[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

Re: Lightning and mast mounted preamps



Joel Black - w4jbb said (in part):
> Your electrical service ground is connected to the neutral that comes
> to your house from the substation which comes from the electrical
> generating plant.  There cannot be a better ground than the one coming
> from the plant - think about it...

Massively WRONG!

This is one that I actually know (look at my signature to see who I work
for).  I will be using terminology as it relates to overhead distribution,
although the concepts are the same for underground service.  First of all,
the neutral coming from your service drop does not get back to the
substation.  Secondly, even if it did, it would not be a good ground for
lightning protection because of the distance involved (for example, my
house is about 2 miles from the serving substation).  The neutral in your
service drop is earth grounded at your meter panel, and also at the
secondary side of the pole-top distribution transformer.  That may well be
as far away as it gets.  Depending on how your the distribution line you
are fed from is configured, there may not even be a neutral connection on
the primary side of your local pole-top transformer.  The substation most
likely sends out a distribution voltage between 4KV and 16KV (there are a
few higher or lower, but the majority are between these values).  This is
generally 3 phase AC power and may be wired in a Delta configuration (3
phases and no neutral) or more likely a Wye configuration (3 phases plus
neutral).  In my neighborhood, the distribution is 12KV Wye configuration.
That means that there is 12 KV between the phases, and 6.9KV between each
phase and neutral.  A pole-top transformer can be wired across either 2
phases (across 12KV) or between one phase and neutral (6.9KV).  Even if the
primary is between one phase and neutral, it may not be earth grounded at
the pole-top transformer.  It also may or may not (depending on how your
utility does things) have the secondary neutral and primary neutral bonded
together (my company does not bond them).  In the case of my neighborhood,
the pole-top transformer primary is connected between two phases.  The
closest primary neutral is 3 blocks away.  A three phase load (industrial
or commercial) will connect to the three phases and can be either Delta or
Wye configuration.  To avoid a long discussion about 3 phase power, I'm
going to limit the discussion to single phase.  If you really want to learn
about 3 phase, there is a fairly good tutorial at:
http://www.elec-toolbox.com/usefulinfo/xfmr-3ph.htm

73
-----------------------
Jim Walls - K6CCC
k6ccc@amsat.org
Mobile Radio Operations
Southern California Edison Co.
Ofc:   626-302-8515   -   PAX   28-515
FAX:   626-302-7501   -   PAX   27-501



----
Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
Not an AMSAT member? Join now to support the amateur satellite program!
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org



AMSAT Top AMSAT Home