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Re: [TCML] X-ray cable best practices for feeder cable
Hi DC, all,
I am not going to try and say that the resonance
won't affect the x-ray cable when used as a trans-
mission line from the pole pig to the base of the
coil, as it's pretty obvious from the statements of
others far more veteran in this subject matter than
myself that it very well could. However, I have per-
sonally never had this problem with my x-ray cable
transmission line and I'm sure many of you remember
my bringing my Green Monster coil to the 2007
Cheesehead Teslathon and firing it off. I ended
up using DC's "Big Bruiser" power supply to po-
wer it, as my power suply/control cabinet weighs
over 1000 lbs. and I do not have access to a fork
lift truck. At the Cheesehead T'thon (as I do at
home with my power supply), I ran the power from
DC's Big Bruiser power supply to the base of the
Green Monster via that single ~ 60 ft. strand of x-
ray cable, running the "hot" end through the central
core conductor and the "return" through the outer
mesh shielding jacket. I HAVE, however, had an 18
kV distribution arrestor one time and more recently,
the .1 uFd, 50 kV rated Hipotronics pulse cap (yep,
the primary cap) :^( to fail on me, but never the trans-
former. Fortunately, I had another .1 uFd, 25 kVAC
rated Plastic Capacitors pulse cap as a standby
to replace the dead Hipotronics cap (thanks Bill
Limeaux) ;^). Maybe this resonance issue IS what
took out these secondary components.?? Maybe
these components "sacraficed" thereselves for the
pig, as that was the intended purpose of the distribution
arrestor, anyway (safety gap substitute). Was not in-
tending on "sacraficing" the Hipotronics cap, though ;^((
----- Original Message -----
From: "DC Cox" <resonance@xxxxxxxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Tuesday, January 6, 2009 1:07:18 PM GMT -06:00 US/Canada Central
Subject: Re: [TCML] X-ray cable best practices for feeder cable
Resonance can be quite wonderful, or, as Phil explains in his examples, very
Resonance in your HV feeder cable is not something you want, so I avoid
using any feeder cable that is coaxial in nature, ie, has a ground
shield around it. X-ray cables were designed strictly for DC power
transmission and not for transferring AC power.
Been there, done that ----- and it cost me a pole xmfr!
On Mon, Jan 5, 2009 at 9:25 PM, <FIFTYGUY@xxxxxxx> wrote:
> In a message dated 1/5/09 10:37:26 P.M. Eastern Standard Time,
> sparktron01@xxxxxxxxxxx writes:
> >I am now in the world of "Power Engineering", and I absolutely
> >concur with DC; I've seen evidence of it in Medium Voltage
> >(>600V, <15kV) systems.
> Dave, how about repeating your story of the direct current power cable
> a pinhole burned through the insulation every foot? :)
> >One of our companies clients had a bad substation ground at
> >2.4kV L-L to a 1000 HP motor. Interesting to see a 45 deg
> >"crucifix" burned around a bonding bushing on a 600A
> >feeder conduit entering the MV MCC. MCC/Motor Ground
> >missing to substation ground, EXCEPT for MV cable shields
> >(not there from original installation, not our companies
> >installation); length of "burn/arc" flashing at least 3" long.
> >So this situation is EXACTLY like using a shielded X-Ray
> >cable in Tesla service.
> Switching (and other transients) can excite resonances in shielded cables
> and other stray capacitances which of course can cause the damage you
> Worse is the problem of these resonances being excited by harmonics from
> non-linear loads.
> >On a delta system (no ground) with a "capacitive" single phase
> >arcing fault to ground, transient over voltages can exceed
> >8X V applied. If you doubt, check the IEEE "Buff" Technical
> >reference for details. I trust we all understand the implications
> >of applying ~1kVAC to a 120VAC branch circuit....
> That's why you stick arrestors and transient devices all over the place
> BTW, Dave, do you still have all those MOV's?
> >Proper grounding is important in house wiring, but MUST
> >be installed correctly at MV; a fire, catastrophic equipment
> >damage (even collateral to unrelated systems), or electrocution
> >will result if improperly installed.
> >Imagine what would happen if a plant technician
> >had his bare hand on 1000HP motor while running, and a single
> >phase (or capacitive gradient) current occurred. At a minimum
> >a severe shock, or more likely death would have occurred.
> >I have made it a personal rule to never touch high horsepower
> >medium voltage motors while running for this reason...
> The root cause is the bad grounding. A 1/20 horsepower motor at 60V, or
> less, can kill you just as dead.
> The worrisome part is the high-resistance grounding utilized in many
> medium voltage systems, or the intentional lack of grounding in many
> where downtime is more costly than safety. Then monitoring devices are
> to prevent disasters. But I wonder if facilities with ungrounded systems
> change their procedures when they know they have a ground fault ("Don't
> anything until we can shut down next Saturday!"). Bad Things have happened
> one ground fault a while later precipitates a second fault, and then a
> line-line fault occurs...
> Or in an electrolytic cell room, where grounding is also intentionally
> avoided to prevent accidents. Now *there's* a low-impedance source for
> -Phil LaBudde
> Center for the Advanced Study of Ballistic Improbabilities
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