DC Traction Motor Ratings - Continuous vs. Short-Time - in Amps/ HP, etc.

[Paul_D_North_Jr]

I’ve been looking for a while for information on the above - both ‘on-line’ and at a recent local train show - but haven’t had much luck in in my search, so I thought I’d try to tap the expertise here. I’ve already done a ‘Search Community’ for ‘‘ratings’’ and found lots of useful and interesting information and discussion and debates - such as the ‘‘AEM-7 vs. GG1’’ thread - but not this specific type of data. Generally, I know that these ratings are governed by limiting the motor winding heating to what they can stand with the blowers running - hence the continuous rating is at one level, the 1-hour rating a little higher, and the 15-minute and 5-minute ratings each a little higher than the last - maybe 5 or 10 percent, but not double, and so on.

What I’m specifically looking for is a set of numbers for those durations for a specific traction motor type, so that I can better understand the quantitative relationships between them. Any one will do - as a most common example, I’ll suggest the D77 traction motor as used under the EMD SD40-2 model locomotives - but if someone has the data or a table on some other EMD or GE motor that would be fine as well. I’m not sure if this can be found in the manufacturer’s operating manuals, on the gauges in the cab, both places or someplace else, etc. Alternatively, if you can point me to a link or reference with that information, I will appreciate that, too.

Thanks in advance for any help you can provide.

• Paul North.

[timz]

Scroll down to the pic near the bottom of

http://krugtales.50megs.com/rrpictale/p030224/p030224.htm

[Paul_D_North_Jr]

Aha ! Thank you ! [bow]

Never would have found that otherwise. I owe you one sometime, timz.

• Paul North.

[Paul_D_North_Jr]

It’s an installment of “Tales From The Krug” dated February 24, 2003, and the segment at the bottom is titled “Darn Hard Pull”. The photo is of a GE B40-8’s ammeter, and here are the values for the markings as best as I can interpolate them:

03 Dec. 2009 - Thurs. 2:45 PM EDIT: Add % below.

Continuous = end of Green / start of Red zone: 1300 Amps = 100 %

60 minutes: 1340 Amps = 103 %

30 minutes: 1360 Amps = 104.6 %

15 minutes: 1400 Amps = 107.7 %

5 minutes: 1500 Amps = 115.4

[blue_streak_1]

By the way - Al Krug’s photo shows the meter nearly pegged’ at 1675 Amps, and he says it was there for 35 minutes. How was he able to do that ? Well, the outside air temperature was only +2 degrees F, so the traction motor cooling blowers were unusually effective that morning

You bring up an interesting question. The traction motor cooling curves would be subject to the ambient temperature and absolute atmospheric pressure. Has anyone ever come across those graphs? And at what temp and pressure are the red zone numbers posted on the ampmeter?

[Paul_D_North_Jr]

Some other points from Al Krug’s article:

• The B40-8 had about 1,000 HP per axle - 4,000 HP / 2 ‘B’ trucks;

• The trailing SD40-2 had only about 500 HP per axle - 3,000 HP / 2 ‘C’ trucks;

• That’s why the SD40-2 was able to keep going with no loss of power - it was at about half the amps of the 4-motor GE;

• Did whoever assigned the power that day think about this at all ? What if it had been a hot summer day, and the B40 couldn’t sustain the load for the entire time with the warmer ambient cooling air ?

[beaulieu]

9 miles from Ranchester to Parkman, the top of the hill, 35 minutes to climb it. That means his average speed was 15.4 mph. He probably had some speed going into the grade so that his speed after the first few minutes would be lower. Good thing his B40-8 has MTP (Motor Thermal Protection) which means that he could let the computer worry about how hot the traction motors were. At that speed the SD40-2 would not be in its Red Zone.

[timz]

Could they have gotten up almost as well with a lower amperage = same tractive effort, but less speed ?

I never have understood the relationship between amps/volts/speed/TE, but I’m guessing lower amps at lower speed means lower TE.

