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munirabbasi

Caution explaination

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CAUTION: The underfloor heat switch must be off

during engine starting and switching of

loads from one generator to another.

Failure to comply could result in a

burned out generator control panel.

Why GCP burn out can some body explain with logic

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CAUTION: The underfloor heat switch must be off

during engine starting and switching of

loads from one generator to another.

Failure to comply could result in a

burned out generator control panel.

Why GCP burn out can some body explain with logic

I don't remember the exact reason, but I seem to remember that this is not an issue with the newer GCU.

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My memory serves me that it has to do with the electrical loads shifting from bus to bus during the start sequence from LSGI to normal RPM. It is non essential at this point so leave it off.

Steve

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After reading this for the tenth time maybe it is a mix of a few issues.

1. Underfloor heat when ON would use Bleed Air during the start of the first/second engine "and" the Cargo Compartment fan would automatically turn ON as soon as the second generator is put on-line.

2. The second generator voltage should drop initially as the generator assumes the LH and RH AC bus resulting in the VR excitation voltage being increase to bring voltage back up to normal.

3. There is no "start sequence" for the CC fan so all three phases (of the second generator) are supplied to the fan at the same time resulting in a fairly high load. This load increase would happen when the voltage should be trying to stabilize from the initial bus transfer.

4. The larger than normal load of the CC fan would cause the generator voltage to drop even further causing the VR to increase the excitation voltage to the generator to compensate.

5. The excitation voltage travels thru the GCP and that is the connection I see. Increase excitation voltage...

Thats my thought process...

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HI-NATOPS1

Thank you for providing Excellent information.Sir you know GCP receive power not more than 7 V such valve that GCP can not burnout ie 3.75 -7.15V

Load applied on Generator not GCP ,Generator should burn out instead of GCP,CC fan load on each phase 5A how?

Munir Abbasi ATI

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My thoughts... Load on the gen (is not the issue) the load on the gen causes the voltage to drop and induces a reaction in the VR thru the GCP so if the VR keeps feeding maximum excitation voltage to the excitation generator (to bring the gen voltage back up) it could cause damage to the GCP.

Fan load is whatever amperage it is. (CBers are rated at 10 AMPs) The "start up" load will be higher than the running load this higher load would occur when the gen voltage is low due to acquiring the LH and RH bus. This would most likely cause the VR to provide the maximum excitation voltage thru the GCP.

Is this the right answer? I do not know but it works for me....

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Sir NATOPS

Thank you for correction i.e CC fan motor CB value 10A.Sir my opinion is Back emf generated by fan motor effect GCP TR unit, it may cause GCP rectifier damage but VR can provides max voltage for exciter field is approximately 7 V. this low power can not damage to any part of GCP i.e GCR

Regards

MUNIR ABBASI ATI

Home of hercules training center Pakistan

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Ok, Good luck finding an answer that explains the Caution ...

These items sometimes don't catch up with the times. These are VERY slow to catch up with the mods or upgrades with the acft. When I was in the school house many times we challenged them and NOBODY knew why or how they were there.

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