| A conversation recently came up in college about 3 phase voltages. More
| specifically 3 phase voltage consisting of 600/347V (delta or wye) as
| compared to 440/220V (delta or wye) It was mentioned that the second
| voltage (440/220) came from somewhere in the east coast (US and Canada) and
| here where I live and most of Canada it is 600/347 (industry) . How is this
| voltage created ? I thought that the difference between phase and
| neutral/ground was a factor of the Sq Rt. of 3 ( 347 * 1.73 = 600) So how
| is 440 / 220 3 phase created /
A more precise value for the square root of 3:
There are quite a number of three phase combinations available, though not
all are available in one place, normally. I'll list utilization (but not
distribution) voltages I know about in the US from high to low:
This is primarily used in mining services, driving underground digging and
drilling machines on very long "extension cords".
575 delta (legacy voltage)
550 delta (legacy voltage)
Heavy industry. May exist in US, but I haven't seen it. Probably exists
in Canada. I've seen transformers offered for this. This could come in
open delta or closed delta.
575Y/332 wye (legacy voltage)
550Y/318 wye (legacy voltage)
Industry and commercial, but with lower line-to-ground voltages. Rare in US
(but I have seen it). Common in Canada. The lower voltage is commonly
referenced as 347, but if you use and accurate square root of 3 to divide
exactly 600, you get 346.41016151377 so the 346 is more technically correct.
Using 1.73 gets you 347.
460 delta (legacy voltage)
440 delta (legacy voltage)
Heavy industry. Still exists in US. This could come in open delta or closed
delta. It may even come in center tapped for 240 volts.
460Y/266 wye (legacy voltage)
440Y/254 wye (legacy voltage)
Industrial and commercial, but with lower line-to-ground voltages. Common
in US, and generally available in Canada or much of North America.
No one seemed to want this voltage, even though it works out nice and
close mathematically :-)
Not common in US, but apparently used by US military as lots of surplus
generators have this voltage set up. Perhaps the intent was to work with
a voltage more common in the world. I've seen this as an available voltage
in one power company tariff.
230 delta (legacy voltage)
220 delta (legacy voltage)
Still common in the US. Usually comes with a center tap on one winding
that can supply a limited load of single phase 120 volts. It is usually
stated as limited to 5% of total capacity, but I don't know if this means
to total load on that one winding, or the imbalance between 120 volt loads
on that tapped conductor.
Similar to delta, and mostly compatible. But it is formed with only two
transformers wired up at 90 degrees different voltages (one has the
highest with the lowest as a center tap, and the other has the middle
voltage and is known as "stinger" or "wild leg").
230Y/133 wye (legacy voltage)
220Y/127 wye (legacy voltage)
216Y/125 wye (legacy voltage)
Available in a few place as a way to get lower line to ground voltages
while being functional with 230/240 volt motors that can't make it down
to 208. 220Y/127 is actually common in Mexico and works out quite close
to the square root of 3.
200Y/115 wye (legacy voltage)
190Y/110 wye (legacy voltage)
The most common three phase voltage in the US, supplying commercial and
idustrial users, and in some cases residential.
This has shown up in some places primarily in an open delta form. One
such place is passenger railroad cars. It's entirely usable just like
single phase 120 volts. But the line to line voltage is 120.
240*/208/120 star (theoretical)
You could build this with three center tapped 120/240 volt transformers
bonding the 3 taps together. You'd get both 240 and 208 as needed. But
I've never seen it used.
There has been some research into using higher order phases for distribution
or transmission: http://phil.ipal.org/electric/powerlines.jpg
Need to power 277 volt lighting w/o getting a three phase extension?
You could construct this system to do it using the 277 volt transformers
common for 480Y/277 systems, but connected on just single phase. I have
never seen or heard of it actually being done.
Commonly used for roadway and tunnel lighting.
The most common service voltage in the US.
Being "phased out".
Not really a service voltage, but can be a utilization voltage under
NEC article 647 for low noise purposes like audio studios.
| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
Click to see the full signature.