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Battery Power In Aircraft - Technical Questions.  
User currently offlineJulesmusician From , joined Dec 1969, posts, RR:
Posted (8 years 9 months 2 weeks 4 days 12 hours ago) and read 3349 times:

Strange question, but always wondered - if a modern Boeing or Airbus landed at an airport that then had a sudden power failure while the aircraft was at the gate, could the aircraft be used, through any systems to assist in powering external appliances/lights etc outside?

Also with the APU (which I assume would generate power if no external power source could plug into the aircraft) what kind of power can it produce is there a wattage figure?

Thanks,

J

16 replies: All unread, jump to last
 
User currently offlinePhilSquares From , joined Dec 1969, posts, RR:
Reply 1, posted (8 years 9 months 2 weeks 4 days 12 hours ago) and read 3340 times:

To answer your question simply: NO!

The APU in a 747 has 2 90KVA generators. No wattage figure available.


User currently offlineSlamClick From United States of America, joined Nov 2003, 10062 posts, RR: 68
Reply 2, posted (8 years 9 months 2 weeks 4 days 12 hours ago) and read 3338 times:

There is no provision for any airliner I know of to back-power the terminal. There are, if I'm not mistaken, reverse-current relays in the system to prevent such a thing.

Chances are the APU is producing 115V 400 Hz alternating current. Chances are the terminal is not wired for that.

I don't remember the output of any APUs off the top of my head, but they are pretty powerful. (65KW ?) Pilot handbooks in the past ten years or so have tended to edit out such facts. That is now called minutiae and is heartily disliked by training department managers.



Happiness is not seeing another trite Ste. Maarten photo all week long.
User currently offlineHAWK21M From India, joined Jan 2001, 31679 posts, RR: 56
Reply 3, posted (8 years 9 months 2 weeks 4 days 12 hours ago) and read 3323 times:

115vac 400hz would never do,especially with 40-45KVA as on a B737.
Although Ground service plugs are Available for Both 115vac & 28vdc in the cabin to power cleaning equipment.
I think the Airport will need to keep a Stby [backup] Generator handy.

regds
MEL



Think of the brighter side!
User currently offlineJulesmusician From , joined Dec 1969, posts, RR:
Reply 4, posted (8 years 9 months 2 weeks 4 days 11 hours ago) and read 3310 times:

Interesting answers, there was an article about how much power the domestic car could give you if you had a long power outage at home, and the results were quite interesting. If the APU can manage such power output then I assume the actual power output with all engines running, even at idle is probably large enough to power a lot... (if you could plug in....)

User currently offlineSlamClick From United States of America, joined Nov 2003, 10062 posts, RR: 68
Reply 5, posted (8 years 9 months 2 weeks 4 days 10 hours ago) and read 3293 times:

One additional note: The use of "battery" in the thread title does not lead in the right direction. The only time the battery powers anything at all on a large airplane is on initial powering up - starting the APU etc. away from the gate. The other event is "loss of all generators" which may include loss of all engines without a RAT or usable APU. In that event the ship's batteries may power "standby power" items, such as captain's flight instruments, number 1 nav and comm, a little bit of lighting etc.

Typically in normal operations, even items powered by the "Battery Bus" are, in fact energized by the battery charger rather than the battery itself. The battery sort of "floats" on the system, being kept topped off by the very smart battery charger.



Happiness is not seeing another trite Ste. Maarten photo all week long.
User currently offlineJetlagged From United Kingdom, joined Jan 2005, 2546 posts, RR: 24
Reply 6, posted (8 years 9 months 2 weeks 4 days 8 hours ago) and read 3260 times:

Quoting PhilSquares (Reply 1):
The APU in a 747 has 2 90KVA generators. No wattage figure available.

90 KVA is roughly 90 kW, if you ignore reactive loads, so that makes 180 kW total.

[Edited 2005-11-16 21:38:43]


The glass isn't half empty, or half full, it's twice as big as it needs to be.
User currently offlineDrDeke From United States of America, joined Jun 2005, 830 posts, RR: 0
Reply 7, posted (8 years 9 months 2 weeks 4 days 7 hours ago) and read 3238 times:

180kW is a fair amount of power, but it would take a lot of APUs running in parallel to fully power an entire large airport. Also, aircraft produce power at a frequency of 400Hz, whereas commercial power grids require 50 or 60Hz power. It would also take a lot of sophisticated control and communication equipment in order to get the APUs in the various aircraft to synchronize the frequency and phase of their alternators. This would be so complex to set up, and would require so many modifications to the APUs that it is undoubtedly much cheaper for an airport to simply build a power plant if they are worried about power redundancy.

