Post by Tom on May 4, 2020 15:06:12 GMT
Typical. I forget to check in on a thread and all sorts of interesting stuff gets discussed!
The current plan is for a straight 33 1/3 to 125Hz conversion of relevant circuits on the Rayners Lane branch, which would basically be limited to track circuits and signal selection (control) circuits. It would be implemented in much the same way as was done on the Bromley-by-Bow to Upney(?) section of the District line, with new feed kiosks and changing of relays as required. Personally, I think a straightforward signal main conversion would have been easier and more effective (there are issues where you mix 33 1/3 and 125Hz supplies on the same piece of kit), but there was a reluctance to install new 125Hz frequency converters in the substations. @aetearlscourt is quite right that there are issues with the supply of relays at the moment - this is a known issue and will have to be overcome.
EBI200 track circuits fell out of favour very quickly after they were first introduced - there is an element of me that believes they were used in preference to FS2550 to make a point about dual sourcing and not being tied to Siemens (Invensys) after some poor performance elsewhere on the SSR which then backfired. My personal feeling is that a 2550 with blockjoints is the best track circuit I've ever worked on - though they can be a bit fiddly to set up, whereas a Capacitor fed track is very simple to set up and test but the fault finding can be a bit involved.
Regarding t697 's point about signal sighting - yes, lot has changed since the days of crew operated 1959 stock! Signal Sighting on LU wasn't massively considered until the advent of more modern stocks such as 1992TS, where a number of signals required co-actors to be fitted for close visibility. It really took off as an industry following the collision at Ladbroke Grove in 1999, though there are still some some really badly sighted signals out there.
It's worth remembering back then we went from crew operated 59TS to crew operated 73TS which theoretically had better visibility thanks to the curved windscreen. Subsequent OPO conversion on the Piccadilly line caused changes to stopping positions as now the front cab had to be in the platform, rather than the rear cab for the guard's benefit, though in the tube this didn't have many issues in practice as there was only a limited range of positions available to install a signal. Where it mattered more was outside stations where the signal positioning wasn't really optimal before but now was made worse by additional furniture such as monitors or mirrors, and there was a greater chance of what became known on BR as 'ding-ding and away' SPADs where the driver lost the independent check on the signal aspect provided by the guard. A few high-SPAD sites have been provided with co-actors or additional repeaters over the years, though it is interesting that very little modification has been done to the majority of the Piccadilly line's safety signalling (with a few exceptions such as Heathrow) since the early 1980s.
The current plan is for a straight 33 1/3 to 125Hz conversion of relevant circuits on the Rayners Lane branch, which would basically be limited to track circuits and signal selection (control) circuits. It would be implemented in much the same way as was done on the Bromley-by-Bow to Upney(?) section of the District line, with new feed kiosks and changing of relays as required. Personally, I think a straightforward signal main conversion would have been easier and more effective (there are issues where you mix 33 1/3 and 125Hz supplies on the same piece of kit), but there was a reluctance to install new 125Hz frequency converters in the substations. @aetearlscourt is quite right that there are issues with the supply of relays at the moment - this is a known issue and will have to be overcome.
EBI200 track circuits fell out of favour very quickly after they were first introduced - there is an element of me that believes they were used in preference to FS2550 to make a point about dual sourcing and not being tied to Siemens (Invensys) after some poor performance elsewhere on the SSR which then backfired. My personal feeling is that a 2550 with blockjoints is the best track circuit I've ever worked on - though they can be a bit fiddly to set up, whereas a Capacitor fed track is very simple to set up and test but the fault finding can be a bit involved.
Regarding t697 's point about signal sighting - yes, lot has changed since the days of crew operated 1959 stock! Signal Sighting on LU wasn't massively considered until the advent of more modern stocks such as 1992TS, where a number of signals required co-actors to be fitted for close visibility. It really took off as an industry following the collision at Ladbroke Grove in 1999, though there are still some some really badly sighted signals out there.
It's worth remembering back then we went from crew operated 59TS to crew operated 73TS which theoretically had better visibility thanks to the curved windscreen. Subsequent OPO conversion on the Piccadilly line caused changes to stopping positions as now the front cab had to be in the platform, rather than the rear cab for the guard's benefit, though in the tube this didn't have many issues in practice as there was only a limited range of positions available to install a signal. Where it mattered more was outside stations where the signal positioning wasn't really optimal before but now was made worse by additional furniture such as monitors or mirrors, and there was a greater chance of what became known on BR as 'ding-ding and away' SPADs where the driver lost the independent check on the signal aspect provided by the guard. A few high-SPAD sites have been provided with co-actors or additional repeaters over the years, though it is interesting that very little modification has been done to the majority of the Piccadilly line's safety signalling (with a few exceptions such as Heathrow) since the early 1980s.
