**5. Conclusions**

The principal conclusion of this paper is the importance of viewing the maintenance strategy of transformers from a strategic sustainability perspective, in order to approach relevant cost-effective sustainable maintenance. This was proven in the empirical study by detecting the faults in the initial stage using the early fault diagnosis (EFD) model. Several conclusions can also be highlighted as follows:


**Author Contributions:** Conceptualization, visualization, investigation, methodology, writing original draft preparation, R.J.; supervision, reviewing and editing of the maintenance part, M.K.; reviewing and editing of the sustainability part, J.S.; providing data, participating in the workshops, and reviewing the outcome of the workshops, M.A. (Mohammed Alhattab), M.A. (May Alhendi), and A.B. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Acknowledgments:** Authors acknowledge the support of the PSMD-power plant, Kuwait Ministry of Electricity and Water, for providing the analysis data and resources. Authors also wish to acknowledge the support of SAECO laboratory of Saudi Arabian Engineering Company for analysis service.

**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.
