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| FCC's Class 313/0. 17/03/2013 at 02:39 #42385 | |
CTCThiago
232 posts |
Hi, All. According to "railway centre" class 313/0 has the air brake, according to some videos I watched, I realized the presence of sound of the engine braking, which made me doubt this, both in the 313 as the 315 and 317. The question: It has the electric brake that uses part of the engine power to help in braking? Regards Thiago. Log in to reply |
| FCC's Class 313/0. 17/03/2013 at 09:45 #42387 | |
Peter Bennet
5360 posts |
Subject to the usual caveats it says here: Class 313s are fitted with rheostatic braking (disabled on London Overground) in addition to conventional 3 step air-operated disc braking; during braking if wheelslide is detected by the WSP (WheelSlide Protection) rheostatic braking is disabled and the disc-braking comes into effect. Peter I identify as half man half biscuit - crumbs! Log in to reply The following user said thank you: CTCThiago |
| FCC's Class 313/0. 17/03/2013 at 15:57 #42390 | |
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CTCThiago
232 posts |
thanks for clarifying my doubt. Cheers. CTC. Log in to reply |
| FCC's Class 313/0. 17/03/2013 at 16:21 #42392 | |
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CTCThiago
232 posts |
Peter did you know the acceleration and deceleration rates for Class 313, at deceleration if you know full service brake and emergency rates? Regards CTC. Log in to reply |
| FCC's Class 313/0. 17/03/2013 at 17:36 #42395 | |
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Peter Bennet
5360 posts |
" said:Peter did you know the acceleration and deceleration rates for Class 313, at deceleration if you know full service brake and emergency rates?Not unless it's on Wikipedia. Peter I identify as half man half biscuit - crumbs! Log in to reply |
| FCC's Class 313/0. 17/03/2013 at 19:46 #42399 | |
dwelham313
139 posts |
The Rheostatic (or Dynamic) brakes on a 313 also won't work when: Train speed is above above 65mph Train speed is below 15mph Traction motors on that driving car are isolated Train speed under 40mph without power notch 4 being selected During snow dynamic brakes must be isolated Dynamic brake MCB tripped in cab Motor Alternator set not working on unit (You're in big trouble!) Class 313 dynamic brakes are notoriously hard to anticipate, every unit seems to have different braking capabilities when using the dymnamic brake. On some units the braking rate can change between stops. As such I would reckon that 95% of drivers isolate the dynamic brake as soon as they enter the cab! I can't say for 315s but 317s/321s don't have dynamic brakes. The Motor Alternator set delivers a surge of power under braking that effectivly uses the motors as a kind of 'reverse thrust' to slow the train. A small amount of air braking still occurs to indicate to the driver that the brakes are on, apart from feel there is no indication to show dynamic brakes are working. Hope of interest. Log in to reply The following user said thank you: CTCThiago |
| FCC's Class 313/0. 17/03/2013 at 20:38 #42404 | |
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Danny252
1461 posts |
" said:Train speed is above above 65mphThose two are very odd - never heard of dynamic brakes being problematic at high speed, and I don't get the second one at all! Log in to reply |
| FCC's Class 313/0. 17/03/2013 at 20:40 #42406 | |
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dwelham313
139 posts |
Also the class 313 is not 12%G modified (?) which means you get no extra brake force in emergency than you do in step 3, however in emergency the brake wires are earthed which prevents any blowdowns if WSP is encountered (I believe). The Dynamic brake will cut out if an emergency brake application occurs. Classes 317/321/365 are 12%G modifiesd which means you get extra brake force in emergency. 365's have 'blended dynamics' which is a mix of air/dynamic brake, basically the same but with a greater proportion of air braking the train when compared to the dynamic brake on a 313. 365 dynamic brake will cut out for the same reasons listed earlier but also if the dynamic is in use through a neutral section it will cut out. After this has happened you'll also get problems powering away with traction motots cutting temporarily at 20mph and 35mph! Log in to reply |
| FCC's Class 313/0. 17/03/2013 at 20:44 #42407 | |
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dwelham313
139 posts |
" said:" said:I think these are both specific to 313s, ive never noticed the under 40mph one myself, but certainly above 65mph dynamic brake won't work on FCC 313sTrain speed is above above 65mphThose two are very odd - never heard of dynamic brakes being problematic at high speed, and I don't get the second one at all! Log in to reply The following user said thank you: CTCThiago |
| FCC's Class 313/0. 19/11/2020 at 20:41 #133980 | |
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Jan
889 posts |
