Rating Impact of Non-isothermal Ground Surface (RINGS)
National Grid Electricity Transmission
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Network Innovation Allowance
The IEC 60287 standard describes algorithms for use with various cable laying conditions including shallow buried cables. The
standard assumes ground surface temperatures to be isothermal. The FEAR R&D project undertaken by Southampton University
confirmed that the use of isothermal surface temperatures was valid for cables buried at more than 1 metre depth but for shallow
buried cables, including those in surface troughs; this assumption was shown to be optimistic, leading to possible overrating of such
cables. Conversely cables may be underrated to mitigate for the unknown affect of non-isothermal temperatures.
The objectives for this project are to;
Understand how the ratings of shallow buried cables and cables in surface troughs are affected by non-isothermal boundary temperatures; and
Recommendations for temperature conditions to be used in modelling of shallow buried cables and cables in surface troughs.
This project will be successful if we understand in greater detail the issues around Cable ratings in non-isothermal ground surfaces.