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AS 3822—2002

Australian Standard™

Test methods for bare overheadconductors

AS 3822

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This Australian Standard was prepared by Committee EL-010, Overhead Lines. Itwas approved on behalf of the Council of Standards Australia on 30 July 2002 andpublished on 23 August 2002.

The following are represented on Committee EL-010:Australasian Railway AssociationAustralian Chamber of Commerce and IndustryAustralian Electrical and Electronic Manufacturers AssociationAustralian Porcelain Insulators AssociationElectricity Supply Association of Australia

Keeping Standards up-to-dateStandards are living documents which reflect progress in science, technology andsystems. To maintain their currency, all Standards are periodically reviewed, andnew editions are published. Between editions, amendments may be issued.Standards may also be withdrawn. It is important that readers assure themselvesthey are using a current Standard, which should include any amendments whichmay have been published since the Standard was purchased.Detailed information about Standards can be found by visiting the StandardsAustralia web site at www.standards.com.au and looking up the relevant Standardin the on-line catalogue.Alternatively, the printed Catalogue provides information current at 1 January eachyear, and the monthly magazine, The Australian Standard, has a full listing ofrevisions and amendments published each month.We also welcome suggestions for improvement in our Standards, and especiallyencourage readers to notify us immediately of any apparent inaccuracies orambiguities. Contact us via email at [email protected], or write to the ChiefExecutive, Standards Australia International Ltd, GPO Box 5420, Sydney, NSW2001.

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AS 3822—2002

Australian Standard™

Test methods for bare overheadconductors

Originated as AS 3822(Int)—1998.Revised and designated AS 3822—2002.

COPYRIGHT© Standards Australia InternationalAll rights are reserved. No part of this work may be reproduced or copied in any form or by anymeans, electronic or mechanical, including photocopying, without the written permission of thepublisher.Published by Standards Australia International LtdGPO Box 5420, Sydney, NSW 2001, AustraliaISBN 0 7337 4773 6

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AS 3822—2002 2

PREFACEThis Standard was prepared by the Australian members of the Joint StandardsAustralia/Standards New Zealand Committee EL-010, Overhead Lines.

After consultation with stakeholders in both countries, Standards Australia and StandardsNew Zealand decided to develop this Standard as an Australian Standard rather than anAustralian/New Zealand Standard.

The objective of this Standard is to provide procedures for purchasers wishing to specifyperformance tests on complete conductors.

Conductor users and manufacturers have recognized that the variety of conductors andconductor constructions available is unlimited and that it is becoming necessary to find thecharacteristics of the complete conductor. In addition there is a need to critically examineexisting conductors that may have suffered degradation because of their service history.Existing conductor Standards specify only the properties of the individual wires. Conductorproperties are calculated from the wire data.

During its 1983 meeting, CIGRE* Australian panel 22 ‘Overhead Lines’ established a localworking group to review the matter and in particular to determine—

(a) which complete conductor characteristics were needed to enable the user to compareconductor types and to confidently predict the performance of conductors in service;

(b) how these characteristics were to be determined; and

(c) which procedures would optimize the handling of conductors during erection.

Items (a) and (b) were completed and this Standard sets out performance tests for completeconductors.

With regard to Item (c), it was recognized that current methods used for the calculation ofsag data for conductor erection include somewhat arbitrary allowances for the effect ofrun-out tensions, time spent in sheaves before sagging and for permanent elongation.

While these methods have proved adequate in most conditions there is a growing need formore precise analysis especially when using unfamiliar conductors and when designing forextreme temperatures.

The information from the tests can be used with the CIGRE temperature compensationmethod (Ref. 1).

In addition, computer models are being developed (Ref. 2) and power line designers andconstructors are encouraged to make use of the techniques.

This Standard provides procedures for purchasers wishing to specify performance tests oncomplete conductors. The tests have three main purposes, as follows:

(i) To provide a basis for comparison of the design of conductors in terms of theirmechanical properties.

(ii) To provide conductor data for the new sag tension computer programs which arebeing developed to provide a more realistic model of conductor behaviour over itsservice life (Ref. 2).

(iii) To provide acceptance criteria for conductor purchasers. It is envisaged that the testswill be regarded as ‘Type Tests’ for a particular conductor type and will not berequired for every production run.

* International Conference on Large High Tension Electric Systems.

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An article, ‘A practical method of conductor creep determination’, published in 1972 inELECTRA No. 24 (Ref. 1) gave results of typical values of permanent elongation based onmeasurements from lines in service. The method of determination of permanent elongationspecified in this Standard is based on principles laid down by CIGRE WG 05 in document22-78(WG 05)02 (Ref. 3), which provides some guidance on the use of predictor equationsand evaluation methods.

‘Permanent elongation of conductors. Predictor equations and evaluation methods’, fromELECTRA no. 75 March 1981, (Ref. 4) contains the final version of the complete creep testmethod. The methods specified in this Standard have taken advantage of experience gainedby previous laboratory evaluation of creep and current technology for improved accuracy inmeasurement and temperature control.

