Conductor insulation tests in oil: aramid vs. kraft

Developments in transformer insulation, leading to increased use of aramid insulation in oil-filled transformers, are briefly summarized. A series of tests designed to gather data on the dielectric strength of aramid paper in oil used as turn-to-turn insulation is presented. The test setup, sample configuration and preparation, and test procedures are described. Turn-to-turn and coil-to-coil results are presented and discussed. It is shown that, turn-to-turn, the aramid paper is stronger dielectrically than the kraft paper by 25% using a full-wave impulse and 20% using a 1 mu s chopped wave. There is little or no difference in the dielectric coil-to-coil strength between the aramid and kraft papers. Thus, it is possible to improve the turn-to-turn impulse strength of liquid-filled power transformers by using aramid paper in place of kraft paper. The aramid also has improved mechanical strength and thermal aging characteristics.<>