| Tom Horne, Electrician 2006-04-16, 2:21 am |
| Charles Perry wrote:
> "Beachcomber" <invalid@notreal.none> wrote in message
> news:4441288a.1249281@news.verizon.net...
>
> The problem with your arguement is that the current system, as applied to
> medium voltage distribution lines in the US, is NOT killing people. Some
> stray voltage problems exist, but they are usually localized problems.
> These stray voltages are not killing people. They do scare people but they
> don't kill them.
>
> In many of the stray voltage cases we have studied, the high levels of 3rd
> harmonic current in the neutral have been a major contributor. These
> currents are created by electronic loads and since they are triplens, they
> add, rather than cancel, in the neutral. I propose that the US adopt a
> European style regulation for all, and I mean ALL, electronic equipment
> requiring power factor corrected power supplies. Fewer harmonics, better
> power factor, everyone wins.
>
> Charles Perry P.E.
>
>
I do not say this to be quarrelsome but I am troubled by your assertion
that the stray current problem is only a nuisance. Stray currents are
causing losses in the dairy industry and many dairy farmers are unaware
that their production is affected. My electrical business is
overwhelmingly suburban residential but I have worked on two farms that
saw an increase in production when the farm was isolated from the medium
voltage Multi Grounded Neutral (MGN). In one case I simply opened the
farms supply including the neutral that was common to the MGN and
production shot up by more than a third. This was obviously not one of
the extreme cases that has been widely publicized. The stock did not
show any obvious sign that they were distressed. I was there to tie in
an Engine Alternator Set (Generator) for outage protection and the dairy
was running on it's PTO generator while I was working on the new
transfer equipment. The farmer mentioned that the animals must like the
tractors white noise because the milking was way up. I got suspicious
and measured the neutral current with the new main breaker open but with
the neutral reconnected. With the cows out to pasture and the PTO
generator shut down the neutral current was over twenty five amps. The
utility agreed to supply power at 240 volts from an ungrounded
secondary. They just unstrapped their secondary at the pole pig. The
neutral was disconnected at both ends of the drop and an outdoor dry
transformer was installed to establish a local only neutral from a true
separately derived system. We did have to clean up several ground
faults caused by the older method of connecting separate structures. I
did that even though the total current flowing on the existing Grounding
Electrode Conductors was less than five amps on PTO alternator power.
If that farmer had not decided to install a Generator during a long
outage caused by a storm the stray current problem might never have been
discovered.
--
Tom Horne
"This alternating current stuff is just a fad. It is much too dangerous
for general use." Thomas Alva Edison
|