REFERENCES

1 A practical method of conductor creep determination. CIGRE ELECTRA no. 24,1972.

2 BARRETT, J.S., DUTTA, S. and NIGOL, O. A new computer model of A.C.S.R.conductors. IEEE Trans. on Power Apparatus & Systems, vol. PAS-102, no. 3, March1983.

3 CIGRE Document 22-78 (WG 05)02.

4 Permanent elongation of conductors. Predictor equations and evaluation methods.CIGRE ELECTRA no. 75, March 1981.

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AS 3822—2002 4

CONTENTS

Page1 SCOPE........................................................................................................................ 52 REFERENCED DOCUMENTS.................................................................................. 53 DEFINITIONS............................................................................................................ 54 PREPARATION OF A SAMPLE FOR TENSILE LOADING OF A WHOLE

CONDUCTOR............................................................................................................ 85 MEASUREMENT....................................................................................................... 86 TEST METHODS ....................................................................................................... 97 TEST RESULTS....................................................................................................... 18

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www.standards.com.au Standards Australia

STANDARDS AUSTRALIA

Australian StandardTest methods for bare overhead conductors

1 SCOPE

This Standard specifies methods for determining the following properties andcharacteristics of bare conductors for use in overhead lines:

(a) Geometric properties.

(b) Breaking load.

(c) Coefficient of thermal elongation.

(d) Stress-strain characteristics.

(e) Creep characteristics (permanent elongation).

(f) d.c. resistance of conductors.

(g) Fatigue characteristics.

(h) Thermal aging characteristics.

2 REFERENCED DOCUMENTS

The following documents are referred to in this Standard:

AS1222 Steel conductors and stays—Bare overhead1222.1 Part 1: Galvanized (SC/GZ)1222.2 Part 2: Aluminium clad (SC/AC)

1391 Methods for tensile testing of metals

1531 Conductors—Bare overhead—Aluminium and aluminium alloy

1746 Conductors—Bare overhead—Hard-drawn copper

2193 Methods for the calibration and grading of force-measuring systems of testingmachines

3607 Conductors—Bare overhead, aluminium and aluminium alloy—Steelreinforced

IEC60468 Method of measurement of resistivity of metallic materials

3 DEFINITIONS

For the purpose of this Standard, the definitions below apply.

3.1 Aeolian vibration

A resonant vibration induced in overhead conductors by steady cross winds.

3.2 Batch

A quantity of conductor from which a sample is to be drawn and inspected to determinecompliance with acceptability criteria. Each batch is assumed, as far as practicable, toconsist of materials of a single type (grade, class, size, and composition), and to have beenmanufactured under essentially the same conditions at the same time.

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AS 3822—2002 6

Standards Australia www.standards.com.au

3.3 Breaking load

The maximum load obtained on a tensile testing machine before failure of a conductor testpiece.

3.4 Calculated breaking load (CBL)

The breaking load determined in accordance with relevant Australian Standards for a bareoverhead conductor.

NOTE: AS 1222.1, AS 1222.2, AS 1531, AS 1746 and AS 3607 specify requirements for bareoverhead conductors.

3.5 Coefficient of thermal elongation

The relationship between the change in the temperature of a material and its resultantchange in dimensions.

NOTE: The coefficient of thermal elongation is often known as the coefficient of linearexpansion.

3.6 Composite conductor

A conductor consisting of two or more wires of different metals, such as aluminium andsteel or copper and steel, assembled and operated in parallel.

3.7 Conductor stress

The force per unit area where area is the nominal cross-sectional area of the individualwires given in the relevant conductor Standard.

3.8 Creep

The permanent elongation of metals held for long periods of time at stresses lower than thenormal yield stress. Creep in conductors is dependent on the material, conductorconstruction, applied stress, time and temperature.

3.9 Dynamic stress

A stress caused by the resonant vibration of overhead conductors by steady cross winds inthe velocity range of approximately 0.5 m.s−1 to 7.0 m.s−1.

3.10 Elongation

The increase in gauge length of a tension test specimen, usually expressed as a percentageof the original gauge length.

3.11 Fatigue

The failure of a metal under the repeated application of cyclic or fluctuating stress belowthe yield point.

3.12 Fatigue life

The number of stress (or strain) cycles that a specimen sustains before failure under a giventest condition and criterion of failure.

3.13 Fatigue limit

The maximum cyclic stress that a metal will withstand without failure for an indefinitelylarge number of cycles of stress.

NOTE: Aluminium does not exhibit a fatigue limit.

3.14 Fatigue strength at N cycles

The stress level at which a specimen would have a life of exactly N cycles.

3.15 Gauge length

The prescribed part of a test piece over which elongation is measured.

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3.16 Initial creep

The early part of the time-elongation curve for creep, in which extension increases at arapid rate.

