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 Post subject: does regular motor or VFD motor affect Arc flash results?
PostPosted: Thu Sep 23, 2021 12:59 pm 

Joined: Thu Sep 23, 2021 12:46 pm
Posts: 2
Hello everyone,

I am new to SKM modeling and arc-flashing study. Now I am having a one line with a transformer lowside feeds to a 4.16kv switchgear without a CB, but a MOD switch, and in this switchgear, there are 5 feeders, each one has a feeder breaker, and one feeder is to a VFD controlled motor.

my question is in SKM modeling, is there any arc-flashing study result difference in SWGR to model the load as a regular motor or a VFD controlled motor?

Thank you


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 Post subject: Re: does regular motor or VFD motor affect Arc flash results
PostPosted: Fri Sep 24, 2021 5:14 am 
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Joined: Wed May 07, 2008 5:00 pm
Posts: 862
Location: Rutland, VT
If the VFD's are non-reg type then there will be no backfeed of motor current to the switchgear. Since it is 4.16kV motors I suspect them to be healthy horsepower and may have a significant contribution if there is backfeed.

Since you are working in software, why not create a model with non-regen VFD's and one with straight motor connection the bus, fault the bus and compare which is the worst case and by how much?

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www.workplacesafetysolutions.com


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 Post subject: Re: does regular motor or VFD motor affect Arc flash results
PostPosted: Fri Sep 24, 2021 7:13 am 

Joined: Thu Sep 23, 2021 12:46 pm
Posts: 2
Thank you for the reply. You are correct, I did the modeling comparation, and the result shows the one with VFD has a little bit lower incident energy level back in SWGR. it seems that a directly connected motor will contribute some energy back to SWGR. Really appreciate the help.


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