A few questions...

[angelic88]

Hey.

I have been a regular train user for some time. I think its about time I learned a little more about them! So theres a few questions that i have.
Firstly... i travel on the FCC thameslink. So i think the class 319s and 377s. My questions may be rather random!
Ok.. so what makes the trains spark? Is this when they are using 3rd rail?
On the 377s... sometimes you may hear a rather quick but loud bang... it sounds like it is coming from the doors. Has anyone heard this and what is it?
On the 319s... in wet conditions... when the trains accelerate they seem jolt as if th3 driver is accelerating on and off until the train reaches a comfortable speed. Im guessing this is a form of wheel spinning. Does the driver control that or does the train just do it?
Approx how fast do these trains travel when no restrictions?
And finally...the london tunnels. Now i know at farringdon.. the pantograph is lowered and the trains swaps to 3rd rail? When travelling north... i have noticed the trains stopping at coty thameslink even when the station is closed. Is this to lower the panto too? How often do the trains swap from overhead to 3rd rail?
i know my questions are on the random side... but I would like to know. I am quite fascinated.

Thank you in advance! And sorry for any typos! Currently sending from mobile!

x

 

[user15681]

Presumably you mean sparking where the shoes are that collect electricity from the third rail? This is called arcing. Once you form an electrical circuit, if the shoe was to break the circuit (I.e when the third rail ends), it can cause arcing which you will see as a spark.

Not sure what the bang may be on 377s, depends where the train is, what type of power it's using, what speed it's at etc.

A lot of trains, not just 319s, will wheel slip on acceleration when weather conditions are poor or there's poor adhesion. I'm unsure whether on 319s the jolting is the driver altering the acceleration or whether it's automatically being adjusted. The problem is also apparent upon braking, where brakes may lock up. Trains have wheel slip protection to prevent the brakes locking and the wheels sliding, which could cause a wheel flat.

Trains running north changeover at City Thameslink. This is to raise the pantograph and changeover from DC to AC. The idea is that if the train fails to make the changeover, it can go into Smithfield Sidings from City TL to prevent blocking the core, or alternatively reverse where possible. They swap from OHLE to third rail, or the other way, once a journey when going through the core.

 

[A-driver]

The sparking is generally when the shoe comes off the third rail for a gap or to swap sides. I suppose it's loosely similar to pulling a live wire out of a connection and watching it arc.

The jolting in acceleration is when the wheels spin as too much power is applied in certain rail conditions. It's a bit trial and error really as you don't know if you will be taking too much power until you try unless you are expecting poor conditions. I know with 317s we are often advised to let it jolt a few times as it can be enough to get over the slipping and carry on accelerating normally. It's a bit of a double edged sword really as if you open up really slowly in these conditions you will loose loads if time and if you open up too quickly you keep overloading the motors. As I say, it's a mix if trial and error and experience.

As for speed-up to 100mph north of London and up to 90 to the south of Croydon. London bridge-east Croydon is up to 70 if on the mainline rather than via the palace which probably averages out at about 25.

Is the bang on the 377s when north if London and coming from the roof? Sort of sounds like a 'pop'? If so then it's the circuit breaker opening and closing when passing through neutral sections. If that's not what you mean then I can't place the noise.

 

[talldave]

Does the bang you refer to occur when another train passes by?

 

[angelic88]

I think it is likely the circuit breaker as it is a pop sound. So that solves my random questions. Ta very much! I will probably end up with more questions at some point!

Does anyone know if the new trains will be faster? Or just more frequent?

 

[A-driver]

I think it is likely the circuit breaker as it is a pop sound. So that solves my random questions. Ta very much! I will probably end up with more questions at some point!



Does anyone know if the new trains will be faster? Or just more frequent?

Faster acceleration will be the main speed improvement. Although they will be lighter to achieve this so I'm not sure how much faster they will be at accelerating when it starts raining...

 

[angelic88]

Im looking forward to seeing them up and running They look very superior to the 319s at least.

 

[L&Y Robert]

I recently chanced upon a series of photographs of the Class 76 1500v DC locomotives working the old Woodhead route. These locos were fitted with two pantographs and I noticed that they seemed always to have both raised and in contact with the wire when at work. I have never seen a modern AC loco or train-set travelling with more than one pantograph in use. Were the two pantos on the Class 76s electrically connected? If so, the loco could electrically bridge a section gap whilst passing. I have pondered the same question with regard to third rail operations. One sees section gaps on the third rail, and it seems that a motor coach could bridge the gap whilst passing if the pickups are connected together on the vehicle. Maybe each panto of the 76s is a dedicated feed to one motor bogie, albeit under common control. Similarly with the third rail train. Or maybe there is a “Power Bus” the length of the train from which all motors take power, in which case the train bus could be supplying the juice across the gap to other trains somewhere down the line!

 

[455driver]

The 2 pans on a 76 were connected because of the amount of current they had to draw.

On 3rd rail no train should enter a de-energised section anyway so the point you are making is mute. If there is a problem further along the line requiring the power to be turned off then the section before it will be de-energised as well so that in the unlikely event of a train entering that section it wont energise the important bit.

 

[angelic88]

Another question.

Assuming that these trains have a cruise control type of option, what would happen if the driver was to become unresponsive? Would they just keep going?

 

[455driver]

Any train with speed set will still have the vigilance (among other systems) so if the driver doesnt move any control for a minute the vigilance will sound, if it isnt cancelled in 5? seconds the brake will go straight into emergency and on lines equiped with CSR or GSMR radio systems but not the geriatric NRN system if it isnt cancelled in 10? seconds it sends a message to the controlling signaller.

 

[A-driver]

Any train with speed set will still have the vigilance (among other systems) so if the driver doesnt move any control for a minute the vigilance will sound, if it isnt cancelled in 5? seconds the brake will go straight into emergency and on lines equiped with CSR or GSMR radio systems but not the geriatric NRN system if it isnt cancelled in 10? seconds it sends a message to the controlling signaller.

Probably varies unit to unit but I'm pretty sure it's 7 secs with vig before a brake application. It's closer to 30 before it sends a message to the signaller-seems to take ages when you are prepping the train and waiting for the DSD alarm to go off on the csr.

 

[455driver]

I have never really taken any notice of how long it takes on prep for it to fire, its just one of the many things you do without really thinking about it.

 

[A-driver]

I have never really taken any notice of how long it takes on prep for it to fire, its just one of the many things you do without really thinking about it.

Indeed. In the same way that I've never been brave enough to find out exactly how long you get to cancel the AWS!