3.17 Lay length

The axial length of one complete turn of the helix (pitch) formed by an individual wire in astranded conductor.

3.18 Lay ratio

The ratio of the lay length to the external diameter of the helix of the corresponding layer ofwires in the stranded conductor.

3.19 May

Indicates the existence of an option.

3.20 Modulus of elasticity

The slope of the elastic portion of the stress-strain curve in mechanical testing (ratio ofstress to strain within the elastic range). The tensile elastic modulus is called ‘Young’sModulus’.

3.21 Proof load

The load that is required to produce a defined, small, permanent elongation (usually 0.1%strain) during a tensile test.

3.22 Secondary creep

The secondary portion of the creep curve following the initial creep stage and in which theexponential rate of creep has reached a constant value, i.e. the linear portion of the creepversus time curve plotted on a log-log scale.

3.23 Shall

Indicates that a statement is mandatory.

3.24 Should

Indicates a recommendation.

3.25 S-N Diagram

A plot of maximum stress amplitude against number of cycles to failure. For N, alogarithmic scale is almost always used. For S, a linear scale is used most often but alogarithmic scale is sometimes used.

3.26 Strain

The deformation expressed as a pure number or ratio. It is normally expressed as ε (epsilon)equivalent to the change in length divided by the original length.

3.27 Stress

The axial force per unit of nominal cross-sectional area. It is usually expressed asσ (sigma).

3.28 Test piece

A prepared piece of a conductor for testing made from or comprising a test sample.

3.29 Test sample

A portion of conductor selected by a sampling procedure from a batch.Pur

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AS 3822—2002 8


4 PREPARATION OF A SAMPLE FOR TENSILE LOADING OF A WHOLECONDUCTOR

Preparation of a conductor test piece is critical to the accuracy and validity of the testresults. Test pieces shall be prepared with due consideration to the prevention of conductorrotation and loosening of wires and to the minimizing of damage to wires.

The selected test sample shall be free from scratches and other blemishes and shall havebeen manufactured under normal production conditions. Test pieces shall be taken at least20 m from the end of a test sample. The total length of the test piece shall allow for thegauge length and terminations. Low elongation binding tape and hose or screw clips havebeen found to be suitable for retaining the wires in position.

The minimum gauge length shall be 3.0 m. The terminations shall be at least 1.0 m fromeach gauge point.

The terminations shall be designed so that the tensile load is distributed evenly to all wires.Care must be taken to ensure that the original position of the stranded layers is maintainedduring termination.

A type test to determine the termination suitability may be necessary to ensure that thetermination will sustain 95% of the calculated breaking load of the conductor for at leastfour hours without any detectable movement.

5 MEASUREMENT

5.1 Temperature measurement

The temperature of test pieces shall be measured by devices attached to their surface. Thereshall be at least three temperature measuring devices equally spaced along the gauge length.The ambient temperature shall also be measured.

For test pieces tested in an enclosed, controlled temperature environment, temperaturemeasurement of the environment is permissible in lieu of contact measurement of theconductor.

Unless otherwise stated, all temperature measurements shall be made with an accuracy of±0.5°C. When gauge bars are used in the measurement of extension, the accuracy oftemperature measurement shall be in accordance with the following criteria:

for ∆α ≥ 4µm/m/°C, T ′ ≤ α∆ε′

for ∆α ≥ 4µm/m/°C, T ′ ≤ 0.5°C

where

T ′ = the temperature measurement error in degrees Celsius

ε′ = the maximum allowable strain measurement error in micrometres permetre

α∆ = the difference between the coefficient of linear expansion of the gaugebar and the conductor.

To avoid the need for extremely accurate temperature measuring devices, it isrecommended that, when used, gauge bars be made of materials with a coefficient ofthermal expansion similar to that of the test piece (i.e. within ±4 µm/m/°C).

5.2 Strain measurement

5.2.1 General

Care should be taken to avoid errors due to rotation of the test piece.

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5.2.2 Creep test

All creep measurements shall be made with an accuracy of 2 µm/m. The measuring devicemay include a reference material for the purpose of making temperature corrections whenapplicable. If gauge bars are used it is recommended that they have similar thermal mass tothe test piece.

5.2.3 Stress/strain and coefficient of thermal elongation tests

Strain measurement shall be made with an accuracy of 20 µm/m.

5.2.4 Conductor elongation during the breaking load test

The extensometer used in this test shall permit simultaneous measurement of conductorelongation while the tensile load is continually increased. The accuracy of measurementshall allow a 0.1% proof load to be determined.

NOTE: A C Grade extensometer complying with AS 1391 will satisfy the requirements ofClause 5.2.4.

5.3 Load measurement

The load measuring device shall be calibrated to meet the requirements of AS 2193 forGrade A.

6 TEST METHODS

6.1 Geometric properties

6.1.1 General

The lay length and diameter shall be measured for each layer of a conductor. The lay ratioshall be calculated for each layer.

