Analysis of operating conditions of ground-fault protection schemes for generator stator winding

This paper presents results of simulation studies of the influence of methods of grounding the stator winding of the unit-connected generator neutral on the operating conditions of a 100-percent ground-fault protection excited by the third-harmonic voltage ratio in the generator neutral and at its terminals. The analysis was performed for a generator with the neutral grounded through a ground-fault neutralizer, a third-harmonic stop filter, a resistor, and a capacitive voltage divider. The influence of the parameters of the particular elements of the grounding circuits on the voltage-feeding measuring element of the protection was determined. The capacitance to ground of the generator breakers was taken into account. The simulations were run for 1110-MVA unit-connected generator at ground faults along the whole length of the generator stator winding. It has been found that the method of grounding the generator neutral and the parameter of the grounding elements significantly influences the operating conditions of this protection. It is shown that through the proper selection of these parameters, the ground-fault protection of whole stator winding, counting from the generator neutral to the terminals is ensured.     

An architecture for software that adapts to changes in requirements

The goal of the research presented in this paper was to study a new software paradigm – adaptive software – in which the structure of an adaptive program is patterned upon the structure of an adaptive controller. Towards this aim, we implemented a domain-specific (object/target recognition) program (A Reconfigurable Architecture for Adapting to Changes in the Requirements (RAACR)) that can adapt to changes in software requirements through the incorporation of feedback. RAACR is a hierarchy of domains (blackboards). Each domain includes multiple knowledge sources (KSs) and a domain scheduler (DS). In response to feedback, KSs change their processing parameters, while DSs change the scheduling policy of the KSs. A generic communication mechanism is implemented on the CORBA compliant SPRING operating system. The adaptability of the program is evaluated quantitatively using a requirements volatility measure and the probability of correct recognition.     

Surface layer condition and the fatigue strength of an AZ91 alloy after ball peening

The present work compares the states of the surface textures and the oscillatory fatigue strengths of specimens made of an AZ91 alloy after turning and dynamic bearing ball peening. It was found that the specimens ball peened at different time have similar surface geometric structure parameters but different strengthening intensity. It was shown that fatigue strength follows greater peening intensity and random and isotropic surface. It was also ascertained that improving (by peening) the condition of the surface layer means enhancing fatigue strength by 20–87% compared with turning.     

N‐Oligo(3‐hydroxybutyrate)‐functionalized polypyrroles: towards bio‐erodible conducting copolymers

New copolymer materials have been prepared by chemical grafting of oligomeric 3‐hydroxybutyric acid (OHB) onto polypyrrole (PPy) derivatives. The influence of grafting density and molecular weight of OHB brushes on the physicochemical properties of prepared copolymers was investigated. PPy substrates were prepared by FeCl₃‐driven oxidative homopolymerization of N‐(2‐carboxyethyl)pyrrole or its copolymerization with pyrrole. The grafting method employed involved controlled anionic polymerization of β‐butyrolactone on pyrrole‐tethered potassium carboxylate active sites. Obtained PPy‐g‐OHB copolymers of varying grafting density and pendant polyester chain length were characterized and the observed structure–property relationships discussed. The impact of real time exposure to phosphate‐buffered saline environment was investigated and the residue products were characterized. Cross‐correlation of spectroscopic, thermal, electrical and elemental analysis data afforded comprehensive evaluation of the structure of prepared materials and their behaviour in hydrolytic medium. Erosion and degradation pathways have been identified, indicating ways to consciously tailor the physicochemical properties of these new biomimetic materials. © 2016 Society of Chemical Industry     

Block Iterations in the Complex Plane

In this note we propose a new technique for execution of the feedback process  z → z²+ c  . The presented method is used to discover a family of sets in the complex plane.     

Electron beam for LHC

A method of delivering a small energy spread electron beam to the LHC interaction points is proposed. In this method, heavy ions are used as carriers of projectile electrons. Acceleration, storage and collision-stability aspects of such a hybrid beam is discussed and a new beam-cooling method is presented. This discussion is followed by a proposal of the Parasitic Ion–Electron collider at LHC (PIE@LHC). The PIE@LHC provides an opportunity, for the present LHC detectors, to enlarge the scope of their research program by including the program of electron–proton and electron–nucleus collisions with minor machine and detector investments.     

Defect Chemistry of (La,Sr)MnO3

Defect-disorder models are derived for undoped and strontium-doped LaMnO₃. A random-defect model and a cluster-defect model are both considered within the regimes that correspond to oxygen deficit and oxygen excess. The models are constructed based on the experimental nonstoichiometry data that was reported by previous researchers. According to both models, the addition of strontium leads to an increase of the concentration of electron holes and oxygen nonstoichiometry. The defect clusters that are predicted by the cluster model have a marked concentration only at very low oxygen partial pressures. Both models are verified against the electrical-conductivity data. A good agreement between the random-defect model and the experimental data is shown.     

Relief making on bearing sleeve surface by eccentric burnishing

The article describes how to obtain regular depressions in hole surfaces by means of eccentric burnishing. The principle of the method was explained and the mathematical formulae showing the relations among the process parameters were derived. A formula enabling the choice of the rotational speed of the burnishing head with regard to the (required) machining trace coverage of the surface was given. The structure of a head used for eccentric burnishing of bearings sleeves was described. Experiments checking the possibility of making various reliefs confirmed the practical application of the head. The investigation of the extent of tribological wear of steel/steel and steel/bronze sliding contacts were carried out. It showed explicitly that the specimen with oil pockets obtained by eccentric burnishing show much less wear than diamond turned ones.     

Centreless burnishing and influence of its parameters on machining effects

The article presents the results of examining the centreless roller burnishing technology worked out by the authors. The structure and the construction details of a prototype device for the centreless burnishing of shafts were presented. The experiments were carried on using 41Cr4 steel workpieces. The effects of the workpiece hardness, the surface roughness before burnishing, the deformation multiplicity and the tool interference on the roughness and the geometric structure after burnishing were investigated. The significant influence of the above parameters was confirmed and described as a mathematical power model. It also showed a beneficial effect of centreless burnishing parameters on roughness and geometric structure of the surface.