Inverter motor side
Inverter motor side
(OP)
Hi,
Please find attached damage caused to one IGBT module on a ACS800, 250 kW 400 V regenerating drive. The drive is used to power a centrifugal machine. There are three IGBT modules in parallel but only one module is affected. I don't think the failure was caused by a surge, any guess !
Thanks
Guardiano
Please find attached damage caused to one IGBT module on a ACS800, 250 kW 400 V regenerating drive. The drive is used to power a centrifugal machine. There are three IGBT modules in parallel but only one module is affected. I don't think the failure was caused by a surge, any guess !
Thanks
Guardiano





RE: Inverter motor side
RE: Inverter motor side
Was that on the line side or the load side transistors? My guess would be the line side, they are much more susceptible to line transients. That's one of the significant down side risks of line regen VFDs that is often downplayed by the salesmen. Diode bridges, for all their faults, are comparatively much more robust. IGBTs on the front end of the drive means you have twice as many potential events to manage in terms of protection and if one small component failure takes that out, the failure of the IGBTs is eminent. Shoot through is the result of mis-firing of the IGBTs, which can happen from high di/dt events. On the load side, that is relegated to load shorts or ground faults. On the line side, add all sorts of potential transient events that you have little control over.
"Will work for salami"
RE: Inverter motor side
IGBTs do not like floating with reference to the ground and the mains supply / DC+ and DC- that they are switching compared to ground should be fixed and preferably equal.
I think it's to do with the stray capacitance between the IGBTs and their mounting arrangement.
ABB may want you to replace all modules in parallel as all IGBTs will have been stressed.
RE: Inverter motor side
"Will work for salami"
RE: Inverter motor side
Guardiano
RE: Inverter motor side
One of the problems associated with inverter drives is that damage can happen MUCH faster than anything can react to it. That's one reason I always recommend using reactors in drives, it slows down the rise time of transients to give the electronics a fighting chance to react and possibly prevent catastrophic failures like this. Many people perceive that reactors only serve to reduce harmonics, so when they buy an expensive AFE drive they feel that a line reactor is redundant, which exposes the AFE front end even more to line transient risks. Salesmen who just got through convincing someone to spend twice as much on a drive just to reduce harmonics are then often loathe to recommend a reactor anyway and so end up further complicating the risk factors. I can't tell you how many times I have been in situations where end users are evaluating a project proposal from me, see the reactors, and say, "Well, XYZ company is not including reactors, so are you saying your proposal is using drives that are less robust?" They just don't get it, reactors are like cheap insurance, but if people are overly sensitive to price, they can end up costing themselves a lot more than the bargain they thought they were getting.
OK, rant complete, sorry if I went too far off on a tangent there.
Back to your problem. Did you follow the special ground connection instructions in the installation manual with regards to high impedance grounded systems by the way? It's been a while since I have read an ACS800 manual, but I believe that they, like all VFD mfrs I have dealt with, have these special instructions regarding the way their surge protection devices on the front end must be reconfigured if the line power grid (network) is resistance or impedance grounded, or ungrounded as is somtimes the case here in the US. If you don't follow those instructions to the letter, you can end up having those SPDs fail catastrophically and take out other components around them, or just leave the drive with ZERO surge protection for the next event, even a low level one.
"Will work for salami"
RE: Inverter motor side
RE: Inverter motor side
Would it be, by any chance, the drive with the longest leads to the motor that failed?
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Inverter motor side
RE: Inverter motor side
Thanks again for the replies. The motor leads are relatively short, the longest is around 20 metres. Surprisingly, there is no DC bus fuse on this regen drive and the flash did not result in any blown fuse on the supply side. I'm looking for the root cause of this breakdown. I can only conclude, for the time being, on a weak supply line.
Guardiano
RE: Inverter motor side
Looks to me like damage to all three modules, not just one.
Do look hard at the grounding and surge protection.
If the supply is not robustly grounded, then any switching transients can cause all three phases to jump relative to ground, at the same time. I have seen transients to ground of thousnads of volts caused by MV and HV power factor correction switching. The transient is capacitively coupled from the primary to the secondary of the distribution transformer.
As the voltage transient is not phase to phase, it is phase to ground, it will not damage the input rectifiers, but this transient cuases the DC bus to move relative to ground and the capacitance of the motor and cables to ground try to hold the transient via the IGBTs.
The speed and energy can be sufficient to cause damage.
Mark Empson
Advanced Motor Control Ltd
RE: Inverter motor side
Thanks for your comments. You're right, the three modules are damaged but these are the modules on the u-phase only.The neutral is not solidly grounded but high-impedance grounded.I tend to agre with your conclusion.
Guardiano