ARM ASSEM. 3N0577 - Caterpillar

Do not operate the generator if the windings are wet. If the generator is operated when the windings are wet, damage can occur due to insulation breakdown.
When moisture is present or when moisture is suspected in a generator, the generator must be dried before being energized. For information on drying the generator, refer to Testing and Adjusting, "Insulation - Dry".If the drying procedure does not restore the insulation resistance to an acceptable value, the winding should be reconditioned.Note: For additional information, refer to Special Instruction, SEHS9124 .Drying Methods
The following methods can be used for drying a generator:
Self-circulating air method
Oven method
Controlled current method
Do not allow the winding temperature to exceed 85 °C (185.0 °F). Temperatures that are greater than 85 °C (185.0 °F) will damage the winding insulation.
Self-Circulating Air Method
Run the engine and disconnect the generator load. running the engine will help circulate air. Operate the generator space heaters.Oven Method
Place the entire generator inside a forced air drying oven for 4 hours at 65 °C (149 °F).
Use a forced air type oven rather than a radiant type oven.Radiant type ovens can cause localized overheating.
Controlled Current Method
Illustration 1 g00614674
External Power Source Circuit (1) Battery (12 VDC) (2) Rheostat (15 Ohm 25 W) (3) Exciter field (stator "L1")
Table 1
TOOLS NEEDED    
Part Number     Tool     Quantity    
225-8266     Clamp-on Ammeter (1200 A)     1    
    External Power Source Circuit     1    Heat can be used in order to dry the generator windings. This heat can be created by allowing a controlled current to flow through the generator. No high voltages are generated during the following procedure. Therefore, insulation breakdown will not occur.
Make an external power source. Refer to Illustration 1.
Disconnect F1+ from the voltage regulator. Disconnect F2- from the voltage regulator. Disconnect the generator load. Connect the generator output leads T0, T1, T2, and T3 together. Install the clamp-on ammeter to generator output lead T1.Note: When the line current is measured on multiple lead units, measure the current in each conductor per phase. The currents can then be added.
Refer to Illustration 1. Adjust the rheostat to the maximum resistance value. Connect the external power source to wires F1+ and F2-.
Start the generator set. Run the generator set at idle speed.
Do not exceed the rated phase current that is listed on the generator nameplate. Exceeding the rated phase current will easily damage the generator windings.
Monitor the phase current. Gradually increase the engine RPM. Increase the engine RPM until one of the following conditions are met:
The rated phase current is obtained.
The full generator set speed is obtained.
If more phase current is necessary, slowly turn the rheostat. Turn the rheostat until the rated phase current is reached.
On an hourly basis, stop the drying procedure. Check the insulation resistance. Repeat the above steps until the insulation resistance is acceptable.