Aurtra's Condition Risk Index is designed to be aligned with CIGRE's technical brochure, "Condition assessment of power transformers" . The index provides a view of the transformer from the multi-dimensional perspective of absolute state and relative state given operational use (how the asset is being used given its state).
The purpose of this assessment index is to highlight the transformers with the poorest conditions so that each can be considered for refurbishment, either to extend the life of the insulation or determine whether the end of life has been reached.
The Condition Index relies on data to make accurate assessments of the condition and operation of the transformer. This requires a combination of data collected and derived from the Aurtra HealthSense as well as oil tests performed by DGA. The absence of either set of data will reduce the effectiveness of this transformer insulation assessment index.
Transformer state is assessed in terms of 4 major risk categories (Solid Insulation, Dielectric, Operations, and Aging Risks). Each of the indexes is broken down into multiple sub-index which relate to specific failure indicators for specific widely understood failure modes. Each of these sub-indexes is assessed based on benchmark limits and assessed in terms of a scoring matrix. The major index is then summarized from the sub-indexes.
Throughout the assessment, the scoring matrix used is as defined in the table from  below. A score will be given from A to F based on the effect of the failure mode on the transformer with A being in the best condition and F being the most critical condition.
Each failure mode is assessed within its respective index. And scored based on a scoring matrix that defines each level, as shown in the table from  below. A score will be given from A to F based on the effect of the failure mode on the transformer with A being in the best condition and F being the most critical condition.
The Aurtra Dashboard simplifies these levels into four colors so that the condition of the fleet can be assessed at a glance. These are shown when looking at the Fleet Summary page. The color mapping is shown below:
A relevant service or maintenance plan can be considered and developed based on the results of the assessment of these indexes.
The Overall Risk is derived from four indexes representing the various types of risk to the life of each transformer.
The Solid Insulation Risk and Dielectric Risk Indexes relate to the state of the solid and liquid insulation and was developed using CIGRE's standards for condition assessment of power transformers.
The Operating Risk and Aging Risk were developed by Aurtra using insights extracted from the data derived by the Aurtra algorithm relating to the way the transformer is being used given its life state.
Within each index, the summation of scoring for the total index value is completed using a non-linear summation method as outlined in . This minimizes the effect of masking and ensures poor indicators in one area are not masked by a large number of good indicates in unrelated areas. This will ensure that the poor condition of a specific component is preserved throughout the assessment process and this poor indicator is brought to the attention of the user.
For more detailed information on the individual risk indexes:
Note: This is an insulation index and should not be used on its own to make asset management decisions. It can be integrated with other transformer assessment indices to build a holistic picture of the condition of the transformer.
 Condition assessment of power transformers. CIGRE Brochure No. 761, March 2019.