Health Index

The Health Index of an asset is a measure of its condition relative to end of life. Test and inspection results are combined in a systematic way to calculate the Health Index score. Our approach to health indexing comprises four steps.

  • Demographics – This element of the analysis answers the question “What do you have, how many, and how old?” It will include defining each asset class. For example, are oil and SF6 HV breakers part of the same class or separate?
  • Degradation processes – This element of the analysis identifies how each asset type ages and ultimately fails.
  • End-of-life criteria – This element of the analysis defines what can be measured to tell us how far each degradation process has progressed (i.e., tests and inspections that relate to the degradations processes)
  • Health index formulation – This element of the analysis determines how important each end-of-life criterion is in establishing the health of an asset? This depends on how important the degradation process is and how strongly the criterion relates to the process, i.e., is it a good measure or not?

Our approach is to gather the stakeholders and subject-matter experts for a series of workshops and work through each of the four steps with them, ensuring buy-in among key personnel.


The output of this is a summary of health index for each population, as shown below.


An asset's [probability of failure can be adjusted based on its Health Index. This can be either an adjustment to Effective Age (i.e., this asset is actually 20 years old, but its condition means we will treat it as a 35-year-old for planning purposes), or a failure probability multiplier. In either case, assets in poor health will have higher Risk than they would otherwise.

There is little data on which to calculate correlations between Probability of failure and health. This is an opportunity for sharing between users.

Continue to failure probability multiplier.


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