Aeolian Vibration Monitoring

ASSESSMENT OF AEOLIAN ASSESSMENT OF AEOLIAN VIBRATION SEVERITYVIBRATION SEVERITYVIBRATION SEVERITYVIBRATION SEVERITY

Umberto CosmaiUmberto CosmaiConvenor CIGRE WG B2.25Convenor CIGRE WG B2.25

Bangkok 28 February 2009Bangkok 28 February 2009

Study Committee B2Technical Advisory Group B2-AG-06

Modern structures slender plain with lowModern structures slender plain with lowModern structures, slender, plain, with low Modern structures, slender, plain, with low internal damping, are very sensitive to windinternal damping, are very sensitive to wind--

induced motionsinduced motionsinduced motions. induced motions.

Study Committee B2 - Technical Advisory Group B2-AG-06

The overhead transmission lines are the mechanical The overhead transmission lines are the mechanical structures with the greatest extension of slender flexible structures with the greatest extension of slender flexible

elements:elements:elements:elements:

the conductorsthe conductors


highly exposed to natural windhighly exposed to natural wind

Overhead conductors are subjected to various wind induced Overhead conductors are subjected to various wind induced vibrations and oscillations.vibrations and oscillations.

Th ll d “ li ib ti ” th t t dTh ll d “ li ib ti ” th t t dThose called “aeolian vibrations” are the most recurrent and Those called “aeolian vibrations” are the most recurrent and the most dangerousthe most dangerous

for the fast accumulation of fatigue cycles (vibration frequencies for the fast accumulation of fatigue cycles (vibration frequencies 55÷÷120 Hz)120 Hz)

d hi h b di t t th fitti ld hi h b di t t th fitti l


and high bending stress at the fitting clamps.and high bending stress at the fitting clamps.

These motions, if not mitigated within safety limits, can These motions, if not mitigated within safety limits, can determine fatigue failures of the conductor strands, determine fatigue failures of the conductor strands,

damages to other line componentsdamages to other line componentsd bl kd bl k t f th lit f th li


and blackand black--out of the lines.out of the lines.

Fatigue failure of a conductor strand due to aeolian vibrationFatigue failure of a conductor strand due to aeolian vibration

Typical fragile shape i.e. without deformation of the material Typical fragile shape i.e. without deformation of the material th f tth f t


near the fracture area.near the fracture area.

Fatigue failures can interest several strandsFatigue failures can interest several strands


in the outer and inner layer of the conductorin the outer and inner layer of the conductor


Fatigue failures develop at points where the motion is Fatigue failures develop at points where the motion is constrained e.g. where the conductor is secured to fittingsconstrained e.g. where the conductor is secured to fittings

Typical location are: suspension clamps, damper and Typical location are: suspension clamps, damper and spacer clamps, etc.spacer clamps, etc.


p p ,p p ,

Another damaging effect of conductor vibration is the Another damaging effect of conductor vibration is the loosening of fittings clamps not suitably designed or loosening of fittings clamps not suitably designed or

incorrectly installed. incorrectly installed.


The loosening of a spacer damper clamp, for example, The loosening of a spacer damper clamp, for example, determines, determines,

at the beginning, the abrasion of the conductor outer layer due at the beginning, the abrasion of the conductor outer layer due t th l lidi tt th l lidi t


to the clamp sliding movements.to the clamp sliding movements.

Increasing the looseness, the strands are broken by the Increasing the looseness, the strands are broken by the hammering of the clamp.hammering of the clamp.

If left unattended this process will lead to theIf left unattended this process will lead to the complete complete


conductor failure.conductor failure.

Fittings whose natural vibration frequency fall in the range of Fittings whose natural vibration frequency fall in the range of conductor vibration frequencies may fail for fatigue. conductor vibration frequencies may fail for fatigue.

Ni ht i d iNi ht i d i


Night warning deviceNight warning device

Vibration dampers incorrectly dimensioned or wrongly Vibration dampers incorrectly dimensioned or wrongly distributed can fail for fatigue while protecting the conductor.distributed can fail for fatigue while protecting the conductor.


