Explain en electrical system item to me...

AggieMike88

AggieMike88

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The original "I don't know it all" of aviation.
This past week and a half at Piedmont Airlines was ground school for systems. Passed the evaluation exam with a 92%.

One area of study was the electrical system... DC bus, AC bus, essential bus, short yellow bus, and a shed bus.

Even poking about Google, I still can't wrap my tired brain around why it's called a shed bus (and that has coffee pot, music, pre recorded announcements, reading lights, taxi lights, etc attached to it.)

How did that get the name "shed bus"?

PS. Procedures training in a few weeks as well as riding the Paper Tiger. Sims happen later in month.
 
AggieMike88 said:
Even poking about Google, I still can't wrap my tired brain around why it's called a shed bus (and that has coffee pot, music, pre recorded announcements, reading lights, taxi lights, etc attached to it.)

How did that get the name "shed bus"?
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That's part of the automatic load shedding that occurs when you lose electrical sources.

I don't know much about the E-145, expect what I see from the jumpseat. What likely happens is that when you're down to less than two power sources (generators) while airborne the shed bus is shed, i.e. de-powered, to prevent overloading the remaining generator.

It'll make more sense in the sense when you get in the sim and see it happen during engine failures.
 
Larry in TN said:
It'll make more sense in the sense when you get in the sim and see it happen during engine failures.
Click to expand...

We have been warned that in the sim, “uneventful” and “normal” won’t be used in the same sentence very often.

FYI, PDT is doing the training AQP style.
 
Larry in TN said:
That's part of the automatic load shedding that occurs when you lose electrical sources.

I don't know much about the E-145, expect what I see from the jumpseat. What likely happens is that when you're down to less than two power sources (generators) while airborne the shed bus is shed, i.e. de-powered, to prevent overloading the remaining generator.

It'll make more sense in the sense when you get in the sim and see it happen during engine failures.
Click to expand...

The EDL will deenergize the shed buses with fewer than 3 generators on-line, though takeoffs at most E145 operators are done with the APU running so an engine failure during takeoff will not result in any load shedding. The shed buses can be energized with only one generator via the override switch, but only on the ground.
 
Ahh the good ole 145 electrical system, five generators and everything is essentially DC you'll hear relays clicking and its ummm quirky about electrical stuf. Shed bus is basically **** you don't need that gets dumped under various scenarios. I loved that plane but man it really was an odd duck. Goes into essential mode randomly on the ground if you aren't careful about how soon you kill/add electical gens.

Also unrelated just a tip. If the gust lock is off hold that yoke forward firmly. It will lure you into complacency for 6 months then one day when the wind hits the tail just right that yoke is coming for your balls and you can't stop it.
 
hindsight2020 said:
Best analogy for an airline career I've heard thus far afaic...... :D
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My 3 year airline career is 2 mergers, a bankruptcy, furlough, 3 contract negotiations (soon to be four once I start at widget) I've been awarded captain twice but never upgraded, also included a stint at 135. 5 type ratings and 4 (soon 5)indocs in 3 years. Been an ALPA member since 2019 but never paid dues since i've never been somewhere long enough to get past probation.

I think i'm hitting myself with the yoke lol.
 
AggieMike88 said:
This past week and a half at Piedmont Airlines was ground school for systems. Passed the evaluation exam with a 92%.

One area of study was the electrical system... DC bus, AC bus, essential bus, short yellow bus, and a shed bus.

Even poking about Google, I still can't wrap my tired brain around why it's called a shed bus (and that has coffee pot, music, pre recorded announcements, reading lights, taxi lights, etc attached to it.)

How did that get the name "shed bus"?

PS. Procedures training in a few weeks as well as riding the Paper Tiger. Sims happen later in month.
Click to expand...


Easy, Brazilian aircraft company designs and sells aircraft with German engineering and American design philosophy. A few things get jumbled in the translation, like the concept of a "non-essential" buss. Engineers talk about "load-shedding" in order to conserve available electrons during an electrical system failure.
 
When you are considering an isolated power system, that is not connected to the electrical grid, one of the problems you have is you cannot overload the generators because if you do you lose all the power sources. Because of this you have to have designated loads that can be shed to prevent overload under certain conditions.

Consider a large office building or hospital that has to have standby power in the event of a utility power failure. Such a building might have four generators on a parallel switchboard. Unlike a marine propulsion or aviation propulsion application all the generators have dedicated engines sized to their load ratings. This means that if the generator is overloaded so is the engine and if that occurs the engine pulls down in frequency and when that occurs all the breakers trip. So if you overload a generator in this scenario you lose the bus you lose all power output. There are buildings out there with four 1,000 or 2,000 KW generators and as many as 50 automatic transfer switches servicing various loads within the building. This allowes for load add schemes as engines are added to the bus and for load shed schemes as engines are removed from a bus that is potentially overloaded.

Generators in aviation are usually driven off of the main propulsion engines, so each engine is much more powerful than the generators could absorb. These generators could be overloaded, but only until their windings burn out, so they must be protected from overload with circuit breakers or fuses.

The main thing to remember is that if one of multiple generators fails the remaining generators are potentially overloaded and in that case overload must be avoided at all costs. if that means shedding all non-essential loads so that the essential loads may receive power then that's what it means.
 
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Congrats man! Good luck on the rest of training. Keep us updated.
 
Sorry! I read "shed bus" and had an vision ... :D

iu
 
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