JOINT GP-UNIV 3901877 - Caterpillar

External Varistor Test
Illustration 1 g02174229
(15) Varistor (external) (16) Mounting nutsThe following procedure tests the normal state capability of the external varistor module that is used with half wave rectifier diode modules. If any meter reading does not fall within the given range, replace the heat sink assembly.
Remove all of the leads that are connected to the varistor module. Discard the star washers.
Place the megohmmeter test leads on the varistor module terminals. The varistor module is not polarity sensitive.
If the megohmmeter is not capable of reading DC voltages, then connect a DC voltmeter across the varistor module terminals.
Select the 1000 VDC range on the megohmmeter.
Apply 1000 VDC across the varistor module terminals.Note: Do not apply voltage for more than three (3) seconds.
The megohmmeter should read between 735 VDC and 910 VDC.
If the reading is greater than 910 VDC, the varistor is "OPEN". The varistor has failed. Replace the varistor assembly. Refer to the "Removal/Installation Instructions" section.
If the megohmmeter reading is less than 735 VDC, then the varistor is "SHORTED" or "DEGRADED". The varistor has failed or is failing. Replace the heat sink assembly. Refer to the "Removal/Installation Instructions".Note: If the varistor module has failed, a reflected voltage transient was most likely imposed upon the main stator, thus the main rotor. Varistor module failure is not typically caused by a failure of the varistor module. The root causes of a varistor module failure include:
Reverse VAR or reverse power event
High ambient temperature (or other application error)
Large, sudden load acceptance or rejection
Paralleling generator out of synchronism or out of phase
Paralleling at the frequency difference of more than 0.1% and voltage difference of more than 5%
Place a new star washer on each varistor module terminal post. The star washer shall be placed between the terminal post and the lead terminal.
Install all varistor module leads and nuts. Torque the nuts that are for the varistor connections. The torque must be between 1.4 N m (12.4 lb in) and 2 N m (17.7 lb in).