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Andrew

Is the IND going back to a higher speed??

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The new trains on the E and F line are very fast like they were efore the whole system was modified back in 1997.Going Uphill now is faster.Is this a sign of hopefully higher speeds coming back,or is this just part of the testing process?? I hope that the new trains arent modified in the future.

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Well, it's true that the NTT's can go at higher speed than the SMEE's.

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The new trains on the E and F line are very fast like they were efore the whole system was modified back in 1997.Going Uphill now is faster.Is this a sign of hopefully higher speeds coming back,or is this just part of the testing process?? I hope that the new trains arent modified in the future.

 

Well, in 1997 the signal system was modified, so that any car model has to move at slower speeds due to the Williamsburg Bridge accident in 1995. The cars were not modified.

 

The new R160 cars on the (E) and (F) have a higher power to weight ratio than the other cars. So uphill acceleration is faster. It has nothing to do with signals.

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Its not the signals,its the trains themselves.Ask anyone who remembers the R46's,R40s,40Ms,42s,38s.etc.The trains were a Lot faster back then.Better acceleration and faster up the hills.The Express runs really meant something.

 

Of course the addition of timers really ruined everything as well.

 

Pacific Street to 36th street was a 50-55MPH Joy Ride back before the stupid timers were installed.

 

59th to 36th street was also a Very fast run back in the 1980s.Trains used to come into 36th street t 50+ MPH,and were able to stop at the 10 car marker.

 

34th to W4th,while OK,is really a former shell of its old self.

 

The Brighton Express sucks compared to its heyday.

 

One of the Greatest Express runs I ever remember was the F train from Union Tpke going on the Express track flying past Sutphin Blvd at over 50MPH.

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Its not the signals,its the trains themselves.Ask anyone who remembers the R46's,R40s,40Ms,42s,38s.etc.The trains were a Lot faster back then.Better acceleration and faster up the hills.The Express runs really meant something.

 

Of course the addition of timers really ruined everything as well.

 

Pacific Street to 36th street was a 50-55MPH Joy Ride back before the stupid timers were installed.

 

59th to 36th street was also a Very fast run back in the 1980s.Trains used to come into 36th street t 50+ MPH,and were able to stop at the 10 car marker.

 

34th to W4th,while OK,is really a former shell of its old self.

 

The Brighton Express sucks compared to its heyday.

 

One of the Greatest Express runs I ever remember was the F train from Union Tpke going on the Express track flying past Sutphin Blvd at over 50MPH.

 

They don't want them going that fast anymore...

 

When field shunting was removed at the higher speeds that was the end of that and cars on tangent track top off around 45 MPH balancing speed...

 

The R160's are the fastest car class currently in the system, not sure about top speed on tangent I'd guess it around 50 or so though...all cars accelerate from stop at the same speed - 2.5mph per second - but the R160's hold their acceleration rate much better and longer than all other car types from 10-25 MPH, most cars the acceleration tapers off in that range but the R160 holds it well...

 

It's not intended to be a "return" to faster cars, the signals still govern, it's just a way of providing faster service between stations so that the train doesn't take a long time taking power and starting toward the next one.

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They don't want them going that fast anymore...

 

When field shunting was removed at the higher speeds that was the end of that and cars on tangent track top off around 45 MPH balancing speed...

 

The R160's are the fastest car class currently in the system, not sure about top speed on tangent I'd guess it around 50 or so though...all cars accelerate from stop at the same speed - 2.5mph per second - but the R160's hold their acceleration rate much better and longer than all other car types from 10-25 MPH, most cars the acceleration tapers off in that range but the R160 holds it well...

 

It's not intended to be a "return" to faster cars, the signals still govern, it's just a way of providing faster service between stations so that the train doesn't take a long time taking power and starting toward the next one.

 

What's field shunting?

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What's field shunting?

