Resistance of lug connections and heat generation

[dbecker]

Hello,

I am a mechanical engineer that is tasked to predict lug metal temperatures of power distribution equipment. I need some type of rough idea on the typical resistances seen at bolted lug connections: For example

Aluminum to copper bolted connections
Copper DLO cable to set screw lugs, all sizes from 373 kcmil up to 646 etc...
Copper to copper bolted connections

I know there are many variables involved in calculating joint resistance. And if I get this wrong please correct me as this is not my field.


Contact area
pressure between faces
surface roughness
temperature
oxidation between faces
current density
frequency

I need a table that can give me a rough idea of resistance for these typical connections.

The purpose of this is to compute heat generation in watts, and eventually apply this as a load in my FEA model as a heat flux upon a face.

If anyone has informtion on this matter, it is greatly appreciated.

Thanks,

- D

 

[rasevskii]

Aluminum to copper bolted connections are not allowed due to electrolysis. Special lugs have to be used that are copper/aluminum forged together or a COPAL plate has to be used between the mating surfaces. COPAL is a rolled sheet that is copper on one side Alu on the other.

Others can offer some other suggestions and comments.

rasevskii

 

[dbecker]

I believe the lugs are aluminum with some type of coating as you mentioned.

 

[jghrist]

I would review the ANSI standards for connectors. The standards will include heat run testing. You could assume that the connectors run at the highest allowable temperature. There are probably too many variables to try to predict metal temperatures from the joint resistance. Temperature would also depend on surface area, emissivity, and other factors affecting heat dissipation.

 

[dbecker]

Thanks for the reply.

I am not too worried about emissivity due to radiation, that is too fine of a prediction. What I really need is a way to compute resistance at these joints, I can handle the rest of the computation regarding heat generation and dissipation using FEA tools.

Where can I get ANSI data on heat run testing?

 

[jghrist]

See

http://www.nema.org/stds/cc1.cfm

 

[dbecker]

Thank you for the document, are there any others out there that are useful references?

 

[rbulsara]

NETA ATS (

http://www.neta.org)

will have specs for maximum allowable joint resistances.

Those are for properly tightened joints, which are not cause of the problems. Cause of excessive lug/bus temperatures are loose connections and lack of ventilation/cooling and there is no predicting there.

Rafiq Bulsara

http://www.srengineersct.com

 

[rbulsara]

You can also ask around local electrical testing companies and/or friendly switchgear/breaker manufacturers.

Rafiq Bulsara

http://www.srengineersct.com

 

[dbecker]

Thanks for the help. I will check out those documents.