1. 1 Faculty of Electrical Engineering and Information Technology , University of Zilina , 8215/1 Univerzitna, 01026 Zilina , Slovakia
2. 2 Department of Electrical Devices and High Voltage Technology, Faculty of Electrical Engineering and Computer Science , Lublin University of Technology , 38A, Nadbystrzycka Str., 20-618 Lublin , Poland
3. 3 Department of Electrical Engineering , Cracow University of Technology , 24, Warszawska Str ., Kraków , Poland