Airbus A320 Series Electrical System

                                             Electrical System Presentation

There are two identical engine driven generators called Integrated Drive Generators (IDG).

They are used as the main power source to supply the A/C electrical network.

The IDG basically contains, in a common housing, a generator and a Constant Speed Drive (CSD). The CSD provides a constant input speed to the generator which is required for a constant output frequency.

Each generator supplies 115V 400Hz Alternating Current (AC) to its own bus:
- generator 1 supplies AC bus 1,
- generator 2 supplies AC bus 2.

This supply is known as split operation, that means the AC power sources are never connected in parallel.

Each AC bus supplies a Transformer Rectifier (TR):

- AC bus 1 supplies TR 1,
- AC bus 2 supplies TR 2.

The TRs convert 115V AC into 28V DC to supply their associated DC buses, DC 1 and DC 2.

DC bus 1 then supplies the DC BAT bus.

DC bus 1 then supplies the DC BAT bus.

The DC battery bus can charge the batteries or receive power from the batteries as a backup supply, if no other power sources are available.

This is the basic electrical system.

We will now introduce some other components which also supply the system.

The entire electrical network can also be supplied by the APU generator.

On the ground, the aircraft electrical network can be supplied by an external power source.

Any one of the power sources can supply the entire electrical network.

As no parallel connection is allowed on this A/C (split operation), we have to give priorities to the different power sources in supplying the bus bars.

AC 1 and AC 2 buses are supplied in priority by their ownside  generator, then the external power, then the APU generator and then by the opposite generator.

The electrical system is also fitted with an ESSential Transformer Rectifier (ESS TR), which supplies the DC ESS Bus in abnormal or emergency configuration.

In abnormal configuration (loss of TR1 or TR2) the ESS TR is supplied by the AC ESS Bus.

 The hydraulic power to drive the EMER GEN is provided by a Ram Air Turbine (RAT) via the blue hydraulic system.

The RAT is located in the belly fairing and extends in case of severe electrical or hydraulic failures.

We will see the RAT activation later.

In emergency configuration (loss of AC BUS 1 and AC BUS 2), the ESS TR is supplied by the emergency generator.

 In emergency configuration with emergency generator not available, BAT 1 supplies the AC ESS BUS via the static inverter and BAT 2 supplies the DC ESS BUS.

 You can see that all the components we have talked about are displayed on the  ECAM page. Notice that each component has a title to aid identification.

GEN 1 and GEN 2 supplying AC bus 1 and AC bus 2.

TR 1 and TR 2 supplying DC bus 1 and DC bus 2.

Two essential busses supplied by the corresponding main buses.

The DC BAT bus and two batteries.

For simplification, the component indications have been removed, let’s now present them.

As shown, each component can be monitored via its indications.

The ELEC panel is located on the overhead panel. On the 318, a commercial pushbutton switch is added on the ELEC panel.

For emergency cases, there is an EMER ELEC PWR panel on the left hand side of the overhead panel.

Now let’s look at the relationship between the ELEC panel and the ECAM ELEC page.

The battery voltage can be monitored either on the overhead panel or the ECAM page.

Each battery is controlled by a pushbutton switch.

Both main generators and the APU generator are controlled by their associated pushbutton switch.

The external power is also controlled by a pushbutton switch.

 The AC ESS FEED pushbutton switch enables the pilots to change the supply for the AC ESS bus from AC bus 1 to AC bus 2.

When the BUS TIE pushbutton switch is in AUTO position, it allows the opening or closing of the bus tie contactors in order to supply the AC 1 and AC 2 buses according to the power supply priorities.

When OFF, both bus tie contactors open to isolate one side of the network from the other (e.g.: smoke configuration).

In case of failure, these pushbutton switches disconnect the IDG from the engine gear box.

The COMMERCIAL pushbutton switch allows the shedding of galleys, cabin and commercial related loads.

The GALY & CAB pushbutton switch allows galleys and some sub-buses to be shed.

 The EMER GEN TEST switch is used to test the emergency generator.

