Modernizing a forty-year-old production plant

The authors describes the modernization of the power system of a forty-year-old industrial production plant. The updated electrical distribution system fulfils requirements which directed the original design. Features to reduce employee exposure to potential electrical hazards were incorporated. Flexibility of operation was achieved along with means to protect operators from inclement weather and switching errors. A supply of electrical power will be available for all critical loads as long as the public utility or the cogeneration unit remains in service, and no two parallel circuits are simultaneously down. Maintenance needs will definitely be reduced. The ability to serve evolving process operating units is inherent in the final system     

Weak Chain Link Breakdown Phenomena of Multigrade Insulation Materials

Several failures of multigrade insulation systems have been experienced in metal clad, metal enclosed switchgear, and miniature isolated phase busduct systems. The failure sequence of the series insulation system appeared to originate from a point farthest away from the ground plane and not from the insulation in contact with the ground plane. However, in actuality, the ground plane was periodically elevated in relationship to the insulated busbar due to the presence of moisture created by load and ambient temperature cycling and adverse weather conditions. The insulation material in contact with the ground plane, being a high quality track resistant material, did not exhibit permanent deterioration. However the weakest insulation material degraded with time, weakening the overall insulation path to a point that an elevated ground plane condition resulted in failures of the series insulation system. The phenomena experienced in a specific application and the alternatives considered to correct the situation are described.     

Finite element visualization of fatigue crack closure in plane stress and plane strain

Elastic-plastic finite element simulations of growing fatigue cracks in both plane stress and plane strain are used as an aid to visualization and analysis of the crack closure phenomenon. Residual stress and strain fields near the crack tip are depicted by both color fringe plots and x-y graphs. Development of the residual plastic stretch in the wake of a growing plane stress fatigue crack is shown to be associated with the transfer of material from the thickness direction to the axial direction. Finite element analyses indicate that crack closure does occur under pure plane strain conditions. The development of the residual plastic stretch in plane strain is shown to be associated with the transfer of material from the in-plane transverse direction to the axial direction. This in-plane contraction also leads to the generation of complex residual stress fields. The total length of closed crack at minimum load in plane strain is shown to be a small fraction of the total crack length, especially for positive stress ratios. This suggests that experimental measurement of plane strain closure would be extremely difficult, and may explain why some investigators have concluded that closure does not occur in plane strain.     

Computer assisted avalanche prediction using electronic weather sensor data

A nearest neighbour model was used to predict avalanches in two highway corridors in British Columbia, Canada. The model accepts hourly electronic weather sensor data dynamically to produce automated predictions of the probability that avalanches will occur in the next 12 h. Output includes a list of nearest neighbours calculated by a Euclidian metric which provides information on patterns of avalanche activity in similar situations in the past. New variables are automatically generated from the hourly interval sensor measurements, including information about accumulated precipitation and maximum and minimum temperatures. A jackknife cross-validation routine generates fitness statistics by selecting test cases that are not temporally autocorrelated. The avalanche prediction system described here was applied operationally in Kootenay Pass, near Salmo, BC, and also at Bear Pass, near Stewart, BC, where accuracies of 76 and 72% were achieved respectively.     

Synthesis and characterization of sonochemically-aminated 1,3,5-triamino-2,4,6-trinitrobenzene

Abstract

A novel method has been achieved for the preparation of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) from TCTNB in toluene by animation with ammonium hydroxide solution under the influence of ultrasonic irradiation. Samples of this sonochemically-aminated TATB (FP-TATB) were studied for its powder characteristics. It was found that the arithmetic median diameter (vol%) and BET surface area of FP-TATB are 15 micrometers and 1.2 m²/g, respectively. To evaluate shock initiation, samples of FP-TATB were pressed to high density (1.8g/cc) and subjected to initiation spot-size testing, and the results were compared with those from micronized TATB (UF-TATB), an IHE booster material. Data from this test indicated that the FP-TATB is slightly more sensitive to shock initiation than the UF-TATB as measured by the dent depth of the witness plate.     

Is combination therapy for encopresis nutritionally safe?

