cigre - tutorial conductor fatigue b2 ag 06 bangkok

Study Committee B2Technical Advisory Group B2-AG-06

CIGR B2-AG-06 Seminar Bangkok

TutorialTutorial

Conductor FatigueConductor Fatigue

Louis Cloutier ConvenorLouis Cloutier, ConvenorAndr Leblond, Secretary

CIGR WG B2.30 "Engineering Guidelines Relating to Fatigue Endurance Capability of Conductor/Clamp Systems"

F b 28 2011February 28, 2011 CIGR 2011

Outline of PresentationOutline of Presentation

Introduction Examples of Conductor Fatiguep g Typical Conductor Configurations Some Characteristics of Suspension Clamps CIGRE Technical Brochures CIGRE Technical Brochures Prediction of Aeolian Vibration Amplitudes

Conductor Profile During Aeolian Vibrations Field Measurements of Conductor Vibrations Analytical Representation of the Fatigue Phenomenon

Laboratory Fatigue Tests Resonant Type Test Benches Fatigue Endurance Data

Vibration Measurement Analysis Case Study Conductor and Clamp Types Lacking Fatigue Data

Study Committee B2 - Technical Advisory Group B2-AG-06 32011-02-28

Conclusion

Introduction (I)Introduction (I) Aeolian vibrations :

Small vibration amplitudes exceeding rarely the conductor diameter; frequency range : 3 to 150 Hz; winds : 1 to 7 m/s May lead to fatigue failure of conductor strands at suspension clamps

Such failures are caused by dynamic stresses resulting from reverse bendingfrom reverse bending

Other wind-induced conductor motions such as wake-induced oscillations and galloping may also be responsible


for fatigue conductor strand failures

Introduction (II)Introduction (II)

Natural vibrations are not sinusoidal but show beatsbeats

Examples :


Examples of Conductor Fatigue (I)Examples of Conductor Fatigue (I)

Conductor fatigue occurs when wind-induced vibration is not controlled

Fretting fatigue has long been recognized as being the cause of strand failures in outer as well as inner layers of the conductors

Steel core can fail by overheating after aluminum layers are Steel core can fail by overheating after aluminum layers are separated

Interstrand microslip amplitude increases, small cracks are t d d t t l t t d f il


generated and some propagate up to complete strand failures

Examples of Conductor Fatigue (II) Strand failures occur mainly at

suspension clamps where such

Examples of Conductor Fatigue (II)

p psingular conditions are created

To a lesser extent, a similar phenomenon can occur at damper

phenomenon can occur at damper, marker or spacer clamps

Early detection of conductor failure i k f f il ( tt ti t

or risk of failure (attentiveness to early warnings)

Wear and failure of conductor strands due to spacer clamp loosening

Fatigue usually takes many years


Fatigue usually takes many years to become apparent

Typical Conductor Configurations (I) An important component of an overhead power line

The conductor cost is up to about 40% of total capital investment

Typical Conductor Configurations (I)

The conductor cost is up to about 40% of total capital investment

The conductor size is chosen to suit electrical and mechanical requirements

The most common conductor type is ACSR (Aluminum Conductor Steel Reinforced)

The ratio of steel to aluminum areas vary widely The ratio of steel to aluminum areas vary widely


Typical Conductor Configurations (II)Some Special Conductors

Typical Conductor Configurations (II)

Trapezoidal Z-shaped compact Self-damping Expanded

Ri i d t River crossing conductor


Some Characteristics of Suspension Clamps (I)Some Characteristics of Suspension Clamps (I) Most of the conductor fatigue

test results refer to those bt i d h th d tobtained when the conductor

is supported in a short metallic clamp

The ideal profile of the clamp The ideal profile of the clamp body follows the natural curvature of the conductor

The ends of the clamp body The ends of the clamp body and the keeper must be rounded to avoid indenting the conductor

The clamp should be able to rotate in a longitudinal vertical plane to accommodate

t i l l d


asymmetrical loads

Some Characteristics of Suspension Clamps (II)

A i i

Some Other Suspension ClampsSome Characteristics of Suspension Clamps (II)