Danny252 in post 42404 said:Those two are very odd - never heard of dynamic brakes being problematic at high speed, and I don't get the second one at all! dwelham313 in post 42399 said: Train speed is above above 65mph I'm not an electrical engineer, so this should be taken with a grain of salt, but two possible factors come to my mind: 1. Power = Force x Speed. With electric traction you're usually power-limited starting from some point well below your top speed, so if you keep the power fixed you'll then get Force = Power / Speed, so the faster you go, the less force you have available (with classic series-wound DC motors, as used on most electric rolling stock before the advent of asynchronous three-phase drives, it's even worse: Once you've exhausted all notches and are running in full parallel with maximum weak field, the current and therefore the motor's achievable power itself starts dropping off the faster you go, so tractive effort drops off even faster than just linearly with speed). For the Class 313 (respectively their close cousins, the Class 507/508 units, which are utilising the same type of traction motors) I've seen balancing speeds of either 75 mph (their rated maximum speed) or even just 65 mph being quoted, which means that at those speeds the available tractive effort just about matches the running resistance (which apparently is in the order of 0.1 - 0.15 m/s²). When operating in braking mode as generators, comparable power limits apply usually, so the electric braking forces you can achieve at those speeds are similarly measly. 2. I've found a thesis containing some interesting diagrams on the exact performance characteristics of the Class 313/507/508's (and 315's as well, I think?) traction motors, though unfortunately only for motoring, not braking. From an university lecture I've found these qualitative diagrams (Fig. 4.11) instead which are depicting the typical relationship between speed and braking forces (and therefore also current, as the braking force is roughly proportional to the current being generated) for a series-wound DC motor operating as a generator. If those diagrams can be trusted, for a given resistance level braking forces (and currents) seem to vary quite significantly with speed, so each level of resistance is only usable for a relatively narrow speed range – too slow and your braking force drops off rapidly, too fast and you're exceeding your permissible current limit. So it seems a conceivable theory that with the set of traction/braking resistors the Class 313 was equipped with, 65 mph might be the maximum speed at which the electric brake could be used without exceeding the allowable current or other limits of the traction system. Using the brake at higher speeds might have required additional resistors and additional notches on the camshaft controller, which given the small resulting braking force at those speeds as per 1.) might have been thought to be not worth the effort. dwelham313 in post 42399 said: Train speed under 40mph without power notch 4 being selected To some extent this can be explained by the fact the the motors are controlled by a rotating camshaft controller which is responsible for automatically cutting in/out the various resistors both when motoring and when braking, switching between series/parallel operation and also controlling weak field operation. Now the way this camshaft works is that both when motoring and when braking it always starts at the lowest (= maximum resistance) notch (going from notch A to R when accelerating and then rotating back from R to B when braking) and then steadily works its way to the other end (cutting out resistances along the way) as long as the motor current is below a certain given limit. According to the 1987 Walton-on-the-Naze accident report, which contains some more interesting details on the working of the Class 313's traction control system (although somewhat frustratingly, the speed of 37 mph given for reaching the last notch when accelerating doesn't match the motor diagrams from the other link further above, according to which the last notch should be reached already at around 45 kph, i.e. 28 mph, which is also confirmed by a set of measurements from a real Class 508), there are 17 braking notches and the camshaft takes approx. ⅓ s per notch when notching up, so almost 6 seconds to go from zero to the last braking notch. This means that if you start braking from a speed not much above the absolute lower limit of 15 mph, by the time the camshaft has notched up sufficiently all the way to the other end to generate an appreciable braking effort you might have already (via the friction brakes) decelerated down to almost 15 mph, where the rheostatic brake would then have to cut out again anyway. So it does make sense that the lowest speed for initiating rheostatic braking is somewhat above the speed where the rheostatic brake actually cuts out in order to avoid wearing out the camshaft mechanism for little gain, although 40 mph does seem a little high for that: For the 1972 tube stock it's supposedly 21 mph, with the brake then cutting out at around 8 mph, so for the Class 313 I might have expected a limit of around perhaps 30 to 35 mph. Plus I have to admit I still don't quite understand the "without power notch 4 being selected" bit either – does it literally mean that simply moving the traction controller to notch 4 for however briefly while accelerating and then the electric brake starts operating at any speed between 15 mph and 40 mph? Two million people attempt to use Birmingham's magnificent rail network every year, with just over a million of them managing to get further than Smethwick. Last edited: 19/11/2020 at 20:48 by Jan Reason: None given Log in to reply |