Chronic constipation accounts for 3% to 5% of pediatric primary care outpatient visits. The most severely affected of this group develop a flaccid colon insensitive to distention, and encopresis. Laxatives and lubricants have been the standard therapeutic agents during the bowel decompression phase of encopretic therapy. Fiber has been the cornerstone of maintenance programs. Each of these agents is accompanied by considerable anxiety in the lay literature. This study evaluates the safety of combined high-fiber, laxative, and lubricant therapy on bowel movement frequency, fecal soiling, and nutritional status over a 6-month period. Blood chemistry values, dietary fiber intake, defecation pattern, and psychological profile were evaluated before and after the 6-month study. Biochemical and anthropometric indicators of nutritional status were not adversely affected by the therapy. Seventy-five percent of the children were able to remain free of soiling and the remaining 4 of 16 had soiling episodes reduced to a frequency of less than once a week. This study confirms that children with encopresis can respond to a combined program of increased fiber intake, laxatives, and mineral oil following a complete bowel cleanout, without experiencing deleterious effects.     

Risk of ignition due to transition currents in medium voltagemotors for classified locations

In 1984, during commissioning of a two-pole 13.2 kV motor driving a compressor in a chemical plant, arcing and sparking were observed at the joints of the enclosure. Later two motor explosions, which occurred on offshore platforms, were presumably ignited by arcing and sparking at the joints of the enclosures. This information instigated further investigations. The research work and measurements, which basically apply to all 1000 r/min and above machines of multisection enclosure design are discussed. In the presence of a flammable vapor, the current transfers at enclosure joints are a potential ignition source. These eddy currents in the enclosure are created by stray fields emerging from the active part of the motor consisting of stator and rotor. On the basis of the investigations, necessary remedial measures for large high-speed (1000 r/min and above) motors are described     

CLOSURE AND GROWTH OF MODE I CRACKS IN BIAXIAL FATIGUE

Abstract— —The closure behavior of mode I fatigue cracks under biaxial loading is studied with an elastic-plastic plane stress finite element model. Biaxial stresses are shown to have a significant impact on crack closure behavior at higher maximum stresses. In general, normalized crack opening stresses are highest for equibiaxial loading and lowest for pure shear loading. The differences are apparently negligible for maximum applied stresses less than about 0.4 σ₀. Experimental crack growth data are quantitatively consistent with these trends. Correlations of the experimental data with a simple Δ K _eff were successful as first-order engineering estimates. Changes in forward and reversed plastic zone sizes with biaxiality are not entirely consistent with trends in crack growth rates.     

Item difficulty and content bias on the WAIS-R information subtest.

252 15–77 yr old patients referred for psychological or neuropsychological assessment were administered the WAIS-R. Of the 4 new items in the Information subtest, 2 were found to be disproportionately difficult in terms of proportions of Ss who passed the item. In addition, 3 of the 4 items that are routinely "Canadianized" were also found to be disproportionately difficult. It is suggested that a normative study to establish the hierarchy of difficulty for a Canadian population is needed. (French abstract) (6 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Electrical Power System Design Features of a Modern Large Polyethylene Plant

A modern large polyethylene plant requires a sophisticated electrical power supply to meet the requirements of a continuous process industry. The principal features of such an electrical power system are summarized. The power system was designed to achieve project objectives which stressed safety of operation, ease of maintenance, and high reliability. Some of the modern design features discussed are dual 230-kV power supply lines; low-profile 230-kV bus work; personnel safety grounding of main substation to reduce step and touch potential to safe levels; transfer trip signals to utilize the utility company's switching equipment; extensive protective devices to detect and initiate switching equipment action for power equipment malfunctions or power system faults; vacuum switched under-load tap changers on main power transformers; vacuum breakers for 13.8-kV switching equipment; climate-controlled elevated substation buildings to permit bottom entrance and exit with all power and control cables; nonmetallic sheathed power and control cables in open cable tray; medium resistance ground derived by zig-zag grounding transformers in the 13.8-kV distribution system; high-resistance grounding at the secondary wye connection of all 4.