May 9, 2022

Transformer health indices and risk matrices

A transformer health index is an estimate of the health of a transformer.

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A transformer health index is an estimate of the health of a transformer: available data is analyzed, combined and ‘boiled down’ to a number, code or some value that can be used in planning or other asset management activities. The index does not tell us anything new about the transformer – we would have the same level of knowledge about the transformer if we did not generate an index. What is novel about an index is the ability to rank assets based on the index.

In this discussion, we will look at some of the key points to remember and / or address in generating and using an index; some of them are ‘obvious’, but some are more subtle. However, it is critically important to start with the endpoint in mind so we can not only realize the value of the index but also see the limitations [1]. Risk matrices often use the output of a health index analysis to act as a proxy for ‘probability of failure’; we will address some of the issues in this approach and some of the issues related to the categorization of both indices and risk matrices which can be misleading.

Setting objectives

The first question is: what problem are we trying to address [1]? We could be looking at an index to help plan for transformer replacement or to identify those which will be most in need of maintenance or refurbishment: identifying

a need to act, an ‘intervention’. If we think of a more familiar analogy, say a car, we might be interested in when it will need maintenance and when it will need replacement: but do we replace the car because the tires are going down in pressure?

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