Ken Sterling wrote:
Bruce (or anyone qualified).....
Three phase power ----- isn't each leg 120 degrees from the others?
Single phase power - 220v - isn't each leg 180 degrees from the other?
If the above is correct (and I'm hoping I understand it correctly) it
would stand to reason, that if you needed to hook up a 220v single
phase machine and you had 3 phase available at that location you
could, (and I am not saying it's correct) connect to two of the three
phases and run the machine, even tho the sine waves wouldn't be 180
out, it probably wouldn't hurt anything. Am I correct in this
assumption??? Any and all comments welcome
Thanks.
Ken.


Ken
To visualize phase angles draw 3 parallel lines the same length, put
a dot at the left end of the top line, and a dot at the right end of the
middle line, and a dot in the middle of the last line. Now imagine those
dots moving at the same time, the same speed from one end to the other.
Their timing is 120 deg apart and if you look only at the top and middle
lines, they are 180 deg apart.
120/208 is star or y just imagine each leg of the y is a coil of a
transformer and the middle of the y is grounded. Each end of the y is a
phase, the voltage is phase to ground 120, phase to phase 208. On a
120/208 bank all 3 transformers will be the same size.
120/240 is delta imagine a triangle, each side is a coil of a
transformer, each point is a phase, in the middle of one side draw a
ground. The transformer you ground is the lighting transformer. It has
all the single phase load. The voltage is hot leg to ground 120, hot leg
to ground 120, power,high,or stinger leg to ground 208, because it is a
coil and a half away from ground. Between any 3 hot is 240v. In a
120/240 bank the middle or lighting transformer will be larger to handle
the 3phase plus the single phase load. To visualize an open delta erase
one side of the triangle. The only way you can tell if you have an open
delta versus a delta is to look at the bank, 2 transformers is open
delta, 3 is delta.
Open delta is not very efficient. It is good for temporary repairs. I
could rebuss a bank to open delta so a farmer could milk his cows and
not have to wait 4hr for a crew to change out 1 transformer.
The secondary coil of the transformers is not center tapped. It is two
coils, you have them serialed for 240 and paralleled for 208.
You can see some pages from a transformer manual at
http://murrayranch.com/Electricity.htm

Don