EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú
24-23-00
ALL ú ú 05 Page 16 ú Jun 10/89
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400 MAINTENANCE MANUAL
b) UV protection is not set.
c) US protection is not set.
d) OC protection is not set.
2) If none of the protective trips are present and power is available for 150 |50 milliseconds, the AGCU signals the APB to close.
(l) Protective Trips
1) The AGCU also causes relays and breakers to trip in order to protect the EPGS under fault conditions. These relays and breakers are the AGCR and the APB.
2) AGCR 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) Fire switch is pressed.
3) APB protective trip occurs if there is an AGCR protective trip, OC protection is set, or if a US condition is confirmed.
(9)
Bus Control Unit (Fig. 6)
(a)
Each of the two BCUs are identical and interchangeable. A BCU provides functions to control and protect the synchronizing bus for coordinated system performance. The BCU analyzes incoming data from the electrical power generating system and performs the following control functions and protection.
(b)
The BCU provides the interface between the GEN FIELD switch and the adjacent AGCU for GCR control. The BCU will also send a GCR trip signal when an auxiliary generator bearing failure is detected continuously for 5 minutes.
(c)
The BCU provides the interface between the APU GEN switch and the adjacent AGCU for APB control. The BCU can also trip the APB directly. 1) The BCU will send a +28 volts dc APB close signal to the
AGCU when the airplane is in ground mode and the following
conditions are all true:
a) APB is open.
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú
24-23-00
ALL ú ú 03 Page 17 ú Jun 10/89
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL
FUNCTION SENSING THRESHOLD DELAY TIME TRIPS REMARKS
EXT PWR OVER-VOLTAGE 1 (OV1) HIGH PHASE VOLTAGE INHIBITED BELOW 125 129 |4 VOLTS INVERSE GSTR, GHR XPC, GSSR, LOCKOUT BELOW 125 VOLTS LINE-TO-NEUTRAL
EXT PWR OVER-VOLTAGE 2 (OV2) HIGH PHASE VOLTAGE OV >140 VOLTS2 260 |10 MSEC INTERNAL EXT PWR CONTACTOR
VOLTAGE (UV) EXT PWR UNDER- 3 PHASE AVERAGE VOLTAGE VOLTS LINE-T0-NEUTRAL 104.5 |1.5 9.0 |1.0 SEC XPC, GSSR, GSTR, GHR INSTANTANEOUS TRIP WHEN VOLTS <60V BACKUP DC BATTERIES <18V
EXT PWR OVER-FREQUENCY (OF) EXT PWR .C OF 427.5 |2.5 Hz 1 OF 437.5 |2.5 Hz 2 1 0.8-1.6 SEC OF SEC 2 .20-.04 OF XPC, GSSR, GSTR, GHR
EXT PWR UNDER-FREQUENCY (UF) EXT PWR .C 1 2 UF 372.5 |2.5 Hz UF 352.5 |2.5 Hz 0.8-1.6 SEC 1 2 UF 0.1-0.2 SEC UF GSTR, GHR XPC, GSSR,
EXT PWR PHASE PHASE A-B-C THE CLOSURES OF XPC, GSSR,
SEQUENCE AND GHR ARE INHIBITED WHEN THE PHASE SEQUENCE IS NOT A-B-C
APU GENERATOR BEARING FAILURE SWITCH/CONTACT CONNECTION GROUND COMPLETED 5 MINUTES AGCR IN AGCU TO BOTH BCU'S THE INPUT IS FROM APU GEN
NEGATIVE PHASE A-B-C 18.5 |6.0 VOLTS INVERSE XPC, APB,
SEQUENCE OF SYNC BUS SSB,
VOLTAGE (NSV) VOLTAGE ADJACENT BTBs
Bus Control Unit (BCU) Protective Functions
Figure 6 (Sheet 1)
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú
24-23-00
ALL ú ú 03 Page 18 ú Jun 10/89
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL
