Running with pantograph down

[roythebus]

This thread reminds me of the day in 1974 I was working an air-braked express from rugby to Euston, probably with a class 82 or 85. It failed to take power after the neutral section at Berhampstead. We coasted all the way to Euston as we'd been doing just over the ton at Berko! Luckily the bobby at Euston had the road for us; we had enough air to keep the brakes off all that way and luckily, it's downhill all the way. The pan was up and the compressor kept running. Modern (in those pre-computer days)stock rolls along way.

[stewartingram]

When the OHL was energised from Bletchley to Euston, and the AM10 units were introduced, I remember reading somewhere that they coasted all the way fro Tring to Euston. Possibly in Modern Railways?

 

Stewart

[Poor Old Bruce]

Crikey - at last we are catching up the mainland in our methods. When I suggested to some Railtrack and mech engineering sorts back in the late 1990s that they should look at running through neutral sections with pans lowered they looked at me as if I'd just arrived from another planet - when I told them that I'd been in the cab of a TGV on an LGV doing exactly that at speeds well in excess of 125 mph I thought they were going to faint.

 

It has been commonplace at neutral sections and some electrification system changeover points (where the change takes place at speed on mainland rail systems for a good many years and goes on hundreds of times every day - and it is great fun to watch from the lineside especially where a train is coming off, say, Belgian ohle and going onto SNCF 25kv ohle because -provided you can see all the operation - you not only see it running with pans down but you watch it lower one and then raise the other after it leaves the neutral section.

 

Sorry about the late response SM (must have missed the thread first time round) but I presume the palarver described above is not just because of a change of phase at the neutral section or a change in voltage but necessitated by changing from ac to dc or vice versa. Some parts of the BR 25kV system were actually at 6.25kV which was detected by a 'potential transformer' mounted on the roof of the trains (only applied to certain EMUs IIRC) which registered the voltage and automatically changed tappings on the main transformer. There was no need to drop the pantographs. Anybody worth their salt on Railtrack should (emphasis on should) have been able to tell you that, it is said that experience has to be re-learned every three generations.

 

Edit to add: There were (are?) trackside magnets just before and just after neutral sections to tell the loco/EMU roof mounted circuit breaker to open before the NS and close after it so that the train is not drawing current (and making big electrical arcs) through the NS.

[Titan]

Problems with the 6.25kV/25kV changeover equipment was a significant factor in the transformer explosions experienced by the class 303's when introduced, particularly in the case of an OLE fault which caused the voltage to drop. Before the breakers tripped on the OLE the units would detect the low voltage and swap to 6.25kV. Then when the fault was cleared and the line re-energised at 25kV, The mercury-arc rectifiers on the unit would back fire creating a direct short circuit on the secondary coil of the transformers, whilst the primary was subject to four times its normal working voltage. Needless to say this did not do them much good...

[Edwin_m]

Tram-trains can use the same pantograph for both 750V and 25kV or 15kV (depending on country).  There must be some clever voltage detection there - perhaps checking for DC versus AC - but as far as I know they've never blown one up! 

[roythebus]

The 6.25kv/25kv change ove was actuated through trackside magnets similar to AWS magnets mounted outside the running rails. There were some on the LTSR that I used to see from the District Line in the early 1970s but can't remember where. Similar sets on the GE line somewhere around Ilford.

 

Slightly off-subject, on the Guildford-Portsmouth line, it is possible to coast from Haslemere to Guildford by shutting off power once the train is over the summint about half a mile from Haslemere. Speeds of over 90mph could be attained on VEP/CIG units, having to brake for Shalford Junction!

[Grovenor]

 

The 6.25kv/25kv change ove was actuated through trackside magnets similar to AWS magnets mounted outside the running rails.

They were just the standard neutral section magnets, as mentioned above,  just the same whether there was a voltage change or not. Trains with the voltage change facility measured the voltage on the new section and reconfigured the windings as needed before closing the line contactor. With the results described by Titan!

Keith

[eastwestdivide]

Resurrecting a relevant thread, rather than starting a new one, I was a bit surprised to see the following arrangement at a moving bridge in Maassluis, NL, when I was exploring the Rotterdam area last week.

 

 

No catenary at all on the moving section of the bridge:

 

and the train coasting over with the panto up:

[Poor Old Bruce]

A lot depends on the contact wire height. In some countries the wire is at a fairly constant height so that the main pantograph mechanism doesn't have to do much, just the head suspension going up and down to accommodate the small movements involved. In this country the contact wire height varies between something like 13ft 6in at some bridges and 18 or 19 ft at level crossings. Simply running off the end of the wire, the pantograph would go up to its limit of travel but how it would meet the wire at the other end of the bridge is another matter. I am not sure how far a British pantograph would go up or how it would cope with the incoming wire from that height.

[modfather]

A lot depends on the contact wire height. In some countries the wire is at a fairly constant height so that the main pantograph mechanism doesn't have to do much, just the head suspension going up and down to accommodate the small movements involved. In this country the contact wire height varies between something like 13ft 6in at some bridges and 18 or 19 ft at level crossings. Simply running off the end of the wire, the pantograph would go up to its limit of travel but how it would meet the wire at the other end of the bridge is another matter. I am not sure how far a British pantograph would go up or how it would cope with the incoming wire from that height.

 

 

Most rolling stock will have an auto drop system, usually as a closed air system, with a positive air feed under a the pan carbons, if a carbon cracks air will vent and lower the pan, same for a pan that rises above its set limit, in many cases it strikes a plunger that vents the pan up pressure, dropping the pan by around a foot rapidly, then damping the final distance. (yes, I paid attention to my pan course - the new mentor pan is something very special)

[Poor Old Bruce]

Most rolling stock will have an auto drop system, usually as a closed air system, with a positive air feed under a the pan carbons, if a carbon cracks air will vent and lower the pan, same for a pan that rises above its set limit, in many cases it strikes a plunger that vents the pan up pressure, dropping the pan by around a foot rapidly, then damping the final distance. (yes, I paid attention to my pan course - the new mentor pan is something very special)

 

Of course. I should have remembered that  .