Survey of current utility practices for testing and treating insulating oil

There has been a significant increase in the number of tests made on each oil sample since the original survey in 1958. The dielectric breakdown voltage test, D-1816, using VDE electrodes, was adopted in 1960 and is now being used by seventeen per cent of the laboratories. Moisture content of insulating oil is being measured by an increasing number of laboratories while the use of the interfacial tension test appears to be decreasing. The overall limits for classifying oils into various categories has not changed significantly since 1958. Most utilities recondition large quantities of insulating oil using a filter press or cartridge type filter. Those that reclaim oil use fuller´s earth, but the quantity of oil is small compared to the amounts reconditioned.