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APU generator frequency C-130H


turbinetom
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Hi,

Wondering if anyone can tell me the APU frequency of the GTCP85-180L (H model APU) in a no load situation, basically APU running, no bleed air or electric being used. What is the max variation in the frequency when fully loaded with AC? Basically looking for the frequency at idle and the maximum droop. What window is considered acceptable by by the pilot and crew?

Thanks,

Tom

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even with max bleed load, electrical system requirements are still 380 to 420Hz/ Keeping this in mind, if the RPM drops

below 95% the bleed air load control valve will be closed. Normal RPM drop when going from no load (100%) to

full load (97.5%)

 

 

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Hi Guys,

 Thanks..that's a big window for frequency...working an APU in a test cell environment and have the frequency at idle (no loads) at about 402/403hz...with 60kw load applied I am right at 400hz....with full bleed load, temperature maxed at 1170F, frequency is at 396 hz. it sounds like in actual installation this will be acceptable. The T.O only provides a "maximum rpm" for the APU, but never specifies an actual value. My thinking is that you guys like to be as close to 400hz as can be maintained...correct?

Tom

 

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All equipment on the bird is manufactured to work +/- 20 Hz. This is out of the -23GS:

40 kVA Engine-Driven Generator

The phase-to-phase voltage is 200 VAC. The generator is connected as a 3-phase wye circuit with a grounded neutral. The output frequency range is from 380 to 420 Hz. 

 

Capture.JPG

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Hey, 

Thanks to all for replies...I have latest (2015) T.O's and also commercial manuals for the GTCP85-185L. Through these manuals there is a lot of conflicting information. Running the unit at 4292 -4311puts frequency at 410-412 hz. In the commercial world, I would expect a phone call right away as a commercial operator wants to see no more than 404 hz. Does the C-130 unit really operate at such a high frequency?

What I would really like to know is what do the guys in the cockpit want to see by way of generator frequency with no load? I understand the window of 380-420hz, but there must be something that seems "normal" or desired. On a related side note, our 85-180's for the A/M32A-60A hold 400hz even within +/- 1hz under any condition as they incorporate a clever stepper motor on the fuel control. The 85-180C for the -95 (LASS) cart  states 43,300 RPM max  by the T.O , but at installation is tweeked down to just around 42,200 -42,500 or else the tachometer reading in the panel looks a bit overspeed.

Thanks again for all the input...I am always working hard to maximize these units.

 

 

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The -60 GPU has a variable controller on the fuel cluster to keep rpm steady ..... sometimes

causes more problems than just a drop in rpm would. The RPM on the run sheet is corrected

for the tach generator and rpm indicator on the test cell. Once APU is installed on aircraft,

it runs at indicated 100% and 400Hz. These figures can be checked in 2G-GTCP85-41-1

 

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Hi,

 Thanks again for your reply. Your response is exactly what prompted my question. If I set RPM by the T.O , the unit is seemingly running at 410-412hz so I am puzzled how the unit runs at 400 hz once installed. Mathematically the numbers do not work out:

4292 tach pad RPM x 10.043-1 gear ratio = 43,104 at the turbine wheel. 43,104 / 7 (planetary to gen reduction) = 6,157 RPM at generator=410.5 hz at the generator. Running at max 4311 tach pad RPM puts generator at 412.3 hz

I'd really like to hear from a pilot or crew that can confirm that the unit runs at 410-412 when installed. Perhaps this is normal? Sorry to drone on about this, I am just wanting to get real world information.

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