Analysis of dielectric properties of refrigerants R134a and R227ea

In order to increase the power density of electrical equipment the direct cooling of live parts by using refrigerants is a possible solution. R134a and R227ea are two refrigerants which are widely used due to their favourable low vapour pressure characteristics. In this study they are analysed concerning their dielectric strength and their discharge behaviour. The dielectric strength is measured by using an arrangement of two hemispherical electrodes according to DIN EN 60156. Hereby the electrode arrangement is housed by a transparent pressure proof vessel. While the temperature during the measurements remains constant the pressure is varied between 0.1 MPa and the liquefaction pressure of R134a and R227ea, respectively. The cooling agents are stressed by a power frequent AC voltage which…