Five methods are commonly used for the assessment of Five methods are commonly used for the assessment of vibration severity on overhead transmission line conductors: vibration severity on overhead transmission line conductors:

1.1. Analytical prediction of vibration intensityAnalytical prediction of vibration intensity

2.2. Tests on outdoor experimental spansTests on outdoor experimental spans2. 2. Tests on outdoor experimental spansTests on outdoor experimental spans

3.3. Laboratory tests on short spans Laboratory tests on short spans

44 Vibration measurements on actual linesVibration measurements on actual lines4. 4. Vibration measurements on actual linesVibration measurements on actual lines

5. 5. Conductor inspections on actual linesConductor inspections on actual lines

Each method offers its own contribution to the total picture. Each method offers its own contribution to the total picture. Although they are interAlthough they are inter--related, their limitations and concepts related, their limitations and concepts

are somewhat differentare somewhat different


are somewhat different. are somewhat different.

Analytical prediction of vibration intensityAnalytical prediction of vibration intensity


The most comprehensive medium to predict the vibration The most comprehensive medium to predict the vibration behaviour of a conductor is the computer simulation behaviour of a conductor is the computer simulation

f d b f ifi tf d b f ifi tperformed by means of specific computer programs.performed by means of specific computer programs.

Others methods based on abacus diagrams andOthers methods based on abacus diagrams andOthers methods based on abacus, diagrams and Others methods based on abacus, diagrams and nomographs can only provide qualitative information. nomographs can only provide qualitative information.

For example, the procedure proposed by CIGRE TF 22.11.04 in For example, the procedure proposed by CIGRE TF 22.11.04 in the brochure titled “Safe Design Tension with Respect to the brochure titled “Safe Design Tension with Respect to

Aeolian Vibration” can usefully determine whether additionalAeolian Vibration” can usefully determine whether additionalAeolian Vibration can usefully determine whether additional Aeolian Vibration can usefully determine whether additional damping (normal or special)damping (normal or special) is required or not but can not is required or not but can not

provide data about the damping system to apply. provide data about the damping system to apply.


Computer analysis is mainly used at design stageComputer analysis is mainly used at design stage

to anticipate the vibration behaviour of single and bundledto anticipate the vibration behaviour of single and bundledto anticipate the vibration behaviour of single and bundled to anticipate the vibration behaviour of single and bundled conductorsconductors

d t d fi h th t it bl d id t d fi h th t it bl d iand to define, when necessary, the most suitable damping and to define, when necessary, the most suitable damping system.system.

Calculations are based on the energy balanceCalculations are based on the energy balancebetween the energy introduced by the wind and the between the energy introduced by the wind and the

energy dissipated by the vibrating conductorsenergy dissipated by the vibrating conductorsenergy dissipated by the vibrating conductorsenergy dissipated by the vibrating conductors

with and without and relevant damping units.with and without and relevant damping units.


Vibration analysis of a bare conductorVibration analysis of a bare conductor

Analytical model Analytical model Vib. frequencies Vib. frequencies yyof the conductorof the conductor

Model of theModel of the

and wave lengthsand wave lengths

Antinode Antinode Model of the Model of the windwind vibration vibration

amplitudesamplitudes

Analytical model Analytical model of suspension of suspension arrangementarrangement

Max strains at the Max strains at the suspension clampsuspension clamp

Computer Computer analysisanalysis


arrangementarrangement

Vibration analysis of a single conductor withVibration analysis of a single conductor withVibration analysis of a single conductor with Vibration analysis of a single conductor with additional dampingadditional damping

Vib f iVib f iAnalytical model of Analytical model of the conductorthe conductor

Vib. frequencies Vib. frequencies and wave lengthsand wave lengths

Vib amplitude ofVib amplitude ofModel of the windModel of the wind

Analytical model ofAnalytical model of

Vib. amplitude of Vib. amplitude of the antinodes and the antinodes and of the dampersof the dampers

Computer Computer Analytical model ofAnalytical model of

Analytical model of Analytical model of the damper(s)the damper(s) Strains at suspen. Strains at suspen.

