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Motor Overload

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Motor Overload
Posted by JPS1 on Thursday, March 11, 2021 10:41 AM

A couple days ago I watched two BNSF locomotives - GP39 and SD40-2 - push a lot of cars up a very slight grade to reposition them in the Temple, TX yard.  The engines were really straining, or at least I assumed they were based on the roar coming from them.  

At what point do the motors cutout as opposed to burning up when they are under heavy load?  

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Posted by BaltACD on Thursday, March 11, 2021 11:44 AM

JPS1
A couple days ago I watched two BNSF locomotives - GP39 and SD40-2 - push a lot of cars up a very slight grade to reposition them in the Temple, TX yard.  The engines were really straining, or at least I assumed they were based on the roar coming from them.  

At what point do the motors cutout as opposed to burning up when they are under heavy load?  

The engineer has a ampmeter or loadmeter that tells him how hard the traction motors are working.  DC locomotives have a maximum continuious amp rating.  That rating can be anywhere between say 800 and 1100 amps depending upon the locomotive and the traction motors it uses.

Lets say that 1000 amps is the maximum continuous load specified - presumably the locomotive can have it's traction motors drawing 1000 amps until the crew goes on the Hours of Service Law.  There is also what is known as a 'Short Time Rating', there are spcified amp loadings above 1000 amps that the traction motors can handle for a specified amount of time - say - 1100 amps for 15 minutes, 1200 amps for 10 minutes, 1300 amps for 5 minutes.  Exceeding time in the short time ratings are what is going to damage the traction motors as the additional amperage the motors are handling generate more heat than the traction motor cooling systems can disapate - overheat electrical motors and they fail.

Different physics of electricity apply to AC traction - the theory of which I don't fully comprehend.

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Posted by Paul Milenkovic on Thursday, March 11, 2021 12:25 PM

What BaltACD is talking about is that it is the electric transmission rather than the diesel engine that you need to worry about in overstressing a locomotive.

This is also what happens when you exceed the towing capacity on your pickup truck -- you risk wrecking the transmission before you wreck the engine.

A friend of mine did this -- he towed a trailer of logs up one of those canyons that people live in in the LA area.  This was for a retaining wall he wanted to shore up against the inevitable rainy season mud slides that destroy canyon homes.  He said he burnt up the transmission in his truck, but that it was worth it to get that retaining wall reinforced so his house wouldn't get destroyed.

I suppose if he knew better, he could have made multiple trips with fewer logs up the hill and not had to purchase a replacement transmission, but there are stories men tell their wives, "Honey, I blew out the transmission in the truck, but I had to do it!"

What BaltACD is talking about are locomotives with DC traction motors, which the GP39 and SD40-2 indeed are.  The other thing I heard is that you can exceed the current rating (and the tractive "pull" is roughly the same as traction motor current), and the damage to the traction motors may not be apparent until later.  Just as if you abuse your truck by exceeding its towing limit, the transmission may not give out until later.

I would say the same physics of you have a transmission with not 100% efficiency holds with AC traction motors.  The difference is that the AC traction motors are a lot more efficient than the DC ones at heavy pulls so there is less heat.  They are also arranged differently that they can tolerate the heat better too.

The locomotive engineer might not have to look at an ammeter either because in the AC locomotives, everything is controlled by the software, and the software might not allow you to damage the traction motors.

If GM "killed the electric car", what am I doing standing next to an EV-1, a half a block from the WSOR tracks?
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Posted by Paul Milenkovic on Thursday, March 11, 2021 12:35 PM

Speaking of short-term ratings of DC traction motors, David Wardale in The Red Devil and Other Tales of the Age of Steam talked about the diesel competition to the ACE 3000 project that L. D. Porta observed first hand from the cab.

CSX, I heard from another source, likes to underpower their trains.  Porta observed CSX using a pair of SD60s to carry a 14,000 ton coal train through the section of their main line through West Virginia where Ross Rowland was testing the 614 to carry about 4000 tons.  From Wardale's description, the ACE people were really thrashing the 614 over territory where an H8 Allegheny was rated at 6000 tons, but Porta observed that CSX was "thrashing" its diesels.

