causes of overvoltage on power semiconductor devices External reasons 4 Overvoltage caused by operation of mechanic withes 4 Overvoltage caused by thunder lightening Internal reasons 4 Overvoltage caused by the reverse recovery of diode or thyristor 4 Overvoltage caused by the turning-off of fully controlled devicesPower Electron cs i 10 Causes of Causes of overvoltage overvoltage on power on power semiconductor devices semiconductor devices External reasons External reasons Overvoltage Overvoltage caused by operation of mechanic caused by operation of mechanic swithes swithes Overvoltage Overvoltage caused by thunder lightening caused by thunder lightening Internal reasons Internal reasons Overvoltage Overvoltage caused by the reverse recovery of caused by the reverse recovery of diode or thyristor diode or thyristor Overvoltage Overvoltage caused by the turning caused by the turning -off of fully off of fully - controlled devices controlled devices