ENGINE AR 4W9129 - Caterpillar

the individual pistons.Voltage surge suppression diodes (CR7 and CR8) connected across power rectifiers (CR3 and CR4) limit abnormal transient peak voltages on the power rectifiers. Suppression assembly (A3) limits abnormal transient peak voltages on controlled rectifier (CR1). Fuses (F1, F2 and F3) are the "fast-blow" type and provide protection against secondary damage of the excitation circuit if any component should fail or malfunction. Surge suppression diode (CR8), surge resistor (R6) and surge capacitor (C1), and suppression assembly (A2) minimize the effects of voltage surges (spikes) in the excitation circuit and protect field rectifier (CR5) against abnormal transient peak voltages.
CONTROL RECTIFIER SYMBOL
1. Anode. 2. Cathode. 3. Third terminal (gate).Control rectifier (CR1) is, in effect, an "on-off" valve that can either allow current to flow or can stop the flow of current through the excitation circuit. A control rectifier has the usual diode terminals, anode (1) and cathode (2), and a third terminal (3) that, for explanation purposes, will be referred to as the "gate". When gate (3) receives an electric impulse, it takes approximately three micro-seconds (.000003 second) for a control rectifier to "turn on" and allow current to flow. The control rectifier stays "on" until no current is flowing; then it turns "off". Because of no circuit from phase 3, current does not flow once during each complete cycle. Therefore, control rectifier (CR1) is "off" once each cycle and "gate" must receive a signal to "turn on" the controlled rectifier some time during the next cycle.The timing of the signal to the gate of the control rectifier (CR1) is a function of regulator assembly (A1). As generator load increases, regulator assembly (A1) signals the "gate" of the control rectifier earlier in the cycle, permitting a longer excitation time to the revolving field thereby providing the required additional excitation to maintain rated voltage with increased load. When generator load decreases, regulator assembly (A1) signals the "gate" later in the cycle and excitation time is less. Even when control rectifier (CR1) is "off" and current form phase 1 and phase 2 is blocked, revolving field excitation current is sustained for a complete cycle by the circuit that includes field rectifier (CR5). (Remember the flywheel analogy.)Build-up relay (K1) has the only moving part (except for the rotating field) in the entire exciting and regulating system. The relay has contact points that operate only when the generator is being started or stopped. The normally closed contact points in build-up relay (K1) are connected, in effect, from phases 1 and 2 to the "gate" of control rectifier (CR1) and through resistance wire (R5) to the cathode of control rectifier (CR1). The build-up relay coil is connected in the excitation circuit by wire (26), fuse (F3), wire (44), wire (49), or wire (40) and wire (18) between terminals (TB2-5 and TB1-5), and wire (17) between terminal (TB2-5) and pin terminal (B) of the build-up relay (K1). The other side of the coil is connected to phases 1 and 2 through wire (21) to