Hi David, > While looking at the 747-400 electrical panel I see that the AC buses are > paralleled.
Looks like it, but they are not paralleled! Each of the 4 AC Buses is seperate from the others. The "Tie Bus" you can see on the panel is normaly not powered unless the APU is running or Ground Power is connected. Only if an engine generator fails will the "Bus Tie" Breaker of the unpowered AC bus connect to the "Tie Bus" (Position AUTO of the Bus Tie Switch). If the Tie Bus is not powered by the APU (or External Power), then the "Bus Tie" Logic will connect one of the other 3 AC Buses to the common bus, so that all 4 AC buses will be powered again. Priority for the supply of the Tie Bus are 1. External power, 2. APU-generator 3. Another engine generator (which I don't know, the B757/B767s I fly only have the other engine generator) > In this case there is a bus called a Tie Bus that serves as the > connection point for the four engine generators and the two APU generators > and the two external power sources. The sychronization of the AC buses must > be automatic (it was manual in the 727 - what a pain). Much better, no synchronization (I'm wondering why they had the complex synchronization on the B727 while this System is much simpler and without side effects.) > Each engine's main > bus is connected to the Tie Bus by an Isolation Switch, which can be used to > protect the Tie Bus from a bad supplier. Yes, the bus tie logic can also isolate a bus if it has a fault (e.g. a short) > > I assume the APU and external sources have an internal logic that prevents > them all from simultaneously powering the Tie Bus, but I don't know what the > logic is. I vaguely remember the 757 and 767 having the same setup, but I'm > getting too old to remember such things. B757/B767 System design is basically the same, with just 2 Eng Generators and only one APU Gen and one Ext. Power. > > Here's a link to my scan of the 747-400 electrical panel layout: > http://home.attbi.com/~davidculp2/747_elec.jpg > > Dave Culp brgds Thomas Holland _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
