Permanent Magnet Motors

[tom baker]

An article in Treatment Plant Operator magazine reviewed permanent magnet motors and that the efficiency can be 94% as there is no slip, but they must be started with a VFD. Also mentioned that motors pull less current you can use a smaller wire, but the NEC sizes motor branch circuits very conservatively, and efficiency is not considered.
Any one have any experience with permanent magnet motors?
Here is the article https://www.tpomag.com/editorial/20...efficiency-pump-motors-from-franklin-electric

 

[letgomywago]

I dont have any experience but it would be interesting if we got another addition to the motor overcurrent table.

 

[zbang]

FWIW, there are videos of large PM synchronous motors being started direct-on-line (

for one of them).

 

[ptonsparky]

I just read an article about PM motors with the cost savings due to their efficiency. I understood they all needed to be used with a VFD.

 

[Sahib]

Please correct me if I am wrong: Due to high starting current of high efficiency motor, a vfd is needed.

 

[ptonsparky]

Please correct me if I am wrong: Due to high starting current of high efficiency motor, a vfd is needed.

Not due to the starting current directly, but to get the motor turning first of all. That is already more than I know.

 

[Sahib]

Not due to the starting current directly, but to get the motor turning first of all. That is already more than I know.

But post by zbang above states direct on line starting of PM motors.

 

[ptonsparky]

But post by zbang above states direct on line starting of PM motors.

I know. That's what has me confused.

I should have put in one of these .

 

[Sahib]

I know. That's what has me confused.

I should have put in one of these .

Okay, okay. The truth is it is for application requirement.

 

[winnie]

At least some types of synchronous motor have rotor cage windings which permit operation as an induction motor during startup.

-Jon

 

[Sahib]

They are called line start permanent magnet synchronous motors.

 

[Besoeker3]

An article in Treatment Plant Operator magazine reviewed permanent magnet motors and that the efficiency can be 94% as there is no slip, but they must be started with a VFD. Also mentioned that motors pull less current you can use a smaller wire, but the NEC sizes motor branch circuits very conservatively, and efficiency is not considered.
Any one have any experience with permanent magnet motors?
Here is the article https://www.tpomag.com/editorial/20...efficiency-pump-motors-from-franklin-electric

I had some experience with those. It was a different division of the company but I still got involved. These were used in the aircraft industry, mostly for Boeing. These were around 56 kW, 800 Hz., water cooled. If I remember correctly, the magnets were Samaritan Cobalt. I don't know if that helps.

 

[zbang]

Sounds like a lot of this discussion comes to "Never generalize."

 

[Sahib]

I had some experience with those. It was a different division of the company but I still got involved. These were used in the aircraft industry, mostly for Boeing. These were around 56 kW, 800 Hz., water cooled. If I remember correctly, the magnets were Samaritan Cobalt. I don't know if that helps.

The implied question of OP it seems is whether smaller size branch circuit for PM motors may be used than is permitted by code.

 

[Besoeker3]

The implied question of OP it seems is whether smaller size branch circuit for PM motors may be used than is permitted by code.

In this case the issues were:
The small physical size
The water cooling
The operating speed
The dynamics. This was awesome. One rotation from full speed to zero and within degree. There was no code requirement.