Cryogenic motor torque and start current 2

[760106]

I am now working for LNG receiving terminal. This is the first time I contact with it. I am interested in LNG pump and motor.I know that the torque and current of motor in cryogenic condition is much lower than the that of motor in normal condition.I also know that is beacause of the cryogenic temperature changing the characters of motor. Is any body know the detailed reason about this much diffirence between the cryogenic and normal condition motor? can anybody give me detailed analytical procedure about it or recommend some books for me? If that, I will greatly appreiate his help.

 

[vanstoja]

Further description of the method of motor cooling in cryogenic pumpmotor is needed as well as the motor winding temperatures likely to be involved. If the motor is process-fluid cooled and the cryogenic coolant flowing through the the gap between the ststor and rotor has a density much greater than air then fluid and friction losses will be much higher than occur in an air cooled motor. Furthermore if the stator windings are protected from coolant immersion by a non-magnetic metal sleeve/liner/can then stator can losses will occur which are also not found in conventional air cooled motor. For these reasons water-cooled canned motor pumps used in some powerplant applications have motor efficiencies typically 10 to 15 points lower than air cooled motors of the same horsepower rating. Further effects on motor performance would accrue if motor winding temperatures approach cryogenic fluid temperatures of the order of -300F. Certainly, the winding conducter resistances would be vastly different but I have no idea how motor efficiency or other motor performance characteristics would affected by very cold windings.

 

[jraef]

I have done a bit of work on LNG pump controls for a cryo pump mfgr. From my understanding, it isn't so much that the pump motor characteristics are so different, it is that the application must be severely limited, mostly for the reasons mentioned by vanstoja. The pump and motor are immersed in the LNG, and use it as the lubricant and coolant. If the rotor temperature is allowed to raise too high, it vaporizes the surrounding LNG and you lose both lube and colling at virtually the same time, leading to instant destruction of the motor. So to ensure that this doesn't happen, the motors are severely derated making the efficiencies look bad when compared to motors of equal HP ratings in other applications.

From a learning standpoint however, you may be out of luck. All of the LNG pump motors that I am aware of are specially designed by the pump manufacturers, so any books or publications are going to be proprietary. I know of one decent report that does have some details on pump and motor construction, but it costs $997.00!

"Our virtues and our failings are inseparable, like force and matter. When they separate, man is no more."
Nikola Tesla

 

[Pumpinterest]

vanstoja,
I am sorry that I can not understand very well the words that "if the stator windings are protected from coolant immersion by a non-magnetic metal sleeve/liner/can then stator can losses will occur".
is that words meaning the magnetic loss?