Common defects of oil-immersed main transformers and handling procedures

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1. Common defects of oil-immersed main transformers: The main transformer is a core component of a substation, and its condition is directly related to the safety and stability of the power grid; therefore, it is necessary to eliminate any defects in the main transformer promptly. Oil-immersed main transformers are the most commonly used type of transformers in power grid systems. According to statistics from professionals specializing in the maintenance of such transformers, based on the proportion of defects present, the common defects in oil-immersed main transformers include the following categories: Ø Leakage-related defects, including leaks in components such as the transformer body, on-load tap changers, and bushings; Ø Abnormalities in test data, such as issues with the DC resistance of windings, the insulation resistance of core components, and oil chromatography tests; Ø Abnormalities in non-electrical protection signals; Ø Abnormalities in the operation of on-load tap changers, including failures to operate, repeated adjustments, and abnormal signals; Ø Defects in the cooling system, including problems with components such as fans, oil pumps, water pumps, oil flow meters, water flow meters, as well as their control systems. In the daily operation and maintenance of main transformers, the aforementioned five categories of defects cover the vast majority of defects that occur in such transformers. Within each category, there are some particularly typical causes of defects and corresponding treatment methods, which are worth learning from by maintenance personnel. Therefore, it can be said that if maintenance personnel can master the causes of these defects and the methods to address them, it will improve the efficiency of maintenance and the quality of equipment upkeep. 2. Correct procedures for handling defects: Proper procedures for dealing with defects generally include the following three steps: 1) Collection of defect information – First, operators or inspectors detect defects in the equipment and report them to the maintenance staff. Usually, since the operators and inspectors are not professionals, it is difficult to determine precisely the location and cause of defects or failures; one can only provide a vague description of the symptoms, such as the transformer fan stopping Operation or the on-load tap changer failing to function properly. Maintenance personnel usually cannot determine the cause of a defect based solely on the reports provided by operators; they must gather additional information about the defect in order to assist in making a judgment. This step is very important, as the defects reported by the operators are usually just individual defects or issues that are not connected to each other. In order to determine the cause of a defect more accurately before going to the site for repairs, save time during on-site repairs, and improve efficiency, repair technicians must ask the people who reported the defects for additional information. They also need to consult repair records and test records to help identify the specific cause of the defect. For example, if the operators report that an alarm signal has been triggered due to slight gas presence in the main transformer, the maintenance personnel must ask the operators further questions: whether it is possible to see gas inside the gas relay, what the oil temperature was at that time, and what position the oil level gauge pointer was indicating. They also need to review the maintenance and testing records to determine whether there have been any activities recently that could affect the position of the switch contacts inside the transformer. 2) Defect cause analysis: The maintenance personnel use the information at their disposal to analyze the causes of the defects. Through the reporting of defect phenomena and the supplementary verification of defect information, including some necessary on-site inspection and testing activities, maintenance personnel can initially determine the main causes of the defects in the main transformer, identify the methods to address each of these issues one by one, and ultimately establish the root causes of the defects. 3) Defect handling: After completing the above two steps, maintenance personnel can implement the corresponding maintenance strategies. Through the analysis of the causes of the defects, the maintenance personnel have gained an understanding of the issues that have arisen. Based on these causes, they replace relevant components or take appropriate measures to eliminate the defects and restore the normal operation of the transformer. The above three steps, namely defect information collection, analysis and determination of the causes of defects, and defect resolution, are the three essential stages for maintenance personnel to eliminate defects. By properly carrying out these three steps, maintenance personnel can target their efforts effectively, accurately identify and eliminate defects, and quickly restore the equipment to its normal operating condition.