Addressing audible noise challenges in the integration of the 6 x IEC 315 conductor on South Africa’s 765 kV transmission network

Audible noise is a key consideration for regulatory compliance and minimizing disturbance to nearby communities. Additional factors assessed include capital and maintenance costs, thermal ratings, electrical losses, SIL and system behaviour, for both the 6 × Tern bundle and the proposed 6 × IEC 315 alternative. Technical evaluations confirm that both conductor options meet the required electrical performance criteria for 765 kV transmission, with audible noise identified as the primary technical challenge on the 6 x IEC 315 conductor. A system life cycle cost (SLCC) assessment indicates that savings in initial capital cost significantly outweigh other cost components.

The IEC 315 conductor offers substantial capital savings, estimated in the range of hundred millions of rands ($5.4 millions of USD) for 2,100 km of new lines (Lines 1 to 6 indicated in Table 1), making it an attractive option from a cost-efficiency perspective. While the 6 × Tern conductor offers higher loss-related savings, the significant capital cost savings achieved by using the 6 × IEC 315 conductor still result in lower system life-cycle costs over a 25-year study period.

The smaller diamter (23.90 mm) IEC 315 conductor results in higher electric field intensity at the conductor surface, which increases corona activity and can lead to elevated audible noise levels, particularly under dry night-time conditions and at higher-altitude sections. These factors necessitate a detailed audible-noise assessment to ensure compliance and minimize potential community impact.

A structured concept-phase methodology was applied, combining route analysis, desktop environmental assessment, and technical simulations. Audible-noise simulations were conducted using Mathcad-based models derived from historic Eskom corona studies. The study considered route-specific parameters including altitude variations, tower types and phase spacing, and environmental conditions such as temperature, humidity, and wet and dry scenarios during day and night. Conductor sag and resulting noise levels were evaluated under night-time low-temperature conditions, which influence conductor height above ground and audible noise.

Lower-altitude sections were found to improve corona performance, supporting the feasibility of the IEC 315 conductor. Design mitigation strategies were considered to manage potential noise exceedances, including optimized conductor bundle spacing, incremental tower-height adjustments, and span modifications. The study demonstrates that through careful planning, targeted design interventions, and adherence to Eskom guidelines, EPRI guidelines, and SANS 10103 limits, smaller-diameter conductors can be deployed without compromising technical compliance.

Overall, the 6 x IEC 315 conductor provides a cost-effective alternative to traditional 6 × Tern bundles, enabling significant capital savings while meeting technical requirements and maintaining system and operational reliability. With appropriate design optimizations, audiblenoise levels of the IEC 315 conductor can be managed to meet guideline thresholds, ensuring minimal environmental and community impact. This work supports Eskom’s objectives of expanding transmission capacity, integrating renewable generation, and achieving infrastructure cost efficiencies, while maintaining high technical and operational standards.