Midland Main Line Electrification

[Zomboid]

Those will be red bonds. Different from normal negative bonds because if they get disconnected from earth they can get to full system voltage which would be very damaging and dangerous.

[Trog]

17 minutes ago, Zomboid said:

Those will be red bonds. Different from normal negative bonds because if they get disconnected from earth they can get to full system voltage which would be very damaging and dangerous.

 

Not sure it is quite that simple, I think that there are red bonds and Red Bonds. I think one ordinary black cross bond a mile is painted red simply to deter the P-Way from knocking them all off when re-railing etc. Conversely there is the neutral bar return a red bond running to the sub-station at neutral sections that we were told was extra specially dodgy to meddle with. But as a rule of thumb if it is painted red leave it to the overheads.

[Edwin_m]

28 minutes ago, Trog said:

 

Not sure it is quite that simple, I think that there are red bonds and Red Bonds. I think one ordinary black cross bond a mile is painted red simply to deter the P-Way from knocking them all off when re-railing etc. Conversely there is the neutral bar return a red bond running to the sub-station at neutral sections that we were told was extra specially dodgy to meddle with. But as a rule of thumb if it is painted red leave it to the overheads.

Those ones look pretty serious, and being just outside a TSC I think they'd be the sort of Red Bond that isn't to be messed with.  

[jim.snowdon]

11 hours ago, Edwin_m said:

Those ones look pretty serious, and being just outside a TSC I think they'd be the sort of Red Bond that isn't to be messed with.  

Indeed not, as those would appear to be the main traction negative connections.  Removing them generally isn't a good idea as it will lead to traction return current finding its way back by all manner of routes, including the earth. I doubt you could get the rails up to full system voltage simply because the rail:earth resistance is relatively low, but they might still be at voltages that bite. The same principle is used on the DC railway, where the running rails are not earthed. Instead, they float at around zero volts to earth, plus or minus 60V. 

 

Jim

[Talltim]

Having finally got round to reading those service patterns, makes me glad I no longer do the regular Harpenden to Chesterfield/Sheffield trips. Used to be easy, quick hop on Thameslink to Luton (or sometimes Bedford) then one train all the rest of the way. Now it looks like a right faff, with two extra changes, which is ridiculous for two places on the same line. I could just about get my head around two changes on such a route (local-express-local).

Edited March 14, 2020 by Talltim

[Edwin_m]

7 hours ago, Talltim said:

Having finally got round to reading those service patterns, makes me glad I no longer do the regular Harpenden to Chesterfield/Sheffield trips. Used to be easy, quick hop on Thameslink to Luton (or sometimes Bedford) then one train all the rest of the way. Now it looks like a right faff, with two extra changes, which is ridiculous for two places on the same line. I could just about get my head around two changes on such a route (local-express-local).

I responded to the consultation suggesting that one of the Nottingham trains should still call at Luton Airport Parkway as it does now.  As well as helping with issues such as this one, it would preserve the airport link for the East Midlands which is useful as Luton has a much better range of flights than the local airport.  

[96701]

Red bonds are traction returns, black bonds create an equipotential zone such that, should there be a short circuit, the current will flow in a predicted direction.

[phil-b259]

On 14/03/2020 at 10:11, Talltim said:

Having finally got round to reading those service patterns, makes me glad I no longer do the regular Harpenden to Chesterfield/Sheffield trips. Used to be easy, quick hop on Thameslink to Luton (or sometimes Bedford) then one train all the rest of the way. Now it looks like a right faff, with two extra changes, which is ridiculous for two places on the same line. I could just about get my head around two changes on such a route (local-express-local).

 

No more of a 'right faff' than goes on on other mainlines!

 

I repeat the ONLY reason the MML service pattern developed as it did was the Beeching era cuts which saw no local trains north of Bedford meaning what SHOULD have been EXPRESS services to the East Midlands had lots of extra calls inserted to keep conectivity at retained stations like Bedford - Wellingborough - Kettering, which are far too close together to be suited to be served by long distance InterCity style operations to / from the East Midlands

 

 

[geoff]

Thanks to those who responded to my query about the red cables connected to the track at Glendon. Does this mean that the old track circuits used for detecting trains are no longer used if these traction return cables are effectively shorting out the rails?

