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

First South East European Regional CIGRÉ Conference - Portoroz, Slovenia, 7—8 June 2016 SEERC

Thank you for your attention