A failure could be any range of events, from a minor repairable defect all the way up to a catastrophic failure requiring replacement of the asset and causing power outages. Characteristics of failure include the following:

  • Affected by capital-level spending The feeder model is intended primarily to support capital spending decisions, particularly related to the replacement cost of aging assets. As such, we are interested only in failure modes that will be affected by capital interventions. For example, replacing the underground cable in a subdivision will reduce the likelihood of faults due to aging insulation, so these can be considered failures of the cable assets. On the other hand, replacement would not reduce the risk of outages due to dig-in or relay mis-operation, so these are not considered failures of the cable.
  • Not a recurring event The asset tools take a life-cycle view of the asset, meaning we are typically looking at changes that occur over many years or several decades. Therefore we are generally not interested in failures due to degradation that occurs on a much shorter cycle than the life of the asset. For example, a circuit breaker's timing may be out of tolerance, but this can simply be corrected as part of normal maintenance, and it may be expected to happen again. A breaker being out of tolerance is not a strong indicator that it is near the end of its service period.
  • Causes significant consequence Another characteristic of a failure is that it creates a meaningful cost for the utility. See consequence of failure for more information about this.

In many cases the lines demarcating these distinctions are not completely clear. Is failure of a load tap-changer considered failure of a transformer? What about mis-operation of a circuit breaker? Judgment is needed to answer these questions. Advanced techniques, such as use of multiple failure modes, can be used to model complex failure scenarios.

Continue to probability of failure.


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