Mechanical faults of three-phase asynchronous motors

Mechanical failure is a type of failure that typically occurs in the internal casing of a three-phase induction motor. These faults are further subdivided into three types, such as:

1. Rotor wire breakage fault
The squirrel cage induction motor consists of a rotor bar and a short end ring. If these guide bars are damaged or locally cracked, then this type of fault is a broken rotor bar fault. There are many reasons for this malfunction, but it is mainly caused by defects in the manufacturer. Because during the brazing process, uneven metallurgical stress may occur on the rotor guide bars, leading to their failure during rotor rotation. As shown in the figure below, the rotor bar is broken due to a fault:

2. Unbalanced rotor mass fault
If we focus on the construction of induction motors, it is easy to know that the rotor of the induction motor is placed in the stator hole and rotates coaxially with the stator. In heavy-duty motors, it is aligned with the center of the stator and its rotation axis is also the same as the geometric axis of the stator. Therefore, the air gap between the inner stator and the outer rotor is the same. Similarly, if the air gap is different, eccentricity will occur. In this eccentric situation, the fault occurs due to rotor imbalance. As a reference, we can see the rotor mass imbalance fault in the following figure:

3. Bearing failure
In a three-phase induction motor, two sets of bearings are installed inside the motor casing to support the motor shaft. The main purpose of these bearings is to allow the motor shaft to rotate freely and reduce friction. They consist of an outer and inner ring (called a seat ring) and a set of rolling elements (called balls). The balls are fixed on the inside and outside of the ring, reducing friction on the shaft. To further reduce friction, the solution is to lubricate these balls. Sometimes, the balls, outer or inner rings of bearings are damaged due to physical issues, resulting in malfunctions. The fault is a bearing fault, and due to this fault, the motor is completely stuck or stuck. We can see the motor bearing failure in the following figure.

Environmental faults of three-phase asynchronous motors
In motors, different faults may occur simultaneously, and among these faults, environmental faults are also very important. The usage environment of induction motors, such as ambient temperature and humidity, has an impact on the performance of induction motors. These factors will reduce the performance of induction motors. In addition, vibration of the induction motor caused by any reason (such as incorrect installation) can also affect the performance of the induction motor. Therefore, when installing three-phase asynchronous motors, these factors should be kept in mind.