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First South East European
Regional CIGRÉ Conference
Portoroz, Slovenia, 7—8 June 2016
SEERC
Unsymmetrical Spacer Damper designed
to control the sub span oscillation of a
conductor bundle
M.M., MASSIMO MUGGIASCA
Paper number 4-15
First South East European Regional CIGRÉ Conference - Portoroz, Slovenia, 7—8 June 2016 SEERC
Outline
Introduction
Vibration Phenomena
Aeolian vibration
Galloping
Subspan oscillation
Subspan Oscillation – Effect & Control
New Spacer Damper Design
Conclusion
First South East European Regional CIGRÉ Conference - Portoroz, Slovenia, 7—8 June 2016 SEERC
Introduction
Two years ago Politecnico di Milano Engineers presented a paper regarding a
work performed with the aim to find out the way to control Subspan Oscillations.
The conclusion of this work was that a special design of spacer damper could
avoid the exicitation of the subspan oscillation in bundle T/L.
Our works started from that conclusion with the aim to develop the concept and
finalize the proper spacer damper.
First South East European Regional CIGRÉ Conference - Portoroz, Slovenia, 7—8 June 2016 SEERC
Vibration Phenomena
Vibrations induced by the wind on single and bundled conductors generate
undesirable and dangerous phenomena on the OHTL:
Aeolian Vibrations (Vortex Shedding)
Galloping
Wake Induced Oscillations (Subspan Oscillations) ))
First South East European Regional CIGRÉ Conference - Portoroz, Slovenia, 7—8 June 2016 SEERC
OHTL – Bundle Configuration
Twin
Different
bundle
configuration
are used on
OHTL
First South East European Regional CIGRÉ Conference - Portoroz, Slovenia, 7—8 June 2016 SEERC
OHTL - Spacer Dampers
Spacer dampers are used
to maintain the bundle
geometry / spacing and to
add damping to the cables
Eight Twin
Triple
Six
Quad
First South East European Regional CIGRÉ Conference - Portoroz, Slovenia, 7—8 June 2016 SEERC
Vibration phenomenaAeolian vibration
First South East European Regional CIGRÉ Conference - Portoroz, Slovenia, 7—8 June 2016 SEERC
Vibration phenomena - Aeolian Vibrations
When >>> Single & Bundle
Caused by >>> Vortex shedding
Winds >>> Low to Moderates
Amplitudes >>> Small vertical (up to 1 cable diam)
Frequencies >>> 5–100 Hz > Cond. size & tensile load
Effect >>> Fatigue (bending + fretting) on the strands of the
conductor close to suspension or dead end clamps
Controlled by >>> Vibration Dampers - Spacer Dampers
WIND
Aeolian vibrations occur almost on any T/L and are due to vortex shedding excitation
First South East European Regional CIGRÉ Conference - Portoroz, Slovenia, 7—8 June 2016 SEERC
Vibration phenomenaAeolian vibration
Fatigue
Fretting
Causes the generation of micro-cracks which, depending on the strain
level, may cause failure of the single wires and finally of the conductor.
Fretting drastically lowers the fatigue limit of a stranded cable with
respect to the fatigue limit of a single wire of the same material.
It is the result of a combined effect of alternate bending strain and
of fretting among the single wires of the conductor.
First South East European Regional CIGRÉ Conference - Portoroz, Slovenia, 7—8 June 2016 SEERC
When >>> Single & Bundle
Caused by >>> Ice accretion shape
Winds >>> Medium - High speed ( V > 15 m/s )
Amplitudes >>> High (up to the sag)
Frequencies >>> Lower than 1 Hz
Effect >>> Phase Clashing – Insulator strings &
Tower breakages
Controlled by >>> Special devices
Vibration Phenomena - Ice Galloping
Occurs due to the aerodynamic forces that wind
induces in the conductor (Lift and Drag)
First South East European Regional CIGRÉ Conference - Portoroz, Slovenia, 7—8 June 2016 SEERC
Vibration phenomena - Ice galloping - Failures
First South East European Regional CIGRÉ Conference - Portoroz, Slovenia, 7—8 June 2016 SEERC
Vibration phenomena -Subspan
First South East European Regional CIGRÉ Conference - Portoroz, Slovenia, 7—8 June 2016 SEERC
When >>> Bundle
Caused by >>> Wake effect
Winds >>> Medium / High speed (V > 10 m/s)
Amplitudes >>> High (up to conductor spacing)
Frequencies >>> 0,7 – 2 Hz
Effect >>> Clashing – Clamp bolts loosening
Controlled by >>> Spacer Dampers Spacing
Vibration phenomena -Subspan oscillation
Occurs only with couple of sub-conductors, one in the wake of the other. It is an instability
phenomenon in which the elliptical trajectory is due to the coupling of vertical and horizontal
modes of vibration.
First South East European Regional CIGRÉ Conference - Portoroz, Slovenia, 7—8 June 2016 SEERC
Subspan oscillations may cause sub-
conductor clashing with possible
breakage
Vibration phenomenaSubspan oscillation
Spacer dampers clamp bolts loosening
due to the high forces transmitted to the
spacers dampers
Effects
First South East European Regional CIGRÉ Conference - Portoroz, Slovenia, 7—8 June 2016 SEERC
Vibration phenomenaComparison
WHEN
CAUSED BY
WINDS
AMPLITUDES
FREQUENCIES
EFFECTS
CONTROLLED
BY
Single & bundle
Vortex shedding
Moderates
Small (< ø conductor)
5 – 100 Hz
Fatigue (bending +
fretting)
Vibration dampers –
Spacer dampers
Only bundle
Wake effect
Medium/ High speed
(V>10 m/s)
High (< spacing)
0,7 – 2 Hz
Conductor clashing –
Clamp bolt loosening
Spacer dampers
Aeolian Subspan
First South East European Regional CIGRÉ Conference - Portoroz, Slovenia, 7—8 June 2016 SEERC
Vibration phenomenaSubspan oscillation
How can it be controlled ?
