The maximum tractive effort is the highest force that a vehicle can exert. The term tractive effort is usually used in connection with trains and rail locomotives. Like all forces, tractive effort is measured in newtons.
For a locomotive to accelerate from a stationary position, it must apply a force to overcome the static friction of the train, and to accelerate it against its inertia. To do this, a particularly high tractive effort is required, usually the maximum tractive effort of the engine is applied. This means that the engine works to produce the highest possible force that it can exert onto the wheels to cause movement or motion.
Few engines can maintain work at the maximum tractive effort for very long, but neither is it usually necessary for an engine to do this.
Once the train is running at a constant velocity the train no longer needs to overcome its inertia to remain at the same velocity, and hence must only provide power to compensate for frictional forces; the tractive effort can hence be reduced to at or below the continuous tractive effort.
A table to illustrate the speed the maximum tractive effort, continuous tractive effort and the speed at which the tractive effort should be reduced on a selection of trains operating in the United Kingdom:
Class
Type
Top speed
Maximum
tractive
effort
Speed to
reduce tractive
effort
Continuous
tractive
effort
Maximum
power
at rail
Mass
mph
km/h
Class 08
Shunter
15
156 kN
8.8 mph
49 kN
194 kW
49.6 – 50.4 t
Class 33
Passenger
85
200 kN
17.5 mph
116 kN
906 kW
77.7 t
Class 56
Light freight
80
275 kN
16.8 mph
240 kN
1790 kW
125.2 t
Class 58
Light freight
80
275 kN
17.4 mph
240 kN
1780 kW
130 t
Class 59
Heavy freight
60 or 75
506 kN
14.3 mph
291 kN
1889 kW
121 t
Class 60
Heavy freight
60
500 kN
17.4 mph
336 kN
1800 kW
129-131 t
Class 66
Heavy freight
75
409 kN
15.9 mph
260 kN
1850 kW
126 t
Class 67
Light freight
125
200
141 kN
?? mph
90 kN
1860 kW
90 t
The power at rail of a train follows the equation power (kW) = force (kN) x speed (m/s)
In general, it is more common for heavy freight trains (such as Class 59, Class 60 and Class 66 locomotives) to have a high maximum tractive effort due to the mass which they haul. Light freight trains (such as Class 56, Class 58 and Class 67 locomotives) and passenger trains (such as Class 33 and Class 43 / Intercity High Speed Train locomotives) usually have much lower maximum tractive efforts.
See also
- Bollard pull
- continuous tractive effort
- power at rail
- power classification
- tractive effort
External links
- A simple guide to train physics
- Tractive effort, acceleration and braking
Retrieved from “http://en.wikipedia.org/wiki/Maximum_tractive_effort”
Categories: Rail transport | Power | Introductory physics