Diesel Generator Coupling 1

[rovineye]

My coupling and alignment instructions for my diesel generator set call for #1 cylinder to be TDC and the generator rotor positioned with the north pole (@ the shaft key position) also TDC.



Why?

 

[potteryshard]

If it is a permanent magnet rotor or exciter it may be so that the magnetic field cancels and doesn't exert a bending force on the rotor shaft. It may also be that this is a position of maximum upward magnetic pull and the intent is to provide an upward pull to offset the non-running diesel crankshaft from wanting to sit in the bottom of the journal.

 

[edison123]

May be they were balanced as a unit? Changing the rotor position would affect the balance ?

Muthu

http://www.edison.co.in

 

[MikeHalloran]

Good point. Some car engines are 'externally balanced', meaning that they expect to see a controlled imbalance on the flywheel, effectively replacing the aftermost counterweight on the crankshaft.
There's no reason you couldn't do that on a generator, too, or add a nominal imbalance in the generator to counterbalance the rocking couple that comes with some engines.



Mike Halloran
Pembroke Pines, FL, USA

 

[rovineye]

No, the two have never met. Both are independently balanced at the factory and I am 100% certain that the generator has no planned balance offset.

 

[TheBlacksmith]

Did you ask the OEM? If they wrote the alignment instructions they should be able to provide the reason(s) behind the requirement.

 

[benta]

Vibration/ripple torque?
The Diesel has a certain torque pulsing and the positioning of the generator poles relative to this might minimze the issue?
Just a thought.

Benta.

 

[waross]

How many cylinders? How many poles? How many KVA?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[rovineye]

Theblacksmith;
Yes I have asked, but no reply yet.

Waross,
That is the interesting aspect to me. The instruction come from coupling OEM, and is identical for both 8 and 9 cylinder engines, which both mate up with identical generators. 11500 kVA, 14 pole.

 

[waross]

A machine that size will have been the subject of a torsional vibration analysis. The torque demands of the generator are in a series of overlapping near sine waves. The torque output of the motor is a series of pulses. The flywheel and other rotating inertia absorb and give up power to match the two torque curves. The alignment may be related to the vibrational analysis.
OR
Someone may have asked:
"What is the proper alignment of the coupling?"
This may have led to a discussion in the offices of the builder somewhat as follows:
"This is the fourth time that someone has asked this. What do we tell them?"
"It is not that important but if we add an instruction to align the north pole with the #1 cylinder they may stop bothering us."
Or there may be some other valid reason.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[rovineye]

Bill you are right on two counts!

#1. From the engine manufacturer: "Research has shown that the requirements were implemented as an aid in analysis of torsional load optimization of the rotating system."

#2 (to make me go away) "That analysis being complete, the requirement is now unnecessary. The requirement is no
longer needed and can be removed from the drawings." And since we ignored the note in the drawing in the past anyway, the OEM stated "All couplings currently installed do not need to be removed for phasing or marking issues."

That is particularly good news, as when I looked at a rotor yesterday I saw that the keyway is acually between poles, not aligned to a north pole. I am NOT going back to the OEM and tell them that.

Well Done!

 

[waross]

Thank you for the update, rovineye.
Yours
Bill

Bill
--------------------
"Why not the best?"
Jimmy Carter