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Analyze The Relationship between Load and Current to Understand Why Low Voltage Operation Can Burn Out The Motor!


For any motor, its rated operating parameters, such as rated power, rated voltage, rated current, as well as the corresponding speed, efficiency, and power factor under rated state, will be marked on the nameplate of the motor.

There is a certain deviation between the rated state parameters of the motor and the actual operating parameter values, that is, as the load changes, the actual operating parameter values will deviate from the rated values to varying degrees.

The actual power and current of a motor vary with the size of the load being dragged. The larger the load being dragged, the greater the actual power and current; On the contrary, the smaller the dragged load, the smaller the actual power and current. When the actual operating power of the motor is greater than the rated power, especially when the temperature rise design margin of the motor is small, the motor winding will burn out due to overheating; The actual power is less than the rated power, which is a typical type of large horse drawn small car, which can cause waste of materials and resources.

For some typical loads, such as air compressor loads, it is generally required that the motor has a certain short-term overload capacity. The motor should be designed according to a certain service factor, that is, the loading coefficient S.F of the motor, such as S.F=1.1, 1.2, 1.25, 1.3, etc., and the rated state S.F is 1.0. The following are the main parameter values of a 2-pole 90kW air compressor motor with a rated voltage of 380V for a certain specification.

From the data in the above table, we can intuitively observe that when the rated voltage remains constant, as the load increases, the current of the motor increases and the speed slows down.

From this, it can be directly inferred that when the rated voltage of the motor is insufficient, to ensure sufficient output power, the current will inevitably increase significantly, and the motor winding will face catastrophic disasters. This is the most common problem of winding burning due to undervoltage in outdoor operating motors. The characteristics of this type of faulty winding are the overall blackening of the winding, severe insulation aging, and the same performance characteristics as motor overload.

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