12 lead deltawye connected motor on vfd

[joncole]

Hello guys and gals.

"If used on a standard across the line starter, soft start or variable frequency drive, these motors should be wired in the delta (RUN) connection for either high voltage (480V) or low voltage (240V). The only time you should use the wye connection is a wye-delta starter. The final connection of the motor is ultimately the responsibility of the installing electrician. If he has any questions, he should contact his nearest motor specialist prior to energization."

The above paragraph was stated in a manual for a 12 lead dual voltage motor. The motor was first wired up as a wye. The vfd would fault for phase lost. Could you explain to me why wiring the motor as a wye would cause the vfd to trip for phase loss? Just curious.

 

[Jraef]

Hello guys and gals.

"If used on a standard across the line starter, soft start or variable frequency drive, these motors should be wired in the delta (RUN) connection for either high voltage (480V) or low voltage (240V). The only time you should use the wye connection is a wye-delta starter. The final connection of the motor is ultimately the responsibility of the installing electrician. If he has any questions, he should contact his nearest motor specialist prior to energization."

The above paragraph was stated in a manual for a 12 lead dual voltage motor. The motor was first wired up as a wye. The vfd would fault for phase lost. Could you explain to me why wiring the motor as a wye would cause the vfd to trip for phase loss? Just curious.

Not all VFDs are the same, so the real answer would have to come from your mfr. But in all likelihood, the drive probably determines phase loss on the output side based on current measurements. It has an idea of what the motor FLC should be because you programmed it with that data, and it knows what speed the motor should be running at, so it is predicting a range of current to look for at whatever speed command it is putting out. With the motor wired incorrectly in Wye, that current will be 1/3 of whatever the VFD is expecting to see, which it may interpret as being the result of a phase loss on the output. A typical current based Phase Loss protection system will say "If any phase current is below this threshold, trip on phase loss.", but "any" also is inclusive of "all".