From: "Terrell W. Fritz"
Date: Sun, 28 Apr 2002 09:41:01 -0600
Subject: Re: [TSSP] Secondary voltage stress factor
Hi Paul,
Sure! Use the Sun as you please. We tend to greatly over design for turn to
turn voltage stress since "we have no idea". A table like you propose could be
very useful!
I see we have some dips in the qvar data charts that seem to correspond to dew
point:
http://jack.atmos.colostate.edu/Plots.html
http://hot-streamer.com/bob/qvar/results/expt4/index.html
Dew may actually be worse that rain since dew collects everywhere while rain
only runs off the roof. The recent bip dips were with relatively nice
weather. It is nice and sunny this morning but we still see a pretty big dip!
The experiments is running perfectly these days. The drop on the morning of
the 28th was my error so we have run almost three days without any odd problems
:-)
Cheers,
Terry
At 10:06 AM 4/28/2002 +0100, you wrote:
>Hi All,
>
>Here's an idea for your consideration.
>
>If a uniform secondary voltage gradient is assumed, ie a constant
>volts/turn all along the coil, then the volts/turn is simply Vtop/N
>where N is the number of turns.
>
>In practice, the voltage distribution is non-uniform and therefore
>the highest volts/turn on the coil must be something in excess of
>the value Vtop/N. The naive value of Vtop/N is thus a lower limit
>for voltage stress. We can characterise a particular coil by
>indicating what its maximum voltage stress is, in units of Vtop/N,
>in other words by specifying a 'voltage stress factor' which is the
>ratio of the highest V/turn on the coil, to the value Vtop/N.
>
>For example, a particular coil with h/d=6 and 1200 turns has a peak
>top voltage of 520 kV, and a max gradient of 0.63kV/turn (at 22%
>height). Thus the uniform gradient is 520/1200 = 0.43 kV/turn and
>we have a 'stress factor' of 0.63/0.43 = 1.46, so that for this
>coil, naive estimates of the insulation requirements need to be
>uprated by at least this factor. These figures were calculated for
>CW steady state resonance, and this provides a lower limit for the
>voltage stress, since in a primary-driven coil the primary induction
>must be added, along with the contributions of higher modes.
>
>I'm wondering whether it would be helpful and possible to produce a
>table of these voltage stress factors, as a function of the shape of
>the secondary.
>
>Consider an arbitrary secondary coil, in cross-section in
>
> http://www.abelian.demon.co.uk/tmp/vcoil.gif
>
>and with no loss of generality we can say that the 'r1' end of the
>coil is the grounded end.
>
>The shape of this coil can be described by two parameters, for
>example, let d be the average diameter, ie
>
> d = r1 + r2
>
>then we could choose the two parameters
>
> A = h/d
>
>and
>
> B = (r1 - r2)/d
>
>to describe the shape of the coil independently of its overall size.
>
>Then cylindrical secondaries will have B = 0 and A between say 1 and
>say 8. Flat secondaries with center-ground will have A = 0 and B
>between -1 and 0. Center-hot flat secondaries will have A = 0 and B
>between +1 and 0. Cone shaped coils, as per the diagram will have
>A between say 1 and 8, and B between 0 and 1. Inverted cones would
>have the same range of A but with B between 0 and -1.
>
>The voltage stress factors could then be tabulated thus,
>
> B
>
> -1 -0.8 -0.5 -0.3 0 0.3 0.5 0.8 1
>A 8
> 6 1.46
> 4
> 3
> 2.5
> 2
> 1.5
> 0 1.75 1.0 2.14
>
>in which cylindrical coils occupy the center column, flat coils
>occupy the bottom row, and the rest of the table covers the various
>cone shapes.
>
>Whether this would work or not depends on whether the voltage
>stress factor is mostly independent of the number of turns on the
>coil, and of the overall size and position of the coil.
>If it turned out that this was the case, ie the stress factor was
>mainly a function of the coil's shape, then such a table would be
>meaningful, and could be potentially useful to coilers.
>
>I propose we run a series of coils through the model to test
>whether the voltage stress factor can be characterised as a
>function of shape only, and if so, to fill in the above table.
>
>This would require processing of a few hundred coils.
>
>Terry, would your Sun computer be available for this, by any chance?
>The program could be set to run at low priority to avoid slowing
>down the qvar results processing. About 600Mbyte of disk space would
>be needed, and about 200-300 hours of CPU time.
>
>Cheers All,
>--
>Paul Nicholson,
>--
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.