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From: msb@sq.com (Mark Brader)
Date: Sat, 25-Mar-89 03:23:43 EST
Message-ID: <1989Mar25.032343.20209@sq.com>
Newsgroups: tor.general
Subject: Re: TTC Subway fault-tolerance
References: <810@mv03.ecf.toronto.edu> <446@ontenv.UUCP> <1989Mar20.211818.27937@sq.com> <383@becker.UUCP>
Reply-To: msb@sq.com (Mark Brader)
Distribution: tor
Organization: SoftQuad Inc., Toronto
Keywords: TTC, Subway, delay, fault,turn-around

Eric Siegerman (eric@becker.UUCP) writes:
> According to a friend of mine, who once worked as an inspector of
> equipment in the subway stations, the emergency power cutoff
> switch (there's one at each end of each subway platform, with a
> blue light and dire warnings as to the consequences of misuse)

Also at regular intervals between stations, each one marked with the same
blue light and, in recent years, a sign giving the distance to the nearest
station or other exit in each direction.

> cuts power to trains in both directions, at the station in
> question and at the two adjoining stations (ie. a total of three
> stations are affected).
> 
> This suggests that each station is in its own zone, with the
> cutoff switch sending a control signal to the neighbouring stations.

Did the ex-inspector say that the power cut is ONLY over the distance
he described, or might it be AT LEAST over that distance?  I repeat that
I know from personal observation (of a darkened train) that the power was
off at Bloor station during the emergency near Davisville that started this
topic.  If the power cut is AT LEAST over the distance he/she described,
no such complicated interlocking is required; each cutoff switch needs to
control at most two sections.

> A way to test this hypothesis:  when riding in one of the old red
> subway cars with the incandescent lighting, see how often the
> lights go off.  I've always assumed that they flicker when the
> train crosses the insulated gap between zones (and that the newer
> cars' lights don't flicker because they are equipped with
> batteries -- necessary because fluorescent lights would take too
> long to come back on once power was restored.)

I suspect that the actual reason is that the track power is 600 volts DC,
and you can't run a fluorescent light on that.  The easiest way to generate
AC power (which can be transformed to any voltage needed) is a motor-
generator pair.  If this was used, the momentum of the armature would
cause the lights to stay lit for, say, 1 second or so after power was
removed.  Guess what?  That is exactly the actual behavior.  If you're on
a new-type car and there is a power failure, or if it stops at a place
where the power rail is interrupted, you'll see the lights fade slowly
over a period of 1 second or so.  So I conclude that motor-generator
pairs are used.

(On the old cars, they must either have special incandescent lights that
run on 600 volts, or they must wire them in series.  I don't know which.)

Both old and new cars are also equipped with emergency lights which are
probably battery-powered: one incandescent light over each door.  On the
old (G, for Gloucester) cars these lights are on continuously, and form
part of the normal lighting; on the newer (M, for Montreal Locomotive Works,
and H, for Hawker-Siddeley (now UTDC)) ones they come on about 1 second
after the normal lights have failed.

By the way, in some other cities the subways use fluorescent lights and
yet the lights do go off, almost instantly, when the power rail is
interrupted.  They usually light up again almost instantly, too.
I guess that these cities' trains are using solid-state devices to
convert the DC track power to AC.  (Use of AC power for subways would
be most unusual; DC motors have better characteristics for this duty.)


And C. Harald Koch (chk@client2.dciem.dnd.ca) writes:

| The reason is actually much simpler. Normally, the power strip is on the
| left side of the train (in the tunnels). In center platform stations, and at
| switches, the power rail is on the right.

True, but the gap in the power rail is very short at these places.
I believe that it is not intended as a section boundary for power
cutoff purposes; those have a longer gap.

Note that every car is equipped with contact shoes on both sides at
each set of wheels.  Power to the lights is cut off only when all the
shoes are out of contact, so it is reasonable to assume that all four
shoes are simply wired together.

(One may observe also that when a train, of any type, enters a place where
the power rail is interrupted, there is an arc when the rear shoe of each car
leaves the power rail, but none when the front shoe does.  This shows both
that every car is independently powered and that the front and rear of each
car are connected to each other.)

Now, suppose a car is situated across one of these short gaps in the power
rail with the rear in section A and the front in section B.  Someone tries
to cut off the power in section B.  But look, the front shoe is still live
from section A, and the rear shoe is connected to it, and the section B
is connected to that.  So section B remains live.  Because of this scenario,
gaps in the power rail intended as section boundaries must be long enough
that in the case of the old cars the lights actually do go off; otherwise
you couldn't count on them working.

I believe that the gaps are in fact often located right at the turnback
switches, perhaps to minimize the number of ends to the power rail.
There are some switches where the power is not interrupted, so it's
possible to do that if desired.


In short, what I conjectured before has not yet been disproved.

Mark Brader			Also, be sure to include your signature TWICE in
SoftQuad Inc., Toronto		each article. That way you're sure people will
utzoo!sq!msb, msb@sq.com	read it.   -- "Emily Postnews" (Brad Templeton)