C27 Generator Set Caterpillar

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

Measure the resistance of the following windings: (L1), (L2), (L3), (L4) and (L5). The winding that is being tested must be disconnected from the other components before the resistance can be measured. The following resistance measurements are approximations. If the measured value is not near the listed approximation, the winding is probably damaged. For a more precise resistance value, consult the Technical Marketing Information (TMI). Refer to the generator arrangement that is in question.

Note: The winding temperature affects the resistance. When the winding temperature increases, the winding resistance also increases. When the winding temperature decreases, the winding resistance also decreases. Therefore, a correct measurement can be performed only when the winding is at room temperature.

The following armature windings have very little resistance: (L2), (L4) and (L5). The resistance of these windings will measure near 0 ohms. Use a milliohmmeter to measure the resistance of the armature windings.

Exciter Armature (Rotor) (L2) - less than 0.1 ohm

Main armature (Stator) (L4) - less than 0.1 ohm

Pilot Exciter Armature (L5) - less than 0.1 ohm

Use a multimeter in order to measure the resistance of field windings (L1) and (L3).

Exciter Field (Stator) (L1) - approximately 3.0 ohms to 6.0 ohms

Main Field (Rotor) (L3) - approximately 0.75 ohms to 2.0 ohms

Note: There should be no continuity between any winding and ground. There should be no continuity between any winding and another winding.