Oil-filled electrical transformers are critical equipment for modern societies where a sustainable energy supply is required. Recently, many severe fire and explosion accidents of transformers have been reported due to copper corrosion problems in the form of copper sulfide deposits on the windings. The most negative impact of such accidents is safety threats to workers and people near the site, which can expose them to toxic chemicals, heat, sound pressure, etc. Another impact is the economic losses due to power outages and loss of profits. These accidents happen even though applying maintenance strategies for fault detection and diagnosis in power plants. Reviewing literature in the related topics revealed the inability of the applied maintenance strategies to detect copper corrosion problems due to shortcomings of an effective Condition Monitoring (CM) procedure that can be used to detect and track such problems in the initial stage, as well as a lack of a clear diagnosis model for defining a threshold that can early trigger an alarm before fault incidence. The main currently applied monitoring parameters are measuring corrosive sulfur compounds, evaluating the corrosivity level of the oil by corrosion tests, and measuring specific gases in the oil. Other parameters are also included, such as onsite electrical testing and online sensor device technology. All these parameters are insufficient for the early detection of copper corrosion problems. The main research problem addressed in this thesis is: how to establish an effective Condition-Based Maintenance (CBM) strategy for oil-filled electrical transformers to reduce copper corrosion problems and provide sustainable energy? The research is a mix of exploratory and explanatory approaches. For studying the current maintenance practices and identifying suitable ways for detecting and solving copper corrosion problems, literature reviews and experimental work were carried out, while artefact building and empirical studies were used for developing and testing solutions. One important result was identifying relevant parameters, such as hydrogen sulfide gas and toluene compound, which are by-products of the corrosion reaction. The finding was utilized in creating a procedure for early fault detection for the purpose of establishing an effective CBM strategy. In this strategy, the corrosion problems can be detected based on the relevant parameters and an Early Fault Diagnosis (EFD) model using a novel numerical method for defining an alarm threshold. The procedure was successfully verified and validated in two empirical studies in a power plant. The relationship between maintenance and sustainability was also explored to study the role of an effective maintenance strategy toward supplying sustainable energy. A framework for approaching sustainable maintenance was proposed based on three pillars, i.e., eco-efficiency indicator, asset management, and digitalization. In this context, a procedure called ABCD was used in an empirical study to assess the sustainability condition and find the prioritized actions toward sustainable energy. The main conclusion of this thesis is that the established CBM strategy, based on the proposed CM procedure, has the capability to reduce the probability of transformer accidents and their negative effects on social, environmental, and economic aspects, as well as provide sustainable energy to the society.

The negative impacts of catastrophic fire and explosion accidents due to copper corrosion problems of oil-filled electrical transformers are still in the spotlight due to a lack of effective methods for early fault detection. To address this gap, a condition monitoring (CM) procedure that can detect such problems in the initial stage is proposed in this paper. The suggested CM procedure is based on identified measurable variables, which are the relevant by-products of the corrosion reaction, and utilizes an Early Fault Diagnosis (EFD) model to detect and solve the copper corrosion problems. The EFD model includes a fault trend chart that can track a fault progression during the useful life of transformers. The purpose of this paper is to verify and validate the effectiveness of the suggested CM procedure by an empirical study in a power plant. The result of applying this procedure was early detection of copper corrosion problems in two transformers with suspected copper corrosion propagation from a total of 84. The corrective action was adding an optimized amount of a passivator, an anticorrosion additive, to suppress the corrosion reaction at the correct time. The main conclusion of this study is the importance of early detection of transformer faults to avoid the negative impacts on societal, company, and individual levels.

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 the regular maintenance strategy in the power plants. The purpose of this paper is to integrate a sustainability perspective into the maintenance strategy. The problem addressed is: how can we approach 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 stage was to carry out a sustainability assessment using the ABCD procedure. In this procedure, gaps to approach 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-effective sustainable maintenance using a fault trend chart based on a novel numerical method. Implementing this 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 is the importance of viewing the maintenance strategy of transformers from a strategic sustainability perspective, in order to approach relevant cost-effective sustainable maintenance.

