Kinetic analysis of the crystallization of poly(p-phenylene sulphide)

Growth rates of spherulites were measured in poly(p-phenylene sulphide) crystallized from the melt and the quenched glass over the temperature range 100°C–280°C, possibly the most extensive overall range yet reported for any polymer and, as such, most propitious for study of régime III crystallization. For a medium M.wt. polymer, a régime II → III transition was obtained at 208°C using values of transport parameters common to many polymers ($\text{U1 = 1400}\text{cal mol}{}^{\mathrm{?1}}$, T_∞ ? T_g = 30°C) together with experimentally determined values of T⁰_m(315°C) and T_g(92°C). Under these conditions, the régime III/II slope ratio was found to be 2.07 (i.e. only 3.5% higher than predicted by régime theory), and reasonable estimates of surface free energies and of the work of chain folding were obtained. Other choices of the transport terms, including WLF and zero values, did not allow successful kinetic analyses. Although a régime I → II transition is predicted to occur at the high-temperature end of our growth-rate data, we found no experimental evidence for it. For a low M.wt. polymer, our analysis showed that régime III kinetics is obeyed at low temperatures, while at higher ones there is a continuous departure from that behaviour without, however, full attainment of régime II kinetics.     

Grounding and ground fault protection of multiple generator installations on medium-voltage industrial and commercial power systems - Part 4: Conclusion and Bibliography Working Group Report

This paper discusses typical grounding practices and ground fault protection methods for medium-voltage generator stators, highlighting their merits and drawbacks. Particular attention is given to applications of multiple generators connected to a single bus. The paper also provides an overview of the generator damage mechanism during stator ground faults. Problem areas associated with each type of grounding are identified and solutions are discussed. The paper also provides a list of references on the topic. The paper is intended as a guide to aid engineers in selecting adequate grounding and ground fault protection schemes for medium-voltage industrial and commercial generators for new installations, for evaluating existing systems, and for future expansion of facilities, to minimize generator damage from stator ground faults. These topics are presented in four separate parts, Parts 1-4. Part 1 covers scope, introduction, user examples of stator ground failure, and theoretical basis for the problem. Part 2 discusses various grounding methods used in industrial applications. Part 3 describes protection methods for the various types of grounding and Part 4 provides a conclusion and bibliography of additional resource material.     

Instructional overview of IEEE 1349-2001-guide for the application of electric motors in class I, division 2 hazardous (classified) locations

This work presents an overview of IEEE 1349-2001, a Guide that assists individuals, organizations, and suppliers with the application of motors in Class I, Division 2 locations, where flammable gases and vapors may occasionally be present. Three-phase and single-phase ac synchronous and induction electric motors in sizes from fractional horsepower through 10 000 hp and beyond are covered in the Guide. Primary emphasis is on the use of general-purpose enclosures and precautions against excessive surface temperatures and sparking of rotor bars and enclosure joints. The Guide also provides guidance for maintaining the life-cycle integrity of motors in Division 2 locations. Existing codes and standards, such as the National Electrical Code, contain cautionary notes for general-purpose motor applications in Division 2 areas. This Guide documents industry experience and established practices for the application of general-purpose motors in Division 2 locations and provides guidance for applying motors in these locations. It is not a specification and is not intended to be used as a specification for purchasing motors installed in Division 2 locations. This paper does not replace the Guide, but should be used to supplement and understand the Guide. Significant motor temperature information is contained in the Guide including maximum recommended Division 2 exposed surface temperatures at full load. Manufacturers, users, and other industry experts worked about eight years to develop this consensus standard. It was approved by the IEEE-SA Standards Board in December 2001 and published in June 2002.     

Protective relaying an medium- and high-voltage system

For this article we reviewed unusual outages, such as nonselective device operations during a fault, at different petroleum industry facilities. We found that changing some types of protective devices and modifying device settings improved both reliability and on-line performance. The following categories of protection problems were reviewed: ground faults on 12 kV feeders; ground faults on 4 kV motor feeders; faults on 115 kV transmission lines; and overexcitation of equipment. Each case is presented with: a brief synopsis of the problem encountered; our evaluation of the problem, including suggested solutions; and the “lessons to be learned” and trouble spots to avoid     

Twisting orientation and the role of transient states in polymer crystallization

A possible connection is suggested and explored between non-planer crystal habits in banded polymer spherulites and disordered chain folding in polymers crystallized relatively rapidly from the melt. It is proposed that, when lateral growth faces and fold surfaces are not orthogonal (because chain stems are tilted with respect to the lamellar normal), different degrees of disorder develop at opposite fold surfaces. Resulting differences in surface stress give rise to bending moments, but these are likely to be of transient existence. It is shown that, on this basis, an appealingly simple rationale can be developed to account for the complex and hitherto puzzling observations of Bassett and Hodge on polyethylene spherulites, including S-bending and non-uniform axial twisting in lamellae, and also an empirical correlation between these deformations. Much depends, however, upon interactions between interleaved crystals and upon relaxation of bending moments. Existing evidence in support of the rationale is outlined. Implications with respect to polymers other than polyethylene, and to kinetics of crystallization in general, are discussed briefly. Calculations concerning axial twisting under the influence of surface stresses suggest that the twisted crystals incorporate twist boundaries, possibly formed by aggregation of dislocations generated during the growth of what must initially be relatively disordered crystals. The ‘chiral’ factor determining handedness of twisting in a given crystal is the direction in which chain stems tilt with respect to the lamellar normal.     

