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SMEE and NTT Braking Questions


R44 5278

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and the NTTs only use friction brakes at speeds lower than 5 mph on a normal basis. all other service braking is done regeneratively.

 

Generally that's true, but like I said if the computer is trying to create a certain stop rate and it's not happening with dynamics for whatever reason, it will apply air to stop the train. But yes, the new techs are designed to rely primarily on dynamics.

 

don't know if the DC cars could do this if they redesigned the brake system on them.

 

It would require major upgrades to components under the car, so the cost savings would not justify the enormous expense. Since it's a modern feature, most car designs would already feature it. Easier to build something the first time than build it one way and go back and try and add it. But needless to say regen braking will be a staple of new car orders going forward.

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The flaming in this otherwise good thread needs to stop. I'm not a moderator, and I don't want to be, but it's nonsense. There are a couple simple rules that people should follow when posting.

 

-If you don't know the answer, don't guess

-If you kind of have an idea, say you "kind of have an idea" and let someone correct you.

-If you have questions, ask them...better to ask than post wrong information

 

Posting opinions as fact is what seems to get people around here into trouble...people here do read this stuff and you know buffs they just repeat what they hear 90% of the time so if it's inaccurate that's how wrong information spreads...

 

just my 2c...now im done with that...

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The flaming in this otherwise good thread needs to stop. I'm not a moderator, and I don't want to be, but it's nonsense. There are a couple simple rules that people should follow when posting.

 

-If you don't know the answer, don't guess

-If you kind of have an idea, say you "kind of have an idea" and let someone correct you.

-If you have questions, ask them...better to ask than post wrong information

 

Posting opinions as fact is what seems to get people around here into trouble...people here do read this stuff and you know buffs they just repeat what they hear 90% of the time so if it's inaccurate that's how wrong information spreads...

 

just my 2c...now im done with that...

i guess the thank button is only for senior members :) oh well.

*clicks imaginary thank button;) aka submit reply.

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i guess the thank button is only for senior members :( oh well.

*clicks imaginary thank button;) aka submit reply.

 

Nah I am a senior member...it's only for TA employees or admins/moderators. A couple others have it but I think it has to do with them drawing things for the site or something. Not being particularly artistically inclined, I'll just wait till I join NYCT to get the thanks button for now I guess, unless Harry thinks otherwise :P:)

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This is gonna get long, but it should answer everything...

 

 

 

First let me start by explaining SMEE and NTT, it will make the rest of this a lot easier if I can refer back to this:

 

SMEE is fairly straightforward. You have two trainline pipes: A straight air pipe, and a brake pipe. Let me start by explaining the whole system without dynamics first so you have a handle on it.

 

The straight air pipe is the "service brake" aka the brake you feel when a station stop is made. This pipe serves ultimately into the brake cylinders which when the air pressure increases, applies pressure to the wheels and stops the train. Because of this function "normal" straight air pipe pressure is zero (release) when moving between stations. Full service aka "maximum" straight air pipe pressure is 80 pounds, which is the most air a T/O can pull using the brake handle without going into emergency. During operation, air from the main reservoir (the big tank of air that the compressor fills), will move into the straight air pipe, and on down into the cylinders to stop the train. The main reservoir air is constantly refilled by the compressor, which shuts on and off like a home heating system when the pressure gets too low or high.

 

The brake pipe is a fail safe emergency brake. Once the train is "charged" ie brought out of emergency, this pipe will charge to 110 pounds (130 pounds on R44 equipment). From there, it is meant to keep that pressure until the train is intended to go into emergency again. Any rapid decrease in brake pipe pressure will cause the train to go into emergency (can be caused by running a red signal - the trip cock hitting the stop arm causes the brake pipe to be rapidly vented of its air, as does a pulled cord, as does the T/O letting go of the deadman or putting the handle in emergency, or a brake pipe rupture). The two pipes function together while the train moves.

 

Now, let's add dynamics.

 

A DC subway motor like on a SMEE car is very straightforward. It's basically a big electromagnet, which means that, like a bisexual, "it goes both ways." Which means when you put power to it, it spins (acts as a motor). However, when you spin it, it generates electricity (acts as a generator). So the car is accelerating, electricity goes to the motor, motor starts spinning and we're on the move. All dynamics are is the opposite. The car wants to slow down now, and it's going fast enough that dynamics are active. The T/O moving the brake handle to service energizes the dynamics wire, which connects the already spinning motor to the grids and therefore places an "electrical load" on them. Now the motor acts as a generator and the spinning of the wheels creates electricity through the motor...that electricity needs somewhere to go, so it goes to the grids, which heat up, and the energy is used up and goes away. And of course, that slows the train down.

