OK VFD Gurus---

[GlennH]

Answer me this.

ABB

40hp 208 volt motor

Abb rep comes out to do a start up of this motor, With it running at 100% he tells a co-worker who was there to "watch this". He does something and co-worker says that the noise from the motor dropped by at least 50% but was still running at the same speed. What did he do??:?:?

 

[jim dungar]

Abb rep comes out to do a start up of this motor, With it running at 100% he tells a co-worker who was there to "watch this". He does something and co-worker says that the noise from the motor dropped by at least 50% but was still running at the same speed. What did he do??:?:?

He probably changed the 'carrier frequency' for the PWM output. Effectively the carrier frequency affects the vibration, and therefore the audible hum, of the motor laminations.

 

[ptonsparky]

I've read about doing it but haven't any idea which frequency to skip. Haven't had the need either.

 

[jim dungar]

I've read about doing it but haven't any idea which frequency to skip. Haven't had the need either.

Skip frequency is different than carrier frequency.

Carrier frequency affects the motor.
Skip frquency deals with not allowing certain motor speeds.

 

[Jraef]

What he didn't tell you is that doing so increases the switching losses inside of the VFD significantly. So much so, that you must de-rate the VFD a little because of the added heat rejected by the transistors into the heat sink.

There aint no free lunch...

 

[Besoeker]

What he didn't tell you is that doing so increases the switching losses inside of the VFD significantly. So much so, that you must de-rate the VFD a little because of the added heat rejected by the transistors into the heat sink.

Most, maybe all, that I have dealt with can operate at their rating over a range of switching frequencies.

 

[ptonsparky]

Skip frequency is different than carrier frequency.

Carrier frequency affects the motor.
Skip frquency deals with not allowing certain motor speeds.

Haven't had to do that either.

 

[GOZ]

What he didn't tell you is that doing so increases the switching losses inside of the VFD significantly. So much so, that you must de-rate the VFD a little because of the added heat rejected by the transistors into the heat sink.

There aint no free lunch...

Took the words right out of my mouth.

Alot of great information in this Manual even though it is a bit dated i Recommend the read.

http://assets.fluke.com/AppNotes/ElectricalPower/GO416b_u.pdf