Size of APU alternators; amount of frequency variation
 

Hamilton Sundstrand is the maker (possibly European sales use a different source) of the alternators driven by the 787 APU. These are 225 KVA units (each; I put that = 180 KW) intended to have a phase to phase voltage of 230. That make the phase current about 600 amps.

Hamilton also makes the blower/compressors for cabin air. They note these as being able to operate on a variable frequency feed with a range of 360 to 800 cycles. That gives us the alternator output frequency specification. Boeing has described it as a variable freqquency system.

Hamilton also makes the turbine main engine-driven alternators. There are four of these and I believe they are also each of the save 225 KVA output. They might differ in the gear ratio to the respective turbines.

Between 1974 and 1978, the labs at Curtis-Wright, with major assistance from GE, worked to build and test a turbine-driven alternator with a rating of 150 KVA. This had a permanent-magnet rotor with salient (misspelled 'sahlen' somewhere) poles of samurium-cobalt-- 14 rotor poles and a 9-phase stator winding, cycloconverted and filtered to a well-formed 3-phase output. Curtis-W labs had earlier tested an equal-sized and similarly constructed machine which had a wound rotor (i.e. suppled with external DC).

Of interest is the rotating speed range, from 12000 to 21000 rpm (that is, within 2:1). I'll have to clearify which unit had that speed as the last report page was a errata sheet dealing with that. I will explain the significance of all these variances, down the road.

What I am looking for is if and how these components and their operating ranges might cause variation of the voltage on the "hot" battery bus. Since we have minimal system details, we can just design what major detail is missing.

For starters, a major question is whether the APU altenators have a wound-rotor design (has then to be a DC winding). Anyone know?

OE

Boeing says:


UTC photo shows it's a good sized lump:

http://utcaerospacesystems.com/wp-co...-generator.jpg

And the one in the background showing the wiring gives an impression what 250 kVA really means... This beast plays in a totally different league than your cars alternator.

PM? starter/generator
 

Since it is brushless and synchronous, i.e. frequency varies with speed, it would seem to be a permanent magnet rotor machine, with 3-phase wye winding plus neutral for the stator.

Looking at the schematic on page 11 of the Airworthiness report there is a functional block diagram for some of the power distribution of the forward and aft E/E.

The starter/generator functions as a starter for the APU (using 3-phase AC?) developed in the APU Controller fed from the P49 APU Batt Elect Panel. It then functions as an alternator/generator producing variable frequency 235VAC that is collected in the P150 APU AC Elect Panel. The AC panels feed the AC busses and the TRU rectifies AC to create the 28 VDC Bus.

Four electrical busses are described: 235 vac and 115 vac both variable frequency, plus 28 VDC and 270 VDC.

i didn't see anything about how grounding is done, but i would think that all the busses are tied and referenced to chassis. In electric cars the high-voltage traction battery packs are isolated from vehicle chassis--i was surprised to find that the Main and APU battery packs have their negative terminals grounded to the airframe chassis.

todays battery test flight..2 hours should be enough for approval...right? :\

http://operationsbasednavigation.com...5193649459.jpg

Hot battery bus. As has been said, is connected directly to the battery. It is not a tie bus. The battery bus is connected to the HBB by a contactor.

The a/c is fitted with a Common Return Network. Big bonding leads and metal busses that run along the fuselage and wings. I understand it weighs about 400 lb.
Each electrical device is connected to it for earth return.


The big loads such as Air con compressors are fed from variable frequency electronic controllers. +/-270vdc.




Posted from Pprune.org App for Android

kenneth house

Not really. Here is a diagram of a CSD and generator:

http://www.pprune.org/tech-log/47743...ml#post7027969

Ignore the mechanical stuff and look at the schematic. Inside the generator, the field winding is supplied by an exciter generator. Essentially a little three phase generator on the same shaft, turned inside-out. Its output windings are on the rotor and rectified to supply the DC to the main generator field.

