1. Professor, Dept. of Railway Engineering, Faculty of Civil and Environmental Engineering, Gdansk Univ. of Technology, 80-233 Gdansk, ul. Narutowicza 11/12, Poland (corresponding author).
2. Dept. of Power Electronics and Electrical Machines, Faculty of Electrical and Control Engineering, Gdansk Univ. of Technology, 80-233 Gdansk, ul. Narutowicza 11/12, Poland.
3. M.Sc., Dept. of Railway Engineering, Faculty of Civil and Environmental Engineering, Gdansk Univ. of Technology, 80-233 Gdansk, ul. Narutowicza 11/12, Poland.
4. Dept. of Railway Engineering, Faculty of Civil and Environmental Engineering, Gdansk Univ. of Technology, 80-233 Gdansk, ul. Narutowicza 11/12, Poland.