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Hard-Drawn Copper Conductors for Over Head Power Transmission 1

Hard-Drawn Copper Conductors for Over Head Power Transmission

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Page 1: Hard-Drawn Copper Conductors for Over Head Power Transmission

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Hard-Drawn Copper Conductors for Over Head Power Transmission

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2FOREWORD

This Indian Standard ( Second Revision ) was adopted by the Indian Standards Institution on 20 May 1982, after the draft finalized by the Conductors and Accessories for Overhead Lines Sectional Committee had been approved by the Electro technical Division Council.

This standard, first published in 1951, was subsequently revised in 1963 to incorporate all quantities and dimensions in metric system. This revision has been undertaken with a view to upgrade many of the essential requirements and to bring it in line with the latest engineering practices being followed in the country.

In the standard, values for constant-mass temperature coefficient of resistance and coefficient of linear expansion are given on the basis of IEC Publication No. 28 ( 1925 ). International Standard of Resistance for copper.

Hard-drawn copper wires covered by Telegraph Wires (Unlawful possession ) Act No. LXXIV of 1950 as amended by Act No. LIII of 1953 have been dealt separately in 18:2532-1965*.

While preparing this standard, assistance has been derived from BS 125: 1970 Hard-drawn Copper and Copper Cadmium Conductors for Overhead Power Transmission Purposes, issued by the British Standards Institution.

For the purpose of deciding whether a particular requirement of this standard is complied with, the final value, observed or calculated, expressing the result of a test, shall be rounded off in accordance with IS :2-196Ot.The number of significant places retained in the rounded off value should be the same as that of the specified value in this standard.

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3METHODOLOGY

SCOPE

This specification covers the requirements for hard-drawn solid and stranded circular copper conductors for overhead power transmission purposes.

TERMINOLOGY

For the purpose of this standard, the following definitions in addition to those given in

1s : lS85 ( Part XXXII )-1971* shall apply.

Stranded Conductor - Conductor consisting of three or more copper wires of the same nominal diameter twisted together in concentric layers . When the conductor consists of more than one layer, successive layers are twisted in opposite directions.

Diameter - The mean of two measurements at

right angles taken at the same crow section

Direction of Lay - The direction of lay is defined as right hand or left hand. With right hand lay , the wires conform to the direction of the central part of the letter 2 when the conductor is held vertically. With left hand lay, the wires conform to the direction of the central part of the letter S when the conductor is held vertically.

Lay Ratio - Ratio of the axial length of a complete turn of the helix formed by an individual wire in a stranded conductor to the external diameter of the helix.

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CONDUCTOR Material -- The conductor shall consist of hard-drawn round copper wire

having the following properties.

Physical Constant for Hard Drawn Copper

Volume resistivity- The resistivity of hard-drawn high-conductivity copper is function of the tensile strength. Within a range of 30 to 50 Kg/mmtensile strength, the following formula has been found to express sufficiently closely the results obtained in practice, and has been adopted in calculating the resistance given in this specification:

where

P = percentage increase in resistivity of the hard-drawn copper over its resistivity when annealed, and

T = tensile strength of the hard-drawn copper in kg/mm².

The resistances given in the tables, are based on standard resistivity of annealed high-conductivity copper at 20°C modified

in accordance with the above formula.

At a temperature of 20°C the volume resistivity of standard annealed copper is 0.017 241 ohm square millimetre per metre ( ohm mm3/m ). Copper which has resistivity at 20°C of 0.017 241 ohm mm2/m is said to have a conductivity of 100 percent.

Density - At a temperature of 20°C the density of hard-drawn high conductivity copper has been taken as 8.89 g/cm3.

Coefficient of linear expansion - At a temperature of 20°C the coefficient of linear expansion of hard-drawn high-conductivity copper has been taken as 0.000 017 per Centigrade degree, This coefficient may be used over a temperature range of 0°C to 150°C.

Constant-mass temperature coefficient of resistance - at a temperature of 20°C the coefficient of variation of the resistance with temperature of hard-drawn high-conductivity copper, measured between two potential points rigidly fixed to the wire, the metal being allowed to expand freely, has been taken as 0’003 81 per Centigrade degree, which is a representative value for copper of 97 percent conductivity.

