Risk Assessment of Power Transformer in Thailand’s Distribution Grid

Once power transformer has been installed in service, it is degraded by thermal, electrical and mechanical stresses. To upkeep its condition and prevent catastrophic consequences from its failure the preventive and condition-based maintenances should be applied appropriately. The appropriate maintenances are considered based on power transformer usage risk, which is evaluated from present condition and importance of power transformer. To determine the present condition, the health index of power transformer and its components are at first determined by scoring the test results of visual inspection, electrical and insulating oil tests. Then, the obtained scores and weights, which were determined by applying the analytical hierarchy process to brainstorm the utility’s expertise, were further calculated as component and overall health index of power transformer. Moreover, the major concerns of power transformer usage, such as loading percentage, load importance, redundancy, system fault level, number of through fault per year, transformer age, operation and maintenance satisfaction, are evaluated as importance index of power transformer by scoring and weighting technique. Then, the health and importance indices are coherently considered to access power transformer usage risk displayed on risk matrix. The aforementioned procedures were developed in Microsoft Excel to access 67 transformer’s usage risks in Thailand’s distribution grid. The software was developed to display the result as traffic light color as red, yellow and green for high, moderate and low usage risk respectively. The obtained risk are used to manage maintenance strategies and proper usage of power transformer according to its condition and usage risk.