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Thread: OT: Starting a 350HP 2400 volt synchronous motor with rotating 'stator'

  1. #1
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    Default OT: Starting a 350HP 2400 volt synchronous motor with rotating 'stator'

    According to the uploader, the 90-year-old motor runs the main line shaft of a flour mill.

    https://www.youtube.com/watch?v=fNuI6keQXYA

  2. #2
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    My best guess - planetary gear box situation, you cannot start the motor up that's linked to so much drag from a dead stop or it will just sit there and cook it's guts,

    Sooo - you allow the planetary system to have a "way out" - still with a thing of mass that takes allot of force to get up to speed but once it does the motor is operating within it's range and the stored mass gets everything going,,, the guy cranking the handle transfers that stored mass to getting the mill "up and running" pretty ****ing cool...


    Edit; oh damn im thinking like a mechanic again lol


    I just read the title of your post and that explains everything to me --- so solly did not mean to mislead... lol but yes do have a grasp on electrical to at least know what the title meant...



    Edit; original though was not even a ggood one by a mechanical engineer --- for the braking system would have to be linked to something of use (and therefore rotating as it braked) otherwise its just power wasted into pure friction,,,

    lot's of drinkng tonight so "excuuuuuuuuuuuuse me"

    Edit ; oh phuck but even mechanical sustems have a range - and especially electrical --------------------- sooooooooooooooooo getting the drive unit up to speed could be the main directive - and themn clamping down to either electically engage or mechanically is the same difference... once at optimum performance let things stabalize

    edtie ; goodammit now eveyone knows how my brain works when im drunk - kit's don't do this and hom,///
    Last edited by A.K. Boomer; 05-15-2019 at 01:49 AM.

  3. #3
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    Quote Originally Posted by A.K. Boomer View Post
    My best guess - planetary gear box situation, you cannot start the motor up that's linked to so much drag from a dead stop or it will just sit there and cook it's guts,

    Sooo - you allow the planetary system to have a "way out" - still with a thing of mass that takes allot of force to get up to speed but once it does the motor is operating within it's range and the stored mass gets everything going,,, the guy cranking the handle transfers that stored mass to getting the mill "up and running" pretty ****ing cool...


    Edit; oh damn im thinking like a mechanic again lol


    I just read the title of your post and that explains everything to me --- so solly did not mean to mislead... lol but yes do have a grasp on electrical to at least know what the title meant...



    Edit; original though was not even a ggood one by a mechanical engineer --- for the braking system would have to be linked to something of use (and therefore rotating as it braked) otherwise its just power wasted into pure friction,,,

    lot's of drinkng tonight so "excuuuuuuuuuuuuse me"

    Edit ; oh phuck but even mechanical sustems have a range - and especially electrical --------------------- sooooooooooooooooo getting the drive unit up to speed could be the main directive - and themn clamping down to either electically engage or mechanically is the same difference... once at optimum performance let things stabalize

    edtie ; goodammit now eveyone knows how my brain works when im drunk - kit's don't do this and hom,///
    We'd never have noticed............if you hadn't mentioned it...
    The comments accompanying the video explain it pretty well...
    Keith
    __________________________
    Just one project too many--that's what finally got him...

  4. #4
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    rough morning - not even going to re-read that as my brain was squirming like a toad...

    I should have just edited it all blank but wanted to leave it as an example should anyone else think it a good idea to pound down a liter of red and then get on line and try to get technical...

  5. #5
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    Large synchronous motors have zero starting torque. The state of the art starting method is to generate a rotating field electronically with a relative of a VFD. Older motors have small squirrel cage windings buried in the rotor pole faces, that provide enough torque to get the rotor spinning if there is minimal load. The method in the video is another way to get the rotor spinning before switching over to synchronous operation.

  6. #6
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    thanks for the proper explanation --- it's an interesting vid and if the things been around that long you know they have burned through many sets of linings on that band brake,,, and you know the earlier linings were most likely made of you know what,,,

    so you got this guy in close proximity who I might add is probably getting winded while cranking and all kinds of fibers flying around right in front of him, don't think it's a job I would want without wearing a mask and bringing a change of cloths for after....

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    Quote Originally Posted by rklopp View Post
    Large synchronous motors have zero starting torque. The state of the art starting method is to generate a rotating field electronically with a relative of a VFD. Older motors have small squirrel cage windings buried in the rotor pole faces, that provide enough torque to get the rotor spinning if there is minimal load. The method in the video is another way to get the rotor spinning before switching over to synchronous operation.
    This doesn’t sound right to me. A synchronous motor has a DC field fully developed right from the start and when 3 phase power is dropped onto the the motor stator you are going to have massive torque instantly. That would tear up everything. So this thing has a planetary gear reducer where the ring gear is free to rotate so no torque is applied to the load. Then braking the ring gear starts applying torque to the load slowly so this is just a clutch mechanism because they don’t have reduced voltage start for the motor.

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    Quote Originally Posted by rklopp View Post
    Large synchronous motors have zero starting torque.
    Not true. 40 years ago, I designed installations for several synchronous motor driven compressors that ranged in power from 800 to 2500 hp all below 600 RPM and also brushless. All were permanently coupled to their compressors and all were started across the line at 2300V. They came up to speed in induction mode on the damper windings( similar to a squirrel cage) on the rotors and as soon as the rotors were at speed and in proper angular position relative to the stator field, the brushless excitation system applied rotor winding power and it snapped into synchronous mode. The compressors were started unloaded of course, but there were significant inertia and pumping loses present even then. The compressors were 2 or 4 cylinder multistage with up to 30,000 psi output pressures.

    RWO

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    Quote Originally Posted by RWO View Post
    Not true. They came up to speed in induction mode on the damper windings( similar to a squirrel cage) on the rotors and as soon as the rotors were at speed and in proper angular position relative to the stator field, the brushless excitation system applied rotor winding power and it snapped into synchronous mode.
    RWO
    My point exactly. The motor has no useful torque in synch mode when starting, so they have to relay on another starting means, like the damper windings ("obturator" windings, I think they are sometimes called).

  10. #10
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    Quote Originally Posted by garyhlucas View Post
    ...you are going to have massive torque instantly. ...
    Nope, completely the opposite. Otherwise, there would be no need for the auxiliary starting monkey-business. The average torque is zero. Sure, you could argue there is large torque, but it is oscillating at 60 Hz, and the rotor's massive inertia can't keep up.

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