6.1.2 Test pieces

The measurement shall be done on a conductor as it is produced in a stranding machine.The test pieces shall represent normal stranding operations.

6.1.3 Apparatus

Measurements shall be made with suitable equipment of appropriate discrimination.Callipers are usually used for the measurement of diameter. A steel rule or tape is usuallyused for the measurement of lay length.

6.1.4 Conductor layer diameter

Diameter shall be measured with a suitable device fitted with jaws broad enough to covernot less than two adjacent wires along the test piece (see Figure 6.1) and shall be measuredon a straight portion of the test piece that is not under tension.

Measurement shall be taken at two locations spaced at least 1 m apart. At each location twodiameters at right angles shall be measured. The average of these four measurements shallbe recorded.

6.1.5 Lay length and lay ratio

Lay length shall be measured and lay ratio shall be calculated as follows:

(a) Ensure that each layer to be measured is well formed and representative of normalstranding for that layer.

(b) Ensure that the test piece is at normal stranding machine tension.

(c) Place a sheet of good quality paper along the strand covering one or more lay lengths.

(d) Take an impression of the wires in the strand on the paper by rubbing a crayon orsimilar rectilinearly on the paper along the longitudinal axis of the strand.

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AS 3822—2002 10


(e) Mark a start point on the impression made by one wire and from this pointcommencing with the next mark count the number of impressions equal to the numberof wires in the layer. Mark the impression of the last counted wire as the finish point.Measure the distance between the two points to the nearest millimetre. This length isthe lay length.NOTE: Greater accuracy may be obtained by counting a multiple of the number of wires inthe layer, taking the measurement and dividing by the multiplier.

(f) Measure the diameter of the layer to the nearest 0.05 mm in accordance withClause 6.1.4 except that the measurement may be made under normal strandingmachine tension.

(g) Divide the lay length measured at Step (e) by the diameter measured at Step (f) foreach layer. Each result is reported as the lay ratio of the corresponding layer.

FIGURE 6.1 METHOD OF MEASURING CONDUCTOR DIAMETER

6.1.6 Nominal cross-sectional area

The nominal cross-sectional area of a conductor may be determined by calculating thecross-sectional area of each wire using the nominal diameter and then summing the cross-sectional areas of all the wires in the conductor.

6.2 Breaking load

6.2.1 Principle

A test piece is subjected to a continuously increasing tensile force until failure occurs. Themaximum value of the load prior to failure is the conductor breaking load. The elongationof the conductor may also be measured.

6.2.2 Apparatus

The apparatus shall include devices to retain the test piece terminations and shall havemeans of applying the desired load. The test piece terminations shall be made in accordancewith Clause 4.

6.2.3 Procedure

The procedure shall be as follows:

(a) Mount and secure the test piece into the test frame and position the extensometer.Conductor elongation shall be measured in accordance with Clause 5.2.4.

(b) Apply the load smoothly and evenly.

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(c) Increase the load progressively until either—

(i) failure occurs (i.e. one or more wires fracture outside the terminations); or

(ii) the terminations fail by either fracture of a termination, or slippage or fractureof the wires within a termination.

(d) Record the maximum load at which failure as defined in Step (c) occurs.

6.2.4 Test validity

The results are valid only for test pieces which fracture outside the terminations.

6.3 Coefficient of thermal elongation

6.3.1 Scope and general

This Clause (6.3) provides a method for determining the coefficient of thermal elongationof bare overhead conductors. A change in conductor temperature will affect the length ofthe conductor. The thermal behaviour of the conductor is characterized by its coefficient ofthermal elongation.

6.3.2 Principle

The temperature of a conductor test piece is incrementally and gradually raised fromambient to 100°C and lowered back to ambient. At regular temperature intervals theconductor tension is briefly raised to 20% CBL and simultaneous measurements ofconductor tension, temperature and strain are taken.

6.3.3 Apparatus

The apparatus shall consist of the following:

(a) A machine capable of supplying the load smoothly and uniformly. The machine shallinclude devices to maintain the specified load and secure the sample terminations.The terminations shall be made in accordance with Clause 4.

(b) A temperature control system capable of controlling the mean conductor temperaturewithin ±2.5°C of the desired temperature so that the variation in temperaturedistribution along the gauge length does not exceed ±2.5°C.

6.3.4 Procedure


(a) Install the test piece in the machine with due consideration given to minimizing theloosening of strands.

(b) Apply tension briefly to the test piece to 20% of CBL. Set the extensometers to zeroand simultaneously measure the gauge length, tension and cable temperature.

(c) With the conductor slack, increase the mean conductor temperature by approximately10°C and briefly raise the conductor tension to 20% of CBL. Simultaneously measureconductor tension, elongation and temperature. It may be necessary to allow time forthe conductor temperature to be uniformly distributed through its cross-section beforetaking measurements.

