In March 2000, a rash of pole fires occurred on the We Energies (formerly Wisconsin Electric) distribution system that affected a significant number of customers, including high-profile commercial and industrial accounts. Investigation into these events determined that the vast majority were in the vicinity of major interstate highways and were due to insulator tracking caused by contamination as a result of excessive road salting.
Under the right conditions, road salt can be kicked up into the air and deposited on electrical equipment in the vicinity. When wetted by fog or misting conditions, leakage current on the scale of milliamperes can track across the insulators. In the case of wood structures, this current, ultimately, can result in surface heating and fires on poles or crossarms.
Based on these events, We Energies developed a strategy to address this issue in a focused manner. The majority of the pole fire events were associated with installations using porcelain line post insulators.
We Energies investigated options with equipment manufacturers and utilities that had experience with insulator tracking caused by other contaminants such as ocean salt spray. We Energies chose new silicone polymer-bodied line post insulators because they are much less likely to suffer from tracking caused by salt contamination. After reviewing locations that might be subject to pole fires based on their proximity to highways, We Energies developed an action plan to replace more than 3000 insulators on more than 750 poles. In addition, the utility applied several polymer skirt extenders to porcelain potheads and replaced a number of porcelain arresters with polymer. The utility also replaced other components such as poles, crossarms and load-break switches that were identified as damaged.
This work was completed prior to the start of the next “pole fire season.” These installations have been free of pole fires since the field construction work was completed, and each year this issue is reviewed to address other locations where problems might occur.
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