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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
Study Committee B2 - Technical Advisory Group B2-AG-06 42011-02-28
for fatigue conductor strand failures
Introduction (II)Introduction (II)
Natural vibrations are not sinusoidal but show beatsbeats
Examples :
Study Committee B2 - Technical Advisory Group B2-AG-06 52011-02-28
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
Study Committee B2 - Technical Advisory Group B2-AG-06 62011-02-28
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
Study Committee B2 - Technical Advisory Group B2-AG-06 72011-02-28
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
Study Committee B2 - Technical Advisory Group B2-AG-06 82011-02-28
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
Study Committee B2 - Technical Advisory Group B2-AG-06 92011-02-28
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
Study Committee B2 - Technical Advisory Group B2-AG-06 102011-02-28
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
Study Committee B2 - Technical Advisory Group B2-AG-06 112011-02-28
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
Study Committee B2 - Technical Advisory Group B2-AG-06 122011-02-28
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
Study Committee B2 - Technical Advisory Group B2-AG-06 132011-02-28
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
Study Committee B2 - Technical Advisory Group B2-AG-06 142011-02-28
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
Study Committee B2 - Technical Advisory Group B2-AG-06 152011-02-28
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
Study Committee B2 - Technical Advisory Group B2-AG-06 162011-02-28
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
Study Committee B2 - Technical Advisory Group B2-AG-06 172011-02-28
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
Study Committee B2 - Technical Advisory Group B2-AG-06 182011-02-28
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 =
a yt ca ep ese tat o o t e at gue e o e o ( )
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)
Study Committee B2 - Technical Advisory Group B2-AG-06 192011-02-28
g ( )
Analytical Representation of the Fatigue Phenomenon (III)
Fatigue of conductors is due to microslip movements of wires inducing fretting fatigue
a yt ca ep ese tat o o t e at gue e o e o ( )
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
Study Committee B2 - Technical Advisory Group B2-AG-06 202011-02-28
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
Study Committee B2 - Technical Advisory Group B2-AG-06 212011-02-28
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
Study Committee B2 - Technical Advisory Group B2-AG-06 222011-02-28
*Ref.: EPRI Orange Book
Fatigue Endurance Data (II)Estimated bending amplitude endurance limits
Fatigue Endurance Data (II)
Study Committee B2 - Technical Advisory Group B2-AG-06 232011-02-28
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
Study Committee B2 - Technical Advisory Group B2-AG-06 242011-02-28
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
Study Committee B2 - Technical Advisory Group B2-AG-06 252011-02-28
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%
Study Committee B2 - Technical Advisory Group B2-AG-06 262011-02-28
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
Study Committee B2 - Technical Advisory Group B2-AG-06 272011-02-28
Case Study (II)Fatigue Endurance Limit Approach
12
PAVICA
Case Study (II)
10
P
a
)
PAVICAFatigue endurance limit
6
8
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a
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i
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e
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o
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b
,
(
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S
s
t
r
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s
s
r
e
l
0
2
Study Committee B2 - Technical Advisory Group B2-AG-06 282011-02-28
0 10 20 30 40 50
Frequency, (Hz)
Case Study (III)Cumulative Damage Approach
12
Case Study (III)
10P
a
)
5% S-N curve50% S-N curve95% S-N curveAccumulated stress curve per year
6
8
a
t
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4
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0
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Study Committee B2 - Technical Advisory Group B2-AG-06 292011-02-28
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
r
s
)
remaining lifetime exceeds 20 years 600
800
i
n
i
n
g
l
i
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t
i
m
e
200
400R
e
m
a
0 10 20 30 40 50 60 70 80 90 100
Probability of survival, (%)
0
Study Committee B2 - Technical Advisory Group B2-AG-06 302011-02-28
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
F
r
e
q
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e
n
c
y
,
(
H
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10
15
20
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0 4 8 12 16 20 24 28
0
5
10
Study Committee B2 - Technical Advisory Group B2-AG-06 312011-02-28
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
Study Committee B2 - Technical Advisory Group B2-AG-06 322011-02-28
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
Study Committee B2 - Technical Advisory Group B2-AG-06 332011-02-28
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
Study Committee B2 - Technical Advisory Group B2-AG-06 342011-02-28
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
Study Committee B2 - Technical Advisory Group B2-AG-06 352011-02-28
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
Study Committee B2 - Technical Advisory Group B2-AG-06 362011-02-28
Thank you !Thank you !
QUESTIONSQUESTIONS
Study Committee B2 - Technical Advisory Group B2-AG-06 372011-02-28