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TANZANIA BUREAU OF STANDARDS

DRAFT TANZANIA STANDARD EEDC 3(3698):P3

All aluminum stranded conductors for overhead power transmission – Specification

(Draft for comments only)

0. FOREWORD

Overhead lines are the commonly means of transmitting and distributing power from generating stations

which are normally far from utilization point. Aluminium conductors provides comparable cheap

alternative for transmission than many other available conductors and hence the most used conductor

for transmission and distribution of power.

This draft Tanzania Standard is intended mainly to cover the technical requirements relating to

hard-drawn stranded aluminium conductors (AAC) used for overhead transmission purposes.

This draft Tanzania Standard specifies requirements for materials used to manufacture aluminium stranded conductor, construction, packing and marking. It also specifies requirements for sampling, inspection and testing.

1. SCOPE

This draft Tanzania Standard applies to the requirements for uninsulated all aluminium stranded

conductors (AAC) for overhead power transmission purposes.

2.0 TERMINOLOGY

For the purposes of this standard, the following definitions shall apply.

2.1 Stranded conductor

A conductor consisting of a number of aluminium wires of the same nominal diameter twisted

together in concentric layers. When the conductor consists of more than one layer, alternate

(successive) layers are twisted in opposite directions.

2.2 Diameter

The mean of two measurements at right angles taken at the same cross-section.

2.3 Standard diameter of wire

Wire diameter on which the requirements for the mass and resistance per unit length and the

breaking strength of the wire are based

2.4 Direction of lay

Lateral direction of inclination to the axis, either right hand or left hand, of the receding helix formed

by a wire of a stranded conductor. With right-hand lay, the wires conform to the direction of the

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central part of the letter Z 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.

2.5 Lay ratio

The 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

2.6 Wire

Aluminium of uniform in diameter and circular in cross section produced by cold drawing

2.7 Lot

not more than 3 000 reels or drums of stranded aluminium conductor of the same reference area,

from one manufacturer, submitted at any one time for inspection and testing

2.8 Reference area

Cross-sectional area to be used for designation and purchasing purposes

3. REFERENCE

The following referenced document is indispensable for application of this draft standard.

TSZ 8:1979 – Specification for reels and drums for bare wires

4. MATERIAL CHARACTERISTICS

4.1 Aluminium

The conductors shall be of hard-drawn aluminium. Aluminium from which the wires are drawn shall be in

the H9 condition and shall comply with the requirements given in table 1 and its volume resistivity,

density, coefficient of linear expansion, and coefficient of variation of resistance with temperature shall

conform clause 4.2 to 4.5

NOTE - Coating using neutral grease may be applied to the centre strand or additionally to wires in specific layers, evenly

throughout the length of the cable depending on agreement between buyer and the manufacturer

4.2 Volume resistivity

The volume resistivity of aluminium wire depends upon its purity and its physical condition. For this

standard the maximum permitted value shall be 2.8264 µ-ohm.cm at 20°C and this value has been used

as the standard resistivity for the purposes of calculation.

4.3 Density

At a temperature of 20°C the density of hard-drawn aluminium wire shall be 2.703 g/cm3

4.4 Coefficient of linear expansion

The coefficient of linear expansion of hard-drawn aluminium shall be per . This value is

applicable over the range of temperatures from 0°C to 30 °C.

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4.5 Coefficient of variation of resistance with temperature

At a temperature of 20°C the constant mass temperature coefficient of resistance of hard-drawn

aluminium wire, measured between two potential points rigidly fixed to the wire, the metal being allowed

to expand freely shall be 0.00403 per °C.

Table 1 — Chemical composition of aluminium EN AW-1350 (99.5)

Element Content %

minimum. Maximum.

Aluminium 99.5* –

Copper – 0.05

Silicon – 0.10

Iron – 0.40

Zinc – 0.05

Manganese – 0.01

Chromium – 0.01

Gallium – 0.03

Impurities max. +

* The aluminium content of unalloyed aluminium not made by a refining process

is the difference between 100.00 % and the sum of all other metallic elements present in amounts of 0.010 % or more each, expressed to the second decimal place before determining the sum. +

Except that in aluminums of designation other than EN AW-1350 other

impurities shall be permitted provided that the content of an individual impurity does not exceed 0.03 %. In addition, in none of the aluminium shall any impurity that is not specifically limited be present in an amount that is generally accepted as having an adverse effect on the product.

5. CONSTRUCTION REQUIREMENTS.

5.1 Wires

The wires that comprise a stranded conductor shall, before stranding, comply with the following

requirements:

a) Diameter. The diameter of a wire, measured in accordance with A.1.1 of Annex A shall be within

the appropriate limits given in table 2.

b) Freedom from defects. The wires shall be smooth, uniform in quality, free from spills, splits, and

other defects, and any departure from circularity of the cross-section shall not exceed 1 % of the

mean diameter.

c) Physical properties. The wires shall be hard-drawn, and shall, except as allowed in terms of

5.2.3(c), comply with the following requirements:

1) Resistance, The resistance of the wires, determined in accordance with Annex B shall not

exceed the appropriate maximum given in table 2.

