Most substation transformer failures, excluding the acts of man or nature, can often be attributed poor maintenance of the transformer or its associated components. Catastrophic failure of a substation transformer can be avoided by accurately testing the oil condition on an annual basis and implementing a monthly visual inspection program. Most checks on a substation transformer are relatively simple: checks for oil leaks, oil level, temperature, on-load tap-changer operation, etc. However, if the oil paper insulation system of the transformer fails, it can only be detected by oil analysis. By testing the physical and chemical properties of transformer oil, a number of problem conditions can be identified before they result in transformer failure. The reason transformer oil servicing and filtering is such an important part of substation transformer maintenance is due to the composition of most transformers. insulation systems. Oil and cellulose paper insulation systems are hydrogen-containing organic compounds, and the gradual oxidation of these compounds allows moisture to form. The byproducts of the process produce increased humidity levels and create an environment that overheats the transformer and further degrades the paper insulation, which in turn produces more byproducts. This cycle continues until the transformer fails. The two main contaminants that cause paper insulation and oil degradation are the presence of oxygen and/or water in the oil. OilTransformer oil is organic and therefore oxidizes and decomposes; creating oxidation byproducts that destroy paper insulation. Aging of transformer oil is caused by the process of oil oxidation; therefore, it...... middle of paper ...... and this leads to transformer failure. Most units pass the oil through several paper cartridges during this process, with the oil passing through a 0.5 micron particulate filter as the final step before entering the transformer. The main advantage of using a HORP unit is that the transformer can be maintained while in operation. is always energized, saving the company the trouble and expense of turning the power off and doing without a valuable transformer that could generate revenue. Conclusion Substation transformers are key pieces of equipment that depend on the quality of their oil in order to provide consistent service, as a substation technician, taking care of the oil will be one of your duties. This lesson does not attempt to detail all the tests that can be performed on a substation transformer, but it should give you an idea of ​​what maintenance and oil filtering involves..