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Tamura Y.,Mitsubishi Group | Tani K.,Mitsubishi Group | Okamoto N.,Shikoku Electrical Power Co.
IOP Conference Series: Earth and Environmental Science | Year: 2014

At both partial and full load of Francis turbines, the unsteady behavior of cavitating draft tube vortices occurs and leads to undesirable matters such as power house vibration, noise and power swing in some cases. This paper presents the investigation of the interaction between the flow pattern at runner outlet and the unsteady behavior of cavitating vortices in draft tube with experimental and numerical approaches. On the experimental research, the pressure pulsation in the draft tube is measured and the unsteady behavior of cavitating vortices is taken pictures with a high speed camera in the model test. On the numerical research, by Computational Fluid Dynamics (CFD) adopting a two-phase unsteady analysis, the analysis domain from the guide vane to the draft tube is carried out for investigating the interaction between the runner outlet flow and the vortex pattern. The pressure pulsation at the upper draft tube and the unsteady behavior of cavitating vortices obtained from CFD results are similar to those obtained in the model test. Detailed analysis of CFD results at overload indicates the repeat of expansion and contraction of cavitating vortices, which were shaped helical vortices with opposite direction of runner rotation, and the corresponding flow pattern in every time step of the pressure pulsations. Source


Kouno K.,Shikoku Research Institute | Nakanishi E.,Shikoku Research Institute | Nagano Y.,Shikoku Electrical Power Co. | Hojo M.,Tokushima University
IEEJ Transactions on Power and Energy | Year: 2015

Constant power factor control of a power conditioning system in a large-scale photovoltaic generation system (PV system), such as a mega-solar system, is introduced to mitigate voltage variations on a distribution line. However, it is difficult for the control to mitigate the voltage variation on a long distribution line because of the loss change on the distribution line. This paper proposes an advanced reactive power control, in which the power factor of the PV system is adjusted both by output power of the PV system and by apparent power of loads not to minimize the voltage variation at the interconnecting point but to minimize the voltage variation over the whole distribution line, and reports the result examined by numerical analysis about mitigating the voltage variation by applying the control. This paper shows that the proposed control can mitigate the voltage variation more than constant power factor control and there is a probability that it will be applied as a measure of suppressing the voltage variation on the long distribution line. © 2015 The Institute of Electrical Engineers of Japan. Source


Matsuzaki S.,Shikoku Electrical Power Co. | Pitarka A.,BAE Systems | Collins N.,URS Corporation | Graves R.,URS Corporation | Fukushima Y.,Shimizu Corporation
Pure and Applied Geophysics | Year: 2011

In this study we present a characteristic kinematic rupture model for an intraslab earthquake of the type of the 2001 Geiyo earthquake. The procedure for developing the characteristic rupture model follows the recipe developed by Irikura and Miyake (Proceedings of the 8th US National Conference on Earthquake Engineering, San Francisco, 2006) with a few modifications. We used the functional form of Nakamura and Miyatake [Zisin (J Seism Soc Jpn), 53, 1-9, 2000] to model the spatial and temporal variability of the slip rate function. In our procedure the earthquake source is specified by the kinematic description of the fault model that incorporates spatial heterogeneity in slip and rise time and constant rupture velocity. In the proposed characteristic model the asperity locations and rupture initiation point were the only parameters that were constrained by the available earthquake rupture models of the target earthquake. The quality of the characteristic rupture model was assessed by comparing recorded and synthetic ground motion time histories from the 2001 Geiyo earthquake calculated with a standard broadband (0. 1-10 Hz) ground motion simulation technique. Our analyses show that the characteristic rupture model performs well in reproducing the recorded ground motion, in spite of its simple representation of the fault geometry and kinematic rupture complexity. The analyses of ground motion sensitivity to relative location of asperities, and their stress drop contrast suggest that the overall ground motion goodness of fit remains the same at short periods, but decreases slightly at periods longer than 1 s. We suspect that, due to the depth of the intraslab source (40-50 km), the higher-frequency ground motions are relatively insensitive to the details of the slip distribution and slip contrast. On the other hand, even for intraslab events, the lower-frequency motions are influenced by rupture directivity effects and slip distribution. © 2010 Birkḧ̈ / Springer Basel AG. Source


Araki S.,Kagawa University | Yoshida H.,Kagawa University | Nakagawa H.,DShikoku Research Institute Incorporated | Naga K.,Shikoku Electrical Power Co.
Theoretical and Applied Mechanics Japan | Year: 2013

It is required to maintain the durability of concrete structures from the viewpoint of the proper control of maintenance. Thus, it is necessary to evaluate the soundness of the structures. The ultrasonic method which is one of nondestructive tests is tried to use as an evaluation method. In the case of the object of which density is high and its distribution is homogeneous, the ultrasonic can detect defects correctly. However, a concrete is inhomogeneous, and the wave spreads intricately if it comes to a crack or a discontinuous portion. Therefore, the limit and usefulness of applicability of the ultrasonic method are indefinite. In order to apply the ultrasonic method to concrete structures, it is necessary to grasp the influence of the properties of the concrete on the propagation of the wave. In this study, numerical analyses are conducted with considering the inhomogeneous of the concrete to check the applicability of the ultrasonic to the concrete. © 2013 by National Committee for IUTAM. Source


Shinka H.,Japan Central Research Institute of Electric Power Industry | Yamamoto T.,Japan Central Research Institute of Electric Power Industry | Komatsu H.,Shikoku Electrical Power Co. | Hongakiuchi T.,Chugoku Electric Power Co.
Electronics and Communications in Japan | Year: 2015

Hollow porcelain insulators are widely used in gas-insulated power apparatus and oil-filled power apparatus. Previously, it was thought that hollow porcelain insulators are not subject to aging deterioration. However, gas and oil leaks caused by the alkali-silica reaction in the porcelain where it is in contact with cementing parts have been reported in recent years. We experimentally verified the generation process of the alkali-silica reaction by using a hollow porcelain insulator removed from the substation, and examined an inhibition method of alkali-silica reaction based on the use of lithium nitrite. It was found that the alkali-silica reaction occurs in the hollow porcelain insulator and that lithium nitrite is effective for inhibition of the alkali-silica reaction. © 2014 Wiley Periodicals, Inc. Source

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