The power transformer is a critical equipment in which the protection process is essential for modern societies where continuous electric power supplies are required. Copper corrosion problems due to the formation of sulfur deposits on the copper windings of mineral oil-filled power transformers are considered a major issue that can lead to sudden failures, and in some cases, to costly fire and explosion accidents in the power plants. These kinds of problems are still being reported regardless of available condition monitoring (CM) parameters applied in power transformers' maintenance strategy. The currently applied CM parameters are based on three different types of technologies. The first is oil analysis focuses more on measurable variables such as measuring the concentration of the corrosive sulfur compounds in the insulating oil, evaluating the oil's capability to form sulfur deposits, and measuring an increase in the concentration of specific gases. The second is on-site electrical testing focuses on the variation of the transformer's electrical properties due to the sulfur deposits. The measurable variables used in the electrical testing are Frequency Domain Spectroscopy test and Polarization/Depolarization Current test. The last is online sensor technology using Corrosive Sulfur Sensor, where the sensor's outcome data provide information about the oil's capability to form sulfur deposits. The research problem addressed is how to establish more effective CM parameters for early detection of copper corrosion problems.  The research problem is divided into three concretized research problems: What are the strengths and weaknesses of the currently applied condition monitoring parameters? Which measurable variables could be utilized to improve the currently applied condition monitoring parameters to be more effective for early detection of copper corrosion problems? And how to establish a procedure for the condition monitoring for detecting copper corrosion? Two research methodologies were applied to answer these questions, literature review and experimental work. The literature review showed significant gaps in the currently applied CM parameters for early detection of copper corrosion problems due to incomplete data of the corrosion reaction mechanism. Therefore, qualitative and quantitative investigations in the experimental work were carried out. The most important result was finding new relevant measurable variables, i.e. hydrogen sulfide gas and toluene compound, which are by-products of corrosion reaction. These measurable variables are utilized to establish more effective CM parameters for early detection of copper corrosion problems. The main conclusion of this thesis is the importance of detection corrosion problems in the initial stage by implementing more effective CM parameters to prevent catastrophic and costly failures, reduce the negative impacts on human life and the environment, and save the economic losses. Another conclusion is the importance of regularly following the measurable variables' uptrend during transformer useful life to avoid incorrect evaluation of corrosion conditions.

The purpose of this study is to determine whether the currently applied conditionmonitoring (CM) techniques are sufficient and effective for early detection of coppercorrosion fault in transformers and to establish a more relevant CM technique forearly detection of such fault. In this study, experimental work is carried out byapplying appropriate methods on different commercial insulating mineral oils for thedetection and identification of additional related by-products of copper corrosionprocess, if any. The major finding of this experimental investigation includesidentification of additional by-products, which could be useful to establish a moreeffective CM technique. Furthermore, the role of sulphur compounds in coppercorrosion fault is considered, and a relevant reaction mechanism of formation CSD isdeveloped based on the findings of the related by-products. It is concluded that, theapplication of a relevant CM technique is necessary for establishing a cost-effectivecondition based maintenance (CBM) to minimize the economic losses, hazardous effectson human life and the environment.

In recent years, many unplanned hazard failures of oil-filled electrical transformers have been reported due to presence of corrosion in form of semi-conductor Copper Sulphide (Cu2S) which result in formation Corrosive Sulphur Deposition (CSD) on the significant internal components. Formation of CSD leads to a continuous current path lead to overheating fault and deterioration of insulation system which can turn towards transformer failure. The purpose of this study is to establish an efficient maintenance plan of corrosion based on relevant Condition Monitoring (CM) to reduce the transformer failures. In this paper, many investigations have been reviewed to get sufficient data to understand and describe currently applied CM for diagnose the corrosion inside the transformers. The problem addressed is: is the currently applied CM relevant for early and definitely detection of the corrosion to reduce the probability of failures? The major result is the described gaps between the currently applied CM and selection of relevant CM suggested for providing definitely indication of corrosion. The currently CM implies two techniques; oil analysis based only on evaluation the quality of the oil against corrosion and electrical testing based on the variation of electrical properties of the transformer which can be occurred due to corrosion process as well as other faults. Conclusion of this review is a need to develop a relevant CM of corrosion for establishing a dynamic cost-effective Condition Based Maintenance (CBM) to prevent unplanned hazard failures at early stage which can reduce the negative impacts such as industries economic loss and hazard effect on manpower life as well as environment.