(d) Repeat Step (c) to 100 ±2.5°C in increments of 10°C, and back to ambient indecrements of 10°C.

6.3.5 Analysis of data

Determine a value of the linear coefficient of thermal elongation (in µm/m/°C) by linearregression analysis of the experimental data.

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AS 3822—2002 12


6.4 Stress/strain


The stress/strain test measures the elongation of a complete conductor when it is subjectedto successive and progressively increasing tensile loads for short periods of time. Thestress/strain behaviour of a conductor is characterized by stress/strain curves. The stressstrain characteristics quantify—

(a) the short-term loading behaviour;

(b) the initial and final modulus of elasticity; and

(c) for non-homogeneous conductors, the stress distribution and the aluminium zerostress/strain point.

6.4.2 Principle

A test piece of the conductor is subjected to a tensile load. The load is applied smoothly anduniformly to a value equivalent to 30% of the CBL. The load is held at this value for adefined period of time and then released at approximately the same rate as the application.Measurements of extension are made at frequent intervals during the load cycle. The cycleis repeated for 50% and 70% of the CBL. Tests at the three levels of CBL may be done onone test piece. From these data stress versus strain curves may be derived.

When composite conductors with reinforcing cores are tested, the tests are repeated on thecore alone. This is done to evaluate the tensile properties of the core and the outer layer.

NOTE: Composite conductors which have wires of different materials in the same layer requirespecial consideration and are not covered by this Standard.

6.4.3 Apparatus

The apparatus shall consist of the following:

(a) A machine capable of suppling the load smoothly and uniformly. The machine shallinclude devices to maintain the specified load and secure the sample terminations.The terminations shall be made in accordance with Clause 4.

The machine shall be able to maintain the specified load within ±1% of its designatedvalue.

(b) A temperature control and measuring system capable of controlling the temperaturewithin ±2.5°C during a test so that the mean test temperature during the core test doesnot vary by more than ±2.5°C from the mean temperature during the completeconductor test.

6.4.4 Procedures

6.4.4.1 Conductors

The procedure for conductors shall be as follows:

(a) Install the test piece in the machine with due consideration to minimizing theloosening of wires. Apply and maintain a load of between 1% and 2% of CBL andmaintain this while measuring the gauge length. Set the extensometer to zero.

(b) First cycle:

(i) Increase the load at a uniform rate up to 30% CBL over 2 to 3 min, taking atleast four simultaneous readings of load and extension over the load range.

(ii) Maintain the load of 30% CBL for 30 min. Take simultaneous readings of loadand extension at 5, 10, 15 and 30 min.P

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13 AS 3822—2002


(iii) Reduce the load at a uniform rate to almost zero over a period of 2 to 3 min,taking at least four simultaneous readings of load and extension during theunloading period.

(c) Second cycle:

(i) Apply load at a similar rate as in the first cycle but up to 50% CBL, taking atleast four simultaneous readings of the load and extension.

(ii) Maintain the load of 50% CBL for 60 min, taking simultaneous readings of loadand extension at 5, 10, 15, 30, 45 and 60 min.

(iii) Reduce the load at a uniform rate to almost zero using a similar rate ofreduction as in the first cycle, taking simultaneous reading of the load andextension at the same intervals as in the first cycle.

(d) Third cycle:

(i) Apply load at a similar rate as in the first cycle but up to 70% CBL, taking atleast four simultaneous readings of the load and extension.

(ii) Maintain the load of 70% CBL for 60 min, taking simultaneous readings of loadand extension at 5, 10, 15, 30, 45 and 60 min.

(iii) Reduce the load at a uniform rate to almost zero using a similar rate ofreduction as in the first cycle, taking at least 10 simultaneous readings of theload and extension.

6.4.4.2 Steel core (if applicable)

The procedure for steel cores shall be as follows:

(a) Set a new test piece of the conductor core in the apparatus. The test piece shall betaken from the same test sample used in Clause 6.4.4.1.

(b) For the holding periods, the core shall be loaded until the elongation at the beginningof each period corresponds to the final elongation obtained on the complete conductorat 30, 50 and 70% CBL respectively.


The data shall be analysed as follows:

(a) Plot the stress (MPa) versus strain (µm/m) for each of the test pieces. A typical plot isshown in Figure 7.1.

(b) Correct the strain data to compensate for any initial slack in the wires in the testpiece. This can be done by extrapolating the linear portion of the increasing loadsection of the first cycle down to the initial curve for the steel core. The resultantstrain offset must then be subtracted from every strain record. A large strain offsetmay indicate incorrect sample preparation (see Clause 4).

(c) Determine a smooth composite stress-strain curve (curve 1 of Figure 7.2) by fitting anappropriate polynomial or curve of best fit to the corrected origin and to the end pointof each holding period.

(d) Determine the final modulus of the steel core, if any, by regression analysis of thedata in the linear portion of the curve obtained on unloading from the equivalent ofthe 70% CBL of the complete conductor.

