Message Board Thread - "Metallic Compund or Paste"

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Metallic Compund or Paste Laland 11/19/2006
Can anybody recommend a metallic compund or paste that can help improve the bonding of conductors. I have scanned a facility wherein most of the hotspot on the busbar are on the joints. They have applied some compound on the surface of the joints and it has solve a part of the problem. I also have observe that the high temperature are on the nuts and bolts that joins the busbar. Maybe it is because of the clearance between the holes of the bus and the bolt. they have tightened the bolt as to its torwue requirment. Another suspicion was that the bus are not even so a clearance is created at the joint between the bus.

Can anybody who has experienced this share his idea and how did they solve the problem.
 
Re:Metallic Compund or Paste cannman 11/19/2006
Try the copper based anti seize from w.w.grainger another is from CC Dickson- its heat transfer paste used mostly for thermometer wells in pipe.
 
Re:Metallic Compund or Paste Laland 11/19/2006
Thank you very much. What about aluminum to aluminum, do you have a suggestion or recommendation?
 
Re:Metallic Compund or Paste cannman 11/19/2006
Go to a boat/marine store and look for any brand of compound that says use for aluminum.
 
Re:Metallic Compund or Paste Bob Berry 11/20/2006
Are you sure you are not seeing a cavity effect on the nuts and bolts?
 
Re:Metallic Compund or Paste Laland 11/20/2006
Actually Bob, I have not seen the joint of the busbar because it is inside the bus duct. When the was opened for maintenance, the joint is insulated. Upon review of the image of the bus duct, the highest temperature is directly located at the bolt.

Attached is a sample of 2 busbars joined together by nuts and and bolts.
 
Re:Metallic Compund or Paste Top Gun 11/20/2006
In my experience in electrical equipment, where conduction between two metallic surface must be maximized, it has always been best to bring the two surfaces as closely together as possible. This means on a MOLECULAR scale. Electrons are not very big and prefer to cross where the two surfaces are touching or in direct contact. Applying any kind of a "lubricant" between these two surfaces adds distance between them and presents resistance to the flow of electrons. Even if the lubricant is conductive, it will eventually break down and become a problem instad of the solution. If the two metallic surfaces are in direct contact, there is no way for contaminants to enter between them and the conductance will remain high. You do not want lubricants between the bars in your image. The bolts are a minor part of the circuit but play a major part in holding the bars tightly together for maximizing conductivity. The "brighter" bolts in your image are a different metal than the bus bars and have a higher emissivity and do look warmer. I suggest you continue to monitor this situation over time and see if the radiometric signals change over time with constant load, and do nothing to mechanically change the system. If you must get better thermal readings via infrared imageing, a high emissivity substance needs to be applied directly to the bus metal surface in a thin layer near the joints. This could be paint, vinyl tape, or even a line from a grease pencil.
I hope this helps.
Steve Moore
 
Re:Metallic Compund or Paste Bob Berry 11/20/2006
Based on what I see in the image above.

Assuming you have ruled out reflected apparent temperature you have a severe problem. When you apply a high emissivity surface to the target your temperature reading will increase significantly and may be closer to failure than you think. You need to revisit this ASAP and make sure this is not a reflection by shielding with cardboard. If this not RAT then you need to look at shutting it down and carrying out a repair.
 
Re:Metallic Compund or Paste Top Gun 11/20/2006
What is the rating of this bus and what is the current load on it at time of imaging? Is it directly attached to a heat source like a dry-type transformer?
 
Re:Metallic Compund or Paste Top Gun 11/20/2006
I also do not recommend using paste or lubricants on fasteners since they may reduce normal friction of tightening, and may lead to overtightening of the bars, which will warp some of the bar material and reduce contact area, and reducing overall ampacity. All of these fasteners have specified torque ratings that ensure best physical bonding, and these ratings should be based on using dry bold and nut threads.
 
Re:Metallic Compund or Paste cannman 11/20/2006
Check out this site about tightening fasteners, this may help with some of your questions . Lubricants aren't always the best thing but sometimes are helpfull.

http://www.boltscience.com/pages/tighten.htm
 
Re:Metallic Compund or Paste newguy 11/22/2006
I have seen a product named Penatrox that is available at electrical supply companies. It's used between on electrical connections, between a SCR and heatsink, etc.
 
Re:Metallic Compund or Paste Git-r-Done 12/6/2006
I agree with Top Gun that it needs to be a good metal to metal fit. I have seen the Copper Coat used before but that is just a crutch. Also the fastener needs to be compatable with the bus material.The use of compatable washers under the bolt and nut helps in spreading out the clamping force. The thermal compound suggested by newguy is not for conducting of electricity but for thermal coupling usually used on heat sinks. Aluminum is not recommended for bus bars because of the buildup of aluminum oxide which creates and high resistance over time and the fasteners must be re-torqued as well. Torqueing of the fasteners is critical too so you need to see what is recommended for the size that you are using.
 
Re:Metallic Compund or Paste Magnumguy 12/7/2006
busbars should never be assembled dry, strip the joint and try " NO-OX-ID " from Sanchem inc. in Chicago. available at most professional electrical contractors suppliers, failing that I know Gulf Petroleum make an excellent paste just for this application.
 
Re:Metallic Compund or Paste colt 12/7/2006
Copper coat is a anti sieze product. Can be used for some electrical connections,equipent such as high voltage switches, if you do not have the proper product.
Defintely use a de-ox product like Ilsco de-ox on aluminum. High resistance oxides built up very quickly otherwise. Can be used on copper,it is slower to build up oxides and depends on enviroment. The bolt is heating up because it is providing a best electrical path for current,you have a high resistance path where the current should be flowing
 


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