 

Geoff

[96701]

12 minutes ago, geoff said:

Thanks to those who responded to my query about the red cables connected to the track at Glendon. Does this mean that the old track circuits used for detecting trains are no longer used if these traction return cables are effectively shorting out the rails?

 

Geoff

Impedance bonds are used to separate traction return from track circuits. Don't ask me how they work.

[geoff]

Thanks 96701. I wondered if that was possibly how it was done.

 

Geoff

[Zomboid]

In many cases only one rail is used for traction return, and the other is used for signalling. I've no idea how that actually works though. (In DC areas both rails are often used for both, with impedance bonds ensuring the necessary separation for the track circuits to work, by being low impedance to DC currents and high impedance to AC currents, which I don't really understand the details of, but I think they must be highly inductive).

 

For new systems it's pretty common for axle counters to be used and both rails are therefore available for traction return. Don't know what they're doing on the MML.

[Edwin_m]

The linked photo seems to show bonds to all the rails with some of them going to a box in the four-foot which does look a little like the impedance bonds on the Southern.  Unfortunately there's a pole blocking the view so we can't see them very well.  Leicester re-signaling in the 1980s included AC immunization and although various bits have been changed including moving control to Derby, the original track circuits may still be there.  In which case perhaps this is an impedance bond in reverse, passing the 50Hz AC electrification return current between the rails but not the track circuit current, which could be DC or in the hundreds of Hz depending on the track circuit type.  

[96701]

8 minutes ago, Zomboid said:

In many cases only one rail is used for traction return, and the other is used for signalling. I've no idea how that actually works though. (In DC areas both rails are often used for both, with impedance bonds ensuring the necessary separation for the track circuits to work, by being low impedance to DC currents and high impedance to AC currents, which I don't really understand the details of, but I think they must be highly inductive).

 

For new systems it's pretty common for axle counters to be used and both rails are therefore available for traction return. Don't know what they're doing on the MML.

It will be difficult to use one rail when real trains don't have insulated axles. It will be the impedance bonds that "encourage" the traction return to stay separate from track circuits. The photos on line all seem to have very heavy cables from both rails into "the black box".

[Zomboid]

The current takes the path of least resistance, so if one rail offers a significantly lower impedance path back to the source then very little will flow in the other.

 

Track circuits and signalling are not really my area of expertise...

Edited March 15, 2020 by Zomboid

[Edwin_m]

11 minutes ago, 96701 said:

It will be difficult to use one rail when real trains don't have insulated axles. It will be the impedance bonds that "encourage" the traction return to stay separate from track circuits. The photos on line all seem to have very heavy cables from both rails into "the black box".

The "traditional" arrangement on AC lines it to have one rail electrically continuous and the other electrically sectioned for DC track circuits.  Traction return will almost all flow along the continuous rail (there will be a bit in the other rail as the insulation is never perfect).  The track circuit relays are only sensitive to DC currents.  Just to confuse things traditional AC mostly uses a booster transformer arrangement to "encourage" the return current to use a separate wire rather than staying in the rail.  

 

On DC lines the traditional arrangement on plain line is to have both rails insulated but connected by impedance bonds, which let the DC traction return current pass through but block the track circuit current which is usually 50Hz.  The track circuit relays are only sensitive to AC.  The reason to do this, I think, is so the traction return can be shared between the two rails so the voltage drop and wasted power in the return part of the circuit is halved.  However areas of switches and crossing were usually fitted with single rail track circuits and one electrically continuous rail.  

 

More recent installations on either electrification system (or unelectrified lines) will probably have used jointless track circuits or axle counters.  

Edited March 15, 2020 by Edwin_m

[geoff]

Thanks guys.

 

Geoff

[Trog]

1 hour ago, 96701 said:

It will be difficult to use one rail when real trains don't have insulated axles. It will be the impedance bonds that "encourage" the traction return to stay separate from track circuits. The photos on line all seem to have very heavy cables from both rails into "the black box".

