News   Apr 19, 2024
45 and 61-Storey Towers Proposed near Oakville GO
 548     0 
News   Apr 19, 2024
DRP Reviews Innovative Affordable Housing at Kennedy Station
 611     2 
News   Apr 19, 2024
Lifetime Helping Craft the Future of Toronto's Neighbourhoods
 1K     3 

Visited Montreal for the first time. Some questions about their Metro system

felix123 said:
I guess that would be an issue until one day when the train decides to go back down the hill.
Click to expand...

It's not that simple. Regenerative breaking will regain some of the work lost by going up the hill, however, you lose a good 50-80% of the potential energy due to the work required to move the train, heat loses, sound loses, the work required to actually make the energy usable, etc. Although the potential energy difference between a grade of 2% and 12% are the same for a 1-meter increase, motor stress is also a huge issue. Now that I look at your claims, I'm finding them extremely hard to believe

For every 100 ft (and note, Azur trains are 500 feet), a train travels up 12 feet. That's twice the average height of a person. Therefore, 8.1 megajoules are required to move the train up the 12 feet. Over the course of let's say, 30 seconds (a full speed train should be able to traverse that distance in closer to 10-15), the train requires 273 kW. The maximum power output of 113 kW for an MR-63 shows that there is no way in hell that the entire train is traveling up a grade of 12% for a distance any greater than 100 feet. That stress is too great for 12% grades to be practical anywhere in the system.
 
Streety McCarface said:
It's not that simple. Regenerative breaking will regain some of the work lost by going up the hill, however, you lose a good 50-80% of the potential energy due to the work required to move the train, heat loses, sound loses, the work required to actually make the energy usable, etc. Although the potential energy difference between a grade of 2% and 12% are the same for a 1-meter increase, motor stress is also a huge issue. Now that I look at your claims, I'm finding them extremely hard to believe

For every 100 ft (and note, Azur trains are 500 feet), a train travels up 12 feet. That's twice the average height of a person. Therefore, 8.1 megajoules are required to move the train up the 12 feet. Over the course of let's say, 30 seconds (a full speed train should be able to traverse that distance in closer to 10-15), the train requires 273 kW. The maximum power output of 113 kW for an MR-63 shows that there is no way in hell that the entire train is traveling up a grade of 12% for a distance any greater than 100 feet. That stress is too great for 12% grades to be practical anywhere in the system.
Click to expand...

I mean that might be a problem if the train only had a single 113 kW (152 hp) motor to generate power, but it has 18 of them. Do you really think that an entire train has the same power output as a 5 seater sedan?
Nice try, though.
 
felix123 said:
I mean that might be a problem if the train only had a single 113 kW (152 hp) motor to generate power, but it has 18 of them. Do you really think that an entire train has the same power output as a 5 seater sedan?
Nice try, though.
Click to expand...
Honest mistake, I swear. I was quoting the wiki article for the MR-63 trains:
Screen Shot 2018-04-18 at 9.41.49 PM.png

It makes it look like the power output for the whole train is 113 kW

In a different article, it stated that the maximum potential power that could be taken by one, a 9-car train is 4,500 kW (but that includes onboard systems, so the actual value is closer to 2,000 kW (113kW*18)).
It looks like a lot, but let's go back to the basic values for a full train going up a 12% grade: height increase: 18.5m. Mass of train: 235,000kg. The amount of energy required to move that train up a 12% grade is 43,475,000 Joules. Assuming a max speed of the train, the power required to go up the grade is 5,797 kW for Traction alone. That's still higher than the maximum rating for the traction motors. If we assume the velocity is half of the maximum speed, 2,900 kW are required for Traction. Going back to the original argument -- that this leads to a lot of stress on the motors. It increases maintenance costs since motors can burn out fairly easily. The advantages for rubber tire metros are not there. Sure, it can climb up larger grades, but the stresses those grades cause on the motors make the change not worth it.
 

Attachments

  • Screen Shot 2018-04-18 at 9.41.49 PM.png
    Screen Shot 2018-04-18 at 9.41.49 PM.png
    10.1 KB · Views: 709
Streety McCarface said:
Honest mistake, I swear. I was quoting the wiki article for the MR-63 trains:
View attachment 140564
It makes it look like the power output for the whole train is 113 kW

In a different article, it stated that the maximum potential power that could be taken by one, a 9-car train is 4,500 kW (but that includes onboard systems, so the actual value is closer to 2,000 kW (113kW*18)).
It looks like a lot, but let's go back to the basic values for a full train going up a 12% grade: height increase: 18.5m. Mass of train: 235,000kg. The amount of energy required to move that train up a 12% grade is 43,475,000 Joules. Assuming a max speed of the train, the power required to go up the grade is 5,797 kW for Traction alone. That's still higher than the maximum rating for the traction motors. If we assume the velocity is half of the maximum speed, 2,900 kW are required for Traction. Going back to the original argument -- that this leads to a lot of stress on the motors. It increases maintenance costs since motors can burn out fairly easily. The advantages for rubber tire metros are not there. Sure, it can climb up larger grades, but the stresses those grades cause on the motors make the change not worth it.
Click to expand...

