Opinions on non-standard and non-contiguous MV drive configuration
Opinions on non-standard and non-contiguous MV drive configuration
(OP)
I'm being asked to bid on a project that involves retrofitting a Medium Voltage VFD into an existing facility that has a MV MCC in place already, and there is no space in the room to fit the MV VFD in it's entirety. The VFD is a VSI drive with an 18 pulse front-end, so it has a large transformer and rectifier section, followed by an inverter section with the DC bus caps etc. In the engineer's mind, he wants to separate the two components; the transformer/rectifier on one end of the room, the DC bus section / inverter on the other end of the room at either end of the MV MCC, a distance of approximately 20ft, with a cable/conduit connection at roughly 6kVDC between the two. They want to lay the MV DC conduit on top of the existing MCC, against the wall.
I'm not really comfortable with this arrangement and think there may be unforeseen regulatory issues (it's here in the US, so NEC applies), such as whether or not the line fuses FEEDING the rectifier would count as Branch Circuit protection for the DC feeder circuit, i.e. is fusing the AC side (ahead of the transformer) providing protection for those conductors. As a complete system all in the same enclosure it is like that now, but what's different here is that have we created a "feeder" circuit here because those conductors left the enclosure? This is new ground for me, I'm looking for opinions mostly.
I'm not really comfortable with this arrangement and think there may be unforeseen regulatory issues (it's here in the US, so NEC applies), such as whether or not the line fuses FEEDING the rectifier would count as Branch Circuit protection for the DC feeder circuit, i.e. is fusing the AC side (ahead of the transformer) providing protection for those conductors. As a complete system all in the same enclosure it is like that now, but what's different here is that have we created a "feeder" circuit here because those conductors left the enclosure? This is new ground for me, I'm looking for opinions mostly.
"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington





RE: Opinions on non-standard and non-contiguous MV drive configuration
I have seen many large MV ADSs split like you have mentioned, but these bad boys are generally 15,000hp and up. In this situation usually the transformer is liquid-filled and located outdoors, the remainder is usually located indoors. The last time I looked into one of these splits, the OEM was very concerned wrt the length of the cabling between the two sections.
I have not seen this done on smaller air-cooled vsi drives (ie < 9000hp), but there is no reason why it could not be made to work.
Have you contacted your drive OEM to see what they can do for you? I'm sure that the TIC will be a tad higher (maybe +25%).
BTW: How large is the drive in question (ie hp)?
GG
"I have not failed. I've just found 10,000 ways that won't work." Thomas Alva Edison (1847-1931)
RE: Opinions on non-standard and non-contiguous MV drive configuration
Gunnar Englund
www.gke.org
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Half full - Half empty? I don't mind. It's what in it that counts.
RE: Opinions on non-standard and non-contiguous MV drive configuration
It was likely a current source drive.
GG
ps I thought that Robicon was bought by Siemens, and that all of the Siemens/Robicon drives were voltage source type. How long ago did you see this drive?
"I have not failed. I've just found 10,000 ways that won't work." Thomas Alva Edison (1847-1931)
RE: Opinions on non-standard and non-contiguous MV drive configuration
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Opinions on non-standard and non-contiguous MV drive configuration
Well then it must be a Siemens (ex Robicon) 'PerfectHarmony' 18-pulse voltage-source ASD with integral transformer.
GG
"I have not failed. I've just found 10,000 ways that won't work." Thomas Alva Edison (1847-1931)
RE: Opinions on non-standard and non-contiguous MV drive configuration
This configuration is apparently the brainchild of the Engineer on the project, who did not sign the drawings I was given (it's still at 90%, so I'm cutting them some slack), ergo I cannot yet ask him/her where they got the idea. No mfr is mentioned in the sketchy specifications yet, but being that they want 18 pulse for 4160V it has to be based on one of the NPC topologies still out there, not the Cascaded H Bridge designs like Siemens/Robicon or most others (now that the original Robicon patent expired) are selling. A CHB would be 24 pulse at 4160V, but more importantly you no longer have a single DC bus, you have separate LV cells in series, so there is no way to do this separation at all. One of my concerns here is that with all these new CHB designs being released now by virtually everyone, even if this is viable with an older design concept, the field of available options might be limited now and this was an indirect way of one of the remaining "old school" VSI vendors to lock in their spec because they know it can't be done with a CHB. I'm going to propose that instead of going through this rigamarole of having the VFD split in two on opposite sides of the MCC, they simply move 3 of the exiting MV MCC sections from one end to the other so that all of the available space is at the one end, allowing plenty of room for a complete new VFD. Yes, there is more conduit work involved, but I still think that ultimately it would be cleaner. The 20ft run of 6kVDC worries me.
Thanks for the opinions so far.
"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington
RE: Opinions on non-standard and non-contiguous MV drive configuration
500hp drive puts you into the smallest footprint for the Siemens M VASD (Gen 4). I am not sure if Gen 5 is out yet, but I heard that it has an even smaller footprint. Of course, Toshiba also flogs a similar type of drive, but with the option of an outdoor enclosure. I have used these in Northern Canada. Could be an option if you can't find any indoor space.
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GG
"I have not failed. I've just found 10,000 ways that won't work." Thomas Alva Edison (1847-1931)
RE: Opinions on non-standard and non-contiguous MV drive configuration
Bill
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"Why not the best?"
Jimmy Carter
RE: Opinions on non-standard and non-contiguous MV drive configuration
RE: Opinions on non-standard and non-contiguous MV drive configuration
"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington
RE: Opinions on non-standard and non-contiguous MV drive configuration