& damper clamps& damper clampspp

analysisanalysisAnalytical model of Analytical model of

the suspension the suspension clampclamp

Number and Number and positioning of the positioning of the dampersdampers


pp

Vibration analysis of a bundled conductorVibration analysis of a bundled conductorVibration analysis of a bundled conductor Vibration analysis of a bundled conductor with spacer damperswith spacer dampers

Vib frequenciesVib frequenciesAnalytical model of Analytical model of

the conductorthe conductor

Vib. frequencies Vib. frequencies and wave lengthsand wave lengths

Model of the windModel of the wind Max and min vib. Max and min vib. Model of the wind Model of the wind for bundlesfor bundles

Analytical modelAnalytical model M iM i

amplitude of the amplitude of the antinodesantinodes

Computer Computer

Analytical model Analytical model and distribution of and distribution of the spacer dampers the spacer dampers

Max strains at Max strains at suspension and suspension and spacer clampsspacer clampspp

analysisanalysisAnalytical model of Analytical model of the suspension the suspension arrangementarrangement

p pp pMax spacer clamp Max spacer clamp amplitude and amplitude and


arrangementarrangement arm rotationarm rotation

O td t t t tiO td t t t tiOutdoor test stationsOutdoor test stations


Outdoor test stations exposed Outdoor test stations exposed to natural wind have been to natural wind have been built in several Countries built in several Countries

worldworld--widewide

for research and for research and development purposesdevelopment purposes

and for the comparative and for the comparative evaluation of damping evaluation of damping

t d ft d fsystems proposed for systems proposed for important transmission line important transmission line

projects. projects.


These stations allow an These stations allow an t i ti ti ft i ti ti faccurate investigation of accurate investigation of

conductor vibrationsconductor vibrations

as they can be fully as they can be fully instrumented withinstrumented withinstrumented with instrumented with

recording and recording and monitoring systems.monitoring systems.


The high costs involved in The high costs involved in these test stationsthese test stations

can be afforded only by can be afforded only by Power Authorities and Power Authorities and

Research InstitutesResearch InstitutesResearch InstitutesResearch Institutes

or justified in some major or justified in some major j jj jtransmission line projects. transmission line projects.


Laboratory test spansLaboratory test spans


Vibration tests on laboratory spans (30Vibration tests on laboratory spans (30÷÷90 m)90 m)C t t t i

Tension clampRigid clamp Conductor

Shaker

Constant tension device

Rigid clampTension clamp

Free span 30÷90mConcrete block Concrete

block

provide data about conductor selfprovide data about conductor self--damping, fatigue damping, fatigue endurance of conductorendurance of conductor--clamp systemsclamp systemsand effectiveness of vibration dampers.and effectiveness of vibration dampers.


and effectiveness of vibration dampers.and effectiveness of vibration dampers.

Extremity block of a laboratory test spanExtremity block of a laboratory test span

T iT i TensionTension Ri idRi idTension Tension devicedevice

Tension Tension clampclamp

Rigid Rigid clampclamp


accelerometeraccelerometer

conductor clampconductor clampload cellload cell

spring steel bandsspring steel bands

flexibleflexibleflexible flexible connection connection between between

shaker and shaker and conductorconductor


InIn--span transducersspan transducersInIn--span transducersspan transducersFor the measurement of vibration levels along the span For the measurement of vibration levels along the span

miniature accelerometers are normally usedminiature accelerometers are normally used

accelerometeraccelerometer

miniature accelerometers are normally used.miniature accelerometers are normally used.

Contactless displacement transducers (laser or eddy Contactless displacement transducers (laser or eddy


current based) are also used on very light conductors.current based) are also used on very light conductors.

Test span layout for conductor self-damping measurementsTest span layout for conductor self damping measurements in accordance with IEEE 664 Standard

AccelerometersTest span ShakerTest span

Load cell

Power amplifier

Waveform generatorg

Computer OscilloscopeTransducer amplifiers

DAC interface

amplifiers


DAC interface

Effectiveness test on vibration dampers in accordance with IECEffectiveness test on vibration dampers in accordance with IECEffectiveness test on vibration dampers in accordance with IEC Effectiveness test on vibration dampers in accordance with IEC 61897 and IEEE 664 Standards61897 and IEEE 664 Standards

The power dissipated by the conductor plus damper is compared with the The power dissipated by the conductor plus damper is compared with the p p y p p pp p y p p ppower introduced by the windpower introduced by the wind

for a certain number of tunable harmonic vibrations of the span, at constant for a certain number of tunable harmonic vibrations of the span, at constant speed or constant bending strains.speed or constant bending strains.speed or constant bending strains.speed or constant bending strains.

Tension clampRigid clamp C d t

Constant tension device

Rigid clampTension clamp

Strain gauges accelerometers

Rigid clamp ConductorShaker

Rigid clamp

damper load cell

Free span 30÷90mConcrete block Concrete

block

cell

The power dissipated by the conductor plus damper shall be greater thanThe power dissipated by the conductor plus damper shall be greater than


The power dissipated by the conductor plus damper shall be greater than The power dissipated by the conductor plus damper shall be greater than power introduced by the wind. power introduced by the wind.

