traction motors

[Anonymous]

Do traction motors ever burn if the locomotive is feeding them electric power, but they can't pull the cargo? I mean if you put the trottle all the way up for some time and the train doesn't move, would the electromotors burn?

And what does that look like? fire? smoke?

anyone witnessed such thing?

[oltmannd]

The commutator will stall burn. The current flowing through the carbon brushes into the commutator will make those particular commutator bars so hot that the solder that holds them in place melts and the bars move out of position. Then, when the motor does start to turn, the brushes bang into the low/high spot and break (or at least wear out very fast).

I have only seen the aftermath of this - not actually seen it happen.

[chad thomas]

Yes, they do fail. And when they do it can be quite a show of arcs and sparks accented by the smell of acrid smoke.

DC traction motors have a minimum continious speed rating. Below this speed you go into what's called "short time rating". The slower you go the shorter the time. Depending on the gearing of the traction motor at say 11mph you might have a short time rating of 1/2 hour. That means you can go that slow for up to a half hour without significant risk of damage. The short time ratings are usually marked on the ampmeter in there corrisponding ranges so when you look at it you can see what short time rating your currently at.

AC traction motors do not generate that much heat at low speed and do not have a short time rating. Therefore a AC unit could pull max tractive effort all the way down to 0 mph.

[daveklepper]

Good answers, but even ac motors can get too hot if stationary when full current is running through them unless cooled by external fans or liquid cooling.

[Anonymous]

QUOTE: Originally posted by chad thomas

Yes, they do fail. And when they do it can be quite a show of arcs and sparks accented by the smell of acrid smoke.

DC traction motors have a minimum continious speed rating. Below this speed you go into what's called "short time rating". The slower you go the shorter the time. Depending on the gearing of the traction motor at say 11mph you might have a short time rating of 1/2 hour. That means you can go that slow for up to a half hour without significant risk of damage. The short time ratings are usually marked on the ampmeter in there corrisponding ranges so when you look at it you can see what short time rating your currently at.

AC traction motors do not generate that much heat at low speed and do not have a short time rating. Therefore a AC unit could pull max tractive effort all the way down to 0 mph.

Interesting

when that happens (the "show") can it be dangerous to stand near the wheels?

[chad thomas]

I've never seen it in person ( but I would pay good $$$ to see it though). I've heard it described as bottled lightening so I imagine it could definatly do damage to your hearing. Beyond that I don't know. I think most of the damage is contained in the tm housing. I think in the worst case the that axle might seise.

I hope Randy or one of our other knowlegeable members will expand on this topic.

[adrianspeeder]

Motors run on magic. If all the magic smoke leaks out, the motor won't run anymore.

Adrianspeeder

[Anonymous]

QUOTE: Originally posted by adrianspeeder

Motors run on magic. If all the magic smoke leaks out, the motor won't run anymore.

Adrianspeeder

Ah! So is that why steam engines are no longer used on big bad railroads?[;)][:p][8D]

[chad thomas]

QUOTE: Originally posted by adrianspeeder

Motors run on magic. If all the magic smoke leaks out, the motor won't run anymore.

Adrianspeeder

The only magic smoke I know of has nothing to do with traction motors.[;)][8D]

Although I have heard some things run on 100% P.F.M. (pure [censored] magic)

[Anonymous]

It would be cool if there were some videos on the internet of such event

[Anonymous]

grids burnin up are cooler.........seen both.

[Anonymous]

what grids?

[jchnhtfd]

QUOTE: Originally posted by electro-ortcele

what grids?

Dynamic brake grids -- better than the 4th of July![:D] They even have big fans on them to spread the merriment around some...

[Anonymous]

Today we had the hottest train on our RR suffer a fire in one of the traction motors. Crew had to get off engine and have local fire dept. put it out. Then had to get a new engine added and ended up needing to recrew, and of course incur a major delay on a highly scrutinized UPS train.

[Anonymous]

DC motors sound like so much trouble. Is there any reason these days for RR's to purchase new DC instead AC -- beside the point that DC loco's can cost $500,000 less, which is no small amount of change.

[adrianspeeder]

money money money

Adrianspeeder

[Tulyar15]

QUOTE: Originally posted by smalling_60626

DC motors sound like so much trouble. Is there any reason these days for RR's to purchase new DC instead AC -- beside the point that DC loco's can cost $500,000 less, which is no small amount of change.

AC motors can interfere with track circuits. When the class 92 electric locos entered service in Britain it was along time before they were cleared to run on all electrified lines (these locos are dual voltage so can run on both 3rd rail 750 V dc and 25 KV ac overhead) because of worries that there AC motors might interfere with track circuits. I'm not sure how much work was needed to modify the track circuits or the locos but they can no run anywhere that's electrified.

But it was for that reason that when EWS ordered the Class 66's from GM they opted for traditional DC traction motors. As a result the 66 is not only the British standard freight loco but is also becoming widespread in mainland Europe too.

I think I may have witnessed a traction motor fire back in 1978. I was making my first visit to the West Highland line in Scotland on a railfan special. It was being hauled by two locos, a Sulzer class 27 (which were the standard loco on that line at the time) and a class 25. These had the same Sulzer engine as the 27's but a different make of traction motor and were not often used on the West Highland line. Anyway going up towards Rannoch, the summit of the line we came to a stop and smoke could be seen issuing from the class 25's bogies. Nevertheless the train crew managed to put out the fire and whatever the cause the 25 behaved itself for the rest of the trip. (Had they had any doubt they could have changed it for another loco at Fort William).

[oltmannd]

QUOTE: Originally posted by adrianspeeder

money money money

Adrianspeeder

you left out "More money"

[Anonymous]

I think a big incentive for going AC is probably in maintenance costs. I remember reading an article when some of the first ACs came out SD70 MACs, and one of the big things mentioned was the reduced cost of maintaning AC traction motors. No brushes,no commutator, and no armature windings. I work in the electric power industy and AC is by far easier to control. Especially when it comes to motor speed. Controlling AC motors requires changing frequency as oppposed to the way a DC motor is controlled. ( changing voltage current and series to parallel etc...)

Variable frequency drives (VFDs) have been around for quite awile but it took awhile for the the technology to make it to the loco applications. I suspect this was mostly because the semiconductors to control AC for such high current flows were pretty large initially and didn't lend themselves well to mobile applications.

[adrianspeeder]

QUOTE: Originally posted by electro-ortcele

It would be cool if there were some videos on the internet of such event

Get a DC powered fan and shove a stick between the blades. Basicly the same thing.

Adrianspeeder

[Anonymous]

QUOTE: Originally posted by adrianspeeder

QUOTE: Originally posted by electro-ortcele

It would be cool if there were some videos on the internet of such event

Get a DC powered fan and shove a stick between the blades. Basicly the same thing.

Adrianspeeder

You could also say, why go watching real trains when you can watch models at home.

[BaltACD]

QUOTE: Originally posted by adrianspeeder

Motors run on magic. If all the magic smoke leaks out, the motor won't run anymore.

Adrianspeeder

The Joseph Lucas theory of electicity.