Re: HV MMCs was Re: Magnifier conversion

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

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

Hi again Jim,

I got out the Ross catalog and saw how Ross makes HV AC voltage dividers:

http://hot-streamer-dot-com/temp/NewMag/0415-01.jpg

That 30-240kV divider looks much like what I need.  A half sphere top and a 
ring at the bottom.  Like a sliced gazing ball and loop of copper 
tubing.  Their's are also filled with SF6...

I'll try something like this.  I don't want to have pressure, oil, DI 
water... just to keep it simple.  I figure the capacitance tap adjustment 
should be near the bottom where the voltage is at ground potential and 
things are easy.

Might have to just try it and see what happens ;-))

Cheers,

         Terry


-----------------
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..