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Post by PiccNT on Dec 12, 2016 12:19:03 GMT
Hi Fish. Always happy to see a photo! I am a Night Tube driver so I have only been around for 6 months.
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Post by fish7373 on Dec 12, 2016 12:34:01 GMT
Hi Fish. Always happy to see a photo! I am a Night Tube driver so I have only been around for 6 months. HI OK thanks for getting back i will send some when back at work.
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Post by tunnelbore on Dec 12, 2016 12:58:51 GMT
If my memory serves me right (from the 72 stock), the rheostatic brake works on the axle to reverse the turn of the wheel, it also kicks in to hold the train in the rheo 1 & hold position. So the view is the polarity being powerful enough to lock the wheels? If you read my earlier post regarding the 508s on the southern, I said there that the rheo brake on those was strong enough to make the wheels turn in reverse; so one can safey assume it is strong enough to lock the wheels too. Rheostatic braking (aka dynamic breaking) means disconnecting the motor from the supply, letting the motor act as a generator and placing a resistor across the generator to absorb the energy generated by the rotating motor. This can not lock the wheels and can not cause reverse rotation. The braking torque is proportional to the current which is set by the voltage and the resistance. The voltage is proportional to the speed (in a simple DC motor). Thus the braking torque reduces as speed reduces and reaches zero then the wheel stops rotating. The wheel has nothing locking it much less causing it to spin in reverse. I don't doubt your observations but they imply that it is not rheostatic braking in use here whatever it might have got called. Because rheostatic braking is ineffective at low speeds it is usually blended with friction brakes. If the blending is poor the friction brakes could cause lock-up. There is also regenerative breaking where the current in the motor is controlled to apply a specific braking torque whatever the speed but this requires more than just a resistor. There is an old technique called plugging which is to throw the motor into reverse connection across the supply: violent, not regenerative and liable to cause reverse rotation if it is not stopped in time. TBFN
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Post by drainrat on Dec 12, 2016 18:51:49 GMT
If my memory serves me right (from the 72 stock), the rheostatic brake works on the axle to reverse the turn of the wheel, it also kicks in to hold the train in the rheo 1 & hold position. So the view is the polarity being powerful enough to lock the wheels? If you read my earlier post regarding the 508s on the southern, I said there that the rheo brake on those was strong enough to make the wheels turn in reverse; so one can safey assume it is strong enough to lock the wheels too. I guess my knowledge on rheo braking really should be better
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Post by 100andthirty on Dec 12, 2016 19:47:58 GMT
Rolythebus, drainrat. Sorry all this isn't what happens. In rheostatic braking, the motors are turned into generators. The wheels need to turn to generate any electricity. It is the work done generating the electricity that provides the braking force. It can't make the wheels turn in reverse and it can't hold the train when stationary when there is no wheel movement.
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roythebus
Pleased to say the restoration of BEA coach MLL738 is as complete as it can be, now restoring MLL721
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Post by roythebus on Dec 12, 2016 21:14:49 GMT
Whilst I can't comment on the Picc stock as it wasn't around in my days on the underground, regenerative braking does what it says on the tin. Generates and feeds current back into the juice rails. It's done by reversing the motor, so in very slippery conditions it is possible to get the wheels turning in reverse. O and P stock done that with its Metadyne braking system.
On BR we were taught that in dire emergency to put the reverser in reverse and open up the controller. The train involved in the Clapham crash (28 years ago today) was I believe found to have the reverser in reverse position and the controller wide open in an attempt to provide additional stopping power.
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Post by fish7373 on Dec 12, 2016 21:39:30 GMT
HI all roythebus you are wrong 100andthirty is right when braking the reverser does not go in REV`S REHO brake works from the motor brake switch and regenerative braking and Metadyne braking are all a different kettle of fish.
