Electricity in Aviation

General Overview of Electric Systems in Aircraft

  • Discussed the fundamental characteristics of electric systems in aircraft, emphasizing simplicity and straightforwardness.

Battery Systems

  • Normal Battery (Main Battery): The primary power source for starting the aircraft, supporting emergency power but not supplying starter motors.
  • Emergency Battery: Engaged only for emergency power, has a crucial role during engine starting.
    • Will not power the starters but transfers to support avionics during cranking.

DC Power Management

  • DC Standby Bus: Critical for avionics, protected during start by transferring to the emergency battery to prevent transients.
    • Important during engine start due to initial 1500 amp current surge.
  • Main Battery Specs:
    • Type: Lead Acid
    • Voltage: 24V
    • Capacity: 40 Amp hour
  • Emergency Battery Specs:
    • Voltage: 24V
    • Capacity: 18 Amp hour
    • Duration: 10 minutes in IMC (Instrument Meteorological Conditions).

Engine Start Procedure and Battery Power

  • The main battery in IMC provides approximately 30 minutes of power.
  • On starting an aircraft, current surges and voltage transients may occur, necessitating protection for avionics.

Generator Systems

  • DC Generators: Mounted in the accessory section of the engine.
    • Engage at 61.5 NH (High Pressure Compressor Speed) for operation.
  • Starter Generator Engagement:
    • Activates at 45% NH and cuts out at 61.5 NH.
    • Important to engage without voltage faults and overcurrent.

Total Electrical Capacity and Restrictions

  • A single generator can run all systems but needs close monitoring during single-sourcing.
  • Load limits per generator are: 400, 600, and 800 amps.
    • 600 amps: Limited to 2 minutes before automatic disconnection.
  • BPC (Bus Power Control): Manages bus switching and load shedding.
  • Generator Control Unit: Controls generation parameters and monitors system states.

AC Power Systems

  • Distributed between inverters that manage avionics operations.
  • Inverter Function: Converts DC to AC power; critical for operating avionics and ensuring continuous power in emergencies.
  • AC Standby Buses: Powered by inverter 1 during battery-only operation, ensures instrumentation is still available to the captain.

Utility Buses

  • There are dedicated utility and service buses for specific functionalities such as cargo lighting and recertification fans on utility bus 1 and 2.
  • Important to manage these with a single switch: termed the "stupid switch" due to its multi-functional nature where turning off one can disable others.
  • DC Service Utility Bus: Important for operational integrity, particularly when safety systems are in play.

Functionality during Failures

  • In dual generator failure scenarios, transition to emergency power modes, maintaining essential systems through battery power.
    • Battery Basic Mode: Core functionality reduced to maintain essential control and circuit operations.
  • Understanding these power configurations is crucial for accident prevention and maximum operational efficiency.

Cross Generator Start Protocol

  • Cross Generator Start described:
    • When engaging in a cross generator start, the generator from the second engine will help only after exceeding 10% NH from the first engine start.
    • This isolates the second engine to protect the active generator until sufficient speed is available.
  • In-Flight Start: Must be battery-only, ensuring generator protection and avoiding dual failures.

Conclusion and Review

  • It is essential to grasp these electrical system functionalities and operational limits.
  • Continuous review and practice are necessary for mastering these protocols and achieving safety in various flight scenarios.