 

Field shunting had to do with an older type of motor, where you'd modify the magnetic field given off by the stator by i think manipulating shoes on the contact sleeve of the motors. Newer motors are "single band" and as the name implies have a single band of RPM HP and TQ. This would give the top speed range in-motor braking to take the edge off, but better brakes, and dynamic current return in NTT have relegated this method to the graveyard in modern transit.

 

- A

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What's field shunting?

The DC motor can be made to run faster than the basic "balancing speed" achieved whilst in the full parallel configuration without any resistance in circuit. This is done by "field shunting". An additional circuit is provided in the motor field to weaken the current flowing through the field. The weakening is achieved by placing a resistance in parallel with the field. This has the effect of forcing the armature to speed up to restore the balance between its magnetic filed and that being produced in the field coils. It makes the train go faster.

 

Various stages of field weakening can be employed, according to the design of the motor and the intended purpose. Some locomotives used as many as six steps of field weakening.

 

http://www.railway-technical.com/tract-01.shtml

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What's field shunting?

 

LOL I see some have beaten me to the punch here. Ehh OK I got a little time...I'll try to explain it in laymen's terms and pull out some references here and there to help with wording :cool: (which will probably make it take twice as long). In the case of a DC traction subway motor, you have two main pieces electrically - the field coils and the armature. The armature is the part in the middle of the motor that spins around. The field coils are on the inside of the motor frame and around the armature, and they stay exactly where they are.

 

OK so you've got the armature (spinning part) and the field coils (stationary on the inside of the motor frame). The armature is connected all the way through the motor. A subway motor is a big electromagnet. When you apply power to the motors, an electromagnetic field is created in the field coils and this causes the armature to spin. As the armature starts to spin, it begins to create an electromagnetic field of its own because it is now moving. Electromagnets work both ways - electricity creates movement and movement creates electricity. Actually without going further into it "movement creating electricity" is the idea behind the dynamic brake. But if you don't know what a dynamic brake is, don't worry about it, that's for another thread.

 

Now let's take what I said above and use a simple example of field shunting, which still exists today. Starting from a stop, you can feel field shunting in place. Shunting the field coils directs a portion of the electrical current away from them. This reduces the initial flow of electrical current to the field coils, causing the train to generate less torque. Think of torque as power. Think of it as the difference between pushing an object using all your strength while walking 2MPH (lots of torque) vs. just casually walking into it using very little of your strength at 2MPH (not much torque). The subway car, with less torque, is now made to accelerate slowly. Then as field shunting drops out, torque increases, and the train can take full acceleration. In practice, this saves riders a nasty jolt if the T/O were to throw the controller into full power, and instead allows the train to accelerate smoothly and gradually so that no one ends up on the floor.

 

Now, since electromagnets work both ways, as speed builds up, the field created by the armature's movement now begins to oppose the original field created by the field coils...IN the field coils themselves. At some point the strength of the electromagnetic field caused by the armature spinning equals that of the one created by energizing the field coils when the T/O took power. Now the motor cannot spin any faster. This is the train's "balancing speed" because everything electrically is balanced...Train can't go any faster unless it hits a nice downhill or falls off a cliff, but that would have nothing to do with the motors :eek:. Anyway this force that's being applied by the spinning armature is called "counter electromotive force" or counter EMF for short.

 

Now, somewhat complicated part: In addition to reducing torque, field shunting also reduces this counter EMF. At low speed, since the motor is barely spinning, reducing torque makes the train accelerate slowly as described above. Reducing counter EMF does barely anything since the motor is barely spinning at any speed at all.

 

At HIGHER speed, reducing torque doesn't do much because the train is already moving and not a lot of torque is really needed at this point to keep it going on level track or downhill. However reducing counter EMF has a huge effect because of the amount of field being generated by the armature basically telling the motor to "stop accelerating"

 

Shunt THAT and the train will be allowed to accelerate much longer. Of course, side effect, torque will be reduced since both go together, so if it finds a nice steep grade it will find itself in need of torque, so its speed will drop like a stone until it's low enough that field shunting would drop back out again and allow the torque to pick back up once more. But leave it on level track and the train will reach a much higher "balancing speed" due to the reduced counter EMF.

