Traction motor

[5][6][7] In the 19th century traction motor passenger car companies began to compete with the dominant citywide horse-drawn railway transportation system.

By arranging the field winding with multiple taps, the speed characteristic can be varied, allowing relatively smooth operator control of acceleration.

[11] Traditionally road vehicles (cars, buses, and trucks) have used diesel and petrol engines with a mechanical or hydraulic transmission system.

In the latter part of the 20th century, vehicles with electrical transmission systems (powered by internal combustion engines, batteries, or fuel cells) began to be developed—one advantage of using electric machines is that specific types can regenerate energy (i.e. act as a regenerative brake)—providing deceleration as well as increasing overall efficiency by charging the battery pack.

The problem with such an arrangement is that a portion of the motor's weight is unsprung, increasing unwanted forces on the track.

In the case of the famous Pennsylvania Railroad GG1, two frame-mounted motors drove each axle through a quill drive.

By mounting the relatively heavy traction motor directly to the power car's frame, rather than to the bogie, better dynamics are obtained, allowing better high-speed operation.

The fixed field windings consist of tightly wound coils of wire fitted inside the motor case.

The commutator collects all the terminations of the armature coils and distributes them in a circular pattern to allow the correct sequence of current flow.

As the DC motor starts to turn, interaction of the magnetic fields inside causes it to generate a voltage internally.

This can be heard and felt in older DC trains as a series of clunks under the floor, each accompanied by a jerk of acceleration as the torque suddenly increases in response to the new surge of current.

To reduce these losses, electric locomotives and trains (before the advent of power electronics) were normally equipped for series-parallel control as well.

All the driver had to do was select low, medium or full speed (called "series", "parallel" and "shunt" from the way the motors were connected in the resistance circuit) and the automatic equipment would do the rest.

In the USSR, per GOST 2582-72 with class N insulation, the maximum temperatures allowed for DC motors were 160 °C for the armature, 180 °C for the stator, and 105 °C for the collector.

In diesel-electric and gas turbine-electric locomotives, the horsepower rating of the traction motors is usually around 81% that of the prime mover.

[citation needed] Calculation: 0.9 × 0.9 = 0.81 Individual traction motor ratings usually range up 1,600 kW (2,100 hp).

In severe cases, this can lead to "birdnesting" as the windings contact the motor housing and eventually break loose from the armature entirely and uncoil.

Because of the high power levels involved, traction motors are almost always cooled using forced air, water or a special dielectric liquid.