I got my 7.2/14.4 kV 25 kVA pig with an 18 kV arrestor. Given that my pig was located in the Styx - I literally cut down the pole - it was likely 7200 volts. Mine worked up to 280 volt input, but the arrestor would occasionally kick in, resulting in frequent temporary dropouts in pig output, and erratic coil behavior. Mine hasn't shorted yet, but eventually would have, as they are only good for so many events, as I understand them. I'm currently running with nothing, but need to get a higher rated arrestor.
I have a 2 horned pig, but ground one end. So electrically, one horn gets shorted to the other horn, the way I had my arrestor.
If I understand you, you are using a second arrester across your SRSG, as a safety gap?
On Saturday, February 10, 2018, 8:56:55 AM EST, David Rieben <drieben@xxxxxxx> wrote:
Hi Steve,
As Bert has already pointed out, pole transformers, i.e. 'pole pigs' are not
totally impervious to being damaged by the HV transient "nasties" that are
always generated by the active resonant circuit of a spark gap driven TC.
That being said, pole pigs are certainly the transformer of choice that is
available to serious coiling hobbiests that crave plenty of power and their
robust design certainly renders them VERY resistant to sustaining damage due
to the aforementioned phenomenon.
Although you didn't mention the resistance rating of your wire wound
resistors, just the POWER rating (100 watts), I assume that they are also
rated at 100 Ohms, from the figures that you plugged into your I*2 x R
formula? If that's the case, then yes, your setup should be fine.
I originally ran my big coil (up to around 18 kVA with 12 to 13 ft. arcs!)
with ZERO protection (and NEVER had a mishap with the transformer), but
eventually decied that I should at least attempt some form of protection.
Since all of my protective horn gap attempts for a pole pig output usually
failed to extinguish once it "fired", due to the heavy current arc that
formed, I personally have been using distribution arresters for this
purpose. (Yup, the devices that your local utility opower company use to
protect their equipment from line transient spikes, due to switching surges
and lightning strikes). I place them in parallel with the output of my pole
pig power supply (also a 10 kVA, 14,400-120/240 volt unit) to address this
issue:
https://www.ebay.com/itm/HUBBELL-OPTIMA-DIST-ARRESTER-2137157314-PDV100-HD/272071557889?rt=nc&_trkparms=aid%3D222007%26algo%3DSIM.MBE%26ao%3D2%26asc%3D44039%26meid%3D5a3f17733d7642709f701c4fa0ba8f8f%26pid%3D100005%26rk%3D1%26rkt%3D1%26sd%3D272469016073%26itm%3D272071557889&_trksid=p2047675.c100005.m1851
With a little persistence, these can sometimes be found on eBay for < $50. I
originally started with an 18 kV rated unit, but it eventually died as a
short circuit. An 18 kV rated arrester is generally rated for 15.8 kV MCOV
(maximum circuit operating voltage - I believe) and my varaic stack was able
to provide up to 280 volts input, which would translate to 16.8 kV out. My
local power company uses 18 kV arresters on their 13.2 kV primary line
circuits. After this incident, I upgraded to a 27 kV rated arrester and have
been running without a hitch ever since. I also more recently located some
21 kV rated arresters and have replaced one of the 27 kV rated ones with
this. (I use the higher rated one right at the (Async)SG assembly and the
lower rated one at the transformer's output).
I have personally had far more issues with the nasty transient kickbacks on
the primary LV side of my pole pig than the secondary HV side. As stated
before, although the HV windings of a pole pig are not totally bullet proof
to these kickbacks, they are much more robust than the fragile NSTs or OBITs
and are actually quite unlikely to sustain debilitating damage from this
issue. The MUCH bigger problem, for me at least, has been what the
transformer sends down stream to the components on the LV voltage input to
the transformer. I use two industrial line filters that are rated to handle
the amperage (and a small line filter at the input of each of my two cabinet
cooling fans), as well as three paralleled 1 KW rated, 1 ohm, ribbon style,
wire wound power resistors (for 0.33 ohms total) in series with my inductive
ballast, AND a pair of 150 Vrms MOVs between each 'hot' leg of the incoming
240 volts and the ground to combat this problem!
https://www.ebay.com/itm/Panasonic-ERZC20EK241-150Vrms-Metal-Oxide-Varistor-Chassis-Mount-3-pcs/160706951833?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2055119.m1438.l2649
Finally, I typically run my coil with about 75 to 80 amps draw with variac
set for about 200 volts input to the transformer, so that translates to
around 15 to 16 kVA and my transfomrmer never even breaks a sweat
processing this rate of power. So you definitely have plenty of room for
"expansion" with your power!
Hope this helps,
David
----- Original Message -----
From: "Steve White" <steve.white1@xxxxxxxxx>
To: "Tesla Coil List" <tesla@xxxxxxxxxx>
Sent: Friday, February 09, 2018 5:37 PM
Subject: [TCML] "Terry" filter and safety gap questions for pole transformer
> My spark gap coil has been running for about 6 months with a 10 KVA pole
> transformer for power. I pull about 4.8 KW from the wall. The only
> transformer protection that I am currently using is a horn gap in parallel
> with the spark gap. I have had no trouble with it but lately I have become
> concerned with damaging the pole transformer. Because of this concern, I
> am in the process of building a low pass RC ("Terry") filter for
> additional protection. I have 2 questions regarding the resistors. I see
> that people are using standard wire-wound resistors. I am surprised that
> the 14.4 HV RMS does not flash across the windings in the resistor. Is
> this type of resistor indeed adequate for such high voltage? The second
> question concerns the power rating of the resistor. Since my worst-case
> RMS current from the pole transformer is no more than 0.5 amperes, the
> power dissipation should be no more than about 25 watts.
>
> Power = (I**2) * R = 0.5 * 0.5 * 100 = 25 watts
>
> Therefore I assume that a pair of 100 watt resistors, one on each HV lead,
> should be more than adequate even for a pole transformer. Is this correct?
>
> I also have a safety gap question. My safety gap is just a simple
> 2-terminal horn gap connected in parallel with my RSG. I see that the
> safety gaps used for NSTs consist of 3 terminals: 2 for the high voltage
> leads and a central ground terminal. For pole transformers, is there any
> advantage favoring the 3-terminal gap vs the 2-terminal gap?
>
> Steve
> _______________________________________________
> Tesla mailing list
> Tesla@xxxxxxxxxxxxxxxxxx
> https://www.pupman.com/mailman/listinfo/tesla
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