Impact of proximity effects on sheath losses in trefoil cable arrangements

Induced losses are a significant part of the total losses generated in HVAC cables. Presently, IEC 60287-1-1 is used to calculate the ratio of induced loss in a cable's metal sheath to its conductor loss (λ1), assuming uniform current density in both conductors and sheaths. Although this assumption is reasonable for smaller cables, it is questionable for larger cables in close proximity, such as three-core (3C) export cables in Offshore Wind Farm (OWF) projects. The effects of this non-uniform current density cannot be easily treated via a straightforward, purely analytical approach, since conductor currents are not effectively represented by linear ones in larger cables, while sheath currents are also unevenly distributed. The present study employs 2-D Finite Element (FE) models to evaluate how accurate the Standard method for calculating the λ1 factor is in cables with non-magnetic armor. Their validity is further enhanced by means of Filament Method. IEC 60287 appears to overestimate the temperature, particularly for larger conductor sizes, by up to 7°C (8%). Finally, suitable Reductive Factors are suggested which could improve the accuracy of the IEC method