Non linear loads + ambient temp correction

[Dave058]

Good evening all nice to be here,
I have a long winded question but I need some peer feedback as I stand alone in my thinking at this point. I reviewed a dwg. that shows a 15K/3000 A MV transformer with local 480/277 v disconnect rated 3000A feeding a 3000amp switchboard approx.125 ft. away.Transformer is outside, conduit rack route is through non climate controlled building back outside to outdoor 3000 amp SWBD. I am in MD/ DC area where summer temps frequently reach above 86 °F. The switchboard is feeding all Battery Elec. Bus charging which are non linear loads.Dwg. shows 8-4" rgs conduits with 4- 500 kcm. I say because of table 310.15(B)(2)(A) and 310.15(B)(2)(C) it should be 5-700 kcm in 5" rgs. One last note no ground shown in conduits. What say you guys?

 

[augie47]

With a 90° conductor sch as THWN-2 or XHHW, the ampacity of the (8) 500s should be no problem.
Is it a POCO transformer or customer (ie: is this a service or SDS feeder)

 

[Dave058]

3 outdoor 15 k transformers are feed from power co.feeders. 500 kcm THWN = 430 amp at 90 degrees ×.80( 4 cc conductors beb chargers are non linear)= 344 amps ×.96 for ambient = 331 amps× 8 sets 2648 Amps < 3000 A ocp. Help me out here thanks.

 

[wwhitney]

Do you have the make/model, or a pointer to the charger data sheet?

Cheers, Wayne

 

[augie47]

sorry..missed then non-linear in the OP. Rare to find the majority of a ,load to be nonlinear.

 

[Dave058]

It's an ABB collaboration with NF buses.I will have to dig through some documents to get model#'s. I will post info. shortly. However my feeling is the feeder to the SWBD has to account for these loads regardless of specific make and model. The chargers could always be swapped out for different manufacturers equipment after initial pilot program. Thanks for your reply

 

[Dave058]

sorry..missed then non-linear in the OP. Rare to find the majority of a ,load to be nonlinear.

Agreed this is new stuff and with ev technology taking over and all ev chargers currently are non linear this is going explode and us guys that are tasked with electrical safety need to pay attention to this, thanks for your reply.

 

[synchro]

The battery chargers may be considered nonlinear loads, but do they draw significant L-N load currents?

Triplen harmonic content of L-N currents will not not cancel in the neutral of 3-phase 4-wire loads, but instead their mean-square currents will add. And so the neutral will be a current carrying conductor for nonlinear L-N loads, but not for nonlinear L-L loads.

 

[Dave058]

For what it's worth I watched a professor guy on you tube. He said that even if the neutral does nothing but terminate on neutral bar at both ends with no neutral load at all the harmonics on the phases will end up inducing a large current on the neutral anyway. I will have to dig up his video and post if you care to see it. Thanks for your reply.