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why there is a need to alter "delta" to "star" ?

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Posted by OZ on February 8, 2004, 1:04 am
 
why there is a need to alter "delta" to "star" ?



Posted by Larry W4CSC on February 8, 2004, 5:19 am
 


I assume you're talking about delta and wye (Y) 3-phase AC power,
right?

Changing the delta configuration (one phase winding straight between
each phase output of the 3-phase output) puts out the AC voltage of
that single winding.  This is a 3-wire system.  As there is one
transformer winding from each wire to the next, you get what's on the
transformer.

Changing the same 3 transformer windings to a wye (Y) configuration
with a transformer winding on each of the three branches of the letter
Y with a 4th (neutral) wire coming off the common center point of the
wye (the middle of the letter Y) gives you different voltages.  From
any of the points of the Y to any other point, there are now TWO
transformer windings in series, but fed out-of-phase sinewaves.  The
voltage from a point to another point is 1.73 x each winding's voltage
(square root of 3), increasing the output voltage.  PLUS, from any
point to the neutral common center point where the Y comes together,
you get the original delta voltage (one winding from a point to the
center neutral).

Hooking the INPUT of the three transformers up in delta or wye (Y)
configuration will also cause the output voltages to yield different
voltages.  (notice how some units read 208, not 240, for instance.)
208VAC 3-phase power comes from Y connected primaries and delta
connected secondaries.  The many possible Y and delta connections of
the same transformers can get these different voltages.  208, 277,
240, 480, 908VAC.....to name a few.

3 phase power is far superior to "house power" 2-phase because there
is always a voltage across some winding of your 3-phase large motors
constantly pulling on the load.  3-phase motor power is very smooth
and more efficient because of it.

It is good to note this is all the invention of the genius Nikola
Tesla, for whom I have great admiration and consider the true genius
behind AC, Radio, etc......Inspite of the idiots at the Smithsonian
Institute who give Thomas Edison credit, ironically lighting the
Edison exhibit not with DC power and carbon filament light bulbs, but
with Tesla's multiphase AC and Tesla's flourescent lighting.
(Mentioning this to any staffer at SI will get you a curt good day.)
Smithsonian has no Tesla exhibit, even though the heat, A/C, lighting,
and every motor in the place was invented and patented by Tesla....(c;
Tesla's invention of remote control and a remotely piloted vehicle
(boat) didn't impress the Navy brass who could see no use of it......



Larry W4CSC

No, no, Scotty!  I said, "Beam me a wrench.", not a WENCH!
Kirk Out.....

Posted by Harry Chickpea on February 8, 2004, 4:27 pm
 not@home.com (Larry W4CSC) wrote:


While this is true, it is more a correction of a fault of AC power than a
superiority over DC motors.  Since DC motors were able to use commutators,
which also supply power to the proper winding, they were initially far superior
to the AC motors.  DC motors were more tolerant of varying speeds and were the
motor of choice for trolleys and electrified railroads for many years.  It took
the improved solid state switching control circuits to allow large AC motors to
finally become superior to the old commutator style motor.


I also have great admiration for this genius.  Variations of his ideas are
constantly being rediscovered.  The passive RFID tags use a variation of his
wireless power technology.  I think it would be fascinating to test his
building oscillators and attempt to use one to level one of the 1950s era
multistory structures slated for demolition.

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