The motor runs normally without load, but the speed drops significantly after loading.
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I encountered such a phenomenon at work today. The motor runs normally without load. After connecting the belt (the load side is the screw blower), after running with load, the speed is obviously slower. The three-phase current of the motor is 835A, 836A.595A. The motor parameters are 75KW, 1480r/m. in, 148A, the main circuit of the motor is an air switch, contactor, and thermal relay (using CT variable ratio control). The component inspection is normal. After measuring the three phases of the motor with a double-arm bridge, the three-phase value is 0.044 ohms. I have been looking for two days and haven't found the problem. Can any expert help me? Thank you very much!
When the motor is no-load, the current is 56A, but since it is running normally, only one current is measured.
The cable is also a cable that has been in operation for more than 20 years. It has been used before. Today I am testing the cable.
If the no-load condition is normal, it means there is no problem with the line. It should be overloaded. Check the Roots blower.
It's not a problem with the motor cable, it's obvious overcurrent.
The three-phase current is unbalanced. First check the voltage and see if there is any problem with the motor. If there is no problem, it is probably because the belt and the motor are not concentric.
The three-phase current is unbalanced. Check whether the voltage is normal, and then check whether there is any problem with the looseness of the motor and belt.