Identification of fault location in power distribution system with distributed generation using support vector machines

This paper presents a multi-class support vector machine (SVMs) approach for locating and diagnosing faults in electric power distribution feeders with the penetration of Distributed Generations (DGs). The proposed approach is based on the three phase voltage and current measurements which are available at all the sources i.e. substation and at the connection points of DG. To illustrate the proposed methodology, a practical distribution feeder emanating from 132/11kV-grid substation in India with loads and suitable number of DGs at different locations is considered. To show the effectiveness of the proposed methodology, practical situations in distribution systems (DS) such as all types of faults with a wide range of varying fault locations, source short circuit (SSC) levels and fault impedances are considered for studies. The proposed fault location scheme is capable of accurately identify the fault type, location of faulted feeder section and the fault impedance. The results demonstrate the feasibility of applying the proposed method in practical in smart grid distribution automation (DA) for fault diagnosis.

Apparatus and method for heat-run test on high-power PWM converters with low energy expenditure

Before installation, a voltage source converter is usually subjected to heat-run test to verify its thermal design and performance under load. For heat-run test, the converter needs to be operated at rated voltage and rated current for a substantial length of time. Hence, such tests consume huge amount of energy in case of high-power converters. Also, the capacities of the source and loads available in the research and development (R&D) centre or the production facility could be inadequate to conduct such tests. This paper proposes a method to conduct heat-run tests on high-power, pulse width modulated (PWM) converters with low energy consumption. The experimental set-up consists of the converter under test and another converter (of similar or higher rating), both connected in parallel on the ac side and open on the dc side. Vector-control or synchronous reference frame control is employed to control the converters such that one draws certain amount of reactive power and the other supplies the same; only the system losses are drawn from the mains. The performance of the controller is validated through simulation and experiments. Experimental results, pertaining to heat-run tests on a high-power PWM converter, are presented at power levels of 25 kVA to 150 kVA.

Contrasting fire regimes in a seasonally dry tropical forest and a savanna ecosystem in the western Ghats, India

Tropical dry forests and savannas constitute more than half of all tropical forests and grasslands, but little is known about forest fire regimes within these two extensive types of ecosystems. Forest fire regimes in a predominantly dry forest in India, the Nilgiri landscape, and a predominantly savanna ecosystem in the Sathyamangalam landscape, were examined. Remote sensing data were applied to delineate burned areas, determine fire size characteristics, and to estimate fire-rotation intervals. Belt transects (0.5 ha) were used to estimate forest structure, diversity, and fuel loads. Mean area burned, mean number of fires, and mean fire size per year were substantially higher in the Nilgiri landscape compared to the Sathyamangalam landscape. Mean fire-rotational interval was 7.1 yr in the Nilgiri landscape and 44.1 yr in the Sathyamangalam landscape. Tree (>= 10 cm diameter at breast height) species diversity, tree density, and basal area were significantly higher in the Nilgiri landscape compared to the Sathyamangalam landscape. Total fuel loads were significantly higher in tropical dry and moist deciduous forests in the Nilgiri landscape, but total fuel loads were higher in the tropical dry thorn forests of the Sathyamangalam landscape. Thus, the two landscapes revealed contrasting fire regimes and forest characteristics, with more and four-fold larger fires in the Nilgiri landscape. The dry forests and savannas could be maintained by a combination of factors, such as fire, grazing pressures, and herbivore populations. Understanding the factors maintaining these two ecosystems will be critical for their conservation.

Microstructural and mechanical behavior study of suction cast Nb-Si binary alloys

The solidification pathways of Nb rich Nb-Si alloys when processed under non-equilibrium conditions require understanding. Continuing with our earlier work on alloying additions in single eutectic composition 1,2], we report a detailed characterization of the microstructures of Nb-Si binary alloys with wide composition range (10-25 at% Si). The alloys are processed using chilled copper mould suction casting. This has allowed us to correlate the evolution of microstructure and phases with different possible solidification pathways. Finally these are correlated with mechanical properties through studies on deformation using mechanical testing under indentation and compressive loads. It is shown that microstructure modification can significantly influence the plasticity of these alloys.

