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Re: [TCML] Terry Filter for OBIT's
Hi Paul,
snip:
So, my question is whether you believe a filter is an absolute necessity
with all but pole pigs or is it simply added insurance? Please note that I
have no opinion or even a dog in this fight. I am just asking.
Paul
Think Positive
There are some that would even espouse the use of a filter with a pole
pig. However, I have been using pole pigs since 2000 and have never
yet suffered a failure of a pole pig (although I've experienced failure in
just about every other primary component at some point during this time).
Not trying to say that pole pigs are absolutely bullet proof, as there have
been reported failures of pole pigs in the past, although the number is cer-
tainly not very high. However, I would say that by its very design features,
a pole transformer is very robust and pretty much overbuilt. As an exam-
ple, the high voltage side of a 14.4 kV pig must be able to withstand a 50
u/second long impulse of 110 kV, as this is the kind of abuse that it can
expect to see in its working environment from lightning strikes or line
switching voltage surges. And they are also desinged to last for a few
decades in this "hostile" operational environment!
As far as the current limited variety of transformers (NSTs or OBITs)
I would strongly recommend the Terry filter with this type of transfor-
mer, from my personal experience. NSTs are desinged to only have
their full rated voltage at the instant that the neon sign is turned on.
Once the sign lights up, the voltage drop becomes much lower (as in
only a few hundred volts). Obviously, the operational requirements
of durability would be notably less for this type of transformer than for
a pole transformer. Before I jumped up to pole pigs, I destroyed a good
number of NSTs and this was before I knew anything about keeping the
SG at a conservative spacing or before I had ever even heard of the
Terry filter for that matter.
Hope this helps,
David Rieben
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