INTEGRATED DRIVE GENERATOR SYSTEM (IDG,GCU) - DESCRIPTION AND OPERATION

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1. General
Each engine (HP rotor) controls its related Integrated Drive Generator (IDG) through the accessory gearbox.
The drive speed changes in relation to the engine rating.
The IDG supplies 115/200 VAC, three-phase, 400 Hz power to the engine and aircraft, at the Point of Regulation (POR).
The IDG has two parts:

The drive with the Constant Speed Drive (CSD), and
The generator.

The hydromechanical CSD with its servo-valve operates the AC generator at constant speed.

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2. Component Location

A. IDG System Control

IDG System Control - Component Location

FIN	FUNCTIONAL DESIGNATION	PANEL	ZONE	ATA REF
** ON A/C ALL
5XT	P/BSW-ELEC/IDG 1	35VU	210	24-21-00
6XT	P/BSW-ELEC/IDG 2	35VU	210	24-21-00
4000XU1	IDG-ENG 1		435	24-21-00
4000XU2	IDG-ENG 2		445	24-21-00
5001XM	OIL COOLER-IDG, ENG		400	24-20-00
1XM1	ADAPTER-QUICK ATTACH/DETACH (QAD), ENG 1 IDG		440	24-20-00
1XM2	ADAPTER-QUICK ATTACH/DETACH (QAD), ENG 2 IDG		440	24-20-00

(1) The IDG is installed on the front side on the engine main gearbox.

(2) The IDG mounting pad is attached to the main gearbox by an IDG Quick-Attach-Detach (QAD) adapter.

(3) The IDG power-feeder-cables disconnect-block is attached to the IDG housing at the twelve o'clock position.

(4) The IDG power-feeder cables are connected, at one end, to the lower IDG power-feeder cables disconnect-block attached to the IDG. The other end of the IDG power-feeder cables is connected to the upper IDG power-feeder cables disconnect-block installed on the right fan.

(5) The fuel-cooled IDG oil cooler is a part of the engine heat management-system. The fuel-cooled IDG oil cooler hoses and tubes connect the IDG to the fuel-cooled IDG oil cooler.

(6) The IDG oil temperature thermocouple is installed in the fuel-cooled IDG oil cooler.

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3. System Description

A. IDG and GCU

(1) In flight, the IDG supplies AC power (115 VAC/400 Hz) to the aircraft through its two units:

The CSD unit
The generator.

(a) The engine-driven CSD unit changes the input speed (XX - XX rpm) from the main gearbox into a constant rotational speed of 24 000 rpm.

(b) The constant 24 000 rpm speed from the CSD unit is transmitted to the generator which supplies 115 VAC/400 Hz power to the aircraft.

(2) The Generator Control Unit (GCU), installed in the maintenance equipment center, is used to control the voltage and frequency, and prevents overcurrent in the electrical-power generation channel. The GCU receives an input speed signal from the IDG speed sensor.

(a) Each GCU controls its related IDG:

GCU 1 controls IDG1.
GCU 2 controls IDG2.

(b) The primary functions for the regulation and protection of the IDG are:

Regulation of the generator voltage at the POR
Regulation of the generator speed
Monitoring and protection of the system.

(3) The fuel-cooled IDG-oil cooler cools the IDG oil and keeps the IDG inlet temperature in the limits. As the oil goes through the oil cooler, heat is transferred from the oil to the fuel. Then the cooled oil returns to the IDG.

NOTE: The normal IDG oil-inlet temperature is between 70 deg.C (158.0 deg.F) and 105 deg.C (221.0 deg.F).

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4. Power Supply

A. Circuit Breaker Table

PANEL	DESIGNATION	FIN	LOCATION
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122VU	ELEC/IDG1/DISC	1XT	T24
122VU	ELEC/IDG2/DISC	2XT	T25

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5. Interface

A. Generator Control Unit (GCU)

(1) Input data

Each GCU receives the signals that follow from its related IDG:

Oil inlet temperature
Oil outlet temperature
Low oil pressure
PMG three-phase output voltage
CT three-phase signal.

(2) Output data

Each GCU supplies the output analog data that follow to the System Data Analog Converters (SDACs), through an ARINC 429 link:

IDG oil-output temperature
IDG oil-inlet temperature
AC load at the POR
AC frequency (phase A)
AC voltage (phase A) at the POR.

It also supplies the SDACs with the discrete information that follows through an ARINC 429 link:

Overload warning
Generator fault
IDG disconnect status
IDG-disconnect pushbutton position
IDG oil-outlet overheat
IDG-oil low pressure
GEN pushbutton-switch position

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6. Component Description

A. IDG

IDG

Oil Cooling System of the IDG

Connectors, Port and Accessory Locations of the IDG

Internal Electrical Schematic of the IDG

(1) The IDG has the components that follow:

(a) Electrical circuit

Terminal block with a terminal block cover
Electrical connectors A, B and C.

(b) Maintenance components

Oil replenishing circuit
Oil drainage circuit
Oil level sight-glass
Oil scavenge filter-element
Oil charge filter-element
Vent valve
IDG reset ring.

