the old heavy drags

Horsespower is foot pounds per second.  If you want to increase the pulling force, you have to give up speed.  The series wound DC motor was particularly well suited to demanding railroad service.  At a given voltage and current, when the speed dropped the torque goes up.  This is ideal for a diesel electric locomotive with a fixed maximum output from the engine-generator.

 

AC drive with AC traction motors have several advantages over the DC traction motor, but are only usable in railway service because computer control can get them to preform in the same way as DC series wound motor works.  The inherent advantages of AC traction motors are they do not go into a spin if they loose adhesion, they do not have commutators (high maintenance item) and they lend themselves to computer control.

 

As far as the AC motors having more power than the DC motor, the horsepower of either motor is determined by IEEE standard type tests.  A 1000 HP traction motor is 1000 HP if  it is DC or AC.  The increase in horsepower in locomotives has to do with the increased capability of the engine-generator.  The traction motors will be sized to match.

Very interesting post, David.

 

* The main advantage I've heard, re: AC equipment is - it's ability to move heavier loads without overworking/heating the equipment, and then having to back off, until it cools down. That allows for longer hours of operation. BTW, I've never seen a workload limit mentioned, for AC equipment.

 

Thoughts?

 

 

Rick

Here's a question I've never got a concise, but well explained, answer to -

 

what does load mean; it's a time thing, re: a locomotives ability to actually start moving a load. I've heard guys complain certain locomotive models take longer to load... than others.

 

Does anyone want to give it a shot?

 

 

Rick

To your first question, in a modern processor controlled locomotive or transit car, the code would not allow the motors to be overloaded.  On older manually controlled equipment, overloads could occur depending on the actions of the operator.  You are comparing old versus new technology, not AC vs DC.

 

On your second question about loading, if a engine-generator is running at a no load condition and a contactor closes to instantly put full load on it, the designer will have design in a system for the engine to come up to full power in time.  Otherwise the engine will just stall.  Different manufactures used different systems to address this, and they responded  differently. Engineers noticed these differences and expressed preferences depending on the service the locomotive was in.

Re: loading - so there's a type of idling mode, until a certain level of power is set, then after that idling threshold is exceeded, the loading process starts to kick in; in the case of a stopped train, the load has to reach a level where it can overcome all the resistance holding the train in place. That's why some engineers go directly to notch 8... full power; that way the load builds the quickest... eventually making enough power, to start turning the wheels and moving the train? As long as there's no significant wheel-slip.

 

Am I on the right track?

 

 

Rick

One of the things that confuses me is - once the contactor closes the system, and the loading process starts - full power is the default setting. Doesn't the operator set the power level, i.e. notch 8?

 

Also, once the contactor closes does the trains resistance directly go up against the power system(prime mover and alternator/generator) You mentioned the system automatically goes to full power mode, to prevent stalling.

 

 

Rick

Let me see if I can explain what "loading" means in this context. For those of you that work for a railroad and already understand this process, keep in mid this is a very simplified explanation. Let's not over-complicate things here.

 

The electrical power generated in a diesel-electric locomotive is controlled by a device called a "Load Regulator." The DC generator (or AC alternator) does not generate any current unless an excitation voltage is applied to the field coils of the generator/alternator. This is what the load regulator does, in response to the throttle position and speed of the locomotive. The excitation voltage is a low voltage, low current source, that controls the output of a high voltage high current generator or alternator.

 

When the throttle is advanced from idle to Run 1, the load regulator moves to apply a small excitation voltage to the field coils. The generator/alternator then produces a low voltage which is fed to the traction motors. The amount of voltage developed is directly related to the throttle position and the speed of the engine. As the throttle is advanced further, the Load Regulator increases the excitation voltage. The generator/alternator also produces a higher voltage, resulting in more current being fed to the traction motors. All the while, the Load Regulator is balancing the demand for power with the speed of the prime mover and the load demanded of it.

 

The current being drawn by the traction motors will show in the cab on the Load Meter. At 100 amps or so, the locomotive will just begin to move. When working all out in Run 8 at the minimum continuous speed for the locomotive, the current draw can be 1,000 amps or more.