-DrDeke



If you don't want it known, don't say it on a phone.
User currently offlineStarlionblue From Greenland, joined Feb 2004, 17030 posts, RR: 67
Reply 8, posted (8 years 9 months 2 weeks 4 days 6 hours ago) and read 3225 times:

Quoting SlamClick (Reply 2):
I don't remember the output of any APUs off the top of my head, but they are pretty powerful. (65KW ?) Pilot handbooks in the past ten years or so have tended to edit out such facts. That is now called minutiae and is heartily disliked by training department managers.

Hmmm, aren't you a training department manager?

Quoting Jetlagged (Reply 6):
Quoting PhilSquares (Reply 1):
The APU in a 747 has 2 90KVA generators. No wattage figure available.

90 KVA is roughly 90 kW, if you ignore reactive loads, so that makes 180 kW total.

Yeah, if the current and voltage are in phase and all that jazz. If you really care: http://www.onlineconversion.com/forum/forum_1079683166.htm


Oh btw this means you could run 1800 100w bulbs off a 747 APU, but I have no idea why you would. It's just a fun fact. Also, the APU itself is more poweful than the engines on a Twin Otter combined.

[Edited 2005-11-16 23:29:21]


"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineJulesmusician From , joined Dec 1969, posts, RR:
Reply 9, posted (8 years 9 months 2 weeks 4 days 6 hours ago) and read 3224 times:

OK very interesting facts. Another situation might be where an airport is serviceable in a disaster area, that is to say that the runway is safe to land on, but there is no power anywhere - a modern aircraft can obviously generate a hell of a lot of power but without conversion equipment or plug in places it would be no use to anyone. I wonder if any military guys know if their aircraft can run outside equipment in the event of needing power outside of the aircraft. I could see it being very useful for lighting, emergency equipment before generators could be bought in....if you could power some basics from the first aircraft that landed you might be able to get runway lights and the basic necessities for safety up and running...

User currently offlineStarlionblue From Greenland, joined Feb 2004, 17030 posts, RR: 67
Reply 10, posted (8 years 9 months 2 weeks 4 days 6 hours ago) and read 3218 times:

Quoting Julesmusician (Reply 9):
OK very interesting facts. Another situation might be where an airport is serviceable in a disaster area, that is to say that the runway is safe to land on, but there is no power anywhere - a modern aircraft can obviously generate a hell of a lot of power but without conversion equipment or plug in places it would be no use to anyone. I wonder if any military guys know if their aircraft can run outside equipment in the event of needing power outside of the aircraft. I could see it being very useful for lighting, emergency equipment before generators could be bought in....if you could power some basics from the first aircraft that landed you might be able to get runway lights and the basic necessities for safety up and running...

Nice, but wouldn't it be easier just to bring a gas or diesel generator on that plane?



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineJulesmusician From , joined Dec 1969, posts, RR:
Reply 11, posted (8 years 9 months 2 weeks 4 days 6 hours ago) and read 3215 times:

Probably, but strange to think you have the best generator of all sitting on the tarmac and you can't plug into it.. Wink

User currently offlineSkydrol From Canada, joined Oct 2003, 969 posts, RR: 10
Reply 12, posted (8 years 9 months 2 weeks 4 days ago) and read 3156 times:

Even though there is no convenient place to 'plug in', in an emergency, I guess it would be possible to connect an external load between T0 and outputs from T1, T2 or T3 from the alternator, or onto the AC bus directly. The 115 V / 400 Hz supply would be fine for resistive loads such as heating elements or incandescent lamps.

For motors or other inductive loads , a device such as a motor VFD would have to be employed to convert the three phase 400 Hz to three phase 60 Hz. At 90 kVA, each APU is producing around 120 HP. VFDs are available up to thousands of horsepower, so a unit for frequency conversion of 120 HP / 90 kVA loads is readily available, but would still be the size of a refrigerator!

VFD (variable frequency drives) are normally used to adjust the speed of an AC motor by changing the frequency of the power supply to a motor. This is accomplished by rectifying the incoming AC power to DC. Then the ripple is filtered with a large capacitor bank. A microprocessor controlled oscillator then modulates the gates of IGBTs (basically super-sized transistors) to create a modified sine wave output usually adjustable from 0 to 400 Hz and 0 to supply voltage. This would describe a single phase unit. For three phase units, there would be three oscillator outputs with phases offset by 120° triggering separate IGBTs.