[oltmannd]

Could they have gotten up almost as well with a lower amperage = same tractive effort, but less speed ?

I never have understood the relationship between amps/volts/speed/TE, but I’m guessing lower amps at lower speed means lower TE.

I think you are right. Amps are roughly proportional to TE and volts to speed, so, lower amps = lower TE. BTW, the early SD50s had a motor temp simulator (MS module) that featured a block of copper (I think) heated by current proportional to that in the TMs and cooled by air piped in from the TM blower duct. No kidding!

[Paul_D_North_Jr]

Thanks much to everyone who has contributed to this thread so far. It appears that I too didn’t quite throughly understand the relationship between those electrical values and HP and TE. However, recalling the tri-power ‘Kiddie Car’ article* in Trains some years ago, the author wrote that he was told by someone from the GE home office - Eric somebody, I believe: ‘‘To hell mit der volts - it’s der amps vot count !’’ Put very simply - volts are proportionately related to/ cause ‘speed’ and HP, but amps are what create the tractive effort force.

*EDIT-2: Ohms vs. Ms
Trains, July 1971 page 44
tripower locomotives on the Lackawanna
( “CRATON, FORMAN H.”, DIESEL, DL&W, TRIPOWER, ENGINE, LOCOMOTIVE, TRN )

Anyway, here’s a link to another good close-up photo of a readable ammeter or ‘amp meter’ on one of the former Erie Mining Co. EMD F9A’s - No. 4211 - at Hoyt Lakes, Minnesota. EDIT-1

[beaulieu]

Could they have gotten up almost as well with a lower amperage = same tractive effort, but less speed ?

I never have understood the relationship between amps/volts/speed/TE, but I’m guessing lower amps at lower speed means lower TE.

It is due to the effect of Lenz’s Law. The power formula changes from W = A * V to W = A* (V-I) where “I” is the Inductance. With a DC series wound motor the Inductance is directly proportional to the rotational speed if the motor field strength is constant. Halve the rotational speed, then you halve the Inductance. Since you are trying to maintain constant power at the motor the effective voltage in the motor circuit increases as the motor’s rotational speed decreases, and because of Ohm’s Law you have to reduce supplied voltage from the main generator to maintain a constant power. And yes the the type of Inductance found in a motor circuit is frequently referred to as Back EMF.

[Paul_D_North_Jr]

Here’s chart for the Tractive Effort and amps of an SD40 from Al Krug’s website, specifically the ‘‘Railroad Facts and Figures’’, ‘‘Amperage to Tractive Effort table for an SD40-2’’, under the heading ‘‘My Tractive Effort vs EMD’s’’ at - http://www.alkrug.vcn.com/rrfacts/amps_te.htm

Al Krug’s Tractive Effort	EMD Tractive Effort	Amps
136297*	97200	1200
95407*	82800	1050
63605	60480	850
47704	48300	720
38162	37800	600
31802	34800	550
27259	26400	480
21202	22920	395
19081	19200	365

*The two lowest speed values, 7 mph & 10 mph, may bit a bit high on the estimated TE account I assume the loco is putting out its full rated 3,000 Hp. But in re

[JayPotter]

I haven’t found anything else other than beaulieu’s explanation above of how voltage interacts with speed, and hence amps and tractive effort.

I recommend the book Diesel-Electric Locomotive Handbook - Electrical Equipment by George F. McGowan. It was published in 1951; and it contains more detailed discussions of basic electrical concepts than I’ve found in more recent publications.

[tree68]

He also seems to imply that Parkman Hill is about 24 miles long per the following, from - http://www.alkrug.vcn.com/rrfacts/hp_te.htm

One mph is kind of slow. It would take us 24 hours just to get up Parkman hill.

On the other hand, an article about AC traction (I think it was in Trains) indicated that an AC locomotive could run as slow as 1/2 MPH in Run 8.

Now Parkman Hill would require three recrews (not to mention the initial crew) to make the trip. Getting on and off the loco at that speed wouldn’t exactly be a challenge…

[Paul_D_North_Jr]

I’m wondering what the HP output of Krug’s B40-8 was that morning.

