[TCML] Variable RSG
FIFTYGUY at aol.com
FIFTYGUY at aol.com
Tue Apr 8 21:58:39 MDT 2008
In a message dated 4/8/08 11:28:41 P.M. Eastern Daylight Time,
resonance at wildblue.net writes:
>Have you had any problems with the VFD setup being affected by the RF or
>magnetic fields under the primary coil, eg, in the base when the RSG is
>placed? Especially with DRSSTCs with their extremely high primary currents
>and fast switching speeds producing large pulses in controller wires, etc.
Who uses a RSG with a DRSSTC?
>Does anything kick back into your controller causing full speed lockon, or
>do you use some filters of some type between the RSG motor and the
>controller which is usually at a remote location?
A common practice is to use a shielded cable between the VFD and the
motor. Of course, we're back to the issue of "what gets grounded to what". For
safety, the motor should be tied to "green wire building ground". And the
recommended practice is to run the motor's grounding wire directly to the drive's
chassis, which is of course also tied to green wire/building ground. But
it's in a close proximity to the spark gaps and primary wiring, not to mention
usually under the primary itself. So it'll probably pick up a lot of RF and
put it on the green-wire system.
If any of the motor windings or the wires going back to the drive's
output get too high a voltage on them, the drive will fail (usually a
"non-passive end-of-life event"!). Another reason for using shielded cable between the
drive and motor.
With the pig coil, I'm paranoid about running any low-voltage winding
out to the coil itself. I run fans off a battery and small inverter. For the
VFD-to-motor, I use shielded drive cable, with the shield tied to green-wire
ground/chassis. But then I run the cable inside flexible metallic conduit when
it gets within striking distance of the coil. The flexible conduit lays on
the ground, and is tied to RF ground. If a streamer hits the conduit, and
manages to get back to green-wire ground, so be it. But it's a *lot* better than
simply using a piece of SO cord.
Center for the Advanced Study of Ballistic Improbabilities
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