 

But meanwhile a lot of brake shoe wear and tear is saved through the dynamics. Electrically, the train is capable of detecting the amount of current created by dynamic braking (since the faster the train is going the higher this will be), and if that is not enough (ie the train is going slowly), the air brakes are added into the equation to help stop the train. (Note: this is also why a truck with dead motors will apply air brakes at higher speeds - because dynamics are doing nothing). Electrically, the train is also capable of detecting how much brake was requested, so it knows how much of the resistor "load" to place on the motors to get the desired stopping rate.

 

Now NTT

 

NTT's are designed to mainly use dynamic braking. Since it gets into computers it gets quickly beyond me but I can explain it simply and particularly the electrical parts. NTT brake is electric brake. A computer controls the brake throughout the train. You still have a brake pipe, main reservoir, compressor, and brake cylinders under the car. When the controller goes into the service brake range, the computer detects, very accurately, a desired stopping rate from the train. "Max Brake" = full service, or about 2.5 mph per second (or maybe it's 3.0? I can't remember). Every step along the braking range is a portion of that. The computer reads that, and "requests" dynamics and/or brake cylinder air to stop the train. What I mean by that is it will use dynamics as much as possible, but if dynamics are not generating that stop rate (the computer detects and monitors this in real time), then it will also apply the air brake as needed to get to that rate. (Again note: This is why a truck with dead motors will still apply the air brakes at higher speeds). Dynamics aren't capable of generating the stop rate desired at lower speeds, so that is when the air brakes kick in...same as a SMEE car but it's detected differently.

 

The regenerative aspect is a bit tricky, now. Technically NTT brakes are not 100% regen, but they usually are. What I mean by that is they are only regenerative if other trains are on the third rail and drawing power. I should also qualify all this by saying that I do not fully understand AC propulsion, as it is much more complicated than DC. But that said... the only way to get rid of the extra power created during dynamics is to use it up. Regenerative braking backfeeds this back into the third rail (through the contact shoe), where it can be immediately used by another train (not the train that is generating the power). In short, the train is basically acting like a substation for a few seconds. This also means it has to push the energy back at higher than 600 volts (but not so much so as to damage the substation) so it has to be very precise.

 

The NTT's do have grids to get rid of the extra energy as heat if need be, like a SMEE would, so this would be if the train was the only one on its particular section of track...the grids would loop in and get rid of the energy then, while slowing the train down.

 

There. Got it all out. Now I'll refer to that below.

 

 

 

Nope. See the end of the shpeel above. The energy created by NTT braking can only be used by other trains drawing power on the line at more or less that exact moment. Collectively the trains draw less energy, but if you were running a one train line, there would be no benefit to regen brakes. If no other train can use the energy from regen, the energy goes to the grids and gets used up and turned into heat by the grids.

 

 

 

Dynamic brakes get their "energy" from the fact that the train is moving and they are connected to a load (whether it's grids or other trains along the line - a longer connection but still a connection). It has to do with a motor being capable of being both a motor and a generator. In dynamics it's a generator. The momentum of the train keeps the motor spinning, which creates energy, which is used to stop the train.

 

 

 

SMEE cars were much older and did not have that technology. There were experiments with it (including one with I believe a handful of R32's that had a flywheel but I don't know how that would have worked), but obviously nothing stuck. A lot of the difficulties had to do with how regen power would get fed back into the "power pool" for trains. If it happened at too high a voltage, it could cause all sorts of problems at the substation when the power was fed back to it. And then the problem would be getting trains to move, not stop :(

 

That helps ALOT :) A thanks to SubwayGuy for the info :P

 

-rr4567 (JFK)

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Regenerative braking is not actually a method of braking. It is a method of consuming the energy created by dynamic braking. When regenerative braking is active the energy created by dynamic braking is thrown into the third rail and is cut away from the resistor grids completely. When regenerative braking is cut out that same energy is dissapated by heat via the grids. This means that on the "new tech" trains there is still only two types of braking friction and dynamic.

 

Note: Regenerative braking can be cut in and out by flipping a toggle switch behind the T/O position in a hatch on the upper left area of the wall behind the T/O.

 

Note 2: On R-142A's the TOD (train operator display) displays the message "regenerative brake cutout" at all times. This is because it poses a hazard to maintainers during maintenance. I do not have the specifics on that situation but it has been decided to keep them cut out for that general reason.

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Regenerative braking is not actually a method of braking. It is a method of consuming the energy created by dynamic braking. When regenerative braking is active the energy created by dynamic braking is thrown into the third rail and is cut away from the resistor grids completely. When regenerative braking is cut out that same energy is dissapated by heat via the grids. This means that on the "new tech" trains there is still only two types of braking friction and dynamic.

 

Note: Regenerative braking can be cut in and out by flipping a toggle switch behind the T/O position in a hatch on the upper left area of the wall behind the T/O.

