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Post by Deleted on Nov 22, 2005 18:35:34 GMT
Which brings me back to this discussion of air brakes. Except for Chicago, all US cities' subway/rapid transit systems use blended air and dynamic braking. (Chicago does not use air brakes because of its smaller, lighter cars and the coincidence of switching to an all-electric braked PCC fleet which were recycled from streetcars. They just continued the no-air-brake precedent when they purchased new cars.) You guys must have a very fail-safe electric brake then! In LU-land the EP brake, which includes the rheo brake IIUTC, is NOT failsafe, and if it fails, all you have is the Westinghouse brake... By blended, I mean that both always apply, and the motorman generally does not have a choice about the proportions of the blend. The same applies to LU stock equipped with rheo braking - everything from the 1967TS on up; the rheo is always applied when available (unless the T/Op doesn't want to use it) and fades at a specific time and speed, unless solidbond can teach us ways to cheat with rheo brakes as well as with the Westinghouse/EP combo The A stock is the only one without rheo; it only has the EP and the Westinghouse, controlled using the traditional double-position brake handle. I know that for trams in Europe, dynamic braking was used from early on. Is the same true for London Underground trains? Is that why most of you drivers seem to think of the dynamic/rheostatic brake as easy or "habitual" to use, and the air brake as something that requires a greater mental effort? Also, from the descriptions given earlier, it sounds as if your brake doesn't have graduated release. Is that right? This is all a little foreign (no pun intended) to my US experience. solidbond is no doubt typing in the procedures right now, but from my reading of the topic, the rheostatic brake is applied as part of an EP brake application; on rolling stock that has it available, when a call for braking is made at speed the brake circuits instruct the control circuitry to switch the motor cars' motors over to rheo mode, whilst simultaneously applying the EP air brake on the trailer cars. Once the train is going slowly enough for the rheo to 'fade', the brake circuitry then cuts out the rheo and applies the EP air brake on the motor cars too, thus 'blending' the application and bringing the train to a stop. The T/Ops would better be able to tell you about whether or not the use of rheo is 'habitual'. As for graduated release, the EP brake (which includes rheo) does have graduated release, but the Westinghouse does not - unless solidbond teaches you how to cheat ;D This is a most interesting board, and although I don't think I'll have much input, I do read it almost every day with relish. I realize that super-technical details are only of interest to a certain segment of readers, but I certainly am one of those. I enjoy whatever you guys post, especially the schematic/wiring diagrams of the equipment. Incidentally, if anyone here is a propulsion/control freak like I am :-), I'd be happy to provide what wiring diagrams and associated information I have on Chicago equipment, by private e-mail of course. That would be quite fascinating. If you want diagrams of LU stock you should go to the Tubeprune and read his rolling stock pages, packed with lots of awesome info on LU rolling stock. www.trainweb.org/tubeprune/Rolling%20Stock.htm
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Post by Admin Team on Nov 22, 2005 19:32:50 GMT
Richard,
Firstly welcome; you join a band of growing international readers and contributors and I - for one - always enjoy the contributions made from overseas!
Thank you for your introduction of yourself too; don't be concerned about any lack of input but do feel free to add at any point - the comparisons across different systems is always fascinating.
I hope that if you enjot this site maybe you'll spread the word amongst your fellow volunteers?
On a light hearted point - you may come to regret the offer of technical and diagramatic matters!!
Very best wishes. I maybe hope to visit a friend of mine in Seattle in the not too distant future and i know that Chicago is one of my route options. Maybe I'll plan on a longer layover in Chicago than I originally intended....
