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Re: Recent derailments - Metro North
Author: Dr Zarkoff
Date: 12-05-2013 - 12:34
Just a few additional comments . . .
>Modern LRVs (and BART-type electric MUs) use 100% dynamic (wasted thru grids) or regenerative (back to the wire) braking down to less than 5 mph where the friction brakes take over, for normal brake applications.
Regenerative braking won't work if there is no load elsewhere on the [trolley] wire or 3rd rail. BARTD originally intended to use regenerative braking, and the first order of cars were equipped to switch between dynamic and regeneration automatically depending on the 3rd rail voltage. However, last I heard it was too problematic in operation and never turned on for use in regular service. This info is about 25-30 years old, and I don't know what subsequent car orders have nor whether regeneration has ever been used at all. Either way, BARTD has always used dynamics.
The need for dynamic braking on PCCs, BARTD, and all equipment which uses resilient wheels is to avoid as much as possible wheel heating caused by friction braking because the heat cooks (vulcanizes) the resilient material, rendering it useless.
>For full-service or emergency braking friction brakes (acting on more than just the powered axles) are added.
Friction brakes are on all axles, at least in US practice.
>Very recent models also seem to have "anti-lock" systems that in normal braking may add sand or adjust braking power distribution automatically to avoid sliding.
On the RRs, this goes back to the 1930s with WABCo's Decleostats and Budd's Rolokron systems. With PCCs it goes back to at least the 1940s, using a differential relay in the dynamic brake circuitry. Diesels have had the same differential relay scheme until the things like EMD's IDAC system of the mid 1970s. GG1s, BTW, had no slip-slide control, other than the engineer backing off on the throttle.
>In addition, most have a magnetic track brake (simply on or off) for added stopping power and (if I recall PCCs in SF correctly)
PCCs have had them since the cars were first introduced in the 1930s. Segmented track brake shoes, a European thing, allow the shoes to follow the contour of the rail head more closely. Some PCCs have at least three strengths of track brake effort (force).
>holding the car when stopped with the doors open.
Normally with PCCs, the track brakes are used for emergency applications only, however, it's not unknown for some motormen may use them to hold the car when the doors are open. Some properties might have specifically redesigned the braking system for this purpose, but regular track brake use will wear out the batteries prematurely, not to mention the track brake shoe's pole pieces, which are difficult to change.
>The friction brakes might be air, but most LRVs at least seem to be all-electric these days
All-electric PCCs first began being produced sometime around WWII, and they use magnetic actuators to operate the friction brakes (drums on the cardan shafts between the motors and gearboxes, not tread brakes).
>Hybrid & electric cars work very similarly, though with the limited electric power available in a hybrid and limits on how fast the battery can recharge, friction brakes combine with regen more often.
Hybrids use an induction motor, just like modern AC-drive diesels, and to regenerate, all you have to do is arrange for the stator's magnetic field to rotate slower than than slip, which is done via the computerized frequency control of the stator. When the battery is fully charged, the engine starts and via the electric motor and CVT (called "rubber band drive" by some gearheads), it's just like driving a stick shift in second gear (or L in a slush-o-matic).
Braking with my plug-in hybrid is very similar to using the blended braking of an F-40, F-59, P-32, P-40, P-42, etc. because if you know what to watch for, you can feel the friction brakes take up for the loss of dynamic/regeration when it fades.
>As noted in various threads recently, transit practice probably doesn't carry over much if at all to Standard Railroading.
There has been a lot of crossover back and forth. For example, dynamic braking was first used in streetcar controllers by modifying the the K controller design and calling it a B controller, some designs of which provided for slip-slide stability. Later, main line electrifications built on these principles (like the MILW, which used regeneration). They were subsequently carried over into diesel-electrics (dynamics). PCCs had extended range dynamics in the 1930s; diesels didn't have them until the 1970s.
Today's method of mounting traction motors in diesels, one end fastened to the axle and the other to the truck frame, was first developed by Frank J. Sprague for his Richmond streetcar installation of 1882, which was the first commercially successful electric railway/railroad installation.
West Penn Rys used dynamic braking to activate it's track brakes (1926), which in turn pressed shoes against the wheels through linkages. The C&LE Red @#$%& (1930) used a track brake for emergency stops, and could stop from full speed (approximately 70-80 mph) in 1000 feet. Prior to these, track brakes saw extensive use in England. No US locomotive that I know of had track brakes.
