AC AUXILIARY GENERATION - DESCRIPTION AND OPERATION

** ON A/C NOT FOR ALL

1. General
The AC auxiliary generation comes from the APU generator. This generator can:

in flight, replace either or both engine generator(s) in case of failure,
on the ground, supply the aircraft electrical network when the electrical ground power unit is not available.

** ON A/C NOT FOR ALL

2. Component Location

AC Auxiliary Generation (APU Generator GCU) Component Location ** ON A/C NOT FOR ALL

The APU generator is installed in the APU compartment. It is attached to the APU gearbox by a button hole flange.
The APU generator is installed in the APU compartment. It is attached to the APU gearbox by a button hole flange.

FIN	FUNCTIONAL DESIGNATION	PANEL	ZONE	ATA REF
** ON A/C NOT FOR ALL
1XS	GCU-APU	91VU	121	24-23-34
** ON A/C ALL
2XS	P/BSW-ELEC/APU GEN	35VU	210	24-23-00
3XS	GLC-APU	120VU	212	24-23-55
** ON A/C NOT FOR ALL
8XS	GEN-APU		310	24-23-51
** ON A/C NOT FOR ALL
8XS	GEN-APU		316	24-23-51
** ON A/C ALL
42XS	CT-AC, APU GEN	120VU	212	24-23-17
** ON A/C NOT FOR ALL
24XG	GAPCU	92VU	122	24-41-34

** ON A/C NOT FOR ALL

3. System Description

APU Generator Configuration - Block Diagram ** ON A/C NOT FOR ALL

** ON A/C NOT FOR ALL

4. Component Description

A. APU Generator FIN: 8-XS
The APU directly drives the APU generator at a nominal 24000 rpm constant speed.
The APU gearbox supplies the oil for cooling and lubrication of the generator. The cooling circuit is common to the APU and the generator.
The APU supplies, scavenges, drains the oil.
The generator is a brushless oil-cooled generator with a nominal 115/200 volt, 90 KVA, 3 phase 400 Hz output.
The generator includes three stages which are:

the pilot exciter,
the main exciter,
the main alternator.

The operation principle is the same as that of the IDG generator (Ref. 24-21, generator section).

NOTE: The PMG frequency for the APU generator is 1600 Hz.

A temperature bulb is included in the auxiliary generator. It senses the generator-oil outlet temperature. This sensor is connected to the Electronic Control Box (ECB) of the APU. Any high oil temperature causes the automatic shutdown of the APU (by the ECB).
This in turn causes the APU speed to decrease to zero.
The APU directly drives the APU generator at a nominal 24000 rpm constant speed.
The APU gearbox supplies the oil for cooling and lubrication of the generator. The cooling circuit is common to the APU and the generator.
The APU supplies, scavenges, drains the oil.
The generator is a brushless oil-cooled generator with a nominal 115/200 volt, 90 KVA, 3 phase 400 Hz output.

NOTE: The frequency range of the APU generator can be from 395Hz to 405Hz. When the APU fuel-saving mode is used, the APU speed is reduced to 99%. In this mode, the frequency of the APU generator decreases to 396Hz.

The generator includes three stages which are:

the pilot exciter,
the main exciter,
the main alternator.

The operation principle is the same as that of the IDG generator (Ref. 24-21, generator section).

NOTE: The PMG frequency for the APU generator is 1600 Hz.

B. Generator Control Unit (GCU)
The overall function of the APU GCU is selected by pin programming.
The 3 GCUs are identical and interchangeable. For details concerning the description and functions of the APU GCU, refer to 24-22-00.

C. Ground and Auxiliary Power Unit (GAPCU)
The GAPCU controls the APU generator and the external Power channels. For the APU generator channel control, the GAPCU has different functions:

voltage regulation,
control and protection of the network and the generator,
control of the various indications,
system test and self-monitoring.
The GAPCU supplied:
directly from the PMG, for generator excitation and 28VDC internal and external supply,
from the aircraft normal network (28VDC) for the internal and external supply.
This dual supply constitutes a back up supply.

(1) Voltage regulation
The voltage regulation is achieved by controlling the current through the exciter field. The voltage is kept at nominal value (115 VAC) at the Point of Regulation (POR).
The POR is located in the electrical power centre (120VU) at the end of the generator feeder, upstream of the line contactor.
The principle of operation of the voltage regulator is by constant frequency variable pulse width modulation of the voltage through the exciter field.

(2) Control and protective functions
The GAPCU controls the connection and disconnection of the power provided by the generator to and from the aircraft electrical system. This control is provided by means of 2 relays:

the Generator Control Relay (GCR) which controls the generator excitation,
the Power Ready Relay (PRR) which controls the generator line contactor and the FAULT warning light in the cockpit.

