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 Post subject: modeling AC and DC drives' buses in software
PostPosted: Wed Jul 22, 2009 8:52 am 

Joined: Thu Apr 02, 2009 5:59 am
Posts: 6
Hi all,

I was wondering what convention/practice people are using to model AC and DC drives (ASDs below 1000V) in their respective modeling software. IEEE 1584 doesn't give too much direction on what this equipment should be classified as (MCC, Switchgear, Panelboard etc.) or the working distance and bus gap associated with this. We have been modeling these drives as MCC/Panelboards with an 18 inch working distance for drives under 1000V which seems to give a worst case on incident energy. Do these practices line up with others?

Thanks for the advice

Tim


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PostPosted: Sat Jul 25, 2009 8:27 pm 
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Joined: Thu Jan 10, 2008 8:49 pm
Posts: 498
Location: New England
18" seems like the right distance for working on them. Just remember that Drives are inherently current limiting.


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PostPosted: Wed Aug 19, 2009 5:22 pm 
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Joined: Sun Aug 16, 2009 8:42 am
Posts: 184
Location: Lawrenceburg KY
Easypower

Easypower software by ESA. In the specfication tab select the variable drive option. Select DC or invertor. In the TCC tab, since the starting current will ramp up from zero to the FLA, a good approximation is to use Reduced Voltage starter type and Reduced Inrush Multiplier of 1 as show in the attached picture. In the TCC, ignore the slight spike/zig-zag at 25 seconds. This was meant for ac induction motors. You can minimize this by setting Locked Rotor Mult to 1.

In my opinion, you can model this but this is not so important in Arc Flash unless you have a very large regent drive. If your doing power flow or other analysis then this may come into play.


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PostPosted: Thu Aug 20, 2009 5:58 am 
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I think the approach you are taking is a good one if you are acutally labeling the drives themselves. They are not current limiting at the lineside power source which is what you are labeling if you are labeling a drive. However most drives are inherently current limiting if you were to fault at a remote location other than the drive itself.....meaning you wont get the same contribution as a normal motor. There a lot of options for this some conservative and others more realistic.....you will have to find your own approach for those cases. If using software most cases you can model the drive as regen or not and this will be based upon the drives themselves.


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