Effect of hinged leaflets on vortex pair generation

We experimentally study the effect of having hinged leaflets at the jet exit on the formation of a two-dimensional counter-rotating vortex pair. A piston-cylinder mechanism is used to generate a starting jet from a high-aspect-ratio channel into a quiescent medium. For a rigid exit, with no leaflets at the channel exit, the measurements at a central plane show that the trailing jet in the present case is never detached from the vortex pair, and keeps feeding into the latter, unlike in the axisymmetric case. Passive flexibility is introduced in the form of rigid leaflets or flaps that are hinged at the exit of the channel, with the flaps initially parallel to the channel walls. The experimental arrangement closely approximates the limiting case of a free-to-rotate rigid flap with negligible structural stiffness, damping and flap inertia, as these limiting structural properties permit the largest flap openings. Using this arrangement, we start the flow and measure the flap kinematics and the vorticity fields for different flap lengths and piston velocity programs. The typical motion of the flaps involves a rapid opening and a subsequent more gradual return to its initial position, both of which occur when the piston is still moving. The initial opening of the flaps can be attributed to an excess pressure that develops in the channel when the flow starts, due to the acceleration that has to be imparted to the fluid slug between the flaps. In the case with flaps, two additional pairs of vortices are formed because of the motion of the flaps, leading to the ejection of a total of up to three vortex pairs from the hinged exit. The flaps' length (L-f) is found to significantly affect flap motions when plotted using the conventional time scale L/d, where L is the piston stroke and d is the channel width. However, with a newly defined time scale based on the flap length (L/L-f), we find a good collapse of all the measured flap motions irrespective of flap length and piston velocity for an impulsively started piston motion. The maximum opening angle in all these impulsive velocity program cases, irrespective of the flap length, is found to be close to 15 degrees. Even though the flap kinematics collapses well with L/L-f, there are differences in the distribution of the ejected vorticity even for the same L/L-f. Such a redistribution of vorticity can lead to important changes in the overall properties of the flow, and it gives us a better understanding of the importance of exit flexibility in such flows.

Stall flutter of NACA 0012 airfoil at low Reynolds numbers

In the present work, we experimentally study and demarcate the stall flutter boundaries of a NACA 0012 airfoil at low Reynolds numbers (Re similar to 10(4)) by measuring the forces and flow fields around the airfoil when it is forced to oscillate. The airfoil is placed at large mean angle of attack (alpha(m)), and is forced to undergo small amplitude pitch oscillations, the amplitude (Delta alpha) and frequency (f) of which are systematically varied. The unsteady loads on the oscillating airfoil are directly measured, and are used to calculate the energy transfer to the airfoil from the flow. These measurements indicate that for large mean angles of attack of the airfoil (alpha(m)), there is positive energy transfer to the airfoil over a range of reduced frequencies (k=pi fc/U), indicating that there is a possibility of airfoil excitation or stall flutter even at these low Re (c=chord length). Outside this range of reduced frequencies, the energy transfer is negative and under these conditions the oscillations would be damped. Particle Image Velocimetry (PIV) measurements of the flow around the oscillating airfoil show that the shear layer separates from the leading edge and forms a leading edge vortex, although it is not very clear and distinct due to the low oscillation amplitudes. On the other hand, the shear layer formed after separation is found to clearly move periodically away from the airfoil suction surface and towards it with a phase lag to the airfoil oscillations. The phase of the shear layer motion with respect to the airfoil motions shows a clear difference between the exciting and the damping case.

System Reliability Analysis of Flexible Pavements

The uncertainty in material properties and traffic characterization in the design of flexible pavements has led to significant efforts in recent years to incorporate reliability methods and probabilistic design procedures for the design, rehabilitation, and maintenance of pavements. In the mechanistic-empirical (ME) design of pavements, despite the fact that there are multiple failure modes, the design criteria applied in the majority of analytical pavement design methods guard only against fatigue cracking and subgrade rutting, which are usually considered as independent failure events. This study carries out the reliability analysis for a flexible pavement section for these failure criteria based on the first-order reliability method (FORM) and the second-order reliability method (SORM) techniques and the crude Monte Carlo simulation. Through a sensitivity analysis, the most critical parameter affecting the design reliability for both fatigue and rutting failure criteria was identified as the surface layer thickness. However, reliability analysis in pavement design is most useful if it can be efficiently and accurately applied to components of pavement design and the combination of these components in an overall system analysis. The study shows that for the pavement section considered, there is a high degree of dependence between the two failure modes, and demonstrates that the probability of simultaneous occurrence of failures can be almost as high as the probability of component failures. Thus, the need to consider the system reliability in the pavement analysis is highlighted, and the study indicates that the improvement of pavement performance should be tackled in the light of reducing this undesirable event of simultaneous failure and not merely the consideration of the more critical failure mode. Furthermore, this probability of simultaneous occurrence of failures is seen to increase considerably with small increments in the mean traffic loads, which also results in wider system reliability bounds. The study also advocates the use of narrow bounds to the probability of failure, which provides a better estimate of the probability of failure, as validated from the results obtained from Monte Carlo simulation (MCS).

