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 Post subject: Filter for VFD Bus
PostPosted: Wed Jun 29, 2011 1:17 pm 

Joined: Fri Oct 30, 2009 9:20 am
Posts: 47
Location: Texas
We have 3 480V feeders that each serve a bus dedicated to VFDs. Before the tie in to each bus we have a Matrix Filter, model MDG1200D. These are 1200A filters, one per bus, each exactly the same, i.e. serial numbers ending in 47, 48 and 49. Looking at a schematic diagram, for arc flash purposes, I am basically dealing with two inductors in series for each phase. I phoned the manufacturer requesting the impedance information for these inductors, and they refused, saying that information was proprietary. I then requested that if I provided them with the available fault current at the input to their filter, they provide me with the bolted 3-phase fault current at the output of their filter. Again they refused on the same basis. I will have this well documented in my report; however, I still need to produce labels with the most rational assumption that I can come up with. Does anyone have any suggestions? The impact of two inductors in series is huge. I do have instantaneous on the upstream breaker that does operate if the filter is neglected. I'll bet for 3 1200A filters, MTE could have provided the information if the request was made before the purchase order was cut.


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PostPosted: Wed Jun 29, 2011 6:10 pm 
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Joined: Sat Jun 07, 2008 5:11 pm
Posts: 143
Location: Connecticut
This is a pretty common setup for VFD's using line reactors on the incoming power. I don't know why this manufacture would state the information is proprietary? Something doesn't sound right. :confused: MTE, Rex and others readily list % impedance, mH, ohms and X/R on their web sites. One of the disadvantages of current limiting reactors is the reduced fault currents after the reactor that can significantly increase the PD clearing time.


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PostPosted: Thu Jun 30, 2011 5:52 am 

Joined: Sun Oct 05, 2008 5:00 pm
Posts: 17
I have heard the term "proprietery" used when the person just doesn't know and doesn't want to go digging for the info. It seems odd because reactors are no big deal in the design as far as being some secret.


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PostPosted: Fri Jul 01, 2011 5:49 am 
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Joined: Sat Jun 07, 2008 5:11 pm
Posts: 143
Location: Connecticut
It's like buying a car and telling you the hp is proprietery. :D I would make a special notation on the report and recommend replacement with a reactor of known value so accurate fault currents can be determined.


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PostPosted: Fri Jul 01, 2011 8:28 am 

Joined: Wed Oct 01, 2008 5:00 pm
Posts: 4
geh7752 wrote:
It's like buying a car.
as in - what will it take to put you in this car today? Just don't look under the hood! Yes I agree with the others. Something sounds fishy.


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