Armor grip suspension (AGS) Elastomeric bushing with

cage of preformed rodscage of preformed rods Metal clamp with

elastomeric insertSpecial river crossing clamp Special river crossing clamp Long saddle to reduce

contact stress


CIGRE Technical Brochures (I)CIGRE Technical Brochures (I)

This TB covers a state of the art review on the following aspects of the problem :the following aspects of the problem :

Fretting behaviour in stranded conductor Determination of fatigue endurance Determination of fatigue endurance

capability Inner conductor mechanics Assessment of vibration severity on actual

lines Evaluation of conductor residual life

This TB covers the determination of possible damage and ways to predict remaining life of conductors as well as new methods to t t d t / l t


test conductor/clamp systems

CIGRE Technical Brochures (II)This TB is a complement to TB 332, which was a state of the art review :

CIGRE Technical Brochures (II)

Meant to be a reference for the practicing line engineer in the application of the latest technology

Reviews the available design tools to achieve engineering solutions

Identifies the inherent gaps in their li tiapplication

Gives the engineer a better comprehension of the two related phenomena Fatigue of conductors Aeolian vibrations

This TB includes a review of those design tools and gives the


g gtransmission line engineer the limits to their application

Prediction of Aeolian Vibration AmplitudesPrediction of Aeolian Vibration Amplitudes

Many utilities have their own design rules (for number of dampers) based on past experiencedampers) based on past experience

Vibration severity can also be measured on existing lines A useful analytical approach is the "Energy Balance

Principle" (EBP)Principle (EBP) The EBP leads to an estimate of conductor vibration

amplitude based on equating the energy input from the wind with the energy absorption (damping) of thewind with the energy absorption (damping) of the conductor and dampers

The EBP can also be used for the direct design of the damping system for a new linedamping system for a new line

The estimate of the expected vibratory motion from EBP is considered an upper bound and is therefore a safe value Conditions can also be assessed through measurements on


Conditions can also be assessed through measurements on existing lines

Conductor Profile During Aeolian VibrationsConductor Profile During Aeolian Vibrations

Parameters describing conductor vibration include:

Bending amplitude Yb, Free loop amplitude ymaxb maxBending angle , Wave length and Loop length

This representation applies to metal clamps, not to


elastomer lined clamps

Field Measurements of Conductor Vibrations (I)

Several methods to measure the vibration intensity of a conductor

Field Measurements of Conductor Vibrations (I)

vibration intensity of a conductor have been employed

The bending amplitude Yb method finally comes out as the most

It measures the differential displacement of the conductor at 89 mm from the last point of contact with the clamp

ypractical

p p The reverse bending amplitude was presented as an alternative

to permit the installation of the vibration recorder directly onto the conductor

The bending amplitude method must be properly interpreted when cushioned clamps are used

Recommended by IEEE in 1966 (also in the 2007 revision) and


CIGRE SC22 WG04 1979 and SC22 WG11 TF02 1995

Field Measurements of Conductor Vibrations (II)Field Measurements of Conductor Vibrations (II)

HILDAOntario Hydro RecorderTVM 90

Pavica Ribe LVRVibrec 400


Scolar III

Analytical Representation of the Fatigue Phenomenon (I)

a YpdE2

H

a yt ca ep ese tat o o t e at gue e o e o ( )

( ) bpxaa Ypxe p+= 14 EIHp =An idealized bending stress in the top-most outer-layer strand (in the plane of the last point of contact) is calculated from the bending amplitude (Poffenberger-Swart formula)

Ea: modulus of elasticity of outer wire material (N/mm2)

d: diameter of outer layer wire (mm)

( )H: conductor tension at average temperature during test period (N)

EI: sum of flexural rigidities of individual wires in the cable (Nmm2)

x: distance from the point of measurement to the last point of contact between the


x: distance from the point of measurement to the last point of contact between the clamp and the conductor

Analytical Representation of the Fatigue Phenomenon (II)

fymEd =


maxaa fyEIEd

The idealized bending stress can be derived from the free loop amplitude, ymax, which is the vibration parameter often measured in indoor test spans