The main field is controlled (indirectly) by varying the exciter field (mounted on the generator case). The end effect is to have a controllable field with no brushes (high maintenance items).

Some generators do have a PMG (permanent magnet generator) in addition to all of the above. But this feeds control circuitry in the GCU enabling the system to 'black start' once the prime mover (turbine) is spinning. But since the 787 cannot start engines without some source of electrical power, the PMG function is less critical. I'm not sure if it has one.
:8

FlightPathOBN

The test flight is a 'nominal' baseline exercise.

The FAA has egg all over its face from its original certification, they will be ensuring with their new brought in experts that everything is checked out and double checked and that all recommended certification tests are totally and painstakingly carried out with all results as expected.

Boeing also with its new brought in experts MUST ensure not only that the aircraft passes these re-certification tests but also that there is no other battery problem in the next several years - or the company would be in a company threatening situation.

I am surprised at the number of people commenting that do not realize that for both FAA and Boeing it is essential that this testing is thorough and completely correctly carried out to the latest standards. There will be no skimping, clever dodges or short cuts for this certification testing, as one or the other or both of FAA and Boeing would really have problems if the aircraft are re-released to fly and another battery issue is found.

Starter windings?
 

@EEngr Thank you for posting the link to the CSD and generator schematics, that is a really clever design to avoid using brushes and magnets for an alternator. Do you also have a schematic for the starter portion--does it use some separate windings to become a motor?

What holds up the 270 VDC buss?
 

@ TURIN:
Are there any battery packs or capacitors to store or hold up the 270 buss, or is it just created as needed?

Kenneth.
No there aren't.

The Common Motor Starter Controllers (CMSC) alter the frequency of the +/-270VDC as required to control the speed & torque of the various big motors such as engine starters, air con compressors etc.
Creates a lot of heat which is why they are liquid cooled.
Much of this is covered in the early posts of this and other 787 threads.



Posted from Pprune.org App for Android

What are you guys talking about, it has been fixed! :mad:

United Airlines puts 787s in schedule for May 31

The NTSB hearing on the batteries is taking place right now...very, very interesting...

National Transportation Safety Board

(and damn, the NTSB chair is a very striking woman!)

in the morning, there was some very revealing data..

Foremost, in my mind, was that with the relative small number of large batteries produced (like on the 787) that there is not enough data to support the 10 minus 6 failure rate protection. The large batteries are produced in small batches, which there just isnt enough data yet to form a solid failure rate. The panel speaker from NASA noted a 3% initial rejection rate on the batteries they get, which is far above 1/10MM.

The battery electrolyte being flammable, not combustible, was a big issue for many on the NTSB Board

Another issue for the 787 battery was the size/shape, several panel speakers noted the large shape, with expansion/contraction from charge/discharge was an issue, and that the rectangular shape, in expansion/contraction, can cause issues. The panel speaker noted that this can cause failures, ie internal shorts, that are not picked up during the initial manufacturers testing of the battery prior to ship.

Hopefully, everyone is watching this....


it is F'n amazing.

from the automated CC of the meeting:

>> WE LOOK AT THAT STATISTICALLY. TYPICALLY THERE HAS BEEN A VERY GOOD SAFETY RECORD FOR LITHIUM BATTERIES OVER THE YEARS. BUT WE ALWAYS HAVE TO LOOK AT THE RISK WHAT IF SOMETHING DID GO WRONG. WHAT IF THERE WAS A FIRE UNRELATED TO THE BATTERY? IT DOES NOT MEAN THEY ARE NOT SAFE BUT THEY ARE PRESENT. IF THERE WAS AN UNRELATED FIRE AND THEY BECAME INVOLVED, WOULD THAT CHANGE ANYTHING? WOULD THAT BE SOMETHING WE SHOULD LOOK AT?

>> HAS DOT DONE ANY EVALUATIONS OF HOW MANY AIRCRAFT WE COULD LOOSE? DUE TO THIS RISK?

