ELMS -FUNCTIONAL DESCRIPTION -LOAD SHEDDING -1
When you use external power, the ELMS reverses the load shed sequence for hydraulic pumps and electronic seat equipment.
Interpanel Operation
If only one power source supplies power to the airplane, P110 and P210 control load shedding together. They use a combined load shed sequence so that all the less important loads shed first and all the most important loads shed last.
Load Shed Limits
Since the power sources can supply different levels of power, there are several load shed limits. These are the conditions that define the load shed limits:
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Power source configuration
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Value of the overload
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Sustained time of the overload.
The ELMS gets load level data from the GCUs and BPCU across the systems ARINC 629 data buses.
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ELMS -FUNCTIONAL DESCRIPTION -LOAD SHEDDING -1
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777 AIRCRAFT MAINTENANCE MANUAL
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ELMS -FUNCTIONAL DESCRIPTION -LOAD SHEDDING -2
Configuration Load Shed
A change in the source(s) of power for the airplane is called a change in the power source configuration. If the configuration change will result in a lower power supply capacity, the ELMS quickly sheds specified loads. This protects the new power source from overloading. The normal computer processing time does not occur fast enough to adequately do this function. Configuration load shed logic uses a hard-wired signal from the power management panel through auxiliary contacts in the BTBs, GCBs, APB, and EPCs to quickly detect a power source configuration change.
Configuration load shed logic sheds loads in groups. If the ELMS needs to shed more loads, it uses its normal computer processing.
Sequential Load Shed
If there is a large overload not due to a power source change , the ELMS sheds loads in groups like a configuration load shed.
If an overload is not large, the ELMS sheds individual loads until the electrical load demand level is below the available power supply level.
The ELMS sheds all loads on a main bus for these conditions:
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There is no power on the bus for over 2.5 seconds
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A failure of interpanel operations
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* Loss of load level data from the GCUs and BPCU.
Load Restoration
After a load shed occurs, the ELMS adds loads in the reverse sequence they were shed. The ELMS continues to add loads until the electrical load demand level would exceed the available power supply level.
The ELMS staggers the starting of the hydraulic ac motor pumps.
After a configuration load shed, loads do not come back on for approximately 3 seconds.
Failure of interpanel operations, prevents any load restoration.
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Indication
When the ELMS does a load shed, the message LOAD SHED shows on the electrical power synoptic display below the utility bus indication for the related channel.
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ELMS -FUNCTIONAL DESCRIPTION -LOAD SHEDDING -2
Training Information Point
If you use an external power source with less than a 90 kva capacity at an external power receptacle, the ELMS can possibly shed and restore all loads four times in about one minute. It then sheds all loads until you supply more power to the airplane.
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ELMS -SPECIAL FUNCTION TESTS
General
There is one special function test for each power management panel. These are the special function tests:
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Initiate P110 EU self test
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Initiate P210 EU self test
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Initiate P310 EU self test.
NOTE: The terms EU and EEU refer to the CCU and SIU combination.
Initiate P110 EU Self Test
This test makes sure that all Electronic LRMs in the P110 electronics unit operate correctly.
Initiate P210 EU Self Test
This test makes sure that all Electronic LRMs in the P210 electronics unit operate correctly.
Initiate P310 EU Self Test
This test makes sure that all Electronic LRMs in the P310 electronics unit operate correctly.
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