31–40 of 60 posts
Earlier quoted context omitted.
Yeah, it's insane because it's 100% not true.
Surprising then that a company sells resistors just for rail speed control applications: https://www.cressall.com/applications/rail-traction-dynamic-... (scroll down to "MOTOR STARTING AND SPEED CONTROL RESISTORS")
I think the Montreal metro faces a lot of these same issues. It works out in the winter where you don't need to actively heat the space. In the summer, it can be unbearable. I'm not sure if the type of rolling stock (rubber tires + tunnel track) has a major difference from other typical subway cars.
It really doesn't matter much - any amount of heat going into the underground system that is not able to be dispelled in a year-round cycle will heat the ground eventually. Reducing the heat entering the system slows it down, but at some point you have to cool it again.
Reducing input heat will lower this equilibrium temperature.
The main cause of heat is the inefficiency of the trains. All the brake energy is converted to heat. The motors and controllers are pretty inefficient too - modern electric motors+controllers are 95-98% efficient, whereas most tube trains are more like 40-60% efficient. For example, to go slowly, they simply put a big resistor in the circuit and waste 50+% of the energy!! Perhaps not coincidentally, the inefficiency…
TFL used to have its own generating stations, which helped keep costs manageable and also meant the trains kept running during power cuts.
That ended around 2000. Now it has at least four separate connections to the National Grid, and is supposed to be moving to 100% renewables within the next decade.
[1] https://content.tfl.gov.uk/fc-20171205-part-1-item08-tfl-ene...
I think the Montreal metro faces a lot of these same issues. It works out in the winter where you don't need to actively heat the space. In the summer, it can be unbearable. I'm not sure if the type of rolling stock (rubber tires + tunnel track) has a major difference from other typical subway cars.
Actually, I'm kind of sad that Montreal has so few cars left that play "Fanfare" [0]
[0] https://web.archive.org/web/20090823173621/http://observator...
The main cause of heat is the inefficiency of the trains. All the brake energy is converted to heat. The motors and controllers are pretty inefficient too - modern electric motors+controllers are 95-98% efficient, whereas most tube trains are more like 40-60% efficient. For example, to go slowly, they simply put a big resistor in the circuit and waste 50+% of the energy!! Perhaps not coincidentally, the inefficiency…
Earlier quoted context omitted.
Magnetic (eddy current) brakes work by converting kinetic energy into heat, which doesn't really solve the problem here. I'm not sure if anyone has devised a system that actually captures electrical energy from the braking action, or if such a thing is even plausible.
Regenerative braking generates electricity and there's really no reason modern trains wouldn't use them. Another approach that can be used when initially building the system is to have a slope leading into/out of stations so that energy can be stored as gravitional potential. I know the Montreal Metro was built this way.
The main cause of heat is the inefficiency of the trains. All the brake energy is converted to heat. The motors and controllers are pretty inefficient too - modern electric motors+controllers are 95-98% efficient, whereas most tube trains are more like 40-60% efficient. For example, to go slowly, they simply put a big resistor in the circuit and waste 50+% of the energy!! Perhaps not coincidentally, the inefficiency…
Source on 40-60%? As some trains are from the early 70s, and others were introduced 10, 5 years ago, which are you referring to?
The new ones are much better, although they still recover very little braking energy.
"Over the years, the heat from the trains soaked into the clay to the point where it can no longer absorb any more heat. Tunnels that were a mere 14 degrees Celsius in the 1900s can now have air temperatures as high as 30 degrees Celsius on parts of the tube network."
Similar issues can happen with geothermal heating/cooling if it's unbalanced - eventually the ground temperature changes and you have to dig deeper or stop using it.
Uncaptured energy is likely turned into pure heat.
They mention energy generation, but what about heat pumps and water heaters for the above ground buildings? Probably cost prohibitive, but wouldn't it be neat if the waste heat from the brakes ended warming a building or hot water heater?