Generator rotation

[norske]

Hi everyone.

I have an application where a 2MVA alternator was retrofitted to a new prime mover. During the change the alternators direction of rotation was changed. I understand the cooling fan was also changed to accomadate this. The alternator has had a troublesome time(several years), lots of over heating, burnt windings once. Could this change of direction have contributed to the issues and if so how?

Many thanks to you all in advance who respond.

Norske

 

[Yuma]

Apart from the rotor fans, the generators I've seen so far are symmetrical; so if fans were changed I can't think of a way in which the rotation direction could influence heating.

 

[sslobodan]

If you change rotation of a fan he will pump out air instead of pumping in. And that is not good because it will overheat. Try rewiring (switch the phase cycle on the device so you can have it all in normal)

 

[powerjunx]

norkse, i bet the change of generator rotation mainly affects winding overheating.
Presently, our generators have cooling fans mounted on the periphery of the rotor body. Apparently, this fans, once reversely installed on the fixed point the air blow direction is reversed, maybe blowing air inside or outside the generator winding as sslobodan pointed out.
With this, we're very careful upon disassembly of this fans in order to prevent reverse air blowing effects.


"..the more, the merrier" Genghis Khan

 

[waross]

I would check the air gaps for symetry.
Another possibility is that the rotor is not longitudinally aligned properly.
Check your protection, the new prime mover may be overpowering the generator. Normally this is not a problem, but a previous protection scheme may have had the settings too high and relied on the maximum power limit of the prime mover to avoid damage. A more powerful prime mover and bad settings may be a possibility.
respectfully

 

[oftenlost]

I have noted instances where the stator wedges were shaped so as to force air through the cooling ducts when the rotor was turning in one direction. There are also rotor forgings which have axial cooling grooves machined in them to facilitate airflow when turned in the proper direction. I would be tempted to contact the OEM. Many of these units are rotor limited so if the stator is getting hot, the rotor could be cooking.

 

[JBinCA]

Some generator rotors are also designed to force air into thr rotor and past the rotor windings. These rotors require rotation in a predefined direction for rated cooling.

If you have any pictures of the rotor when it was removed from the stator, check to see if there are a bunch of holes throughout the rotor casing. That's your clue.

JB

 

[rmw]

You need to confirm whether or not the fans were actually reversed when the direction of rotation was changed. If that was done, the cooling air circuit shouldn't know the difference (unless the stator wedges are as OftenLost has noted. It sounds to me like they might not have been. Also, if this is a brushless exciter, and it has a exciter cooling fan, it may not be able to be reversed. It might need to be changed altogether. Hard to say.

rmw

 

[edison123]

norske

Did the new engine speed match that of alternator ? If not, it could be a V/Hz situation that is overheating the core (and hence the windings).

*Nothing exists except atoms and empty space; everything else is just an opinion*

 

[oftenlost]

Another item of note is that swapping the fans from end to end is not sufficient to maintain air flow through the unit. I am not assuming that the folks who did the swap did not know what they were doing but the fans have to be swapped from end to end and need to be mounted on the fan fit 180 degrees with respect to the rotor body. This requires a symmetrical, straight bore fan. Not all rotors are equipped with this type of fan.