Compact “5-Phases” OHLs: Performances and EMFs

Compact ac Overhead Lines (OHLs) are an effective solution for addressing the needs for reducing EMFs and increasing the active power transfer across existing Right-Of-Ways. Terna, the Italian Transmission System Operator, has recently introduced a new compact solution for HV and EHV lines (the so-called “5-Phases” or “5F”) allowing for a substantial reduction of EMFs exposure and increase of power transfer capacity, if compared to conventional OHLs. Due to the reduced visual impact and EMF, 5F lines can thus be an effective and efficient solution for the refurbishment of existing AC backbones. The proposed line design adopts conventional solutions for towers, insulators, conductors, allowing for a cost-effective adoption without sacrificing mechanical performances. The paper presents the electrical and mechanical performances of 5-phases OHLs, in terms of loadability, insulation, and EMFs. Application to different standard voltages (150 kV, 230 kV, and 400 kV) as well as higher voltages, usually adopted for long-distance transmission (i.e., 735 kV), shows that the novel line configuration can transfer up to 3200 MW at 400 kV over a 400 km distance and up to 6000 MW at 735 kV over 1000 km distance subject to conservative angle displacement and voltage drop limits. At the same time, it can deliver 1000 MW at 230 kV and 483 MW at 150 kV, achieving very low EMFs values, allowing for bulk energy transfer also in urbanized areas.