Freedom from defects - The wire shall be smooth and free from all in perfections such as spills and spurns.

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STANDARD RESISTANCE, WEIGHT AND SIZE OF SOLID CONDUCTOR

After drawing, the wire shall have the resistance, weight and diameter given in Table 1.

STANDARD RESISTANCE, WEIGHT AND SIZE OF STANDARDCONDUCTOR

The size, weight and resistance of stranded circular conductor shall be in accordance with the values given in Table 2.

In Table 2, the areas, weights and resistances of the stranded conductors have been calculated by multiplying the corresponding values for one of the single wires of which the stranded conductor is

composed by the constants set out in Table 3.

The calculated area in each case in Table 2 is given as obtained above ,and is that of a solid conductor of equal resistance assuming to same specific conductivity.

The resistances have been corrected in accordance with the formula Given.

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TOLERANCES ON THE STANDARD DIAMETER AND RESISTANCE OF CONDUCTORS

Tolerances as given below shall be permitted on the standard diameter and resistances of all conductors:

a) Tolerance on standard diameter f I percent, and

b) Tolerance on resistance + 1 percent when corrected to standard weight.

When corrected to standard weight and temperature, the resistance of the conductor shall not exceed the appropriate maximum resistance given in Tables 1 and 2.

The mean diameter of the conductor shall fall within the appropriate maximum and . minimum values given in Table 1.

The cross-section bf any conductor shall not depart from circularity by more than an amount corresponding to a tolerance of 2 percent on the standard diameter.

MECHANICAL PROPERTIES The mechanical properties of the wire shall be such that

the tensile strength and elongation when tested in accordance with 14.3 and 14.4 shall be as shown in Table 1.

Wires smaller than 5.60 mm diameter shall also comply with the requirements of the wrapping test as specified in 14.2.

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JOINTS IN WIRES, EXCEPT DlJRING STRANDING The wires shall be drawn in continuous lengths, without

joints, except those made in the soft rod or wire before final drawing.

JOINTS IN STRANDED CONDUCTORS Conductors Containing Seven Wires or Less -Joints in

wires, other than those permitted under 8, shall not be permitted in any wire of a stranded conductor containing 7 wires or less.

Conductors Containing More than Seven Wires - In the case of stranded conductor containing more than 7wires, a joint in any wire shall be permitted provided that no two joints ( other than those in wires before stranding. permitted under 8 ) occur at points in the stranded conductor nearer than 15 m. Joints shdl be hard-soldered or welded.

The breaking strength of the joint permitted under, shall

be in no case be less than 220 MN/m²

STRANDING The wire entering, into the construction of stranded

conductors shall, before stranding, satisfy all the requirements of this specification for solid wires.

The lay ratios of different layers shall be within the limits given in Table 4.

For all constructions successive layers shall have opposite directions of lay, the outer layer being right handed.

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LENGTHS AND VARIATIONS IN LENGTHS Unless otherwise agreed between the manufacturer

and purchaser, hard-drawn copper conductors shall be supplied in the manufacturer’s usual production lengths with a permitted variation of & 5 percent in the length of any one length.

Unless otherwise agreed between manufacturer and purchaser, it shall be permissible to supply not more than 10% of the lengths on any one order in random lengths, none, of them shall be shorter than 1/3rd of the nominal lengths.

PACKING AND MARKING 12.1 The conductor shall be supplied in coils or on

drums* and one drum or coil shall carry only one continuous length of conductor. Each coil or drum shall be marked with the following information:

a) Trade-name, if any;

b) Manufacturer’s name;

c) Size of conductor;

d) Length of conductor;

e) Weight of the conductor;

f) Drum number; and

g) Any other particulars as specified by the purchaser.

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TEST SAMPLES Solid Conductors - Samples for the tests specified in 14

and 15 shall be taken from approximately 10 percent of the drums included in any one consignment. One sample, sufficient to provide one specimen for each test, shall be taken from each of the selected drums.

