Three-phase "star" and "wye" vs. "delta"
hof...@wmich.edu
the same as "star", because multi-phase other
than 3-phase is almost never used.
The "wye" and "star" configurations are the same:
the three phases are connected together at one
point in the "center", like a "Y" . The other configuration
is "delta" (like the Greek "D"). where the phases
are cconnected in a ring or loop, with no one point
where the three phases are connected together.
Richard Hoffman
fred veenschoten
fred
hof...@wmich.edu wrote in message <4YFnGJboKTV0@winnie>...
S Crook
Phase and 1 phase power, at the expence of a fouth conductor.
Typical useful combos include 277/480V where 277V 1phase is used for
lighting and 480V 3 phase for motors and large resistance heating loads; and
208/120V.
Note that at over 300 volts higher grade insulation (600 V vs 300 V) and
differant wiring methods (bigger enclosures, 600 volt fuses/breakers, larger
clearances, etc.) so 277V is very economical for lighting.
It is possible to supply a few 1 phase loads in a primarily 3 phase system
from a delta system by center tapping ONE transformer winding and grounding
it to form a neutral so a 240V delta system can supply a little 120/240 1
phase, BUT you also have a "wild leg" i.e. if the phases are A, B, & C and
you center tap the A-B winding then the voltage from C to neutral is higher
than 120 V! Beware! (someone help me out, C to CT neutral volts for a 240V
delta = ?)
fred veenschoten <fred...@mindspring.com> wrote in message
news:7opmos$6m1$1...@nntp9.atl.mindspring.net...
mull...@advinc.com
"S Crook" <scr...@iontrack.com> wrote:
> (someone help me out, C to CT neutral volts for a
> 240V delta = ?)
I thought that was the origin of the 277 volts?
Jim (drawing those diagrams now....)
Sent via Deja.com http://www.deja.com/
Share what you know. Learn what you don't.
PeterH5322
>>
I thought that was the origin of the 277 volts?
>>
Nope.
277 comes from line to neutral of a 277/480 volt three phase system.
Ned Simmons
peter...@aol.com.org.gov says...
>
> >>
> I thought that was the origin of the 277 volts?
> >>
>
> Nope.
>
> 277 comes from line to neutral of a 277/480 volt three phase system.
>
>
>
Paul Koning
> ...
> It is possible to supply a few 1 phase loads in a primarily 3 phase system
> from a delta system by center tapping ONE transformer winding and grounding
> it to form a neutral so a 240V delta system can supply a little 120/240 1
> phase, BUT you also have a "wild leg" i.e. if the phases are A, B, & C and
> you center tap the A-B winding then the voltage from C to neutral is higher
> delta = ?)
240 * sin(60deg) which is 208...
paul
PeterH5322
>>
> 277 comes from line to neutral of a
> 277/480 volt three phase system.
>
And that would be a wye (or star) system with the neutral at the center.
>>
Yes, in the same way as the 120/208 system is a Wye (or Star) system.
The question was asked earlier why one system is to be preferred over the
other.
It's been perhaps 30 years since I was employed as an E.E. at the country's
largest municipal electric utility, but in my experience we never used Wye,
certainly not for transmission, which in our system was anything above 69 kV,
nor in sub-transmission, which in our system was either 34.5 kV or 69 kV, not
in primary distribution, which in our system was 4.8 kV.
Secondary was the customer's choice, with 120/240 single phase for residential
and 120/208 for small commercial and 277/480 for large commercial, both three
phase.
Anything "special" such as 4.16 kV (Wye) or 4.8 kV (Delta) or 34.5 kV (Delta)
was at the customer's sole cost.
Our use of Delta for primary distribution and higher undoubtedly had a lot to
do with the method of protective relays we utilized.
There is some anecdotal evidence that there is a trend towards Wye at
sub-transmission and primary distribution voltages.
I seriously doubt that transmission will ever be converted to Wye.
Why employ four wires when three will do the same job?
Eastburn
at 2/3 rd power in what was called 'inverted V'. (lost one leg - other two
will keep up in a brown down mode (maybe).
Most hospital, police, fire and such (mil for sure) - Mil does primary and
secondary
and then buys larger transformers to handle 100% when in inverted V mode.
Martin
--
NRA LOH, NRA Life
NRA Second Amendment Task Force Charter Founder
Martin Eastburn, Barbara Eastburn
@ home on our computer old...@pacbell.net
PeterH5322
>>
Remember - in the use of Delta transmission - the step-down will operate
at 2/3 rd power in what was called 'inverted V'. (lost one leg - other two
will keep up in a brown down mode (maybe).
>>
One of the advantages claimed for delta is three phase can still be transmitted
if a *single* line-to-ground fault occurs.
That probably has to be contrasted with what the protective relays will do.
I can't imagine that the protective relays would allow two phases to be
connected, while a line-to-ground fault was detected on the third phase.
OTOH, for customer use, on the load side of the distribution transformer, this
is true ... the so-called grounded delta connection, which is apparently
outlawed with the 1996 NEC.
Brian Lawson
capabilities. For most of us though, it is in the hook-up for motors
that is of interest.
If you look at a "Y" (star) hook-up, it is apparent that for current
to flow from any one leg (of the 3 phase supply) to any other leg, the
current must pass through 2 of the windings. This of course is a
higher "resistance" than flowing through only one winding. When a
motor is started from a non-rotating energy level, there is no back
emf to limit the current flow, and so the "Y" connection helps limit
the current inrush with its relatively high resistance. The motor can
continue to operate in this configuration, but very often, in larger
motors especially, once it reaches a reasonable rotation speed (in
about 1/2 to 1 second) it is then switched to the delta configuration.
Has a lot to do with motor operational energy costs, rather than
anything practical to us HSMs.