(e) Determine the final modulus of the steel core, if any, by regression analysis of thedata in the linear portion of the curve obtained on unloading from 70% CBL.

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(102

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AS 3822—2002 14


(f) Determine the initial modulus and the final modulus for the aluminium in a compositeconductor by numerical subtraction of the values of the steel core from those of thecomplete conductor. Figure 7.2 shows a typical plot of moduli for a compositeconductor.

NOTE: AS 1391 provides relevant information on the slope of the elastic section of the stress-strain curves.

6.5 Creep


The creep test measures the extension of a conductor with time when held at a constant loadand temperature.

Creep results in changing conductor sag with time. Compensation for creep is required toaccount for this change.

When carrying out creep tests, it is essential that adherence to a strict routine be maintainedthroughout, particularly during the initial stage, to ensure repeatability.

6.5.2 Principle

In a temperature controlled environment a test piece is loaded to a nominated percentage ofits CBL.

A gauge length equidistant from both ends of the test piece is fitted with an extensometer topermit measurement of creep with time.

6.5.3 Apparatus

The apparatus shall include devices to maintain the specified load within ±1%, and tosecure the test piece terminations. Terminations shall be made in accordance with Clause 4.

The test apparatus shall apply the load either—

(a) within 30 s (fast-loading method); or

(b) between 4 min and 5 min (slow-loading method).

The load shall be applied smoothly and uniformly. The load shall be held within ±1% of thespecified test load.

The test piece temperature shall be controlled at 20 ±2.5°C, unless a higher temperature isspecified.

If an immersion oil bath is used to control temperature, the test piece shall be jacketed in asuitable tube to allow heat transfer from the oil to the test piece and to prevent oillubricating the wires during the long period of test.

6.5.4 Procedure


(a) Mount the test piece in the machine with due consideration being given to minimizingthe loosening of wires.

(b) Position the temperature measuring devices in accordance with Clause 5.1. Thetemperature of the gauge bar shall be measured at positions adjacent to the devicesmeasuring the conductor temperature.

(c) Allow the thermal control system to stabilize for at least 24 h so that the test piecescome to the same temperature.

(d) Apply and maintain the specified load. For testing at 20°C, separate test pieces shallbe loaded to 20%, 30% and 40% of the CBL. For testing at elevated temperatures aload of 20% of the CBL shall be used.

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(102

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15 AS 3822—2002


(e) Measurements of strain and temperature shall be taken simultaneously at thefollowing elapsed times after full load has been reached: 1, 2, 3, 4, 5, 10, 15 and30 min; then at 1, 2, 3, 4, 5, 6, 7, 24, 50, 80, 150, 300, 600, 1000 and 2000 h.

(f) The minimum test period shall be 1000 h or until sufficient data have been obtainedto predict the long-term behaviour of the conductor.


6.5.5.1 Correction of thermal strain

Strain measurements shall be corrected for variations in temperature by assuming thetheoretical values of the coefficient of thermal elongation.

6.5.5.2 Load application rate

For the fast-loading method only, data of strain versus time for the first 10 minutes of thetest shall be plotted on linear scales. A curve of best fit shall be drawn through the strainversus time data and the strain at six minutes shall be read from the curve. The strain at sixminutes is subtracted from subsequent readings to minimize the effects of initial varyingload application rates.

6.5.5.3 Strain variation

A graph of strain against time shall be plotted on log-log scales and the best straight linefitted by analysis through the points. The time (ts) from the start of the test until the straightline is established shall be determined. All points for time greater than ts and for which thestrain varies by more than 2% or by more than 20 µm/m from the value predicted by thestraight line shall be discarded.

6.5.5.4 Temperature

The test temperature shall be assumed to be the average of the temperature readings.

6.5.6 Test validity

A test shall be considered to be invalid if—

(a) the time before the straight line is established is greater than 10% of the duration ofthe test; or

(b) if the points rejected in accordance with Clause 6.5.5.3 exceed 10% of the pointstaken after the straight line is established.

6.6 d.c. resistance

Measurements of the resistivity of wires shall be made in accordance with IEC 60468.

6.7 Fatigue

6.7.1 General

Fatigue is caused by repetitive dynamic stress in the wires resulting in crack initiation andpropagation. Crack propagation ultimately results in wire fracture. After one or more wiresfracture redistribution of stress occurs in the conductor which accelerates the crackpropagation in the remaining intact wires. This process of wire fractures may continue untilthe entire conductor fails.

6.7.2 Principle

Fatigue is induced in the test piece at a constant axial tension by mechanically vibrating itat a natural frequency. A series of tests must be performed to generate the complete fatiguecharacteristics of a conductor.

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AS 3822—2002 16


6.7.3 Apparatus

A suitable test span layout is shown in Figure 6.2. The free span length should beapproximately 30 m.

The test span shall have the capability of maintaining a constant test tension.

