Natural ester insulating liquid was recently specified for a 420 kV power transformer, which is the highest voltage unit designed and operating to date. Leading up to this new large power transformer, there are many other small, medium and large power transformers operating new since the early 2000’s.
If small power substation units are combined with medium to large power, there are many thousands of new and retrofilled transformers in operation that are being tracked. In total, there are over 600,000 natural ester transformers operating worldwide without a reported fire or environmental incident.
Laboratory studies and field operation data provided from power transformers and reactors as reported in this paper indicate that natural ester liquids are reliable as dielectric insulation and as a coolant. A case history and laboratory testing data from samples collected during routine maintenance intervals indicate that natural ester fluid results can be used to reliably diagnose operating problems and suggest corrective actions.