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General Metalworking - All aspects of working with metal.
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Posted by DrollTroll on July 23, 2008, 12:23 pm
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Awl--
I noticed my 10 hp baldor is 3400 rpm, vs the 1700 of commercially made
rpc's. Does this affect anything?
In addition, a guy who describes an rpc for laser applications (!!) at
http://www.laserfx.com/Backstage.LaserFX.com/Hobby/PhaseConvert.html
says that an older inefficient motor is better than the newer
mandated-efficiency motors, as the newer ones can overheat. Is this true?
My baldor is a super-E (efficient), and actually runs very cool, but I don't
push it, either.
Does it make a difference whether a 9-wire motor is connected wye or delta,
ito rpc performance?
iiuc 9-wire correctly, at 220, you can wire it either delta or wye; at 440,
you can wire it only wye; (if there were 120 3 ph, you could also configure
a 220 9-wire motor to run but only in delta--or so I think...)
In a multi-idler set-up, would a mixture of delta/wye motors help/hurt
voltage regulation?
Thanks.
--
DT
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Posted by Wes on July 23, 2008, 3:11 pm
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>I noticed my 10 hp baldor is 3400 rpm, vs the 1700 of commercially made
>rpc's. Does this affect anything?
I don't think so, bearing life will be a bit shorter but it is practically
infinite as an
idler already.
One thing that I have always wondered about is how turning on your load affects
the rpm of
the idler and the produced leg. Could it be that faster is better? Or should
one use a
small flywheel. I'm not curious enough to play with the idea but maybe you are.
Wes
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Posted by Grant Erwin on July 23, 2008, 4:41 pm
Please log in for more thread options Wes wrote:
>
>
>>I noticed my 10 hp baldor is 3400 rpm, vs the 1700 of commercially made
>>rpc's. Does this affect anything?
>
>
> I don't think so, bearing life will be a bit shorter but it is practically
infinite as an
> idler already.
>
> One thing that I have always wondered about is how turning on your load
affects the rpm of
> the idler and the produced leg. Could it be that faster is better? Or should
one use a
> small flywheel. I'm not curious enough to play with the idea but maybe you
are.
>
>
> Wes
Idler motor spindle bearings are loaded somewhat by the magnetic forces involved
in creating the 3rd leg. No idler is ever silent for this reason either.
If you have a 3450 rpm motor, go ahead and use it - you can swap it out later
if you decide to.
Grant
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Posted by Robert Swinney on July 24, 2008, 12:57 pm
Please log in for more thread options There is no synchronism between the speeds of idler and load motors in a RPC.
Speeds of each are a
function of the mains frequency, usu. 60 Hz. When a load is a applied, neither
idler or load can
slow down below their specif slip speeds. In a RPC, currents circulate between
3-phase idler and
3-phase load in a complex fashion. There is no separate "generator" and "load"
in a RPC. Current
flow from the mains can be traced from one side of the line through 2 windings
each of both the
idler and load. Thus, there are two 3-phase motors connected across the
single-phase mains each
running as a single-phase motor.
The above is not quite true because the unconnected 3rd leg acts as a
transformer winding within the
rotating mass of copper and iron. If that path is completed the third leg will
be energized by
transformer action. This accounts for the well-known phenomena that enables a
3-phase motor to
start and run if another 3-phase motor is running as a single phase machine
across single-phase
mains.
It is the 3rd leg current that is augmented by capacitance in a RPC. Current
flow analysis of an
idler and load motor would show series currents tending to flow through the
balancing capacitance(s)
in both directions. That, of course, is impossible. However, when when
considered as a network, it
can be shown that series capacitance is used to tune (series resonate) the
"bidirectional" 3rd. leg
current bringing voltage to a value similar to the other 2 legs.
Bob Swinney
** Posted from http://www.teranews.com **
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Posted by DrollTroll on July 25, 2008, 2:30 pm
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> There is no synchronism between the speeds of idler and load motors in a
> RPC. Speeds of each are a
> function of the mains frequency, usu. 60 Hz. When a load is a applied,
> neither idler or load can
> slow down below their specif slip speeds. In a RPC, currents circulate
> between 3-phase idler and
> 3-phase load in a complex fashion. There is no separate "generator" and
> "load" in a RPC. Current
> flow from the mains can be traced from one side of the line through 2
> windings each of both the
> idler and load. Thus, there are two 3-phase motors connected across the
> single-phase mains each
> running as a single-phase motor.
>
> The above is not quite true because the unconnected 3rd leg acts as a
> transformer winding within the
> rotating mass of copper and iron. If that path is completed the third leg
> will be energized by
> transformer action. This accounts for the well-known phenomena that
> enables a 3-phase motor to
> start and run if another 3-phase motor is running as a single phase
> machine across single-phase
> mains.
>
> It is the 3rd leg current that is augmented by capacitance in a RPC.
> Current flow analysis of an
> idler and load motor would show series currents tending to flow through
> the balancing capacitance(s)
> in both directions. That, of course, is impossible. However, when when
> considered as a network, it
> can be shown that series capacitance is used to tune (series resonate) the
> "bidirectional" 3rd. leg
> current bringing voltage to a value similar to the other 2 legs.
Do multiple small rpc's have any inherent advantage over 1 big one--other
than easier starting, more economical operation?
Are five 2hp units in fact as powerful as one 10hp unit?
Is it better to cap each smaller rpc, or just cap the net collection?
Is delta/wye an issue? One preferable to the other? OK to mix?
If current pathways are complicated in multiple delta wound capped motors,
it must be really crazy in wye-wound.
--
DT
>
> Bob Swinney
>
>
>
> ** Posted from http://www.teranews.com **
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>rpc's. Does this affect anything?