generator core repair alternatives 2

[Yuma]

Dear all,

We are in the process of repairing the core of a salient pole generator. This core has a bad hot spot that shorts some of the laminations. The shop offers two alternatives to do the repair:

option 1 - reuse the same core laminations, just relocating them in order to distribute the damaged plates all over the core and thus turn the hot spot into many little hot spots that hopefully will be negligible.

option 2 - build new laminations, dismantle the core until we reach the damaged zone, and replace the damaged zone.

I have never seen the case of option 1 myself, but I recall having heard of it. Does anybody have any experience of such a repair, and in that case, are you satisfied with the result?

As for option 2, the shop tells us that we could replace not only the damaged zone but all the dismantled zone - maybe half of the core- or even the full core with new laminations. Replacing the full core sounds like the best option technically, but my question is, given that the new laminations have 1 W/kg losses and the old laminations have 2 W/kg, do you think that, if we finally replace part of the core, we may have some issues like thermal or magnetical flux imbalance or whatever?

 

[accordlx]

Redistributimg the bad lams throught the restack works well in most cases. Soaking the lams in phosporic acid will aid the process of "restoring " the insulating value of the core plate. An extra long VPI pressure cycle on the finished stator also helps as well if it will fit in your tank. I would go with option 1. We use this process on a regular basis if the lams are not too badly damaged. Excessive grinding labor to repair catastrophic damage can quickly make replacing the damaged lams more economical.

 

[electricpete]

Going back to the grinding option. Another reference, specifically addressing damage in the slot:

2) Method two. (Coil has failed in the slot, thereby melting the laminations, or the stator is moderately rubbed by the rotor.) With a pencil metal grinder, grind away fused metal until a definition of core laminations can be seen. Small, high-speed (25 000 r/min) hand grinders equipped with carbide-tipped, cone-shaped rotary files work best. Grind with light, intermittent pressure (rather than continuously) with movement in the same plane as the laminations until the fused metal is removed. Repaint the ground area and test the core for hot spot in the damaged area. Do not grind an area that will damage the mechanical integrity of the slot. If the damaged area is more than 10% of the total surface area of the core, then go to Method three.

I don't know what a penciel metal grinder is, but I'm guessing it is shaped like a pencil to get into small locations.

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(2B)+(2B)' ?

 

[TurbineGen]

It's basically a narrow die grinder. Generator slots are deep but not wide. The problem is when the coil damages the back of the slot. The pencil/die grinders don't do well with this. Occasionally you might fit a small abrasive wheel in there, but more often it's time to break out the 12" angle grinder. Unfortunately that makes a mess out of the laminations which is why I recommended the muriatic/hydrochloric acid. That breaks down the edges left by grinding fairly quickly and the phosphoric acid does the insulating.

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If it is broken, fix it. If it isn't broken, I'll soon fix that.