Composition and working conditions of traction motor

Traction motors are motors that generate traction power for locomotives or EMUs. There are many types of traction motors, but they all have a characteristic corresponding to the relationship between the traction force and speed of locomotives and EMUs, namely the basic traction characteristics. They can represent the performance of locomotives or EMUs, and can also be converted into the relationship between the torque and speed of the traction motor through the relationship between the wheel diameter and transmission ratio of the vehicle.

Composition of traction motor

The traction motor mainly consists of two parts: the stator and the rotor.

The stator includes the stator core, stator winding and frame. The stator core is made of stacked silicon steel sheets and is used to place the stator winding to form the magnetic circuit of the motor; the stator winding is wound with copper wire to form the circuit of the motor; the frame is generally made of cast iron or cast steel and is the support of the motor.

The rotor also includes an iron core and a rotating shaft. The rotor iron core is similar to the stator iron core and is also made of stacked silicon steel sheets as part of the central magnetic circuit of the motor. The iron core is slotted for placing or casting windings, which are installed on the rotating shaft. It rotates with the rotating shaft during operation. The windings are divided into two types: cage type and wound type. The cage type rotor winding is composed of cast aluminum bars or copper bars, and the ends are short-circuited with short-circuit rings. The wound type rotor winding is similar to the stator winding. The rotating shaft is made of medium carbon steel and supported by bearings at both ends to output torque.

In order to ensure the normal operation of the traction motor, there is an air gap between the stator and the rotor. The size of the air gap has a great influence on the performance of the motor. The larger the air gap, the greater the magnetic resistance, the larger the excitation current provided by the power supply, and the lower the power factor of the motor. However, if the air gap is too small, it will make assembly difficult and easily cause the stator and rotor cores to collide during operation.

Traction motor working conditions

The working principle of traction motor is the same as that of ordinary motor, and its basic structure is similar to that of ordinary motor. However, the working conditions of traction motor are very different from those of ordinary motor, so the design, structure, material, insulation, process and other aspects of traction motor should be carefully considered.

The main characteristics of traction motor working conditions are:

(1) Since locomotives are required to have both large traction and high-speed operation, the voltage and current applied to the motor vary greatly. Therefore, the motor is required to be able to adapt to a larger voltage regulation ratio and have a certain depth of magnetic field weakening capability.

(2) Traction motors work in the open air in a harsh environment and are often attacked by wind, sand, rain and snow. The altitude and ambient temperature of the operating area vary greatly. The humidity, salt content (hot season in coastal areas) and dust content in the air are also different. These can deteriorate the insulation of the motor. Therefore, the insulation material and insulation structure of the traction motor should have good dust and moisture resistance.

(3) Since traction motors are often started, braked, overloaded, and have their magnetic fields weakened during operation, and the impact and vibration of the motors during locomotive operation are more severe than those of ordinary motors, both electromagnetic and mechanical reasons will cause difficulty in commutation of the traction motors, and sparks and even ring fires will often be generated on the commutator. It should be pointed out in particular that commutation and heating of traction motors operating under pulsating voltage are more difficult, so the structural selection of pulsating traction motors must also consider special issues in this regard. In addition to causing deterioration of commutation, impact and vibration during operation can also easily damage the motor components, so the traction motor components must have high mechanical strength.

(4) The installation space size of the traction motor is limited. Since the traction motor is suspended on the locomotive bogie, the motor structure must take into account both transmission and suspension issues. Its radial size is limited by the wheelset diameter, and its axial size is limited by the track gauge. It is also limited by the distance between the wheelset centerline and other components of the locomotive running part. Therefore, the traction motor is required to have a compact structure and usually uses high-grade insulation materials and magnetic materials with good performance.