Even though the frequency output is normally variable, there is no rule that the frequency output could not be set/locked to 60 Hz. And applying 400 Hz instead of 60 Hz to the input of a VFD would actually make the ripple filter caps even more effective.

So this would seem like a way to make this work (in an emergency), but after stating all of this, wouldn't a diesel generator be less complicated and quieter!



LD4



∙ ---{--« ∙ ----{--« ∙ --{-« ∙ ---{--« ∙ --{--« ∙ --{-« ∙ ----{--« ∙
User currently offlineWoodreau From United States of America, joined Sep 2001, 1038 posts, RR: 6
Reply 13, posted (8 years 9 months 2 weeks 4 days ago) and read 3153 times:

Military aircraft suffer the same limitation their civilian counterparts do, the power that is generated by the generators and APU is of the wrong frequency - 400Hz. There's no use for 50Hz or 60Hz power on an aircraft. Actually 50Hz or 60Hz generators tend to be relatively large compared to 400Hz generators. You couldn't fit a 60Hz generator inside an engine nacelle.

However, MEP (mobile electric power) is easily palletized and can be airlifted in on any military transport. Actually the Marine Corps practices putting in expeditionary airfields in remote places, units practice putting together an airfield, they bring their MEPs, ROWPUs (water purification units) and enough equipment and supplies to provide basic life support in an environment where none of that is available.


Someone did have an idea of converting old military destroyers into mobile floating power barges. Ships generate 60Hz power, when a power outage occurred, they'd tow the old destroyers to the location, plug it into the power grid, fire up the boilers to generate steam for the four 1MW 60Hz AC generators onboard, and power up a small town. Although the barge would produce water as a by product, it wasn't potable because the water source (being within 3 miles of the coastline) is by definition contaminated.



Bonus animus sit, ab experientia. Quod salvatum fuerit de malis usu venit judicium.
User currently offlineJarheadK5 From United States of America, joined Nov 2005, 216 posts, RR: 1
Reply 14, posted (8 years 9 months 2 weeks 3 days 12 hours ago) and read 3100 times:

Quoting Julesmusician (Reply 11):
Probably, but strange to think you have the best generator of all sitting on the tarmac and you can't plug into it..

No, it's not the best generator of all. As noted above, the frequency of aircraft AC power is wrong for ground use.
Plus, why have a multi-million-dollar aircraft sitting on the ground making electrical power, sucking down expensive jet fuel, and putting hours on the clocks; when it could have flown a dedicated generator in which uses cheap diesel, then made more resupply trips?

*BTW - I know "expensive" and "cheap" are relative terms these days...



Cleared to Contact
User currently offlineElectech6299 From United States of America, joined Aug 2005, 616 posts, RR: 3
Reply 15, posted (8 years 9 months 2 weeks 2 days 21 hours ago) and read 3033 times:

Quoting JarheadK5 (Reply 14):
Quoting Julesmusician (Reply 11):
Probably, but strange to think you have the best generator of all sitting on the tarmac and you can't plug into it..

No, it's not the best generator of all.

Thanks, JarheadK5, truly not the best, just perhaps the prettiest and the one we all dream about.  cloudnine  The aircraft systems were designed for a specific purpose and don't serve other purposes well. I'm not saying that it can't be done, but it's a waste of talent and resources to try it. Every major airport has generator power. Besides, if fuel is an issue (i.e. post-Katrina) diesel generators will run fine on the locally stored jet fuel. (just pretty darn expensive, so the use better justify the expense) I just can't think of any situation where a commercial aircraft would unexpectedly land at a powerless airport that didn't have local generators. (And if they expected it, as was said before, they'd bring a generator with...)

Quoting Skydrol (Reply 12):

Excellent description of VFDs! Can I quote you on that?  Smile



Send not to know for whom the bell tolls...it tolls for thee
User currently offlineAirIndiaOne From India, joined Mar 2005, 146 posts, RR: 0
Reply 16, posted (8 years 9 months 2 weeks 2 days 17 hours ago) and read 3010 times:

Quoting Jetlagged (Reply 6):
90 KVA is roughly 90 kW, if you ignore reactive loads, so that makes 180 kW total.

The active power is 90 KVA. The real power output for supplying loads would be 90KW given the power factor is unity (in most cases it is close to 0.95)

[Edited 2005-11-18 13:44:47]


"You don't have to be crazy to be in aviation, but it helps", JRD Tata
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