All Engines Pulling?

[TraneMan]

I see most of the train has two engines, Was wondering if all of the engine are pulling the cars at the same time, or do they take turn?

 

[Ryan]

Usually they're both online sharing the load.

 

[had8ley]

With a light train on flat ground, I would isolate the second unit for HEP and use the lead unit for tractive power; reason? The unit running HEP stays reved up at all times.

 

[transit54]

With a light train on flat ground, I would isolate the second unit for HEP and use the lead unit for tractive power; reason? The unit running HEP stays reved up at all times.

My understanding (and you very well may know better than me) is that one unit is indeed used for HEP but also shares the load involved in pulling the train. The other unit has its HEP turned off to save fuel when idle.

 

[Grandpa D]

Interesting thread. And it leads me to a question. On double ended trains, like the Hiawatha, is the rear engine pushing as well as the front engine pulling? Or is the rear engine just along for the ride.

 

[the_traveler]

With a light train on flat ground, I would isolate the second unit for HEP and use the lead unit for tractive power; reason? The unit running HEP stays reved up at all times.

My understanding (and you very well may know better than me) is that one unit is indeed used for HEP but also shares the load involved in pulling the train. The other unit has its HEP turned off to save fuel when idle.

That was my understanding also. (But I don't know any better - if anything at all!

)

 

[the_traveler]

Interesting thread. And it leads me to a question. On double ended trains, like the Hiawatha, is the rear engine pushing as well as the front engine pulling? Or is the rear engine just along for the ride.

I really don't know that specific answer. But on the Acela Express, which has a power car at each end, I believe one pulls and one pushes!

 

[Acela150]

Interesting thread. And it leads me to a question. On double ended trains, like the Hiawatha, is the rear engine pushing as well as the front engine pulling? Or is the rear engine just along for the ride.

I really don't know that specific answer. But on the Acela Express, which has a power car at each end, I believe one pulls and one pushes!

Correct, But both provide HEP with AE.

 

[transit54]

Interesting thread. And it leads me to a question. On double ended trains, like the Hiawatha, is the rear engine pushing as well as the front engine pulling? Or is the rear engine just along for the ride.

I really don't know that specific answer. But on the Acela Express, which has a power car at each end, I believe one pulls and one pushes!

Correct, But both provide HEP with AE.

And the HEP situation is different, since to provide HEP on an electrified train you are just converting the overhead current to the necessary frequency and voltage.

This page provided educated me a lot about HEP and the diesel locomotives: http://trn.trains.com/en/Railroad%20Reference/ABCs%20of%20Railroading/2006/05/Head-end%20power.aspx

 

[AlanB]

Interesting thread. And it leads me to a question. On double ended trains, like the Hiawatha, is the rear engine pushing as well as the front engine pulling? Or is the rear engine just along for the ride.

While there may be exceptions to the rule, I believe that generally the rear unit is pushing.

 

[AlanB]

With a light train on flat ground, I would isolate the second unit for HEP and use the lead unit for tractive power; reason? The unit running HEP stays reved up at all times.

My understanding (and you very well may know better than me) is that one unit is indeed used for HEP but also shares the load involved in pulling the train. The other unit has its HEP turned off to save fuel when idle.

That was my understanding also. (But I don't know any better - if anything at all!

)

That is generally the case, that both motors are providing traction power when needed. Of course whichever engine is providing HEP, and generally as noted by Jay it's the rear unit, is providing less traction power. I seem to recall that the unit providing HEP loses about 3 or 4 thousands of its HP to HEP.

 

[AlanB]

Interesting thread. And it leads me to a question. On double ended trains, like the Hiawatha, is the rear engine pushing as well as the front engine pulling? Or is the rear engine just along for the ride.

I really don't know that specific answer. But on the Acela Express, which has a power car at each end, I believe one pulls and one pushes!

Correct, But both provide HEP with AE.

