Y. Ehara

Phase analysis of discharge magnitude distributions inside a small void and its applications to diagnosis of deteriorating insulations

A breakdown phenomenon of electrical equipment due to the deterioration of insulation was investigated. The degree of deterioration or breakdown of the insulating system was predicted from the distribution of induced electric charges inside small voids in an insulator-the discharge magnitude distribution. This distribution was measured by a special internal-discharge pulse measurement system, which analyzes it according to the phase area of the applied AC 50-Hz voltage. This technique was used to investigate tree progression in the microvoid of PMMA (polymethyl methacrylate). The density and the growing speed of the trees are analyzed in terms of the discharge magnitude distributions.<<ETX>>

Correlation between discharge magnitude distribution and discharge luminescence distribution due to electrical treeing

An investigation was conducted to diagnose deteriorating insulation in order to predict the breakdown of electrical equipment due to the deterioration. An internal-discharge-pulse-measurement system which could analyze the discharge magnitude according to the phase area of the applied AC 50-Hz voltage was used to diagnose the degree of deterioration. The process was analyzed from the occurrence of the discharge to the development of treeing in an artificial void. The discharge luminescence could be observed in detail using digital image processing. Before the initiation of the tree, a swarming pulsed microdischarge occurred. The discharge luminescence was almost constant. After the initiation of the tree, the discharge magnitude and the number of discharge current pulses rapidly increased on the discharge magnitude distribution.<<ETX>>

Analysis of treeing phenomena by simultaneous measurement of discharge magnitude and discharge luminescence of single pulse

This paper reports on the investigation of the treeing phenomena by measuring simultaneously discharge magnitude and discharge luminescence of single pulse. Treeing experiments were conducted using a PMMA block which had a needle shape void on the tip of needle electrode. One cycle of the ac applied voltage was divided into twenty equal phase angle areas, and they were named /spl phi//sub 1/-/spl phi//sub 20/ in order from the negative peak point of the applied voltage. The ac voltage was applied to the needle electrode, and the discharge pulses and discharge luminescences were measured at the same time at /spl phi//sub 3/-/spl phi//sub 9/ in positive polarity. As a result, the discharge luminescence at /spl phi//sub 3/,/spl phi//sub 4/ occurred mainly in the void area independently of the discharge magnitude. At /spl phi//sub 3/-/spl phi//sub 9/, the discharge luminescence was observed in the void area when the discharge magnitude was small, in the tree area when it was comparatively large. The discharge luminescence reached near the tip of tree channel. However at these phase angles, the discharge luminescence was observed only in the void area.

The influence of instantaneous value and dv/dt of applied voltage upon electrical treeing deterioration

In this study, we performed to analyze the treeing phenomena with a void by discharge magnitude and discharge luminous quantity in each phase angle area. The purpose of this study was to apply this analysis to the diagnosis of degradation by electrical treeing. The discharge magnitude and discharge luminous image were measured by the original measurement system to analyze discharge pulses and discharge luminescence at several phase angle areas of applied voltage. One cycle of applied voltage was divided into twenty areas, which were named /spl phi/ 1/spl sim//spl phi/ 20 in order from the negative peak point of applied ac voltage. Each phase angle area has informations of applied voltage that are instantaneous value, differential value of applied voltage (dv/dt) and the product of instantaneous value and dv/dt. The results of this analysis indicate that instantaneous value and dv/dt of applied voltage have a close relation with electrical treeing phenomena. Hence, we investigated the influence of instantaneous value and dv/dt of applied voltage upon electrical treeing phenomena.

