Variable frequency Drives and pumps

[bigbang]

We recently had to change an electric motor (2 pole ,2900 rpm,5 kw) operating at 30 hz through a variable frequency drive.

We replaced it for a 4 pole,1450 rpm and changed the frequency to 60 hz because we had no spare 2 pole motor.

My boss and our plant electrician are currently arguing over this installation.

My boss says it will run better, more efficiently and consume less amps for a given load compared with the original set up using a 2 pole.

The electrician says it will make no difference.

Can anyone tell me who is correct and what is the theory behind your answers.

The motor and pump have been operating now for around 2 days with no problems.

 

[Zoobie]

I suggest posting this in the 'Electric motors & motor controls engineering' forum.

 

[rbcoulter]

I would consult the manufacturer of the VFD. They usually have specific requirements concerning the type/make of motor that can be operated by the VFD. The motor needs to be rated over the frequency range that it will be operated. An off-the -shelf motor may only be rated at one frequency (say 60 Hz).
The problem, I believe, is that a motor operating at low frequency has more difficulty cooling itself and therefore needs to be designed/manufactured accordingly.

 

[Karlando]

Hello!
I changed 1450 rpm 4 kW motor to 2990 4 kW motor, but it took overcurrent all the time at the same flows (waterpump) so I had to change old motor back.
I guess that your boss is right.

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