RE: Three phase conversion In Rush current Concern.

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Leigh Copp" <Leigh.Copp@xxxxxxxxxxx>

Hi Jim,


Depending on your budget, a 3 phase variable speed drive (there is a 50
HP unit on e-bay right now for $330 for example) would not only allow
you to control start up, but it would create true 3 phase from single
phase. Most of the drives out there use a static rectifier (diode, not
SCR or transistor) and will run on single phase provided that you
de-rate them accordingly (50% is typical).

Otherwise, a pair of TRIACs slowly ramped up would be effective as a
soft start.

Simpler, but more expensive would be a tapped autotransformer or
reactor, or even a resistor bank, stepped out with contactors on a time
delay or current basis. All of this was the norm for starting large
motors 30+ years ago, and is still in use today in many cases.

You may find starting a bit troublesome (although you won't require much
starting torque) with reduced voltage techniques however, given that you
are faking your 3 phase with capacitors.

Cheers,

Leigh

-----Original Message-----
From: Tesla list [mailto:tesla@xxxxxxxxxx]
Sent: September 29, 2006 12:51 PM
To: tesla@xxxxxxxxxx
Subject: Three phase conversion In Rush current Concern.

Original poster: "Jim Mora" <jmora@xxxxxxxxxxx>

Hello All,

Here is the schematic of my proposed three phase converter to power my
Raytheon 3 phase 24 KV DC power supply (I also have a generator in
progress). The capacitors are mid-range based on other phase converters
documentation and are subject to trail and error, to achieve balanced
output.

http://hot-streamer.com/temp/JimMora/3PhaseStaticIdlerMotor.pdf

If anyone has experience in this arena I could use some help.

The motor will run at ~3425 rpm which has the benefit of handling sudden
change in current draw (think spark gap) and the disadvantage of inrush
current to start it up.

The motor will draw around 49 amp in static state load conditions. The
LR
rating @ 240v is 290 amps, yikes. I have seen a few schematics of "soft
start" with triac's or SCR's.

I think  my neighbors to the right will see a burnout as will their
computers as we are a distance from the pig and the service wire is
1950's #
4 I think. I have upgraded to 100 amp service. Beef connected to turkey
at
the Mast head.

Any suggestions would be appreciated, I am a novice in poly phase, yet
know
the complexities of a seeming simple circuit.

Thanks Much,
Jim Mora