Re: Indian Pacific hits freight train - Who's the Responsible Investigating body?

[keithm@happy.dca.gov.au (Dave Malcolm)]

In article <mauried.413.37C60947@commslab.gov.au> mauried@commslab.gov.au (Maurie Daly) writes:
>From: mauried@commslab.gov.au (Maurie Daly)
>Subject: Re: Indian Pacific hits freight train - Who's the Responsible
>Investigating body?
>Date: Fri, 27 Aug 1999 03:43:03 GMT


>>Having an insulator between the wheel and the rail is usually fatal for any
>>form of track circuit.

>>Reading the above I think there is some confusion as to how a track circuit
>>operates.  In it's most basic form (Steady DC), the sections are broken up
>>by insulated joints.  At one end of the section, the voltage is fed to the
>>track, and at the other end the track relay is between the rails.  So the
>>circuit goes:
>>B2 (positive side of battery), feed resistor, one leg of the track circuit
>>(rail), relay, other leg of the track circuit (rail), N2 (negative side of
>>battery).

>>So the relay picks up when the track is unoccupied, and drops away when a
>>train enters the section.  This is because the trains wheels act as a short
>>circuit.  The relay will also drop, simulating the presence of a train, if
>>you use a piece of wire to short the rails, (kids living near level
>>crossings find this out annoyingly regularly), or if the bonding between
>>consecutive rails breaks, or the rail itself breaks, or a track lead is
>>broken, or if the ballast resistance falls due to heavy rain, or if the
>>mains power fails and the track battery goes flat.

>>So if a train is either lightweight (Victorian Sprinter), or is sanding
>>VERY heavily (alleged to be 3801), the trainshunt (resistance of the axles
>>of the train) can rise until its not enough to shunt enough current to drop
>>the relay (Ohms law etc...).

>>Therefore, a train drops the relay, and if it drops a lot of sand or goes
>>high resistive, it 'disappears'.  This is what I understand to have
>>happened on Cowan Bank, and with the Sprinters.

>>European railways I believe have an arrangement where the track circuit
>>will not pick up until the next track in sequence is down, apparently due
>>to European ideas on proving relay operation.  This has the effect of
>>ensuring that a train 'dissapearing' off a track circuit doesn't actually
>>cause false operation of signals, points, level crossings, etc...  I
>>remember reading that one of the recent resignallings somewhere in NSW will
>>actually generate some sort of alarm whenever 'non sequentual' operation
>>occurs, this may be what you are alluding to.

>>Why can't this 'sequential testing' be used in Australia, I hear you ask?
>>Well British, American and Australian railways have always used a different
>>philosophy when designing anything vital within a signalling system, i.e.,
>>if you open a contact with a vital relay in a vital circuit, you can
>>usually assume that the relay will drop, whereas the Europeans almost
>>always want to prove that the relay actually dropped.  When applied to
>>track circuits, this philosophy goes that if you design a track circuit,
>>then it must drop whenever a train enter the section.  If we started
>>proving sequential operation, it would create problems if a track circuit
>>drops, then it needs the next track down to pick up, which leaves problems
>>if there is an intermittent fault, instead of self clearing, it would then
>>get stuck down.  This then raises several problems, excessively unreliable
>>tracks then mean more caution orders, hand throwing of points, continuously
>>operating level crossings, all of which mean a reduction in safety anyway.
>>Why bother, when you can put the effort into ensuring that the tracks work
>>properly in the first place(i.e. avoid crummy low voltage circuits)?

>>--
>>Mr Notagunzel.
>>Rail Transportation Connoisseur.
>>notagunzel@bigfoot.com
>>(Waiting for the next move at http://www.bigfoot.com/~notagunzel)


>Fair enuf on all the above.
>The thrust of my argument is that Railway Safeworking systems are supposed to 
>be fail safe , ie if they fail its in the safe mode and not a dangerous mode 
>where multiple trains are allowed to occupy a single track section.
>The provision of sand across the rails is , if we beleive the 3801 explanation
>a failure of the track ccts in the dangerous mode.
>If the Rail Authority knows that sand can cause this effect then they have 
>only a small number of choices.

>1/ Hi voltage track ccts that can break down the insulating material.
>2/ Entry / exit track ccts which are sequential , as you have explained above.
>3/ Axle counting instead of track ccts altogether.
>4/ Banning sanding wherever low voltage track ccts are used.
>5/ Instituting absolute block working where locos that carry sand run over the 
>track circuited terrain.
> 
>If however , the Rail Authority has done none of these, then they are 
>expecting us to beleive that sanding from a steam loco can make the track ccts
>fail in a dangerous mode , but not sand from diesels or electrics.
>Hardly beleivable one would think.
>Prior to the 3801 incident had the SRA , or indeed any other Railway in this 
>country issued warnings about sanding in track circuited terrain?

>MD

Desanding equipment is now fitted to most if not all locos which use sand 
steam and diesel.

Dave Malcolm