Experiences and Actual Research in Controlled Unloaded Transformer Switching

Electricity market Liberalization, electricity industry deregulation, new/distributed energy sources and emerging technologies as a \u22Smart Grid\u22 will increase the amount of switching situations. A random, unloaded transformer energizatinn leads to high inrush currents and voltage disturbances, which can cause unnecessary operations of protection relays and impose mechanical stresses to the transformer windings. Situations have been reported, whereby intensive anda repetitive inrush currents enen caused a thermal explosion of a power transformer. A conventional solution for these issues it to apply a per-insertion resistor. However, the application of a pre-insertion resistor and especially its maintenance are cost intensive and therefore, investigations on controlled transformer core after an unloaded transformer de-energization. First field experiences could br obtained in the year 2004/2005. This papaer shows state of the art techniques of actual controlled systems and proposese new research items