Effective operation method by interdependent use of condenser energy of the voltage transient sag compensator with controlled gradational voltage

This paper presents the efficient operation method of the interdependent use of condenser energy on the new concept of voltage transient sag compensator. This compensator consists of the series connection inverter units, and each inverter unit generates a different output voltage by 2ⁿ times. The method proposed here, in any case of various levels of transient voltage sags on the power line, provides the efficient use of condenser energy of all these inverter units. The method of interdependent use of condenser energy is also verified by the experiment. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 154(3): 56–64, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20290     

Discharge luminescence and discharge magnitude in treeing degradation

This paper describes results of the discharge luminescence and discharge magnitude measurements performed on the insulation materials exposed to partial discharge. Polymethyl methacrylate (PMMA) with an artificial needle shape void were used as the treeing specimens. The discharge luminescence is observed by image intensifier, and the luminous image is processed by computer. At the same time, the discharge magnitude distribution in relation to phase angle of the applied voltage was measured by a partial discharge measuring system. The mechanism of electric treeing was discussed by not only the measurement of the discharge pulses but also the local luminescence intensity of partial discharge. As a result, the luminescence intensity analysis showed the relation between tree growing length and void length when maximum luminescence intensity moved from the void area to the tree area. Both tree growth and maximum luminescence intensity at the tree area increase with constant ratio. The discharge luminescence intensity at the tree area increases significantly depending on the discharge magnitude in the specific phase angle area in positive and negative.     

Double-ice-plug freezing using liquid nitrogen for water pipe repairs

Accidentally a new method of water pipe repairs using liquid nitrogen freezing was discovered in 2008. Freezing water creates an ice plug to stop water flow. The new method uses double-ice-plug freezing instead of the world widely used single-ice-plug freezing. We have investigated the static sliding (shear) friction between the water pipe and the frozen ice-plug(s). The proposed method significantly increases water pressure in order to stop water flow. The experimented result shows that the ice adhesive strength of double-ice-plug freezing is roughly four times higher than that of single-ice-plug freezing. The unfrozen part of the water pipe plays a key role for achieving the high ice adhesive strength by taking advantage of water expansion upon freezing. The brief results were published in Science Advances. Further results are detailed in this note.     

CMOS analog/digital circuit of the hysteresis McCulloch-Pitts neuron for Ramsey numbers

A parallel algorithm for finding Ramsey numbers is presented where analog/digital CMOS circuits for the hysteresis McCulloch-Pitts binary neuron are described. The hysteresis McCulloch-Pitts binary neuron model is used in order to suppress the oscillatory behaviors of neural dynamics so that the convergence time is shortened. The proposed algorithm using the hysteresis McCulloch-Pitts binary neuron found five Ramsey numbers. The analog CMOS sigmoid circuit with variable gain controls has been fabricated and tested using the SAC data acquisition board interfaced with a TMS 32010 processor. Hysteresis can be implemented by the positive feedback in the fabricated CMOS analog circuit.     

Dissolution of malachite in aqueous ethylenediaminetetraacetate solution

The kinetics of malachite dissolution in aqueous ethylenediaminetetraacetate (EDTA) solution has been investigated in the temperature range of 298 to 318 K. The dissolution rate of malachite determined under the present set of experimental conditions was found to be independent of agitation speed. The dissolution rate increased with increasing EDTA concentration, but leveled off at higher concentrations. At constant EDTA concentration, an increase in dissolution rate was detected at higher temperatures. A dissolution mechanism involving Langmuir-type EDTA adsorption was proposed, in which the dissolution rate of malachite is controlled by the removal of Cu(II)-EDTA complex from the malachite lattice. The proposed mechanism can explain the dependency of the dissolution rate on EDTA concentration. The activation energies determined at pHs 5, 7.5, and 10 were found to be 51.4, 50.2, and 57.5 kJ mol⁻¹, respectively. The calculated enthalpy changes of EDTA adsorption equilibrium were −43.2, −35.2, and −45.0 kJ mol⁻¹ for pHs 5, 7.5, and 10, respectively. These values are in agreement with the proposed mechanism. Formerly Graduate Student, Department of Metallurgy, Kyoto University, is Formerly Professor, is Professor Emeritus, Department of Metallurgy, Kyoto University.     

Impact wear of MgO single crystals I. Wear characteristics

The impact wear characteristics of MgO single crystals have been investigated using an impact testing machine provided with a sintered alumina hammer having a tip radius of 2 mm. There is a fixed zero wear duration time for each selected impact load. Plastic deformation caused by slip of the {110} planes and cracking by impact occur during zero wear, but wear fragment are not produced. The zero wear period corresponds to a process of impact fatigue. Measurable wear, which is obtained by repeated impact over the zero wear limit, depends on the impact load and the action of wear fragments. When the test is performed in water wear is accelerated by abrasive erosion caused by impulsive flow of water containing wear fragments between the hammer and the scar wall.