Tatsuya Sakoda

Diagnostics of insulation deterioration of ethylene propylene rubber using an acoustic emission technique

The aim of this study is to investigate the relationship between lowering of the insulation performance of ethylene propylene rubber (EPR) used as a covering material of a cross-linked polyethylene (XLPE) cable and partial discharges (PDs) and to establish a diagnostic technique using an acoustic emission (AE) sensor. An accelerated deterioration test was carried out and then the detected AE signals were evaluated. The results showed that not only the intensity of the AE signal but also the number of counted AE signals of more than a critical value was very useful for diagnosing the EPR. We also proposed a diagnostic sequence using an AE technique.

Fundamental research on characteristics of hydrophobicity disappearance of silicone rubber surface in Dynamic Drop Test

A study on the development of deterioration / performance evaluation method for outdoor electric insulation of polymer materials is pushed forward now in the International Council on Large Electric Systems (CIGRE). The small scale docimasy (dynamic drop test) which could evaluate a disappearance characteristic of the hydrophobicity easily was suggested [1]. This test method is to evaluate the loss of hydrophobicity to drop electrically-charged water droplets on the sample surface continuously. We applied this dynamic drop test (DDT) to polymer materials which differ in the amount of alumina tri-hydrate (ATH) filled and investigated factors about the change of hydrophobicity, in which the surface roughness and difference of the quantity of migration of the low molecular weight (LMW) were examined.

Characteristics evaluation of the Partial Arc Discharge and the Silicone Rubber surface by Dynamic Drop Test

This paper describes the results of experiments made to examine characteristics of hydrophobicity of ATH-filled silicone rubber specimen surface. As the examination method, we used a dynamic drop test (DDT), in which electrolyte solution droplet from an electrode continuously dropped on a sample and the AC voltage was supplied between electrodes. Hydrophobicity loss times of samples for various conductivities of electrolyte solutions were measured. The electric fields before and after hydrophobicity reduction were evaluated. The results showed that the hydrophobicity loss time became short with the increase of conductivity and the electric field increased after hydrophobicity reduction.

Influence of temperature variation on characteristics of ZnO elements

Zinc oxide (ZnO) surge arresters with series gap are equipped to protect the electricity failure for power distribution systems. Although the ZnO surge arresters might have enough performances to protect the electricity failure when they were installed, the performance may decrease with the increase of the number of operation times and the time elapsed after the installation. The aim of this study is to investigate the effects of temperature variation on characteristics of ZnO elements. We first heated ZnO elements up to temperatures of 350 K, 400 K, 450 K, and 500 K, and then characteristics of V-t and 50% flashover voltage were examined. Next, in order to obtain V-I characteristic, the impulse current with 4/10 mus-8kA was applied at each temperature. Finally, V-t characteristic and 50% flashover voltage for each temperature were evaluated, again. The results showed that temperature had an influence on V-I characteristics of ZnO surge arrester. Finally, V-t characteristics and 50% flashover voltages for each temperature were evaluated, again. The results showed that temperature had an influence on V-I characteristics of ZnO surge arrester.

Characteristics of hydrophobicity loss on silicone rubber surface during a dynamic drop test with direct current voltage application

Dynamic drop test for studying the temporal lowering of hydrophobicity on the surface of silicone rubber with direct current voltage application was carried out. In this study, we evaluated the influence of the temporal lowering of hydrophobicity under various conductivities and dropping rates for water droplets. As a result, it was found that the dropping rate and the conductivity of water droplets greatly influenced the hydrophobicity loss time on the surface of silicone rubber.

Location of partial discharge at joint section of XLPE cable using acoustic emission technique

In this study, an acoustic emission (AE) technique was used for diagnosing a joint section of cross-linked polyethylene (XLPE) cable. The correlation between AE signal and partial discharge (PD) current was first investigated. The joint section of XLPE cable was 22 kV T branch joint with a diameter of 91.6 mm. Three AE sensors were located at the cable surface, 140 mm and 130 mm from the head of cable joint. The sensors use magnet holders for detecting PDs. For each distance from the head of cable joint, the AE sensors were placed at cable surface with the angle deviations of 120 degrees. At the tip of the head of cable joint, an artificial void was made with a diameter of 1.5 mm. The AE signal detected by the AE sensors was amplified by a preamplifier and a main amplifier. A high voltage electrode was inserted into the joint section of XLPE cable, and then high voltage was applied to generate PDs. PD current was detected by a Rogowski coil. The AE signal from the main amplifier was sent to a digital oscilloscope and recorded in a personal computer for further analyses, such as the fast Fourier transform (FFT). The correlation between AE signal and PD current was clarified. The increase of AE signal has the same linear tendency with increasing PD current. Furthermore, estimated PD locations were found around the head part of joint section of XLPE cable.

Monitoring of an MgO Degradation in AC Plasma Display Panel Using Multivariate Analysis Method

To investigate the degradation process of the MgO layer in a plasma display panel (PDP) discharge cell, measurements of Mg particles emitted from the surface of the MgO layer during an ac-PDP discharge were performed using the laser-induced fluorescence (LIF) technique. The spatial distribution of LIF signals agreed with the erosion pattern of the surface of the MgO layer. It was also found that a Mahalanobis–Taguchi system (MTS) where multi-dimensional measured values (e.g., discharge current, voltage, and luminance) were consolidated and converted into a standard was useful for the quantitative evaluation of the degradation degree of PDP discharge cells.

Basic characteristics of a heat and electricity combined generation system using biomass fuel

In this paper, we propose a unique co-generation system including a biomass boiler-using a thermoelectric generator (TEG). The boiler burned biomass fuel derived from a cow dung. In this system, warm water is generated through heat exchange in the boiler, and electricity is generated through the TEG that uses the high temperature of an exhaust gas from the boiler. In this study, the co-generation system was not well optimized, with the result that both the heat exchange efficiency of the biomass boiler and hence, - the amount of electric power generated were very low. However, the study demonstrated that the co-generation system that using the biomass as a heat source, and a TEG as an electric power generator can provide an effective energy source.

Studies on Optimal Gas Supply For a Maskless Etching System with Micro- Discharge Plasma Operated at Atmospheric Pressure

An optimal gas supply method for the micro discharge plasma generated along a quartz glass electrode, which was useful for the maskless fabrication of electrode grooves for surface electrodes on solar cells, was examined. We here constructed an electrode system with gas inlet and outlet holes. The gas supply directly to the plasma region contributed to reduce byproducts on the surface being etched, and then it was confirmed that the uniform etching was achieved in the case where the micro-discharge plasma locally produced at the etching area.

Maximum Output Power Control Using Short-Circuit Current and Open-Circuit Voltage of a Solar Panel

A control method to optimize the output power of a solar cell is necessary because the output of a solar cell strongly depends on solar radiation. We here proposed two output power control methods using the short-circuit current and open-circuit voltage of a solar panel. One of them used a current ratio and a voltage ratio (αβ control), and the other used a current ratio and a short-circuit current–electric power characteristic coefficient (αγ control). The usefulness of the αβ and the αγ control methods was evaluated. The results showed that the output power controlled by our proposed methods was close to the maximum output power of a solar panel.