Message Board Thread - "hot connection - inverter output breaker"

Back to Threads | Back to Forums

TitleByPosted On
hot connection - inverter output breaker electricpete 9/28/2004
Thanks for all of your help on your previous question. Since I am brand new to infrared, I hope you will please be patient with all my questions.

I uploaded IR plus visual image side by side.

If visual image is too dark, it may be easier to see here:
http://reliability-magazine.com/pub/inv3.jpg

This is a 120 vac breaker on output of an inverter.

In lower left hand corner of the picture you see the top of a molded case breaker. It is a 2-pole breaker with right-angle metal busbars bolted on, and lugged cable bolted to the busbar.

1 - Cabinet ambient temperature is 24.6C
2 - The upper left connection (on top of bottom left breaker) is 24.6C
3 - The upper right connection (on top of bottom left breaker) is 44.2C.
(We checked sister unit and items 1 and 2 were identical).

The infrared shows green strip surrounded by two red bands. I believe the lower-temp green strip is caused by the thermal insulating effect of the lug electrical insulating sleeve. Since the terminal stud is not particularly hot, I think the heat comes from the crimp wire-to-lug, rather than bolted connection lug-to terminal.

Emissivity set to 0.95 throughout the image.

What is your opinion of the severity? What can we say about the reliability with continued monitoring?
 
Re:hot connection - inverter output breaker electricpete 9/28/2004
Whoops. Correction.
2 - The upper left connection (on top of bottom left breaker) is 27.7C

Is there any edit function available after I screw up? (it happens so rarely LOL).
 
Re:hot connection - inverter output breaker pktsgt 9/29/2004
Pete,

What is your amps. on both cicuits? With out that there is no safe answer. One circuit may have more load on it then the other. Where as the heat is not through the whole wire this is not a real problem at this time with out more info. You may also be getting a little bit of reflection.

Kat
 
Re:hot connection - inverter output breaker electricpete 9/29/2004
We did a follow-up inspection today and found the same temperatures.

Kat - good question. Load is currently 30A. It is relatively stable at this value during normal operation. Identical current through both poles of the breaker (it is a 2-pole breaker in ungrounded system - nowhere else for current to go). A similarly loaded sister unit showed almost identical behavior to the cooler pole on this breaker.

Inverter capacity is 15kva at 120vac - i.e. 125A. 2/0 cable.

I believe if the inverter were loaded to capacity, the existing temperature rise of 20C above ambient would increase to 320C which clearly is a destructive temperature.

This is based on assumptions:
ResistiveWatts = I^2*R
TemperatureRise ~ Resistive watts
Combining the above: TemperatureRise~I^2.
So a 4x increase in current gives a 16x increase in temperature rise above ambient?
Would you agree with this conclusion?

Any more comments?
Thx.
 
Re:hot connection - inverter output breaker IRJay 9/29/2004
It would be good to have the amperage to further qualify the answer I have but this looks like a 3 phase system and my guess is it is balanced as it is an invertor. The heating is definitely attributed to the crimp on that termination not being correct. As for reliability, it is not going to get better, it may solve itself by arc welding itself together but that is not an acceptable solution. Only you can determine the criteria for the repair time frame of this problem. What is the critical nature of this equipment and when can it be repaired most effectively.
 
Re:hot connection - inverter output breaker electricpete 9/29/2004
IRJay - I'll bet our last two responses crossed in the mail.

Load is steady at 30A (approx 25% load).
This breaker is the single-phase output of the inverter.
 
Re:hot connection - inverter output breaker Pete 10/6/2004
It appears that the bend radius on the hot termination is exceeded (bend radius should be no less than 3 X the conductor diameter). Exceeding the bend radius that close to the termination will put stress on the crimp not to mention the possibility of creating a hot spot. In this situation I would continue to monitor and have the conductor re-lugged and fix the bend radius at the next maintenance opportunity
 


  • Back to Threads
  • Back to Forums

     

  •   Copyright © FLIR Systems, Inc 2012