Siemens G120 variable frequency drives 2

[nelson1805]

I've asked this question before, but I can't find it anywhere in the forums. I'll try again.
Has anyone experienced any problems with the Siemens G120 VFD's?
We have experienced flash overs between the dc link bus bars which destroys the main rectifier. When the faulty inverters are changed, we remove the bus bars to reduce the possibility of a similar failure.
When we talk to Siemens engineers about the problem, they infer that it is an ingress of carbon particles (the inverters are used for a newly installed carbon fibre production line) which reduces the resistivity of the air separating the bus bars to the point of flash-over. The panels which contain the VFD's are remote from the production line and great efforts are used to ensure that there is no ingress of contaminants.

 

[jraef]

You removed the bus bars? How does the drive function then? Are you replacing them with wire?

I am familiar with the G120, I have never experienced anything like that. Ozmosis, another member here, is also very familiar with it, hopefully he will chime in as well.

Is it the DC link bus that is flashing over, or is it happening in the rectifier? If I recall, there are issues having to do with the system grounding that must be dealt with in the rectifier by removing or installing a ground strap. Memory fails me to remember which way it went, but it was in the installation manual and if the original installer didn't understand the importance, that may have been an issue.

Also, are you aware that Siemens runs their own user forum? You can get help from people with a lot of very specific experience there.


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[ozmosis]

I'll try and chime in..
I'm aware of issues in the MM4xx series with actual distances between the DC link (external) connections and this was supposed to be overcome with the PM240 and PM250 power modules (used on G120 range). It was related to the physical distance between the DC terminals and the tracks on the power boards.
Ingress of carbon material could be the cause. I know of a similar site where hessian was being burnt outside the plant-room and entered the airflow feeding the plant room and minute particles of carbon caused small levels of arcing on the boards. This level of arcing introduced a plasma flow over the board and this, I recall, is flammable.
It was found that it was not actually the 1st stage of ingress of carbon particles but the eventual impact of arcing creating this flammable gas that ignites and causes the board to fail with a major flashover.
Regarding your actual problem.
Ingress of conductive particles within your panels is a constant battle. Design of airflow feeding the panels is often critical. We have recently been working on an Aluminium plant and here there are issues with conductive particles floating around and we have designed a system with improved airflow management around the drives for higher power units and for lower power units have simply introduced IP66 rated VFD's inside the panels. The issue was that anyone simply opening the door with find the inside of the panel brings in the conductive material and once closed the internal fans were simply blowing this around the inside of the enclosure.
However, the G120 has limited scope to introduce higher IP rated drives and no capability to vent airflow away from the sensitive power sections. The G120 drives have certainly improved over the MM4xx range as they now route the airflow over the heatsink rather than electronics but this still not stop conductive material getting onto the power section due to the "cheese-grater" design of the enclosure (I think you know what I mean there..).
It might be a viable option to get the boards coated. You will have to go to an external company to do this as Siemens do not do it themselves.
I do not work for them anymore and haven't for 3 years so maybe things have changed since then.
Maybe ask them to come up with a solution rather than telling you what the actual problem could be...

 

[nelson1805]

I would like to thank jraef and ozmosis for their replys.
First jraef. The dc link bus bars which were removed were the solid copper bars which connected the pcb to the vfd terminals. These terminals were not used so the bus bars were removed as they provided an ideal path for flash-over.

Next ozmosis. Your description is exactly what has been happening. I have since modified the cooling of the vfd panels so that the air circulates via heat exchangers, rather than drawing outside air into the panels (even though the air was filtered). Since this has been done we have not had so many flash-over problems (not until a panel door was opened).
I have had many discussions with Siemens about the problem. Unfortunately they don't seem to take any suggestions on board. I would have thought it would be in their own interests to make their drives more robust.

 

[Feg]

Guys,

SIEMENS now offer a Sinamics G120P

. With operator unit: IP54/UL Type 12
• With blanking cover: IP55/UL Type 12

Don't know if this helps.

FEG