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c) When IDG power is established on both halves of the sync bus, the two IDGs are automatically brought within acceptable frequency and phase angle limits. The two IDGs then auto-parallel through the SSB.
Generator Control Switches ON and Engines in Operation
a) In this configuration, if external power is supplying one sync bus half and the other half becomes de-energized, the opposite IDGs auto-parallel through their GCBs and supply the de-energized buses.
b) If external power is supplying one sync bus half and the APU generator is supplying the other half, loss of either of these two sources for any reason causes the adjacent IDGs to auto-parallel through their GCBs to supply the associated buses.
c) If the other source is then lost for any reason, the associated IDGs auto-parallel through their own GCBs.
d) Once engine generator power is established on both halves of the sync bus, the IDGs auto-parallel through the SSB.
e) Cycling a GEN CONT switch from ON to OFF and back to ON with the associated engine in operation at normal speed will trip and reclose the GCR and then system operation will be the same as described above for engines not in operation (where cycling GEN CONT switches replaces starting engines).
Generator Control Switches OFF and Engines in Operation
a) When a GEN CONT switch is placed in the ON position and the associated engine is operating at normal speed, the GCR closes and system operation is then identical to that described above for engines not in operation (where placing GEN CONT switches to the ON position replaces starting engines).
Generator Control Switches OFF and Engines Not Operating
a) Starting an engine with the associated GEN CONT switch in the OFF position causes no change in system status. Placing a GEN CONT switch in the ON position with the associated engine not in operation has no effect other than to close the associated GCR.
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(b) External Power Operation to IDG Power Operation - Two External Power Sources Being Used (SSB Open) 1) Generator Control Switches ON and Engines Not in Operation a) When an engine is started and up to normal speed with the associated GEN CONT switch initially in the ON position, the IDG automatically synchronizes with the adjacent external power source. When the frequency and phase angle are within acceptable limits, the GCB automatically closes, momentarily paralleling the IDG with external power until the XPC automatically opens. b) The other half of the system can be transferred to IDG power in a similar way by starting an engine on the other side of the SSB. Once IDG power is established on both sync bus halves, the two halves are automatically brought within acceptable frequency and phase angle limits and auto-paralleled through the SSB. Starting the remaining engines causes the additional IDGs to synchronize and auto-parallel through their GCBs. 2) Generator Control Switches ON and Engines In Operation a) Cycling a GEN CONT switch from ON to OFF and back to ON with the associated engine in operation at normal speed will trip and reclose the GCR and then system operation is the same as described above for engines not in operation (where cycling GEN CONT switches replaces starting engines). 3) Generator Control Switches OFF and Engines in Operation a) When a GEN CONT switch is placed in the ON position with the associated engine in operation at normal speed, the GCR closes and system operation becomes identical to that described above for engines not in operation (where placing GEN CONT switches in the ON position replaces starting engines). 4) Generator Control Switches OFF and Engines Not in Operation 中国航空网 www.aero.cn 航空翻译 www.aviation.cn 本文链接地址：747-400 AMM 飞机维护手册 ELECTRICAL POWER 电源 1(68)