 

Note 2: On R-142A's the TOD (train operator display) displays the message "regenerative brake cutout" at all times. This is because it poses a hazard to maintainers during maintenance. I do not have the specifics on that situation but it has been decided to keep them cut out for that general reason.

 

In the B Div there is a bulletin out that Regenerative braking

must be cut "IN" unless it sealed by Car equipment on the R143's and R160's.

 

I see they still havent figured out how to do that in the A Div huh?:)

 

Times havent changed much since i was over there ...

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Regenerative braking is not actually a method of braking. It is a method of consuming the energy created by dynamic braking. When regenerative braking is active the energy created by dynamic braking is thrown into the third rail and is cut away from the resistor grids completely. When regenerative braking is cut out that same energy is dissapated by heat via the grids. This means that on the "new tech" trains there is still only two types of braking friction and dynamic.

 

Note: Regenerative braking can be cut in and out by flipping a toggle switch behind the T/O position in a hatch on the upper left area of the wall behind the T/O.

 

Note 2: On R-142A's the TOD (train operator display) displays the message "regenerative brake cutout" at all times. This is because it poses a hazard to maintainers during maintenance. I do not have the specifics on that situation but it has been decided to keep them cut out for that general reason.

 

abot note 2:

 

I have worked on the 6 line (142A's) and regenerative braking is active. I do not know about the 142A's on the 4.

 

I currently work on the 2 and the 142's on both the 2 and 5 have the regenerative breaking cutout.

 

Could this be due to design differences between the 142 and 142A? (b4 anyone brings it up the 142S is the same as 142A)

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abot note 2:

 

I have worked on the 6 line (142A's) and regenerative braking is active. I do not know about the 142A's on the 4.

 

I currently work on the 2 and the 142's on both the 2 and 5 have the regenerative breaking cutout.

 

Could this be due to design differences between the 142 and 142A? (b4 anyone brings it up the 142S is the same as 142A)

 

Regen Brake Cutout? Was there a design flaw that poses shock hazard?

 

Possible sign on Regen Brake switch:

icon4.gifDo NOT Touch me I will blow you up!icon4.gif:)

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Regen Brake Cutout? Was there a design flaw that poses shock hazard?

 

Possible sign on Regen Brake switch:

icon4.gifDo NOT Touch me I will blow you up!icon4.gif:)

 

IINM it has to do with feeding the power back into the third rail during regen braking...I think what Tony is saying (correct me if Im wrong) is that can energize an "off" section of third rail and endanger workers working over there.

 

The Hi-V's didn't have regen braking but they had a similar problem...bridge the third rail and the inactive section would go live and threaten worker safety when the train entered the powered off section. Special signals were required to prevent this.

 

Or are you talking about it endangering Car Equipment maintainers?

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IINM it has to do with feeding the power back into the third rail during regen braking...I think what Tony is saying (correct me if Im wrong) is that can energize an "off" section of third rail and endanger workers working over there.

 

The Hi-V's didn't have regen braking but they had a similar problem...bridge the third rail and the inactive section would go live and threaten worker safety when the train entered the powered off section. Special signals were required to prevent this.

 

Or are you talking about it endangering Car Equipment maintainers?

 

Oh. as in it can supply + voltage to dead 3rd rail

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In a previous post I was actually referring to Car Equipment Maintainers.

Reason being that when the r142 receives third rail power it feeds that power to a converter that steps it down to a lower voltage and that voltage charges batteries and powers other auxilary circuits. So when regenerative braking is active the motors that are now acting as generators throw power into the third rail using the same path third rail power originally was fed to the car via the contact shoes. It was discovered that during regenerative braking in the r142's the voltage being thrown into the third rail would also provide a feed to the converter but not at a steady third rail equivelant and actually sometimes at a higher value. In turn batteries are overcharged and poses hazards when a car equipment maintainer services the batteries. The only reason for this is a design defect but as for the specifics of the design that allows this to happen I am not sure what it is at this time.

 

As for maintainers working on the third rails it does not pose a hazard to them. Reason being that during regular maintenance power is removed and if there is a car on the rail they are working on it has no third rail power therefore it will not reach above the 7 mph it needs to make regenerative braking possible even if it is not cut out.

As for working in emergencies where for some reason third rail power cannot be removed the maintainers will know that there is power present and any train feeding power into the rail will pose no more of a hazard than already exists. All maintainers have procedures to follow in these cases.

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In a previous post I was actually referring to Car Equipment Maintainers.

Reason being that when the r142 receives third rail power it feeds that power to a converter that steps it down to a lower voltage and that voltage charges batteries and powers other auxilary circuits. So when regenerative braking is active the motors that are now acting as generators throw power into the third rail using the same path third rail power originally was fed to the car via the contact shoes. It was discovered that during regenerative braking in the r142's the voltage being thrown into the third rail would also provide a feed to the converter but not at a steady third rail equivelant and actually sometimes at a higher value. In turn batteries are overcharged and poses hazards when a car equipment maintainer services the batteries. The only reason for this is a design defect but as for the specifics of the design that allows this to happen I am not sure what it is at this time.