>> THERE IS A RISK ANALYSIS ON THE FAA TECH CENTER WEBSITE. JUST RECENTLY BEEN UPDATED. AN UPDATED VERSION WILL BE AVAILABLE NEXT WEEK. THERE IS ANALYSIS ON THE WEBSITE THAT THEY COMMISSIONED IN TRYING TO ASSESS DIFFERENT MITIGATION STRATEGIES IN DIFFERENT TYPES OF AIRCRAFT, A DIFFERENT WAY OF VIEWING AT TRYING TO PROVIDE MITIGATION WITHOUT A COMPLETE RETROFIT OF FREIGHTERS.

>> DO THEY ESTIMATE THE NUMBER OF AIRCRAFT THEY THINK COULD BE LOST?

>> THEY DO. THE ESTIMATE IS APPROXIMATELY ONE EVERY TWO YEARS.

This is the direction it is going

Chair of NTSB...

ONE OF THE THINGS I WAS STRUCK BY FROM ALL OF THE PANELISTS THIS MORNING AS THERE IS A LITTLE BIT OF A CHICKEN AND EGG PROBLEM WITH THE STANDARD. IT SEEMS LIKE YOU HAVE TO HAVE ENOUGH DEVELOPMENT TO GET TO A POINT TO SAY WE NEED A STANDARD. EARLY ON THERE IS SO MUCH PROPRIETARY INTEREST THERE IS PROBABLY NOT GOING TO BE A LOT OF SHARING ABOUT THE TECHNOLOGY AND STRATEGIES. HOW DO YOU KNOW THAT IS THE RIGHT TIME TO CONVENE TO DO STANDARDS AND ALSO THAT YOU ACTUALLY END UP HAVING PEOPLE BUT ARE NOT SO COMMITTED TO THEIR OWN TECHNOLOGY THAT THEY DRIVE THE STANDARD? I UNDERSTAND YOU HAVE TO HAVE A LOT OF PARTICIPANTS. I THINK IT GETS COMPLICATED.

one very interesting question:

She asked if the batteries from the 787 would be allowed to be carried as cargo.

The FAA answered that yes in the US, as Class 9 HAZ, (but they had a modification to standards to allow it) and no according to ICAO.

Chair:

THE FINAL QUESTION IS PERFORMANCE STANDARDS. THAT IS WHAT WE NEED. WHAT HAPPENS WHEN THE STANDARDS DO NOT BEAR OUT IN THE REAL WORLD OF EXPERIENCE? WHERE IS THE SAFETY VALVE THEN? YOU HAVE CREATED A SET OF EXPECTATIONS PEOPLE ARE SUPPOSED TO PERFORM TWO. IF THAT DOES NOT BEAR OUT, WHAT IS NEXT?

Wrap up question and answers to the testing and cert standards panels (FAA, SAE, UL)

>> ONE QUICK QUESTION , I WANT AN INDUSTRY PERSPECTIVE, STANDARDS PERSPECTIVE. THAT MEANS YOU GET TO DO THIS ON YOUR OWN AND YOU THREE WORK TOGETHER. I'M TRYING TO GIVE YOU TIME. IF YOU COULD HAVE THE BIGGEST SAFETY CHANGE TOMORROW THAT WOULD MAKE A DIFFERENCE, WHAT WOULD THAT BE? NOBODY TYPICALLY COMES AND SAYS WE NEED MORE REGULATION. INSTEAD, YOU HAVE TALKED ABOUT HARMONIZATION, AND NONCOMPLIANCE, REACTION TO THE INNOVATION, I AM CURIOUS, INDUSTRY, REGULATORY AND STANDARDS, WHAT WOULD BE THE BIGGEST THING TO MAKE A DIFFERENCE? PARDON ME? [INDISCERNIBLE] [LAUGHTER] NICE TRY. THEY HAVE TO TALK AND COME TO AN AGREEMENT.

