Lots of good information here provided by all ... for those not specificly tuned to the 747's - CV880 and NSEU have provided most of the correctly detailed info... not saying others are wrong.. but the Classic systems and -400 systems do vary and most greatly in the electrical system ... so one should be careful with the assumptions and what "series" of a/c is being discusssed .. we need to remember this a/c has variations over 40 yrs ... some customer options and production line changes .... all to the same basic airframe and wing design ... one hell of a bird !!! done with pencil and slide rule
The classic does has DC bus isolation switches on the FE panel, DC bus 1, 2, 3 and Ess (#4) to the DC tie bus - for load sharing and isolation. .. also the ESS AC Bus "source" is selectable from each of the 4 Gens with #4 being the normal source, selection of the switch being controlled by the FE and "putting" the ESS BUS amber light out depending on failure ...
The -400 uses the Bus Tie switch it to operate both the respective BTB and the DCIR (DC Isolation relays) at the same time - unless in "auto" which is the normal "on" or in autoland when 1 2 & 3 are isolated to provide a seperate power source
SSB - Split system breaker - normall operated closed ... will only seperate busses 1 & 2 from 3 & 4 ... auto opens when a "difference" of either freq's or volts are found by the "bus power control units" BPCU's or when using both apu gens to share the work laod of the electrical system APU gen 1 powering Bus 1 & 2 - APU gen 2 powering 3 & 4. Most useful when working freighters where APU 1 is used to power the aircraft and APU gen 2 is dedicated to operating the main deck loading system ...
Batteries ? Maybe there is an option for 3 ... I have only seen 2
Battery Chargers ?? 2 .. on the 400's these are also turned into DC power sources via the ground service bus and though the battery/ hot battery bus depending upon which AC bus(es) has failed to ensure power to the standby inverter and standby bus normally (auto position of the standby power sw.) To complicate that even more ... some 400's have an APU Standby bus and inverter which can power the capt's transfer bus ...
Catalytic converters - located in the wing root area and "clean" the engine bleed air before the pack valves ... another mention about bleed air "customer bleed air" is never reused ... however air extracted within the engine for cooling is - ported and reused throughout the engine bearings and blades for Cooling and pressurizing bearings until either being expelled out the gas path or breather .. cheers to all ..