Ch t i ti f th f ti b h i fCh t i ti f th f ti b h i fCharacterization of the fatigue behaviour of a Characterization of the fatigue behaviour of a conductorconductor

Pneumatic tensioning systemDynamometer

Amplitude measuring system

Rubber dampers

Suspension clamp

End clamp

Turnbuckle

Slider

Wire break detectionVibrator

Active length : 7 m2 m 2 m

Turnbuckle

5.5

Laboratory fatigue tests Laboratory fatigue tests y gy gResonant type test Resonant type test

benchesbenches


Vibration measurements on existing Vibration measurements on existing OHTLOHTLOHTLOHTL


Conductor vibration measurements on actual lines are Conductor vibration measurements on actual lines are usually performed: usually performed:

O liO liOn new linesOn new lines-- as final check of the damping systemas final check of the damping system-- to compare different damping systemsto compare different damping systems

On lines in operationOn lines in operationpp-- for assessment of vibration intensityfor assessment of vibration intensity

to evaluate the conductor residual lifeto evaluate the conductor residual life-- to evaluate the conductor residual lifeto evaluate the conductor residual life-- to investigate the cause of damagesto investigate the cause of damages


The direct method to evaluate the conductor vibration severity The direct method to evaluate the conductor vibration severity is the measurement of the conductor bending strain at the is the measurement of the conductor bending strain at the

clamp mouthclamp mouthclamp mouth,clamp mouth,

performed by means of strain gauges glued on the outer performed by means of strain gauges glued on the outer layer strandslayer strandslayer strands. layer strands.

This technique, had been used for a limited period of time but This technique, had been used for a limited period of time but then was abandoned in favour of methods more suitable for then was abandoned in favour of methods more suitable for

fi ld li tifi ld li ti


field application.field application.

Aeolian vibration measurement on actual linesAeolian vibration measurement on actual linesperformed by means of specific recordersperformed by means of specific recorders

has been widely used for the last 45 yearshas been widely used for the last 45 years..


These vibration measurements are based on the These vibration measurements are based on the bending bending amplitude methodamplitude method proposed by the IEEE paper 31 TP 65proposed by the IEEE paper 31 TP 65--

156 1965156 1965156, 1965 156, 1965

89 mm

Yb

89 mm

The bending amplitude YThe bending amplitude Ybb is the peak to peak vibration is the peak to peak vibration g pg p bb p pp pamplitude measured at 89 mm (3.5 inches) amplitude measured at 89 mm (3.5 inches)

from the last point of contact between the conductor and the from the last point of contact between the conductor and the suspension clampsuspension clamp


suspension clamp.suspension clamp.

The bending amplitude is easier to measure than theThe bending amplitude is easier to measure than theThe bending amplitude is easier to measure than the The bending amplitude is easier to measure than the bending strainbending strain

bendingbending amplitude

89 m

bending strain

In a number of cases, the bending amplitude can be converted In a number of cases, the bending amplitude can be converted i t b di t i i th P ff b d S t (P&S)i t b di t i i th P ff b d S t (P&S)into bending strain using the Poffemberger and Swart (P&S) into bending strain using the Poffemberger and Swart (P&S)

formula.formula.In other cases, the conversion factor can be determined by In other cases, the conversion factor can be determined by

f l b t t tf l b t t t


means of laboratory tests.means of laboratory tests.

Bending Amplitude RecordersBending Amplitude RecordersBending Amplitude RecordersBending Amplitude Recorders

HILDAOntario Hydro Recorder TVM 90

Scolar

Pavica

IIIRibe LVR

Vibrec 400 Vibrec 500


Only Vibrec500 and Pavica are still available on the marketOnly Vibrec500 and Pavica are still available on the market.

Modern aeolian vibration recorders are a microprocessor Modern aeolian vibration recorders are a microprocessor based, battery powered, selfbased, battery powered, self--contained devices. The battery contained devices. The battery

autonomy is 3autonomy is 3--6 months6 monthsautonomy is 3autonomy is 3 6 months.6 months.

