A cost effective solution for increasing ratings on underground transmission cables-a case study

The capacity of four parallel 69 kV pipe type cable circuits was evaluated based on measurement of load and temperature data and thermal modelling. Summer normal and emergency ratings were lower than required. The alternatives considered to achieve the rating increase are discussed. Increasing the usable capacity by implementation of a dynamic real-time rating system was recommended. The dynamic rating system, installed in 1997, has provided improved ratings which so far has deferred or possibly eliminated the need for circulation equipment.