Katsuhiko Naito

Simulation of I–V characteristics of a PV module with shaded PV cells

The authors are studying a diagnostic method of a PV power generating system. We consider that the change of I–V characteristics can be utilized for the diagnosis. However, the report on the change of I–V characteristics is very little. In this paper, we investigate the relation between the output lowering due to shaded PV cells and the change of I–V characteristics, utilizing the computer simulation. It was proven from the simulation that I–V characteristics are changed by the condition of the shadow, which covered the module. The change of I–V characteristics of a PV module with shaded PV cells is discussed by the shift of the avalanche breakdown voltage of shaded PV cells.

Diagnosis of oil-insulated power apparatus by using neural network simulation

One diagnostic process for oil-insulated power apparatus is based on the analysis of the chemical composition of gases evolved by the insulating oil. Normally this can be done only by a human expert. A considerable amount of information on the relation between chemical components and the faulty part of the power apparatus has been accumulated. This paper describes a neural network system which can be applied to existing diagnostic methods to enable analysis even by inexperienced engineers.

Probabilistic assessment of the reduction in tensile strength of an overhead transmission line's conductor with reference to climatic data

The tensile strength of an overhead transmission lines conductor in response to a growing load is being assessed in this paper. It is the authors view that the percentage reduction in the conductors tensile strength is a key index that can be used to determine a conductors end of life. This paper describes a probabilistic method of assessing this index for a given line with due reference to the areas climatic data. Such an assessment can be a useful guide to planning engineers.

Behavior of water droplets on silicone rubber sheet under AC voltage application

This paper describes the investigation results of behavior of water droplets on clean/contaminated silicone rubber sheet under ac voltage application. With increase of applied voltage, droplets vibrated first, they were then extended to the direction of applied electric field and finally flashover bridging water droplets occurred. Effect of time lapse after contamination was also studied.

Loss factors affecting power generation efficiency of a PV module

The authors are studying the diagnostic method of a PV system. In order to diagnose a PV system in detail, it is necessary to separate the loss factors affecting power generation efficiency. In this paper, we are investigating the influence of the solar irradiance and the incident angle on power generation efficiency of the PV module installed at tilt angle of 90 degree and azimuth angle of east and west, respectively. Especially, the influence of the incident angle on power generation efficiency is estimated in detail by separating direct and diffuse component of solar irradiance. We investigate the comparison between the measurement and the calculation results related to the change of power generation efficiency with time. The calculation value considering solar irradiance and incident angle of direct and diffuse solar irradiance almost corresponded to measurement value. As a result, it is clear that the change of power generation efficiency with time can be estimated by separating the influence of solar irradiance and incident angle of direct and diffuse solar irradiance and considering these loss factors.

Dynamic simulation of risk of flashover of contaminated ceramic insulators

A computer model is developed which dynamically simulates the risk of flashover of contaminated insulators under real time change of the climatic environmental factors. From data of accumulation of contaminant, cleaning by rain, wetting by moisture, risk of flashover of a ceramic insulator is calculated which then gives the resultant risk of flashover of a system where several hundred number of ceramic insulators connected in parallel are subjected to the same degree of contamination severity and wetting.

Water droplet behavior and discharge activity on silicone rubber surface energized by AC voltage (Part II)

This paper focuses on the behavior of water droplets on silicone rubber sheets and flashover bridging water droplets under AC voltage application. Resonance phenomena of water droplets vibration and the relation between behavior of water droplets and partial discharge activities were also studied. Based on the results obtained, possible surface flashover mechanism of hydrophobic silicone rubber is discussed.

A practical study of semiconducting glaze for insulators

Semiconducting glaze insulators show excellent electrical performance under contaminated conditions. In order to mass-produce this type of insulator, it is first necessary to determine the kind of materials that have such semiconducting properties and to decide on an optimum resistivity of the semiconducting glaze from a practical manufacturing standpoint. n n n nThis paper describes the results of a series of investigations into the macroscopic surface resistivity needed to develop the expected superior electrical characteristics of these insulators, and the optimum distribution of volume resistivity of the glaze over the actual insulator surface, among others. The chemical composition of the glaze ingredients and the manufacturing conditions are critical for realizing the resultant glaze characteristics.

Partial discharge characteristics of wet and contaminated silicone rubber surface

Partial discharge activities such as charge, number of pulses, and soon of non-treated and artificially deteriorated silicone rubber samples were investigated in the clean/salt fog. It was proved that charge and number of pulses depended on the condition of silicone rubber surface and fog conductivity.

A study of the automatic analysis for the I-V curves of a photovoltaic subarray

The authors are studying a diagnostic method of a PV array by utilizing the I-V curve. In this paper, the standard dI/dV-V curve obtained by the I-V curve of normal PV subarray is decided as the standard characteristic for the automatic analysis. This dI/dV-V curve is used to compare with dI/dV-V curves of abnormal shaped I-V curves such as the PV subarray with partial shadow. The dI/dV-V curve of abnormal PV subarray is remarkably different from the standard dI/dV-V curve. And the variance value to evaluate the difference between the standard dI/dV-V curve and the abnormal dI/dV-V curve is calculated. It is clear that the degradation of generating power characteristics of PV subarray can be analyzed by the variance value quantitatively.