For motors with the same power, why is the rated current different? Please advise
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Our company has three motors with specifications of 380V, 160KW, and 8 poles. Two of these motors have a rated current of 363A, while the third has a rated current of 315A. All of them are used under the same operating conditions. The motor with a 315A rating often shuts down due to current overload protection – this happens once every month or two at times, or several times within a single day. This motor has also been used in place of the other two motors, but shutdowns due to overcurrent always occur with this particular motor. Could it be that the lower rated current is the cause? Also, I just can’t figure out why motors with the same voltage, the same power, and the same speed have different rated currents. Could anyone please give some advice?
The rated power of a motor refers to the power at its output shaft (that is, the power used to drive the load). The power consumed by each motor itself varies, and therefore every motor has an efficiency value η; as a result, motors with the same rated power can have different currents
Based on what you said, from the formula for calculating current, it can be seen that voltage and power are constant values; the only variables are the power factor and efficiency. If these two values differ from those of other motors, then the rated current will naturally be different as well. Please check whether these two parameters on the nameplate differ from those of other motors.
The rated current varies depending on the power factor and efficiency of different motors; in addition, the motor’s structure and the number of poles also affect its rated current.
What I want to know is what you mean by current protection shutdown. It is very important to know what the actual current is. Also, what is the power factor of the motor, and what is the power factor in your factory’s distribution room?