Both power cars are providing traction effort, but only one is providing HEP. This is why for example when one crosses some of the bridges on MN that have a break in the catenary one loses HEP in the train as that power car's pantograph loses power. If both power cars were providing HEP, then HEP would never black out on Acela, as at no time ever would both power cars be without catenary overhead.

PRR60 could probably explain better, but the main reason for only using one power car for HEP is that you would have to do something called phase matching, where you must get both power cars providing HEP on the same phase. If you don't, you have big problems. Power companies often have fun trying to bring a power plant onto the grid because of the need to match the phase precisely.

In fact, while not the ultimate cause, one of Amtrak's big power meltdowns a few years back was because of a generator that didn't get properly phase matched. While that generator didn't bring down the entire NEC between DC & NY, that generator started a whole series of events that eventually led to crashing the entire NEC west of NY.

In any event, the last thing in the world that Amtrak is ever going to want to do is to try getting crews to phase match the two power cars. It's a waste of time for little benefit, and probably not worth the risk of screwing the process up. I don't believe you'd crash the NEC with a bad match, but I suspect that you could fry some of the equipment in the cafe car and FC car.

 

[Ryan]

That's close- you only need to worry about phase matching generation as it's brought online. The load (Acela in this case) just picks up whatever the system feeds it, the problem comes when you try to feed the grid with two generators that are out of phase. (I had to learn how to bring generators on line as part of my engineering qualifications on the ship - it isn't all that hard, it just takes a little bit of practice).

When both of the power cars are on the same piece of catenary, they're both in phase with each other because they're both in phase with the catenary. The problem comes when you go through a gap in the catenary (where the train goes dark). If the catenary on either side of the gap aren't in phase with each other (such as at points where the frequency shifts) what you'll end up connecting the two out of phase sections via the train, which will end up blowing things up. You could eliminate the problem by essentially splitting the consist into two 3-car sections fed from the power car at that end, but there's really no reason to do that.

 

[Acela150]

Interesting thread. And it leads me to a question. On double ended trains, like the Hiawatha, is the rear engine pushing as well as the front engine pulling? Or is the rear engine just along for the ride.

I really don't know that specific answer. But on the Acela Express, which has a power car at each end, I believe one pulls and one pushes!

Correct, But both provide HEP with AE.

Both power cars are providing traction effort, but only one is providing HEP. This is why for example when one crosses some of the bridges on MN that have a break in the catenary one loses HEP in the train as that power car's pantograph loses power. If both power cars were providing HEP, then HEP would never black out on Acela, as at no time ever would both power cars be without catenary overhead.

PRR60 could probably explain better, but the main reason for only using one power car for HEP is that you would have to do something called phase matching, where you must get both power cars providing HEP on the same phase. If you don't, you have big problems. Power companies often have fun trying to bring a power plant onto the grid because of the need to match the phase precisely.

In fact, while not the ultimate cause, one of Amtrak's big power meltdowns a few years back was because of a generator that didn't get properly phase matched. While that generator didn't bring down the entire NEC between DC & NY, that generator started a whole series of events that eventually led to crashing the entire NEC west of NY.

In any event, the last thing in the world that Amtrak is ever going to want to do is to try getting crews to phase match the two power cars. It's a waste of time for little benefit, and probably not worth the risk of screwing the process up. I don't believe you'd crash the NEC with a bad match, but I suspect that you could fry some of the equipment in the cafe car and FC car.

While traveling on AE I've never noticed the HEP go out. I believe it was in the design that power would go from the lead power car and end up in the trailing power car. The trailing PC would then send it back to the lead PC. Basically like a loop. Up to the trailing PC on one side of the train and Down the other side. This is what I was told from someone I know in the purchasing departing at Amtrak. Not sure if this is true, but this is what I was told. Keep in mind this was back when AE started back in 2000. I'm not saying your wrong. I'm always willing to learn something new. I'll shoot this guy an email now and ask.

