General Features of Traction Motors: Mechanical Features & Electrical Features

In this article, we will discuss the general features -mechanical and electrical features of the traction motor. The traction motor is used to drive high starting torque-demanding loads, such as electric locomotives, elevators, conveyors, trolley-buses, and other electric vehicles. 

General Features of Traction Motors

The traction motor converts electrical energy into mechanical energy like other electric motors. Therefore, It should meet the electrical and mechanical criteria for delivering the torque to the mechanical load. we can classify the features of the traction motor into two categories

  • Mechanical Features
  • Electrical Features

Mechanical Features of Traction Motors

The followings are the mechanical features of the traction motor.


The traction motor supplies a high starting torque at the start and also supplies the high torque intermittently during the train in motion. Thus, the traction motor experience heavy stress during its operation leading to increased vibrations in the motor. The motor should be capable to withstand the vibrations, without being damaged.

Small Size

The traction motor should be compact in size so that it can be easily installed beneath the motor coach. The dimensions of the motor is reduced in its design by taking care of some electrical parameters, like optimum sizing of the yoke, number of turns in field coils, and number of turns in the armature coils.

Minimum Weight

The lesser weight of the motor cause increase in the load-delivering capacity of the motor. Also, the weight of the locomotive does not increase much if the weight of the motor is less. Therefore, the traction motor should be lightweight.

Totally Enclosed

The traction motor is placed beneath the coach where it is subjected to work against dirt, dust, and mud. The traction motor needs protection against the ingress of such material inside the motor. Therefore, the traction motor must be totally enclosed.

High Efficiency

The efficiency of the motor shows the efficacy of conversion of input power to output power. The output power of the motor is more if the losses are less, and as a result, its efficiency is better. The traction motor should have minimum losses, such as copper loss, iron loss, windage loss, commutation loss, and frictional loss in order to have high efficiency.

Electrical Features of Traction Motors

The followings are the electrical features of the traction motor.

High starting Torque

The locomotive has a large mass and high moment of inertia. Therefore, It requires a high starting torque for its motion from the rest position and also needs a good torque intermittently during running conditions. Therefore, a traction motor must be capable to deliver high starting torque for locomotive operation.

Withstanding High Temperature

The temperature rise of the motor depends on the frequency of starts and stops. The traction motor used for locomotive needs to be stopped and started at every railway station. The motor takes a high starting current to deliver high starting torque. The high starting current cause more copper loss and eventually the temperature of the motor increases.

The traction motor must have the capacity to sustain high temperatures, The traction motor winding has H-class insulation to withstand high temperatures.

High Overload Capacity

In locomotive services, the traction motor has to sustain severe overloads. The motor should have self-reliving properties. The speed of the motor should lower when the torque demand on the motor increase. Therefore, a traction motor must have the capacity to function during excessive overload.

Easy Speed Control 

The traction motor needs frequent starts and stops, therefore it should have a simple speed control system.

Operate in parallel

Many motors operate in parallel in a traction system to drive a single load. For parallel operation of motors, all the motors must have identical speed-torque & current-torque characteristics. The motors can share the load equally if these characteristics are almost identical.

Ability to Withstand Voltage Fluctuations 

The traction motor draws a large starting current and causes a large voltage drop. The voltage dip in the supply system during starting of the motor cause deterioration of the motor’s performance. The traction motor should be capable of handling a large dip in the supply voltage.

Compatible with Electric Braking

The traction motor should be compatible with dynamic and regenerative braking. Electric braking improves the efficiency of the motor.

Good Commutation

The good commutation reduces the sparking at the brushes and commutator segments. Therefore, the traction motor must have good commutation for its better performance.

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