Voltage withstand tests on a full scale overhead line tower model for line upgrading

In times of rising electrical energy demands, higher transmission capacities are getting more and more important; in Europe as well as all over the world. The construction of new overhead lines is not only cost and time intensive, but it is also difficult to get permits. For that reason the trend is towards upgrading the existing grid to higher operating voltage levels, which raises issues in terms of insulation coordination. Especially the dimensioning of required clearances at the overhead line towers is an important point to ensure a safe electricity transmission. These clearances are influenced by the lengthened insulator string as well as environmental factors. In a cooperative research project between Statnett SF and Graz University of Technology a full scale model of a part of an affected overhead line tower has been designed and constructed. Using this model, impulse voltage tests have been performed for several gaps to investigate the gap factor and the withstand behavior. Furthermore the given gap factors in the European standard EN 50341 have been evaluated and compared with the experimental values within the project. This paper will present the development of the model and a summary of the results of the full scale tests as well as some background on the required clearances.