(e)
The utility and galley buses can be manually reset if the airplane is on the ground and at least one thrust lever is not advanced. When these 2 conditions are met, the BPCU receives a "ground mode" signal. After a 10 second time delay the utility and galley buses are reset by cycling the UTILITY BUS switches.
B. BITE (Fig. 4)
(1)
Built-in-test equipment (BITE) in the generator control units (GCU's) and bus power control unit (BPCU) isolates faults quickly and reliably. Two forms of testing are used in the GCU and BPCU: operational and maintenance. Operational BITE continually monitors protective trips, control commands, and control unit status. If a protection trip occurs, operational testing finds the defective line replaceable unit (LRU) or associated wiring. Operational testing makes sure that control commands are followed. For example, if a command is given to trip a breaker, does the trip occur? The testing also tries to find failures which do not cause a protective trip.
(2)
Maintenance testing runs a complete end-to-end check of the GCU and BPCU circuits. The input, output, control, and protection circuits are checked. Communication on the GCU-BPCU data serial link is also tested. Maintenance BITE detects failures that do not cause protective trips, then isolates the LRU. The maintenance test verifies the findings of the operational test, and identifies any software failures in the control units.
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BUS POWER CONTROL UNIT
AC Generation Built-In-Test (BIT)
Figure 4
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(3)
A 2-line, 24-character alpha-numeric display is on the front of the BPCU. Three pushbuttons are also on the face of the unit: a BIT pushbutton, a guarded PERIODIC TEST pushbutton, and a guarded RESET pushbutton.
(4)
Pressing the BIT pushbutton shows any failures picked up by operational BITE. All protective trip information appears on the BPCU display. The display identifies the power channel first, and any fault on that channel next. (With faults that cause a protective breaker trip, two messages appear. The first identifies what trip occurred. (Example: UNDER VOLT TRIP). The second message identifies what LRU failed.) If no fault is found on a power channel, the display shows OK. Power channel information is displayed in the following sequence: 1) external power, 2) left generator, 3) right generator, and 4) APU generator. The first time BIT is pressed, the information of the most recent flight is displayed. The BPCU then identifies the end of this flight cycle. If BIT is again pressed, the data from one flight earlier is shown. This process can be repeated to show seven previous flight cycles, each 1-cycle earlier than the previous one. If a flight cycle ends, and BIT is not pressed during the FOR PREVIOUS FLT PUSH NOW message, the display will go blank again. Pushing BIT then displays information from the most recent flight. As an example, a right channel overvoltage fault results in the following display:
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~...................................................................... | DISPLAY | TIME OF DISPLAY (SECONDS) | ........................................................................ | EXTERNAL | 2 | | POWER SYSTEM | | ........................................................................ | OK | 2 | ........................................................................ | LEFT GEN | 2 | | POWER SYSTEM | | ........................................................................ | OK | 2 | ........................................................................ | RIGHT GEN | 2 | | POWER SYSTEM | | ........................................................................ | OVERVOLT | 15 | | TRIP | | ........................................................................ 中国航空网 www.aero.cn 航空翻译 www.aviation.cn 本文链接地址：757 AMM 飞机维护手册 电源 ELECTRICAL POWER 1(95)
