Regarding Field Strenght between Parallel Plate Electrodes

[sabu31]

Hi all,

I need to design one electrode where the field strength is typically 35kV/cm to 40kV/cm. The voltage applied would be 12kV, 10us at 250Hz.
I designed one electrode with 4.5mm dia and 3.5mm gap. The dia was kept to considering the limit of peak current. In literature, its mentioned that for uniform field the electrode dimensions should be much higher than the gap. What is the limit in dimensions beyond which field is non-uniform? And what would be the typical field in such scenario.

Suppose there is drill through hole on 3.5 mm ground electrode while the 4.5 mm positive edge is remaining same, what would be the effect on the effective field.


Thanks

 

[wwfeldman]

need more information

what are the size, shape and separation between the two electrodes?
what is the diameter and location of the drill hole? (purpose?)

4.5mm dia and 3.5mm gap is NOT sufficient size difference to produce uniform field
through most of the area of the electrodes

i'm usually more conservative in this regard - i like a factor of 10 difference
in dimension vs separation - so a 4 mm separation needs a plate dimension
of 40 mm (side for square, diameter for circle)
(i expect some to say x5 or maybe x3)

then the field will be fairly uniform through most of the area
it will bow out toward the edges

one way to reduce the bowing out is to put a concentric set of electrodes outside
the main set and apply the same voltage. that looks almost like an enlargement
of the main set

 

[mtwieg]

How uniform do you need the field to be, and over what volume of space?

Even if the field were perfectly uniform, 12kV across 3.5mm gives ~34kV/cm, far above the dielectric strength of air (I'm assuming this is an air gap). You're going to get corona discharge, probably around the plate edges. With such narrow pulses, you probably won't be able to see it though (unless you're in a very dark room).

Be safe.