Can someone explain to me why everyone expresses the power of a locomotive by the horsepower the diesel engine generates. Are the electric traction motors, 6 on most locos these days perfectly matched to produce the same horsepower as the diesel engine. On a 4400 horsepower loco each traction motor is rated at 733.33 horsepower.
Thanks,
Kevin
It would be rather a coincidence if the traction motors were rated at exactly 1/6 of the locomotive's rating. I'm guessing they're not.
The locomotive's power is limited by the prime mover; even if the traction motors are actually good for 1000 hp apiece, we can't claim the locomotive is good for 6000 hp.
Diesel - Electric
Diesel drives a electrical generator (or alternator) that converts mechanical power form the engine to electrical power that then gets distributed to the traction motors.
The electrical traction motors move the locomotive and it's attached train. Traction motors on a given locomotive will generally be all of the same type and power rating. What power individual traction motors may be using at any given point in time will be related to the work it is actually performing at any given point in time.
The idea from a design standpoint is for the Main Generator of a locomotive to be able to generate all the power that the traction motors can consume...the more power that the Main Generator must produce, the more power is required from the diesel engine; therefore the designers will design the locomotive as a total package wherein the diesel engine, main generator and traction motors will consume the maximum power at maximum load.
Never too old to have a happy childhood!
I thought that the horsepower rating (nominal) for for traction that is after the power for parasitic loads; traction, motor cooling blowers, air compressor, and radiators is deducted.
BaltACD... the Main Generator of a locomotive to be able to generate all the power that the traction motors can consume
There is very little "matching" involved. Internal combustion engines are normally rated at maximum horsepower. Electrical devices are normally rated at continuous horsepower. The traction motor therefore only has to handle the full output for a short time. Electric motors have a rating known as "service factor". If a motor has a service factor of 2.0 then for a short time it will handle twice it's rated horsepower. So you can see that we are not talking decimal places here. A diesel engine of the locomotive type is capable of producing it's maximum output much longer than say, your auto engine but it rarely does so for a long time.
The capability of an electrical device is governed by it's ability to disperse heat. In industrial applications motors will have load meters and winding temperature gauges. If locomotives don't have temperature gauges for motor windings then it should be safe to assume that they do not get that hot under normal conditions. That would indicate that traction motors are rated substantially higher than the prime mover.
Locomotives are equipped with a Load Meter which displays it's readings in Amperes. Each type of locomotive has it's maximum continuous permitted Ampere reading and with DC Traction motor engines the ratings allowable for short periods of time expressed in minutes. The short time ratings take into consideration the heat that is generated by increasing amperage draws of the traction motors, thus engines are not equipped with temperature gauges for the traction motors.
AC traction engines do not have short time ratings as the characteristics of AC electrical power doesn't develop heat in the same way the DC power does. I am not a Electrical Engineer so I can't explain the reasons for this difference.
tdmidget The capability of an electrical device is governed by it's ability to disperse heat. In industrial applications motors will have load meters and winding temperature gauges. If locomotives don't have temperature gauges for motor windings then it should be safe to assume that they do not get that hot under normal conditions. That would indicate that traction motors are rated substantially higher than the prime mover.
tdmidget .. A diesel engine of the locomotive type is capable of producing it's maximum output much longer than say, your auto engine but it rarely does so for a long time. The capability of an electrical device is governed by it's ability to disperse heat. In industrial applications motors will have load meters and winding temperature gauges. If locomotives don't have temperature gauges for motor windings then it should be safe to assume that they do not get that hot under normal conditions. That would indicate that traction motors are rated substantially higher than the prime mover.
.. A diesel engine of the locomotive type is capable of producing it's maximum output much longer than say, your auto engine but it rarely does so for a long time.
Locomotive engines are engineered to produce their full rated horsepower continuously between maintenance intervals, unlike automotive engines which are engineered only to hit full rated power for a short time. You can take a GEVO, load it up to its rated power, and just let it run 24 hours per day if needed. They are so overbuild, that during developmental testing GE ran the 12 cylinder version at 5500 HP continuously between maintenance intervals, and they showed no additional wear than expected. AC traction motors are also overbulit. The current GE AC traction motor can run at 1800 HP continuously without over heating.
Thanks for the answers, I know how the Diesel Electric works, I really just wanted to know about the traction motors power ratings. I read that they are rated way higher than the diesel itself so that is the answer I was looking for. Thanks again for your answers.
Hi Kevin!
I noticed your question so I did a little research on my last run. On our Dash 9-40CW locos we have the ability to change the screen to view the engine and the traction motor output. Here are some observations that you may find interesting. As the throttle setting is increased, the horsepower is increased. This is irrelevant to speed or load. Here is a breakdown of horsepower according to notch setting on a 4000 HP GE six-axle loco:
Throttle 1 = 190 HP
Throttle 2 = 450 HP
Throttle 3 = 1200 HP
Throttle 4 = 1700 HP
Throttle 5 = 2400 HP
Throttle 6 = 3000 HP
Throttle 7 = 3500 HP
Throttle 8 = 4100 HP
In dynamic braking mode the diesel engine goes to idle and generates about 30 HP but will increase to about 70 HP if it needs to charge the air compressor. At 50 MPH in notch 8 delivering 4100 HP the screen did say I was generating 650 HP per axle.
As a locomotive engineer I am more concerned with the Amperage generated by the Alternator than Horsepower generated by the engine. The amperage is what is actually divided by the number of traction motors on a locomotive and is completely dependent on the load or drawbar pull. On a six-axle Dash 9 this means that the amperage will be much greater when I'm trying to start a train than when I'm moving at 60 MPH. This is important because if I don't keep an eye on the amperage I could break the train in to. That being said the information I am concerned with is how many amps per traction motor that I am pulling. At 50 MPH it might be 500 Amps but at 1 or 2 MPH it might be 1500 Amps in which case I may get a knuckle!
I hope this helps!
Tim
Thanks Tim for the info, very interesting. I didn't think the last time I was on was a month ago. Time is flying. Thanks again
I'm trying to program the dynamic braking effort of a modern diesel loco on the Auran/N3V Trainz simulator. Are their any parameter values available from the engineers display that shows current and voltage or watts drawn from the traction motors for various speeds and positions of the dynamic brake controller? If so could you post some here or email them to me?
Bob Weber
timz BaltACD: ... the Main Generator of a locomotive to be able to generate all the power that the traction motors can consume Presumably the traction motors on an AC44 (or ES44DC) could consume 1000+ horsepower apiece, if the prime mover could supply that much?
BaltACD: ... the Main Generator of a locomotive to be able to generate all the power that the traction motors can consume
Presumably the traction motors on an AC44 (or ES44DC) could consume 1000+ horsepower apiece, if the prime mover could supply that much?
On a DC motor the voltage and current limits are mostly independent of each other, so the motor will produce maximum mechanical power when operated at max voltage and max current. Since the RR's like having the locomotives power available over a range of speeds, diesel electric motors are operated well below their max voltage when running with max current and vice versa.
AC motors "should" be able to produce max continuous torque up to max rated speed - given enough power. Lower limits may be set by the voltage rating of the inverter and possible skin effect losses at high speed.
- Erik
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