Large scale construction of rural electric distribution lines in almost all parts of the United States has given rise to a variety of corrosion problems. Some are the result of special local conditions, while others are related to changes that came about when lines were designed for rural rather than urban construction. The corrosion problems are complicated by a wide range of atmospheric and soil conditions and by the difficulty of observing some kinds of damage before failure occurs.
On multigrounded wye distribution lines all underground metal parts are generally connected to a common system neutral conductor in order to maintain the lowest ground resistance possible. Underground corrosion has been excessive in some locations because of galvanic action between metal surfaces that assume varying potentials with respect to the soil.
Atmospheric corrosion problems in pole line hardware are characterized by replacement costs that are very high compared with the value of the items replaced and by questions of choice of materials and coatings for a wide range of atmospheric conditions. High strength primary conductors, widely used in rural construction, depend on steel for strength while aluminum or copper provide electrical conductivity. These composite conductors have performed well in most atmospheres but corrode excessively under certain conditions.
Durability of transformer paints is being examined with the object of increasing the useful life of the coatings, as transformers represent a large item in the cost of a distribution system. The cost of maintenance painting of distribution transformers is so high that the economy of repainting small transformers is questionable unless they have been removed from service for other reasons.
