BESS AC Cable Sizing

[ladanghods]

Hi All Engineers, I am designing a 4MVA Battery Energy Storage System (BESS). The AC cable is sized in accordance with NEC standards. However, after modeling the underground duct bank, we found that heat dissipation requires us to increase the conductor size. Since this BESS operates for only 4 hours, can we use load factor (LF) for cable sizing, as long as we still comply with NEC regulations and address the heat dissipation issue?

 

[don_resqcapt19]

Underground duct banks where the conductors carry much of a load almost always need larger conductors because of the heat dissipation issue. At one point the table in Annex B was going to be actual code language and not just information because of the heat issue.

Will the cables exceed their insulation temperature rating within the four hours?

 

[ladanghods]

Underground duct banks where the conductors carry much of a load almost always need larger conductors because of the heat dissipation issue. At one point the table in Annex B was going to be actual code language and not just information because of the heat issue.

Will the cables exceed their insulation temperature rating within the four hours?

yes they are

 

[ggunn]

yes they are

Assuming you are using 90 degree conductors, are you comparing 125% of the maximum output current with the 75 degree ampacity of the conductors to determine the conductor sizing?

 

[ron]

The utility will often size using a load factor <100% because they feel the load will vary over 24 hour period. Most EE Consultants do not want the potential "heat" (liability), so I use 100% or pretty close all the time.