Cold start of a 240 MVA generator step-up transformer filled with natural ester fluid

A 240 MVA, 165 GRDY/20 kV generator step-up transformer was insulated with EnvirotempTM FR3TM fluid. The transformer was energized during a cold temperature period in mid-December 2010. This is believed to be the largest generator step-up transformer filled with a natural ester fluid that was energized at low temperatures. The lack of cold start experience of natural ester filled power transformers created questions and at least some uncertainty as to outcome. This paper describes the instrumentation used and data collected during the cold startup procedure. In addition, a computational fluid dynamics analysis of this transformer design was performed that provided calculated temperatures and elapsed times until steady state temperatures were achieved. Comparisons are made between the actual and calculated values. The results indicate that the cold start up procedures for a power transformer are the same whether filled with mineral oil or natural ester fluid of similar characteristics as used for this work.