Rigid non-articulating clamps shall be used at each end to support and restrain the testpiece. These shall not be used to maintain tension on the span and should have a low-friction sleeve to allow longitudinal movement. The inner part of the clamp assembly incontact with the conductor shall be square edged to provide a fixed point for conductorbending.

The inertia of the vibrating mechanism should be small relative to the conductor mass undertest.

The system shall have a frequency selection sensitivity within ±0.1 Hz. A schematicdrawing of a typical conductor vibration system is shown in Figure 6.3. A schematicdrawing of a typical conductor fatigue test measurement system is shown in Figure 6.4. Thelength of test conductor between a linear differential transducer and the nearest clampshould be at least 90 mm.

FIGURE 6.2 A TYPICAL TEST SPAN LAYOUT

6.7.4 Procedure


(a) Install the test piece in the machine giving due consideration to minimizing theloosening of wires and conductor twisting.

(b) Apply a nominated axial load to the test piece. The load shall be maintained within2% of its specified value.

(c) Vibrate the test piece at one of its natural frequencies and at a peak-to-peak amplitudewhich corresponds to the outer strand dynamic stress. The frequency should be in therange of 10 to 50 Hz to avoid overheating.

(d) Terminate the test when either one or more wires fail or at a specified number ofcycles.

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17 AS 3822—2002


FIGURE 6.3 SCHEMATIC DRAWING OF A TYPICALCONDUCTOR VIBRATION SYSTEM

FIGURE 6.4 SCHEMATIC DRAWING OF A TYPICALCONDUCTOR FATIGUE TEST MEASUREMENT

6.8 Thermal ageing

6.8.1 General

The effects of thermal ageing (annealing) on bare overhead conductors are a reduction inconductor strength and a decrease in electrical resistance. The thermal ageingcharacteristics of conductors are influenced by the alloy, the operating temperature, and thediameter of the component wires in the strand. The loss of strength of a compositeconductor will be less than an equivalent AAC or AAAC conductor because typicaloperating temperatures have a negligible effect on the steel core.

It is assumed that the loss of strength of the conductor due to thermal ageing is reflected bythe loss of strength of the component wires. The decrease in strength of the thermally agedwires can be expressed as a fraction of the tensile strength of the wires before thermalageing.

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AS 3822—2002 18


6.8.2 Apparatus

An oven, furnace or other thermal cabinet suitable for containing the required number oftest pieces at the specified temperature and for the specified time is required.

The temperature inside the thermal cabinet shall vary by no more than ±2.5°C from thespecified temperature.

6.8.3 Test piece

Sufficient test pieces shall be prepared from the same test sample for each time periodspecified during the test. For example, for a test duration of 10 000 hours and time periodsof 0, 10, 20, 40, 70, 100, 200, 400, 700, 1000, 2000, 4000, 7000 and 10 000 hours, 14 testpieces are required.

6.8.4 Procedure


(a) Raise the temperature in the thermal cabinet to the specified thermal ageingtemperature. The thermal ageing temperature shall be 75, 100, 125 or 150°C.

(b) Place all but the zero-hour test piece in the thermal cabinet and allow the temperaturein the thermal cabinet to recover to the specified thermal ageing temperature. Thetime to recover to the specified thermal aging temperature shall be no more than10 min.

(c) Measure the test time, starting when the thermal cabinet recovers to the thermalageing temperature.

(d) At each specified time period, remove a test piece from the thermal cabinet and allowthe test piece to cool to room temperature.

(e) Determine the tensile strength of three wires from each test piece in accordance withAS 1391. The test shall be performed with a strain rate not exceeding category S inaccordance with AS 1391.


The average tensile strength of the three wires at each time period can be used to calculateeither the percentage of the original tensile strength (%S) or the percentage change intensile strength (%∆S). These data can be plotted as a function of annealing time to producean isothermal annealing curve. A typical set of curves is shown in Figure 6.5.

7 TEST RESULTS

7.1 Geometric properties (see Clause 6.1)

The test results shall include:

(a) The four measurements of diameter and their average.

(b) The lay length and lay ratio.

(c) The cross-sectional area.

7.2 Breaking load (see Clause 6.2)


(a) The gauge length when applicable, the test length and lay ratios for each wire layer.

(b) The maximum tensile load achieved in the test.

(c) A load-strain curve, if applicable.

(d) The location of the wire breaks, the wire break mode and the longitudinal locationrelative to the end of the conductor terminations.

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19 AS 3822—2002


(e) Any termination failure or slippage.

7.3 Coefficient of thermal elongation (see Clause 6.3)


(a) Gauge length, lay length and diameter.

(b) A description of the procedure used to heat the test piece.

(c) Tabulated results of conductor strain, stress and temperature.

(d) Linear-linear graphical representation of conductor strain versus conductortemperature showing increasing and decreasing temperature cycles.

(e) The coefficient of thermal elongation for the test piece.

(f) A correlation coefficient.

