What is the typical electricity consumption of an aircraft when stationary?

Question

I am looking into the typical energy usage of a passenger aircraft when stationary. There are two options:

1. Using the APU
2. Connection to any ground equipment such as a GPU

I have some data to analyse to see whether an aircraft uses the APU. The data basically shows signals for ground power usage, and I assume that the aircraft uses the APU when no signals are sent. However, this does not always hold. Sometimes you see patterns with a bit of usage and then nothing. The amount of electricity also differs a lot per flight and aircraft. Can anyone tell me more about the typical electricity demand of a commercial, passenger flight?

Are there typical patterns? Does the APU have priority over ground power when both can deliver electricity (so when ground power is connected and the APU is switched on, where does the aircraft take its power from)?

Answer 1

As you provided no information on the type of aircraft I will be vague in most parts. A Boeing 747 will take up some more power than a small business-jet - though the systems internally can mostly compared to each other. And it also depends on the exact situation the plane if in - depending on the number and type of equipment powerd on.

First thing to understand there are two seperate power systems on bord - AC and DC. Both normally are split up in several (normally) isolated buses.

DC (quite often nominally 28V) is either supplied by onboard batteries or transformer-rectifiers (like the normalal DC-power bricks at home) from the AC sources.

AC (110V/400Hz) has normally three main power sources - main engine generators, apu and ground power. What system you draw power from will be decided by the pilots and is normally exclusive - though it was done in earlier aircraft, today planes do not syncronize their AC busses so also the different AC-busses will have distinct power sources. So only one of them...

As a backup for a failed engine generator you can either tie both ac-busses together or bring the APU online on the failed bus. (or turned off engine when doing single-engine taxi)

Ground power is nearly always powering both AC busses at the same time, so you don't mix it with other power sources.

Answer 2

This is from memory from a few years ago. When I was working ground for 767 aircraft the ground power units were typically supplying around 50amps 115v(3phase as I recall) although they would, of course, fluctuate with the number of systems turned on, belly-cargo lights, main-deck lights, or if a cargo door or conveyor was in motion.

There is a switch in the cockpit to manually select APU or GPU electricity, which is usually used after starting the APU or an engine just before disconnecting from the GPU. Most modern aircraft will automatically switch to ground power when it is connected and a cockpit light indicates the source of power.