 

The OHL Dept. did not seem to find it a problem on the WCML back in the days of the 1960's vintage power box signalling. The only place you ever saw impedance bonds on the WCML in those days were near the mouths of the longer tunnels where the track circuits changed from two rail in the tunnels to single rail outside. This was done I believe in the interest of detecting broken rails. As otherwise only a break in the S&T rail would be detected by the track circuits. As the cross bonding to the other return rails would usually bridge out any break in the traction return rail.

[ess1uk]

10 hours ago, Zomboid said:

 

 

For new systems it's pretty common for axle counters to be used and both rails are therefore available for traction return. Don't know what they're doing on the MML.

New axle counters 

[jim.snowdon]

10 hours ago, Edwin_m said:

On DC lines the traditional arrangement on plain line is to have both rails insulated but connected by impedance bonds, which let the DC traction return current pass through but block the track circuit current which is usually 50Hz.  The track circuit relays are only sensitive to AC.  The reason to do this, I think, is so the traction return can be shared between the two rails so the voltage drop and wasted power in the return part of the circuit is halved.  However areas of switches and crossing were usually fitted with single rail track circuits and one electrically continuous rail.  

Frequently with reinforcing cables wired in parallel with the single traction return rails through S&C to compensate for the "missing" running rail. 

 

The advent of axle counters has made things simpler in terms of maintaining the traction return circuit through S&C, although there does seem to be some reluctance exploit this where complex layouts sit in areas of conventional track circuiting. Axle counting seems to be seen as an all or nothing solution and confined to complete resignalling projects.

 

Jim

[Edwin_m]

6 minutes ago, jim.snowdon said:

Frequently with reinforcing cables wired in parallel with the single traction return rails through S&C to compensate for the "missing" running rail. 

 

The advent of axle counters has made things simpler in terms of maintaining the traction return circuit through S&C, although there does seem to be some reluctance exploit this where complex layouts sit in areas of conventional track circuiting. Axle counting seems to be seen as an all or nothing solution and confined to complete resignalling projects.

 

Jim

I think there's a safety concern here that on-train staff will assume that the track circuit clip will provide protection if there is an incident, when it won't necessarily if there are odd bits that have axle counters instead.  There's also the issue of introducing the processes for safe resetting of axle counters which may not be worthwhile, or may run the risk of confusion, if it only applies to small parts of the control area.  

[jim.snowdon]

3 minutes ago, Edwin_m said:

I think there's a safety concern here that on-train staff will assume that the track circuit clip will provide protection if there is an incident, when it won't necessarily if there are odd bits that have axle counters instead.  There's also the issue of introducing the processes for safe resetting of axle counters which may not be worthwhile, or may run the risk of confusion, if it only applies to small parts of the control area.  

Possibly, although I wonder if the Signalling, Track and Electrification engineers have ever got together on this to take a balanced view of the pros and cons, or if the usual rules of silo management apply. I'm not aware of anything in this regard.

 

Jim

[The Stationmaster]

3 hours ago, Edwin_m said:

I think there's a safety concern here that on-train staff will assume that the track circuit clip will provide protection if there is an incident, when it won't necessarily if there are odd bits that have axle counters instead.  There's also the issue of introducing the processes for safe resetting of axle counters which may not be worthwhile, or may run the risk of confusion, if it only applies to small parts of the control area.  

On-train staff shouldn't make such an assumption - because sections where axle counters are in use are clearly identified in the relevant Sectional Appendix.

 

Axle counter resetting procedures have received a lot of attention over the years so should be about as near safe as possible by now, especially as ever greater amounts of the railway are being equipped with them including not just new work but extending to replacement of existing track circuiting.

[iands]

It is not for on-train staff to determine what, if any, train detection systems are employed on the section of track they are requiring to place the track circuit clip on. Their only concern is to place said clip as per instructions, regardless if it "drops a track" or not. 

[Edwin_m]

1 hour ago, The Stationmaster said:

On-train staff shouldn't make such an assumption - because sections where axle counters are in use are clearly identified in the relevant Sectional Appendix.

Yes they are, but if the identification of axle counter sites includes a long list of junctions that are exceptions to the routes they sit on, it increases the risk of people doing the wrong thing when under pressure in an emergency.