A 185kW electric motor, powered by a 220kW inverter, the electric motor runs with U-phase current about half of V-phase and W-phase, works fine, and alarms several times a day!
When the U phase was changed to V phase, the V phase current was again about half of the U and W phases.
Regarding the problem of uneven current in three-phase motors,
which is encountered both in use and in tests, we can screen by changing the conditions. For the sake of understanding, we will start with the analysis of the industrial frequency motor.
If the current is uneven, we can detect it by way of input voltage, so that we can distinguish whether it is a power supply problem or a motor problem.
If the power supply voltage is uneven, we can exclude the electric motor problem; on the contrary, if the voltage is not a problem, we can determine that it is a electric motor problem.
If it is not convenient to measure the voltage, it can be judged by inverting the phase.
If the current is abnormal after inverting the phase and shifting with the inverted phase, it is generally a power supply problem, otherwise, it is an electric motor problem.
As for the VFD motor, the inverter is added between the power supply and the motor, and the abnormality of the inverter can also lead to abnormal operation.
We can make a basic judgment by the balance of the inverter input and output voltage, but also by replacing the inverter or disconnecting the inverter measures to the screen.
As far as the motor itself is concerned, when there is a serious imbalance in the three-phase current, the motor winding temperature will rise significantly, accompanied by the abnormal sound.
Thus, for motors powered through inverters, when there are data abnormalities, it is possible that there is a problem with the variable power supply or a problem with the data feedback system.
The common faults of inverters are divided into main circuit faults and auxiliary control circuit faults.
Among them, main circuit faults include rectifier block damage, charging resistor damage and inverter module burnout; auxiliary control circuit faults include drive circuit faults, switching power supply damage and feedback, detection circuit faults, etc.