Diurnal changes in radionuclides uptake by phytoplankton in small scale ecosystems

A continuous release of cesium-134 and strontium-85 into a simulated river system was maintained for more than 3 weeks for the purpose of evaluating the influence of photosynthetic oxygen production on cesium and strontium uptake. The flow rates and radioisotope concentration were maintained at a constant input throughout the experiment.The flow through time in the model river system was 6 h. Samples were taken from various stations every 4 h over a 36 h time interval. Temperature, dissolved oxygen, as well as other routine measurements were made. Samples were processed for plankton count and radioactivity in both the suspended phytoplankton and the water.The uptake of ¹³⁴Cs by phytoplankton was related to diurnal photosynthetic production of oxygen and a linear relationship exists between rate of change in ¹³⁴Cs concentration and the rate of net photosynthetic oxygen production.     

Application guidelines for instantaneous-trip circuit breakers incombination motor starters

This paper addresses the application of instantaneous-trip molded-case circuit breakers (MCCBs) in combination motor starters. These circuit breakers have been widely used in many industries for motor circuit protection. If they are not properly applied, situations of false tripping on motor starting and contact welding of contactors under low-level faults may occur. Energy efficiency motors compound the issue of false tripping on motor starting. This paper discusses the components of combination starters, reviews testing requirements, and provides examples of coordination with analysis of application issues and solution options     

Grounding and ground fault protection of multiple generator installations on medium-voltage industrial and commercial power systems - Part 3: Protection Methods Working Group Report

This paper discusses typical grounding practices and ground fault protection methods for medium-voltage generator stators, highlighting their merits and drawbacks. Particular attention is given to applications of multiple generators connected to a single bus. The paper also provides an overview of the generator damage mechanism during stator ground faults. Problem areas associated with each type of grounding are identified and solutions are discussed. The paper also provides a list of references on the topic. The paper is intended as a guide to aid engineers in selecting adequate grounding and ground fault protection schemes for medium-voltage industrial and commercial generators for new installations, for evaluating existing systems, and for future expansion of facilities, to minimize generator damage from stator ground faults. These topics are presented in four separate parts, Parts 1-4. Part 1 covers scope, introduction, user examples of stator ground failure, and theoretical basis for the problem. Part 2 discusses various grounding methods used in industrial applications. Part 3 describes protection methods for the various types of grounding and Part 4 provides a conclusion and bibliography of additional resource material.     

Xanthobacter tagetidis sp. nov., an organism associated with Tagetes species and able to grow on substituted thiophenes

Members of the marigold genus of flowering plants (the genus Tagetes), which synthesize and accumulate thiophene compounds in their roots, were investigated as potential sources of bacteria able to degrade substituted thiophenes. Batch and continuous enrichment cultures inoculated with compost from root balls of Tagetes patula and Tagetes erecta reproducibly produced the same predominant type of bacterium when they were supplied with thiophene-2-carboxylate (T2C) or thiophene-2-acetate (T2A) as a carbon and energy substrate. This organism was a yellow-pigmented, neutrophilic, mesophilic, gram-negative, pleomorphic, rodshaped bacterium, which we classify as a new species of the genus Xanthobacter, Xanthobacter tagetidis; strain TagT2C (= DSM 11105) is the type strain. Strain TagT2CT (T = type strain) grew on simple thiophenes, such as T2C, thiophene-3-carboxylate, and T2A, on analogs of these compounds (pyrrole-2-carboxylate and furan-2-carboxylate), and on the condensed thiophene dibenzothiophene. X. tagetidis was facultatively autotrophic, fixing carbon dioxide by means of ribulose bisphosphate carboxylase, and was able to grow on hydrogen, thiosulfate, or sulfide as an energy substrate. It also grew on a wide range of other heterotrophic, chemolithotrophic, and methylotrophic substrates. Its growth on T2C was optimal at 28 to 31 degrees C and pH 7.6 to 7.8, and the maximum growth rate in batch culture was 0.22 h-1. The DNA base composition of X.tagetidis is 68 mol% G + C. A 16S ribosomal DNA sequence analysis of strain TagT2CT showed that this organism represents a distinct lineage within the Aquabacter-Azorhizobium-Xanthobacter cluster of the alpha-2 subclass of the Pro-teobacteria. Discrimination of X. tagetidis from the other genera in this group and from other Xanthobacter species is discussed.     

Simplifying motor coordination studies

Low-voltage motor protection is normally the starting place for coordination studies of new industrial facilities. Also, improper low-voltage motor coordination is the source of many existing facility problems. Some engineers may frequently do coordination studies, but many engineers only occasionally do coordination studies. Trying to recall the applicable codes, standards, and references is difficult. Funds may not be available to hire “experts” for this type of study. The flow chart developed is to guide the “occasional” coordination engineer and to assist coordination “experts” by providing a reliable method for performing low-voltage three-phase motor coordination studies. The flow chart methodology is suggested for simplifying low-voltage overcurrent device coordination studies for new and existing three-phase motor installations. The flow chart provides references to codes and standards, highlights benchmarks for coordination, provides guides to device selection, and notes the overcurrent values of interest. The text elaborates the use of the National Electrical Code (NEC) for complying with legal requirements, and notes some significant changes in the 1999 NEC. The text also discusses some device selection criteria and expands on the decision points of the flow charts. Other flow charts for upstream devices and medium voltage equipment are being developed for future publication