Research Of The New Method For Discriminating The Magnetizing Inrush Current In Transformer

When we connet a transformer to the system without load or remove its exterior fault,it will bring magnetic inrush current,but when there is short fault happened in the coil-to-coil or coil-to-earth,it will bring internal fault current.Because the differential protection has some theory deficiency as transformer main protection,so we need to discriminate that two kinds of current correctly. Because the complexity of the magnetic inrush current,after doing a lot of simulations and tests,we put forward a new method for discriminating the magneting inrush current based on integrating the characteristics of the two kinds of current in this paper.Because of the character that the magnetic inrush current leans to the one side of the time axis and the internal fault current is similar to the sine wave,so we use the difference between the maxmum and minimum and the unitary area in cycle as a general criterion to discriminate the unsymmetrical inrush current . For the symmetrical inrush current,we set a second criterion,which needs to calculate the average standard deviation of the 2- norm between the part data in the half cycle and the sine wave with the same length.We vertify the validity and the feasibility of the new method according to simulating and testing.