Siemens 580 Benutzerhandbuch

- 18 - 

 
Electric Strip Heater Drying 

1.  Remove bearing housings. 
2. Remove 

rotor. 

3.  Direct a fan on stator to carry away the moisture. 
4.  Attach temperature indicators to winding and 

apply heat as specified in the Insulation Drying 
Temperature table and follow procedures 
described for drying insulation. 

5.  Radiant type heaters are not recommended 

because some parts may become scorched 
before remote parts reach desired temperature. 

 
Circulating Current Drying 

1.  Remove bearing housings. 
2.  Center the rotor in the stator core. 
3.  Wedge fiber strips into the lower part of the air 

gap so rotor does not touch stator core, or 
remove rotor. 

4.  Direct fan on unit to blow away excessive 

moisture. 

5.  Attach temperature indicators to windings. Do not 

exceed the drying temperatures in the Insulation 
Drying Temperature table. 

6.  An external source of current can be used to 

circulate direct current through the winding of any 
type of alternating current motor. A portable low 
voltage motor-generator set, such as is used for 
welding, is usually suitable. 

 
When this method is used on the stator, the stator 
phases may be connected in series or in parallel to 
suit the available power supply if both ends of all 
phases are accessible.  If only three leads are 
brought out of the motor, the current may be 
circulated between one terminal and the other two 
connected together.  If this is done, the temperature 
of the single lead connection must be checked 
frequently, and it is desirable to shift the leads 
occasionally.  Usually 50 to 100% of full load current 
will produce the required temperature. The dc voltage 
required for this current will be 0.25 - 5.0% of the 
normal voltage per phase, and the corresponding 
power will be 0.50 - 3.25% of the rating. 
 

 
Alternating current can be used on the stators of 
squirrel cage induction motors if the rotors are 
removed.  Alternating current is usually not as easy 
to control as required voltage control, and a.c. 
requires a higher voltage source, approximately 10 to 
30% of the rated winding voltage.  In addition, care 
must be taken that miscellaneous parts adjacent to 
the windings, such as lead studs, core supporting 
member, etc., do no overheat due to induced 
currents and the lack of normal ventilation. 
 

May cause damage to insulation. 

Avoid hot spots and radiant type heat 

 

Long life of bearings is assured by maintaining proper 
alignment, belt tension, and lubrication at all times.  
Incorrect alignment of solid and flexible couplings can 
cause excessive load on bearings, and excessive 
vibration and thrust.  Misalignment of belt drives can 
cause thrust or harmful shaft oscillation.  Improper 
alignment of gear drives will produce shock loads and 
may bend the shaft. 
 
Excessive belt tension often causes overheating and 
failure of bearings. Bearings tend to overheat when 
pulley centers are too close, pulley diameters are too 
small, or belt speed is too high. 
 
Bearing Construction 
Two types of bearings are employed in induction 
motors.  These are; 
 
1. Antifriction 

bearings. 

2. Sleeve 

bearings. 

 
The type of bearing mounting and supporting 
structure will depend upon the type of bearing. 
 
Bearing housing construction will also vary with the 
type of bearing.  Antifriction bearing motors have one 
piece bearing bracket construction.  Sleeve bearing 
motors have split bearing housings.