Differential Pressure Indicator (DPI) of the IDG oil scavenge filter on the IDG oil-out line.

(d) Cooling system

Oil-in port
Oil-out port.

(2) The IDG has a CSD unit and a generator installed in a magnesium-cast housing.

(a) The speed conversion components are the gear differential and the hydraulic trim unit. The engine gearbox supplies the variable-speed shaft power to the IDG input shaft, which is directly connected to the carrier shaft of the differential.

(3) The IDG CSD unit has a disconnect mechanism to disengage the input shaft attached to the main gearbox. The disconnection is necessary to prevent internal mechanical damage if a failure of the IDG oil-cooling system occurs.

(4) The IDG generator is a three-stage assembly that has three devices connected in cascade.

(a) The first device (pilot exciter) is a twelve-pole Permanent Magnet Generator (PMG).

Its rotor is made of small rare-earth cobalt magnets. The output from the pilot-exciter stator winding:

Has a generator excitation function, and
Supplies power for other components of the electrical system (supply of the GCU and the external relays and contactors). The generator is thus "self-flashing" and "self-sufficient".

(b) The second device (main exciter), a ten-pole stator, receives its field excitation from the pilot exciter through the voltage regulator in the GCU: this gives a stationary field. Rotating diodes rectify the three-phase output of the main exciter rotor. This gives a DC current that supplies the third device (main alternator) rotor winding.

The main alternator receives excitation for the rotating salient four-pole field from the rectified output of the main exciter.

The main alternator has a three-phase star-connected stator winding. The three phases and star point neutral are connected to the generator output terminal block.

The generator is used with an external voltage regulator that is part of the GCU which:

Rectifies the output of the pilot exciter,
Controls the excitation current to the main exciter field winding.
The IDG generator contains three shielded toroidal current-transformers into one assembly. The current transformers supply outputs in relation to the current in the links that connect the neutral ends of the main stator windings to the neutral terminal. They are used for together with the differential feeder current protection-circuit in the GCU.

The secondary windings of these transformers are connected to IDG electrical connector A.

(5) IDG servo valve

(a) Generator speed control

A system with a servo valve in the IDG and an electronic control circuit in the GCU controls the generator speed.
This system sets the position of the wobbler of the variable displacement hydraulic-unit.

(b) Electronic control circuit

The electronic control circuit monitors the generator PMG frequency and compares it with a reference source.
If there is an error signal, the control circuit causes the servo valve to increase or decrease the control piston pressure as necessary to set the generator frequency back to 400 Hz.

(6) The IDG has the components that follow:

(a) Internal components connected to connector A

The main exciter
Three current transformers
The servo valve
The disconnect solenoid.

(b) Internal components connected to connector B

The PMG stator
The oil-in and oil-out temperature bulbs

The charge pressure switch.

(7) The IDG drive splines are lubricated by the engine oil-cooling system, which supplies a stream of oil to the center of the shaft. Oil from the shaft goes through the splines and is released into the gearbox cavity through radial holes in the shaft.

(8) IDG cooling and lubrication system

The oil goes into the IDG at the opposite side of the drive end through the DPI filter and then goes to:
The differential gear
The input seal
The charge pump
The generator stator and rotor.
The oil supplied to the differential gear also cools the PMG stator by spraying and lubricates the disconnect spline. The input housing has rectangular grooves around the main generator stator core in which oil flows to cool the stator and keep a low IDG surface temperature.
The oil flow goes into the charge pump through the suction port and its pressure increases.
The oil that goes into the rotor cools the components that follow:
The exciter and main generator rotors
The exciter and main generator windings
The diodes.

Then, this oil goes directly to the deaerator or to the IDG sump where it is scavenged and pumped to the deaerator.
The oil is deaerated before it goes to the supply pump. There, it goes through the scavenge filter into the external system lines for cooling.

(9) IDG sensors and protective components

(a) IDG oil filter Differential Pressure Indicator (DPI)

The scavenge filter has an oil filter DPI. The indicator shows when it is necessary to replace the oil filter elements.
The sensing device for the oil filter DPI is automatically inhibited during cold oil-running conditions. This prevents unwanted operation because of a high oil viscosity.
It is necessary to replace the two filter elements when the DPI is extended.

(b) IDG automatic and manual thermal disconnect-mechanism

1 The manual disconnect mechanism has a solenoid, a spring-loaded disconnect plunger, a cam shaft and a reset ring. The crew pushes the IDG pushbutton switch when the IDG FAULT legend comes on. When activated, the IDG cannot be connected again in flight.

2 At an IDG oil temperature between 197 deg.C (386.6 deg.F) and 201 deg.C (393.8 deg.F), an automatic thermal disconnect-mechanism disconnects the IDG.

The switch is closed when the IDG does not operate, and open when the IDG operates correctly.
The charge switch operates when the engine is at the normal operating speed. When the IDG charge pressure decreases to a minimum safe value, it transmits a signal to the GCU. The IDG FAULT legend comes on on the ELEC panel. At the same time, the IDG LOW OIL PR caution message is shown on the upper Electronic Centralized Aircraft Monitoring (ECAM) Display Unit (DU).

