Some considerations for new and retrofill applications of natural ester dielectric fluids in medium and large power transformers revisited

Waukesha electric systems has been actively involved in exploring and developing the application of natural ester dielectric fluid in medium and large power transformers in both new and retrofill applications. Initial applications of this material have primarily been to take advantage of the fire safety properties it offers. Many of the initial retrofills have been in power generating plants. There are now a significant number of transmission inter-tie, distribution and industrial installations. Environmental biodegradability has been the second major reason for use of this material. The slower aging rate of cellulose insulation in natural ester fluid has become an attractive attribute. The significantly reduced carbon footprint of natural ester fluid versus mineral oil will likely become another highly desirable attribute. Application consideration for use with de-energized tap changers, load tap changers and forced oil pumps will be discussed. Application considerations of higher viscosity, higher oil temperature rise and transformer ratings will be discussed. Application in mobile transformers will be discussed.