Sizing a fuse on a 1 phase load

[tricard]

Good morning,

I am sizing a fuse for a 1P 37.5kVA transformer that is tapped off of a 600V 3P 4w splitter. See below for one line:

________________________600V splitter 3p 4w
| |
| |
1P fuse 3P motors (200hp total)
|
|
1P 37.5kVA trafo
600V/240V
|
|
______240V 1P splitter
|
|
heater

I use ETAP for modeling and to model a 1P load a "phase adapter" is used, which I have set as a phase AB tap (therefore 600Vp-p).
Calculating the required primary fuse size (by Canadian Electrical Code) I have:
TX FLA: 37.5kVA / 0.6kV = 63A
fuse sized to 125% of FLA: 63 x 1.25 = 80A fuse


When I plot my TCC with the 240V single phase splitter as reference for the fuses I have selected, the 80A primary fuse (using a J class time delay) is far to the left of the transformer inrush of 12xFLA@0.1s. Strangely though, if I use the 600V splitter as reference the 80A primary fuse shifts to the right of the inrush (all other devices shift as they should to the new reference voltage). I am sure one of these TCCs is correct, but I need some guidance on whether I have sized this 1P primary fuse properly (see TCCs as well pariculary FU 1P HTR). Any ideas to what I am doing wrong?

Thanks in advance for the help

Tim

 

[rbulsara]

Fuse sizing per code seems correct. The primary fuse is at 600V so why use 240V in the TCC?

By the way what is a "splitter"? Is this a term used in the great white North?



Rafiq Bulsara

http://www.srengineersct.com

 

[tricard]

rbulsara,

The 240V reference was simply what ETAP spat out for its default reference; I had noticed the odd change in the AJT fuse when I switched the reference to 600V.

As for the term splitter: I never knew it was a term NOT used elsewhere (due to my lack of experience of course . I think I have seen them referred to as distribution racks as well. see the picture on Metalec's website under "distribution rack" (

http://www.metalec.net/Power Distribution_Products_(750V_&_Under).html)

and that is exactly what I am speaking of. They seem to be used quite regularly in the sites I have visited (which is mostly mines and mills).

Referring to the TCCs, would there be any reason why the AJT fuse does not shift properly with the other protective devices? Does it have something to do with 600V being a 3phase reference and 240V being a 1phase reference?

Tim

 

[rbulsara]

The plot reference voltage should be the same for all components on a TCC, regardless of their nominal voltage. Your TCC shows (reads) different plot reference voltages for the two components on the same plot!. I don't quite understand the titles on your TCC plots.

Make the TCC to plot all components to a common reference voltage.




Rafiq Bulsara

http://www.srengineersct.com

 

[tricard]

Hi Rafiq,

It appears to be an issue with ETAP. For one reason or another, the fuse directly upstream of the 1 phase transformer was not referencing properly. I have contacted ETAP with the issue.

Thanks for letting me know I was on the right track with the sizing.

Tim

 

[alehman]

I didn't know anybody actually manufactured those things (distribution rack). Always thought they were field-cobbled from convenient components.

Alan
----
"It’s always fun to do the impossible." - Walt Disney

 

[waross]

I think the alternate term is a "Bus Gutter".
A long, narrow (usually) JB, with bus bars or multi tap terminals suitable for tapping loads.
A common cross section may be 4"x 6" or 6" x 6", and it may be 24", 36", 48" long or longer.
The transformer feeds the splitter and switches for individual loads are tapped off the splitter.
I guess it is a "Great White North" term as Rafiq suggested.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[ScottyUK]

"Bus gutter". [LOL]

Horrible things, the few we have are heading for the scrapyard at first opportunity.


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