Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1999-02-23
2001-10-09
Enad, Elvin (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S090000, C310S066000, C310S069000, C310S06800R, C384S448000, C340S682000
Reexamination Certificate
active
06300701
ABSTRACT:
FIELD OF INVENTION
This invention is useful in determining the performance of hydrodynamically lubricated self contained bearings in a dynamoelectric machine (DEM) during operation of the machine. The invention is applicable to the evaluation of the thickness of an oil film and the condition of the oil forming the film, which film is developed by the pumping action of a rotating oil ring mounted on the rotating shaft of a self contained bearing in a DEM.
BACKGROUND OF THE INVENTION
The evaluation of the performance of self contained hydrodynamically lubricated bearings in DEM's has hitherto been a difficult task to perform. Oil rings mounted on a shaft in a bearing assembly are not readily accessible during operation of the DEM for close examination to determine how effectively the lubricating oil is being transferred to the bearing from the oil reservoir located in the bearing housing.
Because the rotation of the oil ring is reliant on frictional engagement between the shaft and oil ring mating surfaces, it is apparent that any disturbance which alters the coefficient of friction between the oil ring and the shaft will lead to increase slippage of the oil ring on the shaft with a resultant consequent decrease in the volume of lubricating oil delivered to the bearing.
It will be readily apparent that as the shaft speeds of DEM's are increased, the oil ring speed must increase with increasing shaft speed to the point where the oil film between the oil ring and the shaft causes the oil ring to begin to slip on the shaft because the drag force on the immersed portion of the oil ring constantly increases as the oil ring moves through the oil reservoir of the bearing. The shearing forces acting on the oil ring continue to increase while the driving force causing the ring to rotate remains relatively constant. At some point the driving force, tending to turn the oil ring, is largely dissipated in overcoming the shear forces of the oil ring moving through the oil in the bearing reservoir and the ring begins to slip.
Attempts to evaluate the effectiveness of this method of lubricating the bearings of DEM's have usually resorted to the visual observation of the rotation of an oil ring which has been suitably marked to enable the observer to count the rotations of the oil ring during operation of the DEM. The correlation between oil ring rotation and the amount of oil delivered to the bearing in a relationship which is relatively easy to establish by those skilled in the tribological art.
SUMMARY OF THE INVENTION
This invention seeks to overcome the deficiencies of the above prior art methods of evaluation of the oil ring performance by measuring the shaft currents existing in the shaft of a DEM. Shaft currents are a natural occurrence in most DEM's and this invention makes use of the occurrence of shaft currents to monitor the lubrication performance of the oil ring lubrication system.
In a first embodiment of this invention, a pair of Rogowski coils are tightly wound around the DEM shaft at the remote ends of the DEM rotor shaft just inside the location of the shaft bearing. The coil ends are fed to a monitoring station through the shaft. The coils are calibrated and the DEM is started. The monitoring apparatus must preferably be capable of measuring the complete spectrum of voltages induced in the Rogowski coils by the shaft flux in order to obtain meaningful data. The shaft currents must pass through the shaft, the oil film on the bearing surfaces, the bearing structure and the machine frame. In the pathway defined above, the only component which is subject to significant change during operation of the DEM is the oil film present in the bearing. The value of the shaft current may be calculated from the signal produced by the Rogowski coils and a steady state value of shaft current may be established when the shaft speed is slow enough to assure that the oil ring is delivering the required design amount of oil to the bearing. At start up of the DEM when an oil film is not present in the shaft bearing interface, the shaft current will usually be at its maximum value. As the speed of the rotor shaft is increased, the shaft current will drop significantly as an oil film is formed in the shaft bearing interface. This condition will continue to exist within the “design” range for the bearing. If the shaft speed is increased beyond the design range, the oil ring will begin to slip on the rotor shaft at some point. At this time, the bearing oil film will be diminished and the resistance to the flow of shaft current through the bearings will drop significantly due to the decrease in oil film thickness. Consequently, the current circulating through the rotor shaft win dramatically increase at this time (as evidenced by the Rogowski coil output) indicating a potential bearing failure is imminent.
The Rogowski apparatus of this invention may be used to study the performance of the lubrication system of the bearings of a DEM whether the oil is pumped into the shaft-bearing interface by an oil ring, or some other kind of oil pump, the above apparatus will provide a meaningful indication of the presence of a bearing oil film in the DEM.
A second embodiment of this invention will disclose the operation of a Rogowski coil apparatus wherein at least one stationary Rogowski coil is mounted on the DEM (preferably on a bearing housing) so as to be concentric with and closely envelop the rotating shaft of the DEM and supply an output signal to monitoring equipment which is indicative of the current flowing in the rotor shaft.
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A Comparison of Techniques for Measurement of Shaft Currents in Rotating Machines 1997 IEEE PE-557-EC-0-01-1997 Ong et al.
Shaft Current Pheuomeuon. Experimental Testing and Analysis of a Large Induction Motor. Proc. of Iasted International Conference High Technology in the Power Industry Orlando Fl. Oct. 27-30, 1997 Org et al.
Performance of Oil Rings R Baudry et al Mechanical Engineering Feb. 1937.
Bearing Oil-Ring Performance—Lemmon et al Journal of Basic Engineering Jun. 1960.
An Analysis of the Effect of Lubricant Supply Rate on the Performance of the 360° Journal Bearing. H J Connors ASIF Transactions 5 404-417 (1962).
Shaft Current in Electric Machines Alger et al Transactions AIGE—Feb. 4-8, 1924.
Dymond James H
Findlay Raymond David
Kay James Victor
Ong Raymond K. J.
Enad Elvin
General Electric Canada Inc.
Lam Thanh
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