Generator core problems
Generator core problems
(OP)
We are having problems with insulating the core of our 200MW generator and are running out of options. During our loop tests we noticed several hot spot, most of which were fixed via mica inserts. However, there are two hot areas which we cannot easily access to insert mica as they are back behind the packs and at the bottom of the generator.
The problems lie on the splits (the generator was made in three separate 120 degree sections). We have tried acid etching (with phosphoric acid) with limited success. We are now grinding away beind the packs in the hot area and are then acid etching to remove the ground material. We are finding limited success with this as well.
Does weeping epoxy work? If so, how should we go about applying it since the problem is in the lower part of the generator. Do we need to loosen tension on the laminations? Are there any other methods to eliminate hot spots other than restacking?
The problems lie on the splits (the generator was made in three separate 120 degree sections). We have tried acid etching (with phosphoric acid) with limited success. We are now grinding away beind the packs in the hot area and are then acid etching to remove the ground material. We are finding limited success with this as well.
Does weeping epoxy work? If so, how should we go about applying it since the problem is in the lower part of the generator. Do we need to loosen tension on the laminations? Are there any other methods to eliminate hot spots other than restacking?






RE: Generator core problems
RE: Generator core problems
Hot spots in large areas would require core dismantling. In my experience, weeping epoxy/varnish do not work well in deep seated hot spots.
*Why make the same mistake twice when there so many new ones available*
RE: Generator core problems
RE: Generator core problems
Is there any winding or core RTD near this hot spot area to monitor the temperature trend during operation ? Or better yet, can you possibly install a RTD in this area ?
Is this a pumped storage scheme ?
*Why make the same mistake twice when there are so many new ones available ?*
RE: Generator core problems
cracking by mechanical agitation and spreading and perhaps spray with sodium silicate during the process.
Needless to say, these techniques work better when the core clamping system is loosened.
I am not exactly sure what is the mechanism why mechanical agitation improves hotspots. I picture there may be high-spots/burrs on the edges of the laminations that are broken off during movement.
These techniques are discussed briefly on page 5 here:
h
=====================================
Eng-tips forums: The best place on the web for engineering discussions.
RE: Generator core problems
In your spare time, of course....
RE: Generator core problems
Please let us have the following information:
1. Are we dealing with a completely new stator core or is this an old core (how old?) loop tested after removal of the stator winding and prior to the installation of a new winding?
2. Was the stator core loop tested with 1 Tesla or less? What frequency?
3. Loop test duration after which the 15 or 9 degrees temperature difference was recorded?
4. Approximate core dimensions (bore diameter, axial core length, slot number)?