Application : Tower crane

We are using Sinamics G120(PM240-2, 6SL3210-1PE31-8AL0) + DBU(6SE7032-7EB87-2DA1-Z M08).

During hoist down, the capacitors in DBU are heating up. Very hot, and actually one DBU was blown(capacitors got blown). When we trace the dc link voltage of the drive at hoist down, the voltage fluctuation is around 100Vdc, very severe.

When we put the DBU to S120, it is well working..

As we know, the major difference between S120 and G120 is internal dc reactor.

What is the root cause of the trouble?

Please provide motor name plate details, hoist lowring speed & total time it takes to complete one hoist lower travel stroke. Please arrange to provide braking resistor details.

We use external DBU, since we though the braking power rating of the internal chopper is not enough to cover the regen power at hoisting down.