 

The only field shunting that was removed was that second kind, at higher speeds. It was designed to kick in at 30MPH to allow the train to reach faster top speeds.

 

Who's head hurts? B)

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Where did you get the idea that they only took out shunting after 30 MPH? SMEE acceleration on the IND/ BMT basically dies at 25 MPH. IRT SMEEs are noticeably quicker, frequently hitting 30+ MPH, not to mention the IRT as a whole is a bit quicker. They should re-activate the feild shunting on the IND/BMT SMEEs so that service can be improved. It was a dumb idea in the first place, and since the NTTs can go faster, that defeats any "safety" arguement.

 

Also, as side-notes...pretty much all mass transit systems around the tri-state have been "degraded" speed-wise. The NJT- BUDD Arrow IIIs used to be able to go over 100 MPH before their rebuild...now they top out at 80 because the "high tech" stuff has a tendency to burn out, or something with the motors. the PATCO BUDD cars used to be able to go 75, but are now restricted to about 65mph(PATCO BUDDs are FAST in acceleration- looks like warp drive compared to NYCTA). PATH cars used to go 70, but are now limited to about 55(PATH Pa-1 to Pa-4 cars are Rt-2 smees, by the way, with different couplers from NYCTA cars, though they used to have the same couplers as NYCTA pre-GOH).

 

Furtherore, the PRR had METROLINER EMUs that hit 160 MPH and got you to washington FASTER than the acela garbage cans. Now metroliners are cab cars that never go above 125 MPH.

 

Not to mention, NJT's current timetables with multilevels, alp46, and pl42 ac garbage cans make the PRR K-4 pacific hauled trains look like supersonic jets....

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Where did you get the idea that they only took out shunting after 30 MPH? SMEE acceleration on the IND/ BMT basically dies at 25 MPH. IRT SMEEs are noticeably quicker, frequently hitting 30+ MPH, not to mention the IRT as a whole is a bit quicker. They should re-activate the feild shunting on the IND/BMT SMEEs so that service can be improved. It was a dumb idea in the first place, and since the NTTs can go faster, that defeats any "safety" arguement.

 

Everything I posted above has been explained to me by someone who used to work for Car Equipment during the time these modifications were made, so it is all NYCT relevant and accurate. IRT SMEEs are no "quicker" as far as top speed, that has to do with quicker acceleration due to more torque generated by the motors in comparison to weight of the train.

 

As to your point about 30MPH, Trains can and do go much faster than 30 MPH, even today, 30 MPH is just the speed at which field shunting would kick in, reduce counter EMF, and enable the train to continue accelerating quickly. In effect, removing field shunting dropped balancing speed from ~55MPH to ~45MPH. SMEE acceleration on the IND/BMT today does not die at 25, the train accelerates moderately to about 35, slowly to 40, then very slowly after that able to reach ~45MPH on level tangent track.

 

Going back to using field shunting as had been done before will not necessarily improve service. Trains will still be governed by the signal system and have to obey time signals and speed restrictions. The biggest thing is just to accept the reality that rapid transit has now become mass transit and they'd rather move a lot of people slowly than a few people very quickly. Trains really shouldn't need to go more than 45MPH anyway, at least in the subway. Service would be better improved by speeding up timers that are too slow (CPW S/B tk A3), removing unnecessary ones (Fulton (4)(5) N/B), and improving tower/control operation so that trains get their lineups quickly and correctly.

 

Also it's worth noting that while the new techs are generally faster accelerating, it's just the R160's that are noticeably faster, not the R142/A/3. I'm hazy on the details but the R160 if built according to the original builder's spec was MUCH faster. Acceleration rate was decreased somewhat but top speed was to remain unchanged in the final product...something to do with the warranty if I remember correct.

 

As for the rest of your post, I didn't pay much attention to speeds on any of those other systems back in the day and so I can't and won't comment on that, just NYCT.

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Well said Subwayguy. I could not have said it better my self though we both heard this from the mouth of the same horse.

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