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[TCML] Re:Pros and cons

Task of the sparks suppression = Task of controling electrical fields on the charged surfaces.Maximum field on the smooth conductors' surfaces must be lower than minimum field for the corona ignition.The latter,for AC power frequency and DC,is 28-30 kV/cm for air at p=1 bar,T=300 K.Maximum permissible limit in the design ,for indoor HV facilities located below 1000 m altitude,is 20 kV/cm.From the (optimised) geometry and the max permissible field ,max safe operating voltage can be determined.
While 800 kV is  respectable EHV level,if you have adequate technical knowledges and working means,trust me on word that it doesn't represent particular problem to deal with.
Regarding 800 kV and mentioned 1 meter sparking range,that it is a *very* relative thing,even on a single discharge basis.Factors like  gap uniformity degree,shape of the electrodes,polarity,time characteristics of the voltage impulse,in usual conditions influence a LOT.For example,breakdown voltage for D=0.75 m sphere to sphere  gap  configuration for gap lenght d=0.4m is about 800 kV.On the other hand,standard switching impulse of positive polarity in the rod-plane gap configuration can break gap lenght aproximately  d=2.5 m long.
Fine toy to play with.This is a DRSSTC,if I'm not mistaken?
What is the driving resonant frequency,time to  secondary peak voltage,and input rms power  of your DRSSTC?

Fez Zaev



Steve Ward <steve.ward@xxxxxxxxx>

Tesla Coil Mailing List <tesla@xxxxxxxxxx>

Re: [TCML] Re:Pros and Cons

Wed, 9 Dec 2009 13:57:07 -0600

Sounds like a reasonable solution.  Its good to have someone with the
xperience of driving series HV switches.
About the 25 foot discharges (maybe off by a factor of 2, maybe not), this
ccurs because of an effect we call "streamer growth".  Above some
epetition frequency, the previous spark event leaves a heated air channel
or the next spark event to travel along, and further extend its reach.
easurements of large tesla coils revealed that the peak top voltage was
ignificantly less than the spark length suggested.  Anyway, the spark can
ypically grow to perhaps 3X the "single shot" length (the single shot
ength follows the generic kV/cm type figures you see quoted).  So on a
ingle shot basis, 800kV is in the 1 meter range, but as you exceed about
0pps, this streamer growth phenomena starts to show up and you might see 2
eter long sparks.  At 100pps you might see 2.5 meter sparks, and at say 300
ps it might be a full 3 meters long.  So essentially, once a spark
starts*, and you provide sufficient power (in pulse per second) it *will*
row much longer!
Anyway, i seem to recall DC Cox claiming that his "Big Bruiser" Tesla coil
which makes about a 25 foot spark at peak) only generated about 850kV.  If
C could supply the specs on his primary/secondary L/C and peak charge
oltage, we could figure out the theoretical maximum secondary voltage.
Greg Leyh also has some big coils and perhaps has some secondary voltage
So i know pretty much nothing about the DUT, but if it has any exposed radii
f less than maybe 6", its likely a spark will break out and grow to very
uge lengths if operating at 100pps.  To me it sounds like a fairly good
hallenge to suppress spark formation at 800kVAC!

Finn Hammer <f-h@xxxx>

Tesla Coil Mailing List <tesla@xxxxxxxxxx>

Re: [TCML] Re:Pros and Cons

Thu, 10 Dec 2009 08:37:46 +0100

Take a look at this video showing my latest coil. 
It documents 4.07 meters from a coil with only 4pcs. CM600HA24 modules, primary voltage 800V and primary cap. 1.5uF 
Breakrate 58Hz 
This may give you a pointer in what direction we are going, and what is possible. 
Cheers, Finn Hammer 

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