Derating drive when increasing carrier frequency

I bumped my carrier frequency on my NEMA 4 AC tech 3hp VFD from the baseline of 4kHz to 10kHz.

The manual says that In needs to be derated to 86% to account for this.

When I input the overload current (P108) do I use the full In (9 amps) or 86% of In (7.74 amps). If I use full In, the overload would be at 73% of drive output. If I use the derated In, the parameter should be set to 90%

-Joe

I'm not sure what your question is???

When you up the carrier frequency, the MAX output current decreases. With hitachi drives, temperature actually comes into play. As long as you don't exceed a certain ambient temp, you can up the carrier frequency without derating the drive. That's actually shown in a graph, showing output current, temperature, and carrier frequency. The ONLY thing that happens is the max output current the drive can handle decreases. So, you leave all the settings the same. The overload current should stay the same, if you reduce it you may get overcurrent trips if you push the motor hard. It's got nothing to do with the motor's specs. Honestly, I don't see why you've bumped it up unless the electrical noise was a problem, or the sound it made was obnoxious. Unless there's a reason for changing it, that's actually harder on the components in the drive. It can cause it to operate at higher temperatures, and decrease it's life. Don't put up any higher than it needs to be. The higher it is, the more problems it can cause.

Kinda what I figured.

I went to 10kHz because I hated the high pitch whine the motor made at lower frequencies.

-Joe

The reason for the derating is because it causes the output transistors to produce more heat. Transistors like to be either ON or OFF and it is the region in between that causes them to heat up. They upshot is that if you raise the carrier frequency on some drives and run them at full load for an extended period of time they will fault with an over temp. Not all drives are engineered for a 4kc carrier frequency. Some will take a full load at a 15kc carrier frequency without any sort of derating.

Honestly, I don't see why you've bumped it up unless the electrical noise was a problem, or the sound it made was obnoxious.

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Another reason to bump the freq is that a higher freq sometimes eliminates (or reduces) harmonics. My Hitachi drive had an annoying vibration at the default freq ... increasing the carrier freq reduced that to almost nothing.

I hated the high pitch whine the motor made at lower frequencies.

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You've paid good money to hear that whine - enjoy it

carrier Hz increase

There is also some concern over bearing frosting and early failure with increased carrier frequency. A shaft grounding brush I believe negates most of the potential for this however.

Lloyd H said:

There is also some concern over bearing frosting and early failure with increased carrier frequency. A shaft grounding brush I believe negates most of the potential for this however.

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I have not seen a single documented case where there was a bearing issue when the motors were run at 230 volts.

Plenty of documented cases when the motor was operating at 460 or higher, but nothing at 230.