Fuse blowing (F002)

I have a SIMOVERT VC INVERTER 6SE7018-0TA21-Z with a 540V DC mains input, supplied by a rectifier (6SE7028-6EC85-1AA0). This rectifier feeds four different drives, including this one. Each drive has its own separate external fuses, which are not part of the drives themselves.

The other day, while all the drives were running, we needed to work on this particular drive. We stopped the drive and removed the external fuses to cut the DC supply. After completing the work, we reinserted the external fuses while the 24V DC connector was still connected. As soon as we reinserted the external fuses, we heard a pop. We ignored the sound and attempted to start the drive, but it displayed an F002 alarm.

Upon dismantling the drive, we found that the internal fuses in the power section had blown. After replacing the internal fuses, the drive operated normally again.

I should note that the rectifier was still running when we reinserted the external fuses, as we couldn’t stop the other drives. Therefore, when the external fuses were reinserted, the DC supply was applied instantly. Additionally, the 24V DC connector was still plugged in at the time.

Does it matter that the 24V DC connector was still connected when we reinserted the external fuses? I want to understand why the drive's internal fuses blew. Did this happen because of the capacitor charging? My colleague suggested the internal fuses blew because the rectifier was on and the 24V DC connector was still connected when the external fuses were reinserted. However, I don’t think it makes a difference whether the rectifier is on or not when reinserting the external fuses, as the DC supply would be applied in either case whether re-inserting the external fuses or by turning on the rectifier.

What caused the internal fuses to blow, and how can we prevent this from happening again in the future? This has already occurred twice.

Note:

External fuses: Not part of the drive. Externally installed. These didn't blow. These fuses were removed and reinserted

Internal fuses: These are inside the drive feeding the whole power section. These popped and blew when the external fuses were put back in. These were then replaced. 

Technology Team

Hello,

please refer to the Masterdrives catalogue note:

"The DC bus must be in a de-energized state when inverters or braking units are switched in or out."

If this is not the case and no external pre charging circuit for the DC link capacity exists, fuses blow or even the inverter itself can be destroyed by direct switching to a charged DC link.

To get more information, you could also refer to the application note for SINAMICS S120 regarding that topic.

Ok. As far as I understand it this is how it works. When I connected the inverter to the already live DC bus it supplied maximum power to the inverter and there was an inrush current because the DC bus tries to charge the inverter's capacitors almost instantly. But if the rectifier is turned off first to deactivate the DC bus and then the inverter is connected to the bus and then the rectifier is turned on the inverter fuse won't blow because the rectifier will gradually charge the inverter's capacitors through its own inbuilt pre-charging circuit and limit the current. Am I understanding it right?