Siemens induction motors- generators cgii Manual De Usuario

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At the first sign of oil discoloration or contamination, 
replace with new oil. Rapid discoloration is caused by 
bearing wear, often from vibration or thrust. Change 
oil as required to keep clean. 

 

When assembling the bearing, it is possible to foul 
the rings so that they will not turn freely. Check ring 
operation by rotating shaft by hand after assembly 

 

 

The 680, and 800 frames use fixed labyrinth oil seals. 
The oil seals should be centered radially on the shaft 
and set so that the radial clearance is  uniform on all 
sides. 

 

The 500, 580 and 1120 frames use self-centering oil 
seals that can accommodate small radial movements 
in the shaft. These floating labyrinth seals should be 
free to move radially in the bearing housing.  A 
jammed seal could lead to bearing overheating and 
poor vibration due to excessive seal rubbing during 
operation. 

 

The primary purposes of the oil seal are: 
1.  To prevent the entrance of dirt into the bearing 

cavity. 

2.  To retain the oil in the bearing cavity. 
3.  To provide pressure regulation in the bearing 

cavity. 

 

To achieve these purposes it is necessary that a 
specific diametrical clearance of oil seal to shaft be 
held.  The cooling fans of the motor tend to create 
suction or pressure in the bearing cavity, which, if 
large enough, will push or draw oil mist out along the 
shaft.  The 500, 580 and 1120 designs are equipped 
with a close fitting air seal that serves as a barrier 
against excessive pressure or suction inside the 
bearing. 
 

 
The bearing cavities and oil seals on the 680 and 800 
frame designs are vented to the outside air in order to 
keep the bearing cavity pressure as close to 
atmospheric as possible. For these designs, it is 

important that the piping and venting for these oil 
seals be kept clean. 
 

When a sleeve bearing becomes worn and requires 
replacement, the labyrinth oil seal should also be 
replaced. 

 
Bearing Clearance Too Large 
The clearance between the journal and the bearing 
will permit the journal center to be slightly below the 
bearing center.  With the motor operating, the 
presence of the oil film between the journal and the 
bearing will cause the shaft to rise slightly. 
Too large a bearing clearance or clogged oil return 
holes in the bearing will permit excessive oil to seep 
out the ends of the bearing.  This seepage, combined 
with the rotation of the shaft, will create an oil mist 
inside the bearing cavity that will tend to leak through 
the oil seals.  Excessive pressure in a force feed 
lubrication system can also cause an oil mist to build 
up. 
 
Cavity Pressures 
Motors are sensitive to the amount of pressure or 
vacuum existing in the bearing cavity.  The table 
below shows the maximum allowable oil cavity 
pressure or vacuum in terms of plus or minus inches 
of water: 
 

 
For the correction of a high or low reading it is 
important that: 
1.  The parts and joints around the bearing cavity 

and oil seals are sealed. 

2.  Condensation drains, piping, sight gauges and 

breathers are functioning properly. 

3. Auxiliary equipment extending into close 

proximity of the motor bearing housings   is 
shielded from the oil seals to prevent a transfer of 
air from inside to outside the motor. (ex. motor 
coupling) 

4. All fixed oil seals are centered properly on the 

shaft.