24-20-00
 ALL  ú ú 06 Page 11 ú Jun 10/90
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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747-400 MAINTENANCE MANUAL
IDG Power Operation to External Power Operation - One External
 Power Source Available (SSB Closed)
 1)  With one external power source available and with one or more IDGs supplying all buses, placing the available EXT PWR switch in the ON position causes the IDG(s) to synchronize with the external power source. When the frequency and phase angle are within acceptable limits, the XPC automatically closes, paralleling the IDG(s) with external power before automatically tripping the GCB(s).
IDG Power Operation to External Power Operation - BTB Open
 1)  The transfer operation from IDG power to external power is not inhibited if one or more BTBs are open. A no-break transfer occurs for those IDG channels with closed BTBs.
 2)  On those channels operating with BTBs open and GCBs closed, external power will not be transferred to the associated buses. Those buses are powered by the respective IDG. If the BTB is open because the BUS TIE switch is in the unlatched (ISLN) position, the BTB will remain open through engine shutdown.
 3)  If a BUS TIE control switch is placed in the AUTO position, the power transfer will occur as described above with SSB Closed.
IDG Power Operation to Auxiliary Power Operation (SSB Open or
 SSB Closed)
 1)  The transfer method from IDG power to auxiliary power is the same as that for the transfer from IDG power to external power. The IDG(s) synchronize and parallel with the auxiliary power source before the GCB(s) trip. All IDG power to auxiliary power transfers are inhibited when the AIR/GRD switch is in the AIR mode or the airplane is in takeoff or landing rolls, and any IDG is available (GCB closed). When in the AIR mode, APB closure is not inhibited if all GCBs are open.
External Power Operation to Auxiliary Power Operation - One
 External Power Source Being Used (SSB Closed)
 1) One APU Generator Available a) With one external power source supplying all airplane buses, pushing the APU GEN switch (of the available unit) causes the APU to synchronize with the external power source. When the APU generator frequency and phase angle are within acceptable limits, the APB automatically closes, momentarily paralleling the two sources until the XPC automatically trips.
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 24-20-00
 ALL  ú ú 06 Page 12 ú Jun 10/90
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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747-400 MAINTENANCE MANUAL
 2) Both APU Generators Available a) With one external power source supplying all the airplane buses, pushing the adjacent APU GEN switch causes the APU to auto-parallel with the external power source and trip the XPC same as with one APU generator available. b) Pushing the APU GEN switch opposite the connected external power source causes the APU generator to synchronize and the APB to close, paralleling the APU generator and external power until the SSB trips, leaving the external power source on one side of the sync bus and the APU generator on the other.
External Power Operation to Auxiliary Power Operation - One
 External Power Source Being Used (SSB Open)
 1)  Pushing the APU GEN switch adjacent to the external power source in use causes a power transfer similar to that with one APU Generator available. Pushing the opposite APU GEN switch connects that APU generator to its side of the sync bus, leaving the external power source on the other half.
External Power Operation to Auxiliary Power Operation - Two
 External Power Sources Being Used (SSB Open)
 1)  With both external power sources supplying power to the buses, pushing either APU GEN switch causes that APU to auto-parallel with the adjacent external power supply and then trip its XPC. The other half of the system can be brought onto auxiliary power in a similar way by pushing the other APU GEN switch.
Auxiliary Power Operation to External Power Operation - One APU
 Generator Being Used (SSB Closed)
 1) One External Power Source Available a) With one APU Generator supplying all the airplane buses, pushing the EXT PWR switch (of the available source) causes the APU to synchronize with the external power source. When the APU generator frequency and phase angle are within acceptable limits, the XPC automatically closes, momentarily paralleling the two sources until the APB automatically opens.
　
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