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Post by kf9vp on Nov 22, 2005 19:33:30 GMT
You guys must have a very fail-safe electric brake then! In LU-land the EP brake, which includes the rheo brake IIUTC, is NOT failsafe, and if it fails, all you have is the Westinghouse brake... Indeed, the electric brakes are fail-safe- on the PCC design (the 6000 class cars in Chicago) the flow of dynamic braking current operates a contactor which keeps power applied to the (battery-operated) friction brake actuator. Once brake current drops off, the contactor drops out and the friction brakes (a drum brake arrangement on each traction motor driveshaft) apply by spring pressure. If the motorman desires a greater rate, or if he puts the train in emergency, magnetic track brakes also apply, also powered by battery. ...when a call for braking is made at speed the brake circuits instruct the control circuitry to switch the motor cars' motors over to rheo mode, whilst simultaneously applying the EP air brake on the trailer cars. Once the train is going slowly enough for the rheo to 'fade', the brake circuitry then cuts out the rheo and applies the EP air brake on the motor cars too, thus 'blending' the application and bringing the train to a stop. This brings about the big difference between US and London systems: you have unmotored cars. We haven't had such a thing in any significant quantity since braking was strictly by air only. That would be quite fascinating. If you want diagrams of LU stock you should go to the Tubeprune and read his rolling stock pages, packed with lots of awesome info on LU rolling stock. I actually found this site through Tubeprune. I've read just about the entire of his site thoroughly. On this board, on the Diagrams forum a couple months ago, someone posted prints for Q and 38 stock. Suffice it to say, I had them printed out and perused right away! Thanks, Richard
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Post by Deleted on Nov 22, 2005 19:48:00 GMT
Indeed, the electric brakes are fail-safe- on the PCC design (the 6000 class cars in Chicago) the flow of dynamic braking current operates a contactor which keeps power applied to the (battery-operated) friction brake actuator. Once brake current drops off, the contactor drops out and the friction brakes (a drum brake arrangement on each traction motor driveshaft) apply by spring pressure. If the motorman desires a greater rate, or if he puts the train in emergency, magnetic track brakes also apply, also powered by battery. So if there was a power failure and the dynamic braking current went into the Z state, the contactor would open and the friction brakes would be applied by springs, correct? That sounds similar to the SAPBs (Spring Applied Parking Brakes), which are held up by air pressure in the main line air circuit. When the main line air gets low the springs overcome the low pressure and apply the brakes to hold the train in place until the main line air is recharged. SAPBRCs (SAPB Release Cocks) are used when the main line air isn't going to recharge and the train needs to be moved. This brings about the big difference between US and London systems: you have unmotored cars. We haven't had such a thing in any significant quantity since braking was strictly by air only. The only rolling stock in LU-land that is fully motored is the 1992TS on the Central Line; all the others have DMs (Driving Motors), UNDMs (Uncoupling Non-Driving Motors), and trailers. 1992TS is formed of A-B units (DM-UNDM), B-C units (UNDM-UNDM) and C-D units, in which one of the UNDMs has de-icing equipment. I actually found this site through Tubeprune. I've read just about the entire of his site thoroughly. In that case, you'd absolutely LOVE this site! www.railway-technical.com/On this board, on the Diagrams forum a couple months ago, someone posted prints for Q and 38 stock. Suffice it to say, I had them printed out and perused right away! That was Q8, a top DR man who brought a lot of knowledge to this forum. He's on haitus right now.
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towerman
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Post by towerman on Nov 22, 2005 20:41:46 GMT
There was a mod done on 72Mk2's,don't know about other stocks,if the EP brake supply is lost the deadman operates.
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Post by Deleted on Nov 22, 2005 21:08:57 GMT
There was a mod done on 72Mk2's,don't know about other stocks,if the EP brake supply is lost the deadman operates. That sounds like an unusual mod - do the 72mkIIs have Westinghouse brakes like the 72mkIs? If so, why can't the driver use the failsafe Westinghouse brake instead?
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towerman
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Post by towerman on Nov 22, 2005 21:54:36 GMT
Mk2's do indeed have Westinghouse,I think the idea was the brake would be more instantaneous than the T/Op realising the EP had failed and then applying Westinghouse,seconds could count esp at dead ends.
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towerman
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Post by towerman on Nov 22, 2005 21:59:08 GMT
Mind you when I was a fitter at Stonebrige Pk,got called to a train alleging no EP.Rode on train,coming into Willesden Junc SB,got audible warning no EP deadman didn't operate.Straight o/o/s,when they checked train,whoever did the mod had miswired at the back of the relay board.
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Post by Deleted on Nov 22, 2005 22:08:11 GMT
Mk2's do indeed have Westinghouse,I think the idea was the brake would be more instantaneous than the T/Op realising the EP had failed and then applying Westinghouse,seconds could count esp at dead ends. I still think it's an unusual mod - it only makes the Westinghouse usable when the drver actually wants to use it, as opposed to also being able to use it when the EP fails...
