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Old January 29th, 2010, 02:30 PM   #1
bigbuckaroo
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General VFD question

When setting up a VFD by putting in the motor data like motor rated voltage, motor rated speed ect, what happens if in the motor rated frequency you put in say 75 Hz instead of 60 Hz like it is supposed to be?ThanksTom
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Old January 29th, 2010, 02:36 PM   #2
DickDV
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It is essential that you put the correct motor data into the drive so it can manage the motor properly. If you are looking for overspeed or other special features, you must do that with other parameters. The motor nameplate data must be correct if any kind of good performance is to be expected.
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Old January 29th, 2010, 02:37 PM   #3
kamenges
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The relationship between the motor rated voltage and the motor rated frequency establishes the volts/hertz relationship at the drive output. For example, if the motor nameplate indicates a 460VAC / 60 Hz motor and you request half speed from the drive the drive will put out 230 VAC at 30 Hz.

Assuming the motor rated voltage is correctly entered and the rated frequency is 60 Hz, entering 75 Hz for a rated frequency will undermagnetize the motor. The motor won't generate the amount of torque one would expect. However, the motor would run above the nameplate rated speed if asked to go to 100% of drive entered nameplate speed.

Keith
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Old January 29th, 2010, 02:45 PM   #4
bigbuckaroo
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I agree 100% about entering the data correctly. What happened is a VFD went bad and a maintenance tech. replaced it. After a couple of days there were complaints as to the pump that the VFD drives was not keeping up with a CIP (clean in place) process. I was asked to look at increasing the maximum frequency in the drive and thats when I noticed the motor rated frequency was at 75 Hz. I put it back to 60 but we have not run it yet in the affected mode so i was just wondering if this was causing the issue.ThanksTom
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Old January 29th, 2010, 03:33 PM   #5
DickDV
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As kamenges said, setting the drive parameter for 75hz on a 60hz motor will starve the motor for voltage over its whole operating range. The result will be less torque so, yes, that may well be the reason that the pump couldn't "keep up".

If, at full speed, you have surplus hp, you can run the motor and pump overspeed as long as the pump is rated for that. Simply set the max drive speed (or hertz) and the max speed reference speed (or hertz) higher than 60hz. Take this in little steps because the motor will run out of hp at some speed and then you can't go any farther.

In any case, the entry for motor nameplate frequency must stay at 60hz.
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