Breakdown Voltage of PFAE Containing Non-bridged and Bridged Cellulose Fiber Under Lightning Impulse Stress

Abstract

This research investigated the influence of cellulose bridging skeleton on the breakdown strength of Palm Fatty Acid Easter (PFAE) under Standard Lightning Impulse Voltage (SLIV). A commercial cellulose fiber of 20 µm size is selected as artificial contaminants in PFAE oil. The concentration of the cellulose contamination is 0.004wt%. The standard lightning impulse of 1.2/50 µs is generated from a single stage test transformer and the waveform is applied according to the IEC60897 to obtain the breakdown voltage. The cylindrical test cell fitted with spherical-spherical configuration with 0.5 mm gap is utilized to generate the quasi-uniform field between the electrodes. The cellulose bridging skeleton is created artificially under a DC electric field by using a +10 kV DC power supply and its microscopic optical digital images of the bridge forming process is observed and captured via microscope fitted with HD camera. The experiment results show that the cellulose contamination without bridges reducing the breakdown strength by 4.5% from the clean oil. The breakdown strength curtailment of PFAE become more prominent when the bridge skeleton is observed between the electrodes gap, where the curtailment is by 27.96% from the clean oil. The simulation results revealed that the presence of cellulose fiber distorted the field lines and at the same time, it created own non-uniformity flux line on the cellulose fiber surface and surrounding. The high field stress and high intensity also obtained between individual cellulose fiber that are potential to lead a local breakdown nearby the fiber.