At work I have a machine with 9 small Variable Frequency Drives powered on a common DC bus from a very large Variable Frequency drive through sliprings. There are 50A main DC bus fuses and 16A fuses on each of the small drives. all the small drives are in parallel. see drawing attached. twice in the past week, all of these fuses have blown simultaneuosly. I can't figure out WHY. The HOW is already figured out: I found a short between + and - near the sliprings. In my quest to figure out WHY, I contacted the manufacturer and they said to check for a short near the sliprings; I told them I already found that and they basically said "well, there you go" and didn't give me a WHY. In my thinking, if a short occurred near the sliprings, only the main bus fuses would blow. if the short occurred on one of the small drives then the smaller 16A fuses for that drive (that drive only) would blow; worst case scenario, both the 16A fuses (for that drive) and the 50A main bus fuses would fuses blow. I cannot think of a scenario other than all 9 small drives simultaneously shorting out and blowing their fuses withinin the fraction of a second that it takes the main bus fuses to blow. any insight?
FYI, while running, these small drives (all 9) draw about 2A combined, whether accelerating, decelerating, or running constant speed.
FYI, while running, these small drives (all 9) draw about 2A combined, whether accelerating, decelerating, or running constant speed.
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