 

As for maintainers working on the third rails it does not pose a hazard to them. Reason being that during regular maintenance power is removed and if there is a car on the rail they are working on it has no third rail power therefore it will not reach above the 7 mph it needs to make regenerative braking possible even if it is not cut out.

As for working in emergencies where for some reason third rail power cannot be removed the maintainers will know that there is power present and any train feeding power into the rail will pose no more of a hazard than already exists. All maintainers have procedures to follow in these cases.

 

Ah OK got you thanks for that info...

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As SubwayGuy stated, in short one is mainly computerized, the other isn't. Both SMEE and NTT use dynamic braking. That means the motors slow down, and go in reverse. That is why you hear the motors making their sounds in reverse when braking (reverse polarity). At a certain speed they stop, and the friction brakes kick in. A car with dead or weak motors will get more friction, or all friction brakes. The SMEE use straight air, which is for the service brakes, and brake pipe, which feeds the service brakes, and is use to apply the brakes in emergency. When a train goes into emergency, the dynamic brakes are null and void. The power gets cut to the motors (that is why you get no dynamics), and all the friction brakes are applied. That is why on the SMEE trains, I usually will say, I am grabbing brake, and releasing brakes......

 

With NTT, you still have a brake pipe, but for the service brakes, you brake cylinder air instead. That is why you get different pressures for a fully charges train with these. On these trains, when one goes for brake or power, that request is passed through the CPU, which then tells the system to brake, or take power (at the rate you request through the MC). That is why on these trains, I say I am requesting a brake. It's fun when the request gets denied at times........

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About regenerative brakes, weren't there technology invented when the SMEE braking was at the peak performance? My AP Physics BC teacher mentioned something about a Centripetal Force Tech (sorry for lack of better term) that allowed the current to go back at the correct voltage. Even if there was technology, why didn't the T/A reinstall regenerative components into the SMEE brakes in spite of acknowledging that they can save some power? Also, did the R44 P-Wire brakes have a regenerative braking component?

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About regenerative brakes, weren't there technology invented when the SMEE braking was at the peak performance? My AP Physics BC teacher mentioned something about a Centripetal Force Tech (sorry for lack of better term) that allowed the current to go back at the correct voltage. Even if there was technology, why didn't the T/A reinstall regenerative components into the SMEE brakes in spite of acknowledging that they can save some power? Also, did the R44 P-Wire brakes have a regenerative braking component?

 

I'm not sure what you mean. Centripetal force just refers to the forces created on something when it is spinning. Don't know if he's talking about electromagnetics? which is what a DC subway motor is...

 

As far as the voltage the regenerative energy flows back to 3rd rail for other trains it has to be slightly higher than 600 because everything else is at 600, think of voltage as the "pressure" behind the electricity if there's not enough you can't feed energy back into the third rail.

 

Installing regen brakes into SMEE cars retroactively = more expensive than the cost savings, simple as that. Cost > Benefits so don't do it...

 

P-wire was just a method for controlling brake requests on the R-44's, had nothing to do with how the cars actually stopped...standard "dynamics + friction" and the dynamics dissipated the energy to the grids. The "P" wire (stood for pneumatic I belive) was trainline and spanned cars at the coupler and had a little bit of energy that could run through it (1 amp? I think?). 0 amps was full service, 1 amp was released, anything else was stages in between. Problem was, train takes a turn, or goes on a grade and the coupler doesn't want to line up perfect then you break the electrical contact which means 0 current = 0 amps = full service and the train is stuck.

 

Also I believe there was some sort of "card" that the T/O had in the console to control this and sometimes THAT would need a "reboot" as well so brakes were always getting stuck with P-wire, lots of problems = no good...aka why those cars became "like SMEE" as they are today.

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P-wire was just a method for controlling brake requests on the R-44's, had nothing to do with how the cars actually stopped...standard "dynamics + friction" and the dynamics dissipated the energy to the grids. The "P" wire (stood for pneumatic I belive) was trainline and spanned cars at the coupler and had a little bit of energy that could run through it (1 amp? I think?). 0 amps was full service, 1 amp was released, anything else was stages in between. Problem was, train takes a turn, or goes on a grade and the coupler doesn't want to line up perfect then you break the electrical contact which means 0 current = 0 amps = full service and the train is stuck.

 

Also I believe there was some sort of "card" that the T/O had in the console to control this and sometimes THAT would need a "reboot" as well so brakes were always getting stuck with P-wire, lots of problems = no good...aka why those cars became "like SMEE" as they are today.

 

Quick question ... do the SIR R-44s still have P-wire?

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