>> IS THREE AND THREE AGAINST ONE. I WOULD HAVE TO SAY -- AGAIN, THE LACK OF HARMONY IN THE U.S. HAS BEEN DIFFICULT. IF I HAD MY WISH, I WOULD WISH THEY WOULD PUBLISH A FINAL RULE TOMORROW. THE ICAO DANGEROUS GOODS PANEL DID A FANTASTIC JOB NAVIGATING WHAT IS A VERY COMPLEX ISSUE. THAT WOULD BE THE NUMBER ONE THING. AN IMMEDIATE RULE TO HARMONIZE.

>> GREAT. ONE SENTENCE OR LESS. FROM A REGULATORY PERSPECTIVE. WHAT WOULD YOU WANT TO CHANGE?

>> DEVELOP AND INHERENTLY SAFE BATTERY.

>> INTERESTING. -- DEVELOP AN INHERENTLY SAFE BATTERY.

>> INTERESTING. FASCINATING. GREAT. THE THIRD ONE.

>> A TEST METHOD TO ASSESS THE RESILIENCE TO THERMAL PROPAGATION OF A BATTERY SYSTEM.

>> THOSE ARE THREE GREAT ONES. THANK YOU VERY MUCH.

jees if one takes a negative stance to the responder one could read:
DEVELOP AND INHERENTLY SAFE BATTERY. (these lithiums are inherently unsafe)
A TEST METHOD TO ASSESS THE RESILIENCE TO THERMAL PROPAGATION OF A BATTERY SYSTEM (we have no idea what will happen if a cell explodes/ignites)
THEY DO. THE ESTIMATE IS APPROXIMATELY ONE EVERY TWO YEARS (the faa expects an aircraft every two years to be lost due to the risks of external fires setting the batteries off)

and lets not forget someone put the first design in the air the first place

i have to say i like the idea posted earlier about using the 787 for freight only for some time till they have seen how well the various fixes have stopped the fires

if they had so many problems initially it should be easy to see what differences exist due to the new design

i may be being a party pooper but with a bucketload of innocent lives on the line a little more caution than has been displayed recently seems to be not too much to ask

Before glibly commenting, I recommend studying today's presentations at the NTSB's Forum on Lithium Ion Batteries in Transportation:


Panel One

Introduction to Batteries and Li-Ion Cells - M. Stanley Whittingham, M. A., D. Phil, Binghamton University

Advances in Lithium Ion Technology and Applications - Yet-Ming Chiang, Department of Materials Science and Engineering, Massachusetts Institute of Technology

Saft's Approach to High Quality Lithium Ion Products - Glen Bowling, Saft Specialty Battery Group

Failure Mechanisms of Li-ion Batteries - Daniel H. Doughty, Ph.D., Battery Safety Consulting Inc.

End User Acceptance: Requirements or Specifications, Certification, & Testing - Judith Jeevarajan, Ph.D., Power Systems Branch, NASA-Johnson Space Center, Engineering Directorate

Recent High Profile Safety Events In Lithium-ion - Vincent Visco, Quallion LLC


Panel Two

UN Lithium Battery Transport, Tests & UL Battery Safety Standards - Status Update - Laurie Florence, UL LLC

RTCA Background on Standards for Lithium Batteries - Margaret Jenny, RTCA

Regulations and Standards - George A. Kerchner, PRBA – The Rechargeable Battery Association

Air Safety Cargo Transport initiatives - Janet McLaughlin, Federal Aviation Administration

Automotive Industry Standards for the Safe Use of Lithium-Ion Battery Packs - Keith Wilson, SAE International

Lithium-Ion Battery Regulations - Duane Pfund and Kevin Leary, Pipeline and Hazardous Materials Safety Administration

Thanks for the link machaca...do you know if the transcript will be available?

FlightPathOBN:
Even though the live feed is over, the caption window at that link will allow you to copy and paste the entire 713 line auto-caption content, beginning to end. Not nearly as friendly as a proper transcript, but still better than nothing.

inet,

thanks...I would certainly point others to look at this, the content, and the intent.