Frequency / Current motor curve
Frequency / Current motor curve
(OP)
I have a 460 VAC 200 HP electric motor rated 1800 RPM
I am using a VFD (45 HZ) to run this motor at 1400 RPM
My load is a fan pulling 180 HP at that speed
The problem I am having is that my VFD faults out because of a over current situation.
Is there a graph/curve showing generally what is happening with frequency and current with a constant load or can someone explain what is happening here.
Thanks.
I am using a VFD (45 HZ) to run this motor at 1400 RPM
My load is a fan pulling 180 HP at that speed
The problem I am having is that my VFD faults out because of a over current situation.
Is there a graph/curve showing generally what is happening with frequency and current with a constant load or can someone explain what is happening here.
Thanks.





RE: Frequency / Current motor curve
Do the maths: decrease voltage to 78% of base volts. Decrease power to 90% of base power. Current has to go up to 115% of base amps to maintain this relationship.
Power factor might skew the numbers a little, but the principle holds: your drive isn't big enough.
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RE: Frequency / Current motor curve
The HP/Speed relationship is essentially linear. So (assuming 60Hz) at 45Hz you are at 75% speed, the HP load the VFD can provide for is 75% of 200HP or 150HP. You have 180HP connected to a drive and motor that can only provide 150HP, it's the definition of an Overload.
Either reduce the load (air flow) or buy a bigger motor and drive.
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RE: Frequency / Current motor curve
This application is belt driven, so if I swap my motor sheaves and run this setup at 90 HZ while maintainig the same load from the fan. Would this approach eliminate the over current problem.
RE: Frequency / Current motor curve
RE: Frequency / Current motor curve