CLIP 4H8878 - Caterpillar

Illustration 1 g00609958
SR4B Generator (1) Generator terminal strip (2) Main armature (Stator) (3) Main field (Rotor) (4) Rotor shaft (5) Permanent magnet pilot exciter (6) Exciter (7) Bearing (8) FanAn engine supplies the power in order to turn rotor shaft (4). The armature of exciter (6) and main field (3) attach to the rotor shaft. As the rotor shaft turns, the exciter generates AC current. The rectifier components convert the AC exciter current to DC current. This DC current is supplied to the main field. A magnetic field is created around the poles of the main field. As the main field turns with the rotor shaft, the magnetic field also rotates. The magnetic field induces an AC voltage into stationary main armature (2). The main armature is a coil with many turns of wire. The current that flows through the main armature flows to the load. Two rectifiers supply DC current to main field (3). The load voltage is controlled by varying the current that goes to the exciter's armature. There are two methods for excitation that are used on SR4B Generators:
Permanent magnet pilot excited (PMPE)
Self-excited (SE) Permanent Magnet Pilot Excited (PMPE) Generator
Illustration 2 g00609975
PMPE 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 (R5) Resistor (RFA) Rotating field assembly (TR1) Optional Voltage droop transformer (T0, T1, T2, T3, T7, T8, T9) Generator terminals and/or Generator leadsPermanent magnet pilot excited generators receive power for the voltage regulator from a pilot exciter. Self-excited generators receive power for the voltage regulator from the main armature. The pilot exciter consists of permanent magnet (PM) and Pilot Exciter Armature (L5). The pilot exciter operates independently from the generator output voltage. Constant excitation during a large load application is possible. Constant excitation is possible because the irregularities that occur in the generator output voltage are not fed back into the exciter. The irregularities that occur in the generator output voltage are caused by load conditions. The independent operation also allows the generator to sustain excessive currents for short periods of time. When the engine starts turning the Rotating Field Assembly (RFA), the permanent magnet (PM) induces an AC voltage in the pilot exciter armature (L5). The pilot exciter armature has three coils of wire. The pilot exciter armature generates three-phase alternating current (AC). The resulting AC flows through wires "11", "12", and "13" to the voltage regulator. Within the voltage regulator, the three-phase alternating current is rectified to direct current (DC). A controlled amount of DC is fed to exciter field (L1) through terminals "F1" and "F2".Direct current now flows to exciter field (L1) which creates a magnetic field. Exciter armature (L2) rotates in this magnetic field. The exciter field and the exciter armature generate three-phase alternating current. The AC is then rectified by a three-phase full-wave bridge rectifier circuit. This rectifier circuit is made of the following diodes: CR1, CR2,