FIGURE 6.5 TYPICAL ISOTHERMAL ANNEALING CURVE

7.4 Stress/strain (see Clause 6.4)

The test results should include the following:


(b) Tabulated results of conductor elongation, conductor test temperature and conductortension for each of the three load cycles for the complete conductor and the corecomponent when applicable.

(c) Graphical representation of conductor stress versus conductor strain for each of thethree load cycles for the complete conductor and the core component when applicable(see Figure 7.1).

(d) Zero correction of the complete conductor, and the core component when applicable.Pur

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AS 3822—2002 20


(e) Linear-linear graphical representation of the initial and final modulus curves for thecomplete conductor and its constituent components as stress versus strain (seeFigure 7.2).

(f) If required, coefficients in an appropriate polynomial or curve of best fit describingthe initial loading curve of the complete conductor and the core component and, whenapplicable, the determined loading curve of the aluminium component.

(g) Final modulus of elasticity for the complete conductor and, when applicable, for thecore components.

(h) The correlation coefficient for the data used for the linear regression to determine themoduli of elasticity for the complete conductor and components as applicable.

7.5 Creep (see Clause 6.5)

The test results shall include the following:


(b) Tabulated results of conductor strain, time elapsed, conductor temperature andconductor tension expressed as a percentage of the CBL.

(c) Logarithmic-logarithmic graphical representation of the tabulated conductorpermanent elongation versus time elapsed for given conductor tensions expressed as apercentage of the CBL.

(d) A linear-logarithmic graphical representation of temperature versus time elapsed.

(e) A linear regression analysis of the conductor logarithmic strain curve from at leastone hour elapsed time to the final reading time, which shall take the following form:

1n

1 tAE =

where

E = the conductor strain in micrometres per metre

A1, n1 = constants determined by the linear regression analysis

t = time in hours.

(f) A linear correlation coefficient for the data used for the linear regressiondetermination.

(g) A multiple regression analysis of the conductor logarithmic strain curves for varyingtemperature and conductor tension from at least one hour elapsed time to the finalreading time which may take the following form:

E = ( )201nnn

2321 −σ TetA

where

E = the conductor strain in micrometres per metre

A2, n1, n2, n3 = constants determined by the multiple regression analysis

t = the elapsed time in hours

σ = the conductor stress in megapascals

T1 = elevated conductor temperature in degrees Celsius.

(h) A statistical correlation coefficient for the data to be used for the multiple regressiondetermination.NOTE: Alternative forms of predictor equations may be used, if deemed appropriate.

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21 AS 3822—2002


FIGURE 7.1 TYPICAL FORM OF GRAPH FROM STRESS AND STRAIN CYCLE

(Composite conductor shown)

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AS 3822—2002 22


FIGURE 7.2 TYPICAL TEST RESULTS—ACSR

7.6 Fatigue (see Clause 6.7)


(a) The vibration amplitude, vibration frequency and elapsed time.

(b) The total number of wire breaks, if any, and the layers in which they occurred.

(c) The location of the wire breaks and wire cracks, if any, within the cross-section of theconductor and their longitudinal location relative to the vibration termination block.

(d) The position at which fatigue cracks were initiated.

(e) General qualitative comments on wire fretting, wire deformation and otherobservations as applicable.

(f) The total elapsed time.

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23 AS 3822—2002


7.7 Thermal ageing (see Clause 6.8)


(a) The breaking loads of each group of test pieces, their average, their thermal ageingtemperature, and their time at the thermal ageing temperature.

(b) The isothermal annealing curves plotted from the data in Item (a).

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AS 3822—2002 24

NOTES

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(102

1520

8).

Standards AustraliaStandards Australia is an independent company, limited by guarantee, which prepares and publishesmost of the voluntary technical and commercial standards used in Australia. These standards aredeveloped through an open process of consultation and consensus, in which all interested parties areinvited to participate. Through a Memorandum of Understanding with the Commonwealth government,Standards Australia is recognized as Australia’s peak national standards body.

Australian StandardsAustralian Standards are prepared by committees of experts from industry, governments, consumersand other relevant sectors. The requirements or recommendations contained in published Standards area consensus of the views of representative interests and also take account of comments received fromother sources. They reflect the latest scientific and industry experience. Australian Standards are keptunder continuous review after publication and are updated regularly to take account of changingtechnology.

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Electronic StandardsAll Australian Standards are available in electronic editions, either downloaded individually from our Website, or via on-line and CD ROM subscription services. For more information phone 1300 65 46 46 orvisit us at

www.standards.com.au

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(102

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Administration Phone (02) 8206 6000 Fax (02) 8206 6001 Email [email protected]

Customer Service Phone 1300 65 46 46 Fax 1300 65 49 49 Email [email protected]

Internet www.standards.com.au

ISBN 0 7337 4773 6 Printed in Australia

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as 3822-2002 test methods for bare overhead conductors

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