Estimation of fracture properties for high strength and ultra high strength concrete beams and size effect

This article presents the details of estimation of fracture parameters for high strength concrete (HSC, HSC1) and ultra high strength concrete (UHSC). Brief details about characterization of ingredients of HSC, HSC1 and UHSC have been provided. Experiments have been carried out on beams made up of HSC, HSC1 and UHSC considering various sizes and notch depths. Fracture characteristics such as size independent fracture energy (G(f)), size of fracture process zone (C-f), fracture toughness (K-IC) and crack tip opening displacement (CTODc) have been estimated based on the experimental observations. From the studies, it is observed that (i) UHSC has high fracture energy and ductility inspite of having a very low value of C-f; (ii) relatively much more homogeneous than other concretes, because of absence of coarse aggregates and well-graded smaller size particles; (iii) the critical SIF (K-IC) values are increasing with increase of beam depth and decreasing with increase of notch depth. Generally, it can be noted that there is significant increase in fracture toughness and CTODc. They are about 7 times in HSC1 and about 10 times in UHSC compared to those in HSC; (iv) for notch-to-depth ratio 0.1, Bazant's size effect model slightly overestimates the maximum failure loads compared to experimental observations and Karihaloo's model slightly underestimates the maximum failure loads. For the notch-to-depth ratio ranging from 0.2 to 0.4 for the case of UHSC, it can be observed that, both the size effect models predict more or less similar maximum failure loads compared to corresponding experimental values.

Small-scale mechanical testing of materials

Small-scale mechanical testing of materials has gained prominence in the last decade or so due to the continuous miniaturization of components and devices in everyday application. This review describes the various micro-fabrication processes associated with the preparation of miniaturized specimens, geometries of test specimens and the small scale testing techniques used to determine the mechanical behaviour of materials at the length scales of a few hundred micro-meters and below. This is followed by illustrative examples in a selected class of materials. The choice of the case studies is based on the relevance of the materials used in today's world: evaluation of mechanical properties of thermal barrier coatings (TBCs), applied for enhanced high temperature protection of advanced gas turbine engine components, is essential since its failure by fracture leads to the collapse of the engine system. Si-based substrates, though brittle, are indispensible for MEMS/NEMS applications. Biological specimens, whose response to mechanical loads is important to ascertain their role in diseases and to mimic their structure for attaining high fracture toughness and impact resistance. An insight into the mechanisms behind the observed size effects in metallic systems can be exploited to achieve excellent strength at the nano-scale. A future outlook of where all this is heading is also presented.

Performance Evaluation of OBS Networks with INI Signaling Technique

In this paper, we evaluate the performance of a burst retransmission method for an optical burst switched network with intermediate-node-initiation (INI) signaling technique. The proposed method tries to reduce the burst contention probability at the intermediate core nodes. We develop an analytical model to get the burst contention probability and burst loss probability for an optical burst switched network with intermediate-node-initiation signaling technique. The proposed method uses the optical burst retransmission method. We simulate the performance of the optical burst retransmission. Simulation results show that at low traffic loads the loss probability is low compared to the conventional burst retransmission in the OBS network. Result also show that the retransmission method for OBS network with intermediate-node-initiation signaling technique significantly reduces the burst loss probability.

Experimental analysis of composite single-lap joints using digital image correlation and comparison with theoretical models

The demand for energy efficient, low weight structures has boosted the use of composite structures assembled using increased quantities of structural adhesives. Bonded structures may be subjected to severe working environments such as high temperature and moisture due to which the adhesive gets degraded over a period of time. This reduces the strength of a joint and leads to premature failure. Measurement of strains in the adhesive bondline at any point of time during service may be beneficial as an assessment can be made on the integrity of a joint and necessary preventive actions may be taken before failure. This paper presents an experimental approach of measuring peel and shear strains in the adhesive bondline of composite single-lap joints using digital image correlation. Different sets of composite adhesive joints with varied bond quality were prepared and subjected to tensile load during which digital images were taken and processed using digital image correlation software. The measured peel strain at the joint edge showed a rapid increase with the initiation of a crack till failure of the joint. The measured strains were used to compute the corresponding stresses assuming a plane strain condition and the results were compared with stresses predicted using theoretical models, namely linear and nonlinear adhesive beam models. A similar trend in stress distribution was observed. Further comparison of peel and shear strains also exhibited similar trend for both healthy and degraded joints. Maximum peel stress failure criterion was used to predict the failure load of a composite adhesive joint and a comparison was made between predicted and actual failure loads. The predicted failure loads from theoretical models were found to be higher than the actual failure load for all the joints.

