Message Board Thread - "More on Magnetic Heating"

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More on Magnetic Heating Laland 6/7/2007
I have done a thermal scanning on a bus bar and bus duct recently. I have shared before on a hotspot on the bus duct (not on the bus bar as intially suspected because we could not open the duct for safety reasons). But recently the end-user allows us to open the bottom section and we found out that the external heating on the bus duct was not coming form the bus bar because the bus bar has a lower temperature than the bus duct hotspot. Further investifation reveals that the hotspot on the duct are on the bolts, however not on all bolts but on certain bolts. The certain that I mentioned are one or non on every section of the bus duct connection. Please note section (meaning the bus dict is scetionalize).

Am I correct to assume or say that the heating on the bolt in the bus duct (not busbar) is due to magnetic heating. How am I going to correct this.

Am sorry that I cannot post the image taken because I cannot upload the image from my file becaue it is an IMG file.

Thanks..
 
Re:More on Magnetic Heating Bob Berry 6/8/2007
If you use Thermacam explorer you can convert the files to bitmap. This is freeware and can be found on http://www.flirthermography.com/support/downloads/TCEXPSETUP.zip

I would like to see an image of this, but from what you describe it is inducted heat on the bolts. The easiest cure is to replace the bolts with non-ferrous bolts, preferably stainless steel. Although you should check with the manufacturer first, I am always carefull introducing new materials into an installation, disimular metals are sometimes a problem, so be carefull if you are going to introduce new metals. Again it is difficult to say for sure without an image, but I am assuming your bolts are not on the busbar itself and that you have completely ruled out differences in emissivity, and reflections. You also dont mention the temperature or emissivity of the bolts.
 
Re:More on Magnetic Heating jvoitl 8/24/2007
Please, never confuse the terms non-ferrous, non-magnetic, and non-conductive at the risk of damaging equipment and/or bodies. In the dictionary ferrous is defined “of or pertaining to iron”. Stainless is about 80% iron with other elements, two of which are chromium and nickel, to make it tarnish and rust resistant. It is however ferrous. Some stainless steel in the 400 series is even magnetic. To generate current all that is required is to have a magnetic field moving in relation to a conductor, ferrous or not, and a completed circuit. A perfect example is a standard 3-phase squirrel cage induction motor. The rotor bars are normally made of aluminum in the smaller motors and copper in the larger ones, neither of which is ferrous. The moving magnetic field from the stator induces a voltage in the bars. The end rings on the rotor short the bars together creating a completed circuit, and current flows. Under the right conditions, such as overload or frequent starting, the current can even overload the bars and cause them to melt.



A moving or alternating magnetic field will induce a voltage into a conductor and a current if the circuit is complete no matter what the conductor is made of. It can be iron, copper, aluminum, gold, silver, or even graphite, a wet string or a puddle of muddy water. The amount of current and heat generated by it will vary depending on the conductivity and resistance of the material, but there will be current flow, and therefore heat.
 
Ferromagnetic - an Induced Current Multiplier John C. Lafeber, P.E. 9/3/2007
jvoitl wrote:
never confuse the terms non-ferrous, non-magnetic, and non-conductive at the risk of damaging equipment and/or bodies. In the dictionary ferrous is defined “of or pertaining to iron”. Stainless is about 80% iron with other elements, two of which are chromium and nickel, to make it tarnish and rust resistant. It is however ferrous. Some stainless steel in the 400 series is even magnetic. To generate current all that is required is to have a magnetic field moving in relation to a conductor, ferrous or not, and a completed circuit. A perfect example is a standard 3-phase squirrel cage induction motor. The rotor bars are normally made of aluminum in the smaller motors and copper in the larger ones, neither of which is ferrous. The moving magnetic field from the stator induces a voltage in the bars. The end rings on the rotor short the bars together creating a completed circuit, and current flows. Under the right conditions, such as overload or frequent starting, the current can even overload the bars and cause them to melt.



A moving or alternating magnetic field will induce a voltage into a conductor and a current if the circuit is complete no matter what the conductor is made of. It can be iron, copper, aluminum, gold, silver, or even graphite, a wet string or a puddle of muddy water. The amount of current and heat generated by it will vary depending on the conductivity and resistance of the material, but there will be current flow, and therefore heat.
Ferromagnetic materials have a magnetic PERMEABILITY much greater than 1. This increases the magmetic flux density. The induced current (eddy current) goes up with flux density. Don't use ferromagnetic steel bolts (normal bolts) in bus bar. Non magnetic stainless is a LOT better.

 
Re:More on Magnetic Heating Pete 9/19/2007
Hate to ask the obvious but, I will. Are all the bolts torqued to the proper torque specs? It won't matter what material your connecting hardware is if the connections are loose. You will have high resistance connections.
Resistance = heat. I have seen it on the covers on our 25kv flex link compartments.

We have changed out all our connecting hardware to stainless and torqued to the proper specs.

Just a thought,
Pete
 
Re:More on Magnetic Heating Redzuan 1/16/2009
I got a problem with my bus duct.
there is a high temperature(heating) at the
joining part and bus duct surface.
any solutions for this?
 
Re:More on Magnetic Heating manuel-thermoimagen 1/17/2009
can you share to us infrared image and picture?..
 


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