>Modern LRVs (and BART-type electric MUs) use 100% dynamic (wasted thru grids) or regenerative (back to the wire) braking down to less than 5 mph where the friction brakes take over, for normal brake applications.
Regenerative braking won't work if there is no load elsewhere on the [trolley] wire or 3rd rail. BARTD originally intended to use regenerative braking, and the first order of cars were equipped to switch between dynamic and regeneration automatically depending on the 3rd rail voltage. However, last I heard it was too problematic in operation and never turned on for use in regular service. This info is about 25-30 years old, and I don't know what subsequent car orders have nor whether regeneration has ever been used at all. Either way, BARTD has always used dynamics.
The need for dynamic braking on PCCs, BARTD, and all equipment which uses resilient wheels is to avoid as much as possible wheel heating caused by friction braking because the heat cooks (vulcanizes) the resilient material, rendering it useless.
>For full-service or emergency braking friction brakes (acting on more than just the powered axles) are added.
Friction brakes are on all axles, at least in US practice.
>Very recent models also seem to have "anti-lock" systems that in normal braking may add sand or adjust braking power distribution automatically to avoid sliding.
On the RRs, this goes back to the 1930s with WABCo's Decleostats and Budd's Rolokron systems. With PCCs it goes back to at least the 1940s, using a differential relay in the dynamic brake circuitry. Diesels have had the same differential relay scheme until the things like EMD's IDAC system of the mid 1970s. GG1s, BTW, had no slip-slide control, other than the engineer backing off on the throttle.
>In addition, most have a magnetic track brake (simply on or off) for added stopping power and (if I recall PCCs in SF correctly)
PCCs have had them since the cars were first introduced in the 1930s. Segmented track brake shoes, a European thing, allow the shoes to follow the contour of the rail head more closely. Some PCCs have at least three strengths of track brake effort (force).
>holding the car when stopped with the doors open.
Normally with PCCs, the track brakes are used for emergency applications only, however, it's not unknown for some motormen may use them to hold the car when the doors are open. Some properties might have specifically redesigned the braking system for this purpose, but regular track brake use will wear out the batteries prematurely, not to mention the track brake shoe's pole pieces, which are difficult to change.
>The friction brakes might be air, but most LRVs at least seem to be all-electric these days
All-electric PCCs first began being produced sometime around WWII, and they use magnetic actuators to operate the friction brakes (drums on the cardan shafts between the motors and gearboxes, not tread brakes).
>Hybrid & electric cars work very similarly, though with the limited electric power available in a hybrid and limits on how fast the battery can recharge, friction brakes combine with regen more often.
Hybrids use an induction motor, just like modern AC-drive diesels, and to regenerate, all you have to do is arrange for the stator's magnetic field to rotate slower than than slip, which is done via the computerized frequency control of the stator. When the battery is fully charged, the engine starts and via the electric motor and CVT (called "rubber band drive" by some gearheads), it's just like driving a stick shift in second gear (or L in a slush-o-matic).
Braking with my plug-in hybrid is very similar to using the blended braking of an F-40, F-59, P-32, P-40, P-42, etc. because if you know what to watch for, you can feel the friction brakes take up for the loss of dynamic/regeration when it fades.
>As noted in various threads recently, transit practice probably doesn't carry over much if at all to Standard Railroading.
There has been a lot of crossover back and forth. For example, dynamic braking was first used in streetcar controllers by modifying the the K controller design and calling it a B controller, some designs of which provided for slip-slide stability. Later, main line electrifications built on these principles (like the MILW, which used regeneration). They were subsequently carried over into diesel-electrics (dynamics). PCCs had extended range dynamics in the 1930s; diesels didn't have them until the 1970s.
Today's method of mounting traction motors in diesels, one end fastened to the axle and the other to the truck frame, was first developed by Frank J. Sprague for his Richmond streetcar installation of 1882, which was the first commercially successful electric railway/railroad installation.
West Penn Rys used dynamic braking to activate it's track brakes (1926), which in turn pressed shoes against the wheels through linkages. The C&LE Red @#$%& (1930) used a track brake for emergency stops, and could stop from full speed (approximately 70-80 mph) in 1000 feet. Prior to these, track brakes saw extensive use in England. No US locomotive that I know of had track brakes.
