Ricerc@Sapienza

In view of the contemporary scenario and importance of alternative liquid dielectrics, IEEE DEIS Technical Committee on Liquid Dielectrics laid emphasis on pre-breakdown phenomena of ester dielectric fluids. The present article reports the background knowledge on the breakdown theories and behavior of streamers in insulating oils. The major influencing properties of the streamers aroused in liquid insulating systems are discussed keeping in view of the ester based dielectric fluids.

Over the past years, there has been an increasing interest in natural ester insulating liquids for application in power transformers, thanks to their higher environmental compatibility and lower fire point, as compared to conventional mineral oils. The main function of a transformer oil is its ability to dissipate heat, while ensuring electrical insulation. Among the various influencing parameters, it is well known that heat exchange in a liquid is also affected by its viscosity.

The recent evolution in electricity distribution systems has led to the development of new intelligent structures, better known as Smart Grids, Microgrids and Prosumers. The consequent advantages regard mainly both economy aspects and environmental safeguard. In a microgrid, producers and consumers can exchange energy in peer-to-peer way. Normally, the microgrid is connected to a Smart Grid in a single common point. In this case, the microgrid can be easily disconnected from the external grid and continue to work in 'island' mode.

Power transformers represent the highest value of the equipment installed in transmission substations, comprising up the 60% of the total investment. They are expected to operate for several decades without faults and possibly without relevant unscheduled maintenance practice. The new approach is developed for reducing time based maintenance and, increasing condition based maintenance and to introduce predictive maintenance as well.