From: Joe Foley (redmenaced@yahoo.com)
Date: Tue Mar 16 2004 - 08:42:59 PST
Spikes and surges induced by lightning or whatever had
no path to drain off, with a grounded neutral they do.
Not only that but spikes tend to be amplified when
there is no path to ground.
Closed delta three phase is just such a problem, the
code requires three lights on the service to monitor
the condition of the whole system, if one leg gets
grounded nothing will happen except that one light
will be dim while the other two will be brighter
alerting the maintenance crew that something is wrong.
Now, IF another leg should go to ground :
KABOOOOOM!!
Other funny things will happen in the mean time, too,
the engineering books say, "... the system becomes
unstable,..." which understates the situation. Refer
to that big black-out that hit the USA recently.
"Unstable" is definable but only in relation to one
certain event, the next time it could be something
totally different so there's really no sense in
quantifying it.
Joe
--- noel shelley <noel@shelley1722.freeserve.co.uk>
wrote:
>
>
>
> > Hi Frank , or anyone else competent in matters
> electrical ,
> > Can you offer any thoughts on this one !
> Though not MV it has
> > relevance as a safety issue !
> > A bird sits on a bare overhead power line and
> doesn`t not fry , because he
> > does not form a current path , I have a 20 Kva
> 415 50cs 3Ph generator .
> No
> > part of the machine is in contact with earth and
> star point is insulated .
> > If one earths the machine , then in the event of a
> fault there is a path
> to
> > earth through you , where as if left insulated
> there is no circuit to
> earth
> > and IN THEORY no risk of shock . This question has
> been asked of several
> > people in the industry all of whom have said "
> interesting " never thought
> > of that { because in normal supply star point
> [neutral] is earthed at
> power
> > station so the above is not an option} .
> >
> > My turn to ask a question , look forward to some
> interesting answers
> >
> >
> Noel
> >
> >
>
>
> ===Mil-Veh is a member-supported mailing list===
> To unsubscribe, send e-mail to:
> <mil-veh-off@mil-veh.org>
> To switch to the DIGEST mode, send e-mail to
> <mil-veh-digest@mil-veh.org>
> To reach a human, contact <ack@mil-veh.org>
__________________________________
Do you Yahoo!?
Yahoo! Mail - More reliable, more storage, less spam
http://mail.yahoo.com
This archive was generated by hypermail 2.1.4 : Sat May 07 2005 - 20:29:12 PDT