Traction motor facts for kids

A traction motor is a special type of electric motor. It's designed to create a powerful spinning force, called torque, which is then often used to make things move in a straight line.

These motors are super important in many vehicles and machines that run on electricity. You'll find them in electric multiple units and locomotives on railways. They're also used in electric cars, electric milk floats, and even in elevators and conveyor belts. Vehicles that mix electric power with other types, like Diesel-electric locomotives and hybrid vehicles, also use traction motors.

How Traction Motors Work

Traction motors turn electrical energy into movement. They're built to be strong and reliable, especially for moving heavy things or for starting quickly.

Motors for Trains

Trains first used DC motors, which typically ran on about 600 volts. Later, new technology called semiconductors helped control AC motors better. This made AC motors, especially induction motors, a much better choice. AC induction motors are simpler and more reliable because they don't need contacts inside the motor itself. They are sometimes called asynchronous traction motors.

In the past, a single large motor might power several wheels using connecting rods, similar to how steam locomotives worked. But now, it's common to have one traction motor for each axle, connected through a gear system.

Often, a traction motor is mounted between the wheel frame and the axle it drives. This is known as a "nose-suspended traction motor." One small problem with this setup is that some of the motor's weight rests on the axle, which can cause the track and the train's frame to wear out faster over time. Some older electric locomotives, like the "Bi-Polar" ones from General Electric, had direct drive motors where the motor's spinning shaft was also the wheel's axle.

Parts of a DC Motor

A DC motor has two main parts:

• The rotating armature (also called the rotor). This is a set of wire coils wound around a central shaft.
• The fixed field windings (also called the stator). These are tightly wound coils of wire that surround the armature inside the motor case.

The armature connects to the field windings through brushes. These are spring-loaded contacts that press against the commutator. The commutator helps send electricity in a circular pattern to the armature windings, making it spin.

A series-wound DC motor connects the armature and field windings in a series. This type of motor has low electrical resistance. When electricity is applied, it creates a very strong magnetic field inside, which produces a lot of torque. This high torque is perfect for getting a heavy train moving from a stop. To prevent too much current from flowing and potentially damaging the motor or making the wheels spin too fast, Resistors are used to limit the current when the motor first starts.

Controlling Speed

As a DC motor begins to turn, the magnetic fields inside create an internal voltage. This electromagnetic force (EMF) works against the voltage being sent to the motor. The EMF helps control how much current flows into the motor. As the motor speeds up, the EMF gets stronger, so less current flows in, and the motor produces less torque. The motor will stop speeding up when its torque matches the drag (resistance) on the train.

To make the train go faster, more voltage needs to be sent to the motor. This is done by removing one or more resistors from the circuit. Removing resistors increases the current, which boosts the torque and makes the train accelerate. Eventually, all resistors are removed, and the motor receives the full voltage directly.

In early electric trains, the driver had to manually change the resistance to control speed. By 1914, automatic systems were developed. These systems used a special relay, often called a notching relay, in the motor circuit. This relay would monitor the current and adjust the resistance automatically. The driver just had to select a general speed setting, like low, medium, or full speed. These settings were often called shunt, series, and parallel based on how the motors were wired.

Motors for Road Vehicles

For a long time, road vehicles like cars, buses, and trucks mostly used diesel or gasoline engines with a transmission. However, in the late 1900s, vehicles with electric transmission systems started to appear. These vehicles get their electricity from batteries or fuel cells, and some even combine this with an internal combustion engine.

One great advantage of using electric motors in vehicles is that some types can also generate energy. When the vehicle brakes, the motor can act like a dynamo, turning the vehicle's movement back into electricity. This helps save energy and makes the vehicle more efficient.

Keeping Motors Cool

Traction motors handle a lot of power, which means they get very hot. Because of this, they usually need a cooling system, often using fans to blow air over them.

Images for kids

• 

  Swiss Rhaetian Railway Ge 6/6 I Krokodil locomotive, showing a large traction motor above each bogie, with drive by coupling rods.

• 

  Nose-suspended traction motor for a Czech ČD class 182 locomotive.

See also

In Spanish: Motor de tracción para niños