Vibration Vibration b at ob at osensorsensor

Temperature probeTemperature probeWind sensorWind sensor


VIBREC|500 WT

The most recent version of the vibration recorder Vibrec 500 The most recent version of the vibration recorder Vibrec 500 allows wireless connection with the ground instrumentation.allows wireless connection with the ground instrumentation.

Th t i t d d bTh t i t d d b


The autonomy is extended above one year.The autonomy is extended above one year.

VIBREC|500 WIRELESS CONNECTIONVIBREC|500 WIRELESS CONNECTION

SEARCHFOUNDVR500WT


The recorder is installed on the suspensionThe recorder is installed on the suspension clamp.

898989 89 mmmm

The vibration sensor is positioned at 89 mm from the last point of The vibration sensor is positioned at 89 mm from the last point of


contact between the conductor and the suspension clamp.contact between the conductor and the suspension clamp.

On small conductors and On small conductors and shield wires as well as at shield wires as well as at

damper and spacer damper and spacer clamps vibration recorders clamps vibration recorders

with split sensor can bewith split sensor can bewith split sensor can be with split sensor can be usedused..


Another type of vibration recorder is installed on the Another type of vibration recorder is installed on the conductor, with the clamp positioned at 89 mmconductor, with the clamp positioned at 89 mm

89 mm

from the last point of contact between the conductor and from the last point of contact between the conductor and


the suspension clamp.the suspension clamp.

The tip of the vibration sensor is positioned at the last point of The tip of the vibration sensor is positioned at the last point of contact between the conductor and the suspension clamp.contact between the conductor and the suspension clamp.

This vibration recorder measures the soThis vibration recorder measures the so--called “inverted called “inverted b di lit d ”b di lit d ”


bending amplitude”.bending amplitude”.

Due to its low weight (about 0.6Kg) this recorder can be Due to its low weight (about 0.6Kg) this recorder can be installed along the span near dampers, spacers and other installed along the span near dampers, spacers and other

fitting clamps.fitting clamps.

For small conductors a version with split sensor is also For small conductors a version with split sensor is also


ppavailable.available.

I t ti l St d d d d ti f liI t ti l St d d d d ti f liInternational Standards and recommendations for aeolian International Standards and recommendations for aeolian vibration measurements on overhead transmission linesvibration measurements on overhead transmission lines

IEEEIEEE paperpaper 31 TP 6531 TP 65 156 1965156 1965IEEE IEEE paper paper 31 TP 6531 TP 65--156, 1965 156, 1965 Standardization of conductor vibration measurementsStandardization of conductor vibration measurements

CIGRE SC22 WG04 CIGRE SC22 WG04 Recommendations for the evaluation of the lifetime of transmission Recommendations for the evaluation of the lifetime of transmission line conductorsline conductorsELECTRA nELECTRA n°°63, 197963, 1979

CIGRE SC22 WG11 CIGRE SC22 WG11 Guide to vibration measurements on overhead linesGuide to vibration measurements on overhead linesELECTRA nELECTRA n°°163 1995163 1995ELECTRA nELECTRA n 163, 1995163, 1995

IEEE Par P1368 2006IEEE Par P1368 2006Guide for Aeolian Vibration Field Measurements of Overhead Guide for Aeolian Vibration Field Measurements of Overhead


Conductors Conductors

Evaluation criteria of conductorEvaluation criteria of conductorEvaluation criteria of conductor Evaluation criteria of conductor

vibration severity vibration severity


E l ti it i f th ib ti it fE l ti it i f th ib ti it fEvaluation criteria of the vibration severity for Evaluation criteria of the vibration severity for aluminium based conductorsaluminium based conductors

IEEE 1966IEEE 1966 Criterion of the maximum allowable Criterion of the maximum allowable bending strain.bending strain.

EPRI & IEEE 2006EPRI & IEEE 2006 Criterion of the maximum allowable Criterion of the maximum allowable bending amplitude.bending amplitude.Criterion of the maximum allowableCriterion of the maximum allowable

CIGRECIGRE Criterion of the accumulation of fatigueCriterion of the accumulation of fatigue

Criterion of the maximum allowable Criterion of the maximum allowable bending stress.bending stress.

CIGRE CIGRE Criterion of the accumulation of fatigue Criterion of the accumulation of fatigue (lifetime calculation based on Miner (lifetime calculation based on Miner hypothesis and a “Universal” conductor hypothesis and a “Universal” conductor SS N Curves called Safe Border Line)N Curves called Safe Border Line)


SS--N Curves called Safe Border Line).N Curves called Safe Border Line).