2) Breaking strength, The breaking strength, determined in accordance with C.1 of Annex C

shall be at least equal to the appropriate minimum given in table 2.

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3) Ductility, The ductility shall be such that the wires withstand lapping in accordance with

Annex D without showing any sign of cracks (when examined by unaided normal vision)

or of breaking.

Table 2 - Hard-drawn circular aluminium wires for stranded aluminium overhead conductors

Wire diameter

(mm)

Nominal

mass

per km a

Kg

Resistance per km at 20 °C

Breaking strength

a

N, min Standard Maximum Minimum Standard

b Maximum

c

2.21 2.235 2.185 10.37 7.368 7.538357 690

2.65 2.6765 2.6235 14.91 5.125 5.228986 950

3.00 3.03 2.97 19.11 3.999 4.080061 1190

3.18 3.2118 3.1482 21.47 3.559 3.63124 1310

3.4 3.434 3.366 24.54 3.113 3.176518 1490

3.78 3.8178 3.7422 30.33 2.519 2.569956 1800

3.99 4.0299 3.9501 33.80 2.260 2.306553 2000

4.39 4.4339 4.3461 40.91 1.867 1.905374 2400

4.65 4.6965 4.6035 45.90 1.664 1.698257 2700

4.72 4.7672 4.6728 47.30 1.615 1.648258 2780

a Based on standard diameters.

b These resistances are based on standard diameters and a volume resistivity of

2.8264 µ-ohm.cm at 20 °C.

c Based on minimum diameters.

5.2 Joints in wire strands

The wires shall be smooth and free from inequalities, spills and splits.

5.2.1 Conductor having seven wires or less

There shall be no joints in any wire forming a stranded conductor containing seven wires or less, except

those made in the base rod or wire before final drawing.

5.2.2 Conductor having more than seven wires.

Joints in individual strands are permitted in addition to those made in the base rod or wire before final

drawing provided that no two such joints are less than 15 m apart and the joint shall not increase the

diameter of the complete stranded conductor. Such joints shall be made by resistance or cold - pressure

butt-welding. Joints made by resistance butt-welding shall, subsequent to welding, be annealed over a

distance of at least 200 mm on each side of the joint.

5.2.3 The section of a wire containing a joint shall be exempt from the requirements given in table 2.

5.3 Stranding

5.3.1 General

The number and diameter of the wires in a stranded conductor shall conform to the values given in table

4 appropriate to the reference area specified by the purchaser. The wires in each layer shall be evenly

and closely stranded. The stranding shall be such that

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a) the overall diameter of the stranded conductor complies with the requirements of 5.4.1.

b) the diameter, determined in accordance with A.1.2 of individual wires taken from the stranded

conductor is not more than 1 % below the appropriate minimum given in table 2 and

c) the mean and the minimum breaking strengths, determined in accordance with C.2 of individual

wires taken from the stranded conductor are at least 95 % and 90 % respectively of the

appropriate minimum given in table 2.

Note – Stranding / configuration other than those specified in table 4 are allowed subject to purchaser order, such

configuration shall conform to relevant requirements of this draft standard

5.3.2 Direction of lay

In all constructions, successive layers of a stranded conductor shall have opposite directions of lay, the

outermost layer being right-handed. The wires in each layer shall be evenly and closely stranded.

5.3.3 Lay ratio

The lay ratio of the different layers shall be within the limits given in table 3. In aluminium stranded

conductors having multiple layers of wires, the lay ratio of any layer shall not be greater than the lay ratio

of the layer immediately beneath it.

Table 3 - Lay ratios for stranded aluminium conductors

Number of wires in conductor

Lay ratios

6-wire layer 12-wire layer 18-wire layer 24-wire layer

max. min. max. min. max. min. max. min.

7 19 37 61

14 16 17 17

10 10 10 10

– 14 16 16

– 10 10 10

– –

14 15

– –

10 10

– – – 14

– – –

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5.4 Completed conductor

The completed conductor shall be free from dirt, grit, excessive amounts of drawing oil and other foreign

deposits and shall have the following properties:

5.4.1 Overall diameter

The overall diameter of a conductor, determined in accordance with A.1.3 of Annex A shall not exceed

the appropriate maximum given in table 4.

5.4.2 Resistance

The overall resistance of a conductor, determined in accordance with Annex B and multiplied by the

appropriate constant given in Table E.1 shall not exceed the appropriate maximum value given in table 4.

