Due to the superior transmittance properties of terahertz waves against plastic and ceramic materials, this sum-millimeter wave technology is considered to be promising for detecting deformation under coatings. The present paper provides brief review on detection of underfilm corrosion as well as integrity evaluation of thermal barrier coating used for gas turbine blades.
For accurate simulations of transformer inrush currents, modeling of magnetizing circuits which represent iron-core characteristics is important. Existing magnetizing circuit models are classified into the two categories: behavior-based modes and physics-based models. The parameter determination process of the behavior models is relatively simple, but these models cannot properly reproduce residual fluxes which has a significant influence on the magnitudes of inrush currents. On the other hand, the physics-based models are able to reproduce residual fluxes, but their parameter determination process is complicated. Considering the above, this paper proposes a behavior-based magnetizing circuit model which is capable of reproducing residual fluxes. The proposed model consists only of standard circuit elements, and its parameters are determined in a simple way using the information of name plate, test report and current-flux curve. In this paper, inrush currents of two transformers with Y-Δ and Δ-Δ connections have been calculated using the proposed magnetizing circuit model, and good agreement is found with laboratory test results.
This paper presents a prediction method of photovoltaic power generation amount as a fundamental technology for distribution system. This method is based on correlation analysis of insolation between two locations. The analysis was made using data measured by actinometers which were installed in several places around a distribution area. Based on the analysis, parameters for prediction which are moving direction and speed of insolation fluctuation were identified. And photovoltaic power generation amount was predicted based on the parameters. From the evaluation using measured insolation data, it found the method considerably improved the prediction accuracy in the case of high correlation through comparison with the conventional method.
The ICCG (Incomplete Cholesky decomposition Conjugate Gradient) method is widely applied to the electromagnetic field analysis using edge-based finite element method. The elapsed time of ICCG method holds the majority of electromagnetic field analysis. The main parts of ICCG method, which are composed of IC decomposition, forward-backward substitution and matrix-vector product, substantially influence the elapsed time. Therefore, the arrangement of reasonable implementations for main parts contributes to the realization of fast electromagnetic field computation in domestic research institutes. This paper presents the practical implementation of main components in ICCG method. Further, we make the meaning of diagonal scaling in ICCG method clear.
This paper presents the estimation technique of machine parameters for power transformer. This technique was developed using A. Ralston's Runge-Kutta method and genetic algorithm for only inrush current waveforms. Using machine parameters calculated by this estimation technique, EMTP-ATP simulation of the inrush current was carried out. Consequently, the EMTP-ATP simulated waveforms reproduced the measured waveforms.
Overseas utilities have been employing Substation Automation Systems (SAS) based on IEC 61850 in which Generic Object-Oriented Substation Event (GOOSE) provides a fast mechanism of transferring event data such as transfer trip. The GOOSE messages are required to be reliable enough to maintain electric supply reliability, even though off-the-shelf devices composing SAS have their fixed configurations about GOOSE. This paper proposes a method to improve reliability of GOOSE with redundant dispatchers and message retransmissions that can use the fixed configurations as is. It also describes experimental results using a test system dispatching GOOSE messages of transfer trip, and shows the advantage of our proposal.
A reliability evaluation method of traditional Substation Automation System (SAS) has ever been well developed based on its physical configurations. However, appearance of Intelligent Electronic Devices (IED) based on IEC 61850 requires another type of evaluation with a functional viewpoint, because they integrate control and protection functions. This paper proposes a quantitative reliability evaluation method using an event tree method and unavailability of a module constituting an IED. It also states experimental results of the method applied to two types of protection systems that have a model of double bus bar and two transmission lines, and shows its effectiveness.
