Insulated Cable watts loss calculation

[Exhibitionist]

Can someone please offer advice on how to calculate watts losses from insulated power cables. It is easy to calculate the watts loss of the actual conductor based on current and resistance (I squared R), but when the cable is insulated, what are the actual losses through the insulation.

I am trying to calculate the amount of cooling required in a large switchroom and using the straight I2R calculation the amount of cooling require seems too high, therefore expensive.

The type of cable we are using is a flexible fire rated power cable (110 deg rating). Each circuit is aroung 2500A and we are using 5 x 240mm sq cable per phase & neutral (415V 3ph 50hz system).

We have sought help from the cable manufacturer but they had never been asked the question before and could not give us the answer. The engineer there wanted to put a length of cable in an oven to see how hot it got (basically had no idea).

Look forward to input on this issue.

 

[MintJulep]

I^2R losses are converted to heat.

Heat has nowhere to go except through the insulation into the space around it. So all of the I^R loss goes to heat in the room.

The the thermal insulation value of the the cable's (electrical?) insulation determines the temperature difference between the conductor and the air.

 

[Skogsgurra]

You have got essentially the same answer in all three fora where you posted this question.

It is a rule not to douple-post. Triple-posting is even worse. It will make the discussion of the topic at hand a very confused one. So, don't double-post in the future, please.

Gunnar Englund

http://www.gke.org

 

[Exhibitionist]

Thaks for the answer everyone, and apologies for posting this on in several forums. This is the first time on here and wasn't sure where I might get the best response.

 

[Skogsgurra]

OK, Exhibitionist. I see that jraef explained this to you. And, as he said, welcome to these fora. We try to help each other - but sometimes we can be really, really mean and say things that we think are funny. But no flames in here. We are actually nice people.

Gunnar Englund

http://www.gke.org