 

When the throttle ultimately gets to Run 8, the Load Regulator will be adjusting the excitation voltage to the maximum it can be without over loading and slowing down the prime mover. Incidentally, no engineer is his right mind would EVER go from idle directly to Run 8. Not only is it against the rules, it is terrible train handling practice and will result in a lot of wheel slip or yanking the train in two. That's NOT how it is done. There are situations where Notch No. 2 pulls better than Notch No. 8.

 

When an engine is said to load quickly, it means that there is a very quick response between the throttle and increased amps on the load meter. In other words, when the throttle is moved, the engine quickly starts to move. Switchers are typically set to load faster than road engines. Thus they respond quickly to changes in throttle position, which is a big help when switching. When I say "quickly" I mean they respond within one or two seconds to a change in throttle position.

 

GE locomotives are notoriously slow to load when compared to EMD models. You can make a throttle change in a GE and it may be 10 seconds before you see any change in the load meter. And when the Load Regulator in a GE starts doing it's thing, it does it VERY slowly. The amps (and the pulling force) increase very slowly in a GE when the throttle is advanced. I think this is GE's way of making sure that their locomotives provide smooth train handling, regardless of how ham-fisted the engineer might be. Switching with a set of GE's is a nightmare because they are sooo sloooow to move when the throttle is opened.

AC vs DC Traction Motors...

 

A DC traction motor is a high-maintenance device. It has a commutator and brushes that ride on that commutator. (Think of the old Lionel Pull-Mor motors.) The brushes wear down, the commutator wears, etc.

 

DC motors are limited in the amount of current the brushes and commutator can handle, and by the heat the motor generates. As the motor slows down when loaded to maximum (as in climbing a grade) the current drawn by the motors goes up. As the current goes up, the heat generated also goes up. At some point the motor generates heat faster than the traction motor blowers can carry it away. When in this situation, the motors are into their "short time ratings" which means you can overload the motor like this, but only for a certain amount of time, then you have to stop and let the motors cool.

 

When the motor is generating heat at the same rate that the blowers can carry it away, the motor is operating at its "Minimum Continuous Speed." Depending on the gearing, this speed could be anywhere between 7 and 22 mph. Most freight diesels are going to reach MCS around 9 mph.

 

An AC traction motor has no brushes or commutator. It is an induction motor and has no rotating parts inside that physically touch another (other than the shaft bearings, of course.) AC motors do not have a MCS. In fact they can be run right down to a stall without damage. AC locomotives even have an "electric parking brake" whereby a fixed current is applied to "lock" the motors from turning.

 

Precise control of an AC traction motor is possible - far more precise than any DC motor. This is why AC diesels have higher factors of adhesion than a comparable DC locomotive. Their wheel slip can be VERY precisely controlled so that they can operate right on the edge of maximum traction all the time - automatically.

Thanks for taking the time to explain "loading", Rich

 

I think this process would be much easier for me to understand, if the various components of the equipment involved where being observed, while the explanation is given, i.e.

 

seeing an actual load regulator - how it acts/reacts during throttle manipulation etc would be a great asset, for teaching how this process works.

 

When I operated a multiple unit power set, a few years ago, the lead unit I was working in, was an SD40-3. When I adjusted the throttle, to move the train, there seemed to be an immediate response; I never noticed any delay. I was pretty preoccupied, though, so I might have missed it.

 

BTW, you cleared up another uncertainty for me - I knew new equipment used alternators for power generation, and I knew generators were used, on some models; I just wasn't sure when.

 

So it's alternators for AC equipment and generators for DC.

 

 

I assume the latest wheel-slip technology, helps too... when it comes to heavy hands.

 

 

Rick

I just noticed your AC/DC equipment explanation - sounds like I was correct when I stated AC traction equipment can work longer and harder... without overheating/damaging the traction motors. You're paying about $1,000,000.00 more for a modern six axle, outfitted with AC equipment, so they had better be worth it.

 

One of their noted praises is - being able to move heavy trains, from a dead stop, parked on an uphill grade, without wheel-slip issues...

 

Good information, thanks.

 

 

Rick

 

 I know this much from pulling heavy tonnage coal trains on river level (Kenova Districtof the NS).

