Re: HV MMCs was Re: Magnifier conversion

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Terry Fritz" <teslalist-at-qwest-dot-net>

Hi Jim,

Do you thing the corona will be a big problem?  Antonio's caps had very 
heavy ionization right across the dielectric since he had a single 
layer.  But in this case, it is just a few sharp metal edges.  Spewing a 
few electrons into free air.  The power loss should be nil and the voltage 
is over a long distance so it should not arc over.  I could add a corona 
ring (or a full series of grading rings), but I was not thinking this would 
be a big problem.

Perhaps I might get regular streamers going of the terminals and such?  Not 
sure...

Cheers,

         Terry



At 02:22 PM 4/15/2003 -0700, you wrote:
>At 01:50 PM 4/15/2003 -0600, you wrote:
>>Original poster: "Terry Fritz" <teslalist-at-qwest-dot-net>
>>
>>The C2 MMC (High Voltage => (HV-MMC)) is easy to make.  It is far easier 
>>than I thought it would be, so I don't think these "small" magnifiers 
>>mentioned by Antonio are hard to make at all.  With a large toriod, C2's 
>>value is pretty high which lowers the secondary voltage (<80kV peak) 
>>helping to prevent primary to secondary breakdown and putting the voltage 
>>easily into the HV-MMC range.  At first, I forgot about the other stray 
>>capacitances so my HV-MMC probably should have had smaller value 
>>caps.  But I can go down to 100pF right now which should still be fine 
>>(it can be tapped at 99 points ;-)).  The HV-MMC seems like it will be 
>>perfect and it can even self heal if it takes streamer hits ;-))  I am 
>>also putting in the bleeder resistors since they will work just as well 
>>in this case.  A 150pF cap at 150kV could pack a pretty big punch 
>>especially considering it could arc 3 inches!!
>
>While getting the right capacitance for a 200kV MMC isn't all that tough, 
>getting low corona losses might be more of a challenge. Those caps have 
>wire leads.. You might need some sort of grading rings or such to keep the 
>local field around the lead junctions controlled.
>
>Given that this is a short pulse kind of application, DI water as a 
>dielectric might be way to go, or, use the C of a transmission line 
>connecting secondary to tertiary as your capacitor.
>
>here's some calculations on a coaxial capacitor made of metal tubing.
>
>For an OD of 6" and an ID of 4", the capacitance is 137 pF/meter
>For an applied voltage of 1 kV, the field is .485 kV/cm (200kV is about 96 
>kV/cm.. well over breakdown for air)
>
>For 6" ID and 12" OD you get 37.8 kV/cm (almost within reason) and 80 pF/meter
>
>10/16 >> 118pF/meter, 33.5 kV/cm  Starting to be reasonable, and the OD is 
>getting reasonable to reduce corona off of it, if it's the HV side.
>
>C = 2*pi*8.85E-12*epsilon*ln(router/rinner)
>E = V/(rinner*ln(router/rinner))
>
>For the smaller tubes, pressurizing the air is an option.. 15 or 30psig is 
>easy to get, not too stressful, and increases the breakdown by a factor of 
>2 or 3.
>
>Water dielectric has an epsilon of 80..
>