Reliability Based On Evaluation of Insulation and Mechanical Conditions of Step-Lp Transformers of Gurn Power Plant at CVG EDELCA in Venezuela

For CVG EDELCA, reliability of power transformers is a very important matter for its power system performance. Taking in consideration that at Guri hydro power plant there are power transformers older than twenty years old, it was decided to select a group of step-up transformers for evaluation of insulation and mechanical conditions based on: dissolved gas analysis (DGA), tests of oil, and electric tests, for the last five years. Due to an incipient fault condition detected by DGA, a program of off-line tests on a group of three-phase and singlephase transformers of Guri power plant was scheduled in cooperation with Hydro Quebec International experts. Frequency response stray losses, frequency response analysis, recovered voltage measurement and dissipation factor versus frequency tests were applied on each selected transformer. As a result of the investigation, it was found that mechanical and insulation conditions were good for most of these transformers