1. 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 15 th July 2011, ICWE 13, Amsterdam, The Netherlands

2. 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

3. 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?

4. 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

5. Model scaling

6. Model layout Distorted horizontal length scaling (Loredo-Souza & Davenport 2001) 1:100 length scaling of one line span, for all 

7. Model scaling Scaling of aerodynamic drag D = C D · 0.5 ·  · U 2 · A Drag coefficients from Mara et al. (2010) section model tests 3-D assembly2-D projection Projected areas from CAD model

8. Lattice tower modelled as an equivalent mast Model scaling Scaling of flexural rigidity about two axes pp n n conductor tower

9. Model scaling

10. Model installation

11. 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)

12. Response to boundary layer wind forcing

13. Response to downdraft outflow wind forcing

14. BL

15. Comparison of peak responses across-wind along-wind across-wind along-wind

16. Comparison of peak responses 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 1.3 to 1.7 1.5 0.96 to 2.4 1.84

17. 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

18. Future work Yaw angle effects

19. Acknowledgements Financial 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)