Prediction of tree initiation by phase angle analysis of discharge magnitude and discharge luminescence on partial discharge

Partial discharge is one of the causes of degradation in insulating polymer materials subjected to high voltages. Of particular importance in this case is the degradation which occurs due to partial discharges inside gaps, such as voids inside an insulator. In this study, the prediction of tree initiation due to partial discharge occurring from void 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 was noted that some samples revealed different time dependence of partial discharge patterns even under the same measurement condition. These patterns were the case of the occurrence of Swarming Pulsive Micro Discharges before tree initiation. The prediction of tree initiation is analyzed by using moving average of the discharge magnitude. A proposal of the typical variances seen in the time dependence of partial discharge which symbolize a pre-tree initiation mode will be made as well as evaluation of the usefulness of this technique.

Analysis of discharge magnitude and discharge luminescence of phase angle area on tree initiation

This 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 /spl phi//sub 1-20/ in order from the negative peak point of applied ac voltage. The discharge magnitude and luminous quantity in /spl phi//sub 3/ increase immediately before tree initiation. In this experimental condition, /spl phi//sub 3/ 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 /spl phi//sub 3/ 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 considered to be useful information for prediction of tree initiation.

Analysis of discharge luminous location and discharge magnitude on treeing phenomena at each phase angle

This research is performed to analyze the treeing phenomena by discharge magnitude distribution and luminous intensity distribution at each phase angle area. The discharge pulses and the discharge luminous image are measured by a special measurement system to analyze the discharge magnitude and the luminous intensity distribution according to several phase angle areas of the applied voltage. Each phase angle area is named /spl phi/1/spl sim//spl phi/20 in order from the negative peak of the applied voltage. In this study, we are interested in the discharge magnitude and the discharge location of the luminous intensity distribution at each phase angle area. In particular, we determine the quantity of partial discharge at the phase angle area of /spl phi/7 and /spl phi/17 in relation to the tree length.

Analysis of treeing phenomena by discharge magnitude and discharge luminescence in each phase angle

This paper reports on the investigation of the treeing phenomena by measuring discharge magnitude and discharge luminescence. Treeing experiments were conducted using a PMMA block which has a needle shape void on the tip of needle electrode. One cycle of the ac applied voltage was divided into twenty equal phase angle areas, and they were named /spl phi/1/spl sim/20 in order from the negative peak point of the applied voltage. The ac voltage was applied to the needle electrode, and the discharge pulses and discharge luminescence were measured at the same time in each phase angle area. In this paper, the discharges at /spl phi/4 and /spl phi/7 phase angle area were especially given attention and the discharge pulse and discharge luminescence caused by only one partial discharge were measured at the same time. As a result, the discharge luminescence at /spl phi/4 occurred mainly in the void area independently of the discharge pulse magnitude. At /spl phi/7, the discharge luminescence was observed in the void area when the discharge pulse was small, and observed in the tree area when it was comparatively large.

The fractal analysis of the treeing process

The purpose of this study is to analyze the growth mechanism of trees which generate from a pointed tip of a needle electrode inserted into insulating materials. The fractal dimension of the discharge luminescence pattern was determined from fractal theory. The fractal analysis of the treeing process was performed by correlating the fractal dimension to the tree growth length, the quantity of luminescence in the tree area, and the luminous length measured in each phase angle area. One cycle of applied voltage was divided into twenty equal areas, which were marked by /spl phi/1/spl sim//spl phi/20 in order from one negative peak to the next negative peak of applied ac voltage. A correlation between the tree growth length and the fractal dimension of the discharge luminescence pattern of the tree region in /spl phi/7 and /spl phi/17 was obtained.

Influence of void surface state on swarming pulsive micro discharge

The degradation examination on applying high voltage of high polymer insulation material used for an electric power cable has been conducted widely. In this degradation examination, a decrease and a disappearance of electric discharge current and maximum magnitude of discharge are observed with the lapse of time. This phenomenon is called SPMD; the discharge magnitude becomes very small, and then the electric discharge current pulse frequency per unit time increases greatly. It has been reported that this phenomenon is related to the roughness of the void surface. However, there are many unknown points yet. The relation between the degree of the roughness of the void surface and SPMD is investigated in this paper.