Fatigue Endurance Capability Of Conductor/clamp Systems Update

Transcript

CONSEIL INTERNATIONAL DES GRANDS RÉSEAUX ÉLECTRIQUES TF B2.11.07 Fatigue Endurance Capability of Conductor/Clamp Systems Update of Present Knowledge Technical Brochure Presentation to SC B2, Helsinki, July 2007 Louis Cloutier, Convenor André Leblond, Secretary 1 CONSEIL INTERNATIONAL DES GRANDS RÉSEAUX ÉLECTRIQUES TF B2.11.07 FATIGUE ENDURANCE CAPABILITY OF CONDUCTOR/CLAMP SYSTEMS UPDATE OF PRESENT KNOWLEDGE „ „ „ Fretting fatigue has long been recognized as being the cause of strand failures in outer as well as inner layers of the conductors In planes where conductor motion is constrained, the curvatures are much larger than in the free span Interstrand microslip amplitude increases, small cracks are generated and some propagate up to complete strand failures 2 CONSEIL INTERNATIONAL DES GRANDS RÉSEAUX ÉLECTRIQUES TF B2.11.07 FATIGUE ENDURANCE CAPABILITY OF CONDUCTOR/CLAMP SYSTEMS UPDATE OF PRESENT KNOWLEDGE „ Strand failures occur mainly at suspension clamps where such singular conditions are created „ To a lesser extent, a similar phenomenon can occur at damper, marker or spacer clamps 3 CONSEIL INTERNATIONAL DES GRANDS RÉSEAUX ÉLECTRIQUES TF B2.11.07 FATIGUE ENDURANCE CAPABILITY OF CONDUCTOR/CLAMP SYSTEMS UPDATE OF PRESENT KNOWLEDGE The main cause of conductor fatigue strand failures is the presence of Aeolian vibrations: „ A phenomenon far from having a nice constant sinusoïdal form „ Small vibration amplitudes exceeding rarely one conductor diameter „ In the frequency range of 3 to 150 Hz „ For winds of 1 to 7 m/s (2 to 15 mph) Other wind-induced conductor motions such as Wake-induced oscillations and Galloping may also be responsible for fatigue conductor strand failures. 4 CONSEIL INTERNATIONAL DES GRANDS RÉSEAUX ÉLECTRIQUES TF B2.11.07 FATIGUE ENDURANCE CAPABILITY OF CONDUCTOR/CLAMP SYSTEMS UPDATE OF PRESENT KNOWLEDGE Conductor vibration and its detrimental effects has been the subject of several studies for many decades „ „ „ „ The following aspects have been of particular interest to the transmission line engineer : In situ measurement of conductor motions Simple analytical representation of the fatigue phenomenon Characterization of the fatigue behaviour of a conductor Evaluation of the conductor residual life 5 CONSEIL INTERNATIONAL DES GRANDS RÉSEAUX ÉLECTRIQUES TF B2.11.07 FATIGUE ENDURANCE CAPABILITY OF CONDUCTOR/CLAMP SYSTEMS UPDATE OF PRESENT KNOWLEDGE In situ measurement of conductor motions (I) Several methods to measure the vibration intensity of a conductor have been employed. The bending amplitude Yb method finally comes out as the most practical : It permits a measure of the differential displacement of the conductor at 89mm from the last point of contact with the clamp. „ Introduced by Tebo in 1941 „ Pursued by Edwards and Boyd in 1963 „ Recommended by IEEE in 1963 (also in the 2006 revision of the IEEE Guide) „ Recommended in CIGRE SC22 WG04 1979 and SC22 WG02 1995 6 CONSEIL INTERNATIONAL DES GRANDS RÉSEAUX ÉLECTRIQUES TF B2.11.07 FATIGUE ENDURANCE CAPABILITY OF CONDUCTOR/CLAMP SYSTEMS UPDATE OF PRESENT KNOWLEDGE In situ measurement of conductor motions (II) „ The reverse bending amplitude was presented as an alternative to permit the installation of the vibration recorder directly onto the conductor „ The bending amplitude method suits particularly well the configuration of a conductor supported in a short metallic clamp „ The last point of contact is easily located „ The bending amplitude method must be interpreted correctly when cushioned clamps are used 7 CONSEIL INTERNATIONAL DES GRANDS RÉSEAUX ÉLECTRIQUES TF B2.11.07 FATIGUE ENDURANCE CAPABILITY OF CONDUCTOR/CLAMP SYSTEMS UPDATE OF PRESENT KNOWLEDGE In situ measurement of conductor motions (III) Ontario Hydro Recorder Vibrec 400 HILDA Ribe LVR TVM 90 Pavica 8 Scolar III CONSEIL INTERNATIONAL DES GRANDS RÉSEAUX ÉLECTRIQUES TF B2.11.07 FATIGUE ENDURANCE CAPABILITY OF CONDUCTOR/CLAMP SYSTEMS UPDATE OF PRESENT KNOWLEDGE Simple Analytical Representation of the Fatigue Phenomenon (I) „ „ „ The conductor/clamp system is represented as a cantilever beam Bending amplitude method is valid only for armored or unarmored conductors fitted with solid metal-to-metal clamps Invalid for cushioned clamps (armored or unarmored) σ a b oror ε ab Yb Xb=89mm 9 CONSEIL INTERNATIONAL DES GRANDS RÉSEAUX ÉLECTRIQUES TF B2.11.07 FATIGUE ENDURANCE CAPABILITY OF CONDUCTOR/CLAMP SYSTEMS UPDATE OF PRESENT KNOWLEDGE Simple Analytical Representation of the Fatigue Phenomenon (II) „ An idealized bending stress (Poffenberger-Swart formula) is calculated in the top-most outer-layer strand in the plane of the last point of contact (LPC) σa = ( 4e Ea d p 2 − px − 1 + px ) Yb Ea: modulus of elasticity of outer wire material (N/mm2) d: diameter of outer layer wire (mm) p = (H/EI)½ H: conductor tension at average temperature during test period (N) EI: sum of flexural rigidities of individual wires in the cable (N mm2) x: distance from the point of measurement to the last point of contact between the clamp and the conductor. 