Aircraft Electrical Power Distribution Systems

021-09-04Pablo Asensio Martínez2026-03-242 min

Bus Bars

  • Definition: Thick copper bars that act as a central distribution point for electrical power.
  • Function: Simplifies wiring (lighter than individual wires to each consumer). Collects power from sources and distributes it to consumers.
  • Consumers: Connected in parallel (isolating one doesn't affect others).
  • Protection: Protected by circuit breakers.
    • Short Circuit on Bus Bar: If a bus bar faults (short circuit), its protection isolates it. All consumers on that bus lose power for the rest of the flight.

Distribution Systems

Split Bus System

  • Normal Operation: Each generator feeds its own dedicated AC bus bar. Source are isolated (never paralleled).
  • Typical Setup: Modern twin-engine aircraft.
  • Generator Failure:
    1. Failed generator GCB (Generator Circuit Breaker) opens.
    2. BTB (Bus Tie Breaker) closes.
    3. Result: The remaining working generator feeds BOTH bus bars. (Or APU takes over the failed side).
    4. Load shedding may occur due to single source capacity.

Parallel Bus System

  • Normal Operation: All generators feed into a common distribution network (synchronizing bus).
  • Requirement: Generators must be paralleled (Synchronized).
  • Conditions for Paralleling:
    • Equal Voltage.
    • Equal Frequency.
    • Equal Phase Sequence.
  • Generator Failure: Failed generator GCB opens. The remaining generators continue to feed all buses (load is shared among remaining sources).

Types of Buses

  • AC BUS: Main distribution for AC loads.
  • DC BUS: Main distribution for DC loads (fed by TRUs).
  • ESSENTIAL BUS: Powers critical systems. Can be fed by emergency sources (e.g., batteries/inverter) if main power fails.
  • HOT BATTERY BUS (Direct Bus):
    • Directly connected to the battery.
    • Always powered (even when aircraft is unpowered).
    • Powers vital items (e.g., fire extinguishers, clocks).

Power Conversion

  • TRU (Transformer Rectifier Unit):
    • AC $\rightarrow$ DC.
    • Lowers voltage (115V $\rightarrow$ 28V).
  • Inverter (Static Inverter):
    • DC $\rightarrow$ AC.
    • Used to power Essential AC loads from batteries in an emergency (Total AC failure).
  • Battery Charging: Batteries (DC) are charged by the DC Bus (fed by TRUs).

Contactors & Reconfiguration (Logic)

  • External Power: Can feed main buses on the ground via External Power Contactors.
  • APU: Can feed main buses (replaces main generators).
  • Cross-Tie (X-TIE): Allows one side's DC bus to feed the other side's DC bus (if a TRU fails).
  • Emergency Configuration:
    • Loss of all generators $\rightarrow$ Batteries feed DC ESS BUS $\rightarrow$ Static Inverter feeds AC ESS BUS.

Protection Systems

Electrical systems monitor and protect against:

  • Over-voltage
  • Under-voltage
  • Over-current
  • Over-speed (IDG/CSD)
  • Under-frequency