A single-span aeroelastic model of an overhead electrical power transmission line with guyed lattice towers A study by W.E. Lin, E. Savory, R.P. McIntyre,

A single-span aeroelastic model of an overhead electrical power transmission line

with guyed lattice towers

A study by

W.E. Lin, E. Savory, R.P. McIntyre, C.S. Vandelaar & J.P.C. King

The University of Western Ontario

With funding from

Friday 15th July 2011, ICWE 13, Amsterdam, The Netherlands

Overview• Scope: design and test a physical model of a section

that failed due to downdraft outflow winds

• Direct comparison of tower and line response to synoptic wind profile versus downdraft outflow wind profile

• Aeroelastic model of a transmission line system with length scaling of 1:100

• In successive order, the experimental model was subjected to boundary layer and downdraft outflow wind forcing in a single test facility

Purpose and motivation

• Examine feasibility of the required design and fabrication

• Characterize the structural response to the two different types of wind forcing

• Why do transmission line failures occur in downdraft winds?

Lattice tower: 44.4 m

Two x-arms

Four guy wires

Two insulators

Two conductor pairs: 488 m span

One lightning shield

Full-scale structure

Model scaling

Model layout

• Distorted horizontal length scaling (Loredo-Souza & Davenport 2001)

• 1:100 length scaling of one line span, for all

Model scaling

Scaling of aerodynamic drag

D = CD · 0.5 ·· U2 · A

• Drag coefficients from Mara et al. (2010) section model tests

3-D assembly 2-D projection

• Projected areas from CAD model

• Lattice tower modelled as an equivalent mast

Model scaling

• Scaling of flexural rigidity about two axes

p p

n

n

conductor

conductor

tower

Model scaling

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5

Section 1 (z = 0 to 0.06 m)

Section 2 (0.06 to 0.07)

Section 3 (0.07 to 0.10)

Sections 4, 5, 6 (0.10 to 0.41)

Guy wire x-arm (0.35 to 0.38)

Conductor x-arm (0.38 to 0.41)

Section 7 (0.41 to 0.45)

Total (z = 0 to 0.45 m)

tow

er

reg

ion

mass (g)

scaled lattice tower ± 2.5 %

mast model

Model installation

Response to boundary layer wind forcing

• ASCE (2010):

Subconductor oscillation at 0.15 to 10 Hz

Galloping at 0.08 to 3 Hz

• Conductor axial force spectra also had spectral peak at 0.6 Hz with 0.5 Hz bandwidth

• Spectral peak centred at 0.6 Hz (full-scale) with bandwidth of 0.4 Hz (f-s)

Response to boundary layer wind forcing

Response to downdraft outflow wind forcing

Response to downdraft outflow wind forcing

BL

Comparison of peak responses

across-wind

along-wind

across-wind

along-wind

Comparison of peak responses1.3 to 1.7

1.5

0.96 to 2.4

1.84

1.3 to 1.7

1.5

0.96 to 2.4

1.84

1.3 to 1.7

1.5

0.96 to 2.4

1.84

Conclusions

• Observed imbalance between peak load on the upstream and downstream conductors was particularly severe for the downdraft outflow forcing

• Fundamental mode of vibration was evident, but response was generally quasi-static to both types of wind forcing

• Resonant dynamic response was less significant with downdraft outflow wind forcing

• Peak values of tower response to downdraft outflow forcing were significantly larger

Future work

• Yaw angle effects

AcknowledgementsFinancial sponsors:

• Natural Sciences & Engineering Research Council of Canada

•

• Centre for Energy Advancement through Technological Innovation

•

• Association of Universities and Colleges of Canada

• www.mitacs.ca

Colleagues: J.K. Galsworthy, T.G. Mara, K. Barker, S. Hewlette, G. Dafoe,

AFM Research Group (www.eng.uwo.ca/research/afm/main.htm)