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Post by Deleted on Dec 12, 2016 21:39:33 GMT
Whilst I can't comment on the Picc stock as it wasn't around in my days on the underground, regenerative braking does what it says on the tin. Generates and feeds current back into the juice rails. It's done by reversing the motor, so in very slippery conditions it is possible to get the wheels turning in reverse. O and P stock done that with its Metadyne braking system. On BR we were taught that in dire emergency to put the reverser in reverse and open up the controller. The train involved in the Clapham crash (28 years ago today) was I believe found to have the reverser in reverse position and the controller wide open in an attempt to provide additional stopping power. I didn't think the Piccadilly line's 1973 stock had regenerative braking - I thought the line couldn't absorb all the regenerated current. Instead they have - I believe - just rheostatic braking, which, as has been said, puts the current so generated through a resistor (or maybe many resistors, not sure), getting rid of the kinetic energy of the train as heat (same thing friction brakes do). This has the advantage of reducing brake wear and brake dust. I am told that regenerative braking systems can revert to this if need be.
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Post by fish7373 on Dec 12, 2016 21:56:09 GMT
Hi TUT yes you right in saying this.
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Post by norbitonflyer on Dec 12, 2016 22:04:20 GMT
A physics graduate writes:
In regenerative braking, the motors do not literally turn backwards - it is only the transfer of energy that is reversed. A motor and a generator are essentially the same - the only difference is whether you are turning it mechanically to make electricity, or using electricity to make it turn.
A miller's son writes: In the same way, a fan can be turned into a windmill if you blow air past it. The air flows, and the blades turn, in the same direction whether you are using the wind to grind down (or make electricity), or using electricity to blow air.
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Post by 100andthirty on Dec 12, 2016 22:09:00 GMT
Actually rheostatic and regenerative are similar. As TUT says, the motors act as generators. In rheostatic, the electricity generated is fed into resistors and in regenerative the electricity is fed into the current rails. in both cases, the motors rotate at road speed if there is enough adhesion. If the rails are slippery, then the wheels tend to slow down relative to the speed of the train, but still in the same direction. All LU's trains with regenerative braking can revert to rheostatic braking if for some reason the line is not able to accept current (eg over gaps).
I don't doubt what roythebus was taught, but in my experience, if a train is put into reverse on the move, it's a jolly good way to get the traction equipment overloads to trip!
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Post by fish7373 on Dec 12, 2016 22:14:50 GMT
HI copyed and paste from a LUL Manual
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Post by drainrat on Dec 12, 2016 22:29:01 GMT
Actually rheostatic and regenerative are similar. As TUT says, the motors act as generators. In rheostatic, the electricity generated is fed into resistors and in regenerative the electricity is fed into the current rails. in both cases, the motors rotate at road speed if there is enough adhesion. If the rails are slippery, then the wheels tend to slow down relative to the speed of the train, but still in the same direction. All LU's trains with regenerative braking can revert to rheostatic braking if for some reason the line is not able to accept current (eg over gaps). I don't doubt what roythebus was taught, but in my experience, if a train is put into reverse on the move, it's a jolly good way to get the traction equipment overloads to trip! Yes, and you don't have to put the train into reverse to trip the overloads, and if overloads are tripped then all you get is an EP application, which speaking for the 92ts, is a better slowing system on slippery rails than the regen brake.
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Post by drainrat on Dec 12, 2016 22:34:34 GMT
Rolythebus, drainrat. Sorry all this isn't what happens. In rheostatic braking, the motors are turned into generators. The wheels need to turn to generate any electricity. It is the work done generating the electricity that provides the braking force. It can't make the wheels turn in reverse and it can't hold the train when stationary when there is no wheel movement. I assume this is PWM in action
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Post by 1018509 on Dec 12, 2016 23:26:58 GMT
Last Thursday 15th December saw a Routemaster on the rail replacement buses at Rayners. Now that is progress. Can't be long before the remaining RT's, RF's or perhaps some TD's from the fifties can be pressed into service
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Post by Deleted on Dec 13, 2016 14:55:09 GMT
HI copyed and paste from a LUL Manual Which manual is that from? Sounds like a good read.
