While overhead-line electricity transmission grids are generally well established in Europe, and there is not a big incentive to install new or replace existing conductors, there is a high interest in improving reliability and maximising current flow with minimum impact on operating lifetime. This is the focus of the CONFAT project.

Typically, a 30mm diameter E-AlMgSi high voltage overhead line conductor comprises ~60 individual ~3mm diameter wires counter-wound in 4 rows about a central core by a stranding process intentionally responsible for a complex internal residual stress distribution to maintain form during service duty. One cause of failure can be the consequence of Aeolian vibration and fatigue due to fretting between conductor wires in the outer and penultimate layers at locations close to suspension clamps.

The risk of fretting fatigue crack initiation may be minimised by reducing the magnitudes of mean stress and/or stress amplitude in conductor wires in the vicinity of suspension clamps. In the CONFAT project, the dynamic stress state in the conductor has been determined by advanced non-linear 3D finite element analysis. The risk of cracking at critical locations has then been determined with reference to experimentally determined conductor wire fretting fatigue properties.

The effectiveness of the new analysis methodology to demonstrate the respective advantages associated with local thermal treatments and alternative suspension clamp designs has been verified with the results of full-size conductor fatigue tests performed in a new facility specifically constructed for the purpose at Empa.

Enhanced Fretting Fatigue Resistance of Conductors for High Voltage Overhead Lines (CONFAT)
Figure 1: Enhanced Fretting Fatigue Resistance of Conductors for High Voltage Overhead Lines (CONFAT), Courtesy: Kilian Schillai & Stuart Holdsworth, Empa

The CONFAT project involves a research collaboration between PFISTERER SEFAG AG and the ESC member Prof. Dr. Edoardo Mazza. The work is being conducted by the High Temperature Integrity Group which is part of his Laboratory for Mechanical Integrity of Energy Systems at Empa. The Group develops new high temperature mechanical assessment procedures, primarily for energy systems, and verifies their effectiveness by service-like benchmark testing complemented by metallurgical condition assessment. In this thematic area, the Group cooperates with the High Voltage Laboratory of ETH Zurich (Prof. Dr. Ch. Franck) and Swisselectric Research.

Tweet: Enhanced Fretting Fatigue Resistance of Conductors for High Voltage Overhead Lines