The Government of Japan plans to expand photovoltaic and wind power drastically. However, since those power outputs fluctuate according to weather conditions, they may require additional load frequency control (LFC) capacity, thereby reducing efficiencies of thermal power generation. In order to evaluate these problems, we developed an optimal power generation mix model named as MM-OPG that deals with multiple modes of operation of each thermal power generation as well as the LFC constraint that the LFC requirements must be secured every moment. The model uses the hourly power demand curves and hourly power supply curves of renewables that are estimated from the actual data for 2010. The purpose of this study is to analyze the power generation mix in Eastern Japan in 2030 with a large penetration of photovoltaic and wind power. We conducted simulations using the model and obtained the following results. The case with the LFC constraint results in more frequent cutoffs of wind power that requires LFC capacity intensively, and an increase in pumped hydropower generation that provides the LFC, compared to the case without such constraint.
A large number of aged switchgears are now operating in the field. However it is difficult to obtain maintenance parts for aged switchgear, and the main components are manifesting signs of degradation due to their longtime operation. As a solution to the issue, systematic replacement of aged switchgears is being planned to maintain their reliability. On the other hand, the replacement equipment must fulfill certain requirements such as minimization of the outage area, shortening of the replacement period, maximization of the usage of existing facilities such as equipment foundations, and easy connection with existing equipment. The enclosure size of the conductor has been reduced in the effort to streamline various areas such as the reduction of phase-to-phase impulse test voltage and the limitation of temperature rise. Along with the use of the new spacer, we were able to develop a simplified GIB. This will be used in future projects involving refurbishment of aged substation equipments.
This paper introduces excellent insulating features of dielectric molded electrodes, studying the flashover and the puncture characteristics under repetitive discharges in SF6 gas. The goal of the study is to clarify the essential breakdown characteristics of thick dielectric-layered electrodes when applied as substitutes for metallic electrodes in high voltage power equipment. The flashover characteristics are investigated by optical measurements in view of the partial discharge onset properties. The puncture characteristics are studied based on the observation of the punctured trace and the utilization factor in the epoxy at the moment of the flashover in SF6. Considering both of the flashover and the puncture characteristics, the remarks on the selection of the appropriate filler in the epoxy is also presented.
In this paper, a novel nonlinear control method of Doubly-Fed Induction Generators (DFIGs) is presented to replace the traditional Proportional-Integral (PI) method in the control scheme of DFIG Wind Turbines (WTs). The proposed method is based on a new hysteresis current controller, which can modulate the voltage space vector directly in the dq rotation frame. Therefore, the new method can be easily employed in the vector-oriented-control scheme of DFIG without changing the structure of the scheme. The feasibility and performance of the proposed method are examined by using Matlab/Simulink. The simulation results demonstrate the very fast transient response of the proposed method under step-changes of power demands and wind speed. Also, the new method can overcome errors of machine parameters, which strongly impact traditional PI methods, to regulate the power output. Finally, the capability of low voltage ride-through (LVRT) is validated in the simulation study. With this capability, the proposed method can improve stability of DFIG WTs during voltage dips.
An electric line having lower insulation voltage is often installed together with a medium-voltage distribution line and in the case of direct strokes to an OHGW (overhead ground wire), the sparkover of such a line occurs prior to that of a medium-voltage line. In this paper, the authors picked up a low-voltage distribution line as a representative of such a line and investigate the influence of the configuration of a low-voltage line on the sparkover rate of a medium-voltage line associated with direct negative lightning flashes based on the numerical calculation of the insulator voltage by the EMTP. The low-voltage line grounded by the sparkover plays a role similar to the OHGW installed below a medium-voltage line and it turns out that the line installed together with a medium-voltage, represented by a low-voltage line in this paper, greatly influences the sparkover rate of a medium-voltage line.
The authors have carried out measurement of the current waveforms associated with lightning strokes to wind turbines at south Kyushu. In this paper measured waveforms on summer in 2013 are reported and it is shown that the return strokes with steep rate of rise and/or with high energy are observed in summer. This result is of practical importance for the insulation design of the wind turbine at the area of high lightning activity on summer.