New-to-me term: "High Saturation Motor"
New-to-me term: "High Saturation Motor"
(OP)
I've been in this business 30+ years, yet today I heard this for the very first time from a customer wanting me to help him specify a VFD. He has an 18 pole 200HP AC SCIM and all the time we were talking, he kept want me to assure him that I understood that "this is a high saturation motor, it's not like a regular motor. I need you to understand that when you spec the drive." Not being born yesterday, I gave the appropriate nods and grunts, said "No problem" and eventually went away leaving him satisfied that he was understood. I later found out that I was the first person he has not rejected for this task, all of the others said they didn't understand what he meant by "high saturation motor", and he would promptly escort them out the door. Sometimes old age and treachery win out I guess.
The problem is, I of course have no idea what he means by that either, I was just smart enough to let him finish talking. Now I'm curious if this is anything anyone else knows about. I understand what being an 18 pole motor will mean to the VFD, it's just the term "high saturation" I'm curious about.
Anyone?
The problem is, I of course have no idea what he means by that either, I was just smart enough to let him finish talking. Now I'm curious if this is anything anyone else knows about. I understand what being an 18 pole motor will mean to the VFD, it's just the term "high saturation" I'm curious about.
Anyone?
"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
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RE: New-to-me term: "High Saturation Motor"
Guess 1 - The volts per hz required to get to saturation is high (compared to nameplate base volts/hz).
Guess 2 - The nameplate base volts per hz already puts portions of the iron far into saturation
Thinking about design of slow speed motor, it is more likely to be designed like Guess #1. It is harder to magnetize the larger airgap circumference, and these tend to operate at lower airgap flux densities, generally resulting in lower tooth flux densities. Also the backiron tends to be larger for structural reasons, resulting in lower back iron flux densities.
Just a guess. Could be totally wrong.
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(2B)+(2B)' ?
RE: New-to-me term: "High Saturation Motor"
That could suggest another guess:
Guess 3 – “High saturation motor” = motor made with “high saturation” alloy steel.
I’m not up on cutting edge technology, but from the discussion it seems unlikely to use this unless there is some reason this motor needs to be compact. If guess 3 were correct, I don’t think it would tell us much useful. Knowing the physical flux density limit of the iron doesn't tell us where it lies in relation to operating flux density (presumably machine would be designed to take advantage of the high flux density steel).... so we wouldn't particularly know any more about the volts/hz behavior of a guess-3 type motor than we would any other.
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(2B)+(2B)' ?
RE: New-to-me term: "High Saturation Motor"
"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> FAQ731-376: Eng-Tips.com Forum Policies
RE: New-to-me term: "High Saturation Motor"
In a "standard" induction motor, you cannot raise this setting much higher than that which would result in the Volts/Hz at regular 50/60 Hz line operation for the motor. This is because achieving higher magnetic saturation levels costs money, and there is no advantage to this in off-the-line or even most VFD applications.
When running these motors under field-oriented control, you can reduce the magnetization current above this base speed (field weakening) to extend the high speed range of the motor by reducing its back EMF constant. But you cannot to any significant degree increase the magnetization current at lower speeds to increase the torque capabilities, due to magnetic saturation of the rotor.
However, if you have a motor with a higher rotor magnetic saturation level, you can increase the magnetization current to much lower speed values, permitting increased torque levels there. This extends the constant power range of the motor so it goes both above and below the "base speed" of the motor. I'm pretty sure that the induction motors used in electric vehicles like the Tesla (and the old EV1) have high rotor saturation levels, because operation in the constant power range provides a continuously variable software transmission.
Curt Wilson
Delta Tau Data Systems
RE: New-to-me term: "High Saturation Motor"
My day is complete now because I have learned something new. Thank you so much.
I'm taking the rest of the day off.
"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> FAQ731-376: Eng-Tips.com Forum Policies
RE: New-to-me term: "High Saturation Motor"
-SceneryDriver
RE: New-to-me term: "High Saturation Motor"
In a nutshell vector drives, be they "Sensorless" or "Closed Loop" vector drives* , require the development of a complex mathematical motor model and the monitoring of the motor performance via a feedback signal; an encoder if it is "closed loop" vector or Field Oriented Control, a current monitor inside of the drive if it is "Sensorless" Vector Control. They use that model and the feedback signal to determine an error in performance agains what you have commanded the drive to do, then apply the best algorithm in determining the correct vectors of all of the output current components to get the motor to reduce that error. Less expensive drives tend to have less complex vector algorithms, which means you may not have the ability to program in the magnetic current control component separately, or separately enough, to be of use in this situation. That was the case with the drive that the customer had been asking for because he wanted to match existing drives in use elsewhere. So with the info from Curt, I moved him up into a more advanced drive to allow this to take place.
Thanks again Curt and you too E-pete if for nothing more than the signpost.
*(None are really without sensors of some kind, all are really closed loop in some way, this is just how the market describes them for simplicity's sake.)
"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> FAQ731-376: Eng-Tips.com Forum Policies
RE: New-to-me term: "High Saturation Motor"
RE: New-to-me term: "High Saturation Motor"
RE: New-to-me term: "High Saturation Motor"
Scenery Driver - As jraef explained, the drive must have the smarts to be able to vary the magnetization current level automatically as a function of speed to exploit this feature. Many simpler drives cannot do this.
Brad1979 - I'm not a motor design expert, but I'm pretty sure that the difference is in the material (and maybe the treatment) of the rotor core's steel laminations (more than the geometry, which doesn't. Pete gives an example above of a cobalt steel with a much higher saturation point than typical steels.
OperaHouse - It's the Volts/Hertz ratio actually used, which determines the airgap flux density, that matters, not the available voltage. Remember that a drive will modulate the available voltage at every instant.
Curt Wilson
Delta Tau Data Systems
RE: New-to-me term: "High Saturation Motor"
"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> FAQ731-376: Eng-Tips.com Forum Policies