What hazards can arise from inconsistent resistance in a three-phase motor?

What hazards can arise from inconsistent three-phase resistance in motors?

1. Causing motor overheating

When three-phase resistances are inconsistent, the phase with higher resistance generates more heat when carrying current. For example, in a three-phase asynchronous motor, if Phase A's resistance is 10% greater than Phases B and C, Phase A will produce relatively more heat during operation.

Prolonged exposure to this uneven heating pattern elevates the motor's overall temperature. Excessive heat accelerates the aging of insulation materials. Standard insulation materials (such as common Class B insulation with a maximum operating temperature of approximately 130°C) have specific temperature limits. Overheating degrades insulation performance, shortens the motor's lifespan, and may even cause insulation breakdown, leading to short-circuit failures.

2. Causing Torque Imbalance

The torque of a three-phase motor is closely related to its three-phase currents, which in turn are influenced by the three-phase resistances. When these resistances are inconsistent, it leads to unbalanced three-phase currents.

This current imbalance results in uneven torque generation. For example, in three-phase motors used in lifting equipment, torque imbalance causes the crane hook to sway during lifting or traversing operations, compromising work precision and safety. For high-precision positioning equipment like machine tool feed motors, torque imbalance may also degrade machining accuracy and adversely affect product quality.

3. Exacerbating Motor Vibration

Torque imbalance caused by inconsistent three-phase resistance subjects the motor rotor to uneven forces, which in turn induces rotor vibration.

Increased motor vibration triggers a cascade of issues. On one hand, it accelerates mechanical wear, such as bearing deterioration. Bearings are critical components of the motor. Frequent vibration increases friction between the bearing balls and inner/outer rings, shortening bearing lifespan. On the other hand, intense vibration may loosen connecting components, such as coupling bolts between the motor and load, or even cause the motor to shift during operation, disrupting normal equipment functioning.