Maintenance
Rotor Cleaning
Remove rotor. Inspect and clean.
Stator Cleaning
MICLAD™ form wound VPI (vacuum pressure impregnated) insulated coils may be cleaned with a quick drying solvent and lint free cloths or steam cleaned with
The stator winding insulation resistance should be measured before and after any cleaning operation.
The windings may be cleaned with a solvent compatible with the insulation system and oven dried. Water and detergents with an oven drying cycle may be used as an alternate on MICLAD™ VPI insulation systems.
MICLAD™ is a Siemens trademark.
DANGER
Hazardous voltage.
Will cause death, serious injury, electrocution or property damage.
Disconnect all power before working on this equipment.
CAUTION
High Voltage.
May damage
Disconnect from circuit before testing insulation resistance.
Insulation Resistance
Check insulation resistance periodically. Use a hand cranked or solid state insulation resistance tester and test with at least 500 volts, but not greater than motor rated voltage.
For motors with newer insulation systems such as MICLAD™ VPI, the insulation resistance after one minute should be greater than 1000 megohms. (Values in excess of 5000 megohms are common.) For older motors, the minimum value recommended in IEEE Standard 43 can be used. The value in
megohms, when corrected to 40°C, is equal to the motor rated voltage in kilovolts plus 1. For example, for a motor with a rated voltage of 2300 volts, the limit value would be:
2.3 + 1 = 3.3 (megohms).
Drying Insulation
If the insulation resistance is less than satisfactory, and the cause is believed to be excessive moisture in the windings, dry the windings by applying heat from:
1.A warm air oven.
2.Electric strip heaters.
3.Circulating currents through the coils.
The heat should be applied slowly so the desired temperature will not be obtained in less than six hours.
Insulation Drying Temperature*
Class “B” | Class “F” | Class “H” |
|
|
|
200°F | 245°F* | 275°F* |
94°C | 118°C | 135°C |
|
|
|
*Class “F” and “H” insulated units should be baked at 70% specified temperature (to avoid steam inside winding) for about six hours, before temperature is raised to drying temperature.
Insulation resistance should be measured before the heat is applied, and every six to eight hours thereafter.
NOTE
Insulation resistance will decrease as the motor warms up; but will begin to increase as the drying process continues.
A uniform temperature must be maintained in the motor to obtain constant resistance readings. When the megger readings remain constant, the drying process is complete and may be discontinued. Check for other causes if readings are still low.
Warm Air Oven Drying
1.Remove bearing housings.
2.Remove rotor.
Bake in oven at temperatures specified in Insulation Drying Temperature table, and follow procedures described for drying insulation.
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