 The older GE'S would stall out several times with big trains.I especially disliked the slip-control on the N&W units.

 On the older EMD's you had to watch how long you pulled high amperage.The traction motors would get hot and then do the same as the GE's ,stall out.

 

 The newer A/C's are sort of a new thing for me,and have only had some serious tonnage (200+ loads) behind me a couple of times.The main thing with the A/C's is how you start the train.You have to be a little more gentile when starting off with a heavy train.They like to slip around.And although dynamic is a tremendous advantage I think with the A/C's,it also comes with a little trickery.The A/C's have a tendency to first slip-up and "chatter" the wheels.But when they grab the rail they will stop you much better than the D/C's will.

   

 Hope this helps

Recently, I read somewhere that some guys(hoggers) used to think there was something wrong with some of EMD's AC models; turns out they are supposed to "earthquake"(sort of bounce around, while digging in... starting out).

 

I can't remember if it was one of the older MAC models or the new ACe's.

 

I appreciate your contribution - nice getting real experiences... Mack.

 

 

Rick

  I have referred to it as "humping" ....no not in that way

 

 But the new EMD A/C's do hump,jump,earthquake or what ever,but the do move up and down when they start out under a heavy load.But then they will slip around also like mentioned.

Hey Mack, as long as they stop playing, and get down to work, in a reasonable amount of time, enjoy the ride.

 

 

Rick

Speaking of heavy haulers -

 

check out 9211, for a few seconds, starting at the 49 second mark; that's my idea of a cool DC locomotive. It's outfitted with EMD's original version of the North American cab... sporting the three-piece window; part of BN's first 50 unit order.

 

http://www.youtube.com/watch?v=RaRk26arPTs

 

I like the cab that followed, with the tapered nose and two-piece window, even better. There's something about these fairly basic models that really appeals to me.

 

I lean to the best(AC); but, these DC machines, are railroading...

 

 Has anybody, taken one for a spin?

 

 

Rick

 

 

Not necessarily.

 

Most DC traction-motored diesels actually use an alternator to generate the power. That AC power is then rectified into DC for the motors.

 

An AC alternator is more efficient and less maintenance intensive than a DC generator. I'm not exactly sure when the changeover took place, but I'm pretty sure that the EMD 38-series (GP38, SD38) and 40-series (GP40 and SD40) ushered in the AR10 alternator in place of the old DC main generator. I could be wrong about that, however.

I thought the AC was an option late in the GP38 lineup designated GP38AC.  And standardized in the Dash 2?

 

And since we're talking AC/DC, what is a ground fault and how is it corrected?

quote:

The older GE'S would stall out several times with big trains.

Collin,
Ever have those old GE's trip the "Hot Diode" breaker? What a pain in the butt they were, making for a long day.

http://en.wikipedia.org/wiki/Alternator

 

I've just got way too many questions... to learn, here, in a short time, exactly what's going on... how this equipment actually works. Hands on would be my choice, for totally understanding...

 

My method of learning is to ask questions, until all my questions have been satisfactorily answered; and, I totally understand what's going on... This is not the place, for such in depth instruction.

 

I appreciate the help I have received; thanks.

 

 

Rick

 

 

 

Wyhogg, no confusion on my part between alternators and generators.  Working with old cars, I am familiar with the highly superior (more power output and better durability) of alternators over the equivalent generators.  My understanding is that that is why EMD made the transition.  

 

Still confused over what a ground fault is though.  Is that basically a short in the system or what?

Wy,

 

Nice contribution; I like hearing personal observations...

 

I've heard guys complain about the reflection issues, you mention, with the current EMD 70 line(ACe/M-2).

 

I mentioned earlier, here, that some of EMD AC models act up a bit, trying to get their footing... apparently, they're supposed to do that.

 

 

Rick

 Wyhog is right about the heart in your thoat

 

 The  D/C units will just flat out lunge and shake back and forth,and  if you don't keep your hand on the throttle and knock it down a few notches you'll get a knuckle or draw bar.

 

 BigJim I've not really experienced too many troubles with the diodes that I can remember.I really hated those 38 and 3900's though.

