Testing and diagnostics of power transformer in PT. Indonesia Power Kamojang Geothermal Power Plant unit 1

This paper presents testing and diagnostics of 40 MVA, 150/11.8 kV,Ynd5 main transformer and 4 MVA, 11.8/6.3 kV auxiliary transformer on PT. Indonesia Power Kamojang Geothermal Power Plan unit 1, that have been in operations for more than 25 years, since 1982. Although the main and auxiliary power transformer installed have been fulfilled their design life, the concept of simple replacement of power transformer in the system considering it as weak or potential source of trouble is no more valid in the present scenario of financial constraint. Today the paradigm has changed and many efforts are being directed to explore new approach/techniques of testing, monitoring, diagnosis, life assessment and condition evaluation and possibility of extending the life of existing power transformer. In this effort of extending the life of existing power transformer, testing and diagnostics of power transformer conditions become very important step whether it is possible to extend certain time of useful life beyond design life and save investment on new power transformer. This paper mainly asses the life condition of total insulation system of power transformer due to failure of insulation material considered to be major factor in power transformer, Testing and diagnostics done on main and auxiliary power transformer based on Transformer Turn Ratio (TTR) test, Winding Resistance (Rdc) test, Insulation Resistance (IR)Test, Tan delta test, Dissolve Gas Analysis (DGA) test and Dielectric Response Analysis (Dirana) test. This kind of tests gives in depth information regarding power transformer conditions and abnormalities. The test results show that the oil and paper insulation of both power transformers were very wet and need immediate purification. Condition of winding resistance on main power transformer also showed very significant increase value (300%) compare to the previous commissioning data that mean also increasing load losses significantly.