FRAME GP-UPPER 3806465 - Caterpillar

Illustration 2 g03774165
Measuring individual phases (6) Generator frame (7) Stator winding being tested (8) Megohm meter (9) Grounded windings (10) Neutral connectionResistance Check for Rotor, Exciter, and Accessories
Measurement of the Main Rotor Winding
Use the following steps to measure the rotor windings.
Illustration 3 g03774475
(15) Exciter stator (16) Exciter rotor (17) Diode connections (18) Diodes
Illustration 4 g03774508
(19) Rotor cables to be disconnected
Disconnect the rotor cables (19) from the set of diodes (18) on the exciter rotor (16) .
Connect the megohm meter between the rotor winding and the shaft of the alternator.Note: The measurement current cannot pass through the bearings.
Perform the test. Record the information.Resistance Check for the Exciter Stator
The following steps are for checking the resistance of the exciter stator.
Illustration 5 g03774590
(25) Rotor cables to exciter
Disconnect the rotor cables (25) that are connected to the exciter stator. Refer to Illustration 5.
Connect the megohm meter between the exciter stator winding (terminals I and K) and the frame of the generator.
Perform the test. Record the information.Measurement of the Rotor Winding of Main Exciter
The following steps are for checking the resistance of the rotor winding.Note: The megohm meter current cannot pass through the bearings.
Disconnect the exciter rotor cables that are attached to the set of diodes on the exciter.
Connect the megohm meter between the rotor winding and the shaft of the alternator.
Perform the test. Record the information.Measurement of the Stator Winding of the PMG (GP Model)
Disconnect cables that are connected to the PMG exciter from the voltage regulator.
Connect the megohm meter between the PMG stator winding and the frame of the generator.
Perform the test. Record the information.Note: The test voltage for the rotor, main exciter, PMG exciter, and the space heater must be 500 VDC. The test voltage for other accessories must 100 VDC. Do not measure the insulation resistance of thermal protectors.For machines that are already in operation, higher values of insulation resistance can exist compared to the initial values found at the time of commissioning. Multiple tests of the insulation will provide a better source of information for acceptable values than the values obtained in a single test. Values obtained in previous tests need to have the same parameters for comparisons with later tests. The parameters include the following:
Tests on the same machine
Tests in similar conditions of load
Same temperature
Same humidityAny large increase or reduction in values must be considered as suspicious.
Table 2
Insulation Resistance Value    Evaluation of Insulation    
2 M ohm or lower     Dangerous    
Less than 50 M ohm     Bad    
50 to 100 M ohm     Normal    
100 to 500 M ohm     Good    
500 to 1000 M ohm     Very Good    
Greater than 1000 M ohm     Excellent    Minimum Insulation Resistance
If the measured insulation resistance is less than 100 M ohm at 40° C (104° F), the windings must be:
Inspected
Cleaned
Dried (if needed)Dry the windings as per the following procedure before the machine is placed into operation.
Disassemble the generator by removing the rotor and bearings.
Place the winding components, which have low resistance, in an oven. Heat