DC bus operation, Drive system, blowing of fuses when connecting the mains

Question:
Why do the fuses sporadically blow (mains-side fuse or DC-bus fuse) when starting a drive system with central supply?

Answer:
The cause might be the selection of the fuses of the central supply. With mains connection of drive controllers with DC bus there are increased charging currents under normal operating conditions. The initial charging currents of the different frame sizes depend on the DC bus capacity and the type of charging current limitation. For the fuse selection the regular initial charging currents of the different controllers are to be considered in order to avoid activation when switching on the mains.

Blown fuses in spite of correct fuse selection:
If a drive system supplied centrally via a supply unit (9360) or by a regenerative power supply unit (9340) also contains 9321, 9322, 8241 or 8242 drive controllers (small units), the connected mains fuses or the DC bus fuses release, especially when the minimum time according to the Operating Instructions are not adhered to. In this case, especially high initial charging currents of the above-mentioned axis controllers might occur.
For these drive controllers (smallest frame sizes of the series) the switch-on charging current limitation for the DC bus is realized by a NTC resistor. If the drive system was restarted too early, these resistors would have not cooled enough and would therefore have a too low resistance to sufficiently limit the switch-on charging current. A restart at this point leads to an especially high initial charging current, which may cause a release of the fuses.

Remedy:
After switching off the mains must not be switched on again within 3 minutes on the control side. Further information regarding minimum time for mains connection can be found under Doc-ID 20023430 'Mains connection, minimum time for switching cycles, charging current limitation'.