Distribution systems fault analysis considering fault resistance estimation

Fault resistance is a critical component of electric power systems operation due to its stochastic nature. If not considered, this parameter may interfere in fault analysis studies. This paper presents an iterative fault analysis algorithm for unbalanced three-phase distribution systems that considers a fault resistance estimate. The proposed algorithm is composed by two sub-routines, namely the fault resistance and the bus impedance. The fault resistance sub-routine, based on local fault records, estimates the fault resistance. The bus impedance sub-routine, based on the previously estimated fault resistance, estimates the system voltages and currents. Numeric simulations on the IEEE 37-bus distribution system demonstrate the algorithm`s robustness and potential for offline applications, providing additional fault information to Distribution Operation Centers and enhancing the system restoration process. (C) 2011 Elsevier Ltd. All rights reserved.

Extended Fault-Location Formulation for Power Distribution Systems

In this paper, an extended impedance-based fault-location formulation for generalized distribution systems is presented. The majority of distribution feeders are characterized by having several laterals, nonsymmetrical lines, highly unbalanced operation, and time-varying loads. These characteristics compromise traditional fault-location methods performance. The proposed method uses only local voltages and currents as input data. The current load profile is obtained through these measurements. The formulation considers load variation effects and different fault types. Results are obtained from numerical simulations by using a real distribution system from the Electrical Energy Distribution State Company of Rio Grande do Sul (CEEE-D), Southern Brazil. Comparative results show the technique robustness with respect to fault type and traditional fault-location problems, such as fault distance, resistance, inception angle, and load variation. The formulation was implemented as embedded software and is currently used at CEEE-D`s distribution operation center.

Hybrid fault diagnosis scheme implementation for power distribution systems automation

Power distribution automation and control are import-ant tools in the current restructured electricity markets. Unfortunately, due to its stochastic nature, distribution systems faults are hardly avoidable. This paper proposes a novel fault diagnosis scheme for power distribution systems, composed by three different processes: fault detection and classification, fault location, and fault section determination. The fault detection and classification technique is wavelet based. The fault-location technique is impedance based and uses local voltage and current fundamental phasors. The fault section determination method is artificial neural network based and uses the local current and voltage signals to estimate the faulted section. The proposed hybrid scheme was validated through Alternate Transient Program/Electromagentic Transients Program simulations and was implemented as embedded software. It is currently used as a fault diagnosis tool in a Southern Brazilian power distribution company.

Further improvements on impedance-based fault location for power distribution systems

In this study, further improvements regarding the fault location problem for power distribution systems are presented. The proposed improvements relate to the capacitive effect consideration on impedance-based fault location methods, by considering an exact line segment model for the distribution line. The proposed developments, which consist of a new formulation for the fault location problem and a new algorithm that considers the line shunt admittance matrix, are presented. The proposed equations are developed for any fault type and result in one single equation for all ground fault types, and another equation for line-to-line faults. Results obtained with the proposed improvements are presented. Also, in order to compare the improvements performance and demonstrate how the line shunt admittance affects the state-of-the-art impedance-based fault location methodologies for distribution systems, the results obtained with two other existing methods are presented. Comparative results show that, in overhead distribution systems with laterals and intermediate loads, the line shunt admittance can significantly affect the state-of-the-art methodologies response, whereas in this case the proposed developments present great improvements by considering this effect.

Hybrid Method to Assess Sensitive Process Interruption Costs Due to Faults in Electric Power Distribution Networks

This paper shows a new hybrid method for risk assessment regarding interruptions in sensitive processes due to faults in electric power distribution systems. This method determines indices related to long duration interruptions and short duration voltage variations (SDVV), such as voltage sags and swells in each customer supplied by the distribution network. Frequency of such occurrences and their impact on customer processes are determined for each bus and classified according to their corresponding magnitude and duration. The method is based on information regarding network configuration, system parameters and protective devices. It randomly generates a number of fault scenarios in order to assess risk areas regarding long duration interruptions and voltage sags and swells in an especially inventive way, including frequency of events according to their magnitude and duration. Based on sensitivity curves, the method determines frequency indices regarding disruption in customer processes that represent equipment malfunction and possible process interruptions due to voltage sags and swells. Such approach allows for the assessment of the annual costs associated with each one of the evaluated power quality indices.

Reconfiguration of distribution networks to minimize loss and disruption costs using genetic algorithms

In this paper a computational implementation of an evolutionary algorithm (EA) is shown in order to tackle the problem of reconfiguring radial distribution systems. The developed module considers power quality indices such as long duration interruptions and customer process disruptions due to voltage sags, by using the Monte Carlo simulation method. Power quality costs are modeled into the mathematical problem formulation, which are added to the cost of network losses. As for the EA codification proposed, a decimal representation is used. The EA operators, namely selection, recombination and mutation, which are considered for the reconfiguration algorithm, are herein analyzed. A number of selection procedures are analyzed, namely tournament, elitism and a mixed technique using both elitism and tournament. The recombination operator was developed by considering a chromosome structure representation that maps the network branches and system radiality, and another structure that takes into account the network topology and feasibility of network operation to exchange genetic material. The topologies regarding the initial population are randomly produced so as radial configurations are produced through the Prim and Kruskal algorithms that rapidly build minimum spanning trees. (C) 2009 Elsevier B.V. All rights reserved.

