Jong-Wook Jung

The effect of thermal ageing on the electrical characteristics of insulating oil for pole transformers

This paper describes the electrical characteristics of insulating oil employed in pole transformers. In the experiment, temperature and frequency were selected as variables, and dielectric characteristic values such as the relative permittivity, the tandelta and the specific resistance of the insulating oil were measured by a WinDETA system. As a result, the dielectric characteristics of the testing objects were temperature and frequency-dependent, and especially, the relative permittivities of each object showed considerable difference. In addition, the specific resistance acted as a key factor determining the insulating performance, and it was rather frequency dependent than temperature dependent. And, the dielectric values measured before ageing was slightly different from those after ageing. Dielectric dispersion due to the space charge polarization was observed in all testing objects.

The Accident Hazards and Properties of the Surface Leakage Current on the Polymer Insulation caused by Salt-water and Dust

It is necessary to study on the prevention and the management of electrical facilities because the electrical fault took place at the dust occurrence area due to environmental pollution. In particular, the dust accumulates easily on insulation material which is exposed an external long time. Therefore, we measured surface leakage current and surface variation of insulation material due to the dust and salt-water. From the results, the surface of bakelite is bad effect for salt-water than other material. The surface leakage current increases by repeated salt-water pollution and the surface of material is carbonized with arc occurrence. Also, it is need to variation of surface coating and shape of material to repress a leakage current on electrical material.

A Consideration of the Expected Service Life Cycles of Electrical Equipments in Buildings

This paper considers and suggests the life cycle of the power equipments installed in buildings. The target equipments were divided into 5 groups by a couple of conditions, and a theoretical consideration and domestic foreign case studies were carried out. As a result, the most appropriate life cycles and monitoring periods were suggested for each group. The suggested results are expected to practically help the field electricians determine whether they have to replace the deteriorated equipments or not.

Thermal analysis of varnish treated insulating papers for transformers

This paper describes the thermal characteristics of varnish treated Kraft and aramid papers in order to understand the effect of the varnish concentration on the heat flow pattern. The insulating papers were impregnated by the varnish diluted with solvent and then dried completely. The heat flow of the specimens was obtained using a differential scanning calorimeter (DSC) and analyzed. As a result, the heat flow curves of varnish and varnish treated insulating paper linearly changed with the varnish concentration and it was confirmed that the varnish concentration could be determined by comparing with the changing patterns in heat flow of the varnish treated insulating papers with temperature.

Case Studies for Potential Distribution due to Power Source by Environmental Condition

In this paper, potential distribution analysis through the six kinds of case studies examined in the environmental conditions change within a limited space, by the power supply system installed. To interpret the potential distribution using electromagnetic field analysis program and the parameters were state of the ground, the outer wall of the configuration state and the presence of human potential distribution was simulated. Potential distribution analysis, the size of nominal voltage, depending on the impedance of human body to be determined on the impact of surprise decision, but if equipped with appropriate protective equipment can be protected from lightning have been confirmed.

A Safety Assessment of Splice of 6/10[kV] Class CV Cables with Different Conductor Size

This paper describes the safety assessment of power cable splices connecting different sized 6/10[kV] class power cables. To assess the safety, AC withstand voltage tests, partial discharge tests and impulse tests were carried out to the cable splice specimens and thermal rise due to overload and cross section of joint were examined as well. As a result, a breakdown due to the application could not found for 5 minutes. Under application, partial discharges of 4~8[pC] were detected. In impulse tests, all the specimens withstood to the standard waveforms of without any breakdowns. In addition, the temperature on the splice rose by when the 200[A] flew through the splice for 20minutes, however the thermal rise of was considered due to the atmospheric temperature. After all the electrical tests, the cross section of the splice was visually examined. The conditions of the conductors of both and were good.

Determination of Shading Ratio Outputting Minimum Critical Power of Photovoltaic Panel

In this paper, the shading ratio about to output the minimum critical power of a photovoltaic panel was determined by experiment and simulation. A 2.475[kW] poly-crystalline photovoltaic panel consisting of 11 modules was used in the experiment and its surface was covered with shading curtains, thus the amount of light incident to the modules were controlled. In order to compare with the experimental results, the experimental circuits were modelled with the CASPOC (power electronics electrical drives simulator) and module parameters were applied to it, by which the minimum critical power was calculated. As a result, the photovoltaic panel was about to generate the power when the 5th shading curtains were removed from the module surface, after then the output power linearly increased by removing the shading curtains. In addition, the CASPOC simulation results were similar to the experimental results in the abrupt decreasing pattern of power.

A Study on the Actual Operating Conditions of Guard Lamps and its Maintenance Problems

This paper describes the checking results and some problems of guard lamps installed in the field. The guard lamp providing night security for people is installed outdoors and exposed to the natural factors causing secular ageing and the people`s vandalism, etc., thus it is prone to get troubles in function. In fact, the guard lamps has been left without considering the fundamental measures in the legislative system in spite of the loss of lives due to the electric shock accidents repetitively taking place every year. This study arouses people`s attention to the risk due to the lack of management and maintenance of the guard lamp by investigating the recent technology and the actual operating conditions and some problems and countermeasures were ultimately deduced. In this process, we reflected on the various opinions through fieldwork and had a couple of consultations with field staffs, manufacturers concerned and active officers with local autonomous entities.

Development of an Inspection Box for a Guard Lamp with an Automatic Switch

In this paper, a device for safety inspection of a guard lamp with an automatic switch which has been recently employed in some local autonomous entities was developed. It is technically enhanced by installing a separate inspection box down below, which allows the inspectors can measure the leakage current, the sound function of the electric leakage breaker(ELB), the insulation resistance and the grounding resistance, on the ground. This inspection box makes the inspectors free from the electric shock by being designed to minimize the potential direct contact with the energized terminals. The deliverables of this paper are expected to contribute to carry out the inspection for the guard lamps safely and effectively.

ATPDraw Simulation for Transient Phenomena Analysis of Electrical Shock Underwater

This paper describes the analysis of transient phenomena on the point that a human body suffers an electrical shock. A couple of case studies were discussed by using an ATPDraw simulation tool. Two models for the case studies were constructed on the assumption that the electrical shock event takes place under water to simulate the severest condition ; the first model that the human body contacts with an energized part exposed to water ; the second model that both hands and feet simultaneously contact with the ground under water. After modeling, the transient phenomena for the models were analyzed by comparing the voltages and currents calculated at each part of the human body. As a result steep front kicks in voltage and current were observed as transient phenomena on the point that the human body contacts with the energized part exposed to water in the first model and the magnitudes of the kicks considerably increased. It was considered however, the effect of the kicks due to the commercial power source on the human body could be neglected because the product of the current through the body and the short duration is less than the safety limit. When both hands and feet simultaneously contact with the ground in the second model, the voltage generally decreased all over the body parts, while the current flowing through the chest abruptly increased. The duration of this current was very shot, as well, thus its effect on the electrical shock is considered insignificant. After all, it was confirmed through the simulation results that the electrical shock depends on the magnitude in voltage and the body impedance.