The Airbus A320 is renowned for its advanced fly-by-wire technology and sophisticated onboard systems, one of the most critical being its electrical power system. From engine generators to backup batteries, the A320’s electrical network ensures seamless power distribution across all aircraft systems, in both routine and emergency operations. In this article, we’ll break down the A320 electrical system basics, focusing on the differences and interplay between its AC and DC systems.
Overview of the A320 Electrical Architecture
The A320’s electrical system operates using a combination of alternating current (AC) and direct current (DC). The AC system is the primary power source and provides constant-frequency three-phase 115/200 V at 400 Hz. The DC system, rated at 28 V, supports equipment that requires direct current and acts as a backup power source during specific scenarios.
Key power sources include two engine-driven generators, one APU generator, and emergency provisions such as the hydraulic-driven emergency generator and onboard batteries. The system is designed to be highly redundant, with multiple backups and automatic transitions to maintain continuous power flow.
Engine-Driven Generators
The aircraft has two primary AC generators, each powered by one of the main engines. Known as GEN 1 and GEN 2, these generators supply up to 90 kVA of three-phase, 115/200 V, 400 Hz power. They are controlled by dedicated Generator Control Units (GCUs), which regulate frequency and voltage while also managing protective functions such as opening or closing line contactors.
In normal flight, the engine generators provide full electrical supply to the aircraft, including the conversion of some AC power into DC through transformer rectifiers.
APU Generator and External Power
The Auxiliary Power Unit (APU) includes a third generator that can supply the entire AC system when engines are off or when redundancy is required. Like the engine generators, the APU generator produces the same 115/200 V, 400 Hz output and is especially useful during ground operations or when starting the engines.
External power can also be connected via a receptacle near the nose landing gear. When available and selected, external power takes precedence over the APU generator. A Ground Power Control Unit (GPCU), or the more advanced Ground and Auxiliary Power Control Unit (GAPCU), monitors voltage and frequency and manages power switching logic safely.
Emergency Generator and Redundancy
Should all main AC sources fail, the aircraft automatically switches to the emergency generator. Powered by the blue hydraulic circuit, this generator delivers 5 kVA of three-phase 115/200 V, 400 Hz AC power to essential systems. A GCU ensures stable operation by maintaining correct speed, voltage, and contactor control.
This mechanism provides the flight crew with crucial instrumentation and control systems during a complete electrical failure scenario, maintaining flight safety until landing or generator restoration.
Static Inverter Functionality
When only battery power is available, the A320 uses a static inverter to convert DC from Battery 1 into 1 kVA of single-phase 115 V, 400 Hz AC. This inverter supplies part of the AC essential bus and is triggered automatically based on aircraft speed and battery configuration.
If the aircraft is above 50 knots, the inverter activates regardless of battery switch status. Below 50 knots, both BAT 1 and BAT 2 must be selected ON for the inverter to engage.
Transformer Rectifiers and DC Power Supply
AC power is converted to DC by three main transformer rectifier units: TR 1, TR 2, and the ESS TR (Essential Transformer Rectifier). Each TR unit supplies up to 200 amps of 28 V DC to different sections of the aircraft’s systems. The ESS TR is particularly important during emergency conditions, supplying power to the essential DC bus when main TRs or generators fail.
An additional TR, known as TR Entertainment, is dedicated to powering the In-Flight Entertainment (IFE) DC bus and is separate from flight-critical systems.
Battery System and Backup Power
The A320 is equipped with two main batteries, each with a capacity of 23 amp-hours. These batteries are permanently connected to the hot buses and managed by Battery Charge Limiters (BCLs), which regulate charging and monitor battery health. During a complete loss of generation, these batteries support essential systems and, with the help of the static inverter, provide AC to critical buses.
Source Priority Logic
The electrical system follows a defined logic for source selection and priority:
- Engine generators have the highest priority during flight.
- APU generator is used when engine generators are unavailable.
- External power is prioritized over the APU when manually selected.
Only one engine generator is required to power the full aircraft network, excluding the DC Entertainment bus. Two power sources are needed to power the DC Entertainment bus, except on the ground where the APU or external power may be sufficient if load conditions permit.
Circuit Breakers and Monitoring
The A320 includes both monitored (green) and non-monitored (black) circuit breakers. If a monitored breaker remains open for more than one minute, a C/B TRIPPED message appears on the ECAM, along with the panel location. Non-monitored breakers do not generate alerts, and red-capped breakers (such as those for Wing Tip Brakes) must not be reset by flight crew.
Monitored panels include the overhead panel, left and right electrical bays, and rear panels labeled J-M, N-R, S-V, and W-Z.
Why This System Matters
The Airbus A320 electrical system offers redundancy, flexibility, and automation—all of which enhance aircraft safety and reliability. By balancing AC and DC systems, integrating multiple generation and conversion sources, and embedding intelligent control logic, the aircraft ensures continuous electrical availability even under failure conditions. Understanding these A320 electrical system basics is essential for pilots, engineers, and aviation enthusiasts alike.
Frequently Asked Questions
What type of electrical power does the Airbus A320 use?
The A320 uses a three-phase 115/200 V, 400 Hz AC system as its main power source and a 28 V DC system for backup and specific systems requiring direct current.
How many generators does the A320 have?
The A320 is equipped with two engine-driven generators, one APU generator, and one emergency generator driven by the blue hydraulic system.
What does the static inverter do on the A320?
The static inverter converts DC power from Battery 1 into single-phase 115 V, 400 Hz AC power, supplying part of the AC essential bus during battery-only operations.
What is the purpose of transformer rectifiers (TRs)?
Transformer rectifiers convert AC power into 28 V DC power, which is used by DC-powered systems and essential buses.
Can external power be used during flight?
No. External power can only be used on the ground. In flight, the aircraft uses engine generators first, then the APU generator, and finally the emergency generator if needed.