Dynamic Line Rating of overhead transmission lines under natural convective cooling

One of the problems for the implementation of a Dynamic Line Rating Scheme (DLRS) in Switzerland is that the wind, the largest cooling mechanism for a transmission line, can not be reliably predicted. A first step to deliver a practical solution for this problem requires an assessment of the worst-case-scenario for the convective cooling power of lines. That is, the situation when only natural convective cooling is present. In this document it is reported an experimental study of the natural cooling power on an All Aluminum Alloy Conductor (AAAC) used in the Swiss transmission grid. Then it is shown that the formulas available in the literature for natural convective cooling power follow closely the experimentally measured natural cooling power. Also, a natural convection worst case scenario is evaluated by comparing a zero-wind DLRS with the seasonal line rating scheme which is currently in use in the northern low lands of Switzerland. This comparison shows that the use of a DLRS can help to assess the safety and current capacity of the grid.