RE: 3 phase converting

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Harvey Norris <harvich@xxxxxxxxx>


--- Tesla list <tesla@xxxxxxxxxx> wrote:

> Original poster: "Steve Conner"
> <steve.conner@xxxxxxxxxxx>
>
>  >You can run a three phase
>  >motor okay, but you can't generate a true rotating
> magnetic field
>
> That's kind of a contradiction in terms. If you
> didn't have a rotating
> magnetic field then by definition you would not be
> able to start a three
> phase motor.
>
> I once visited the EE department at Glasgow
> university and they demonstrated
> a spinning "Beer Can Of Columbus" that worked off
> single phase current. It
> used two coils 90 degrees apart with one fed
> directly from the line and the
> other fed via a capacitor. I think they used low
> voltage AC like 24v or
> similar.
Very interesting concept there! After mulling things
over it would seem that a single phase can be
manipulated to appear as polyphase. In air core terms
one could measure the voltage rise of the resonant
coil, and then supply the reactive coil with the same
voltage as a reactance coil. The magnetic fields
produced would be out of phase, which is a requirement
for a rotating magnetic field. Heres some further
negative text book comments on the issue.
> My conclusion- You don't need three phases to
> generate a rotating magnetic
> field. It just happens to be the most efficient and
> economical way of doing
> it.
Jackson's Intro to Electric Circuits defines
polyphased currents in the following way.
" Less copper is required to supply a given load power
at a given voltage with a polyphase system then with a
single-phase system."
    This is based on the usage of a common return
line. For two 90 degree phased currents carrying one
amp, the return line, designated as neutral in further
polyphase schemes, will contain the vector sum of the
phase currents, or the sq rt of 2, being 1.4 Amps. By
combining the return lines, what would be 2 Amps in a
dual single phase system has become 1.4 Amps. Likewise
in the 3 phase delivery system both the enter and exit
points made by the stator currents carry shared
currents, where in that case 1.7 amps will divide into
dual 1 amp currents 120 degrees out of phase.
"If the load on each phase of a polyphase source is
identical, the instantaneous power input of the
alternator is constant."
On a single phase this does not apply, since there is
a point in time when the amperage is zero during the
polarity change. To produce the effect of a magnetic
field in rotation, a magnetic field must be
continually present on one of the coils producing this
rotating magnetic field effect. This is done by the
amount of off phasing present on the delivery lines,
which ideally for the perfect example is 90 degrees.
"A single phase system can produce only a magnetic
field that increases and decreases in flux density and
reverses its direction each 180 degrees but does not
rotate."
Apparently then  magnetic rotation has the
prerequisite that a magnetic field  that has a
collective constant flux density in time appears to
rotate through space when expressed through coils
arranged in space. It is the effect of two phases
acting together magnetically producing the illusion of
movement of a constant flux density through space.
Thomas further comments;
"Also with two currents 180 degrees out of phase, we
cannot produce a rotating magnetic field."

In the production of magnetic fields by resonance from
the alternator frequency, a most perculiar perplexing
problem developed conceptially. A table of 30 coils
lined in two rows of 15 was split into groups of 10,
where the first two columns of ten coils was attached
as two phases to the alternator. These columns of .15
henry were resonated, whereby the peculiarity of loose
magnetic coupling showed that while in reactive
measurements they exhibited no mutual inductance, at
resonance the mutual inductance effects were very
evident. The two outputs appeared as 180 phases, not
as two phases at 120 degrees as would be suspected.
Both the input amperage lines and the internal voltage
rise differeneces of the phases showed that a near 180
degree difference was present on two of the phases,
making a combined q factor in the 40's. Now then the
third coil system as phase 3 was added as a folded
column of 5 coils each, also .15 henry, but this
system would not conduct a balanced amperage with the
other phases, giving about half the value of
conduction as the columns in mutual induction
lengthwise. Normally the extraction of a third phase
current will detract from the currents formerly found
on two phases, but in this example the reverse
situation occurs. The former phase angle measured near
180 is only slightly reduced by the addition of the
third phase, but its interphasal voltage difference
has increased.  The first measurement of the added
voltage difference of phase 3 now shows another 180
phase angle. This should only leave about 20 degrees
for the remaining phase angle voltage measurement.
However this measurement shows about 60 degrees.  More
voltage is measured inside the three phases series
resonant voltage rises then can be accounted for in
time.

In this proposition it seems incredible enough to
blindly assume that three magnetic fields in
opposition on these columns would in turn produce a
more expanded interphasal voltage difference, to the
point where it can be made experimentally measureable
employing spirals in mutual inductance. In the
previous example the voltage rise of phase 1 and 2
were 372 and 387 volts, producing 722 volts beween
them. This 95% of the amount that would be present if
the angles were 180 in phasing. The third phase has a
resonant voltage rise to 188 volts from the 14 volt
stator, and the next interphasal voltage measurement
shows 372 volts and 188 volts combining to yeild 561
volts, slightly over a perfect 180 phasing! Thus the
remaining phase angle should only contain the 5%
voltage difference contained in the first phase angle
example of a summation of 759 volts being expressed as
a 722 volt difference, only a mere 37 volts
difference. Yet that measurement shows a 388 volt and
188 volt potential combining to form 387 volts between
them, which should at least form a 60 degree phase
angle. On the three phase circle then we have 60 and
180 and one measured near 95% of the summed voltage
values that would mean a 180 phase angle. The sin-1 of
.95 is 1.25 rad vs 1.57 rad for a quadrant
circumference making the phase angle deviance
(1.25/1.57)*90= 79.6 degrees. Thus we actually have
about a 160 degree phase angle, a 180 degree one and a
60 degree one, adding to 400 degrees when it should
only add to 360.

Obviously the 30 coil structure needs to be rebuilt
with the ten groups all aligned together so that all
three are loosely magnetically coupled chains at
resonance. It may be rediculous to assume that three
180 phased systems can be built but the idea is there.
The requirements of capacity for mutually coupled
spirals for each phases use becomes quite large for
making such a system, where the interphasal voltage
gain made by three 180 phased magnetic fields is
compromised by the fact that the q factors of the
spirals themselves will have been reduced. I am going
to look at some reactance data of these spirals, where
my tests showed that mutual induction can double the
reactance currents.
HDN

> As an aside- Even with only one phase and no added
> capacitors (so no
> rotating magnetic field at all) a three phase
> induction motor will run. But
> pretty poorly and the starting torque is zero.
>
> Motor textbooks explain this by saying that the
> single phase pulsating field
> is the sum of two rotating fields spinning in
> opposite directions. When the
> rotor is at rest they cancel giving zero torque. But
> set it spinning by hand
> and the torques no longer cancel because the slip
> frequencies for the two
> fields are different.
>
> Steve C.
>
>
>


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