Untersuchungen zur Strombelastbarkeit der Geräte der Elektroenergieübertragung unter Freiluftatmosphäre

Due to the liberalization of the electricity market and the increasing expansion of the generation of wind power the transport of electric power in the power grid is increasing. Due to that the electrical equipment is loaded higher up to its thermal limits. However the electrical power supply should be anytime reliable. Because the new construction and upgrade of overhead lines and substations is expensive and approval procedures can take up to ten years, solutions have to be found, to ensure in short and medium term the transport of electrical power through the power grid. In this paper a possibility is introduced and analyzed to increase the current carrying capacity of the electrical equipment without carrying out extensive reconstructions or new buildings. For that the method of thermal networks is used. For the different devices of the electric power transmission (overhead lines, electrical fittings, circuit-breaker, disconnecting switch and current transformer) thermal networks are designed. The heating on examples of all devices was studied and tested under laboratory conditions and the thermal networks were verified. By expansion of the thermal networks with elements for forced convection (wind velocity) and additional heat sources (solar radiation) the ambient conditions were considered. With the help of the so expanded thermal networks parameter studies depending on the wind velocity, ambient temperature and solar radiation were carried out. The studies showed that depending on the ambient conditions the current carrying capacity of all devices can be increased without changing the devices. The rated currents of all devices are specified for a high ambient temperature (e.g. 35°C) and low wind speed (e.g. 1 m/s). Most of the time in a year the ambient temperature is lower and the wind speed is higher than the specified values. So the devices can carry a higher current than the rated current without exceeding its thermal limits. The calculations show the possible increasing of each device depending on the ambient conditions. For completing the results weather data have been collected and analyzed. When increasing the current it has to be noticed that the devices will age faster due to the higher operating temperature. Exemplarly calculations on an electrical fitting show how the increased current cause a considerable reduction of the life time of the fitting. So when loading the overhead lines and the other components with higher currents, depending on the ambient conditions, the grid should be regularly checked to avoid early failures. The studies introduced in this paper should help to take decisions by increasing the current carrying capacity depending on the ambient conditions considering all the mentioned aspects.