(d) IDG oil-out and oil-in temperature sensor

The oil-out and oil-in temperature sensors of the IDG are sensed by the GCU to do the ECAM oil-out temperature and delta (oil-out minus oil-in) temperature reporting. The oil temperature sensors are thermistor components and have a nominal resistance of 100 +10 ohms -10 ohms at ambient IDG case temperature.

(10) IDG servicing

(a) IDG oil-pressure filling

The IDG and external oil circuit are filled with oil that is pumped into the IDG through the pressure fill port on the IDG. The oil pumped into the IDG, through the pressure fill port, flows through a scavenge filter and then through the external oil circuit and into the IDG case.

The oil pushes the air out of the circuit and releases through the open overfill-drain port.
When the oil level in the IDG sump becomes stable at the top of the open overfill standpipe, the level in the IDG system is correct.

NOTE: Motoring is not necessary for an oil level check or oil replenishment.

(b) Vertical oil-level sight-glass
Different colors (red, yellow and green), related to the oil level, show when the oil servicing of the IDG is necessary.

(c) IDG reset ring
A mechanical reset ring is installed on the IDG. The handle is used to connect the drive again while the engine is stopped and stationary on the ground.

(11) The IDG is a Line Replaceable Unit (LRU).

B. IDG Power Feeder Cables

IDG Power Cables

(1) Four IDG power cables supply IDG-generated 115VAC/400 Hz power to operate the aircraft electrical systems.

(2) The IDG power cables are connected independently (not as a bundle) to terminal blocks at each end. Line blocks and clamps hold the cables in position along the left side of the engine core.

(3) The IDG power cables are LRUs.

C. IDG QAD Adapter

IDG QAD Adapter

(1) The IDG QAD adapter is used for quick replacement of the IDG. It attaches the IDG to the engine accessory gearbox. When the QAD ring is rotated with the tension bolt, the IDG mounting flange engages the adapter plate on the QAD adapter.

(2) The IDG QAD adapter-kit includes a gasket, a bracket, two adjusting nuts, one adapter plate and eight screws for the main gearbox mounting-pad and has the components that follow:

(a) QAD ring - mates with the IDG input flange.

(b) QAD ring lugs - mate with the IDG input-flange lugs and the white open-position marks on the IDG and QAD ring are aligned.
In this position, the locator pin on the IDG is aligned with the locator hole in the QAD ring.

(c) Tension bolt - tightened to engage the IDG input-flange lugs into the QAD ring until the ring turns into the locked position.

(3) The IDG QAD adapter is an LRU.

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7. Operation/Control and Indicating

A. Monitoring of the Oil System Operation

IDG System - Generator Drive Control and Indicating

Speed Regulation Loop

(1) Oil temperature sensors monitor oil-in and oil-out temperatures for overheat detection.
A pressure switch operates when the charge oil pressure decreases.
In these two conditions, a warning is sent to the upper ECAM DU and the FAULT legend of the related pushbutton switch comes on.

(2) The oil-out temperature is shown on the ECAM electrical page.

NOTE: At a set oil temperature value, an advisory mode is shown on the lower ECAM DU.

B. Disconnection of the IDG

IDG 1 Oil Low-Pressure - Upper and Lower ECAM Display Unit

IDG-1 Oil Overheat - Upper and Lower ECAM Display Unit

IDG-1 Oil-Overheat Advisory - Upper and Lower ECAM Display Unit

(1) On the ELEC section, the amber FAULT legend of the IDG 1(2) pushbutton switch comes on and the master warning system starts if:

There is an oil overheat (when the temperature of the oil that comes out of the IDG is high).
The oil pressure decreases but not because of the drive underspeed.

When the operator opens the safety guard and pushes the IDG 1(2) pushbutton switch on the ELEC section of overhead panel 35VU, the operator energizes the disconnected solenoid. Thus, the input shaft of the IDG becomes disengaged.

The FAULT legend of the IDG 1(2) pushbutton switch cannot be on during the engine shutdown (underspeed).
The FAULT legend of the IDG 1(2) pushbutton switch goes off when the IDG disconnection occurs (speed less than 2000 rpm).

If the IDG operates for more than 50 hours in the disconnected mode without a reset, the operator must replace it and send the removed IDG for a shop inspection. This is because there is a risk of damage to the ball bearing assembly on the input shaft and to the aircraft engine. After the IDG disconnection, the operator must not connect it again.

(2) The operator must not disconnect the IDG when the engine is stopped.
The operator cannot connect the IDG in flight. The connection of the system is then possible only on the ground with the engines stopped. To connect the IDG in flight, the operator must move the pawl with the IDG reset ring.

C. Connection of the IDG

(1) Mechanical reset handle
The mechanical reset handle is used to connect the drive while the engine is stopped on the ground.

D. Oil Filter

(1) A local visual pop-out indicator shows when the oil filter is clogged. The indicator is installed opposite the drive end of the IDG.

[Rev.10 from 2021] 2026.03.31 23:19:34 UTC