Abstract: We acquired two actinomyces from abandoned medium oil, mycoplana SP. and rothia SP., with liquid medium JOA made up by ourselves. Both mycop lana and rothia can grow with the medium oil as only carbon source. Mycoplana greatly affects the dielectric loss of transformer oil, and the extent of the loss increases with increasing the concentration of actinomyces as well as the running time of transformer.

Key words: transformer, medium oil, actinomyces, dielectric loss