What happens when one HST power car is disconnected?

[antharro]

I was wondering about this following on from the Stonehaven accident.

In a standard HST formation ( PC + carriages + PC ), if the leading power car gets disconnected unexpectedly, either through major electrical fault or, as in the case of Stonehaven, physically, what happens to the other one?

Presumably if the train is under power, under direction of the leading PC, then the rear car will keep running, but having lost its "control" from the leading PC, will drop to idle?

Or, does a complete disconnection of the leading PC result in the rear PC losing its "control" and therefore it shuts down completely?

Would there be some sort of emergency shutdown procedure wired into the engine's electrics to shut it down immediately and safely, or does it just turn off like someone turning the key off for a car engine?

 

[Richard Scott]

I'm not familiar with HSTs but a traditional loco if brake pipe is broken the brakes will apply and the power will be cut when the brake pipe falls below a pre-determined value. Would imagine the same is true of an HST.

 

[43096]

I'm not familiar with HSTs but a traditional loco if brake pipe is broken the brakes will apply and the power will be cut when the brake pipe falls below a pre-determined value. Would imagine the same is true of an HST.

If the jumper cable breaks you lose traction power and get an emergency brake application as the signal to the rear E70/DW2 brake controller is lost. Of course the air pipe breaking will also dump the brake.

 

[rebmcr]

the signal to the rear E70/DW2 brake controller

Is that a continuous voltage, or a repeated pulse? If it's the latter, then the action could lag behind the cable severance, by however long the 1970s electronics are set to leave between pulses (plus however many missed pulses are tolerated, if any).

 

[Clarence Yard]

One of the faults we had on the ecml in the very early days of the HSTs was the Buckeyes dropping due to being incorrectly coupled, usually on curved sidings. The unit would then tank down the main line at 125mph as effectively two trains unless a cable parted.

I was on one once and noticed the gangway plates buffeting to and fro above the affected coupling. It was a bit of a scary moment as I realised what was going on. Me and my mate got the train stopped at the next station, Peterborough. Everybody out.

The emergency solution to all this was to put a huge jubilee clip round the gravity block on the coupler!

 

[43096]

Is that a continuous voltage, or a repeated pulse? If it's the latter, then the action could lag behind the cable severance, by however long the 1970s electronics are set to leave between pulses (plus however many missed pulses are tolerated, if any).

Continuous voltage AFAIAA.

 

[No Fault Found]

One of the faults we had on the ecml in the very early days of the HSTs was the Buckeyes dropping due to being incorrectly coupled, usually on curved sidings. The unit would then tank down the main line at 125mph as effectively two trains unless a cable parted.

I was on one once and noticed the gangway plates buffeting to and fro above the affected coupling. It was a bit of a scary moment as I realised what was going on. Me and my mate got the train stopped at the next station, Peterborough. Everybody out.

The emergency solution to all this was to put a huge jubilee clip round the gravity block on the coupler!

Really?
And this happened more than once?

 

[Clarence Yard]

Quite a few times in a very short period, a matter of weeks, iirc. At first it was just thought to be poor staff attention on coupling before it was realised it was a wider issue.

Curved carriage sidings was the real culprit - something the ER had quite a few of at some locations, including Bounds Green.

 

[coppercapped]

I was wondering about this following on from the Stonehaven accident. In a standard HST formation ( PC + carriages + PC ), if the leading power car gets disconnected unexpectedly, either through major electrical fault or, as in the case of Stonehaven, physically, what happens to the other one? Presumably if the train is under power, under direction of the leading PC, then the rear car will keep running, but having lost its "control" from the leading PC, will drop to idle? Or, does a complete disconnection of the leading PC result in the rear PC losing its "control" and therefore it shuts down completely? Would there be some sort of emergency shutdown procedure wired into the engine's electrics to shut it down immediately and safely, or does it just turn off like someone turning the key off for a car engine?

In the Usenet newsgroup uk.railway a GWR driver posted this yesterday in answer to the same question:

https://groups.google.com/forum/#!original/uk.railway/5q4lDAPCO8Y/YnDqE4_MCQAJ

If the train was still under power at the time of impact and the driver was unable to take any action, then two things will happened pretty much simultaneously. Let’s assume that the brake pipe and the 36-way jumper
cable both sever at the same time. Until they do, the rear (and front) power cars keep powering. As soon as the jumper cable severs, traction power will be lost instantly (there's a short-circuiting device on the
alternator output). The brake will also apply in the rear power car, though it's slightly slower (I've never observed the precise behaviour of the rear power car during shutdown, and it may depend how much of the ATP equipment ScotRail have removed (ATP has its own valve to dump the brake pipe, which is the characteristic air-release sound of a GW HST arriving at terminus and shutting down; I've rarely driven non-ATP fitted power cars (or with ATP isolated) and can't remember exactly what happens). If, in a different circumstance, the brake pipe is severed but the jumper cable remains intact, the power cars will keep powering until brake pipe pressure drops below around 4bar, at which point the Brake Pipe Relay operates and cuts power on both power cars.

 

[Poppysdad]

Its along time since i did anything on loco's aqnd brake piped systems but from what i remember there is a pressure switch on the loco's and i assume that same would apply to the class 43's, which would cut traction in the event of the brake pipe falling below a preset level. On EMU's the train continuity wire performs the same function as a brake pipe and when this is broken the Emergency Brake Relay (EBR) is tripped which cuts traction amongst other things

 

[Railengineer]

If the control cable connection is broken the brake applies and whole train should stop. The electric train supply will also go off because the train supply cable separation breaks the interlock for that as well. Unless there is a very specific electrical fault on the control cable at the time, the rear engine will revert to idle and stay like that until it is shut down.

 

[Merle Haggard]

One of the faults we had on the ecml in the very early days of the HSTs was the Buckeyes dropping due to being incorrectly coupled, usually on curved sidings. The unit would then tank down the main line at 125mph as effectively two trains unless a cable parted.

I was on one once and noticed the gangway plates buffeting to and fro above the affected coupling. It was a bit of a scary moment as I realised what was going on. Me and my mate got the train stopped at the next station, Peterborough. Everybody out.

The emergency solution to all this was to put a huge jubilee clip round the gravity block on the coupler!

I'm not disputing what you say, but my understanding (presumably wrong!) was that one difference between L.L. Mk3s and HST trailers (which needed to be changed when LH stock was converted for use in HSTs) was that the latter had 'fixed head' buckeyes, implying that they couldn't fall to the vertical position. Or possibly 'fixed head' means something different?

 

[Railengineer]

You misunderstand Clarence Yard's description. The buckeye did not 'drop' to a vertical position it stayed horizontal but the internal section of the buckeye dropped and allowed them to uncouple in service. Hence the temporary jubilee clip to hold the release arm in the 'coupled' position.

 

[43096]

I'm not disputing what you say, but my understanding (presumably wrong!) was that one difference between L.L. Mk3s and HST trailers (which needed to be changed when LH stock was converted for use in HSTs) was that the latter had 'fixed head' buckeyes, implying that they couldn't fall to the vertical position. Or possibly 'fixed head' means something different?

They are fixed head - technically they are knows as Alliance couplers - as the photo below shows of one removed from a power car.