If the 1300 Amp Red Zone rating is for full parallel - not likely for a low speed - that would be:

600 volts (nominal) x 1300 amps rated = 780,000 watts = 780 KW

Divide by 0.746 KW per HP = 1,045 HP per motor x 4 = 4,180 HP for the whole unit.

OK, that makes sense so far.

But since he was probably running in full series instead due to the low speed, it would only be 1/4 of that nominal voltage, or 150 volts, since it was spread across all 4 motors - hence, about 261 HP per motor, or 1,045 HP for the entire unit.

But since the actual amperage was 1,675, the motors and unit were putting out more than that. By proportions, about 337 HP per motor, or 1,350 HP for the whole unit.

Of course, the actual voltage was probably somewhat higher, since the engine and generator were not likely loaded to the max.

What’s interesting to ponder - and why I posted the original question - is what if that had been a straight electric locomotive instead, with the unlimited catenary supply. Then potentially each motor could have had the 600 volts at 1,675 amps = 1,005 KW / 0.746 = 1,350 HP per motor, or 5,400 HP for the entire unit = a 35 % increase, very temporarily. In actual day-to-day operation, the cold weather of that morning can’t be counted on to occur, of course, so the potential short-term power boost is more in line with the percentage increases that I posted alongside the ammeter markings above. Still, it’s interesting to think about.

• Paul North.

EDIT: Here’s the link to an interesting webpage from a traction motor manufacturer and repair shop:

http://www.swigercoi

[timz]

But since he was probably running in full series

Road locomotives never run in full series, and never have. It’s a safe bet all the Dash-8s kept their traction motors in parallel; if they used any transition, it would have been in the generator/alternator.

600 volts (nominal)

That’s a familiar phrase, but no idea where it originated. No reason to assume the GE’s generator/alternator was producing that voltage at the time.

[oltmannd]

I’m wondering what the HP output of Krug’s B40-8 was that morning.

If the 1300 Amp Red Zone rating is for full parallel - not likely for a low speed -

All four axle locomotives from GE and EMD post Dash 2 and Dash 7 are full time parallel machines. The six axles of the Dash 8 and 50 series (and newer) have transition, but it’s generator transition. The generator voltage varies with speed. At low speeds, low votlage! The trouble is the high end…

[erikem]

Thanks much to everyone who has contributed to this thread so far. It appears that I too didn’t quite throughly understand the relationship between those electrical values and HP and TE. However, recalling the tri-power ‘Kiddie Car’ article* in Trains some years ago, the author wrote that he was told by someone from the GE home office - Eric somebody, I believe: ‘‘To hell mit der volts - it’s der amps vot count !’’ Put very simply - volts are proportionately related to/ cause ‘speed’ and HP, but amps are what create the tractive effort force.

Might well have been me, the quote is from Hermann Lemp who invented the three winding traction generator excitation design. Trains did carry an article on the Lemp system in the late 70’s - thinking it might have been early 1979.

• Erik

[beaulieu]

I haven’t found anything else other than beaulieu’s explanation above of how voltage interacts with speed, and hence amps and tractive effort.

• Paul North.

Here are a few links to the relevant formulae

Faraday’s Law of Inductance

Faraday’s Paradox

Lenz’s Law

[Paul_D_North_Jr]

I was trying to remember that article, too - I’m thinking it might have been in the last article of the 3 in this series: About the railcars which (unintentionally) forecast dieseldom Trains, November 1973 page 36 How it all began ( “CORLEY, RAYMOND F.”, GAS-ELECTRIC, GE, “HAMLEY, DAVID H.”, RAILCAR, ROSTER, TRN )
Take the seats out of a railcar and what do you have? A locomotive Trains, December 1973 page 40 How it all began ( “CORLEY, RAYMOND F.”, FREIGHT, GAS-ELECTRIC, GE, “HAMLEY, DAVID H.”, LOCOMOTIVE, TRN )
How to control and engine of limited power <