AN ANALYSIS OF THE INCREASE ON TRANSFORMERS FAILURE RATE PHENOMENA AND MEASURES TAKEN TO IMPROVE TRANSFORMERS RELIABILITY

摘要

Since the middle of 90's an increase in the failure rate of new power transformers and reactors was observed. The failures occurred both during factory acceptance tests and during the first months of operation. In this paper it will be discussed the investigation performed to find out possible reasons for this abnormal failure rate. After it will be presented the proposed measures that are and will be undertaken to improve transformers and reactors reliability. As the technical specification was not modified and system conditions remained the same nothing was found from the customer's point of view that could justify the increase in the number of failures. In order to clarify the situation a comprehensive investigation took place in which initially was made an analysis of all failures. This analysis showed us that acceptance tests failures occurred mainly during dielectric tests and those units that failed during operation, had their active part, windings and/or insulation involved. A conclusion of this analysis indicates that project, manufacturing or components could be considered as causes of the transformers failures. It will be shown that the increase on the number of transformers failures has occurred at the same time Brazilian electrical market became more competitive and deregulated. This modification on Brazilian market led to new utilities to be installed, privates ones, and as consequence there was a high pressure on equipment prices as well as manufacturing time. A discussion will be made about the possibility that the new market has led to a reduction on transformer design safety margins and if this could justify the increase on the failure rate. Finally the actions that has been performed in order to decrease the failure rate will be present, actions that leads to a closer integration between operation and engineering people in order to get information about transformers performance during operation and failure mode, more discussions with the manufacturer about transformer specific applications, and also design review in complex designs, detailed inspection during manufacturing and tests, installation of monitoring system, transformer transfer surge analysis and frequency response measurement will be presented.