Transient stability limit issues at three-phase short-circuit in parallel running of both a superconducting generator and a conventional one

Experimental studies using20-kVA superconducting generators (SCG) have been performed in an attempt to understand some of the characteristics of SCG in power systems. It is necessary to investigate the characteristics for the parallel operations of both an SCG and a conventional generator (CG) when an SCG is installed in a present power station. Some of the results of the authors' studies on parallel running of the 20-kVA SCG and the 20-kVA CG are described in this paper. In the experimental system, the SCG is connected to a regional power system (infinite bus) through reactors (artificial transmission lines) and the CG is connected to the terminal of the SCG. Using experiments and computer simulations, the transient characteristics at three-phase short-circuit faults are investigated: 1) when the CG is not disconnected; and 2) when the CG is disconnected after reclosing the line with the fault cleared. Two kinds of stable limit curves are obtained for output power at three-phase short-circuit fault for the aforementioned two cases.     

Evaluation of leak flow rate and jet impingement related to leak before break

Leak flow rate and jet impingement load are experimentally evaluated using very narrow and short artificial slits which simulate a through-wall fatigue crack. The following items are clarified in the experiments under BWR fluid conditions: (1) the leak flow rate from the rectangular slit is experimentally clarified and it agrees well with the analytical result when the estimated thermodynamic nonequilibrium parameter N in the present experiment is introduced; (2) the orifice effects are experimentally evaluated concerning the through-wall fatigue crack, in which the discharge coefficients C_D between 0.75 and 0.25 are obtained as a function of the exit to the stagnation area ratio A_e/A_o; (3) when very narrow and short slits are used in the jet impingement experiments, the maximum pressure on the target is higher than that of a large diameter pipe and it increases with the decrease of the flow path length to hydraulic diameter ratio L/D of the slit because of the thermodynamic nonequilibrium effect.     

Elastic properties of real elastomers at small deformations

Elastic properties of real elastomers were examined by using partial derivatives of the strain energy density function (W) with respect to the invariant (I_i, i=1,2,3) of deformation tensor. The values of the derivatives at zero strain limit for styrene-butadiene rubber (SBR), nitrile-butadiene rubber (NBR) and butadiene rubber (BR) were compared with those derived from the theory shown in the previous paper, where compressibility of the materials was taken into account. The asymptotic behavior of the derivatives for isoprene rubber (IR) and segmented polyurethaneurea (SPU) was also compared with those of the three types of rubbers. It was shown that the theoretical predictions for the limiting value agreed fairly well with the experimental values of the elastomers.     

Pure gas and vapor permeation properties of poly[1-phenyl-2-[p-(trimethylsilyl)phenyl]acetylene] (PTMSDPA) and its desilylated analog, poly[diphenylacetylene] (PDPA)

The permeabilities of He, H₂, N₂, O₂, CO₂, CH₄, C₂H₆, C₃H₈, and n-C₄H₁₀ in poly[1-phenyl-2-[p-(trimethylsilyl)phenyl]acetylene] (PTMSDPA) and poly[diphenylacetylene] (PDPA) are presented and compared to those of poly(1-trimethylsilyl-1-propyne) (PTMSP), poly(1-phenyl-1-propyne) (PPP), and polysulfone. Like PTMSP, PTMSDPA, a disubstituted glassy acetylene-based polymer, exhibits higher permeabilities to organic vapors than to permanent gases due to its rigid polyacetylene backbone and bulky side groups, which provide a relatively high fractional free volume (FFV) value of 0.26. Desilylation was performed on PTMSDPA. The resulting material, PDPA, is totally insoluble in common organic solvents, so it has much higher chemical resistance than PTMSDPA. Additionally, due to its insolubility in polymerization solvents, desilylation provides the only known route to high molar mass PDPA. The FFV of the resulting membrane (PDPA) is reduced by approximately 12% relative to that of PTMSDPA. This leads to a decrease in gas permeability values and selectivity of organic vapors relative to nitrogen. For example, the oxygen permeability is reduced from 1200 to 500 Barrers upon desilylation. The pure gas selectivities decrease from 9 to 3 for n-C₄H₁₀/N₂ and from 26 to 9 for C₃H₈/N₂.     