 

 It's been about 18 years ago,I was pulling about 110 loads off the hill at Kenova to take around the river (Belt Yard on the Ohio River ) with one GP-38 ,and it was doing good for about the first ...Oh car ,car and a half and when it pulled up against the 3 tightly placed handbrakes on the opposite end....well it all fell apart we heard popping, started seeing smoke and we were all done for .The unit I later found out from mechanical ,had burnt three modules up ,probably because of high amperage just a little too long 

 

 But the yardmaster told me to do what I could with what I had, and I tried.Maybe a little too hard

 

 

OK, that makes sense.  I can imagine that trying to track a short through all the cable on a locomotive would be a major undertaking.  I was talking with a UP engineer awhile back and he was talking about the SD90MACs and how they would get ground faults and hard crowbars.  I thought the crowbar reference was what the crews wanted to do to them, but I would guess it's not?

There are several reasons why AC traction motors have higher power and thermal capability than DC motors. One reason is that they are much larger. Locomotives using DC traction motors generally had a max wheel diameter of 40" (for freight locos). New locomotives have wheel diameters of 42-44+" so an AC motor can have a larger diameter and not infringe on the minimum clearance to rails with fully worn wheels which from my memory is 4.25". Another reason for the higher power capability of AC traction motors is that the work of "commutation" is now above the deck of the locomotive in the power electronics. Since a commutator on a DC motor was about one third of the armature, that space can now be filled with active core material, which is power (in spades!)

No locomotive is of any use when it is slipping. AC traction motors are synchronous. That is, if the electronics tell them to run at 57 Hz (cycles per second), they will ALL run at exactly that rotational speed and not slip. It is "the next best thing to side rods....)

On the Missouri Pacific, in the late 1960-1990s, coal trains from southern Illinois to the power plant at Labadie, Mo had , about 100 cars, 11 to 12000tons. and normally had 4 U30C's (3000HP each) for the climb over Kirkwood Hill, (about 1% grade), in suburban St. Louis. That's 12000 HP to propel the 12000 tons up a hill, or 1HP to 1 ton. That train really struggled. It was common for wheel slip. to help stop the wheels from slipping an engineer would apply 15 to 25 PSI of independent brake pressure so the brake shoes would help stop the spinning. The speed would often be below 5MPH for extended periods and the Amp meter would be maxed out, (I think 1200-1500Amps?) 

It was normal to exceed the short time rating.  What was particularly bad about the U30C was when it got wheel slip it would drop its load to stop the spinning, so from 1000Amps to zero and then slowly start loading back to maximum power, it was often thought that this was a cause for the occasional knuckles. In practice, all the units would not drop the load at the same time.

Stalling on the side of the hill did happen from time to time, especially in rain or in the fall when leaves were on the rail. Either a road train would have to cut off their engine and shove (or pull), or even a switch engine out of St. Louis was called to assist.

Those U30C's put on quite the show, really worked hard.From time to time, the GE units developed flame thrower status with 1 -2 foot flames out the stack, that was really cool at night!

For the most part, you ran the engines until they died! 

 

Today, the UP uses 3, 4500 HP AC units, (distributed power, 2 on front one on rear) to pull 145 cars, up to 21000 tons, coal trains up the west side of the hill, again about 1% grade at  8 to 11MPH.  

Only once or twice have I ever see the Kilo-pounds meter,  max out on an AC unit.  

 

Dan  

   

Dan,

 

I like those older 3000hp GE's, thanks for sharing... Sounds like you could just about walk faster than some of those old drags.

 

 

Rick

Another thing is when the brutes made transistion, Series to parallel or visa versa, they would drop their load, That was a problem because if you had two or more, they did it around 26-26mph I think, they could both do it at the same time.

 

A cool thing about the Mopac's U30C's is that were briefly renumbered into the spot series, 1-34.

Dan

 

Image of #6

 

Image of#964 on Labadie coal train

 

 

NOTE FROM THE WEBMASTER:

PLEASE learn how to use the LINK tool! Do NOT just copy and paste huge, long URL's here. It destroys the page formatting for some members.

Dan,

 

Tough(scrappers) - seems to fit GE's 30's; thanks.

 

 

Rick