A320 IDG Frequency Adjustment

This post is not a reference for maintenance or an alternate to aircraft maintenance manual.

It is only intended to increase awareness of some aircraft maintenance tasks and it is not for official use.

So, what is the IDG ?

IDG Integrated Drive Generator is the main power generator on the large commercial aircrafts.

It consists of two parts ( Generator + CSD Constant Speed Drive )

Yo can think of it as much like the power generator on your car that is driven by the car engine.

The IDG is also installed on and driven by the aircraft engine. So, each aircraft has IDGs as much as it has of engines.

The car generator generates Ac current that is directly rectified into DC current by rectification circuits.

But the IDG generates AC current that has part of it used as AC and another part is rectified into DC current using dedicated units.

The car generator moves at the same speed of the engine and so the output AC frequency varies according to that speed. This is not an issue as the AC current is not used on the car.

The aircraft generator moves by the speed regulated by a mechanical unit called CSD Constant Speed Drive that limits the speed variation of the generator and hence limits the variation in frequency output whatever the speed of the aircraft engine during the different aircraft phases ( Takeoff, Cruise , Landing ... ).

Also, the frequency is electrically controlled inside the generator to make the output frquency set to exactly 400Hz +/- 5Hz.

Sometimes the frequency deviates to another value due to mechanical or electrical parameters deviation and needs to be calibrated to the allowable value.

The manufacturer limits the frequency deviation to 400 +/- 20 Hz.

If the deviation is larger than this value the IDG needs to be replaced.

Also, this calibration is limited to once during 400 Flight Hours.

In this case, the IDG frequency output was 410Hz and so it was allowable to be calibrated.

So, let's begin the task.

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Print the task from the AMM Aircraft Maintenance Manual.

Open fan cowls . Remove the lock-wire installed on the governor screw.

Drive the screw to adjust the frequency as follows

- CW Clock Wise rotation decreases frequency

- CCW Counter Clock Wise rotation increases frequency

- one rotation makes 3 Hz change. In our case we rotated the screw 3 rotations in CW direction

Do an engine run and monitor the IDG parameters

Make sure that the output frequency is 400 +/- 5 Hz on the ECAM ELEC page

Wait until the engine cools and install a piece of lockwire to secure the governor screw.

Close the engine fan cowls.

Make an entry in the aircraft technical log book.

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