Fire and explosion accidents of oil-filled electrical transformers are leading to negativeimpacts, not only on the delivery of energy, but also on workplace health and safety as well asthe surrounding environment. Such accidents are still being reported, regardless of applying theregular maintenance strategy in the power plants. The purpose of this paper is to integrate asustainability perspective into the maintenance strategy. The problem addressed is: how can weapproach the relevant cost-effective sustainable maintenance for oil-filled electrical transformers?For this purpose, an empirical study in a power plant in Kuwait was introduced. The first stagewas to carry out a sustainability assessment using the ABCD procedure. In this procedure, gaps toapproach sustainability were identified and actions prioritized to close these gaps were demonstrated.Applying this procedure yielded an early fault diagnosis (EFD) model for achieving cost-effectivesustainable maintenance using a fault trend chart based on a novel numerical method. Implementingthis model resulted in an extension of the lifetime of transformers with suspected failure propagation,leading to a deferral of the replacement investment costs. The principal conclusion of this paper isthe importance of viewing the maintenance strategy of transformers from a strategic sustainabilityperspective, in order to approach relevant cost-effective sustainable maintenance.