Supercharging a 3 Phase Motor 1

[GHaulk]

I'm wondering if anyone has any experience with using a 480V 3 phase inverter and connecting it to a 230V 3 Phase motor? I have done this in the past with no problems. I now have an application where I did the same thing in order to over speed the motor and not loose any torque (V/Hz ratio) and at around 10 hertz, the motor is pulling too many amps. I was wondering if I wired it back to 480V and reprogrammed the drive, if I would see better results at the low end? I am using a Leeson Gear Motor 230/480VAC and a PowerFlex4M drive.
Thanks

 

[DickDV]

It sounds like you've left the base frequency at hz. For double voltage you'll need double frequency in order to keep the V/Hz ratio constant.

 

[waross]

Good catch, Dick.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[GHaulk]

I tried wiring the motor back to 480V and reprogramming the drive accordingly and it worked. This particular motor will not need to run very fast. (as I recently found out) By the way, the drive was set so that the motor rated Hz was 120 and the Max. Hz. was set to 120. Did I miss something else?

 

[rockman7892]

Dick

It sounds like what you are suggesting is that if the base frequency of 60hZ was set in the drive than the drive V/Hz ratio would have been set for 480/60 = 8 V/Hz.

Because this V/Hz is higher than the motor was designed for as a given speed such as 10hZ the fulx density in the motor would be too high and the motor could be driven into saturation which is causing the high current as mentioned.

 

[EEBubba]

Also, be aware that when you change the base frequency you also need to look at the carrier frequency. The carrier frequency helps determine the “Sinewav-iness” of the produced power; a higher carrier gives you more square waves with which to approximate a perfect wave.

For Example:

60 Hz fundamental frequency with a 5 kHz carrier frequency : 83 Pulses per 360° of sinewave.

120 Hz fundamental frequency with a 5 kHz carrier frequency : 41.5 Pulses per 360° of sinewave.

When you operate below a certain number of pulses per sine wave revolution you begin to see odd effects and some fairly harsh spike voltage dv/dt effects and harmonic influences. All of these lead to increased temperature or insulation degradation and premature failure of the winding.

I was once told that the ideal is around 76 Pulses per 360° sinewave electrically to get a “clean” sinewave.

That being said this is not my main focus and I would welcome any discussions about my math or assumptions.