Tests of Operational Wear of Trolleybus Traction Wires—A Case Study

This study presents an experimental evaluation of operational wear in Djp 100 trolleybus contact wires used in the city of Lublin (Poland). The objective was to determine quantitative geometric and mechanical indicators of wear and to propose empirically based replacement criteria. New and long-service wires were examined using 3D scanning, optical profilometry, nanoindentation, and tensile testing. The results show significant changes in the cross-sectional geometry and mechanical performance: the maximum local profile deviation reached ≈2.5 mm, the average cross-sectional area decreased by ≈17%, and the moment of inertia Jx was reduced by ≈30% (from ≈878 mm4 to ≈610 mm4). Tensile tests revealed a drop in breaking force from ≈37 kN (new wire) to ≈27 kN (used wire). Surface roughness Sa decreased approximately threefold, while nanoindentation showed local near-surface strengthening, with hardness and elastic modulus increasing up to twofold in worn zones. Based on these quantitative changes, combined geometric–mechanical wear indicators were formulated and used to derive practical replacement thresholds for trolleybus contact wires. These findings demonstrate that integrating cross-sectional wear, loss of load-bearing capacity, and local surface property changes provides a consistent and technically justified foundation for maintenance decisions in overhead contact line systems.