747-400 AMM 飞机维护手册 ELECTRICAL POWER 电源 2(8)

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 the fault occurred. 3) ALL ARINC 429 data link outputs stop. 4) Redundant analog generator DP protection remains in
 operation to trip the BTB if a main bus fault occurs.Fail-safe protection is initiated by the GCU when any of the following take place: 1) The CPU power supply fails. 2) The CPU software cycle exceeds its time limit. 3) Three software errors occur in the CPU within a given time
 limit. 4) The CPU power supply goes overvoltage or undervoltage. 5) The watchdog circuit is detected as failed during a
 power-up reset.Power Ready 1) Power from the IDG is available (ready) when the following
 conditions are present:
 a) OV protection is not set.
 b) UV protection is not set.
 c) OF protection is not set.
 d) UF protection is not set.
 e) US protection is not set.

 2)  If none of the protective trips are present and power is available for 150 |50 milliseconds, the GCU signals the GCB to close.
Protective Trips
 1)  The GCU also causes relays and breakers to trip in order to protect the EPGS under fault conditions. These relays and breakers are the GCR, the GCB, and the BTB.
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 2)

3)
4)

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GCR Protective Trip occurs if one of the following is
 confirmed:
 a) OV protection is set.
 b) UV protection is set.
 c) Differential current fault protection is set.
 d) OP protection is set.
 e) Generator diode fault protection is set.
 f) A SPMG condition.
 g) Fire switch is pressed.
 h) IDG disconnect switch is pressed.
 i) UF or OF conditions are detected and it is from a

 isolated power source on the sync bus.
The GCB protective trip occurs if there is a GCR protective
 trip or if a US condition is confirmed.
The BTB protective trip occurs if one of the following is
 confirmed:
 a) OP protection is set (refer to first NOTE).
 b) UF protection is set (refer to first NOTE).
 c) OF protection is set (refer to first NOTE).
 d) OE protection is set (refer to first NOTE).
 e) UE protection is set (refer to first NOTE).
 f) Differential current fault protection is set (refer to

 first NOTE). g) The GCB is closed and one of the BCUs detects a sustained out-of-limits source (refer to first NOTE). h) A sync bus or DP2 protective trip command is received from the adjacent BCU (refer to second NOTE).
 NOTE: The BTB protective trip is reset if faults are
____ not present and the BTB is required to close (from an auto-parallel command, a dead bus function, a BTB reclose command, or a power transfer from external power to IDG power with the BTB switch in the AUTO position).
 NOTE: The BTB protective trip reset occurs only if the
____ faults are no longer present and the BUS TIE switch is in the ISLN position.
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 (8)  
Auxiliary Generator Control Unit (Fig. 5)

 (a)  
Each of the two AGCUs are identical and can be used on either APU generator channel. The AGCU provides system protection, control, and voltage regulation for its associated generator.

 (b)  
The AGCU provides the following protective functions:
 1) Overvoltage
 2) Undervoltage
 3) Underspeed
 4) Differential current

 (c)  
The AGCU provides the following control functions:
 1) Generator field control and indication
 2) Auxiliary power breaker control
 3) Auto paralleling
 4) APU generator power ready
 5) Anti-cycling
 6) Syncronizing signal output

 (d)  
During fault conditions, the excitation level to the generator is automatically controlled to limit current and/or power output of the associated generator to within safe levels.
　
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