INVESTIGATION ON THE DEGRADATION BEHAVIOR OF CREEPAGE DISCHARGE ON PRESSBOARD IMMERSED IN PALM FATTY ACID ESTER (PFAE) OIL

Creepage discharge at the oil-pressboard interface is known as the development of a conducting path which is characterized by white and carbonized marks.  This phenomenon tends to cause damage on the cellulose pressboard insulation which is subsequently promote to the catastrophic failure of a transformer.  One of major defects that may cause the creepage discharge to occur along the pressboard surface is an excessive moisture content in pressboard insulation.  Previously, there is an extensive research concerning the effect of moisture content in pressboard on the degradation of creepage discharge at mineral oil-pressboard interface.  However, none has been found on the study of the effect of moisture content in pressboard on creepage discharge using ester oil.  Therefore, this paper attempts to present the investigation on the degradation behavior of creepage discharge at Palm Fatty Acid Ester (PFAE) oil-pressboard interface by using a needle-bar electrode configuration under a constant AC voltage.  Dry and wet pressboard samples (moisture content of 3 %) are used in this experiment to differentiate the degradation behavior.  The development of creepage discharge is analyzed by correlating the visual records of creepage discharge and phase-resolved partial discharge (PRPD) pattern.  An unexpected result has been found that the number of partial discharges (PDs) for wet pressboard is lower than the dry one as the formation of white mark with bush-like pattern is observed.  Eventually, as the white mark is seen about halfway of the gap distance, the PDs number for wet pressboard sample significantly dropped, i.e. by 99 % compared to the dry board which is only 38 %. Variations in the PRPD data is due to constructive and destructive superpositions of electric field. The results suggest that the destructive effect is higher on the wet pressboard compared to the dry one.