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 Post subject: Modeling Bus Ducts in SKMPosted: Wed May 29, 2024 4:19 am

Joined: Fri Mar 22, 2024 12:20 pm
Posts: 3
I am performing my first Arc Flash study for our facility and i am having to draw out the single lines

we have a 170ft bus duct that runs though the building and the machines are coming off of disconnects on the bus duct.
how would i model this properly for getting accurate measurements during the short circuit study / arc flash evaluation?

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 Post subject: Re: Modeling Bus Ducts in SKMPosted: Wed May 29, 2024 6:04 am

Joined: Fri Sep 28, 2018 7:32 am
Posts: 40
Location: Sioux Falls, SD
It depends on the level of accuracy and model complexity you desire. I previously modeled a large automotive facility with thousands of feet of overhead bus duct in EasyPower. We modeled every 10' section of bus including any bus plugs installed on that section. We then used busway to connect to the next segment. Some busducts were double fed (feed from one substation fed one end of the bus duct and a feed from a second substation fed the other end). This detail allowed us to determine the most accurate hazard severity within each segment of busduct. It identified some sections as less than 8 calories while others may exceed this value.

In SKM you can use different types of busway from the cable library. If you want to be most accurate you can enter real lengths for each segment and model the bus plugs accordingly. 175' of busduct isn't terribly long so you may be fine modeling a single busduct and connecting all bus plugs to it.

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 Post subject: Re: Modeling Bus Ducts in SKMPosted: Wed May 29, 2024 10:20 am
 Sparks Level

Joined: Fri Jul 08, 2016 10:01 am
Posts: 317
Location: Indiana
What software are you using?

If SKM, it doesn't have bus duct in the library for use as a bus - as-in calculating incident energy at that bus. It does have feeder bus for use as just that and it has an impedance component.

Are you trying to calculate IE for the bus as if the bus itself is what you are exposing yourself to live parts on or are you exposing yourself to the live parts at the disconnects or both? Is this plug-in bus that can have new switches plugged into while energized? The reason that the difference may or may not be important is, there is no enclosure or box per se while plugging in a new switch. There is of course the disconnect switch enclosure itself for exposure to live parts inside the switch.

The next question is, are you labeling the just the busway or just the disconnects or only the worst case between the two?

To model the busway you'll have to just add a bus, or segments of bus with a feeder bus of whatever amps between segments as jmoore suggests. Then you'll have to customize the bus gap and enclosure type and bus configuration (PNL, SWG, CBL, AIR, MCC) and (VOA, VCB, VCBB, HCB) To model each disconnect you'll have to add very short segments of feeder bus to additional busses representing the line side of each disconnect and customize the enclosure size and bus configuration again.

That is a lot of work to go to that extent and I expect your results between the bus plug and inside the disconnect will be similar if your bus gaps are similar. The biggest difference would be if you choose to model the bus plug in points as in AIR or in an enclosure. Here are a couple of screenshots from SKM to hopefully help describe what I am talking about.

Attachment:
BUSWAY SEG2.png

Attachment:
BUSWAY SEG2 arc.png

Attachment:
BUSPLUG1.png

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