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Post by kf9vp on Nov 22, 2005 23:24:40 GMT
Firstly welcome; you join a band of growing international readers and contributors and I - for one - always enjoy the contributions made from overseas! Thank you, sir, for the hearty welcome. I enjoy all sorts of rapid transit operations; London's is all the more interesting, and easy to understand, being in an English-speaking country and all. :-) I hope that if you enjot this site maybe you'll spread the word amongst your fellow volunteers? I will let them know of this site; I don't know that any of them are Tube fans, so no promises. Very best wishes. I maybe hope to visit a friend of mine in Seattle in the not too distant future and i know that Chicago is one of my route options. Maybe I'll plan on a longer layover in Chicago than I originally intended.... I would be happy to show you around the CTA and our Museum, if you should have the time. I do not work for the CTA, so I can't show you much other than what any old passenger can see, but I can explain what you do see. Thanks, Richard
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Post by kf9vp on Nov 22, 2005 23:42:53 GMT
So if there was a power failure and the dynamic braking current went into the Z state, the contactor would open and the friction brakes would be applied by springs, correct? That is correct, except for the power failure part. Dynamic brake does not directly depend on the traction power. All cars on the CTA that have dynamic are four-motor cars. The motors maintain some level of magnetism, and thus field, at all times. The dynamic braking circuit is arranged (on a PCC) so that each motor pair will have its armatures connected in series with the other motor pair's fields, and completes the loop through the resistance, so brake current builds up very quickly from that small level produced by the magnetized iron in the motors. Newer cars arrange it similarly, and even have a (battery-supplied, transformer-isolated) "field forcing" circuit to induce the current faster. That sounds similar to the SAPBs (Spring Applied Parking Brakes), which are held up by air pressure in the main line air circuit. When the main line air gets low the springs overcome the low pressure and apply the brakes to hold the train in place until the main line air is recharged. SAPBRCs (SAPB Release Cocks) are used when the main line air isn't going to recharge and the train needs to be moved. Here the parking brake function simply swaps electric actuators for air cylinders. For mechanically releasing brakes for moving a train dead, there are "actuator cut-outs" that perform the same function as your release cocks. Thanks, Richard
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Post by Deleted on Nov 23, 2005 0:12:16 GMT
That is correct, except for the power failure part. Dynamic brake does not directly depend on the traction power. All cars on the CTA that have dynamic are four-motor cars. The motors maintain some level of magnetism, and thus field, at all times. The dynamic braking circuit is arranged (on a PCC) so that each motor pair will have its armatures connected in series with the other motor pair's fields, and completes the loop through the resistance, so brake current builds up very quickly from that small level produced by the magnetized iron in the motors. Newer cars arrange it similarly, and even have a (battery-supplied, transformer-isolated) "field forcing" circuit to induce the current faster. Say what? I read that twice and still can't seem to figure it out - are there any diagrams of that setup? Here the parking brake function simply swaps electric actuators for air cylinders. For mechanically releasing brakes for moving a train dead, there are "actuator cut-outs" that perform the same function as your release cocks. Makes sense - how are the actuators energised?
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Post by kf9vp on Nov 23, 2005 0:25:35 GMT
Say what? I read that twice and still can't seem to figure it out - are there any diagrams of that setup? Hmmm, maybe I'm not the best at explaining things. I will try to get the relevant page scanned out of the wiring diagrams when I get home tonight. Makes sense - how are the actuators energised? They are the same actuators that operate the friction brakes on the driveshafts, the ones that automatically apply as dynamic fades. They are set up to be applied as soon as the motorman calls for brake but are "locked out" by the dynamic current flowing (thus the contactor that does this function is named LO). As dynamic drops out, the current to the friction brake actuators is automatically reduced or cut off entirely, depending on what rate of deceleration was called for. This reduces the pull against the spring, and allows it to press the brake on. I will get those diagrams scanned tonight, I am telling myself! - - - As promised (threatened?), the diagrams for the CTA 6000 series cars are online at: pages.ripco.net/~rws/schematics/. I recommend visiting www.chicago-l.org to get a sense of what type of cars I'm talking about here. First in service 1950, last retired 1992. - - - Richard
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Post by jimmy on Nov 23, 2005 9:36:23 GMT
Regarding all-electric braking, this is not uncommon in Scandinavia either. In the 90s Oslo bought second-hand M25 trams from Göteborg which were equipped as you describe for the PCC cars. The difference here was that the spring-applied brake was only used to hold the tram still, not for braking other than in emergencies. For normal service braking the driver would use the rheo, then when the speed went below about 1 km/h the spring would be released and brakes applied with a bang. To move on a 600V solenoid operating off the traction supply would wind the spring back up and release the brakes. This rendered the trams immovable in case of power failure, unless the springs were wound up manually. Such action caused a horrible accident in Göteborg some years back.
Everything was controlled by an early relay-based PLC that interpreted signals from the drivers foot pedals, quite sphisticated for a 1960s design. M25s are loosely related to the PCC, and trams like this still roll in Göteborg, although in newer versions. Oslo scrapped theirs in 2002, they weren't too well-liked by the drivers either. They said it was impossible to stop nicely with them, but the repairmen loved their robustness. And the enthusiasts loved the looks of the fat swede, as well as the feel of "real tram" as opposed to the italian rubbish that replaced them.
Oslos newest trams (italian-made SL95) use electro-hydraulic disc brakes that can be be used as replacement for the dynamic brakes if necessary. The failsafe function is again spring-based, hydraulic pressure is required to keep the brakes off thus a failure causes application. The same system is also to be used on our new Siemens metro-cars. These have a feature to enable towing them with an old "air-train" that interprets the train pipe pressure and translates this for the hydraulic system. There is also the possibility of controlling air brakes on a train in tow, so the new trains have a compressor in order to send brake "commands" if needed.
Finally, Bergen has a heritage tramway that operates all-electric reko-trams from Berlin, GDR. These are not fail-safe, so if the driver falls asleep, well, bang! Therefore they are always double manned.
JiSC your norwegian correspondent
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