An application of the residual voltage for diagnoses for detecting irradiated degradation of insulating materials

Electrical cables in nuclear power generating stations must be highly reliable. For further improvement of reliability, the development of nondestructive diagnoses seems desirable for cable maintenance. The authors have been studying residual voltage for developing a diagnosis of electrical cables. The purpose of this paper is to give a foundation for development of diagnostic technology for detecting the irradiated degradation; the relations between γ-irradiation dose and the leakage current, the discharge current, and the residual voltage were studied and attempts made to calculate the amount of polarized charge and characteristic dielectric relaxation times by using data on the residual voltage. The calculated results agreed with the results obtained from the leakage current and the discharge current. These results suggest that the residual voltage in diagnostic technology for detecting the irradiated degradation can be employed.     

Mixed method of aggregation and i.s.e. criterion approaches for system reduction

A combination of dominant-eigenvalue concept and integral-squared-error criterion approach is proposed for the reduction of a high-order system.     

Remarks on the time moments of composite systems

The moments of a composite system are expressed in terms of the moments of the subsystems for the case when the composite system is built up from three basic connections: parallel, tandem and feedback. These expressions are useful for control-system design.     

Numerical simulation on the behavior of a liquid jet into an air flow

A numerical simulation has been performed to clarify the effects of turbulence in a liquid on the deformation of the liquid jet surface into an air flow. The turbulences in the liquid jet were simulated by the Rankin vortices, and the liquid jet surface was tracked numerically by the volume of fluid method. By numerical simulations, the onset of the protrusions on the liquid jet surface is caused by the vortices in the liquid, and the surrounding air flow plays an important role in the amplification of the protrusions. The amplification rate of the trough displacement is proportional to the air‐to‐liquid velocity ratio. At large imposed vortex intensities, the trough displacement increases with the vortex intensity. On the other hand, at small imposed vortex intensities, the amplification of the trough displacement is also affected by factors other than vortex intensity. © 2001 Scripta Technica, Heat Trans Asian Res, 30(6): 473–484, 2001     

Numerical simulation on liquid jet behavior issued into still air

Numerical simulations have been conducted to clarify the effects of turbulence, in the onset of protrusions on liquid jet surfaces. The turbulences in the liquid jet were simulated by the Rankin vortices. The liquid jet surface was tracked numerically by the VOF method. From numerical simulations, the protrusions on the liquid jet surface are induced by the vortices in the liquid, whose rotational direction decelerates the jet surface. Despite the distance between vortices, the displacement of the liquid jet surface from the initial surface location increases linearly, in time, at almost the same growth rate. In the initial region, the growth rate of the displacement increases as the major semiaxis‐to‐minor semiaxis ratio of the ellipsoidal vortex increases. The initial growth rate of displacement is almost proportional to the vortex intensity. © 2003 Wiley Periodicals, Inc. Heat Trans Asian Res, 32(2): 141–152, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10078     

Electron diffraction study of flake graphite extracted from molten pig iron

Single graphite flakes segregated from molten carbon or silicon-rich iron at 1200° to 1500°C were subjected to electron diffraction experiments. The results indicated that the well developed thick flakes are composed of one single crystal, while the thin almost colorless flakes consist of two or three single crystals oriented with the basal plane parallel to the flake surface and rotated at an angle of 15°, 18°, 22°, 25° or 28° about the C-axis. The stacking of the atomic layers in each single crystal indicates that they are α and β-type, or a more disordered structure, at each instant. Double diffraction evidence and additional electron microdiffraction observations showed that the thin single flake has an aggregate structure with two close-packed single crystals.     

Estimation of power outage size based on the dominating differential equation

This paper describes a method to estimate how much power will drop after severe generation outage. When a large generation outage occurs, system frequency plummets to an unacceptable frequency level. Frequency drop affects both customers and generation systems. Thus adequate and quick load-shedding must be done to prevent problems. To institute any load-shedding policy effectively, the size of the generation outage must be precisely estimated in a very short time. So far, several methods have been proposed to estimate the power outage amount by measuring the decaying frequency variations that are obtained at each local bus. These methods are easily applied, but cannot be expected to provide good results in real power system operations because of the noises that are a part of decaying frequency variations. To cope with this problem, a new estimation method based on one that uses the dominating differential equation is proposed in this paper. The most precise estimation at this point is obtained by using additional factors, such as the sine wave included in the decaying frequency fluctuations and considered as a part of the equation. Simulation studies on a model power system consisting of five generating stations and four load points show that the newer method is encouraging. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 118 (3): 39–49, 1997