SR 4 GENERATORSYSTEMS OPERATIONINTRODUCTIONThe SR 4 Generator has no brushes and nocommutator. This gives better performance and longerservice life. It uses a solid-state, automatic voltageregulator. This regulator has only one moving part in thevoltage build-up system. This part is a completelysealed relay that is activated only when the generator isstarted or stopped.From the outside, the SR 4 Generator looks verysimilar to the SRCR generators.Here are the design characteristics of the SR 4Generator:The windings of the alternator coils are the stator(L6). The windings of the alternator field coils are thepoles of the rotor, shown in the wiring diagram asrotating field (L5). The rotating field assembly (RFA)also has:1.Exciter armature (L4).2.Rotating rectifiers (CR1 thru CR6).3.Surge suppression diodes (CR7 and CR8).4.Positive (E1) and negative (E2) heat sinks.5.Suppression resistor (R6).REAR OF GENERATORL3 Exciter field L4 Exciter armatureAll of these components are installed on the rotorshaft. The shaft is connected through a flexible plate-type coupling to the flywheel of the engine. The rear endof the rotor shaft uses an anti-friction bearing for support.The stationary exciter field (L3) has a six-poledistributive winding on a core that is part of the generatorend housing. Both the field coils of the exciter and thealternator have their windings on magnetic steel. Thismetal keeps a small amount of residual magnetism.START UP VOLTAGE GENERATIONWhen the engine starts turning the rotating fieldassembly (RFA), the residual magnetism in the exciterfield (L3) causes a small amount of alternating current(AC) voltage to be generated in the exciter armature(L4). This voltage causes an AC current to flow which ischanged to direct current (D.C.) by the three-phase full-wave bridge rectifier circuit (CR1 thru CR6). The DCcurrent then goes to the rotating field (L5) of thealternator. Here it adds to the residual magnetism of therotating field (L5). With this field turning, an AC voltageis generated in stator (L6) which causes a current to flowto the output terminals (T0, T1, T2 and T3). Part of thisAC current is changed to half wave DC and is sent backto exciter field (L3). As a result, the magnetic field in theexciter becomes stronger. The flow of current back to(L3) is explained in more detail on the pages that follow.INSIDE GENERATOR HOUSINGE1 Positive heat sinkL5 Rotating fieldE2 Negative heat sinkL6 Stator24
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