TM5-6115-593-34 NAVFAC P-8-631-34 TO-35C2-3-463-2 NOTE Low insulation resistance may be caused by dirt or excessive moisture.  Insulation failure may be caused by wrong voltages, induced voltages caused by opening field circuits too quickly, oil and grease, high temperatures or excessive vibration. If the insulation fails to meet the test standards, the generator may be dried out by heat from a warm air oven, heat lamps, or strip heaters.  The temperature should not exceed 167°F (75°C). CAUTION When oven drying, use a forced air circulation oven, not a radiant type.  Radiant type oven would overheat some generator parts before remote parts reached a satisfactory temperature. NOTE If the generator must be dried out, then it is necessary to revarnish the equipment immediately after drying to prevent damage to the unit. (2) Generator and excitation system test. (a) Generator  Stator.    Disconnect  all leads  to  voltage  regulator  and  all other  points  to  completely  isolate the winding before meggering. (b) Generator Rotor.  Disconnect field leads     from     the     rotating     diode assembly before meggering. (c) Exciter   Stator.      Disconnect   both field  leads  from  terminals  1  and  2 of TB210. (d) Exciter  Rotor.    Check  this  only  if other windings have low insulation resistance as the leads must be unsoldered from all diodes before meggering (e) Tag and disconnect the two leads from the voltage regulator to terminals in the lead separation box.  Connect positive side of a DC ammeter to negative field terminal (F-) and the positive output of an adjustable DC source to the positive field (F+) terminal. Connect negative output of DC source to negative side of DC ammeter.  The exciter field is rated at 5.6 amps and 50V DC.  The adjustment should be set to minimum voltage. (f) Select 60 Hz and start the engine. With the speed at 1800 rpm, turn on the adjustable DC power supply.  Adjust the DC voltage so that the generator output voltage (no load) reads 208 or 416 volts depending on low or high voltage connection.  The exciter field should draw approximately 1 ampere to produce rated voltage at no load.  The voltage across the exciter field under these conditions is approximately 10.8V DC, ±15 percent. (g) If the DC ammeter indicates incorrect input exciter current to obtain rated voltage in step (f) above, the generator has failed.  If, however, the output is as specified, the voltage regulator, control or PM generator has failed. (h) Test rotating rectifier diodes (paragraph 11-8b).  If any 11-8