Impact of Proximity Effects on Sheath Losses in Trefoil Cable Arrangements

Abstract

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.

Loss Allocation in Submarine Armored Three-Core HVAC Power Cables

“…It is observed how the analytical approach underestimates the sheath losses, with differences generally greater than 10 %. This is in good agreement with [1], [15], where it is suggested that 𝑃𝑃 𝑠𝑠 𝑒𝑒𝑐𝑐 may be proportional to circulating losses, especially in larger cables, so 𝜆𝜆′′ 1 should not be neglected. If so, better results are obtained (Fig.…”

Use of 3D-FEM Tools to Improve Loss Allocation in Three-Core Armored Cables

“…Another point of controversy is found in the bibliography regarding the source of the induced losses in the sheaths. Some studies [6,7,33,34] suggest that eddy-current losses may be proportional to circulating-current losses for large cables, so they should not be ignored in the computation of the SB-case sheath losses. However, there is no expression in [5] especially designed for evaluating eddy losses in this type of cable (Equation ( 7) is in fact only valid for SP single-core cables).…”

“…As mentioned before, there is a controversial point regarding loss allocation in the sheaths, since [5] assumes that eddy losses may be neglected when sheaths are in SB, although some studies suggest the opposite for large cables [6,7,33,34]. Therefore, to clarify this point it is required to find a way to evaluate these terms separately, especially in TCACs.…”

“…It is also noticed that Equation (26) overestimates the induced current in the cases with no armor and stainless-steel armor. This is a consequence of the non-uniform current density distribution in the conductors due to skin and proximity effects, something not considered in Equation (26), where I c is assumed to be applied in the center of the conductor [10,33]. Therefore, both Rs and Xs are also affected by all these aspects.…”

Active Cable Sheath Current-Based Protection Scheme for an Offshore HVAC Wind Transmission System

“…For these single-core cables, to limit the circulating current on the metal outer sheath of the cable under normal operation, the metal outer sheath of the cable is generally grounded at a single end or cross-connected. Song- Wang et al (2018) and Chatzipetros and Pilgrim (2020) analyze common cable faults and divide them into the following six types: harsh environment, man-made damage, factory defects, nonstandard operation or untimely maintenance, and equipment aging (Zhang et al, 2021). The statistical data of cable fault current provided in Li et al (2019a) show that a large number of cable faults would lead to excessive sheath current, resulting in insulation damage of cable sheath and insulation breakdown between cable sheaths.…”