The method to control the sub-span oscillation is the choice of the correct spacer
damper’s geometry combined with the optimization of their spacing along the span.
Particularly, taking care of :
Correct Design of OHTL (Conductor, tension load, towers )
Limiting the maximum subspan length – increase of SD
Alternating different subspan lengths with a correct ratio
New geometry of the Spacer Damper
Classical
approach
Salvi’s upgrade
First South East European Regional CIGRÉ Conference - Portoroz, Slovenia, 7—8 June 2016 SEERC
Vibration phenomenaSubspan oscillation
The phenomenon is due to the coupling of horizontal subspan mode with bundletorsional or vertical subspan mode of vibration.
Mandatory is a proper definition of sub-span lengths.
Long subspans have to be avoided because as the lenght increases, thefrequency decreases and the vibration amplitude increases
An alternance of different sub-span lengths has to be properly used becauseproduces a change in the horizontal mode frequency and then in the couplingbetween the modes.
.
Classical approach
First South East European Regional CIGRÉ Conference - Portoroz, Slovenia, 7—8 June 2016 SEERC
Vibration phenomenaSubspan oscillation
Salvi, with the cooperation of Politecnico di Milano, studied a new quad bundle
spacer damper, having a different shape to improve its effectiveness.
Salvi’s upgrade
Classical design Salvi New concept
First South East European Regional CIGRÉ Conference - Portoroz, Slovenia, 7—8 June 2016 SEERC
Salvi’s Upgrade – New Spacer Damper
New
design
New
software
New
concept
First South East European Regional CIGRÉ Conference - Portoroz, Slovenia, 7—8 June 2016 SEERC
Salvi’s Upgrade – New Spacer Damper
NEW SOFTWARE. Salvi sponsored a research
with Politecnico di Milano aimed at improving the
knowledge on subspan oscillation. The first step of
the research produced a new software for subspan
effect calculation.
NEW CONCEPT. Another outcome of the
research has been the development of a new
concept of spacer damper, not only featured to the
control of aeolian vibration but also oriented to the
control of subspan oscillations.
NEW DESIGN. All the quad Spacer Dampers in
use were designed to control the vibration of a
symmetric bundle and consequently their structure is
symmetric with respect to the vertical plane. The
upgrade was to introduce the possibility of a not
symmetric shape.
First South East European Regional CIGRÉ Conference - Portoroz, Slovenia, 7—8 June 2016 SEERC
No Wind
The natural frequency of the vertical mode is lower than
the horizontal one
At the increasing of the wind
The vertical mode increases up to be very close to the
frequency of the horizontal one
Conclusion
This determines the coupling of the two modes and the
consequent beginning of the conductor elliptical
motion and subspan phenomenon on the bundle.
Classic Symmetric Spacer Damper
First South East European Regional CIGRÉ Conference - Portoroz, Slovenia, 7—8 June 2016 SEERC
No Wind
The final result of the research performed by Salvi with
Politecnico di Milano is the design of a Spacer Damper able to
guarantee that the natural frequencies of vertical modes are
always higher than the horizontal ones
Conclusion
The new spacer design must be ASYMMETRICAL
New Spacer Damper –New Concept – New Design
At the increasing of the wind
The clear consequence is that the coupling of vibration modes
cannot happen, preventing the line from subspan phenomenon
First South East European Regional CIGRÉ Conference - Portoroz, Slovenia, 7—8 June 2016 SEERC
New Design - Asymmetric spacer damper
First South East European Regional CIGRÉ Conference - Portoroz, Slovenia, 7—8 June 2016 SEERC
New Design - Asymmetric spacer damper
Typical application
Asymmetric Standard
Conductor type ACAR ø 30,38 mm
Conductor tensile load [N] 20870
Span Length [m] 420
N° Spacer dampers 8 12
Maximum aeolian [µs] 62 44
Maximum sub-span
oscillation [mm p.p.]0 68
First South East European Regional CIGRÉ Conference - Portoroz, Slovenia, 7—8 June 2016 SEERC
New Design - Asymmetric spacer damperState of the art
Span with asymmetric
Lenght 447 m
N° of s.d. 10
Span with standard
Lenght 420 m
N° of s.d. 12
Salvi has equipped with asymmetric spacers dampers some spans of
a TL in very severe working conditions.
The first survey of the T/L has already been done
with no evidence of negative events.
A field measurement campaign is currently in progress.
It is performed also with the intent to compare
the classic solution with the new design.
First South East European Regional CIGRÉ Conference - Portoroz, Slovenia, 7—8 June 2016 SEERC
New Design - Asymmetric spacer damperState of the art
Fully tested and approved
mechanical and electrical type
tests foreseen by IEC 61854
Specification
Spacer dampers supplied in T/L
already in service
First South East European Regional CIGRÉ Conference - Portoroz, Slovenia, 7—8 June 2016 SEERC
Asymmetric spacer damperAdvantages & Gains
Savings
Reduced quantities
Reduced assembly
Reduced maintenance
Performances
Prevents the subspan
occurrence
Quality
Assures the control of aeolian vibrations
Guarantees proper functional
mechanical-electrical
performances
Innovation
Introduces a totally new concept and
design