Re: [TCML] Primary Grounding was [Control Cabinet ...]

[FIFTYGUY@xxxxxxx]

In a message dated 12/17/08 8:21:03 P.M. Eastern Standard Time,  
yurtle_t@xxxxxxxxx writes:

>FWIW, I have killed two VFD's and a Lincoln 225 Welder (the old  100% copper 
kind) with my set-up. >Perhaps there's a better  way?

    I killed two VFD's and had arcs from my (line  grounded) control cabinet 
to nearby objects until I added a Terry Filter. I see  you have an overvolt 
gap and a lightning arrestor, but a filter will block the  high frequency spikes 
before they get to the pig.
    Yes, I see you have a big line filter on the  primary side. But I already 
had a line filter for the mains and a small one  for 110V accessories, and I 
still had the aforementioned problems until I added  the Terry Filter. In 
fact, you might want to consider moving your line filter  ground from RF ground to 
line ground - the filter may be a path for bad stuff  getting from the pig 
secondary to the pig primary side. At RF frequencies, if  the filter isn't 
properly mounted through a steel bulkhead, the RF can just  radiate around the 
filter body and bypass it and make it a moot point.
    I also now run my VFD output to the rotary in a  shielded cable (line 
grounded at cabinet), and inside a PVC pipe to ward off  secondary strikes. The 
issue of grounding the motor is a tough one, so I just  left it floating. I 
also added varistors between each motor lead and line ground  right at the 
cabinet receptacle.
    Since I did the above modifications, the cheapest  VFD I could find 
(Dart) has survived just fine, including through multiple  primary-secondary strike 
episodes.
 
-Phil LaBudde

Center for the Advanced Study of Ballistic  Improbabilities
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