Global 7500 electrical system load shed

Global 7500 electrical system load shed  

Effectivity: Global 7500 aircraft 

ATA 24 

By: David Gosselin – Technical Services

Some of the electrical load may be shed in certain instances, impacting non-essential load, depending on the electrical power source configuration. 

Load shedding occurs if: 

• Only one Variable Alternative Generator (VFG) remains (note: maximum of two Alternative Current Motor Driven Pump (ACMPs) can be operated by a single airplane generator) 

• One or more Transformer Rectifier Unit (TRU) fails/overloaded or overheated 

• A high-load system is started such as the APU, or a hydraulic system ACMP 

• An airplane AC generator or AC external power source is overloaded 

Load shedding is managed by the Electrical Data Management Unit (EDMU). The non-essential AC and Direct Current electrical users are grouped into four (4) defined groups. 

The EDMU detects the configuration shedding condition (Priority Group 1) if only one generator (Left VFG, Right VFG, APU VFG) is available and without the Ground Power Unit (GPU) source.  

The EDMU shedding by escalation (Priority Group 1 to Priority Group 4) There is an escalation as required until all four groups are shed to protect the airplane electrical system. 

Only three (3) “green” loads are allowed to be shed and they are in the Priority Group 1. The other remaining three (3) groups are completion loads and depend on the completion electrical configuration: 

Shedding load Priority Group 1  

• Lowest priority level, first group to be shed 

• Only three (3) green loads in this group: 

• FLASH LTS - SPDA1-2-8 

• L HEATED MAT - SPDA1-3-3 

• R HEATED MAT - SPDA2-2-6 

  Shedding load Priority Group 2 

• Few completions loads 

• Shedding load Priority Group 3 

• Few completions loads  

• Shedding load Priority Group 4 

• Highest priority level, last group to be shed 

• Few completions loads 

  The common situation when shedding is noticed during aircraft operation occurs when the aircraft is on the ramp with the APU running only; the electrical system is in shedding configuration Priority Group 1 since only the APU generator is supplying the power.