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EasyPower Software- How do I correctly model the incomming line for main breakers
https://brainfiller.com/arcflashforum/viewtopic.php?f=15&t=2438		 Page 1 of 1
Author:  Dug [ Thu Sep 13, 2012 12:10 pm ]
Post subject:  EasyPower Software- How do I correctly model the incomming line for main breakers
Hello, I am new to EasyPower and I am wondering how to correctly model the incomming line connected to the main breakers in MCCs and distribution panels for arc flash purposes. Currently, I have the cable (incomming line from substation feeder breakers) connected to a bus (Type: conductor, Material: Copper) upstream and directly connected to the main breaker for a MCC. The main breaker is then directly connected to another bus (Type: MCC, Material: Copper), which is used to represent the MCC. However, I have been getting unexpected values for incident energies with the conduit type bus having a higher incident energy than both the substation and MCC. If I change the conduit type bus to MCC type the unusual incident energy dissapears, but I don't know if this is the correct way. I have also tried altering the feeder breaker, main breaker, and cable data settings, but still no luck. What am I doing wrong or is the incident energy correct for the conduit type bus?

Attached distribution panel example (Same thing that happens with MCCs):
Substation bus is 4.5 cal/cm2
Conduit type bus is 5.0 cal/cm2
Panelboard type bus is 3.8 cal/cm2

Attachments:
Time-Current Curves.pdf [1.89 MiB]
Downloaded 338 times
Author:  Satish Shrestha [ Thu Sep 13, 2012 5:04 pm ]
Post subject: 
Different bus types have different Gap between conductors and Distance Exponents. This is as per IEEE 1584 Std -2002. You can find the Gaps and Distance Exponents in the standard library under Arc Flash -> Defaults. The arc flash hazard report will display the arc current and the trip time. All of these factors affect the final result.
Author:  Dug [ Fri Sep 14, 2012 5:16 am ]
Post subject: 
I geuss what I'm really trying to understand is when do I use or not use each different type of bus for arc flash purposes? For example, the definition in EasyPower of the conduit type bus is "Conductor: wire ways, bus ways, etc". So if I put this type of bus directly upstream of a main breaker on a MCC type bus then what does the arc flash result mean? Is it showing what the arc flash would be if a fault occured on the conductor on the primary side of the main breaker for the MCC or is this bad practice? I also noticed in a few EasyPower samples that the cable is directly connected to the main breaker with no bus inbetween and this raises the question of what does the arc flash result on the main breaker represent. Basically, I am trying to use the arc flash results to create labels for the incident energies for the MCC and upstream substation?
Author:  Satish Shrestha [ Fri Sep 14, 2012 12:09 pm ]
Post subject: 
The Distance Exponent for "Cable" is 2.0 while for MCC it is 1.461. If the cable or conductor is the incomer for the MCC and is within the MCC enclosure, then it would be better to specify the bus as MCC. This is how most people are modeling equipment.
Author:  Dug [ Mon Sep 17, 2012 5:07 am ]
Post subject: 
Thank you!!!
Author:  viper57 [ Mon Sep 17, 2012 6:16 am ]
Post subject: 
Dug... I don't put a bus on the line side of the main, just attach the cable to the breaker/fuse. When doing the AF analysis, select "Both Including and Excluding the main" and you will get the AF calculation on the line side and load side of the breaker.
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