Heat loss in cable

[joner1]

Hi Guys, first of all sorry if this is posted in wrong section.
I am doing a building services design course at southbank university and have an assignment on cable sizing for a submain, I need to calculate the heatloss in this cable.

As i remember heat loss is calculated using P=I*R,
Do i have to calculate the resistance of the Line AND Neutral conductor for this calculation or is it just the resistance of the Line conductor?

Many thanks in advance

 

[joner1]

I'm using 16mm from table 4D2A, and the OSG states that 16mm has a resistance of 2.3 for R1 -R2, or R1 and Rn in this case

 

[Marvo]

Heat loss from the actual cable is encouraged but I²R losses should be kept as low as possible in general.

 

[Chr!s]

OK have got a different answer from each formula-

Using I²R i have 65.2² * 0.0414 = 176W
Using V.d * Ib i have 2.73 * 65.2 = 118W

OK 16 mm = 2.8 mV/a/m, length 50 meters so- 50 x .0028 = .14

So 2.8x65.2x50/1000 = 9.13 v x 65.2 = 595 watts

I2R =( 65.2 x 65.2) x .14 = 591.5 watts

Take your pick

 

[i=p/u]

so keeping them low as possible ,just means use bigger size cable for less resistance.....


good examples guys..

 

[joner1]

Chris, Thanks so much for taking the time to do all of that, I applied the 1.2 correction factor to the resistance(taking into account how it changes with temperature) Does it not apply?
Anyway, my answers aren't massively different so, Looking at what you've done, i'm quite happy with it, Once again thanks a lot for all your help.

 

[Chr!s]

Chris, Thanks so much for taking the time to do all of that, I applied the 1.2 correction factor to the resistance(taking into account how it changes with temperature) Does it not apply?
Anyway, my answers aren't massively different so, Looking at what you've done, i'm quite happy with it, Once again thanks a lot for all your help.

Well the osg uses DC resistance i think, these will differ from the ac impedances in the BGB due to the skin effect and the proximity effect. Alos the conductor temps are adjusted to 70 C, so the 1.2 will not apply, if any thing you would be reducing the mV/A/m due to conductor temp.

Regards Chris

 

[joner1]

Thanks Chris, that would actually bring my answers closer to each other, so i'll drop the 1.2 factor