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Re: [TCML] measure VDG voltage
Vladimiro Mazzilli wrote:
Can anyone suggest me suggest a method to measure the voltage present
on a topload of a Van de Graaf generator?
Thank a Lot.
Vladi
Hi Vladi,
You can estimate the corona-limited maximum voltage for the VDG based on
the radius of curvature of the top terminal. However, this only provides
the maximum that the VDG generator could achieve, not necessarily what
your generator is achieving. The following relationship assumes an air
breakdown voltage of 30 kV/cm at sea level and a polished sphere. The
maximum voltage will be reduced for locations with higher elevations or
if the sphere's surface was not polished. The Radius of Curvature (ROC)
is in centimeters. So, a spherical topload 20 cm in diameter would have
a ROC of 10 cm, and an estimated maximum VDG voltage of 300,000 volts.
Vmax = 30*ROC
You can also approximate the actual maximum voltage by using a spark gap
and a suitable table that converts gap distance to voltage. This has the
advantage of not loading down the VDG until actual spark-over occurs.
You can use the VDG top terminal as one gap electrode and a similarly
curved grounded spherical terminal (a gazing globe or a metal "float"
ball or even a suitably round metal bowl) as the other gap electrode.
Jim Lux's HV Handbook contains sphere gap construction hints and a
gap-voltage table:
http://home.earthlink.net/~jimlux/hv/spherev.htm
Bert
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