Electrics

  • Power Source:

    • Three integrated engine-driven generators mounted on engines 1, 2, and 3.

    • Controlled hydraulically.

  • Generator Control Units (GCU):

    • Each Integrated Drive Generator (IDG) has a corresponding GCU.

    • The GCU controls all generator functions and protection features.

  • GCU Tripping:

    • If the GCU is tripped manually, it cannot auto-reset.

    • A manual reset command (BTB manual reset) is required to restart the generator.

  • Distribution:

    • Each IDG connects through a generator control breaker to its own load bus.

    • Load buses are interconnected through a bus tie breaker (BTB) to the synchronizing bus.

  • Parallel Operation:

    • The bus tie breaker (BTB) allows parallel operation of generators.

  • AC Power Supply:

    • The AC system supplies AC power to all AC-Powered systems.

    • It also supplies AC power to two transformer rectifiers (TRs) for conversion to DC Power.

  • On-Ground Power Sources:

    • On the ground, if IDGs are not operating, AC power can be supplied by:

      • Onboard Auxiliary Power Unit (APU).

      • External power cart.

  • Bus Power Control Unit (BPCU):

    • The BPCU is the central control unit responsible for managing power distribution.

    • It allows for the safe addition of external or APU power through the synchronizing bus.

  • External Power Receptacle Door:

    • If the external power receptacle door is open, the APU cannot be connected to the synchronizing bus.

Direct Current (DC) System

  • Power comes from two TR’s that are the primary source of DC power for the aircraft

  • TR’s convert AC power to DC for distribution to DC operated equipment

    • Backup Source of DC power s the main aircraft battery or APU battery through the battery bus

  • Each TR supplies separate DC buses linked together by current limiters that allow one TR to power all DC loads if a TR fails

  • One TR can supply DC power to the entire system

  • Batterues can provide backup of the power system

    • APU battery - power to the apu

    • Main Battery - power to the aircraft

  • Batteries also supply power to the battery bus and are wired so that either may supply power to the aircraft DC system

  • Battery chargers are located with the batteries in the latrine

    • Main receives input power from No 3 gen

    • Apu receives input power from No 2 gen

  • Buses

    • TR buses - the two TR buses distribute power from the two TR units to various airplane DC loads

    • Switched DC Bus - Receives primary power from TR bus No 1 when the battery power switch is in normal

    • Battery bus - distributes power from the main and/ or APU batteries

Copilot Instrument Power System (CIPS)

  • Consists of one hydraulically-powered generator and a 28 Volt TR

    • If power is unavailable it can be supplied by the main power system

    • This system is normally independent of the aircraft electrical system 

    • If main AC power is unavailable, the CIPS will supply power to the copilots instruments

    • TR supplies DC power to the connected loads