What amazed Wardale was that locomotive crews were disciplined for stalling a train but not for overloading the traction motors, leading to an early trip to the shop for repair.  Or at least this is what Wardale heard from Porta who must have been told that from an engine crew.

In other words, we don't care if you have to damage your traction motors, just don't stall on a hill!

If GM "killed the electric car", what am I doing standing next to an EV-1, a half a block from the WSOR tracks?
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Posted by SD70Dude on Thursday, March 11, 2021 3:10 PM

Paul Milenkovic

What amazed Wardale was that locomotive crews were disciplined for stalling a train but not for overloading the traction motors, leading to an early trip to the shop for repair.  Or at least this is what Wardale heard from Porta who must have been told that from an engine crew.

In other words, we don't care if you have to damage your traction motors, just don't stall on a hill!

The operating and mechanical departments form separate 'silos' within the company.  The costs associated with stalled trains are assigned to operating supervisors, and the costs of locomotive failures are borne by the mechanical department (if a locomotive dies enroute and causes a train to stall that is also mechanical's fault).  So operating supervisors do not care about locomotive damage, only whether or not the train gets over the road, and they treat crews accordingly.  

This must have been during the time when crews would calculate how much tonnage their power could handle, today that descision is made above our heads.  We take the train we are given, and if it stalls it is not our fault.  

Greetings from Alberta

-an Articulate Malcontent

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Posted by SD70Dude on Thursday, March 11, 2021 3:23 PM

JPS1

A couple days ago I watched two BNSF locomotives - GP39 and SD40-2 - push a lot of cars up a very slight grade to reposition them in the Temple, TX yard.  The engines were really straining, or at least I assumed they were based on the roar coming from them.  

At what point do the motors cutout as opposed to burning up when they are under heavy load?  

The short time ratings are more like guidelines instead of rules.  If the train is still moving just keep pulling, and if something blows up get another one.  

Some newer units have systems designed to detect when motors are overheating and then reduce load accordingly (this is annoying to say the least, the system is far too cautious and a bad sensor can result in a train stalling).  Older units do not, and will keep pulling hard until something blows up.  

It is possible to overheat AC traction motors, but they will pull harder for much longer without suffering damage.  

Greetings from Alberta

-an Articulate Malcontent

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Posted by BaltACD on Thursday, March 11, 2021 6:26 PM

Paul Milenkovic
What BaltACD is talking about is that it is the electric transmission rather than the diesel engine that you need to worry about in overstressing a locomotive.

The diesel engine of a diesel-electric locomotive (presuming there are no mechanical defects) is designed to run at maximum load until the fuel supply runs out or the job has been accomplished.

I doubt diesel engine in railroad use are 'tuned' to produce maximum horsepower and/or torque.  The fuel delivery and other operating parameters are designed for the engine to develop the rated output for each throttle notch.

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Posted by Overmod on Thursday, March 11, 2021 8:17 PM

BaltACD
I doubt diesel engine in railroad use are 'tuned' to produce maximum horsepower and/or torque.  The fuel delivery and other operating parameters are designed for the engine to develop the rated output for each throttle notch.

There are examples where diesel prime movers have been 'tweaked' to make more power and longevity has suffered as a result.  With medium-speed engines like the 7FDL or 567/645 this is done with additional Run 8 speed, and what look like very small speed changes can have colossal effects 'too far'.

These engines are also replete with various critical speeds, where damaging resonance in one component or system or other might develop.  These are well-known and reasonably well documented, and are (as mentioned) an important reason for the relay-logic 8-bit speed-determined MU arrangement rather than a continuous stepless servo like a model railroader's speed pot...

Look in the SAE paper on the development of the 567 -- I believe there is a chart there showing all the critical speeds and notes about what produce them.

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Posted by BaltACD on Thursday, March 11, 2021 9:50 PM

 

Overmod
 
BaltACD
I doubt diesel engine in railroad use are 'tuned' to produce maximum horsepower and/or torque.  The fuel delivery and other operating parameters are designed for the engine to develop the rated output for each throttle notch. 