The following control or fault signals cause generator shutdown or de-energization:

No controlled Shutdown recognized upon power-up of the control unit
Overvoltage Fault
Undervoltage 1 Fault
Undervoltage 2 Fault
Overfrequency 1 Fault
Overfrequency 2 Fault
Underfrequency 1 Fault
Underfrequency 2 Fault
SRD/PMG to Chassis Short Fault
Differential Protection Fault
Overcurrent Fault
Fire switch Fault
Phase Sequence Fault with the Power Ready Relay "absent"
AGC Control Circuit Fault
AGC welded Fault
Shorted/Open PMG Fault with the Power Ready Relay "absent"
Pin Programming

The generator shall be "reset" when the protective faults (identified above) are still not present and one of the following occurs:

Cold Start (which is defined as POWER-UP RESET or the application of 28 volts to the control unit) occurs,
Generator Control Switch (GCS) is toggled (OFF to ON).

The following functions shall be limited to a total of 2 resets after which a cold start will be required for reset:

Overvoltage Fault
Overfrequency 2 Fault
Differential Protection TD Fault
Overcurrent Fault
AGC Welded Fault

A table listing all these functions is shown below.
GAPCU DETECTION:

-------------------------------------------------------------------------------

! FUNCTION ! SENSING ! THRESHOLD ! TIME DELAY ! TRIPS !

!------------------!-------------!--------------!-----------------!-----------!

! Overvoltage (OV) ! Highest POR ! 130 +/- 1.5V ! Inverse Curve ! GCR, PRR !

! ! phase ! ! (max) ! !

!------------------!-------------!--------------!-----------------!-----------!

! Undervoltage ! ! ! ! GCR, PRR !

! (UV1) ! Lowest POR !101.5 +/- 1.5V! 4.5 seconds ! !

! ! phase !4V Hysteresis ! (max) ! !

! (UV2) ! Lowest POR ! 68 +/- 1.5V ! 160 milliseconds! !

! ! !4V Hysteresis ! (max) ! !

!------------------!-------------!--------------!-----------------!-----------!

! Overfrequency ! ! ! ! GCR, PRR, !

! (OF1) ! PMG ! 435 +/- 1 Hz ! 4.0 seconds ! SVS !

! ! !4Hz Hysteresis! (max) ! !

! (OF2) ! PMG ! 452 +/- 1 Hz ! 160 milliseconds! !

! ! !4Hz Hysteresis! (max) ! !

!------------------!-------------!--------------!-----------------!-----------!

! Underfrequency ! ! ! ! GCR, PRR !

! (UF1) ! PMG ! 361 +/- 1 Hz ! 4.0 seconds ! !

! ! !4Hz Hysteresis! (max) ! !

! (UF2) ! PMG ! 343 +/- 1 Hz ! 160 milliseconds! !

! ! !4Hz Hysteresis! (max) ! !

!------------------!-------------!--------------!-----------------!-----------!

! Underspeed (US) ! Gnd signal ! Discrete ! 80 milliseconds ! PRR !

! APU (RDY) ! from ! Input ! (max) ! !

! ! APU ECB ! ! ! !

!------------------!-------------!--------------!-----------------!-----------!

! Shorted Rotating !Exciter Field! > 175 VDC ! 3 seconds (max) ! GCR, PRR !

! Diode (SRD) ! Current vs. ! Rippled ! ! !

! ! Load ! detected ! ! !

! ! Current ! ! ! !

! ! Voltage ! ! ! !

!------------------!-------------!--------------!-----------------!-----------!

! Differential ! Generator !50 +/- 10 A ! 60 milliseconds ! GCR, PRR !

! Protection (DP) ! and Line ! ! (max) ! !

! ! CT delta for! ! ! !

! ! each phase ! ! ! !

! ! measurement ! ! ! !

!------------------!-------------!--------------!-----------------!-----------!

! Overcurrent (OC) ! Generator ! APU Imax ! Inverse Curve ! GCR, PRR !

! ! CTs ! + 15 A (min)! (min) ! !

! ! Line CTs ! ! 10.0 seconds ! !

! ! (Aux Gen) ! ! (max) ! !

!------------------!-------------!--------------!-----------------!-----------!

!Delta Overcurrent ! Generator ! Delta I ! Inverse Curve ! GCR, PRR !

!(DOC) ! CTs ! > 75 A (min) ! (min) ! !

!------------------!-------------!--------------!-----------------!-----------!

! Overload (OL) ! Generator ! APU Imax ! 10.0 +/- 3 ! None !

! ! CTs ! + 15 A (min) ! seconds ! (Galley !

