In practical applications, it is normal for the three-phase current of the motor to have deviations; but if the three-phase currents have a large deviation, it is necessary to find out the reason.The national standard document GB 8680.1-1998 stipulates that the current unbalance of a three-phase motor shall not exceed 10%.

　　There are two possible reasons for the unbalanced motor current:

　　1 Is the three-phase voltage balanced?

　　In the daily work process, the motor current is unbalanced, we should first consider whether the power supply voltage is normal.For example: Whether the deviation of the three-phase voltage is too large and whether it is equal or not.

　　If the power supply voltage is unbalanced, it will directly affect the current unbalance of the three-phase motor.When the motor is working normally, the unbalance of the three-phase voltage at the motor terminal must not exceed 5%, that is, 380*5%=19V.

　　Note: When measuring whether the three-phase voltage is balanced, the motor must be disconnected first to avoid affecting the measurement result.

　　Short circuit between 2 turns

　　Another possibility is that there is a short circuit between turns. For some reason (for example, insulation breakdown somewhere in the coil), some coils in the middle of the winding are short-circuited.In this way, the short-circuited one-phase coil has fewer turns, and the normal one-phase coil has more turns, the resistance is not the same, and the current is unbalanced.