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R44 5278

SMEE and NTT Braking Questions

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I understand that the SMEE trains utilize a dynamic braking system, whereas the NTT trains utilize a regenerative braking system. Can someone please describe the difference in the braking processes between a SMEE and a NTT? Also, is it true that the energy dissipated after a NTT braking is reused in accelerating the train so the train can consume less energy. Also, where do the NTT brakes get their energy from if they don't use the energy generated by the traction motors? Lastly, why can't the SMEE trains utilize a regenerative braking system while the NTT trains can?

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All I have to say is lulz to the above post. I think you should just stick to shouting car names as the pass by and playing with roll signs.

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All I have to say is lulz to the above post. I think you should just stick to shouting car names as the pass by and playing with roll signs.

 

What in the world is the matter with you??? Robert was just trying to share his knowledge and here you go trashing him, just like how you trashed 33rd Street last week. Do me, yourself and everyone else here a favor: behave like a moderator!!!

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What in the world is the matter with you??? Robert was just trying to share his knowledge and here you go trashing him, just like how you trashed 33rd Street last week. Do me, yourself and everyone else here a favor: behave like a moderator!!!

 

But what Robert is saying is incorrect.

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But what Robert is saying is incorrect.

 

Well, if what Robert is saying is incorrect, then why won't someone here say so? I'm awaiting SubwayGuy's insight on the matter, since he said he would fill us in with some details.

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Well, if what Robert is saying is incorrect, then why won't someone here say so? I'm awaiting SubwayGuy's insight on the matter, since he said he would fill us in with some details.

 

And he is working on it as I write this. The workings of a subway car, contrary to popular belief are complicated.

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And he is working on it as I write this. The workings of a subway car, contrary to popular belief are complicated.

 

How true. I was amazed with SubwayGuy's specific analyzation about the different SMEE cars, old, retrofitted and new, something that I had to take in and contemplate for a bit.

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How true. I was amazed with SubwayGuy's specific analyzation about the different SMEE cars, old, retrofitted and new, something that I had to take in and contemplate for a bit.

 

Since we both do work up at BERA on the subway cars, we know our stuff. He is much more mechanical and I am very hands on. I could explain most of the breaking system but that is not my area, now if you wanted to talk operations and physical plants workings thats my thing.

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Since we both do work up at BERA on the subway cars, we know our stuff. He is much more mechanical and I am very hands on. I could explain most of the breaking system but that is not my area, now if you wanted to talk operations and physical plants workings thats my thing.

 

That's something I may consider doing next year, head out and volunteer for BERA, not to mention that I may have the chance of operating a subway car as well! :cool::P

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All I have to say is lulz to the above post. I think you should just stick to shouting car names as the pass by and playing with roll signs.

 

You know, you dont have to be such an ass about incorrect info.

Don't ruin society further.

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

 

I understand that the SMEE trains utilize a dynamic braking system, whereas the NTT trains utilize a regenerative braking system. Can someone please describe the difference in the braking processes between a SMEE and a NTT?

 

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.

 

Also, is it true that the energy dissipated after a NTT braking is reused in accelerating the train so the train can consume less energy.

 

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.

 

Also, where do the NTT brakes get their energy from if they don't use the energy generated by the traction motors?

 

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.

 

Lastly, why can't the SMEE trains utilize a regenerative braking system while the NTT trains can?

 

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 :P

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What in the world is the matter with you??? Robert was just trying to share his knowledge and here you go trashing him, just like how you trashed 33rd Street last week. Do me, yourself and everyone else here a favor: behave like a moderator!!!

 

33rd Street got banned from here because he consistently provoked fights with other people on here. At least that's the story I've been made aware of. Part of acting grown up is knowing when to walk away from petty bickering, and airing his dirty laundry from here on Subchat was a very immature thing to do.

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33rd Street got banned from here because he consistently provoked fights with other people on here. At least that's the story I've been made aware of. Part of acting grown up is knowing when to walk away from petty bickering, and airing his dirty laundry from here on Subchat was a very immature thing to do.

 

Being provocative is definitely inexcusable, you're on the ball with that. But if you're a moderator, your job is to prevent flaming, and not instigate it, which really gets me mad to see people with a higher ranking abuse it, and by no means should that make them any different from a regular member of any forum/site. Let's face it, we all have lots of learning and growing up to do, and even I'll admit that I'm still young and I'm learning something new every day.

 

By the way, I'd like to thank you for that rather-lenghtly but indeed useful post! Lol :P

There should be no reason we shouldn't have fun though! Now, back to this topic.

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Since we both do work up at BERA on the subway cars, we know our stuff. He is much more mechanical and I am very hands on. I could explain most of the breaking system but that is not my area, now if you wanted to talk operations and physical plants workings thats my thing.

 

Yep we got our system down pretty good heh:

Car Equipment - Me

Operations - Both of us

History - Both of us, although he knows the IND better I know the IRT better

Tunnels/Stations - matted

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Yep we got our system down pretty good heh:

Car Equipment - Me

Operations - Both of us

History - Both of us, although he knows the IND better I know the IRT better

Tunnels/Stations - matted

 

And the BRT/BMT gets lost in the middle.

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33rd Street got banned from here because he consistently provoked fights with other people on here. At least that's the story I've been made aware of. Part of acting grown up is knowing when to walk away from petty bickering, and airing his dirty laundry from here on Subchat was a very immature thing to do.

 

about time;):eek::confused::P. every time i used to open a post to check if there was anything new, there would be this 5-7 page flame war caused by his retarded attitude. i mean come on... if your going to post information that you claim to know but arent willing to disclose your sources, keep your friggin mouth shut!:mad:

ok now i'm good.:cool::P

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oh and about the brakes thing. thanks for the in depth info.

 

as news, Bombardier now has there new MITRAC energy saver for trams. it basically converts the regenerative brake energy into usable energy that is stored in the high capacity / output battery. if they could only apply it to metro cars now.

 

and the NTTs only use friction brakes at speeds lower than 5 mph on a normal basis. all other service braking is done regeneratively. don't know if the DC cars could do this if they redesigned the brake system on them.

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What about me? :)

 

You just try to rip on people for their lack of knowledge about subway cars. You know I don't sit here and read all about 'em 24.7

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Would you both please stop flaming at each other? A correction can be made whenever someone is incorrect, not replacing it with something absurd. Btw, thanks again SubwayGuy!

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