Kyung-Soon Cho

The electrical breakdown properties of low density polyethylene film due to morphological change

In order to investigate the effects of morphological changes on electrical breakdown, we studied direct current and impulse breakdown phenomena of low density polyethylene films annealed at 100/spl deg/C for 60 minutes in silicone oil and subsequently cooled in various ways. The degree of crystallinity was estimated by infrared absorption and X-ray diffraction measurements for specimens slowly cooled in air, cooled in water, and cooled in liquid nitrogen (LN/sub 2/). The crystalline size and distribution of the specimen were measured by differential scanning calorimetry methods. The impulse breakdown strength at 30 and 50/spl deg/C increased with decreasing crystallinity, suggesting a thermal electronic breakdown process. The impulse breakdown strength decreased with increasing temperature in line with Frohlich-type breakdown theory. The DC breakdown strength was only dependent on crystallinity in the high temperature region.

Partial discharge classification and diagnosis of power cable joint by statistical processing

The prefabricated type used generally in Korea to join cable runs on new installations, because installation is very simple and save time. This type is a permanent, shielded and submersible cable joint for direct burial or vault application. It confirms to the requirements of IEEE std. 404-2004 by factory testing, but many problems of insulated cable systems are caused by internal defects of the joint part which have to be mounted onsite. Faults arise from impurities or voids. A suitable solution for a monitoring of cable joints during the after-laying test and service is partial discharge detection. This paper described the influence on partial discharge distribution of various defects at the model power cable joints interface by statistical processing. As the result of analyzing Phi-q-n patterns, several parameters i. e. maximum discharge qmax, average discharge q and average angle of discharge thetasg were found to depend upon the defect type varying applied voltage. As the result of analyzing discharge number distribution of Phi-n cluster using K-means clustering, clusters shifted to 0deg and 180deg with increasing applying voltage. It was confirmed that discharge quantity and Euclidean distance between centroids were increased with applying voltage from the analyzing centroid distribution of Phi-q cluster.

Dielectric Properties of Low Viscosity Silicone Oils with Degree of Polymerization

The characteristics of dielectric constant and of low viscosity silicone oils with changing degree of polymerization were investigated. The result shows dipole loss mechanism at low temperature range. The dielectric loss in the range of low frequencies are predominantly of ionic nature with temperature increase. The peak of dielectric loss is the detrapping of the electrons which is were trapped in the localized level of the silicone oils at the frequency of 30 kHz. The increase of ionic conduction is attributed to the presence of ionizable oxidation products and their increased dissociation feature. The activation energy and dipole moment were increased whit increasing degree of polymerization.

Electrical Characteristics of Organic Light-emitting Diodes Fabricated by Varying a Hole-size in Evaporation Boat

Electrical characteristics of organic light-emitting diodes were investigated by varying a hole-size in evaporation boat in the device structure of ITO/tris(8-hydroxyquinoline) aluminum/Al. The device was manufactured using a thermal evaporation under a base pressure of Torr. The emitting organics were evaporated to be a thickness of 100 nm at a deposition rate of . A cylindrical-shaped evaporation boat was made out of stainless steel with a small size of hole on top of the boat. Several evaporation boats were made having a different hole size on top; 0.8 mm, 1.0 mm, 1.5 mm, and 3.0 mm. We found that when the hole size on top of the evaporation boat is 1.0 mm, the average roughness is rather smoother compared to the other ones. Also, luminance and external quantum efficiency are superior to the others. Compared to the ones from the devices made with the hole-size of 0.8 mm boat. The luminance and external quantum efficiency of the device made with the hole-size of 1.0 mm boat were improved by a factor of seventy and thirty three, respectively. Also operating voltage is reduced to 2 V.

Partial Discharge Diagnosis of Interface Defect by the Distribution Statistical Analysis

Most of the high voltage insulation systems, such as the power cable joint having hetero interface, are composed of more than two different insulators to improve insulating performance. The partial discharge(PD) in these hetero interface is expected to affect the total insulation performance. Thus, it is important to study electrical properties on these interfaces. This study described the influence of copper and semiconductive substance defects on -q-n distribution between the interface of the model cable joints to classify PD source. PD was sequentially detected for 600 cycles of the applied voltage. The K-means cluster analysis has been analyzed to investigate the -q-n distribution. The skewness-kurtosis(Sk-Ku) plot from K-means clustering results was defined to quantify cluster distribution and classify distribution patterns. The Sk-Ku plot is composed of skewness and kurtosis along abscissa and ordinate which indicate the asymmetry and the sharpness of distribution. As a result of the Sk-Ku plot, it was confirmed that the data was distributed in 1st 2nd and 3rd quadrant at copper foreign substance defect, but in case of semiconductive foreign substance, the data was distributed in 2nd quadrant only.

Partial Discharge Distribution Analysis on Interlace Defects of Cable Joint using K-means Clustering

To investigate the influence of partial discharge(PD) distribution characteristics due to various defects on the power cable joints interface, we used the K-means clustering method. As the result of PD number(n) distribution analyzing on graph, the phase angle() of cluster centroid shifted to increasing with applying voltage. It was confirmed that the PD quantify(q) and euclidean distance of centroid were increased with applying voltage from the centroid distribution analyzing of plane. The dispersion degree was increased with calculated standard deviation of the cluster centroid. The PD number and mean value on graph were some different by electric field concentration with defect types.

Partial Discharge Characteristics of the XLPE/EPDM Interface in Power Cable Joint

This paper describes the influence on partial discharge characteristics of defects at the model XLPE/EPDM interfaces of power cable joints. The defects of void and copper which could inadvertently be present at the joint interface. We measured patterns by a computer-aided partial discharge measuring system. Several parameters i, e, maximum discharge [pC], average discharge q [pC/cycle], and average angle of discharge [deg] were found to depend upon the defect type varying applied voltage. As the result of time evaluation, partial discharges are small different at copper defects, but is decreasing obviously about 20 minutes at void defect. It considered that difference of magnitude of total positive discharge of Q+ [pC] and total negative discharge of Q- [pC] is SPMD(swarming pulsive micro discharges).

The electrical conduction properties of low density polyethylene and crosslinked polyethylene film

A study has been carried out about the electrical conduction properties of LDPE and XLPE film for power cables. As for increase of temperature, the current density of LDPE is increased with constant ratio in low electric field, but changes with exponential function in high electric field. The tunnel current of prebreakdown region is shifted toward low field as much as thermal excitation energy. XLPE shows dominant electrical conduction properties by thermal excitation energy in low electric field, and transformation of the electron is resisted by the crystal in high electric field.