There are examples where diesel prime movers have been 'tweaked' to make more power and longevity has suffered as a result.  With medium-speed engines like the 7FDL or 567/645 this is done with additional Run 8 speed, and what look like very small speed changes can have colossal effects 'too far'.

 

These engines are also replete with various critical speeds, where damaging resonance in one component or system or other might develop.  These are well-known and reasonably well documented, and are (as mentioned) an important reason for the relay-logic 8-bit speed-determined MU arrangement rather than a continuous stepless servo like a model railroader's speed pot...

Look in the SAE paper on the development of the 567 -- I believe there is a chart there showing all the critical speeds and notes about what produce them.

When CSX took delivery of their GEVO DC traction engines - they were rated at 4400 HP the same as the GEVO AC's.  Shortly after their arrival CSX had the derated to 4000 HP.  I was never 'clued in' on what the 'beneficial reasons' were for this derating beyond fuel economy.

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Posted by Overmod on Thursday, March 11, 2021 10:23 PM

BaltACD
When CSX took delivery of their GEVO DC traction engines - they were rated at 4400 HP the same as the GEVO AC's.  Shortly after their arrival CSX had the derated to 4000 HP.

Over on NS, a fairly large number of Dash-9s were ordered as '40' rather than '44'; subsequently a large number were reprogrammed to develop 4400hp but their cab designation stayed 40 ... I never heard otherwise than that this was strictly a matter of software restricting the HP output, probably some combination of fuel saving and longevity concerns.

Leo Ames will probably know exactly -- at the very least he will know someone with the full story.

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Posted by Erik_Mag on Thursday, March 11, 2021 11:33 PM

BaltACD

Different physics of electricity apply to AC traction - the theory of which I don't fully comprehend.

Biggest difference is that high current windings are on the stator where it is easier to arrange for cooling. The "windings" on an induction motor rotor are large copper or aluminum bars with no insulation to burn out.

Another difference is that when an induction motor is producing maximum torque at zero speed, there is a bit of "slip"between the slowly rotating field generated by the stator, so all conductors are seeing the same duty cycle as when the rotor is turning and producing max torque. In a DC motor at zero speed, some windings are carrying the maximum current continuously, while other windings are carrying zero current. This is why DC locomotives have a minimum continuous speed.

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Posted by Paul Milenkovic on Friday, March 12, 2021 1:10 PM

SD70Dude

 

 
JPS1

A couple days ago I watched two BNSF locomotives - GP39 and SD40-2 - push a lot of cars up a very slight grade to reposition them in the Temple, TX yard.  The engines were really straining, or at least I assumed they were based on the roar coming from them.  

At what point do the motors cutout as opposed to burning up when they are under heavy load?  

 

 

The short time ratings are more like guidelines instead of rules.  If the train is still moving just keep pulling, and if something blows up get another one.  

Some newer units have systems designed to detect when motors are overheating and then reduce load accordingly (this is annoying to say the least, the system is far too cautious and a bad sensor can result in a train stalling).  Older units do not, and will keep pulling hard until something blows up.  

It is possible to overheat AC traction motors, but they will pull harder for much longer without suffering damage.  

 

Is it possible to go past the short-time rating and do damage to DC traction motors that is not immediately apparent?

Yeah, you could always lug a locomotive to get it to fail then and there.  But can you overload one in a way that it becomes the next crew's problem or maybe a problem a week or two later?

And if that is possible, is there any supervisory oversight of this?  For example, my cell phone still works, but I got it splashed up on the bathroom vanity, and now the battery bears the "pink badge of shame" that it was exposed to water.  Is there such a system from running a locomotive beyond its short-time rating, or is it an honor system for crews to 'fess up when a failure occurs later on?

If GM "killed the electric car", what am I doing standing next to an EV-1, a half a block from the WSOR tracks?
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Posted by jeffhergert on Friday, March 12, 2021 8:18 PM

SD70Dude

 

 
  

Some newer units have systems designed to detect when motors are overheating and then reduce load accordingly (this is annoying to say the least, the system is far too cautious and a bad sensor can result in a train stalling).  Older units do not, and will keep pulling hard until something blows up.  

