Variable Speed Drive – Hope Nobody Was Near When These Two IGBTs Blew Up
A long standing client brought in a VSD which was installed in their customer’s machines. Our client did not know the actual fault but said he smelt charcoal when he put it in his van. No fault description, manuals or schematics could be provided which is the status quo for most of our repair requests 🙂
The Siemens Micromaster 440 Inverter Drive is the size of a small suitcase. It specs label it as a 55Kw high performance vector controlled inverter. Siemens proudly rate this VSD to withstand 200% of its rated current for 3 seconds, and 150% of the rated current for 60 seconds. We have seen this type of VSD from other clients and we knew whatever the fault was, it was going to be BIG. The drive did not disappoint.
When we opened up to inspect, what we saw was captured in the picture above. Two IGBTs were catastrophically blown apart and the damage to the control circuitry was extreme.
As the control circuit board was mounted directly above the IGBTs, the underneath side of the control board was badly burnt and soot stained. Our thoughts were this VSD has seen a huge surge in current for a sustained length of time, and hopefully no one was standing near it.
From experience, we knew that the IGBTs were discontinued so we referred to our repair database and identified the exact same replacements. We also cleaned and fully refurbished the control circuit board (that took some hard scrubbing) by replacing most of the components. After inspecting all of the other printed circuit boards in the drive, we connected to our test bed and followed our QA procedure to check and test it operated as new.
Our client was delighted as he was able to tell his customer that the drive is fully operational at a fraction of the cost of a replacement.