Ea: Youngs modulus for the outer-layer strand material (N/mm2)

d: diameter of outer layer wire (mm)

f: frequency of the motion (Hz)f: frequency of the motion (Hz)

m: conductor mass per unit length (kg/m)

EI: sum of flexural rigidities of individual wires in the cable (Nmm2)


g ( )

Analytical Representation of the Fatigue Phenomenon (III)

Fatigue of conductors is due to microslip movements of wires inducing fretting fatigue


fretting fatigue The phenomenon is complex and its exact

modelling has yet to be completed Contact areas between round strands Contact areas between round strands

are elliptical Fretting and microslip occur in these contact areas Fatigue cracks develop out of these contact areas The knowledge on fatigue performance of conductors mostly

relies on results of laboratory tests made on conductors in fixed short metallic clampsshort metallic clamps It is not possible at the moment to determine the fatigue endurance of a

conductor alone There is a wide diversity of design and geometry of conductors


y g g yand supports

Laboratory Fatigue Tests Resonant Type Test BenchesLaboratory Fatigue Tests Resonant Type Test Benches

Constant amplitude excitation Measurement of the bending Pneumatic tensioning systemDynamometer Suspension clamp g

amplitude Yb and/or the free loop amplitude ymax

Most tests done with conductors supported in short metallic clampsSlider

DynamometerAmplitude measuring system

Rubber dampers

Wire break detectionVibrator

End clamp

Turnbuckle

5.5 deg.supported in short metallic clamps

Clamps usually held in a fixed position on the test bench

Active length : 7 m2 m 2 m


Fatigue Endurance Data* (I)

The results of fatigue tests ultimately lead to the presentation of a fatigue (S N) curve

Fatigue Endurance Data (I)

a fatigue (S-N) curve Note scatter in the data The endurance limit is determined

at 500 megacyclesat 500 megacycles Idealized bending stress relative to

Yb vs megacycles to failure Endurance limits Endurance limits

22.5 MPa for single-layer ACSR 8.5 MPa for multi-layer ACSR

*R f EPRI O B k


*Ref.: EPRI Orange Book

Fatigue Endurance Data (II)Estimated bending amplitude endurance limits

Fatigue Endurance Data (II)


Vibration Measurement Analysis (I)Vibration Measurement Analysis (I)

Rule of Thumb Approach to Interpreting Fatigue Data (IEEE)

Widely used set of empirical criteria (Guide for Aeolian Vibration Field Measurements of Overhead Conductors,

1368 200 )IEEE P1368, 2007) The bending amplitude may exceed the endurance limit

during no more than 5% of total cyclesduring no more than 5% of total cycles No more than 1% of total cycles may exceed 1.5 time

the endurance limit No cycle may exceed 2 times the fatigue endurance limit


Vibration Measurement Analysis (II)Multi-Layer ACSR Fatigue Endurance Data

Vibration Measurement Analysis (II)

Statistical analysis S-N curves without wire

f ilfailure Average 95% probability of survivalp y


Vibration Measurement Analysis (III)

Based on Cumulative d th (Mi

Vibration Measurement Analysis (III)

damage theory (Miners rule)

Total damage D at several stress levels i cumulates linearly:

D = n /ND = ni/Ni Failure is predicted when

D n /N 1D = ni/Ni =1 The accuracy of the resulting

estimate of lifetime is between 50% d 200%


50% and 200%

Case Study (I)Report evaluated on 02/05/2002

Transmission line Circuit 3002

Case Study (I)

Voltage (kV)Conductor typeLocation of measurementTerrainSpan length (m)

315ACSR PheasantTower 313 facing Tower 312Flat348 4Span length (m)

Recorder (Type and No.)Remarks

348.4PAVICA n 5P02Installation date : November 21, 2001 @ 0C

First measurement atLast measurement atDuration of one measurement (s)Measurement cycle time (s)

21/11/2001 18:0024/02/2002 18:0010900

Total duration of measurement (s)Factor for extrapolation to one yearTotal number of measurements taken

91200345.7899120


Case Study (II)Fatigue Endurance Limit Approach

12

PAVICA

Case Study (II)

10

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)

PAVICAFatigue endurance limit

6

8

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0 10 20 30 40 50

Frequency, (Hz)

