Improvement of reliability & lifetime of oil immersed power transformers through condition monitoring

Abstract

Power Transformers are very critical in any power system and they are very expensive. Maintaining the Reliability and Well-being of Power Transformers shall be the fundamental responsibility of Electrical Engineers. Proper periodical maintenance of Power Transformers, Carrying necessary tests including Condition Monitoring Tests and attending to foreseen faults will enhance the reliability and life time of them. Fault diagnosis using the condition monitoring test results by skilled engineers and Keeping technical staff and required spare parts readily available will make the power system more reliable by avoiding unexpected and expensive outages. Therefore it is important to have an Index for a transformer that can imply the present condition. Selected condition monitoring tests for the Winding and Insulation oil are used to determine the Transformer Fitness Index (FI) which will indicate the well-being of the transformer. Depending upon the Fitness Index, recommendations are made how to increase the lifetime (If Possible) and the reliability. This thesis describes the insulation paper, Insulation Oil, faults and testing methods for winding and oil. In the literature survey, detailed study about the selected tests and analyzed available test results of various power transformers of Ceylon Electricity Board (CEB) by referring to IEEE, ICE standards and relevant books. Two prequalification tests were selected to detect the moisture content in the insulation. If both prequalification tests are passed Fitness tests were done and FI values were calculated. Depending on the FI values, recommendations and statements on the transformer condition is described. Those statements will be very helpful for the improvement of reliability and life time of existing transformers and to take the decision which transformers are to be replaced and when to be replaced.