*2.3. Empirical Study Design*

The ABCD procedure was applied in the Primary Substation Maintenance Department (PSMD) power plant, an organization of the Ministry of Electricity and Water in Kuwait State. The PSMD power plant is responsible for moving toward sustainability, primarily to prevent fire and explosion accidents of transformers, which recently increased. According to statistical data from PSMD power plant, around 1.5% of 3950 transformers were reported as out of service due to fire and explosion accidents during the last two decades, regardless of applying the regular maintenance strategy. In addition, there is also a growing problem of oil waste due to the replacement of many old and scraped transformers with new ones. The PSMD power plant was selected among others in this study due to the availability of good historical data of a massive quantity of transformers, and the appreciated cooperation of the maintenance team. Two online workshop meetings were organized by the first author with the PSMD team from maintenance, safety, and economic departments. The first workshop took around three hours, where relevant questions were addressed to the PSMD team. The main questions discussed the vision, current condition monitoring practices, actions need for sustainable maintenance, and current sustainability challenges. The problem of the increasing rate of fire and explosion accidents was also discussed. The second workshop took around two hours, where the problem was defined and bounded, and the propositions were studied. Accordingly, the capability to implement the ABCD procedure to integrate a strategic sustainability perspective in the current maintenance strategy was proposed. Besides, the need for the development of an effective diagnosis model for early fault detection was also proposed. The PSMD team approved to provide access to oil analysis data of 972 nominated oil-filled electrical transformers, with medium and large power rates, from the laboratory's application software in order to evaluate the transformers' condition and study the current activities from a sustainability perspective. The outcome of the gathered data of the oil analysis was analyzed and categorized according to the fault type (see Figure 2). The importance of the categorized data is identifying the fault types and defining the category that can be utilized in the ABCD procedure.

**Figure 2.** Fault type mode analysis of 972 transformers of the PSMD power plant.

The category of "Arcing Fault" is at 6% of the fault mode. The arcing fault can be indicated by detecting a high concentration value above the caution limit of the two gases, hydrogen and acetylene. This arcing can generate extremely high temperatures over 700 ◦C, though for a short time, in the oil, leading to fire accidents [4,13,16]. The category "Partial Discharge Fault" is at 7% of the fault mode. Partial discharge can be indicated by detecting a high concentration value above the caution limit of the hydrogen gas in the oil. This fault can occur at any temperature over 200 ◦C [4,13,16]. The category of "Oxidation Deposits Fault" is at 10%, the most dominant fault mode. Oxidation products such as acidity may convert to ester and thereafter form sludge deposits on the transformers' windings. This fault can be indicated by detecting a high concentration value above the caution limit of the acidity in the oil [5,15]. The category of "Corrosion Deposits Fault" is at 3% of the fault mode. The corrosion deposits are in the form of copper sulfide on the windings of the transformers. This fault can be indicated by detecting a high concentration value above the caution limit of the hydrogen sulfide gas and toluene compound in the oil [2]. The category "Starting Fault" is at 7% of the fault mode. This category represents the transformers with suspected failure propagation, that have a fault in progress and need corrective action. The investigation in this study focused on the "Starting Fault" category to apply a model of early fault diagnosis in order to follow up the fault before progression to a risky level. The last category "Good Condition" represents the transformers which have not any fault's indication.
