Feasibility of Horizontal-Vee Insulator Configurations for Overhead Lines in Undulating Terrain

H-Vees remains a critical design consideration, with particular emphasis on Axis of Rotation

(AoR) in maintaining stability under climatic loading.

This study investigates the stability of H-Vees mounted on steel poles through a two-stage modelling approach using PLS-CADD and PLS-POLE (industry standard software). In the first stage, AoR inclinations between 5° and 30° were analysed on flat terrain to establish baseline behaviour. In the second stage, the analysis was extended to a terrain profile representative of the undulating Scottish landscape.

The results demonstrate the importance of AoR for H-Vee stability. Inclinations of 15° or less consistently led to snap-through, while 25–30° provided self-restoration capacity across all span configurations considered. A practical stability threshold was identified at around 30°, which ensured stability in line sections of up to 13 spans in flat terrain. Beyond this point, instability appeared under high wind, particularly when loads acted perpendicular to the alignment.

The uplift loading scenario (Case 1b: 3-year return wind at –20°C) was confirmed as the most onerous condition, with zero or near-zero weight spans failing across all configurations. For a 150 m mean span, iterative modelling identified minimum stable weight span thresholds of approximately 129 m under still air (–5.6°C) and 111 m under the uplift load case. Below these limits, the insulators exhibited snap-through behaviour, confirming that stability is lost when the available vertical load falls below roughly 35–40% of the ruling span. The assessment confirmed that the high wind case produces greater swing and loss of restoring moment when compared with combined wind and ice cases.

By establishing limits for span sectioning, minimum weight spans, and tension support frequency, the study contributes further insight into the design challenges associated with the application of H-Vees. The case study demonstrates the challenges for profiling an OHL with

H-Vees in undulating terrain and the consequences for support heights and ultimately cost. The work directly supports the objectives of CIGRE Study Committee B2 and aligns with the objectives of WG B2.96 (Composite Insulated Cross-arms for New-build and Retrofitting) [1], particularly in “developing analytical models to evaluate the longitudinal stability of pivoting cross-arms and defining mechanical design procedures for complete composite ICA assemblies.”