Bending stress/strain safety limitsBending stress/strain safety limitsBending stress/strain safety limitsBending stress/strain safety limits

Bending stress/strain values can be derived from the Bending stress/strain values can be derived from the measured bending amplitudes using the Poffemberger andmeasured bending amplitudes using the Poffemberger andmeasured bending amplitudes using the Poffemberger and measured bending amplitudes using the Poffemberger and

Swartz (P&S) formula or through lab tests. Swartz (P&S) formula or through lab tests.

The P&S formula is valid only for solid metal to metal The P&S formula is valid only for solid metal to metal suspension clamps without armour rods.suspension clamps without armour rods.

General reference limits are available for conventional General reference limits are available for conventional aluminium based conductors.aluminium based conductors.

No internationally accepted reference limits are available for No internationally accepted reference limits are available for other conductors and conductor /clamp combinations.other conductors and conductor /clamp combinations.


other conductors and conductor /clamp combinations.other conductors and conductor /clamp combinations.

Bending stress/strain endurance limits for aluminium Bending stress/strain endurance limits for aluminium based conductorsbased conductors

IEEE (1966)IEEE (1966) 150150--200 200 µεµε peak to peakpeak to peak

Utilities Technical SpecificationsUtilities Technical Specifications 151500 300300 peak to peakpeak to peak

EPRI EPRI &&

Bending stress Bending strainBending stress Bending strain

Utilities Technical SpecificationsUtilities Technical Specifications 151500--300 300 µεµε peak to peakpeak to peak

& & IEEEIEEE20062006

MultiMulti--layer ACSR 8.5 MPa 247layer ACSR 8.5 MPa 247µεµε peak to peakpeak to peakMultiMulti--layer layer AAAC 5.7 Mpa AAAC 5.7 Mpa 165 165 µεµε peak to peakpeak to peak

A bending stress/stain endurance limit can be derived from The CIGRE A bending stress/stain endurance limit can be derived from The CIGRE Safe Border Line and usually taken at 5x10Safe Border Line and usually taken at 5x108 8 cycles. This value cycles. This value

correspond to a bending stress of 9.09correspond to a bending stress of 9.09 MPa and to a bending strain ofMPa and to a bending strain of


correspond to a bending stress of 9.09correspond to a bending stress of 9.09 MPa and to a bending strain of MPa and to a bending strain of 264 264 µεµε peak to peak.peak to peak.

Bending amplitude endurance limits (EPRI)Bending amplitude endurance limits (EPRI)Bending amplitude endurance limits (EPRI)Bending amplitude endurance limits (EPRI)

Available for Available for 74 ACSR conductors (0.2174 ACSR conductors (0.21-- 0.32mm)0.32mm)4 steel conductors (7 strands) (0 964 steel conductors (7 strands) (0 96 --1 67 mm)1 67 mm)4 steel conductors (7 strands) (0.96 4 steel conductors (7 strands) (0.96 --1.67 mm)1.67 mm)2 AAAC conductors (7 strands) (0.40 2 AAAC conductors (7 strands) (0.40 -- 0.59 mm)0.59 mm)

(a general limit of 0.23mm for ACSR conductors is also provided)(a general limit of 0.23mm for ACSR conductors is also provided)

The limits are valid The limits are valid onlyonly for conventional suspension clamps with and for conventional suspension clamps with and without armour rods.without armour rods.

No specific values are available for other conductors and conductor No specific values are available for other conductors and conductor /clamp combinations. These values can be obtained through /clamp combinations. These values can be obtained through

laboratory testslaboratory tests


laboratory tests.laboratory tests.

Conductor lifetime estimationConductor lifetime estimation

Miner’s cumulative damage theory for elastic structures Miner’s cumulative damage theory for elastic structures is suggested by CIGRE to evaluate the conductor is suggested by CIGRE to evaluate the conductor

lifetimelifetime. .

Bending stress/strain values, derived from field Bending stress/strain values, derived from field measurements, can be used to define the curve of the measurements, can be used to define the curve of the stresses accumulated by the conductor in one year of stresses accumulated by the conductor in one year of y yy y

service.service.


The curve shows for each stress level “The curve shows for each stress level “σσ” the number of ” the number of cycles “n” to be expected in one year.cycles “n” to be expected in one year.


