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A VFD makes most sense if you use a DC resonant charging system. A
properly designed DC resonant design will allow you to smoothly vary
output voltage and power without the need for any phase-syncing, since
the tank cap is always recharged between firings at any firing rate.
This approach works especially well for high power systems using 3-phase
gap motors.
However, A VFD can be used to make an asynchronous variable speed gap.
Using a VFD in your existing system would work in a fashion similar to
driving a DC motor from a variable DC supply. You WILL lose the
capability of truly syncing and properly phasing your motor to the line.
Also, some speeds near multiples of line frequency have the potential to
overvolt your tank cap or HV transformer, so make sure you have a safety
gap bridging your rotary gap or a Terry filter.
I like Jim's idea of driving your HV transformer from the same VFD and
using a true synchronous motor would permit you to sync the gap to the
line. I'm not sure just how well the VFD, HV transformer, and motor will
all play together, and I don't recall any coilers using this technique
before. If you try this method, you'll probably need to use a fixed
mechanical phase adjustment on your gap since the Freau controller's
phase relationship will change with operating frequency.
Bert
--
Bert Hickman
Stoneridge Engineering
http://www.capturedlightning.com
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coils@xxxxxxxxx wrote:
Hey everyone, I have been using an srsg and a Freu phase shifter for
some time now, with great results. I am planning a new rsg with
variable speed. My question; with vari speed, will I still need to
tweek the angle of the moving electrodes to stationary electrodes? I
have not decided on ac or dc vari speed, but if I were to go with ac,
could I use a Freu phase shifter with something like a vfd, or one of
the ACTech speed controlers?
thanks for your thoughts,
Cheers
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