Hard-Drawn Copper Conductors for Over Head Power Transmission

Hard-Drawn Copper Conductors for Over
Head Power Transmission
1

FOREWORD
 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.
2

METHODOLOGY
 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.
3

 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/mm² tensile 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.
4

 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.
5

 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.
9

 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.
10

 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.
12

 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.
13

 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.
14

 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.
15

 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.
16

Hard-Drawn Copper Conductors for Over Head Power Transmission

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