How does the traction power of mixed consists of subway and EMUs work?
Around 15 years ago, the Washington DC Metro decided to try to save money in operations by allowing the mixing of railcars from different manufacturers. First they experimented with the rebuilt cars that had largely similar AC traction motors, then mixed them with the newer rehabs and 5000-series cars with more modern AC, and finally mixed all cars with the remaining cars (4000-series) that remain with DC traction. Manufacturers range from Alstom, GE, and Bombardier for AC, and Westinghouse for the DC.
Regardless of whether they used AC or DC traction, each series horsepower output varies from 1,000 HP per car (1000-series), 800 HP per car, 850 HP, 940 HP, and 890 HP.
How does a train with mixed cars balance? Do the more powerful cars pull harder than the weaker ones? Is there any sophisticated balancing mechanism going on to prevent one set of cars from doing more work than it's supposed to?
There is nothing sophisticated about it. Each vehicle works to the extent it is commaded by the operator.
Same thing happens in railroads with MU'd diesel power - each unit produces its rated power when commaded by the operator. The only time it would get trickey is where you have DC traction units in the same consist with AC traction units. DC traction motors have short time ratings when stressed to their maximum aperage; AC traction motors don't. The operator must remain mindful of the DC limitations when operating from an AC engine.
Never too old to have a happy childhood!
As I understand it they are all set up to accelerate at 2.8 M/S (at least in automatic mode) so they should behave similar in that manner. Otherwise they just contribute what they have, although all the cars have more power than they probably need.
They apparently do brake at different speeds, though, which may account for some rough ride and buffeting when braking.
All the train operator has is a speed control stick. I've personally ridden in 4000-series cars, which are DC, mixed with 1000 HP cars with older AC and newer 2000- or 6000-series cars with the most modern AC propulsion at lower 800 HP and 850 HP power and wonder how it can work.
Surely there's a computer balancing the power? Is that 1000 HP car pushing the 800 HP car along? I glanced at the operator's panel years ago and saw the term "balancing speed" but I don't know what that means.
"Balancing speed" is more or less the speed a car will achieve on level track with the controller wide open. As long as the balancing speed and acceleration rates aren't too far apart for mixed car series, interoperation isn't a problem.
In the old day some systems mixed cars with different balancing speeds in trains (Chicago comes to mind, in mixed steel (50 MPH) and wood (40-45 MPH) consists). The result isn't too bad until you get to or near the lowest balancing speed, above which pushing and pulling can happen.
Looking across the wider ocean, heavy EMU in Japan often include non-powered cars in their consists - one in three car subsets, two in four car subsets. They 'balance' power through the couplers/draft gear, and the ride is at least as good as the best the New York subways could offer.
So the 1000hp car might pull or push the 800hp car. As long as they are geared for something like the same speed, so what. There's no rule that says the coupler/draft gear has to be completely unloaded while the wheels are turning.
Chuck (EMU rider living where there aren't any)
Why any different than double heading with different sized steam locomotives.?
tomikawaTT Looking across the wider ocean, heavy EMU in Japan often include non-powered cars in their consists - one in three car subsets, two in four car subsets. They 'balance' power through the couplers/draft gear, and the ride is at least as good as the best the New York subways could offer. So the 1000hp car might pull or push the 800hp car. As long as they are geared for something like the same speed, so what. There's no rule that says the coupler/draft gear has to be completely unloaded while the wheels are turning. Chuck (EMU rider living where there aren't any)
Until recently many London commuter EMUs were 4 car sets, 3 trailers and one power car.
Typical consist of a ten-car IRT subway train was seven motor cars and three trailers. Even today, the five-car IRT "Nostalgia Train" includes one trailer.
Typical consist of a seven-car IRT elevated gate-car or mudc train was four motors and three trailers.
Typical consist of a seven-car BMT "steel" train was one B-unit, one BX, unit and one A. Six motors and one trailer (middle of the 3-car BX.) However, if it ran over the Manhattan Bridge, it would be all motors, with the BX replaced by another B (3 motors).
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