The stress curve is compared with a “universal” SThe stress curve is compared with a “universal” S--N curve N curve known as “safe border line” (or with the Sknown as “safe border line” (or with the S--N curve of the N curve of the specific conductor) showing forspecific conductor) showing for each stress level “each stress level “σσ” the” thespecific conductor) showing for specific conductor) showing for each stress level each stress level σσ the the number of cycles “N” that can be endured indefinitely.number of cycles “N” that can be endured indefinitely.


The life time, in years, is then calculated as followsThe life time, in years, is then calculated as follows

=1Lifetime

∑=

i

1i

i

NnLifetime

iN

C id i th k bl tt i th d tC id i th k bl tt i th d tConsidering the remarkable scatter in the conductor Considering the remarkable scatter in the conductor fatigue characteristics, conductor life expectancy is fatigue characteristics, conductor life expectancy is

considered to have only qualitative significance.considered to have only qualitative significance.


Bending amplitude P&Sor lab tests

Miner’srule

Bending stress/strain

rule

EPRI IEEE CIGRE

Lifetime

E l ti f ib ti it

EPRI limits limits Utility limits


Evaluation of vibration severity

Inverted bending amplitude

P&Sor lab tests

Miner’srule

Bending amplitude

Bending stress/strain

Lifetime

EPRI IEEE CIGRElimits

Lifetime

Utility limits

E l ti f ib ti it

EPRI limits limits Utility limits


Evaluation of vibration severity

Criteria adopted by the industry for the Criteria adopted by the industry for the evaluation of vibration severity of evaluation of vibration severity of

overhead conductoroverhead conductor


C it i f th t f li ib ti itC it i f th t f li ib ti itCriteria for the assessment of aeolian vibration severityCriteria for the assessment of aeolian vibration severityon aluminium based conductors, resulting fromon aluminium based conductors, resulting from

the review of 80 Utility Specificationsthe review of 80 Utility Specifications

Max bending

the review of 80 Utility Specificationsthe review of 80 Utility Specifications

58%

16%

Max bending strain

Max bendingamplitude

6%Lifetime

20%

0% 10% 20% 30% 40% 50% 60% 70%

No requirements


Required values of maximum bending strainRequired values of maximum bending strain

60%

Required values of maximum bending strainRequired values of maximum bending strain

50%

60%

51%30%

40%

27%18%10%

20%

*4%

0%150 200 247 300

microstrainmicrostrain peak to peakpeak to peak* * corresponding to 8.5 MPacorresponding to 8.5 MPa


p gp g

Criteria for the assessment of aeolian vibrationCriteria for the assessment of aeolian vibrationCriteria for the assessment of aeolian vibration Criteria for the assessment of aeolian vibration severity on steel based shield wires, found in 15 severity on steel based shield wires, found in 15

Utility SpecificationsUtility Specifications

13%Max bendingamplitude

0%

67%

Lifetime

Max bending strain

amplitude

20%

0%

No requirements

Lifetime

0% 10% 20% 30% 40% 50% 60% 70%


Required values of maximum bending strain for steelRequired values of maximum bending strain for steelRequired values of maximum bending strain for steel Required values of maximum bending strain for steel based conductors (13 specs reviewed)based conductors (13 specs reviewed)

30%

35%

20%

25%

30%

10%

20%

30%

10%5%

10%

15%

10% 10%

0%

5%

300 400 450 600 1000

i t ii t i k t kk t k


microstrainmicrostrain peak to peakpeak to peak

During the survey, it was found that, in the industry, evaluation During the survey, it was found that, in the industry, evaluation criteria of vibration severity are frequently prescribedcriteria of vibration severity are frequently prescribedy q y py q y p

with no consideration of whether the relevant reference limits, with no consideration of whether the relevant reference limits, a ailable in literat rea ailable in literat reavailable in literature,available in literature,

are applicable or not to the specific conductor and/or are applicable or not to the specific conductor and/or d t / l bi tid t / l bi ticonductor/clamp combination.conductor/clamp combination.

CIGRE SC B2 and IEEE WG on Conductor Dynamics are CIGRE SC B2 and IEEE WG on Conductor Dynamics are yycommitted to provide the industry with detailed and committed to provide the industry with detailed and

comprehensive guides on this subject. comprehensive guides on this subject.


