277/480 volt history

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Tony S said:
Talking of odd voltages and this is one I never did find the reason for. We used either 433V or 550V, the plant this was on had all German equipment which at that time normally would be 415V.

A 440V transformer would be a special order, I don’t know why?
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Probably not special order at the time. When I first started in the field it was 440/250. Later 415/240. Now 400/230. Nominally. Will we revert to 415V and red/yellow/blue for phase colours whe/if we leave the EU?
 
electrofelon said:
This might be an example of that. This is a Seattle City Light transformer. I dont know what their "official" distribution voltage is, but it is often called 25.5KV. You can see the transformer doesnt say that.
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The transformer does say that.
25570/14750
120/240

that means the transformer is for a 25 kV system, and outputs whatever the input is Divided by 61.45
so for that one, if the input is 14750V primary to gnd voltage, the output is 120/240 split phase
if it’s 14,400 in, then it’s 117/234 split phase.
it all has to do with thenXF TTR.

the TTR on transformers is wound with compensation for voltage regulation to standard nominals.
The POCOs run their voltages a little high through the regulators at the station or out on the line.
the “odd” readings you see are nothing more than fluctuations in the utility primary voltage.

on the transformer, rating is 25570 gndY/14750
that it 25570 primary L-L, and 14750 primary L-G

so, divide the 14750 by the 240, you get the XF TTR.

Take your voltage you read on your voltmeter (forget voltage drop on your wires in the house for now), multiply it by 61.45, or whatever your TTR calculates on your specific XF. That is the primary voltage at that moment.
We try to stay within a specific bandwidth.
 
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Hv&Lv said:
The transformer does say that.
25570/14750
120/240

that means the transformer is for a 25 kV system, and outputs whatever the input is Divided by 61.45
so for that one, if the input is 14750V primary to gnd voltage, the output is 120/240 split phase
if it’s 14,400 in, then it’s 117/234 split phase.
it all has to do with thenXF TTR.

the TTR on transformers is wound with compensation for voltage regulation to standard nominals.
The POCOs run their voltages a little high through the regulators at the station or out on the line.
the “odd” readings you see are nothing more than fluctuations in the utility primary voltage.

on the transformer, rating is 25570 gndY/14750
that it 25570 primary L-L, and 14750 primary L-G

so, divide the 14750 by the 240, you get the XF TTR.

Take your voltage you read on your voltmeter (forget voltage drop on your wires in the house for now), multiply it by 61.45, or whatever your TTR calculates on your specific XF. That is the primary voltage at that moment.
We try to stay within a specific bandwidth.
Click to expand...

No it doesn't say 25500, it says 25570. So the nominal voltage is actually 25570? I don't know why SCL came up with this odd ball voltage. Anyway yes I understand there may be rounding errors. Many people will say 12.5kv vs the actual nominal 12.47. it can be a point of confusion. Often I will ask a Poco what the voltage is and sometimes I will get a rounded number and think wow that is an odd voltage before I realize they rounded to the nearest 1000. They didn't realize I wanted the exact nominal not an approximate.

A note on compensated windings. This has been discussed here and I believe the verdict was that most other than control transformers typically used under the NEC do not have compensated windings. Perhaps it is different for transformers typically used in utility applications though.
 
Hv&Lv said:
The transformer does say that.
25570/14750
120/240

that means the transformer is for a 25 kV system, and outputs whatever the input is Divided by 61.45
so for that one, if the input is 14750V primary to gnd voltage, the output is 120/240 split phase
if it’s 14,400 in, then it’s 117/234 split phase.
it all has to do with thenXF TTR.

the TTR on transformers is wound with compensation for voltage regulation to standard nominals.
The POCOs run their voltages a little high through the regulators at the station or out on the line.
the “odd” readings you see are nothing more than fluctuations in the utility primary voltage.

on the transformer, rating is 25570 gndY/14750
that it 25570 primary L-L, and 14750 primary L-G

so, divide the 14750 by the 240, you get the XF TTR.

Take your voltage you read on your voltmeter (forget voltage drop on your wires in the house for now), multiply it by 61.45, or whatever your TTR calculates on your specific XF. That is the primary voltage at that moment.
We try to stay within a specific bandwidth.
Click to expand...

