cable or metal rod connected to earth.

The distance between the top of the insulator metal fitting and the point of anchorage shall be not less than 1 m.

B-1.2.2 The other end of the insulator shall be provided with a metal trod about 1 m long and the

whole arrangement maintained in an approximately horizontal position by any convenient means.

B-1.2.3 No object shall be nearer to the axis of the insulator than 1 m or 1.5 times the length of

the insulator whichever is the greater. B- 1.2.4 The test voltage shall be applied between the end of the metal rod and the earthed point

of anchorage. B-2 HIGH VOLTAGE TEST B-2.1 The high voltage test shall be conducted in accordance with IS: 2071 (Part I to III). B-3 PRECAUTIONS AGAINST EXCESSIVE HUMIDITY: B-3.1 Special precautions shall be taken to avoid condensation on the surface of the

insulator when the relative humidity is high. For example, the insulator shall be maintained at the ambient temperature at the test location for a sufficient period to attain thermal equilibrium before commencing the test. Except by agreement between the manufacturer and the purchaser, the test shall not be made if the relative humidity exceeds 85%.

☺☺☺☺☺☺☺☺☺☺☺

ti spc ohe inscom 1070

Documents