How is electrical power generated and distributed on the Boeing 787, and what are the principal components involved?

The Boeing 787 uses a variable-frequency electrical power system. Electrical power is generated by four engine-mounted Variable Frequency Starter Generators (VFSGs) and two APU generators, then controlled and distributed through generator control units and the aircraft's primary power distribution system.

Unlike many conventional transport aircraft that rely primarily on constant-frequency generation, the 787 uses variable-frequency starter generators. Each main engine has two VFSGs, giving four engine generators in total. The APU provides two additional generators. Generator Control Units (GCUs) control and protect the individual generators and participate in power-system reconfiguration following generator or system failures. The generated power is routed through the primary power distribution system, which distributes electrical power to the aircraft's various electrical loads. The FAA's Boeing 787 systems review identifies the VFSGs, GCUs and primary power panels as major elements of the aircraft's electrical power generation and start system. The FAA's B-787 MMEL also identifies the Primary Power Distribution System and VFSG-related equipment within ATA Chapter 24, Electrical Power.

• Four engine-mounted VFSGs provide main-engine electrical generation and engine-start capability. • Two APU generators provide additional electrical power. • Six GCUs are associated with the six generators. • The GCUs provide generator control, voltage regulation, protection and system reconfiguration functions. • Primary power panels and the Primary Power Distribution System distribute electrical power to aircraft loads. • The 787 electrical system is a variable-frequency system.