Re: Near miss at Victoria (London)

[jjjim <jjjim@bigpond.com>]

Yes  I  appologise  I guess you cant call it an air gap ,  you wont see arcing
thru air gaps therefore, (power is turned of anyway) ,  I have seen some minor
arcing wehn i used to stand outside the back of a shop  i was workgng at  for
lunch, just out of toowong station heading south,  Theres a section almost every
train would let a juscy spark out  as it passed , specially since they were
accelerating  at that point. (aplied to loco's and comuters)

Chris Downs wrote:

> In Sydney (and elsewhere) I thought the "air gap" was the space between the
> two sets of overhead at an overhead anchorage/transition point on main lines,
> that is, the span(s) where the finishing and the commencing overhead wires run
> parallel and the pantograph will have simultaneous contact at some point.
> Both wires are mostly electrically connected by additional conductors but
> where the overhead is to be electrically sectioned (sub-stations, section
> huts, certain outer-suburban crossovers) the two sets of wire are electrically
> isolated (unless a pantograph is passing beneath) providing a gap of air
> between the two sets of overhead.
>
> The other type of section was initially provided by "continuous-feed
> wood-break section insulators" (the diamond shaped overhead arrangements).
> The wood was replaced by another type of insulator at some stage.  What I
> think of as "ski jump" section insulators are now used.  I thought that prior
> to ski jumps sectioning insulators being used the older type could be powered
> "over" in switching or series only (notches 1 and 2), not in parallel or weak
> field (notches 3 & 4).  Thus the ponderous starts from the up Illawarra Local
> at Sydenham in single deck sets where two of these older type of sections were
> encountered within about 400m of the train leaving Sydenham and drivers would
> hold notch 2 for 500+m.  Notches  3 or 4, if used, would produce a very
> noticeable buck as power was momentarily lost (the sections weren't so
> continuous).  Regen. on the chopper cars encountered exactly the same problem
> when braking across such sections.
>
> I surmised (rightly or wrongly?) that the notch 2 restriction was lifted with
> the introduction of the ski jumps sections.  (Although bucking is still
> noticeable sometimes, the up approach to Glenbrook is a notable example where
> the buck regularly knocks out regen. on V-sets.)
>
> Sydney has no equivalent to Bizzie's 25kV arrangement (such as between Roma St
> station and the Merivale Bridge or opposite Mayne Car Sheds) where the
> pantograph traverses a lengthy dead section of contact wire rather than what I
> think of as "air gaps".  Brizzie also has "ski jumps" but only for crossovers
> and sidings.  Other mainline sections (not air gaps or dead sections) have a
> more intricate version of Sydney's old diamonds that does provide truly
> continuous power.
>
> A question to those in the know:  In many thousands of km travel on Brizzie's
> sparks I have never seen serious arcing between the pantograph and overhead as
> I've seen in Sydney on occasions.  But my old man told me such arcing was
> common on some trips he made under 25kV in the UK (loco hauled trains in all
> cases I think).  Why is this so, overhead quality/age, higher current for
> electric locos or?
>
> Ta
>
> Chris
>
> jjjim <jjjim@bigpond.com> wrote in message
> 3A56AFF9.E35DE68B@bigpond.com">news:3A56AFF9.E35DE68B@bigpond.com...
> > I would argue that :P
> >
> > The 25KV arc would stretch quite a distance , Elec units here have vacum
> Breakers
> > Which are set to break power to the train before hitting an airgap,  if not
> the
> > arc would be drawn right thru the air gap because of the High voltage.
> where as i
> > am led to belive sydney's DC trains dont have to have / need such a system,
> could
> > be wrong but
> >
> > David Johnson wrote:
> >
> > >
> > >
> > > I would suggest a breaker or knife switch opening 25kVAC at 50 Amps would
> have
> > > a much smaller arc than opening 1500VDC at 1000 Amps.
> > >
> > > --
> > > David Johnson
> > > trainman@ozemail.com.au
> > > http://www.ozemail.com.au/~trainman/
> > > ------------------------------------
> > > These comments are made in a private
> > > capacity and do not represent the
> > > official view of State Rail.
> > > C.O.W.S. Page 11.
> >