Case Study (III)Cumulative Damage Approach

12

Case Study (III)

10P

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5% S-N curve50% S-N curve95% S-N curveAccumulated stress curve per year

6

8

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0.01 0.1 1 10 100 1000 10000 100000 1000000

N = Accumulated megacycles per year

Case Study (IV)

Evaluation of remaining lif ti D 1

1400

Case Study (IV)

lifetime, D=1 There is a 86%

probability that the 1000

1200

e

,

(

y

e

a

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)

remaining lifetime exceeds 20 years 600

800

i

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200

400R

e

m

a

0 10 20 30 40 50 60 70 80 90 100

Probability of survival, (%)

0


Case Study (V)

Assessment of the t d i

55

60

65Case Study (V)

most damaging frequencies

Helpful for 4045

50

) Helpful for choosing the right damping system

25

30

35

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10

15

20

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0 4 8 12 16 20 24 28

0

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0 4 8 12 16 20 24 28

Damage share, (%)

Conductor and Clamp Types Lacking Fatigue Data

The extrapolation of fatigue data available to other types of conductors or to different types of support is not recommended

Conductor and Clamp Types Lacking Fatigue Data

conductors or to different types of support is not recommended

Bending amplitude method is valid only for armored or unarmored conductors fitted with solid metal-to-metal clamps

Not valid for cushioned clamps (armored or unarmored) Little test data for conductors except ACSR and aluminum alloys Some data for ACSR conductors with armor rods There is a need for more published data on conductor fatigue


Some Important Recent Contributions

Guide for Aeolian Vibration Field Measurements of Overhead Conductors, IEEE P1368, 2007 (a revision of

Some Important Recent Contributions

, 3 , (IEEE 1966 Report)

Transmission Line Reference Book, Wind Induced Conductor Motion, Second Ed. EPRI 2007 (Chapter 3, , ( p ,Fatigue of Overhead Conductors), a revision of the 1979 Orange Book

Fatigue Endurance Capability of Conductor/Clamp g p y pSystems Update of Present Knowledge, CIGRE TF B2.11.07, TB No. 332, October 2007

Engineering Guidelines Relating to Fatigue Endurance g g g gCapability of Conductor/Clamp Systems, CIGRE WG B2.30, TB No. 429, October 2010


Conclusion

Fatigue endurance capability of conductors is a very useful

Conclusion

parameter at the design stage as well as for a maintenance program Aeolian vibrations and conductor fatigue are both highly complex

phenomena

So far, design tools proposed are a good example of the engineering approach to solve a complex problemg g pp p p

Adequate determination of the fatigue characteristics of a conductor/clamp system is very important in the design of a line Acceptable level of conductor vibrations Acceptable level of conductor vibrations Determination of safe design tensions

Future work is needed to better understand the importance of many other parameters


many other parameters

CIGRE WG B2 30

Members : L Cloutier (Convenor) A Leblond (Secretary) U

CIGRE WG B2.30

Members : L. Cloutier (Convenor), A. Leblond (Secretary), U. Cosmai, P. Dulhunty, M. Ervik, D.G. Havard, D. Hearnshaw, H.J. Krispin, M. Landeira, P. Mouchard, K. Papailiou, D. Sunkle, B. WareingWareing

Corresponding Members : J.A. Arajo, H. Argasinska, J.M. p g j , g ,Asselin, O. Cournil, G. Diana, K. Halsan, C.B. Rawlins, R. Stephen, P. Timbrell

Associated Experts : T. Alderton, J. Duxbury, A. Goel, C. Hardy, A. Laneville, A. Manenti Diana, S. Pichot, T. Sepp, P. Van Dyke


Speaker's Contact InformationSpeaker s Contact Information

Andr Leblond, Ph.D., Eng.

Tel: 1-514-879-4100 ext. 5734Tel: 1 514 879 4100 ext. 5734Fax: 1-514-879-4855E-Mail: [email protected]

Address :85, rue Ste-Catherine Ouest, 2nd floorMontreal QuebecMontreal, QuebecH2X 3P4CANADA


Thank you !Thank you !

QUESTIONSQUESTIONS


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