CASE-DIFFERENTIAL 5197018 - Caterpillar

Personal injury or death can result from improper troubleshooting and repair procedures.The following troubleshooting and repair procedures should only be performed by qualified personnel familiar with this equipment.
Refer to Safety Section, "Generator Isolating for Maintenance" for information regarding the procedure to safely isolate the generator.If the insulation resistance values are less than the recommended values, one of the following drying procedures must be selected. This decision should be based on the following factors:
the size of the unit
the location of the unit
the equipment that is available
the experience of personnelNote: For more information on drying methods, refer to Special Instruction, SEHS9124, "Cleaning and Drying of Electric Set Generators".Remove the voltage regulator. Cover all of the inlet openings. Cover all of the discharge holes. Provide an opening at the top of the machine. This opening will allow moisture to evaporate. Preferably, this opening will be located at the fan end. Monitor the winding temperatures. DO NOT APPLY HEAT TOO RAPIDLY. Winding temperature should be raised gradually at a rate of 10 °C (50 °F) per hour up to 85 °C (185 °F). Measure insulation resistance in 1 hour intervals. Typically, the insulation resistance will slowly drop while the temperature is rising. The insulation resistance will then start to increase at a slow rate until the insulation resistance reaches a constant level. The following methods can be used for drying a generator:
Self-circulating air method
Oven method
Controlled current methodSelf-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
Table 1
Tools Needed
Part Number Description Qty
225-8266 Ammeter Tool Gp 1
External Power Source 1
Rheostat 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.
Illustration 1 g00669571
Generator Wiring Diagram
(CR1-CR6) Diodes
(CR7) Varistor
(L1) Exciter field (stator)
(L2) Exciter armature (rotor)
(L3) Main field (rotor)
(L4) Main armature (stator)
(L5) Pilot exciter armature
(PM) Permanent magnet
(RFA) Rotating field assembly
(CST) Customer supplied transformer
Make an external power source.
Refer to the above diagram. 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". 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 the above diagram. Connect the rheostat. 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.
Monitor the phase current. Gradually increase the engine RPM. Increase the engine RPM until one of the following conditions are met:
The rated phase