Re: Vegas pole pigs can't take the heat (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

---------- Forwarded message ----------
Date: Sun, 8 Jul 2007 13:22:01 EDT
From: FIFTYGUY@xxxxxxx
To: tesla@xxxxxxxxxx
Subject: Re: Vegas pole pigs can't take the heat (fwd)

 
 
In a message dated 7/8/07 12:58:11 P.M. Eastern Daylight Time,  
tesla@xxxxxxxxxx writes:

>The answer is simple.  There is no "excessive current" that is  causing the 

>problem.



Well, less current helps, and more current  hurts. At some point the current 
becomes "excessive" for the conditions, since  as it increases it "exceeds" 
the limitations of the system - specifications  notwithstanding.
 
>Normal current under high temps --- the oil can not adequately handle  the 

>cooling requirements of the xmfr and the core gets hotter and hotter  as the 

>day progresses, especially if the xmfr is operating at full load but  yet 
not 
>in overcurrent conditions.  The xmfr oil and case can not  dissipate the 
heat 

>into the surrounding ambient air fast enough to prevent core  overheating.


Then that would be either AB-normal ("excessive")  current for the 
conditions, or abnormal (excessive) conditions/application. Or  maybe a poorly-defined 
specification of what "normal" is.

>Excessive thermal problems under normal load conditions,  aggrevated by high 

>heat, produce problems.


Then the "normal" load needs to be de-rated for  those conditions, or a 
different device that can handle the same "normal" load  needs to be used!
    This is no different than choosing wire size and  type for an application 
- or engineering any other device in a system.  The application tables in the 
NEC are based on engineering data (which they  give you, and you can use if 
you want to). The tables are based on an 86 deg F  ambient, but the NEC has 
tables for de-rating the wire for "excessive"  temperatures. You also have to 
de-rate for things like packing wires together  in conduit (raceways) or cables. 
And you have to make sure the wire doesn't  get hot enough to harm the 
terminals that it's attached to. Voltage drop is  generally important, and hotter 
wire has more resistance.
    Very simple - when you choose a piece of  equipment for an application, 
if it's not designed to survive the application,  it probably won't.
    How do you make a pole pig survive high ambient  heat? Make it more 
efficient at getting rid of heat (bigger and/or more  expensive pig), make it 
generate less heat(bigger and/or more expensive  pig), or design it to withstand 
higher temps(bigger and/or more expensive  pig). See the trend? 
    So unless the Vegas pigs are the unlucky victims  of occasional abuse or 
quality control, the blame still rests squarely on  those who are trying to 
get those pigs to do more than they were designed to.  Hence my previous post...

>A lot like the human body.  Under "normal loads" it does  fine.  Throw it in 

>Iraq or some other high-temp area and it can not function at  "full-load" 

>without encountering some problems.  Extra precautions have to  be taken. 
 
    Same goes for any other device, like pole pigs.  The simplest extra 
precaution to take would be to reduce the average  loads.
 
>In this example, adding more water and more salt help.  In the  case of the 
poor 
>pole xmfr it has to survive on what it has --- it  doesn't get extra help. 
 
    In the human case, doing less work per time  (power) produces less heat 
issues. So does running at times of lower ambient  temperatures. Or do the same 
work at the same ambient, but with people that  handle the heat better 
(acclimated/trained/native). Same goes for pole  pigs...

>As a former U.S. Marine in Vietnam during the late 60's I know  all to well 

>how these thermal effects can overload a human.  Same applies to  xmfrs.



    Humans have lousy efficiency compared to xfrmrs,  but we do have the 
luxury of sentience. If only those Vegas pigs could  speak...
 
-Phil LaBudde
Center for the Advanced Study of Ballistic  Improbabilities



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