I'd like to understand what electrical power sources are available (engines? APU? GPU? Other?) on a larger jet like the G550, and how much power they can provide, depending on whether the airplane is flying at cruise speed or on the ground. I'm curious about how much electrical load can be added to the aircraft and how.
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There are some answers to common electrical questions about the G550 here according to them the engine integrated drive generator (IDG) unit delivers 40KVA, 400HZ, 115V; they don't list a power factor but lets be conservative and assume .8 (it must be between 0 and 1). This would result in 32 Kilowatts per IDG. So you have 64 Kilowatts at your disposal. The minimum load will depends on the avionics installed and can vary from plane to plane. At night load will be increased as a result of the use of interior lights as well as landing lights during takeoff and approach. Your load will be highly variant on the interior of the aircraft. As this is a luxury plane there could be a whole host of things inside like TV's, lights, kitchen equipment etc. You can find specific equipment installations in the POH/loading info for a given airframe. You can find a nice breakdown of the G450's electrical system here.
As for how you can add it, you can simply add it as you would add any accessory, to the main bus (by an A&P of course). You will need to make sure the item can be added to the craft and in some cases there may be a stipulation along the lines of not using it during takeoff or landing. The amount of load will vary by aircraft and dependent on what else is installed.
I'd like to understand what electrical power sources are available (engines? APU? GPU? Other?)
The engines (while running) are generally the main source of power. The APU is often used on the ground when the engines are off but the plane needs electronics on and can also serve to help start the engines. It does appear the G550 has an APU. According to this data sheet the G550 runs a Honeywell RE220 APU that can output 45 Kilowatts. According to the site it will operate up to 37,000+ Ft. so it in theory could be run for the duration of a flight.
A GPU is only available on the ground and only at airports that have them. Their output varies widely and a large variety of types may be available at any given airport.
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$\begingroup$ Thanks a lot this is very helpful! I looked at your links and I also noticed there's a mention of "main" buses and "essential" busses. I guess the essential one is for all the most important functions that keep the jet flying. How does this work? Is a fixed amount of power usually allocated to the essential bus? Finally, do you know where I can find similar info for other jets, such as Citation X, Hawker 800 or Global 5000? Thanks again for all the invaluable info! $\endgroup$ May 26, 2016 at 14:12
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$\begingroup$ Based on these answers it sounds like the essential bus drives things necessary for flight and most importantly can be driven by some of the emergency power sources in the event of a generator failure etc. Depending on the source the bus should always be able to drive the minimum systems to fly the plane. If the main power units are working there will be more than enough available on the bus. $\endgroup$– DaveMay 26, 2016 at 14:30
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$\begingroup$ As for finding this info on other planes, try a search for wiring diagrams, electrical layouts etc (thats how I found the stuff linked above). You could also reach out to an A&P or the the company them selves for more info. Some (not all) POH's can be found online. A search for "{airplane type} POH" should give you what you seek. If you have a specific question on installing a particular component you may want to ask it here and see what people say. $\endgroup$– DaveMay 26, 2016 at 14:33
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$\begingroup$ Awesome, I'll have a thorough look into all of that. Thanks for your help! $\endgroup$ May 26, 2016 at 14:42