How does low line voltage to my VFD affect the maximum HP the motor can develop?

The calculation for determining the maximum power you can get out of your motor when the incoming line voltage to the VFD is low can be calculated.*

Here is an example of a PowerFlex 525 drive where the Actual Line Voltage is within the drives operating range, but it will affect the motor's maximum power and speed:

25B-D017N104 (10 Hp) / 460Vac, 60Hz Motor

Your anticipated Nominal input voltage is 415Vac.

415/460 = 0.9022 x 100 = 90.22%

90.22% x 10 Hp = 9.02 Hp

90.22% x 60 Hz = 54.13 Hz

At 415Vac (Actual Line Voltage) to the PowerFlex 525, the maximum power the 460V, 10 Hp motor can produce is 9.02 Hp at 54.13 Hz.


Another example is the Actual Line Voltage of 415Vac is low by 10%.

415Vac x 0.10 = 41.5Vac.

415Vac - 41.5Vac = 373.5Vac

Anticipated Low input Voltage of 373.5Vac:

373.5/460 = 0.8120 x 100 = 81.20%

81.20% x 10 Hp = 8.20 Hp

81.20% x 60 Hz = 48.72 Hz

At 373.5Vac (Actual Anticipated Low input Voltage) to the PowerFlex 525, the maximum power the 460Vac 10 Hp motor can produce is 8.20 Hp at 48.72 Hz.

* More information on this topic can be found in the Rockwell Automation Knowledgebase, Document ID QA27583.

You can also find the calculations in the PowerFlex 750 Series AC Drive Technical Data, publication  750-TD001.