About 3-phase AC

[Jack// ani]

Hi there,

In 3-phase AC wiring, if phase to neutral voltage is 110V, then why is
phase to phase voltage 220? I know phase difference between any two
phases differ by 120 degree, so they should add up to give something
less than 220V! It should sum up to give 220V if the phase difference
were 0 degree or 360degree!

Thanks

 

[Jack// ani]

I think you got something wrong, or I didn't expressed it correclty!
Say you have two AC sources of 110V, now if I put them in series they
should add up to give 220V if their instantaneous phases are same(0 or
360) or if they are 180 phase out they should sum up to zero. I think
these two AC sources are just like two phases of 3-phase AC supply
which are 120degree phase apart. And they should give a voltage less
than 220V when summed up.

Any Help...Thanks

 

[svetoslav belchev]

Here in bulgaria a 3 phase AC is 220 V phase-ground and 380 V phase-prase

 

Bob Eldred wrote:

"John Larkin" <jjSNIPlarkin@highTHISlandPLEASEtechnology.XXX> wrote
in
message newsc5g51dq554au92781i64ffmr6olg1v7en@4ax.com...
On Sat, 09 Apr 2005 03:43:44 GMT, "Bob Eldred"
nsmontassoc@yahoo.com
wrote:


"John Larkin" <jjSNIPlarkin@highTHISlandPLEASEtechnology.XXX
wrote in
message news:bhie515gc9n9lf1m10juetul1n0e842ffq@4ax.com...
On 7 Apr 2005 11:03:49 -0700, "Jack// ani"
nospam4u_jack@yahoo.com
wrote:

Hi there,

In 3-phase AC wiring, if phase to neutral voltage is 110V, then
why is
phase to phase voltage 220? I know phase difference between any
two
phases differ by 120 degree, so they should add up to give
something
less than 220V! It should sum up to give 220V if the phase
difference
were 0 degree or 360degree!

Thanks


One common but bizarre US wiring practice is to have a 240 volt
line-to-line delta three-phase system in which one side of the
triangle is center-tapped and is neutral. So 120 single-phase is
available for regular outlets, 240 single-phase is available for
things that need it, and 240 line-to-line is available for three
phase
loads. That's fairly common in small commercial buildings. The
leg
opposite the neutral is call the "bitch leg" or the "stinger."

John

I can't see how that can be a delta. I think what you have
described is a
six phase "Y", center neutral as usual. It's 120 Volts out any leg
and
240
Volt center tapped any leg to it's stinger. And, 208 Volts leg to
leg.
It's
also 120 Volts from any leg to the adjacent stinger. It's not all
that
bizarre and can be created from any three phase system with a
transformer.
Bob



What I described is this:


C
/ \
/ \
/ \
/ \
/ \
/ \
/ \
/ \
/ \
/ \
/ (gnd) \
/ | \
A------------N------------B
| | |
| | |
120 N 120



John


Why would anybody do that? What is the voltage from A to C? A to N?,
What
is the relation of N to ground. Clearly this kind of a bastard
connection
would be prone to gross unbalance or to parasitic voltages on the
neutral.
If its 240V leg to leg, with N in the center of one leg, what is N to
B for?
What is the voltage B to C? Furthermore if its 240 Volts three phase
on all
legs, what equipment uses it, most are 208? Since 120 Volts is only
available from one leg with a neutral how is power distributed in a
building
say to lighting or to other 120 Volt circuits maintaining some
semblance of
balance between the phases. I'm not saying you have never seen this
but I
never have and it can't be very common.
Bob
It's still common in the US where houses are mixed with small motor

installations. That unexpected 208-to-neutral is(was) a problem on
water-well controls when you needed 120v for the control-circuit.
WAde H