 

 

Our SD70M have that self-protection system.  Their ammeters don't show the various short time ratings on the gauge face.

Jeff 

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Posted by bogie_engineer on Sunday, March 14, 2021 6:55 PM

The EM2000 control computer on the SD70's makes a continuous calculation of traction motor temperature based on motor current and cuts back power when a programmed limit is reached to protect the motors. Some earlier models, I think starting with the SD50, used an analog system consisting of a block with a temperature sensor on it installed in the motor circuit exposed to the traction motor cooling air to simulate the motor temperature.

When doing radial truck development testing, we were using SD60 EMD3 with D87B traction motors with an 1175 amp continuous rating. To try to measure improvement in adhesion in curves, we had special software for the MOD3 system with the motor temp cutback disabled and the ability to direct full alternator output to the 3 motors in the truck under test. We routinely pumped 1700-1900 amps into the motors at 5 mph and watched the simulated motor temperature on the EM2000 display; when it got to 300C we would throttle down but occasionally pushed it higher. Sitting in the cab over the test truck, we could tell when we were near the temperature limit by the smell of the motors, but we never had a motor fail in hundreds of hours of testing. When the testing was finished, we prudently sent the motors for rebuild before EMD3 was released to revenue service.

Dave 

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Posted by SD70Dude on Sunday, March 14, 2021 10:57 PM

My experience with the TM temperature detection system:

In about 2013 or 2014 EMD came out with an updated version of the software for the SD70M-2.  This would cause the locomotive to drop its load entirely and reduce the engine to idle if the computer detected what it deemed to be a "traction motor stall", which seems to have been defined as the locomotive loading at least X amps while moving below about 5 mph for more than a few minutes. 

At the time these units were regularly assigned to unit coal train service, where they were expected to operate in Pacesetter at 0.3 mph or less under heavy load for hours on end as the train was flood loaded.  Resetting the alarms every few minutes quickly became annoying (insert various profane railroader phrases here), and the stops and surges caused havoc for the loadout operators, not to mention train delays. 

There was a trick to resetting the TM stall alarm on a DP remote without actually going back to it.  There were several steps, the only one I can remember was flicking the lead unit's generator field switch up and down three times in a row. 

An EMD tech ended up going for a ride along to experience this firsthand, and asked if the trains could be loaded at 5 mph (the answer was no). 

It took years, but eventually the fleet must have slowly gotten updated versions of the software as the problem seemed to go away, of course they also became less and less common in coal service as our AC fleet grew over the past 8 years.

Greetings from Alberta

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Posted by BigJim on Monday, March 15, 2021 11:52 AM

Overmod
Over on NS, a fairly large number of Dash-9s were ordered as '40' rather than '44'; subsequently a large number were reprogrammed to develop 4400hp but their cab designation stayed 40


Actually, the NS Dash-9 "40" could make "44"!
All you had to do was insert a match book (or the like) in the proper place and you got the extra 400 hp. 

On the Dash-9's you could also pull up a display screen and watch the temperature of the traction motors. If the temp got too high, you could watch the unit derate the power.

.

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Posted by Overmod on Monday, March 15, 2021 1:16 PM

BigJim
Actually, the NS Dash-9 "40" could make "44"! All you had to do was insert a match book (or the like) in the proper place and you got the extra 400 hp. 

This made my day.

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Posted by mvlandsw on Monday, March 15, 2021 10:42 PM

I hadn't heard of the matchbook method. It went in a relay contact I presume.

I heard that there was a keyed switch that could be operated by authorized personnel to raise the hp output.

I could tell when traction motors were starting to overheat. You can smell the insulating varnish starting to cook.

The same odor came from the Motor Coils plant in Braddock, Pa. that rebuilt traction motors.

Mark Vinski

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Posted by daveklepper on Tuesday, March 16, 2021 4:57 AM

As far as I know, the software in all modern AC-motor locomotives, diesel or straight=electric, will not permit motors to be overloaded.

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