 

[the_traveler]

One (very dumb) question. How can the rear power car provide HEP (HEAD end power) - shouldn't it provide REP (REAR end power)?

(OK, I'm very tired!

)

 

[TraneMan]

One (very dumb) question. How can the rear power car provide HEP (HEAD end power) - shouldn't it provide REP (REAR end power)?

(OK, I'm very tired!

)

LOL I think it's bed time for you!

Great thread we have going here!

 

[AlanB]

While traveling on AE I've never noticed the HEP go out. I believe it was in the design that power would go from the lead power car and end up in the trailing power car. The trailing PC would then send it back to the lead PC. Basically like a loop. Up to the trailing PC on one side of the train and Down the other side. This is what I was told from someone I know in the purchasing departing at Amtrak. Not sure if this is true, but this is what I was told. Keep in mind this was back when AE started back in 2000. I'm not saying your wrong. I'm always willing to learn something new. I'll shoot this guy an email now and ask.

I've had the HEP go out many, many times. Oddly for reasons that I don't understand, it seems to happen more going east to Boston, than going west from Boston. But it does happen usually at least once a trip going east, and often more than that.

As for the loop, that could still be the case, but it would be a closed loop. Meaning that the rear power car wouldn't be adding any power to the loop, just returning what it got from the head end. As least as far as hotel power in concerned.

The rear power car will still pull Cat power for the traction motors, just not for HEP.

 

[AlanB]

That's close- you only need to worry about phase matching generation as it's brought online. The load (Acela in this case) just picks up whatever the system feeds it, the problem comes when you try to feed the grid with two generators that are out of phase. (I had to learn how to bring generators on line as part of my engineering qualifications on the ship - it isn't all that hard, it just takes a little bit of practice).

When both of the power cars are on the same piece of catenary, they're both in phase with each other because they're both in phase with the catenary. The problem comes when you go through a gap in the catenary (where the train goes dark). If the catenary on either side of the gap aren't in phase with each other (such as at points where the frequency shifts) what you'll end up connecting the two out of phase sections via the train, which will end up blowing things up. You could eliminate the problem by essentially splitting the consist into two 3-car sections fed from the power car at that end, but there's really no reason to do that.

Again, I'm far from a power expert, which is why I rely on Bill (PRR60) to explaing these things to me. So I may be wrong about the phasing.

However, you do have to consider that the power cars aren't just pulling down the power from the Cat and sending it down the HEP cables. The power cars have to step down the voltage and on half the NEC, the power cars must convert the power from 25 Hz to 60 Hz for HEP. That conversion may be what requires matching, I'm not sure.

 

[amtrakwolverine]

Interesting thread. And it leads me to a question. On double ended trains, like the Hiawatha, is the rear engine pushing as well as the front engine pulling? Or is the rear engine just along for the ride.

My understanding is both engines are running one is pushing one is pulling. Since both the rear and lead loco are moving the train the locomotives computers downgrade the power of both locos down to 50%.

 

[GiantsFan]

Interesting thread. And it leads me to a question. On double ended trains, like the Hiawatha, is the rear engine pushing as well as the front engine pulling? Or is the rear engine just along for the ride.

My understanding is both engines are running one is pushing one is pulling. Since both the rear and lead loco are moving the train the locomotives computers downgrade the power of both locos down to 50%.

Or they both run at full power because they need all the HP to get up to speed and maintain it? (example - to keep the train on schedule)

 

[Ryan]

That's close- you only need to worry about phase matching generation as it's brought online. The load (Acela in this case) just picks up whatever the system feeds it, the problem comes when you try to feed the grid with two generators that are out of phase. (I had to learn how to bring generators on line as part of my engineering qualifications on the ship - it isn't all that hard, it just takes a little bit of practice).

