777 AIRCRAFT MAINTENANCE MANUAL
ELMS -FUNCTIONAL DESCRIPTION -CONTROL
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ELMS -FUNCTIONAL DESCRIPTION -MONITORING
General
In addition to the distribution of electrical power, the ELMS also monitors the status of the power to many electrical loads for control purposes.
Monitor
The EEUs monitor electrical loads in several different ways. The EEUs can use different combinations of these ways to monitor the electrical loads:
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Bus voltage
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Circuit breaker position
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Relay position by voltage (option A)
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Relay position by ground (option B)
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Load current
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Analog discrete signal.
The EEUs use this load data to control the loads and to report faults. The EEUs also supply external control units with load data.
Bus Status
The EEUs monitor the power on buses by sensing the bus voltage. This is done with a voltage sensor (V SEN).
Bus/CB Status
The EEUs monitor the position of circuit breakers by sensing the voltage downstream of the circuit breaker. This is done with a circuit breaker monitor (CB MON).
Bus/CB/Relay Status -Opt A
Additionally, the EEUs can monitor the position of relays by sensing the voltage downstream of the relay contact. The signal conditioning module (SCM) makes the signal satisfactory for the EEU.
Bus/CB/Relay Status -Opt B
The EEUs sometime use an alternative to option A by sensing a ground (or power) through one contact of the relay. The SCM makes the signal satisfactory for the EEU.
Bus/CB/Relay/Current Status
The EEUs can also monitor load current with a current sensor (CUR SEN).
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ELMS -FUNCTIONAL DESCRIPTION -MONITORING
Bus/CB/Relay/Current/Sense Status
In addition to the above, the EEUs can monitor load status with an analog discrete supplied by the load. The SCM makes the signal satisfactory for the EEU.
NOTE: These are examples. They only show, in increasing complexity, ways the ELMS can monitor electrical loads. The ELMS may not use some of these combinations.
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ELMS -FUNCTIONAL DESCRIPTION -MONITORING
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ELMS -FUNCTIONAL DESCRIPTION -LOAD SHEDDING -1
General
The ELMS protects the electrical power system. It sheds (disconnects) electrical loads to keep the load levels below the power supply levels.
Power Sources
The ELMs monitors the status of these five power sources for load shed control:
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Left IDG (120 kva)
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APU generator (120 kva)
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Secondary external power (90 kva)
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Primary external power (90 kva)
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Right IDG (120 kva).
The ELMS does not monitor the backup generators for load shed control.
The GCUs and the BPCU digitally supply the ELMS with the power source status information. The ELMS also monitors the status of the power sources with hard-wired signals (configuration load shed signals). These signals come from circuits that go through the auxiliary contacts of the breakers and contactors in the power panels.
Load Shed Control
The P110 left power management panel and the P210 right power management panel control load shedding. P110 and P210 can shed loads independently or operate together (interpanel operation). If two power sources supply power to the airplane, the panels operate independently. If only one power source supplies power to the airplane, the panels operate together.
Independent Operation
If two power sources supply power to the airplane, P110 controls left side load shedding, and P210 controls right side load shedding. These are the loads that the ELMS can shed and the general sequence it sheds them:
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Galley loads
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Utility buses
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Equipment cooling vent fan
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Galley chillers
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Recirculation fans
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Lavatory/galley fans
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Electronic seat equipment
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Hydraulic pumps.
During independent operation, more important loads on one side can be shed while less important loads on the other side remain.
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