Condition Assessment of Transmission Network Infrastructures (April 2007)

Electrical transmission infrastructures operate usually well over many decades of years before degradation processes appear. Nowadays the competitive market environment drives the electric power industry to minimize the effects of this potential function loss of high voltage systems effectively by well focused asset management. The prevailing technical status of individual assets turns out to be an information source of crucial importance in this regard. Different data from technical diagnostics and from economical and societal strategic requirements are taken together using condition indexes, which are transferred to integral knowledge rules in a decision support system. Experiences with condition assessment of high voltage components in 50-380 kV transmission networks in the Netherlands are discussed. The actual performance of equipment is obtained by using advanced, non-destructive on-site and online techniques such as non-conventional partial discharge diagnosis methods for detecting and localizing the weak spots, e.g. cavities in XLPE cable insulation. Furthermore global indicators like tan-delta losses and DGA are used to assess the overall degradation phenomena as these occur in oil, paper-oil or mass insulation. To diagnose the vulnerable part of a power transformer, i.e. the on-load tap changer, resistive contact wear measurement is a very adequate tool. Based on criteria developed for each component and each diagnostic tool, all different information sources are processed together for asset classification into three maintenance categories.