How may one find a 3-phase motor's rotation direction if it is not accessible or visible?

The rotation direction of a three-phase motor can be determined by analyzing the three-phase relationship of the motor winding.

1. Observe the Peak of Back EMF: By observing the sequence of back EMF peaks on the motor's teeth, you can determine the direction of the motor's rotation. If tooth 1 reaches the peak first, followed by tooth 2 and then tooth 3, the motor is rotating clockwise; if tooth 3 reaches the peak first, followed by tooth 2 and then tooth 1, the motor is rotating counterclockwise.

2. Analysis of Winding Magnetic Impulse: Based on the physical position of the coil (clockwise or counterclockwise arrangement) and the electrical angle, draw the electrical relationship of the three-phase winding, then analyze the rotation direction of the winding magnetic impulse to determine the rotation direction of the motor.

3. Utilize detection tools: By using detection tools such as Hall-effect speed sensors, you can determine the rotation direction and speed of the motor by detecting the pulse signals related to the rotation frequency.

4. Comparison of Power Phase Sequence and Motor Input Phase Sequence: By comparing the phase sequence of the power supply with that of the motor input, when they are consistent, the motor rotates in the forward direction.

5. Phase Sequence Determines Rotation Direction: The rotation direction of the motor is determined by the phase sequence, i.e., the order of phases. For specific tooth sequences such as ABC, CAB, BCA, the motor rotates clockwise; for CBA, ACB, BAC, the motor rotates counterclockwise.

6. Difference between Electrical Angle and Physical Arrangement: In motor design, there may be a difference between the electrical angle and physical arrangement, such as a 240° difference where the rotation direction is opposite to the winding space arrangement direction. This requires considering the relationship between the electrical angle and physical position to determine the rotation direction.