Antimicrobial terpenes from oleoresin of ponderosa pine treePinus ponderosa: A defense mechanism against microbial invasion

The oleoresin of the ponderosa pine,Pinus ponderosa (Pinaceae) exhibited broad antimicrobial activity. In order to identify the active compounds, the oleoresin was steam distilled to give a distillate and residue. The distillate contained mainly monoterpenes and some sesquiterpenes, while the residue consisted chiefly of four structurally related diterpene acids. An antimicrobial assay with the pure compounds indicated that the monoterpenes were active primarily against fungi, but there was also some activity against gram-positive bacteria. The diterpene acids, in contrast, only exhibited activity against gram-positive bacteria. Although not all of the identified sesquiterpenes could be tested, longifolene showed activity only against gram-positive bacteria. Therefore, it appears that the oleoresin ofP. ponderosa functions as a biochemical defense against microbial invasion.     

Nuclear relaxation in the superconducting state of (MDT-TTF)2AuI2

We report the results of our attempt to measure the proton nuclear relaxation rate, 1/T ₁, in the superconducting state of the title material. The relaxation rate in the superconducting state at a field of 1 T was found much longer than that in the normal state, but it became clear that the dominant contribution came from the normal core region. The nuclear relaxation at zero field was examined by using the field cycling technique. An ln(t) term in the relaxation curve was observed at low temperatures, suggesting the contribution of the creeping motion of vortices. We discuss the possibility to determine the intrinsic temperature dependence of 1/T ₁ in the superconducting state.     

Transient analysis of blowdown thrust force under PWR LOCA

The analytical results of blowdown characteristics and thrust forces were compared with the experiments, which were performed as pipe whip and jet discharge tests under the PWR LOCA conditions. The blowdown thrust forces were obtained by Navier-Stokes momentum equation for a single-phase, homogeneous and separated two-phase flow, assuming critical pressure at the exit if a crifical flow condition was satisfied.The following results are obtained:

1. (1) The node-junction method is useful for both the analyses of the blowdown thrust force and of the water hammer phenomena.

2. (2) The Henry-Fauske model for subcooled critical flow is effective for the analysis of the maximum thrust force under the PWR LOCA conditions. The jet thrust parameter of the analysis and experiment is equal to 1.08.

3. (3) The thrust parameter of saturated blowdown has the same one with the value under pressurized condition when the stagnant pressure is chosen as the saturated one.

4. (4) The dominant terms of the blowdown thrust force in the momentum equation are the pressure and momentum terms except that the acceleration term has large contribution only just after the break.

Synthesis and viscoelastic properties of new thermosetting resins having isocyanurate and oxazolidone rings in their molecular structures

A new type of thermosetting resin can be obtained from solventless varnishes composed of polyfunctional isocyanates and epoxides. The IR spectra show that the cured resins have isocyanurate and oxazolidone rings in their chemical structure, hence their name, isocyanurate–oxazolidone resins. The viscoelastic behavior of the cured resins can be varied considerably by selecting an appropriate reactant species and changing the equivalent ratio of the isocyanate and epoxy groups in the varnishes. Three relaxations, labeled α, β, and γ, characterize their dynamic mechanical spectra. The α-dispersion is due to the glass transition, the β-dispersion, to local mode motions of the backbone chains of resins, and the γ-dispersion, to the molecular motions of long alkyl chains. If certain additives are mixed into the varnishes before curing, microphase separation takes place during the reactions. The resins finally obtained have a peculiar physical structure in which rubber particles are dispersed throughout a matrix phase as confirmed by scanning electron-microscopic analysis and viscoelastic behavior.     

Conformation of single PMMA chain in uniaxially stretched film studied by scanning near-field optical microscopy

The conformation of the single polymer chain in uniaxially stretched poly(methyl methacrylate) (PMMA) films was studied by scanning near-field optical microscopy (SNOM), which enabled us to observe the elongated conformation of each polymer chain embedded in the film. The conformation of the individual PMMA chains was quantitatively evaluated from the fluorescence intensity distribution. Observation of films with different strains showed that the microscopic strain of the single chain was smaller than the macroscopic strain (?) of the film. Especially at the later stage of the deformation (? > 1.5), the PMMA chain was not stretched with the increase in the macroscopic elongation of the film, suggesting the presence of slipping of polymer chain on the course of stretching.