Detailed investigation of contact deformation in ZrN/Zr multiplayer-understanding the role of volume fraction, bilayer spacing, and morphology of interfaces

A systematic study was done to understand the influence of volume fractions and bilayer spacings for metal/nitride multilayer coating using finite element method (FEM). An axisymmetric model was chosen to model the real situation by incorporating metal and substrate plasticity. Combinations of volume fractions and bilayer spacings were chosen for FEM analysis consistent with experimental results. The model was able to predict trends in cracking with respect to layer spacing and volume fraction. Metal layer plasticity is seen to greatly influence the stress field inside nitride. It is seen that the thicker metal induces higher tensile stresses inside nitride and hence leads to lower cracking loads. Thin metal layers < 10 nm were seen to have curved interfaces, and hence, the deformation mode was interfacial delamination in combination with edge cracking. There is an optimum seen with respect to volume fraction similar to 13% and metal layer thickness similar to 30 nm, which give maximum crack resistance.

Delamination Tolerance in Composites under Fatigue Loading

Delamination is one of the most commonly occurring defects in laminated composite structures. Under operating fatigue loads on the laminate this delamination could grow and totally delaminate certain number of layers from the base laminate. This will result in loss of both compressive residual strength and buckling margins available. In this paper, geometrically non-linear analysis and evaluation of Strain Energy Release Rates using MVCCI technique is presented. The problems of multiple delamination, effect of temperature exposure and delamination from pin loaded holes are addressed. Numerical results are presented to draw certain inferences of importance to design of high technology composite structures such as aircraft wing.

Failure modes and fatigue behavior of conventional and refilled friction stir spot welds in AA 6061-T6 sheets

The fatigue behavior of conventional friction stir spot welding (FSSW) and friction stir spot welding refilled by the friction forming process (FSSW-FFP) in aluminum 6061-T6 lap shear specimens, are investigated based on the experimental observations. Optical micrographs of the welds after fatigue failure in both the cases are examined to study the fatigue crack propagation and failure modes. Experimental results indicate that the fatigue strength of the FSSW-FFP weld samples is higher than that of the conventional FSSW samples at all loads. Fracture surfaces are analyzed in detail using the scanning electron microscope. (C) 2013 Elsevier Ltd. All rights reserved.

Tectonic inheritance of the Indian Shield: New insights from its elastic thickness structure

A new evaluation of the elastic thickness (Te) structure of the Indian Shield, derived from isotropic fan wavelet methodology, documents spatial variations of lithospheric deformation in different tectonic provinces correlated with episodic tectono-thermal events. The Te variations corroborated by shear velocity, crustal thickness, and seismogenic thickness reveal the heterogeneous rheology of the Indian lithosphere. The thinned, attenuated lithosphere beneath Peninsular India is considered to be the reason for its mechanically weak strength (<30 km), where a decoupled crust-mantle rheology under different surface/subsurface loading structures may explain the prominent low Te patterns. The arcuate Te structure of the Western Dharwar province and a NNE-trending band of low Te anomaly in the Southern Granulite Terrane are intriguing patterns. The average Te values (40-50 km) of the Central Indian Tectonic Zone, the Bastar Craton, and the northern Eastern Ghats Mobile Belt are suggestive of old, stable, Indian lithosphere, which was not affected by any major tectono-thermal events after cratonic stabilization. We propose that the anomalously high Te (60-85 km) and high S-wave velocity zone to the north of the Narmada-Son Lineament, mainly in NW Himalaya, and the northern Aravalli and Bundelkhand Cratons, suggest that Archean lithosphere characterized by a high velocity mantle keel supports the orogenic topographic loads in/near the Himalaya. The Te map clearly segments the volcanic provinces of the Indian Shield, where the signatures of the Reunion, Marion, and Kerguelen hotspots are indicated by significantly low Te patterns that correlate with plume- and rift-related thermal and mechanical rejuvenation, magmatic underplating, and crustal necking. The correlations between Te variations and the occurrence of seismicity over seismically active zones reveal different causal relationships, which led to the current seismogenic zonation of the Indian Shield. (C) 2013 Elsevier B.V. All rights reserved.