Heat losses from large switchboards 1

[EEJaime]

Hello,
We have an installation with a total of four switchboards whose combined bus load rating is 13.75 MVA in one room. There are four switchboards made up of Metal Enclosed Low Voltage Switchgear. While giving the Mechanical fellows our anticipated heat loads for the transformers in the room, it occured to me that the "rule-of-thumb" that I normally use to allow for heat loss into the room from loaded switchgear, (I have used a 1% figure for years-don't really recall where I got that), is quite a load in this case, (over 171kW). Does anyone know of published data on this? I've looked through manufacturer's websites and have a call into my switchgear rep, but I was just curious as to other's experience.

 

[alehman]

GE used to publish heat dissipation data on some of their circuit breakers and switchboards. I can't find it on their web site now, but you might ask your friendly local salesperson. Obviously it is highly dependant on the load.

Alan
“The engineer's first problem in any design situation is to discover what the problem really is.” Unk.

 

[rbulsara]

ASHRAE has table for heat gain of electrical equipment, I believe. A Google search on the topic also turns up a few hits.

Rafiq Bulsara

http://www.srengineersct.com

 

[crisleon]

Well, I calculated such a case a few years ago, it was more estimation than calculation. I found some Schneider Electric data referring to their BCs and used it in the Excel sheet (I uploaded this Excel to Engineering.com, I am not sure if efficiently).
After summarizing all heat from BCs I added about 30% of total quantity representing busbars and all cables and wires in the rooms. Then I multiplied it by the coefficient 0,6 (similarly with the coefficient of the simultaneousness, however higher a bit than this one of electrical circuits, being roughly 0,45 for my building). My results were about 28kW total heat in comparison to 8MW of electrical total (maximum) power. So your 1% in my oppinion is too much, I think that should be less than 0,4% or even 0,3% (in my case it was about 0,35%, however it was in 3 rooms).
I hope you may take this Schneider's data "per analogiam" or get your own from the producer of your equipment.
Regards

 

[crisleon]

Sorry, once more.
The enclosed Excel sheet is Ok, apart from a bloomer that at the "D" column should have the title "Heat (for 3 poles)".

 

[EEJaime]

Thank you all. Good data crisleon! Very helpful and your results are exactly what I am finding from my factory rep sources.

 

[crisleon]

What total result have you obtained after your re-calculating? First calulations gave you about 170kW, how much have you got in the second estimation?