Thread: VFD question
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Old January 12th, 2021, 07:59 PM   #11
GaryS
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Join Date: Aug 2003
Location: Lancaster Pa.
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A few things to think about on this
The voltages don’t sound right 400V Delta / 600V Star
The windings are usually all the same voltage meaning 400V Delta / 800V Star
The Star / Delta is usually a start up configuration to limit the starting inrush
Delta is a single winding phase to phase voltage is 400v
Star is 2 winding in series to a center point each winding is still 400v
2 400v windings in series “ Star” would be a phase to phase line voltage of 800v
You say it as a 50hz system what is the number of poles on the motor or the base speed of the motor.
A 2 pole motor at 50 hz would have a base speed of 3000 rpm
If as you say the vfd set point is 120Hz then a 2 pole motor would run at 7200 rpm. That’s way over the what would be a normal running speed and could be in a dangerous condition. Anything over 5000 rpm should be considered carefully
Most consider 3000 to 3500 rpm the max for a motor
I have done jobs where we ran a motor over 7000 rpm but I had the motor rebuilt with precession bearings and had it balanced to the expected max speed never had a problem with them but as I said before I took the time to have the motor redone to meet my needs.
Remember with an ac motor running below base speed it’s running in constant torque and variable HP and above base speed it’s running at constant hp and variable torque. With a set point of 120hz it sounds like the equipment was originally from North America with a max output freq of 120hz
400v on the vfd would mean it’s a 400v class 400v to 480v input
You can select the operating the output voltage Volts / Hertz 400v motor would be 8v per hertz that would also be the same volts / Hertz as 480v 60hz motor
What you show is possible but proceed with caution
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