The Airbus A320 electrical system provides AC and DC electrical power for all aircraft systems and equipment. Understanding electrical power generation, distribution, and emergency configurations is critical for type rating exams and safe flight operations. This guide covers all essential aspects tested during A320 type rating.
How Does the A320 Electrical System Work?
The A320 electrical system consists of three main AC power sources and multiple DC conversion systems. The architecture is designed with redundancy to ensure electrical power availability even during multiple failures.
⚡ AC Power Sources
Two engine-driven generators (GEN 1 & 2), APU generator, external power, emergency generator (RAT)
🔋 DC Power Sources
Two Transformer Rectifiers (TR 1 & 2), battery chargers, two main batteries, emergency generator
📡 Distribution
AC BUS 1 & 2, AC ESS BUS, DC BUS 1 & 2, DC ESS BUS, DC BAT BUS, HOT BUS 1 & 2
🚨 Protection
Generator Line Contactors (GLC), Bus Tie Contactors (BTC), automatic load shedding, circuit breakers
AC Power Generation
Engine Generators (GEN 1 & GEN 2)
Each CFM56 or IAE V2500 engine drives a 90 kVA Integrated Drive Generator (IDG). The IDG maintains constant 115V AC at 400 Hz regardless of engine speed variations. This is the primary electrical power source during normal flight operations.
🔧 IDG Characteristics
Output: 115V AC, 400 Hz, 3-phase
Power: 90 kVA per generator
Frequency Regulation: Constant 400 Hz via Constant Speed Drive (CSD)
Connection: Automatic when engine starts, disconnection via IDG DISC pb
⚠️ IDG Disconnection
Once an IDG is disconnected (via overhead panel IDG DISC pushbutton), it CANNOT be reconnected in flight. Reconnection is only possible on the ground by maintenance. This is a critical limitation to remember for type rating exams.
APU Generator
The Auxiliary Power Unit (APU) can provide electrical power both on ground and in flight. The APU generator is a 90 kVA unit capable of powering the entire aircraft electrical system up to approximately FL250 (limited by APU bleed extraction).
- Ground Use: Primary power source before engine start
- In-Flight Use: Backup for generator failures up to maximum APU altitude
- Automatic Start: APU auto-starts in flight if both engine generators fail (if APU MASTER SW on)
External Power
Ground power can be connected via the external power receptacle. External power automatically takes priority over APU power when connected, allowing APU shutdown to save fuel during ground operations.
Emergency Generator (RAT)
The Ram Air Turbine (RAT) deploys automatically when AC BUS 1 and AC BUS 2 are both unpowered. The RAT drives a hydraulic pump on the blue hydraulic system, which in turn powers a 5 kVA emergency generator.
🚨 RAT Deployment Conditions
RAT deploys automatically when:
• AC BUS 1 AND AC BUS 2 both lose power, AND
• Aircraft speed > 100 kt
Once deployed, the RAT cannot be retracted in flight. It powers AC ESS BUS and DC ESS BUS only, resulting in emergency electrical configuration.
DC Power Generation and Distribution
Transformer Rectifiers (TR 1 & TR 2)
Two Transformer Rectifiers convert 115V AC to 28V DC. TR 1 normally powers DC BUS 1, while TR 2 powers DC BUS 2. Each TR can supply the entire DC system if needed.
Batteries
The A320 has two 23 Ah Nickel-Cadmium batteries. These batteries provide:
- APU Start Power: Essential for APU starting when no other power available
- Emergency DC Power: Automatic takeover if all AC power lost
- Duration: Approximately 30 minutes of essential DC services
- Hot Bus Power: Permanent power to critical systems even when aircraft unpowered
| Battery | Normal Function | Emergency Function |
|---|---|---|
| BAT 1 | Powers HOT BUS 1, charges from DC BUS 1 | Powers DC BAT BUS (essential systems) |
| BAT 2 | Powers HOT BUS 2, charges from DC BUS 2 | Powers DC ESS BUS (critical flight instruments) |
Emergency Electrical Configuration
This is one of the most important concepts for A320 type rating exams. Emergency electrical configuration occurs when normal AC power is lost.
When Does It Occur?
Emergency electrical configuration is triggered when AC BUS 1 and AC BUS 2 are both unpowered. This could result from:
- Dual engine failure
- Both generators failed or disconnected
- Loss of all AC power sources (engines, APU, external power)
What Happens in Emergency Configuration?
- RAT Deploys: Automatically if speed > 100 kt
- Load Shedding: Non-essential electrical loads automatically disconnected
- Battery Power: BAT 1 and BAT 2 power essential DC buses
- Limited Systems: Only essential flight instruments and controls remain powered
🔌 Buses Powered in Emergency Config
AC Power: AC ESS BUS (via emergency generator from RAT)
DC Power: DC ESS BUS (from BAT 2), DC BAT BUS (from BAT 1)
Available Systems:
• Captain's PFD, ND, upper ECAM
• ISIS (standby instruments)
• Essential flight controls (limited degraded modes)
• Essential lighting
• VHF 1
Duration: Approximately 30 minutes on batteries alone
Common Electrical Failures (Type Rating Questions)
Single Generator Failure
If one generator fails (e.g., GEN 1 FAULT):
- Bus Tie Contactor (BTC) automatically closes
- Remaining generator (GEN 2) powers both AC BUS 1 and AC BUS 2
- Galley load automatically shed to prevent overload
- All systems remain operational
AC BUS Loss
Loss of AC BUS 1 or AC BUS 2 individually:
- Associated systems lose power (check ECAM for specific losses)
- TR associated with lost bus fails (DC bus still powered by other TR)
- Aircraft remains fully operable with redundant systems
Battery Charging Failure
If battery charging fails, batteries will slowly discharge even with generators running. ECAM will show battery voltage decreasing. Flight should be completed expeditiously as emergency electrical backup is degrading.
Frequently Asked Questions
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