The purpose of this study is to establish an efficient maintenance plan based on relevant Condition Monitoring (CM) to reduce unplanned hazard failures due to presence of Corrosive Sulphur Deposition (CSD) in transformers. Many investigations have been reviewed to get sufficient data to understand and describe applied CM used in the maintenance plan. Problem addressed is: is the currently applied CM relevant for early detection the corrosion to reduce the probability of failures? The major result is the described gaps between the currently applied CM and selection of relevant CM suggested for providing specific indication of corrosion fault to approach cost-effective Condition Based Maintenance (CBM). The main conclusion: there is a need to develop a relevant CM technique to detect CSD at early stage and establishing a cost-effective CBM to reduce the negative impacts of failures such as industries economic loss and hazard effect on manpower life as well as environment.

This paper presents experimental findings of the effect of temperature on corrosive sulfur formation in transformers. To conduct the experimental study, new transformer oil was randomly selected and heated at 40, 60, 80, 120, and 150 degrees C temperature for 72 hours each along with copper strips wrapped with insulation paper and immersed in oil in accordance with IEC-62535 standard test covered conductor deposition (CCD). The oil, copper strips, and the insulation paper samples were evaluated using gas chromatography-sulfur chemiluminescence detector (GC-SCD), X-ray fluorescence spectroscopy (XRF), inductively coupled plasma optical emission spectrometry (ICP), and scanning electron microscopy (SEM) tests after 72 hours exposure at each temperature. The values so obtained, were analyzed and effect of temperature on various parameters was studied individually and as well as collectively. It was found that temperature plays an important role on corrosive sulfur formation process inside the transformers and hence the temperature of the oil should be kept within the allowed operating ranges for avoiding unforeseen failures.

The study presents the results of experimental investigation of finding out the maximum acceptable concentrations of DBDS, sulfur mercaptan, and optimal concentration of passivator for safe and prolonged operation of power transformers in the local environmental conditions of Saudi Arabia. For experimental investigation of optimal concentrations of DBDS and sulfur mercaptan, new oil free of sulfur compounds was acquired. Four specimens of this were spiked with different concentrations of DBDS and another four with free sulfur mercaptan RSH concentrations. The covered conductor deposition (CCD) tests were performed in accordance with IEC 62535 method on all the specimens. Next, to study the effect of passivator concentrations and temperatures on corrosive sulfur formation, 10 specimens from new oil were spiked with different concentrations of BTA and Irgamet 39. Copper strips were immersed in these specimens and the vials containing the oil and the copper strips were subjected to different temperature from 50 to 150 degrees C for 24 hours in the oven. The experimental results indicated that the concentration of DBDS should always be <4 ppm and sulfur mercaptan < 1 ppm in the new oils before putting in to the service. Based on the effectiveness of the passivators, BTA was found to be effective with 50 ppm concentration at 150 degrees C compared to Irgamet 39 which was effective only with 150 ppm concentration.

The study presents the results of experimental investigation of finding out the limit concentrations of DBDS and sulfur mercaptan for safe and prolonged operation of power transformers in the local environmental conditions of Saudi Arabia. For experimental investigation of limit concentrations of DBDS and sulfur mercaptan, new oil free of sulfur compounds was acquired. Four specimens of this were spiked with 2.2, 3.9, 5.4 and 10.2 ppm of DBDS and another four with free sulfur mercaptan RSH concentrations of 0.00, 0.52, 1.07, 2.13, and 7.10 ppm. The covered conductor deposition (CCD) tests were performed in accordance with IEC 62535 method on all the specimens. The experimental results indicated that the concentration of DBDS should always be <5 ppm and sulfur mercaptan <1 ppm in the new oils before putting in to the service.