SUMMARYPartial discharge is one of the causes of deterioration of insulating polymer materials subjected to high voltages. In this case, the deterioration that is caused by partial discharges in gaps, such as voids inside an insulator, is of particular importance. In this study, the prediction of tree initiation due to partial discharge occurring in voids is considered. New tree initiation diagnostic methods are proposed by measuring discharge magnitude and discharge luminescence in each phase angle section of the applied voltage. It is noted that some samples revealed different time dependence of partial discharge patterns even under the same measurement condition. These patterns were the case of occurrence of swarming pulsive micro discharges (SPMDs) before tree initiation and the case of no occurrence of SPMDs. The prediction of tree initiation by using moving average of the discharge magnitude is discussed. We propose the parameters to reflect a pre-tree initiation mode and also evaluate their usefulness for the prediction of tree initiation by using moving average analysis.
1.AbstractThis research is performed to analyze the treeing phenomena by discharge magnitude and discharge luminous quantity in each phase angle. The purpose of this study is to predict the tree initiation from the void. The discharge magnitude and the discharge luminous image are measured by the special measurement system to analyze discharge pulses and discharge luminescence at several phase angle areas of applied voltage. One cycle of an applied voltage was divided into twenty areas, labeled @ ,-20 in order hom the negative peak point of applied ac voltage. The discharge magnitude and luminous quantity in @ increase immediately before tree initiation. In this experimental condition, 4 is the phase angle area in which the discharge initiates. The discharge magnitude is proportional to the product of (dv/dt) and instantaneous value (Veb) of applied voltage. dv/dt is the differential value of applied voltage. However, the discharge magnitude at 4 increases just before tree initiation and then it is not the proportional relation. Therefore, that it is not the proportional relation is imminent in the tree initiation. It is However, to prevent an insulation destruction accident by the electric tree the establishment of the technique to predict the initiation of tree deterioration is wanted. In this study, a discharge magnitude and discharge luminescence during the void discharge for every phase angle area of applied voltage are measured, and it did the examination having to do with a basis for the tree initiation is made. 3.Experimental MethodSample and electrodes The test sample with a steel needle (diameter of lmm, tip radius of 10 EL m) is shown in Fig.1. PMMA (polymethylmethacrylate) was used as an insulating material of the sample. For inserting the needle, the PMMA block was heated up to 140°C and cooled down to room temperature. The steel needle was pulled out and inserted it again to make a void of 1.5mm. The needle was used as a H.V. electrode. The opposite side of the block was coated by conductive paint to use as a ground electrode. considered to be useful information for prediction of -I tree initiation. 2,IntroductionHigh molecule material is used as the insulation material for electric power cable. It is said that the electric tree, which occurs in a void and alien substances in the insulator, is one of the trouble factors of the cable. As for the tree deterioration, a lot of studies are accomplished so far and the mechanism of the initiation and growth of tree is made clear gradually but the details aren't sufficiently made clear yet. Fig.1 Test sample 0-7803-5035-9/98/$10.0001998 IEEE.
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