Electric Corrosion in Generators

There are generally two parts of the generator where electric corrosion occurs: one occurs between the anti-corona layer and the stator slot, usually called external corrosion, and the other occurs between the anti-corona layer and the main insulation, usually called internal corrosion.

In mild cases of electric corrosion, the anti-corona layer of the bar and the surface of the main insulation turn white and are eroded to varying degrees; in severe cases, the anti-corona layer is damaged, the main insulation is exposed or pitted, causing burning of the anti-corona layer on the bar surface, and even the main insulation and gaskets. This kind of damage to the bar's anti-corona layer, main insulation, gaskets, etc. is collectively called "electric corrosion".

According to the location where electric corrosion occurs, it is divided into external corrosion and internal corrosion. External corrosion refers to the electric corrosion that occurs between the anti-corona layer and the stator slot wall; internal corrosion refers to the electric corrosion that occurs between the anti-corona layer and the main insulation.

The main causes of electric corrosion in Cummins generators are:

1. The stator slot was not sprayed with low-resistance semiconductor before wire insertion

2. The used electrical strips are unqualified and not tightened properly

3. The fixing method of the stator bars is not standardized

4. The size and straightness of the bars are not standard, and the disc tolerance does not meet the requirements, etc.

Recommended measures to prevent electric corrosion for Cummins diesel generator sets:

① Spray low-resistance semiconductor paint in the stator slot before wire insertion.

② Select appropriate low-resistance semiconductor gaskets, tighten the slot wedges, ensure the integrity of the anti-corona layer on the surface of the straight part of the bar, and ensure good contact between the anti-corona layer on the bar surface and the gaskets or iron core walls.

③ Improve the fixing method of the bars in the slot.

④ Improve the manufacturing process level, such as the size and straightness of the bars, the manufacturing and lamination tolerances of the iron core, etc. Good bar manufacturing process and overall machine manufacturing level are a strong guarantee for reducing the occurrence of electric corrosion.

At present, China has made great progress in the anti-corona and anti-electric corrosion of bars, such as the simultaneous hot pressing of main insulation and anti-corona layer, semiconductor conformable felt technology, and the use of semiconductor slot liners for in-slot fixing of bars.

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