10 CONSEIL INTERNATIONAL DES GRANDS RÉSEAUX ÉLECTRIQUES TF B2.11.07 FATIGUE ENDURANCE CAPABILITY OF CONDUCTOR/CLAMP SYSTEMS UPDATE OF PRESENT KNOWLEDGE Simple Analytical Representation of the Fatigue Phenomenon (III) LPC The free loop amplitude of vibration, ymax, is also a useful practical parameter m The Poffenberger-Swart formula becomes: σ a = π d Ea fymax EI „ Ea: Young’s modulus for the outer-layer strand material (N/mm2) d: diameter of outer layer wire (mm) f: frequency of the motion (Hz) m: conductor mass per unit length (kg/m) EI: sum of flexural rigidities of individual wires in the cable (N mm2) 11 CONSEIL INTERNATIONAL DES GRANDS RÉSEAUX ÉLECTRIQUES TF B2.11.07 FATIGUE ENDURANCE CAPABILITY OF CONDUCTOR/CLAMP SYSTEMS UPDATE OF PRESENT KNOWLEDGE Characterization of the fatigue behaviour of a conductor (I) „ Laboratory fatigue tests ― Resonant type test benches Pneumatic tensioning system Suspension clamp Dynamometer Amplitude measuring system End clamp Rubber dampers Turnbuckle Wire break detection Slider 2m Vibrator Active length : 7 m 5.5E 2m 12 CONSEIL INTERNATIONAL DES GRANDS RÉSEAUX ÉLECTRIQUES TF B2.11.07 FATIGUE ENDURANCE CAPABILITY OF CONDUCTOR/CLAMP SYSTEMS UPDATE OF PRESENT KNOWLEDGE Characterization of the fatigue behaviour of a conductor (II) Important test parameters „ „ „ „ Constant amplitude excitation Measurement of the bending amplitude Yb and/or the free loop amplitude ymax Most tests done with conductors supported in short metallic clamps Clamps usually held in a fixed position on the test bench 13 CONSEIL INTERNATIONAL DES GRANDS RÉSEAUX ÉLECTRIQUES TF B2.11.07 FATIGUE ENDURANCE CAPABILITY OF CONDUCTOR/CLAMP SYSTEMS UPDATE OF PRESENT KNOWLEDGE Characterization of the fatigue behaviour of a conductor (III) „ „ The results of such tests ultimately lead to the presentation of a fatigue (S-N) curve The endurance limit is determined at 500 megacycles s N 107 108 109 14 CONSEIL INTERNATIONAL DES GRANDS RÉSEAUX ÉLECTRIQUES TF B2.11.07 FATIGUE ENDURANCE CAPABILITY OF CONDUCTOR/CLAMP SYSTEMS UPDATE OF PRESENT KNOWLEDGE Evaluation of the conductor residual life (I) Fatigue Endurance Data „ „ Idealized bending stress (Poffenberger-Swart formula) at conductor surface vs megacycles to failure Endurance limits z 22.5 MPa for single-layer ACSR z 8.5 MPa for multi-layer ACSR 15 CONSEIL INTERNATIONAL DES GRANDS RÉSEAUX ÉLECTRIQUES TF B2.11.07 FATIGUE ENDURANCE CAPABILITY OF CONDUCTOR/CLAMP SYSTEMS UPDATE OF PRESENT KNOWLEDGE Evaluation of the conductor residual life (II) „ „ Statistical analysis S-N curves without wire failure z Average z 95% probability of survival Poffenberger-Swart stress relative to Yb (MPa) Multi-Layer ACSR Fatigue Endurance Data 40 30 20 10 Average S-N curve (50%) 95% probability of survival curve 0 1 10 100 1000 N = Megacycles to failure 16 CONSEIL INTERNATIONAL DES GRANDS RÉSEAUX ÉLECTRIQUES TF B2.11.07 FATIGUE ENDURANCE CAPABILITY OF CONDUCTOR/CLAMP SYSTEMS UPDATE OF PRESENT KNOWLEDGE Evaluation of the conductor residual life (III) „ „ Based on Cumulative damage theory (Miner’s rule) Total damage D at several stress levels σi cumulates linearly: D = Σ ni/Ni „ Failure is predicted when D = Σ ni/Ni =1 17 CONSEIL INTERNATIONAL DES GRANDS RÉSEAUX ÉLECTRIQUES TF B2.11.07 FATIGUE ENDURANCE CAPABILITY OF CONDUCTOR/CLAMP SYSTEMS UPDATE OF PRESENT KNOWLEDGE Some important recent contributions Guide for Aeolian Vibration Field Measurements of Overhead Conductors, IEEE P1368, 2007 (a revision of IEEE 1966 Report) „ Transmission Line Reference Book, Wind Induced Conductor Motion, Second Ed. EPRI 2007 (Chapter 3, Fatigue of Overhead Conductors), a revision of the 1979 “Orange Book” IEC TC7 approved recently : „ Method for Conductor Fatigue Testing, Project 451(sec)/NP 94-08 CIGRE SCB2 intends to complete the following: „ Fatigue Endurance Capability of Conductor/Clamp Systems ― Engineering Guidelines and Recommendations „ 18