Re: [TCML] Variable RSG

[FIFTYGUY@xxxxxxx]

In a message dated 4/8/08 11:28:41 P.M. Eastern Daylight Time,  
resonance@xxxxxxxxxxxx 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.  
 
-Phil LaBudde 
Center for the Advanced Study of Ballistic  Improbabilities



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