Stranded Conductors

Tests Before Stranding - Samples for the tests specified in 14 and 15 shall be taken by the manufacturer before stranding from not less than 10 percent of the individual lengths of wire which will be included in any one consignment of stranded conductor. One sample, sufficient to provide one test specimen for each test, shall be taken from each of the selected lengths of wire.

Test After Stranding - Alternatively, when the purchaser states at the time of ordering that he desires tests to be made in the presence of his representatives, samples of wire shall be taken from lengths of stranded conductor selected from approximately 10 percent of the drums included inany one consignment. One sample, sufficient to provide one specimen for each test, shall be taken from each of the selected drums.

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MECHANICAL TESTS

General - In the case of both solid and stranded conductors, the mechanical tests shall be carried out on single wires only.

Wrapping Test

This test shall be carried out only on wires of less than 5.60 mm diameter.

The wire shall not break when tested in the following manner,

The wire shall be wrapped round a wire of its own diameter to form a close helix of eight turns. Six turns shall then be unwrapped and again closely rewrapped in the same direction as the first wrapping.

Tensile Test

This test shall apply to solid conductors and to the component wires of stranded conductors. Wherever practicable, tests of wires shall be made before stranding.

If it is not possible to test the component wires of a stranded conductor before stranding, the test may be made on wires taken from the stranded conductor. In such cases, the tensile strength of any of the wires shall be not less than 92.5 percent of the values given in Table 1 and the average tensile strength of the wires in a

stranded conductor shall be not less than 94 percent of the values specified in Table 1.

A tensile testing machine shall be used the accuracy of which can be easily checked and the machine adjusted, if necessary. The test samples being placed in the machine shall be straightened, if necessary, in such a way as to cause the minimum alteration in the physical properties.

When an automatic tensile testing machine is used, the load shall be applied gradually and the rate of separation of the jaws of the testing machine shall not be greater than 10 cm per minute and shall be so adjusted that the total time of testing from the moment of application of the load till fracture is between 15 to 60 seconds.

When a hand-operated lever testing machine is used 90 percent of the breaking load shall be applied quickly and the load shall then be increased steadily until the specimen breaks. The time taken to apply the balance 10 percent of the load shall be approximately 15 seconds and the total time from the application of the load to the break shall be approximately 20 seconds.

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Elongation Test

This test shall be performed only on wires of 5.60 mm diameter and over.

The load shall be applied on straightened lengths of wire having an original gauge-length of 25 cm. The extension shall be measured on the gauge-length after the fractured ends have been fitted together, provided that the fracture occurs between the gauge marks and not closer than 25 mm to either mark. If the fracture occurs outside these limits and if the required elongation is not obtained, the test shall be discarded and another test made.

RESISTANCE TEST The dc resistance of the conductor shall be measured at

room temperature. The conductor shall be in the test room which shall be at a reasonably constant temperature for sufficient time to ensure that the conductor temperature is equal to the ambient temperature.

The electrical resistance as measured shall be converted to

resistance per kilometer which when multiplied by

K = standard weight per km,

W = weight per km of test sample, and

C = multiplier constant for correction to 20°C;

The multiplier constant shall be in accordance with Table 6.

The measurement of resistance shall be carried out to an accuracy of one part in a thousand. The length of the sample selected for the test of electrical resistance shall be sufficient to give the accuracy required and shall be suitable for the method of testing employed. Certificates as to the accuracy of the apparatus shall be provided, and either party concerned shall have the right to satisfy itself that the apparatus and the method of testing are correct.

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REJECTION AND RETESTS 16.1 Should any one of the test pieces first selected fail to pass the

test ,three further samples from the same batch shall be selected, one of which shall be from the length from which the original test sample was taken, unless that length has been withdrawn by the supplier.

16.2 Should all of the three test pieces from these additional samples satisfy the requirements of the tests, the batch represented by these samples shall be deemed to comply with the standard. Should the test pieces from any of the three additional samples fail, the batch represented shall be deemed not to comply with the standard.

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