When both of the power cars are on the same piece of catenary, they're both in phase with each other because they're both in phase with the catenary. The problem comes when you go through a gap in the catenary (where the train goes dark). If the catenary on either side of the gap aren't in phase with each other (such as at points where the frequency shifts) what you'll end up connecting the two out of phase sections via the train, which will end up blowing things up. You could eliminate the problem by essentially splitting the consist into two 3-car sections fed from the power car at that end, but there's really no reason to do that.

Again, I'm far from a power expert, which is why I rely on Bill (PRR60) to explaing these things to me. So I may be wrong about the phasing.

However, you do have to consider that the power cars aren't just pulling down the power from the Cat and sending it down the HEP cables. The power cars have to step down the voltage and on half the NEC, the power cars must convert the power from 25 Hz to 60 Hz for HEP. That conversion may be what requires matching, I'm not sure.

Right - I'm curious to hear what Acela150's friend has to say. We had the same type of converters on the ship to convert 60 Hz into 400 Hz for the radar and combat systems and at least with that style converter there weren't any phase adjustments that you could do. The phase of the 400Hz output depended only on the phase of the 60 Hz input, that was never a problem. It was possible to split bus on the ship so that 2/3 of the ship were being fed by one generator and 1/3 was fed by another (we had 3 generators connected to 3 load centers that then distributed the power, so for example you could have #1 generator feeding load centers #1 and #2 and than #3 feeding #3). In that case you'd have to make sure that all your 400Hz converters were being fed from the same load center. (I think - it's been a few years and splitting the bus was something that we didn't do very often)

 

[GG-1]

Aloha

I would think a front and rear engine would not power the train equally as then a car in the middle would be bounced (If right word) as things shift from being pulled then pushed.

 

[Crescent ATN & TCL]

Well with freight trains that use Locotrol the engineer sets operation to "synchronous" or "independent". In Synchronous all locomotives operate as one unit, if the throttle is at notch 1 in the lead unit, it is notch 1 in all other units, same applies to dynamic and friction braking. In independent mode each set of MU'd locomotives operates as one unit, but each set can be operated independently of the other. In other words the lead units can pull harder than the rear units to pull out all the drawbars and spread the train out, or the rear units can push harder to bunch up the drawbars. Synchronous is what is generally used and independent is used to adjust slack in the consist.

It is my understanding that Amtrak hardwires units through the train when using distributed power. That's why only certain cars can be used for push-pull operation. If that's the case they operate the same way they would if they were both up front. So unless there is a problem with one of the units both should be pulling at the same amount at the same time. Of course the one with HEP would have less HP for the same throttle notches than the one that is just for traction.

 

[had8ley]

It is my understanding that Amtrak hardwires units through the train when using distributed power. That's why only certain cars can be used for push-pull operation. If that's the case they operate the same way they would if they were both up front. So unless there is a problem with one of the units both should be pulling at the same amount at the same time. Of course the one with HEP would have less HP for the same throttle notches than the one that is just for traction.

I may be mistaken but Amtrak does not employ distributed power. Distibuted power is radio control engines that are placed in the middle or rear (most of the time) on freight trains. What Amtrak is running with two units is commonly referred to as 'push-pull." You are correct that some equipment is not able to operate in this mode.

 

[GG-1]

It is my understanding that Amtrak hardwires units through the train when using distributed power. That's why only certain cars can be used for push-pull operation. If that's the case they operate the same way they would if they were both up front. So unless there is a problem with one of the units both should be pulling at the same amount at the same time. Of course the one with HEP would have less HP for the same throttle notches than the one that is just for traction.

I may be mistaken but Amtrak does not employ distributed power. Distibuted power is radio control engines that are placed in the middle or rear (most of the time) on freight trains. What Amtrak is running with two units is commonly referred to as 'push-pull." You are correct that some equipment is not able to operate in this mode.

Aloha Jay

Isn't this exactly what the Acela is? and somewhere in the thread was a reference to a power unit at each end. and therefore the question about how that power is used. I s one unit only working, of are both working and how hard is each working