EXTERNAL POWER -FUNCTIONAL DESCRIPTION -BPCU
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EXTERNAL POWER -GROUND HANDLING/GROUND SERVICE POWER -FUNCTIONAL DESCRIPTION
General
The BPCU controls the power to the ground handling bus and the ground service bus. Ground handling power is available only on the ground. Ground service power is available on the ground and in flight.
Ground Handling Power
When you apply good power to the primary power receptacle, the BPCU energizes one coil of the ground handling relay. This connects the primary external power to the ground handling bus.
If no primary external power is available but the APU generator power quality is good, the BPCU energizes the other coil of the ground handling relay. This connects the APU generator to the ground handling bus.
The ground handling bus will not have power if the engines are running or if the airplane is in the air.
Ground Service Power
When you apply good power to the primary power receptacle, power is available at the ground service transfer relay. When you push the ground service switch, the BPCU energizes the ground service transfer relay. This connects primary external power to the ground service bus. With primary external power on the ground service bus, the BPCU turns on the light in the ground service switch.
When you push the ground service switch with no primary external power available, but the APU generator power quality is good, the BPCU energizes the ground service select relay. This connects the APU generator to the ground service bus. With APU power on the ground service bus, the BPCU turns on the light in the ground service switch.
When the right main ac bus has power, it automatically supplies the power to the ground service bus. In this case, the ground service switch has no effect on the ground service bus. The light in the switch does not come on or it goes out if it was on.
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EXTERNAL POWER -GROUND HANDLING/GROUND SERVICE POWER -FUNCTIONAL DESCRIPTION
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EXTERNAL POWER -FUNCTIONAL DESCRIPTION -PRIMARY/SECONDARY POWER
General
The BPCU controls external power on the airplane. You use the external power switches on the electrical panel to supply command signals to the BPCU.
Primary External Power
When you apply power to the primary power receptacle, power is available at the primary EPC. With good power quality, the BPCU turns on the AVAIL light in the primary external power switch. When you push the primary external power switch, the BPCU energizes the primary EPC. This connects primary external power to the right main ac bus. When the EPC closes, the BPCU turns off the AVAIL light and turns on the ON light.
The BPCU must keep control power on the EPC to keep it closed. If you push the primary external power switch again, the on command in the BPCU goes away. This removes power to the EPC and it opens. The ON light goes off and the AVAIL light comes on again.
Secondary External Power
Secondary external power works the same as primary external power except the secondary external power connects to the ac tie bus through the secondary EPC.
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EXTERNAL POWER -FUNCTIONAL DESCRIPTION -PRIMARY/SECONDARY POWER
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777 AIRCRAFT MAINTENANCE MANUAL
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EXTERNAL POWER -OPERATION
General
To apply external power to the airplane electrical system, do these steps:
*
Connect ground power plugs
*
Observe indications
*
Operate control switches.
Placards inside the external power panel access door give specific information about connecting external power.
Connect Ground Power Plugs
To connect to the power receptacles, you must loosen the restraining straps and remove the hooks from their stow points.
You should always use the primary receptacle. If you need more power, you can use the secondary receptacle.
Put in the ground power plug. Put the correct hook around the power cord behind the plug and tighten the restraining strap. Turn on power at the power source.
Observe Indications
If the quality of the power to the primary receptacle is good, the two lights above the receptacle come on. When the lights above the primary receptacle are on, the ground handling buses have power.
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