Why 112kVa?

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chris kennedy

chris kennedy

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Miami Fla.
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Retired electrician
Why is 112 a standard transformer size. Why not 110 or 120? I figure it has to be a math issue but I don't see the numbers.

Thanks
 
You left out the .5 :)

Good question. While we're at it why 45 KVA and not just 50? :unsure:
 
Mr. Serious said:
So someone long ago decided to use the arithmetic mean instead of the geometric mean for this one.
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Apparently there was a call for transformers between 25kVA and 50kVA (or 75kVA and 150kVA), and someone decided to split the difference.
 
xformer said:
What about fuel efficiency? I know comparing 2000lbs is miniscule to 44 ton, but it does add up over the lifetime.
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The problem with an analogy is that at its root it's just an analogy. What is true for the analogy does not necessarily have any bearing on the situation being analogized, which is, to my surprise, actually a word. :D
 
xformer said:
What about fuel efficiency? I know comparing 2000lbs is miniscule to 44 ton, but it does add up over the lifetime.
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The GE 44-ton switcher is a four-axle diesel-electric locomotive built by General Electric between 1940 and 1956. It was designed for industrial and light switching duties, often replacing steam locomotives that had previously been assigned these chores.

This locomotive's specific 44-short ton weight was directly related to one of the efficiencies the new diesel locomotives offered compared to their steam counterparts: reduced labor intensity. In the 1940s, the steam to diesel transition was in its infancy in North America, and railroad unions were trying to protect the locomotive fireman jobs that were redundant with diesel units. One measure taken to this end was the 1937 so-called "90,000 Pound Rule," a stipulation that locomotives weighing 90,000 pounds (41,000 kg) – 45 short tons – or more required a fireman in addition to an engineer on common carrier railroads.[citation needed] Industrial and military railroads had no such stipulation. The 44-ton locomotive was designed to abrogate this requirement. Other manufacturers also built 44-ton switchers of center-cab configuration.
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I knew it had something to do with the crew, I just couldn't remember exactly what. I used to do work for a couple of short lines, and I was hanging around at one of the locomotive shops talking to an old timer who was telling me all about GE 44 Tonners. All those short line guys loved them.
 
Joethemechanic said:
I knew it had something to do with the crew, I just couldn't remember exactly what. I used to do work for a couple of short lines, and I was hanging around at one of the locomotive shops talking to an old timer who was telling me all about GE 44 Tonners. All those short line guys loved them.
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I got to operate one briefly once. :)
 
GoldDigger said:
But shouldn't it be geometrically (logarithmically) halfway instead of arithmetically halfway? That is 25 x sqrt(2)? Which is 35.35kVA
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Why? Someone decided that the choices weren't granular enough so they added a size in between 25kVA and 50kVA. What difference does it make if it's 37.5 or 35.35kVA? Some people are going to see yet another decimal place and freak out. :D
 
ggunn said:
Why? Someone decided that the choices weren't granular enough so they added a size in between 25kVA and 50kVA. What difference does it make if it's 37.5 or 35.35kVA? Some people are going to see yet another decimal place and freak out. :D
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They could round it off to 35 and it's still closer to the geometric mean than 37.5 is. Circuit recloser sizes (amps) for power distribution: 15, 25, 35, 50, 70, 100, 140. It's more of a geometric sequence.

But it's really not much difference between 35 and 37.5.
 
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