What causes the imbalance of the three phases of motor current?
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The motors used in factories sometimes fail to start after tripping, with very high starting currents; it was later found that the issue was imbalance in the three-phase currents. What usually causes such a situation?
Generally, the reasons are as follows: 1. Unbalanced three-phase power supply, which is a problem with the power supply itself. 2. One or two phases of the three-phase power supply are open-circuited. 3. The three-phase resistance of the load is unbalanced. 4. In a three-phase load, one phase may have an excessively high single-phase resistance due to loose wiring or other reasons.
Unbalanced current in a three-phase motor can lead to insulation breakdown of the motor. Whether breakdown occurs depends on the magnitude of the current in the motor windings. During motor startup, the inrush current is very high, and breakdown is more likely to occur at this time; however, this is not absolute, as it is related to factors such as the current level and the insulation rating. Unbalance in three-phase current will definitely cause instability in motor torque. In my opinion, the reason for the imbalance in the three-phase currents of a motor is mainly due to the imbalance in the motor’s three-phase windings, which is directly related to the manufacturing process of the motor. I’m not sure if this is relevant to you, but good luck.