5.4.3 Breaking strength

The overall breaking strength of a conductor, determined in accordance with E.3 of Annex E shall not be

below minimum value given in table 4.

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Table 4 — Stranded aluminium conductor

Reference

Area

mm2

Number and

diameter of

wires

No./mm

Overall

diameter

mm, max.

Approximate

mass per

km a

kg

Calculated

maximum

resistance per

km at 20 °C a

Ω

Calculated

breaking

strength a

kN, min.

25 7/2.21 6.63 74 1.091 4.59

40 7/2.65 7.95 106 0.757 6.32

50 7/3.00 9 136 0.59 7.91

60 7/3.40 10.2 174 0.46 9.91

100 7/4.39 13.17 290 0.276 15.96

150 19/3.18 15.9 415 0.195 23.65

200 19/3.78 18.9 587 0.138 32.49

240 19/3.99 19.95 654 0.124 36.10

300 19/4.65 23.25 888 0.091 48.74

330 19/4.72 23.6 915 0.088 50.18

400 37/3.78 26.46 1145 0.071 63.21

a See Annex E

5.5 Lengths and variations in lengths

Unless otherwise agreed between purchaser and manufacturer conductors shall be supplied in the

manufacturer's usual production lengths and with a permitted variation of five per cent in the length of

any one conductor lengths. Additionally, it shall be permissible to supply not more than five per cent of

the length on any one order in random length, none of which shall be greater than one third of the

manufacturer’s usual production lengths.

6. PACKING AND MARKING

The conductor shall be wound in reels or drums conforming to TZS 8 legibly and indelibly marked with

the following:

a) Trade name, if any

b) Name of manufacturer,

c) Size and type of conductor,

d) Length of conductor,

e) Country of origin,

f) Gross mass in kg

g) Year of manufacture and

h) Voltage range

Unless otherwise acceptable, each continuous length of a stranded conductor shall be packed

individually. The conductor may also be marked with TBS Certification Mark.

NOTE— The TBS Certification Mark may be used by manufacturers only under license from TBS.

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7. SAMPLING, INSPECTION AND TESTING.

7.1 Sampling

The following sampling procedure shall be applied in determining whether a lot complies with the

appropriate requirements of the specification. The samples so drawn shall be deemed to represent the

lot for the respective properties.

7.1.1 Sample for inspection

From the lot take at random a sample of the size given in table 5.

7.1.2 Sample for testing

After inspection (see 7.2) of the sample taken in accordance with 7.1.1 cut off and discard the first

300 mm length of the outer end of the wire or conductor on each reel or drum and then cut the length

required for the test pieces.

Table 5 — Sample sizes for stranded conductors

Lot size, coils, reels or drums

Sample size, coils reels or drums

Number of defectives

1 – 30

31 – 500

501 – 800

801 – 1 300

1 301 – 3 000

All

30

40

55

75

0

1

2

2

3

7.2 Inspection Inspect the sample taken in accordance with 7.1.1 for compliance with the requirements of 5.5 and section 6. 7.3 Testing Before testing the sample taken in accordance with 7.1.2 check each length for compliance with the requirements of 5.3 and 5.4 The test samples shall then be subjected to the tests for compliance with the requirements of 5.4.1 to 5.4.3 NOTE: The test methods described in this section are the methods to be used to determine whether a product complies with the specification or not and apply to samples taken in accordance with section 7.1.1. The manufacturer is at liberty to use whatever tests he chooses to apply as quality control in his factory.

7.4 Compliance

If after inspection and testing of the samples taken in accordance with 7.1.1 the number of defectives

found does not exceed the appropriate number given in table 5 the lot shall be deemed to comply with

the relevant requirements of the specification.

8. Certificate of Compliance

The manufacturer shall, if requested, furnish the purchaser with a certificate giving the results of the tests made on samples taken in accordance with 7.1.1

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ANNEX A

Normative

Measurement of Diameter A.1 Measurement of wire diameter.

A.1.1 Measurement of wire diameter before stranding.

Take at random, about 10 % of the total number of wires to be used to construct the conductor and

determine the diameter of each wire with a micrometer by taking two measurements at right angles to

each other at the center and near each end of the wire. Take the average of all six measurements as the

wire diameter.

A.1.2 Measurement of wire diameter after stranding

Take at random from each sample of completed conductor, at least one wire, careful straightens them

not to stretch and determine the diameter of each wire with a micrometer by taking two measurements at

right angles to each other at the center and near each end of the wire. Take the average of all six

measurements as the wire diameter.

A.1.3 Measurement of overall diameter of a conductor

From each sample, cut a 300 mm long test specimen and careful straightens them not to stretch.

Determine the diameter of each specimen with a micrometer by taking two measurements at right

angles to each other at the center and near each end of the specimen. All measurements of a stranded

conductor shall be made over the strands and not at the interstices.

