Insulating Oils, Fluids, and Gases:Less Flammable Insulating Fluids

Less Flammable Insulating Fluids

There has been a great increase in the use of less flammable liquids as an insulating and cooling medium in transformers. As these liquids are chemi- cally different from mineral oils, they cannot be substituted in equipment designed for the use of mineral-oil type liquid. The NEC has officially desig- nated these synthetic liquids as less flammable. They are askarels, silicone, RTemp, Wecosol R113, envirotemp (FR-3), and others. As is the case with mineral oil, the dielectric strength of askarels, silicone, RTemp, Wecosol, and other less flammable fluids is reduced by the presence of emulsified water. Silicone, Wecosol, and RTemp characteristics are similar to those of askarel.

The maintenance and testing of less flammable insulating fluids is similar to oil. The inspection and maintenance of these fluids are discussed in Section 4.5. The battery of tests (screening tests) that are normally performed on these fluids are listed in Table 4.2. These fluids should be maintained and tested on the same frequency as used for insulating oil. The oil sample for conducting the tests should be taken from the bottom of the transformer tank for RTemp, and from the top of the tank for silicone and askarel. The test limits for acidity, IFT, dielectric breakdown voltage, power factor, and color for service-aged less flammable fluids are given in Table 4.9. It should be noted that the dielectric breakdown voltage test limit given in Table 4.9 for these fluids is for the ASTMD877 method using disk electrodes.

Acceptance Values for Less Flammable Fluids