A New Drying System for the Continuous Desiccation of Power Transformers, Function - Operation Experiences

Tthe application of insulating liquids together with a solid insulant immersed therein is used sinse more than one hundert years in transformers and it seems to be used also in the futer especially in power transformers. A significant risk, reducing the strength of such insulations, is water, thus drying procedures are required to extend lifetime and operation reliability. Actually transformer drying is in most cases performed as a maintenance action where it is tried to remove water by vacuum and heat. Such a procedure has to be performed offline and also comprises the risk of insulation endangerment. Such disadvantages can be avoided by an online drying procedure which is not only valuable for aged insulations where it increases the residual lifetime but also for new devices where it reduces the risk of early outages. In this contribution an innovative procedure for the drying the insulation of power transformersduring service is introduced. This procedure not only performs a complete desiccation, it also purifies the liquid without influencing the dissolved gas analysis (DGA) or any other physical property. The application of the system on a power transformer has shown, that the procedure is beneficial for insulating liquids as well as for solid insulations immersed therein.