The field experience of a dynamic rating system on overhead power transmission lines

Considering the safe operation of power grid, the actual thermal capacity of overhead transmission lines is far above their designed thermal capacity. How to fully explore the potential capacity of the existing overhead transmission lines becomes one of the greatest concerns. We propose a fire-new model for calculating the real maximum thermal capacity of transmission lines, high temperature equivalent model (HTEM). This model does not need to measure meteorological parameters, such as ambient wind velocity, ambient temperature and sunlight intensity. Therefore, the computational accuracy of real maximum thermal capacity is greatly improved. An on-line monitoring system has been designed, not only to carry out the new model, but also to measure the wire temperature, current and sag. The system has already been trial running on 110kV∼500kV high voltage transmission lines for more than 30 months. The data obtained by the system has provided a strong evidence for this model.