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Post by tunnelbore on Jan 19, 2024 8:11:28 GMT
Thanks for the answer. TfL App showing both platforms closed today so perhaps they'd got plant in to fix those stones.
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Post by tunnelbore on Jan 18, 2024 18:43:22 GMT
Can anyone tells us why trains haven’t been able to stop east bound on D&C at South Kensington yesterday (17th) and today. Notices and announcements say it’s a problem with the platform that raises more questions than it answers
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Post by tunnelbore on Jul 5, 2017 19:51:13 GMT
Gear changing sounds 🤔 You mean the clicking 🙄 The way the motor pitch rises steadily and then drops suddenly, a cycle repeated three or four times in the first few seconds as it moves off, as heard on the 465/9 at the beginning of this clip. Sounds just like a mechanical transmission changing rapidly up through the gears. (Some 465 versions now have new traction packages which don't do this - the clip demonstrates the differnce) 1996 stock does it too, but I couldn't find a good recording of one. You maybe know this already but just in case: these drives used synchronous PWM (pulse width modulation) with the GTOs switching at given multiple of the AC frequency fed to the motor. For instance, 33 times faster than a 5Hz supply would give 165Hz switching that would be a note you could hear (you hear it because the lamination in the motor core vibrate slightly at that frequency). As the train accelerates and the AC frequency is increased to keep it accelerating, the GTO would switch faster and the note would rise. However, you can't let the GTOs switch too fast or they'll overheat so at say, 15Hz AC / 495 Hz switching, you'd then drop the ratio to 21 times and at the same 15 Hz AC produce a note at 315 Hz which would then go on rising until the next time you needed to drop the ratio. I don't know the rations and upper switching frequency limits for the drives in question so the numbers are for illustration only. This was known as Gear Changing PWM. More modern IGBT drives don't often need any of this. The IGBTs can switch fast and are held at a constant and quite high switching frequency. Class 377s are in this category I think. The class 700s make a rather strange warbling sound to my ear. I suspect they have something similar to gear changing PWM but with some additional modulation to mask the sound.
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Post by tunnelbore on May 17, 2017 12:20:24 GMT
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Post by tunnelbore on Dec 17, 2016 11:09:41 GMT
I asked this in the Southern thread and it looks like everyone skipped over it so I am asking it here. I have not used Southern at the weekends. GTR'S website makes it hard to tell but do the strikes affect weekend services or are they generally normal? Especially on Sundays? Oh, you don't want normal. Normal is bad. Normal includes crew shortages due to some combination of overtime ban by union members; overtime withdrawal by GTR, displaced crew, underlying lack of crew with confusion added by fibs by those describing the reasons for cancellations and delays. Also includes failed trains, failed track circuits and management indifference to service meltdown. But yes, weekends are normal.
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Post by tunnelbore on Dec 15, 2016 22:44:56 GMT
There is a plausible case for having a guard because of how long the trains are: London Overground currently has up to five cars, while Southern and Thameslink will be dealing with up to 12, and unstaffed stations. Two staff on a train carrying 1,500 people seems like a good idea to me. I don't mind too much what the duties of the second person are and I'm happy for the driver to use body-side cameras for door closing such that guard becomes on board supervisor OBS. How many of the PTI accidents and near misses are with body-side cameras? The one sticking point I can see is that if the OBS is not available during disruption and the train leaves without one, what provision is made for wheelchair users at unstaffed stations? RMT have recently latched onto this issue which strikes me as shabby opportunism. If the strike is ultimately about this only, then surely there is a way to solve this problem without a strike.
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Post by tunnelbore on Dec 15, 2016 22:37:56 GMT
Abandon Southern Trains south of Croydon and don't re-let the franchise until it will work Give season ticket holders their money back Sort out four-tracking (Balcombe Tunnel) and approaches to East Croydon (Windmill Bridge) Increase length of trains - increase frequencies - Thameslink; Hastings-Tonbridge-Orpington-Sevenoaks; Brighton-Havant-Portsmouth; Sutton-Epsom-Horsham Let TfL facilitate movement of passengers east-west-west-east across south London and South Croydon northwards Don't find excuses - Make it happen What does the first point mean - I can't make sense of that. Southern is clear three types of service: south London Metro; longish distance commuting from the Haywards Heath, Brighton, Eastbourne, Worthing etc.; and south coast local markets. It's not just Balcombe Tunnel but also Ouse Valley Viaduct. Main capacity problem is BML and lengthening beyond 12 cars does not look like a prospect.
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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 tunnelbore on Jun 18, 2016 18:28:15 GMT
Should a 25,000 volts cable drop onto a train before the circuit trips you could have serious problems. 25kV cable dropping on to the train will be earthed by the train and the circuit breakers will one very quickly, probably in less than 0.25s. The coach body may rise in potential a bit but people inside will be safe because of the Faraday-cage formed by the coach body (which keeps the charge on the outside surface). This report on the incident at Walkergate was alarming for what is shows about the arcing and fire risk when the fault current / protection settings are not well configured and the breakers aren't opened.
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Post by tunnelbore on Jun 2, 2015 16:08:51 GMT
I was mid journey today using an annual season on theKey (Southerns's ITSO) which includes an all-zones travelcard and it stopped working. Touched in at my local station, out at Victoria Mainline, in at Victoria District Line and then got denied exit (on all gates) at another district line station. Gate-line staff said it wasn't a valid card. I protested that it was valid just not working. They said it wasn't Oyster therefore couldn't be used on the tube. I tried the ticket office (yes, there still was one), first person said it wasn't valid, second person did seem to recognised that theKey might possibly be valid but the ticket office Oyster reader showed a comms failure. Showing the paper "gold record card" which can be used to get discounts didn't seem to carry any weight despite it having a roundel and saying Zones 1-6 because also it says not valid for travel.
Eventually I wore them down and they were glad to see the back of me. I'm not sure how I'm going to get back to Victoria tonight.
My question is: do gate-line staff get told about the various ITSO cards that are now becoming common on London commuter lines? Southern are making a lot of use, the rest of GTR will soon, SWT on its way etc.
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Post by tunnelbore on Apr 7, 2014 20:41:31 GMT
It is arcing. It's essentially the current jumping between the conductor rail and the shoe, ionising the air, giving the blue flash and the noise. Arcing will happen with just about any electric train, 4th rail, 3rd rail, or even OLE, so its as much of a problem for S stock as it was for A stock and is for every other electric train. Yes I know, but it is an inefficiency and surely you should aim to cut it . Similar to how you would try to reduce eddy currents in an electromagnet Italian engineers I know have been known to call it arching because in Italian there is no distinction between arc (as in electrical spark or geometric feature) and arch (as in arch over a window or in a bridge). An arc, formed of hot ionised air as domh245 says, actually conducts electricity quite well which is why they sustain so well on DC circuits (but extinguish on AC as they cool when the current drops to zero). Best reason for trying to suppress them is probably to prevent eating away at shoe and rail material rather than power losses. Hard to avoid them completely because shoe and rail (or pantograph and wire) will loose contact with each from time to time.
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