Announcement

Collapse
No announcement yet.

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

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Tobias-B
    replied
    ...I just kept waiting for smoke to start coming off the brake band...

    that was cool.

    t

    Leave a comment:


  • J Tiers
    replied
    They do, since they can have a lot of poles. IIRC, a 50 Hz synch motor can have a normal speed of as low as about 75 rpm. Must have torque out the wazoo, since the diameter for a motor of significant power is large.

    Leave a comment:


  • tlfamm
    replied
    Originally posted by J Tiers View Post
    Very interesting. Technically, nothing much new, but an interesting application technique that gets around many of the normal issues, by moving the location of the clutch, so it is not between the load and the motor.

    ...
    If it is true, as I read, that synchronous motors have inherently lower speed than equivalent (and more common, at the time?*) induction motors, substituting the former for the latter in an industrial setting potentially removes any intervening mechanical speed reduction, bringing motor and load that much closer. However, the complexity, cost, and maintenance of the speed reducer is more or less transferred to the startup-related mechanisms of the supersynchronous motor.


    * more common: meaning commonly used in start-under-load applications
    Last edited by tlfamm; 05-17-2019, 09:55 AM.

    Leave a comment:


  • J Tiers
    replied
    Very interesting. Technically, nothing much new, but an interesting application technique that gets around many of the normal issues, by moving the location of the clutch, so it is not between the load and the motor.

    Actually does use the concept of the rossman drive, but uses the variable speed only for starting. Puts a heck of load on that clutch, but so would the normal arrangement of a clutch between motor and load.
    Last edited by J Tiers; 05-16-2019, 10:48 PM.

    Leave a comment:


  • tlfamm
    replied
    Several youtube posters have identified the motor under discussion as a "supersynchronous" motor; here is an in-depth, satisfying discussion of same:

    https://forums.mikeholt.com/showthre...61#post1722161


    Full credit to poster Phil Corso of the Mike Holt website for the linked information.


    Here's a very short article in the publication "The Blast Furnace and Steel Plant", April 1923, when the supersynchronous motor was still considered a "recent" development:

    https://books.google.com/books?id=Ua...page&q&f=false
    Last edited by tlfamm; 05-16-2019, 10:12 PM.

    Leave a comment:


  • J Tiers
    replied
    That is an interesting motor. I wonder if it was originally made for a "Rossman" drive, which is an old variable speed drive where the outer portion of the motor, the part that has the brake in the video, is driven with a DC motor that can be varied in speed by series armature and field resistors.

    With that old drive, the total power is considerably less than using a variable speed DC motor would have used. The output rpm is the difference of the synchronous rpm and the rpm of the outer portion.

    These days, it would probably be done with a VFD, but back then there was no such option. The drives were made up to 2500 HP or more.

    Leave a comment:


  • Noitoen
    replied
    About 40 years ago when we were in South Africa, my father an I built a 75 KVA 3 phase 50Hz power stabilizer by coupling 2 brushless alternator front to front on a single shaft. One of the alternators worked as a synchronous motor and the other as a alternator. To start, we made a centrifugal switch that shorted the 4 pole rotor windings up to around 1300 RPM. After this speed, the short was removed and the alternator's AVR regulated both motor and alternator voltage. Before modern electronics this was a good method to power a instruments calibration shop.
    There was very little "hesitation" of the rotor at startup but there was no load untill the regulator was connected.

    Leave a comment:


  • MaxHeadRoom
    replied
    A while ago I used to maintain some 100+hp old synchronous motors driving 1 'lung' compressors, they stood about 6ft+ tall.
    The motors were ran up as induction motors, they also had a rotor winding with a pair of slip rings, the slip rings served double purpose by detecting the slip frequency, when it was up to around 5-7 cycles slip, then DC was injected into the slip rings and the motor came up to 60Hz sync.
    They sound similar to those of RWO!
    Max,
    Last edited by MaxHeadRoom; 05-15-2019, 03:29 PM.

    Leave a comment:


  • rklopp
    replied
    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.

    Leave a comment:


  • rklopp
    replied
    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).

    Leave a comment:


  • RWO
    replied
    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

    Leave a comment:


  • garyhlucas
    replied
    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.

    Leave a comment:


  • A.K. Boomer
    replied
    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....

    Leave a comment:


  • rklopp
    replied
    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.

    Leave a comment:


  • A.K. Boomer
    replied
    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...

    Leave a comment:

Working...
X