State of the Art of Conductor Galloping
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STATE OF THE ART OF CONDUCTOR GALLOPING A complementary document to “Transmission line reference book –Wind-induced conductor motion Chapter 4: Conductor galloping,” Based on EPRI Research project 792 Task Force B2.11.06 Members: Lilien, Jean-Louis - Belgium (Convenor) Van Dyke, Pierre - Canada (Secretary) Asselin, Jean-Marie - Canada Farzaneh, Masoud - Canada Halsan, Kjell - Norway Havard, Dave - Canada Hearnshaw, Dave - England Laneville, André - Canada Mito, Masataka - Japan Rawlins, Charles B. - USA St-Louis, Michel - Canada Sunkle, Dave - USA Vinogradov, Alexandre - Russia International expert who contributed: Yamaguchi, Hiroki - Japan The authors of this brochure have asked detailed comments to: Tunstall, M.J. (former chairman of B2.11.06) - UK Ervik, M. - Norway Obrö, H. - Denmark Okumura, T. - Japan Shkaptsov, V. - Russia FOREWORD TO THE GALLOPING BROCHURE Of all the wind induced motions of Overhead Transmission Line conductors or other suspended cables, galloping is the most noticeable and spectacular and the resulting damage can be equally dramatic and very costly, with broken conductors and fittings, damaged tower components and even whole towers collapsing! The consequential economic and social costs of power loss to whole areas can also be very considerable. Galloping is an oscillation of single or bundled conductors due to wind action on an ice or wet snow accretion on the conductors, although there are recorded instances of non-ice galloping arising from the conductor profile presented to the wind. Conductor motions are characterised by amplitudes that may approach or exceed the conductor sag (possibly >10m) and depending on the amplitudes and number of loops, frequencies up to 3 Hz. Galloping of conductors received particular emphasis by incorporation of a CORECH work group within Task Force 6 (Galloping) of CIGRE SCB2 WG11. The focus was on field observations of galloping, effectiveness of control devices, documentation of damage, refinement of clearances required for design to avoid flashovers and instrumentation to record galloping. Emphasis was also placed on research on aerodynamics, on shapes of accretions of ice or wet snow and on the development of theories describing galloping behaviour. A galloping reporting format for the field was published in 1995 and a ‘State of the Art’ report reviewing galloping control methods was published in 2000. This brochure is both up to date and comprehensive in its treatment of this important topic and will be valuable both to researchers, who are seeking to better understand the fundamental causes of galloping and Transmission Line engineers, who are faced with the practical consequences of galloping on their lines and need to find remedies. It will also compliment the revised EPRI ‘Orange Book’. In conclusion, I would like to recognise the hard work of the Task Force volunteers who have carried this work through to completion and thank them on behalf of CIGRE and the wider industry. David Hearnshaw C Eng Convenor, SCB2 WG11 09 December 2005 CIGRE ad hoc SC CONTENT 1. EXECUTIVE SUMMARY ...................................................................................................................................... 1 2. INTRODUCTION .................................................................................................................................................... 5 3. COST OF GALLOPING .......................................................................................................................................... 7 3.1 Costs Related to Galloping Events............................................................................................................................ 7 3.1.1 Damage Repair................................................................................................................................................ 7 3.1.2 Inspection........................................................................................................................................................ 7 3.1.3 Loss of revenue ............................................................................................................................................... 7 3.1.4 System reliability and quality of service ......................................................................................................... 7 3.1.5 Social impacts of outages due to galloping..................................................................................................... 8 3.1.5.1 Impact on utility image ................................................................................................................................... 8 3.1.5.2 Impact on utility image ................................................................................................................................... 8 3.1.5.3 Impact on hospitals ......................................................................................................................................... 8 3.1.5.4 Impact on production industry ........................................................................................................................ 8 3.1.5.5 Impact on population confidence and safety................................................................................................... 8 3.2 Costs Related to Prevention of Galloping................................................................................................................. 8 3.2.1 Design criteria................................................................................................................................................. 8 3.2.2 Anti-galloping devices .................................................................................................................................... 9 3.2.3 Research and Studies ...................................................................................................................................... 9 4. THE APPEARANCE AND THE OCCURRENCE OF GALLOPING.................................................................. 11 4.1 Types of motion...................................................................................................................................................... 11 4.2 Causes of galloping................................................................................................................................................. 12 4.3 Ice Forms ................................................................................................................................................................ 15 4.4 Factors influencing galloping ................................................................................................................................. 15 4.5 Incidence of galloping............................................................................................................................................. 16 4.5.1 Summary of verbal galloping reports – 1988 to 2005................................................................................... 16 4.5.1.1 Introduction................................................................................................................................................... 16 4.5.1.2 Countries reporting at meetings .................................................................................................................... 17 4.5.1.3 Summary by country..................................................................................................................................... 18 4.5.2 Detailed galloping observation summaries ................................................................................................... 24 5. GALLOPING MECHANISM, AMPLITUDE AND RESULTING LOADS ON TOWERS ................................ 29 5.1 Mechanisms of galloping........................................................................................................................................ 29 5.1.1 Basic physics of galloping on overhead lines ............................................................................................... 29 5.1.1.1 Case 1: No torsion (infinitely rigid) ............................................................................................................. 30 5.1.1.2 Case 2: Torsion ............................................................................................................................................ 31 5.1.1.3 Discussion..................................................................................................................................................... 32 5.1.2 Aeolian vibrations and galloping of conductors............................................................................................ 32 5.1.3 The quasi-steady hypothesis and a non-linear model.................................................................................... 33 5.1.3.1 Validity of quasi-steady theory ..................................................................................................................... 33 5.1.4 Galloping in turbulent flows ......................................................................................................................... 36 5.1.5 Possible control of galloping mechanism?.................................................................................................... 36 5.1.6 Equations of galloping .................................................................................................................................