Subspan oscillation measurementsSubspan oscillation measurements


Subspan oscillation has been studied extensively in Subspan oscillation has been studied extensively in p yp ywind tunnels and outdoor test laboratorieswind tunnels and outdoor test laboratories

but to a much lesser extent on actual transmission linesbut to a much lesser extent on actual transmission linesfor lack of suitable instrumentsfor lack of suitable instrumentsfor lack of suitable instruments.for lack of suitable instruments.

Recently, a subspan oscillation recorder has been made Recently, a subspan oscillation recorder has been made available on the marketavailable on the marketavailable on the market.available on the market.


The subspan oscillation recorderThe subspan oscillation recorderThe subspan oscillation recorderThe subspan oscillation recorder

consists of a displacement transducer installed between a consists of a displacement transducer installed between a i f d t h i t ll li di f d t h i t ll li dpair of conductors horizontally alignedpair of conductors horizontally aligned

and connected via cable to the recorder body installed on the and connected via cable to the recorder body installed on the tt


nearest spacer.nearest spacer.

Layout of the subspan under testLayout of the subspan under test

displacement displacement transducertransducer

spacerspacer spacerspacer

subspansubspansubspansubspan

recorder recorder bodybodyconnecting cableconnecting cable


Vibration recorders are Vibration recorders are generally installed duringgenerally installed duringgenerally installed during generally installed during

an outage of the line.an outage of the line.


The installation of the recorders The installation of the recorders can be also performed on live can be also performed on live pp

lines using the bare hand lines using the bare hand technique.technique.


Conductor inspectionsConductor inspections


Some general procedures are available that are suitable, Some general procedures are available that are suitable, to a limited extent, for assessing the occurrence of to a limited extent, for assessing the occurrence of

conductor damages produced by severe wind induced conductor damages produced by severe wind induced vibrations. They are: vibrations. They are:

Visual inspectionVisual inspection

Thermographic inspectionThermographic inspectione og ap c spect oe og ap c spect o

Radiographic inspectionRadiographic inspection

ElectroElectro--magneticmagnetic--acoustic inspectionacoustic inspection


Visual inspectionVisual inspectionVisual inspectionVisual inspectionIt is appropriate when there is a specific evidence that It is appropriate when there is a specific evidence that damages or at least severe vibrations have occurreddamages or at least severe vibrations have occurreddamages or at least severe vibrations have occurred.damages or at least severe vibrations have occurred.

For example, black spots on the surface of the conductors For example, black spots on the surface of the conductors i di t ib tii di t ib ti


may indicate severe vibrations.may indicate severe vibrations.

However, stand failures in inner layers can not be visually However, stand failures in inner layers can not be visually detected and strand failures inside clamps and or below detected and strand failures inside clamps and or below

armour rods can be overlooked unless these components arearmour rods can be overlooked unless these components arearmour rods can be overlooked unless these components are armour rods can be overlooked unless these components are removed. removed.


Thermographic inspectionThermographic inspection

Can be performed from the ground but can only detect Can be performed from the ground but can only detect j i t bl d t t d f ilj i t bl d t t d f il


joints problems and not strand failures. joints problems and not strand failures.

Thermographic inspectionThermographic inspection

Tests demonstrated that failures of up to three strands do not Tests demonstrated that failures of up to three strands do not produce appreciable temperature variationsproduce appreciable temperature variations


produce appreciable temperature variations.produce appreciable temperature variations.

Radiographic inspectionRadiographic inspectionRadiographic inspectionRadiographic inspection

Can detect strand failures but it is costly complex and not Can detect strand failures but it is costly complex and not completely reliable. Strand failures are sometimes overlooked.completely reliable. Strand failures are sometimes overlooked.


Radiographic inspectionRadiographic inspection


Can be performed on energized lines also.Can be performed on energized lines also.

Radiographic inspectionRadiographic inspectionRadiographic inspectionRadiographic inspection

Example of strand failure detected by radiographyExample of strand failure detected by radiography


Example of strand failure detected by radiographyExample of strand failure detected by radiography

ElectroElectro--magneticmagnetic--acoustic inspectionacoustic inspection

Can be performed on energized lines to detect strand Can be performed on energized lines to detect strand f il d t l t d if il d t l t d i


failures and steel strand corrosion.failures and steel strand corrosion.

Thank you for your attention !Thank you for your attention !Thank you for your attention !Thank you for your attention !


Aeolian Vibration Monitoring

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