Phase Rotation for motors controlled by VFDs

[mjc1060]

:?Does anyone know if the rotation (L1-L2-L3) of the 3-Phase motor leads to the line side of a VFD controlling a motor make a difference (will the motor spin backwards)? Is the AC Voltage rectified to DC on the load end of these devices?

 

[petersonra]

:?Does anyone know if the rotation (L1-L2-L3) of the 3-Phase motor leads to the line side of a VFD controlling a motor make a difference (will the motor spin backwards)? Is the AC Voltage rectified to DC on the load end of these devices?

The line voltage is rectified and then back to ac for the motor, so the phase rotation at the line side just does not matter.

 

[GoldDigger]

The line voltage is rectified and then back to ac for the motor, so the phase rotation at the line side just does not matter.

Which is also why, with the right adjustments to capacity, you can feed a VFD with single phase and still drive a three phase motor.

 

[Jraef]

The line voltage is rectified and then back to ac for the motor, so the phase rotation at the line side just does not matter.

The ONLY time it matters is if you have a bypass starter system for keeping a motor running while the VFD is removed for servicing, something common in HVAC drive systems. In that case, the motor will run in the direction of the utility phase sequence, whereas with the VFD, the VFD was electronically determining the phase sequence, so it they not match. What happens to people is that they check rotation using the VFD, get it working, then when they switch to bypass the motor spins backward. The trick to making sure that doesn't happen is to check motor rotation while in BYPASS first, then make the VFD output rotation match that.

 

[Besoeker]

The ONLY time it matters is if you have a bypass starter system for keeping a motor running while the VFD is removed for servicing, something common in HVAC drive systems. In that case, the motor will run in the direction of the utility phase sequence, whereas with the VFD, the VFD was electronically determining the phase sequence, so it they not match. What happens to people is that they check rotation using the VFD, get it working, then when they switch to bypass the motor spins backward. The trick to making sure that doesn't happen is to check motor rotation while in BYPASS first, then make the VFD output rotation match that.

Excellent observation if I may say so.

 

[Jraef]

Excellent observation if I may say so.

Heh, there's a reason I know this...