RING 8W9827 - Caterpillar

Illustration 1 g00851777
Generator Components (1) Shaft (2) Exciter Armature (Rotor) (3) Main Armature (Stator) (4) Main Field (Rotor)An engine supplies the power in order to turn rotor shaft (1). Exciter armature (2) and main field (4) attach to rotor shaft (1). As rotor shaft (1) turns, exciter armature (2) and related components generate DC current. This DC current is supplied to main field (4). A magnetic field is created around the poles of main field (4). As main field (4) turns with rotor shaft (1), the magnetic field also rotates. The revolving magnetic field induces an AC voltage into stationary main armature (3). Main armature (3) is a coil with many turns of wire. The current that flows through the main armature also flows to the load. The exciter supplies DC current to main field (4). The load voltage is controlled by varying the current that goes to exciter armature (2). There are two methods for excitation that are used on SR4 generators:
Permanent magnet pilot excited (PMPE)
Self-excited (SE) The permanent magnet pilot excited (PMPE) generator better sustains an overload for a short duration. The PMPE generator provides excitation power to the voltage regulator that is isolated from regulator sensing.Self-Excited (SE) Generators
Illustration 2 g00874825
SE Generator Wiring Diagram (CR1-CR6) Diodes (CR7) Varistor (L1) Exciter Field (Stator) (L2) Exciter Armature (Rotor) (L3) Main Field (Rotor) (L4) Main Armature (Stator) (RFA) Rotating Field Assembly (CT1) Optional Voltage Droop Transformer (T0, T1, T2, T3, T7, T8, T9) Generator Terminals and/or Generator LeadsSelf-excited generators receive the power for excitation from the generator armature (the generator output). When the engine starts turning rotating field assembly (RFA), the residual magnetism in exciter field (L1) causes a small amount of AC voltage to be generated in exciter armature (L2). Induced voltage causes AC current to flow. AC current flows through three-phase full wave bridge rectifier circuit (CR1-CR6). DC current then flows through main field (L3). The flow of DC current through main field (L3) creates a magnetic field which adds to the existing residual magnetism of main field (L3). As main field (L3) rotates, an AC voltage is induced into main armature (L4) which appears as a three-phase AC voltage at output terminals (T0), (T1), (T2), and (T3). The voltage regulator taps the AC output through wires 20, 22, and 24. During start-up, this tapped output is sensed by the voltage regulator. The voltage regulator senses the output as a low-voltage output condition. Therefore, the voltage regulator output to exciter field (L1) is increased so that the generator output will continue to increase up to the rated voltage. The amount of current that flows through the exciter directly affects the generator output voltage. The voltage regulator maintains a constant generator output voltage with changing loads. The voltage regulator output is a DC voltage and a DC current to exciter field (L1). The voltage regulator senses the generator output voltage at wires 20, 22, and 24. The voltage regulator then supplies the controlled DC voltage and DC current to the