I'm confused. Whats the highest allowable voltage for 25kv class equipment? I always thought it was 25kv.
 
electrofelon said:
No it doesn't say 25500, it says 25570. So the nominal voltage is actually 25570? I don't know why SCL came up with this odd ball voltage. Anyway yes I understand there may be rounding errors. Many people will say 12.5kv vs the actual nominal 12.47. it can be a point of confusion. Often I will ask a Poco what the voltage is and sometimes I will get a rounded number and think wow that is an odd voltage before I realize they rounded to the nearest 1000. They didn't realize I wanted the exact nominal not an approximate.

A note on compensated windings. This has been discussed here and I believe the verdict was that most other than control transformers typically used under the NEC do not have compensated windings. Perhaps it is different for transformers typically used in utility applications though.
Click to expand...

Yes, it does say that.
25570 is a 25.5 KV system
Nominal doesn’t mean exact, it means close
ours is 24940 and 12470. It is 25KV system and 15 KV for purposes of ordering transformers.
we have many station transformers rated at 7620 secondary, 115kV primary. We want our customers to see nominal 120. Our distribution XFS are 60:1
by the math that won’t work.
We lower the voltage at the station with regulators through the control panel or with setting the station transformer at something like 117500/7620.
With our 115kV system, that puts me somewhere around 7400v.
thats a good number to leave it at. Between transmission voltage variances the voltage regulators will take care of the rest. Ideally I want them no more than +4 to -4, hovering around 0 or +1,-1 for most of the time.


again, it’s all about the TTR more than about the actual numbers.
take a transformer that has taps.
it is in 5% taps on many XFs.
they come to us set at 100%
if our voltage doesn’t exactly match the primary nominal, we can set the taps to get the secondary real close. Close enough for use.
 
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mbrooke said:
I'm confused. Whats the highest allowable voltage for 25kv class equipment? I always thought it was 25kv.
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I believe I read some time back it’s somewhere about either 26 or 27 kV.
after that it should be a 34.5 kV class

btw, that one in the picture is pushing the limits of 25KV class IMO.
UNLESS it’s insulated at 35 kV now.
then it’s a 35 kV class XF on a 25 kV system.
 
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Hv&Lv said:
I believe I read some time back it’s somewhere about either 26 or 27 kV.
after that it should be a 34.5 kV class
Click to expand...

I've seen it at 27kv, but also at 25kv for some pole equipment. I can't figure it out. Never put much effort into it as 22 and 23kv is my go to voltage.
 
mbrooke said:
I'm confused. Whats the highest allowable voltage for 25kv class equipment? I always thought it was 25kv.
Click to expand...

It is odd. I don't know why they came up with their own voltage when there were (presumably at the time) other more standard similar voltages. Also seems like that gets you just barely above 25 kv class and you might as well gone to 35 kv class. I have seen some of their primary cables and they do say "25.5 kv " on them. Maybe they get it custom made? Most likely at the time these decisions were made, the MV kv class stuff wasn't as standardized - that's all I can think of
 
electrofelon said:
It is odd. I don't know why they came up with their own voltage when there were (presumably at the time) other more standard similar voltages. Also seems like that gets you just barely above 25 kv class and you might as well gone to 35 kv class. I have seen some of their primary cables and they do say "25.5 kv " on them. Maybe they get it custom made? Most likely at the time these decisions were made, the MV kv class stuff wasn't as standardized - that's all I can think of
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I want to say custom made, all the cable I've seen are 25kv rated.
 
electrofelon said:
Yeah no doubt. An old building I worked in had a 600V ungrounded service. It had a fault and who knows how long it had been like that, could have been decades. I finally did find it when I was re-routing the elevator circuit into a transformer after upgrading the service to 120/208.



That makes sense. That would make it a lot more efficient for larger buildings to take 277/480 without need to transform most of the lighting. I really hate our low voltages. Hate 208. Even 240 is too low. Like the way Europe does it with 230/400 - except I do like our 60hz:p

Another question: What happened to 600v? was that a fad that faded out? Lots of the mills in New England were 600. Pretty much never see 600 anymore.
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FWIW, Dunkin Doughnuts or Burger King typically has a 600amp service. In reality they could get away with a 300amp service.


300x208x1.73= 108,079va

108,079 @ 400 volts is 156 amps.

So a 200amp panel could suffice in theory:

https://www.amazon.com/Siemens-S426...386046&sprefix=200amp+panel+3+,aps,158&sr=8-1



I know its 240, but 240 straight rated breaker and 120/240 22kaic breakers will work fine on 240/415.

Might need a sub, but hey, it will work.
 
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