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737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL Generator Excitation The APU starter-generator is a three-phase brushless AC generator. The generator consists of these components: * Exciter rotor (armature) * Main generator rotor (field winding) * Permanent magnet generator (PMG) rotor * Main generator exciter * PMG stator * Neutral current transformer (NCT). The APU gearbox turns the rotor. As the PMG rotor turns, it induces an AC voltage in the three-phase windings of the PMG stator. This AC voltage goes to the start converter unit (SCU). A voltage regulator (VR) in the SCU transforms and rectifies the power to DC. Also in the SCU, is a generator control relay (GCR). With the GCR in the closed position, DC power goes to the exciter field windings. The stationary magnetic field caused by the DC voltage in the windings of the exciter field (stator) makes a three-phase AC excitation voltage in the windings of the exciter armature (rotor). This AC voltage rectifies to DC voltage by the rotating rectifier assembly in the rotor. The DC voltage goes to the field windings of the main generator. Current flow in the field windings causes a rotating magnetic field. The rotating magnetic field causes an AC voltage in the windings of the main generator stator. The AGCU monitors the voltage and current of the generator. The SCU monitors and controls the voltage output from the generator. The APB can close when the voltage and frequency are within power quality limits. The voltage regulator in the SCU controls AC power output by control of excitation power. The generator control relay (GCR) in the APU GCU (AGCU) is not part of the excitation power circuit for the APU generator. The AGCU GCR closes to send the voltage regulator (VR) enable signal to the SCU. The VR enable signal completes the excitation circuit in the SCU. APU Starter-Generator Start Mode The APU starter-generator starter is integral with the generator. The SCU attaches electrically to the starter-generator through connections (splices) to the feeder wires at the back of the power distribution panel (PDP). The SCU voltage regulator uses these connections as a point of regulation (POR). The SCU also uses this connection to supply power to the starter-generator during APU starting. The AGCU protection circuits monitor power quality at connections to the feeder wires inside of the PDP. See the APU ignition/starting section for more information. (SECTION 49-40) AC GENERATION - AGCU - PROTECTION AND EXCITATION EFFECTIVITY GUN ALL 24-20-00 Page 47 D633A101-GUN Oct 10/2005 BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details. 737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL 24-20-00-108 AGCU Protection The AGCU monitors voltage, current, and frequency. The AGCU opens the APB and removes the excitation from the generator to protect the electrical channel. The AGCU removes the VR enable signal to turn off excitation. The AGCU has these protective functions: * Overvoltage * Undervoltage * Overfrequency * Underfrequency * Unbalanced phase current * Phase sequence * Overcurrent * Differential fault * Underspeed protection * AGCU fail-safe. Overvoltage and Undervoltage Protection The AGCU monitors each of the phase voltages. Overvoltage protection starts when the highest phase voltages is more than 130 volts. Undervoltage protection starts when the lowest phase voltage is less than 101 volts for more than 7 seconds. If there is a voltage fault, the AGCU removes the VR enable signal. The SCU removes the excitation from the generator and the AGCU commands the APB to open. Frequency Protection The SCU monitors the frequency at the PMG. Proper generator frequency is 400 Hz. The AGCU receives a conditioned PMG signal from the APU SCU. The AGCU removes the VR enable signal to the SCU and opens the APB if the frequency is more than these limits: * 425 Hz for more than 1.5 seconds * 435 Hz for 35 milliseconds. The AGCU removes the VR enable signal and opens the APB if the frequency is less than these limits: * 375 Hz for 1.5 seconds * 355 Hz for 150 milliseconds. Unbalanced Phase Protection The AGCU monitors the three phases of the APU generator line current transformer. Unbalance phase protection occurs if the current unbalance between any two phases is more than 140 amps. The AGCU commands the BPCU to open BTB 2. If the fault remains, the BPCU opens BTB 1 and re-closes BTB 2. If the fault clears, there is no further action. If the fault remains, the www.aero.cn 航空翻译 www.aviation.cn 本文链接地址：737NGAMM5
