An Intercomparison of Weather-Based Thermal-Rating Methods for a High Voltage Transmission Line in British Columbia

To determine the amount of electricity a high voltage transmission line can safely transmit at a given time, power utilities have consistently used conservative assumptions of weather variables that affect the temperature of the transmission line conductor.  This leads to transmission lines being greatly underutilized, and at risk for damage when weather conditions do meet the assumptions used in static thermal ratings.  Alternatively, thermal ratings that use real time weather conditions are more realistic.  These dynamic thermal ratings allow transmission lines to be used more efficiently and safely, however they are more expensive and difficult to implement. 

Here, thermal ratings, ranging from static to quasi-dynamic to dynamic, will be compared in an effort to show the extent to which real-time weather conditions can improve a thermal rating.  All thermal-rating methods will be applied to a span of a high voltage transmission line located in British Columbia.  Air temperature, wind speed, and wind direction observations from nearby weather stations will be averaged over different time periods for quasi-dynamic thermal ratings, and the real-time values will be used in the dynamic thermal rating.  Quasi-dynamic thermal ratings will be developed that incorporate averaged and real-time values of weather conditions.  Dynamic thermal ratings will be computed using ensemble numerical weather model output of the same parameters at every point along the transmission line span. Finally, probabilistic dynamic thermal rating forecasts will be produced using ensemble output to supply a quality thermal overload risk assessment product.