! ! Line CTs ! ! ! Shed) !

! ! (Aux Gen) ! ! ! !

!------------------!-------------!--------------!-----------------!-----------!

! Phase Sequence ! POR ! ABCN ! 40 milliseconds ! GCR !

! (PSEQ) ! ! ! (max) ! !

!------------------!-------------!--------------!-----------------!-----------!

! AGC control ! Line !Line Contactor! 300 milliseconds! GCR, PRR !

! circuit failure ! Contactor ! Status ! (max) ! !

! (AGCCF) ! !disagrees with! ! !

! ! ! contactor ! ! !

! ! ! "drive" ! ! !

! ! ! command ! ! !

!------------------!-------------!--------------!-----------------!-----------!

! AGC failure ! Generator ! Generator ! 160 milliseconds! GCR, PRR !

! (AGCF) ! current ! current ! (max) ! !

! ! (after AGC ! > 25 +/- 5 ! ! !

! ! commanded ! Amps (after ! ! !

! ! open) ! APU PR is ! ! !

! ! ! open) ! ! !

!------------------!-------------!--------------!-----------------!-----------!

! Shorted/Open PMG ! PMG ! Open Phase or! 4.2 seconds ! GCR !

! ! !Phase to Phase! (max) ! !

! ! ! Short ! ! !

!------------------!-------------!--------------!-----------------!-----------!

! Pin Programming !Parity error ! N/A ! 40 ms ! PRR !

! Error ! ! ! ! !

!------------------!-------------!--------------!-----------------!-----------!

! APU ! ECB ! < or equal to! 80 ms ! PRR !

! underspeed ! ! 95 % of ! ! !

! ! ! nominal speed! ! !

-------------------------------------------------------------------------------

D. Electrical Generation Interface Unit (EGIU)
EGIU2 channel 2 is for the APU generator. Its main function is to give the main electrical parameters of the APU generator channel to the SDACS. This is via the ARINC 429 data links.
For more details on the EGIU description and functions, refer to 24-22-00 .

E. Power Contactor
Refer to Chapter 24-22-00.

F. Current Transformer (CT)

AC Auxiliary Generation (APU Generator GCU) Component Location ** ON A/C NOT FOR ALL

AC Auxiliary Generation (APU Generator GAPCU) Component Location ** ON A/C NOT FOR ALL

Current Transformers - Block Diagram ** ON A/C NOT FOR ALL

There are two CTs for AC auxiliary generation channel:

one CT is built into the APU generator,
one three-hole CT is installed upstream of the generator line contactor.

(1) Functions

(a) Generator CT
The generator CT is used for differential and overcurrent protections.

(b) Three-hole CT
The three-hole CT contains three toroidal transformers, one for each of the power feeder cables. The three-hole CT is connected in electrical opposition to the CT of the APU generator.
This CT is used for differential and open cable protections.

(2) Functions

(a) Generator CT
The generator CT is used for differential and overcurrent protections.

** ON A/C NOT FOR ALL

5. Operation/Control and Indicating

A. APU Generator Control

Auxiliary Generation Operation - Schematic Diagram ** ON A/C NOT FOR ALL

The operation of the APU generator is through the APU GEN pushbutton switch, which has two stable positions:

when in OFF position, the pushbutton switch is released, and the white OFF legend is on. The generator is shut down (de-energized) and the line contactor is open,
when the pushbutton switch is pushed, the generator is energized, because its rotational speed is high enough. If the electrical parameters are correct, the GCU controls the line contactor closing: this causes the supply of the transfer circuit.

The operation of the APU generator is through the APU GEN pushbutton switch, which has two stable positions:

when in OFF position, the pushbutton switch is released, and the white OFF legend is on. The generator is shut down (de-energized) and the line contactor is open,
when the pushbutton switch is pushed, the generator is energized, because its rotational speed is high enough. If the electrical parameters are correct, the GAPCU controls the line contactor closing: this causes the supply of the transfer circuit.

The APU GLC supplies the aircraft electrical network if the other power sources are not available.

GLC - APU Supply - Schematic Diagram ** ON A/C NOT FOR ALL

NOTE: On the ground, the generator line contactor closes only if the ground power unit does not already supply the transfer network.
For the power supply of the aircraft, the ground power unit is more important than the APU generator.

APU GEN FAULT - Upper and Lower ECAM Display Unit

When the FAULT legend comes on, there is a failure of the channel.
At the same time:

the single chime operates,
the MASTER CAUT light comes on,
on the upper ECAM display unit, an amber message is shown,
on the lower ECAM display unit, the ELEC page is automatically shown.

[Rev.10 from 2021] 2026.04.01 05:40:22 UTC