In the case of three-phase DC resistance balance, when there is three-phase running current imbalance, should check the three-phase terminal voltage balance. A slight unbalance of voltage can cause a great unbalance of current. Under normal circumstances, the unbalance is large when no load and small when full load. When the unbalance degree is not more than 10% in full load, it can operate normally.
When the three-phase current imbalance is found, the three-phase DC resistance of the motor can be measured with the double arms bridge. If the three-phase DC resistance is balanced, it does not belong to the motor quality problem, and the power supply and electrical control system need to be found.