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 ( λ ₁ ), 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 export cables in the Offshore Wind Farm 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 two-dimensional finite element models to evaluate how accurate the Standard method for calculating the λ ₁ factor is in cables with a nonmagnetic armor. Their validity is further enhanced by means of filament method. The 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.