Original poster: Finn Hammer <f-h@xxxx>
DC,
Toroids are great and classic devices in the quest for a more uniform field.
A tertiary magnifier coil is a good example, where the potentials of
both ends of the resonater are above ground level, and the field
strength is aligned in the coils axial direction. A toroid in both
ends of this coil is mandatory, to avoid corona loss. This applies
particularly to the bottom end. In the other end we do of course not
only accepy, but ultimately rather desire corona loss.
In the example you put forth, where discontinuities exist on a
conductor at high potential, a toroid is also advisable at each discontinuity.
I do however fail to grasp, what a toroid at the bottom of the coil
in question would acheive in the line of field controll, since both
coils at the bottom are terminated at ground potential.
The field strength in this example is aligned in the radial
direction of the space btwn. both coils.
How do you expect to smooth a _radial_ field with toroids?
Cheers, Finn Hammer
Tesla list wrote:
Original poster: "D.C. Cox" <resonance@xxxxxxxxxx>
One impovement to this design would be using a toroid on the bottom
of the coil as well as on the top. Just using one on top shapes
the field but the smaller dia copper tubing in the base area does
not provide effective electrostatic field control in this
area. Using a toroid on the bottom as well as on the top will help
provide better control of the fields and reduces the insulation
required. As you noted just using more insulation does not give
good uniform field control. You need to shape the fields with
proper electrostatic shielding techniques.
These principles are used in very high potential 60 Hz xmfrs used
for research work. A nice toroid is placed in the case entry area
and many times actually inside the case near both the bushing tip
and also near the area when the bushing departs the case.
Dr. Resonance
Original poster: Ed Phillips <evp@xxxxxxxxxxx>
People who work with tightly coupled transformers for high voltage
know it already, but I have only recently found out:
I cannot insulate my way out of a corona problem. The more
dielectric I stuff into the gap, the more severe the corona gets
in the remaining air.
Ain't that the truth..."
Of course; "it has to be that way". The more (higher
dielectric constant than air) material you put in the gap the
greater the voltage drop across the remaining air and hence more
corona. IF you completely fill the gap and IF you exclude all
residual air the corona will be suppressed. If a little air
remains somewhere it will break down due to corona and may very
well result in breakdown of the associated dielectric
material. Major failure mechanism for capacitors operated at high AC voltages.
Ed