In avionics smoke condition, the GEN 1 LINE pushbutton disconnects the generator from the busbar but it remains energized to supply fuel pumps.

MAN ON pushbutton
The RAT is automatically extended by the system in case of loss of AC 1 and AC 2 buses in order to pressurize the blue hydraulic system.
Then the emergency generator automatically supplies the essential network, if its parameters are correct.
NOTE: The RAT may be extended manually by pressing the red guarded MAN ON pushbutton.

The RAT + EMER GEN LIGHT comes on red when the emergency generator is not yet on line (transient configuration about 3 sec or generator faulty).

The static inverter converts the direct current from battery 1 into an AC current if no other source is available.

The Battery Charge Limiters (BCLs) control the battery coupling and uncoupling to the DC BATTERY BUS to ensure battery charging and protection.

Each battery is rated at 24 V with a capacity of 23 Ah.

All TRs are identical and interchangeable.

 The Ground Power Control Unit (GPCU) connects the external power to the A/C network if all parameters are within the limits.

It is also the central unit connected to the Centralized Fault Display Unit for on-board maintenance purposes.

The Electrical Generation Interface Units (EGIU) used by the ECAM  to display the AC electrical power parameters.  

The Generator Control Units (GCUs) protect and control the A/C network and generators.

The main C/B panels are located in the cockpit.

In the EEPGS, the GPCU is replaced by a Ground and Auxiliary Power Control Unit (GAPCU). The GAPCU controls the APU Gen and the external power channels.





















The ESS TR is identical to TR 1 and TR 2. It converts 115 VAC to

28 VDC at a rate of 200 A.

The EMER GCU connects the EMERgency GENerator to the ESSential network, if all conditions are met.

The Ground Power Control Panel (GPCP) and the external power receptacle are located in front of the nose landing gear.

On this panel, 2 Lights indicate the Ground Power Unit availability (AVAIL light) and connection to the A/C network (NOT IN USE light).

The Ground Power Unit should provide 400 Hz 3 phase 115 VAC rated at  90 kVA minimum.

 The MAINTenance BUS switch, located on the forward cabin C/B panel, allows the AC and DC service buses to be supplied without energizing the whole A/C electrical network.

The aft cabin C/B panel contains only C/Bs.

 The RAT will extend automatically to pressurize the blue hydraulic system, which powers the EMERgency Generator, if the A/C speed is sufficient and AC BUS 1 and 2 are no longer supplied.

CAUTION:   The RAT will extend also if  the red guarded MAN ON
  pushbutton is pressed, even if the A/C is not electrically
  supplied (cold A/C).

 The GPCU is the interface between the GCUs and the CFDIU for test purposes and fault reporting on the MCDUs .

Both the BCLs and the EMER GCU communicate with the CFDIU for the same purposes.

The TRs are connected to the CFDIU so that they can be reset via the MCDU.

 In the EEPGS, the GAPCU is the interface between the GCUs and the CFDIU for test purposes and fault reporting on the MCDUs.

 When you work on the electrical system, make sure that you obey all the AMM safety procedures. This will prevent injury to persons and/or damage to the aircraft. Here is an overview of main safety precautions relative to the electrical system.

When you perform any maintenance task on the electrical system, make sure that no AC or DC power source is connected to the aircraft electrical circuits. There is a risk of electrocution if the AC or DC power remains connected.

Some components are heavy. You must make sure that you can hold the component before you remove/install it. If it fails, it can cause injury to persons and damage to equipment.

Before you connect/disconnect the ground power unit connector to the external power receptacle of the aircraft, make sure that the external electrical power is not energized, dangerous arcing can occur. Make sure that all the electrical circuits in maintenance are isolated before you supply electrical power to the aircraft.

Be careful when you work on the engine components after the engine is shutdown. The components can remain hot for up to one hour. Hot parts can cause an injury and hot oil can burn your eyes and skin. Oil is poisonous.

When you are in contact with oil, fuel or other harmful products use goggles, insulated gloves and other protective clothes. Use solvents/cleaning agents, sealant and other special materials only in a good ventilated work area. These materials are poisonous.

Anyway, get medical aid if necessary.