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Post by roybadami on Dec 15, 2016 22:53:30 GMT
Was today the first day that the Piccadilly wasn't showing severe delays on the entire line, or have I not been paying attention? On my commute home around 18:30 the web was showing severe delays only between Acton Town and Heathrow/Uxbridge - with minor delays on the rest of the line. Service interval seemed normal (around every 3 minutes) - with the trains being if anything slightly less busy than normal for the time of day (people having got used to avoiding the line, perhaps?)
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Post by Chris M on Dec 15, 2016 23:45:14 GMT
Late morning the line was advertised as having minor delays on the whole line and no serious delays when I passed through Euston. There were certainly serious delays still on Tuesday, but I didn't use the network yesterday so can't comment on that.
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Post by MoreToJack on Dec 16, 2016 1:24:11 GMT
Correct. Thursday was the first day that the line was no longer Severe Delays to all destinations.
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Post by alpinejohn on Dec 16, 2016 9:09:09 GMT
Correct. Thursday was the first day that the line was no longer Severe Delays to all destinations. It is good to hear services are starting to improve. I guess this means the maintenance teams are getting ahead of the wheel flats problem. I assume someone in LUL will now be arranging a post mortem to identify what more could be done to avoid or at least minimise the impact of leaf fall season in future years. It seems aggressive pruning back of lineside vegetation has not been a total success, so what else can be done? Ordering a heap of extra spare wheel sets to avoid delays waiting for access to wheel lathes? Extra wheel lathes? More RHTT visits? Identifying the hot spots where wheel flats are occurring? Additional driver training for leaf fall conditions? Temporary timetable allowing lower speed limits in high risk areas? Run less trains (eg. no night tube?) or run more trains? (eg. prior to the first service train operate a ghost train - but ensure it is given a clear run of greens and instructed not to stop at any stations or other high risk locations, which should hopefully avoid the first scheduled service encountering track with very poor adhesion.
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Post by Chris M on Dec 16, 2016 11:39:08 GMT
According to a report from the Mayor's Question Time there is already an ongoing independent investigation into the issue. No doubt various bits of LU will also be running investigations.
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towerman
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Post by towerman on Dec 16, 2016 16:36:06 GMT
Bet the lifting shop/wheel lathe staff got some overtime out of it.
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Post by rsdworker on Dec 17, 2016 16:56:33 GMT
today i noted status showing good service again - its seems first time the line returned to normally
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Post by mb2014 on Dec 17, 2016 22:05:59 GMT
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Post by rsdworker on Dec 17, 2016 23:04:53 GMT
well website showed good service - didnt not show as minor delays
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roythebus
Pleased to say the restoration of BEA coach MLL738 is as complete as it can be, now restoring MLL721
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Post by roythebus on Dec 18, 2016 4:13:26 GMT
Replacement buses were running until close of service on Friday evening.
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Post by tubetraveller on Dec 18, 2016 8:51:43 GMT
There's still a 73 stock train sitting in Neasden as of this morning, so they're not all completely fixed yet
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Post by PiccNT on Dec 18, 2016 14:15:29 GMT
There's still a 73 stock train sitting in Neasden as of this morning, so they're not all completely fixed yet I don't think we're out of the woods yet. One of the trains I had last night had severe flats on it.
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Post by snoggle on Dec 18, 2016 23:05:07 GMT
There's still a 73 stock train sitting in Neasden as of this morning, so they're not all completely fixed yet I don't think we're out of the woods yet. One of the trains I had last night had severe flats on it. I'd be surprised if the fleet had been fully rectified in such a short time. I wonder if some trains with more minor issues are being temporarily declared OK for service subject to being attended to within a defined time period?
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Post by jamesb on Dec 20, 2016 11:05:45 GMT
I was just thinking: could the Piccadilly line have run shorter trains i.e. run 3 car trains instead of 6 car trains? As an interim measure to maintain frequency with less capacity?
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