The overall diameter of a conductor shall be the average of the six measurements

Note – The micrometer used for diameter measurement should have flat surfaces on both the anvil and the end of

the spindle, with a resolution of 0.01 mm or better.

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ANNEX B

Normative

Resistance measurement

The wire shall be kept in the test area for sufficient time to ensure that its temperature has reached a

level which permits an accurate determination of resistance using the correction factors provided.

Measure and record the d.c. resistance of the wire together with the ambient air temperature. Convert

the measured values to standard values, in ohms per kilometre, using the equation

Rs = R × 1 000 kt /L

Where

Rs is the standard value of resistance, in ohms per kilometre;

R is the measured resistance, in ohms;

kt is the temperature correction factor given by the exact formula

. Where t refers to

the temperature of the wire at the time of measurement in

L is the cable length, in metres.

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ANNEX C

Normative

Measurement of Breaking Strength

C.1 Measurement of breaking strength of the wire before stranding

Take at random, about 10 % of the wires to be used to construct the conductor (400 mm), and make

two thin gauge marks symmetrically about the mid-point and 250 mm ± 2.0 mm apart.

So clamp each wire in turn in the tensile testing machine that the gauge marks are between, but just

clear of, the jaws. The load shall be applied gradually and the rate of separation of the jaws of the testing

machine shall be not less than 25 mm/min and not greater than 100 mm/min.

Elongate the specimen until it breaks. If a break occurs outside the gauge length or within 25 mm of

either gauge mark, discard the result and repeat as above until the specified number of breaks is

obtained within the prescribed portion. Force required for breakage is then recorded.

The average of all the measurements shall be taken as being the breaking strength.

C.2 Measurement of breaking strength of the wire after stranding

Use the method described in C.1 above to determine the breaking strength of wires taken in accordance

with table 6 from each stranded conductor. The wire specimens shall not be straightened other than as

needed to ensure a materially straight pull between clamps.

Table 6 - Specimens for breaking strength test

Number of wires in a conductor

Number of specimens Number of per layer

Centre wire 1st

layer 2nd

layer 3rd

layer 4th

layer

7 1 1 - - - 19 1 1 2 - - 37 1 1 2 3 - 61 1 1 2 3 4

Discard the lowest result, and record the mean and the lowest of the remaining results as the mean and the minimum individual breaking strengths respectively of the wires of the stranded conductor.

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ANNEX D

Normative

Lapping Test

Take at random, from each sample of completed conductor, about 10 % of the total number of wires

each 500 mm long.

Tightly wind each wire at a time, nine turns round a mandrel of diameter equal to wire diameter to form a

close helix. Unwind six turns and again wind these six turns closely in the same direction as in the first

winding. Wind and unwind the wire at a rate of approximately one turn per second. Keep the portion that

is being winded or unwinded under uniform tension, especially during unwinding, and at approximately

90° to the longitudinal axis of the wire on to which it is being winded.

The wire shall not show any signs of cracks or of breaking.

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ANNEX E

Informative

NOTES ON THE CALCULATION OF CONDUCTOR PROPERTIES

E.1 Increase in length due to stranding.

When straightened out, each wire in any particular layer on a stranded conductor, except the central

wire, is longer than the stranded conductor by an amount depending on the lay ratio of that layer.

In calculating the stranding constants in Table E.1 the mean lay ratio, i.e. the arithmetic mean of the

relevant minimum and maximum values in Table 3 has been assumed for each layer.

E.2 Resistance and mass of conductor.

The resistance of any length of a stranded conductor is the resistance of the same length of any one

wire multiplied by a constant, as set out in Table E.1

The mass of each wire in any particular layer of stranded conductor, except the central wire, will be

greater than that of an equal length of straight wire by an amount depending on the lay ratio of that layer

(see A 1 above). The total mass of any length of an aluminium stranded conductor is therefore, the

product of the mass of an equal length of straight wire and an appropriate constant as set out in Table 5.

Table E.1 — Stranding constants for aluminium conductors

Number of

wires in

conductor

Stranding constants

Mass

Electrical

resistance

7

19

37 61

7.091

19.34

37.74 62.35

0.144 7

0.053 57

0.027 57 0.016 76

E.3 Calculated breaking load of conductor.

Stranding reduces the breaking strength of a stranded conductor to below the sum of the strengths of

the individual component wires .The breaking load of an aluminium stranded conductor containing not

more than 37 wires, in terms of the strength of the individual component wires, may be taken to be 95%

of the sum of the strengths of the individual aluminium wires calculated from the specified minimum

strength.

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BIBLIOGRAPHY

BS 215-1:1970 - Specification for aluminium conductors and aluminium conductors, steel-reinforced for overhead power transmission. Aluminium stranded conductors

SANS 182-2:2008: Conductors for overhead electrical transmission lines; Part 2: Stranded aluminium conductors