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Re: skin effect
Dear Jeff Colin,
First of al I think that you mixed up the skin effect together with the corona
effect. These two effects are different as the skin effect only can appear by
high frequencies and not by 60 Hz.
It's true that for some countries in Europe the maximum voltage is 10 kV, but
here in Holland the by law allowed maximum is still 8 kV and I hope that will be
for ever so, as it is in my opinion for neon discharge to high. For pure filled
neon tubing I say that the maximum should be 6 kV depending on the
charasteristic of the transformer. It's possible to install 8 kV transformers
but then the operating voltage must be half the open voltage and not higher. I
don't think they produce in your country transformarers with that regulation. So
a 8 kV transformer (open voltage) delivers 4 kV operating voltage installed
under nominal conditions. The nominal condition is when the secundary is
sypplying its nominal secundary current. That's the only thing that matters. I
was quite amazed to see that American transformers only have their secundary
short circuit curent on the indication plate iso the nominal curent. Now one
must calculate the nominal secundary current, and one must know the fabrication
specs of that specific transformer. It is must easier, and more logical, as the
nominal secundary curent was on the indication plate. An easy to handle
electromagnetic type current meter will read out the nomainal (true rms) value
all the time.
Jeff the capacitance of the wiring will for sure not drain the power of the
transfomer, no, the opposit will hapen. The reistance of the wire is of no
importance and not of any influance to the voltage. It is the capacitance of the
wiring ( 6 to 8 pF.mtrE-1) that is of importnce. As a (strayfield) neon
transformer is a great inductive device (power factor cos phi = 0.5 to 0.6) the
capacitance of the long wires makes the transformer less inductive, so more
ohmic. What will hapen then is this: the operating voltage will rise to a mugh
to high value burning out the primairy winding of the primary coil. The primairy
coil will always burn out becouse that's the one who must supply the energy and
when the amount of energy rise the diameter of the wiring is too thin, so it
will be overheating itself and burn out sooner or later, mostly soner. Never in
my life I saw transformers opearting properly with wiring of about 50 meters
installed to it. Transformers installed that way ae rising their output voltage
and ae oscillating producing ignite spikes of over 35 kV. I don't think that
there is one tansfomers who likes that, or the heat of that. Looking to the
current is not a big deal, because the current will be still low. Look to the
voltage on a oscilloscope and you will be amazed about the spaghetti curves you
see. There is not the desired square-wave with the desired operating voltage in
a factor as 2:1. When you have a transmission line, as in your own example of a
few miles, there is no voltage drop, no, there is a undesired unacceptable too
high voltage rise.
So using transformers of a maximum for Hg discharge with a maximum of 8 kV and
using transformers for red discharge with a maximum of 6 kV we never, (I mean
never) have wires burnout. You were telling me "wire burnouts becomes
negligible" and I have no idea what I am supposed to think about that.
"Negligible" ?, even one wire burnout is one to many (much? forgive me my lack
of English) installing these high voltage devices. For that reason it is not
enough to calibrate your sign in the workshop. You always must recalibrate on
location because of the differant circumstances and the long cables (wires?). So
meassure the prymary current and one can see if a transformer is overloaded.
I will make one last remark (for this time) about over- and underloading.
Reading this list reguarly I was surprised to see that you overthere are
mentioning a transformers installed with not enough glasslength onto it
underloade and a transformers with a too big (great?) glasslength overloaded.
Guys the opposit is the fact. A neon tansformer installed with not enough
glasslength will be overloaded as it is. A transformer is overloaded when the
primary winding is pulling out of the mains a too high current and blow itself
up by overheating. That is overloading. A neontransformer with too many feet
(I'am learning) of tubing is underloaded because the primary current will be
lower then it's nominal rate.Never, never compare it with bulbs, becouse that's
the differance between a series and a parallel circuit. More bulbs (glass) in a
parallel circuit will overload the transformer, but we are installing neon in
series.
For Telford, If you can do it better in your words, please do. Maybe we can help
ST with articles about this matter as they are asking frequently now for good
stuff.
BTW there is a magazine who is covering only neon and signs. It's callend SIGN
TxT but unfortunately for you overthere it's only writen in the Dutch language,
so it covers The Kingdom of the Netherlands and the halve of Belgium.
As we are considering to visit Orlando there is another question I cannot deal
with. David Ablon asked (invited) the American benders to visit the Neon Show. I
cannot interpetate his saying "bring with you your own blowhose", as I have it
for over 50 years with me in the right leg of my trousers. Am I missing
something?
Best regards to you all
from dirk a. boonstra
teacher neon techniques at the Dutch Neon School in Delft Holland
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