View Full Version : Constant Speed Drive Unit/IDG.

12th Jun 2006, 04:43
Could anybody please enlighten me on the difference between the CSDU (Generator) and the Integrated Drive Generator (IDG).

Mr @ Spotty M
12th Jun 2006, 05:39
The CSD is a Constant Speed Dive Unit and a IDG is a Integrated Drive Generator, the difference is what you placed in brackets.
In that a CSD does not have a Generator, it is used to drive a Generator which is attached to it and IDG is a combined unit.
I hope this helps.:ok:

Capt Claret
12th Jun 2006, 07:47

In broad terms, a constant speed generator will be driven by something like an APU which runs at fixed RPM, usually 100% in my experience, thus the AC frequency remains constant.

An IDG is a device which converts variable RPM, from the engine accessory gearbox, to a constant drive RPM for the generator, so that the generator output stays constant, again in my experience, 115v 400Hz. Without the IDG, the output frequency would vary with varying engine speed.

As a comparrison, DC generators vary the strength of the field windings to maintain constant voltage and frequency doesn't apply to DC power.

12th Jun 2006, 13:07
Mr @ Spotty M is correct.

An I.D.G is one unit that incorperates a Constant Speed Drive AND a Generator. It is smaller and lighter than than the older C.S.D. plus Generator combination. The IDG incorperates a CSD within its design. Thus "intergrated".

A Generator driven by most A.P.U.'s does not require a C.S.D. as the A.P.U. itself is regulated at constant speed and the generator is driven through a gearbox to the correct RPM tpo provide 400Hz.

e.g. Early a/c had a CSD and a Generator. Later a/c have only an IDG

The old bull :ok:

12th Jun 2006, 13:56
A380 will not have a CSD neither an IDG

12th Jun 2006, 15:18

Is that 'cos someone cut the cables then?:\

sorry I'll get me coat

12th Jun 2006, 16:39

Is that 'cos someone cut the cables then?:\

sorry I'll get me coat

No, it's not wireless. Just free speed.

12th Jun 2006, 18:11
Like the VSCF (http://www.b737.org.uk/generators.htm) that the 737 had 15 years ago?

Swedish Steve
12th Jun 2006, 18:45
Like the VSCF (http://www.b737.org.uk/generators.htm) that the 737 had 15 years ago?
The VSCF was designed as a plug in replacement for the IDG. It was very unreliable as the electronics that converted the frequency wild to 400Hz did not survive under the cowling.
The B777 has a frequency wild BUG Back up generator mounted on each engine for use when one of the IDGs fails. But the electronics to convert to 400Hz are mounted in the ECS bay in a big air cooled box. This seems to work OK but the box is big and only handles 20Kva. I wonder how big the unit is for a full sized unit?

14th Jun 2006, 05:19
Generators like the A380's (also on the Global Express) set the gearing such that at normal cruise the output frequency approximates 400 Hz (voltage is taken care of by regulating the field coil). There is an apparent weight saving in that you've removed the CSDU but you then have to size all the electrical system (wiring, contactors, motors etc) to cope with the increased current when the frequency falls to around 380 Hz. This is often well in excess of any CSDU weight & can lead to very unreliable units - maybe worse than the CSDU you're trying to eliminate.