Don't worry about it. It is pretty funny when people try to show off the physics they vaguely remember from high school though - guys in my office do that every now and then and it almost never ends up well - let that be a lesson to you ;)

As for the utility of rubber tires, they were not necessary for Montreal at the outset, but rather it was a matter of them being in vogue at the time, as Mayor Drapeau couldn't resist the Parisian angle. Whatever benefits they may have were secondary to him just wanting that kind of metro in the city.
As for modern-day applications, there are steep lines in Paris (including the new line 14) and Lausanne, Switzerland, and the purpose of the tires is to prevent the train from slipping down the rails, as it would on steel wheels. I don't believe that anyone is using rubber-tired metros in an attempt to save power or decrease engine-wear, though there is a persistent opinion that the ride is smoother and that there is less brake-squeal with them.
I guess one of the notable results is that Montréal can claim to have an entirely-underground metro at this point, even if that has significantly increased costs.
 
felix123 said:
Don't worry about it. It is pretty funny when people try to show off the physics they vaguely remember from high school though - guys in my office do that every now and then and it almost never ends up well - let that be a lesson to you ;)
Click to expand...
I'm currently taking university physics II.
 
Streety McCarface said:
I'm currently taking university physics II.
Click to expand...
Don't worry - I'm sure your prof will get to the lesson on 'not digging the hole deeper' soon!

I had assumed you must be in your 50s or 60s because you were using feet in your calculations. Switching between (antiquated) and metric units is always a dangerous game.
 
felix123 said:
Don't worry - I'm sure your prof will get to the lesson on 'not digging the hole deeper' soon!

I had assumed you must be in your 50s or 60s because you were using feet in your calculations. Switching between (antiquated) and metric units is always a dangerous game.
Click to expand...
I am a Dual citizen, spent much of my young life in the US. I just used feet initially because those where the units available on the Wiki, and they were nice numbers (500'). But yes, SI units are significantly better, especially from a scientific perspective.
 
nephersir7 said:
For reference, AFAIK, the max slope in the Metro network is 6.3%, between Jean-Drapeau and Longueuil
View attachment 140634
Click to expand...

Awesome, thanks - raw data is always best :) Looks like the final answer on the subject is that steel-wheel trains could not have been used when the system was created, but that there are apparently some modern ones that could now handle the steepest grades in Montreal's system. Maybe, way down the road, that could open up options for MTL.
 
nephersir7 said:
For reference, AFAIK, the max slope in the Metro network is 6.3%, between Jean-Drapeau and Longueuil
View attachment 140634
Click to expand...

Ah, maybe that elevation map explains why there is no yellow-line station in Old Port. From this, I would guestimate that the tunnel doesn't get reasonable flat until north of Viger.

Although really, the yellow line alignment was a mistake, more built as a shuttle for Expo 67 than as a commuter line. They should have pointed it towards McGill and had it intersect the orange and green line at separate stations. That way, instead of forcing everyone to transfer at Berri-UQAM (and overloading the central section of the green line) more people would have a one-seat ride. It also means that you no longer have the entire network shutting down because of an incident at one station.

Here is my fantasy alignment. Because the yellow line has a longer route, there is a small enough elevation change to allow for a station in Old port.

yellow_line_new.png


The original mistake of putting it under Saint-Denis means that the STM is planning on building the silly extension pictured below to McGill before expanding the line further into the South Shore, because of concerns about all the transfer traffic.

upload_2018-4-19_15-44-59.png
 

Attachments

  • yellow_line_new.png
    yellow_line_new.png
    630.5 KB · Views: 618
  • upload_2018-4-19_15-44-59.png
    upload_2018-4-19_15-44-59.png
    291.6 KB · Views: 514
begratto said:
Well that was an exceptionnal situation. I take the orange line everyday, it's every 150-180 seconds at 8:30.
Click to expand...
I hear it's become quite a frequent problem. It's nothing I recall ever happening in the 1980s, unless the power for the entire city went off (which certainly happened often enough ... :) )

begratto said:
But anyway, my point is that they are increasing the frequency. The orange line will be at every 120 seconds at rush hours once all Azur trains are received.
Click to expand...
120 seconds! I'm surprised that they could get them in and out of the terminals that fast ... I wonder how they do it. It's been years since I've road a metro train, doing a track change in-service. They used to do it when Place St. Henri was the Orange-line terminus ... and it was so amazingly slow ... but it was only ever temporary. I'm not sure how the mechanics of it even worked - but you could here the steel wheels going on the steel rails of the switches ... and it wasn't a smooth ride.
 
You must log in or register to post here.

Back
Top