Planning and operation of large-scale water distribution systems with preemptive priorities

This paper describes the development of an optimization model for the management and operation of a large-scale, multireservoir water supply distribution system with preemptive priorities. The model considers multiobjectives and hedging rules. During periods of drought, when water supply is insufficient to meet the planned demand, appropriate rationing factors are applied to reduce water supply. In this paper, a water distribution system is formulated as a network and solved by the GAMS modeling system for mathematical programming and optimization. A user-friendly interface is developed to facilitate the manipulation of data and to generate graphs and tables for decision makers. The optimization model and its interface form a decision support system (DSS), which can be used to configure a water distribution system to facilitate capacity expansion and reliability studies. Several examples are presented to demonstrate the utility and versatility of the developed DSS under different supply and demand scenarios, including applications to one of the largest water supply systems in the world, the Sao Paulo Metropolitan Area Water Supply Distribution System in Brazil.

Structure and properties of low temperature plasma carburized austenitic stainless steels

Austenitic stainless steels cannot be conventionally surface treated at temperatures close to 550 degrees C due to intense precipitation of nitrides or carbides. Plasma carburizing allows introducing carbon in the steel at temperatures below 500 degrees C without carbide precipitation. Plasma carburizing of AISI 316L was carried out at 480 degrees C and 400 degrees C, during 20 h, using CH(4) as carbon carrier gas. The results show that carbon expanded austenite (gamma(c)), 20 mu m in depth, was formed on the surface after the 480 degrees C treatment. Carbon expanded austenite (gamma(c)), 8 mu m in depth, was formed on the surface after the 400 degrees C treatment. DRX results showed that the austenitic FCC lattice parameter increases from 0.358 nm to 0.363 nm for the 400 degrees C treatment and to 0.369 nm for the 480 degrees C treatment, giving an estimation of circa 10 at.% carbon content for the latter. Lattice distortion, resulting from the expansion and the associated compressive residual stresses increases the surface hardness to 1040 HV(0.025). Micro-scale tensile tests were conducted on specimens prepared with the conditions selected above, which has indicated that the damage imposed to the expanded austenite layer was more easily related to each separated grain than to the overall macro-scale stresses imposed by the tensile test. (C) 2009 Elsevier B.V. All rights reserved.

Tempering temperature effects on abrasive wear of mottled cast iron

The effects of different tempering temperatures (300-600 degrees C) on abrasive wear resistance of mottled cast iron were studied. Abrasive wear tests were carried out using the rubber-wheel test on quartz sand and the pin test on Al(2)O(3) abrasive cloths. The retained austenite content of the matrix was determined by X-ray diffraction. The wear surface of the specimens was examined by scanning electron microscopy for identifying the wear micromechanism. Bulk hardness and matrix hardness before and after the tests were measured. The results showed that in the two-body (pin-on-disc test) system, the main wear mechanism was microcutting and high matrix hardening was presented. The wear rates presented higher correlation with the retained austenite than with the bulk and matrix hardness. In the three-body system (sand-rubber wheel), the wear surfaces presented indentations due to abrasive rolling. The wear rates had better correlation with both the bulk and matrix hardness (before and after the wear test) than with the retained austenite content. There are two groups of results, high and low wear rates corresponding to each tribosystem, two-body abrasive wear and three-body abrasive wear, respectively. (C) 2009 Elsevier B.V. All rights reserved.

Determination of particle concentration in the breathing zone for four different types of office ventilation systems

Many factors affect the airflow patterns, thermal comfort, contaminant removal efficiency and indoor air quality at individual workstations in office buildings. In this study, four ventilation systems were used in a test chamber designed to represent an area of a typical office building floor and reproduce the real characteristics of a modern office space. Measurements of particle concentration and thermal parameters (temperature and velocity) were carried out for each of the following types of ventilation systems: (a) conventional air distribution system with ceiling supply and return; (b) conventional air distribution system with ceiling supply and return near the floor; (c) underfloor air distribution system; and (d) split system. The measurements aimed to analyse the particle removal efficiency in the breathing zone and the impact of particle concentration on an individual at the workstation. The efficiency of the ventilation system was analysed by measuring particle size and concentration, ventilation effectiveness and the indoor/outdoor ratio. Each ventilation system showed different airflow patterns and the efficiency of each ventilation system in the removal of the particles in the breathing zone showed no correlation with particle size and the various methods of analyses used. (C) 2008 Elsevier Ltd. All rights reserved.

A simple and effective inverse projection scheme for void distribution control in topology optimization

The ability to control both the minimum size of holes and the minimum size of structural members are essential requirements in the topology optimization design process for manufacturing. This paper addresses both requirements by means of a unified approach involving mesh-independent projection techniques. An inverse projection is developed to control the minimum hole size while a standard direct projection scheme is used to control the minimum length of structural members. In addition, a heuristic scheme combining both contrasting requirements simultaneously is discussed. Two topology optimization implementations are contributed: one in which the projection (either inverse or direct) is used at each iteration; and the other in which a two-phase scheme is explored. In the first phase, the compliance minimization is carried out without any projection until convergence. In the second phase, the chosen projection scheme is applied iteratively until a solution is obtained while satisfying either the minimum member size or minimum hole size. Examples demonstrate the various features of the projection-based techniques presented.

Comparison between DC(+) and Square Wave AC SAW Current Outputs to Weld AISI 304 for Low-Temperature Applications

Welded equipment for cryogenic applications is utilized in chemical, petrochemical, and metallurgical industries. One material suitable for cryogenic application is austenitic stainless steel, which usually doesn`t present ductile/brittle transition temperature, except in the weld metal, where the presence of ferrite and micro inclusions can promote a brittle failure, either by ferrite cleavage or dimple nucleation and growth, respectively. A 25-mm- (1-in.-) thick AISI 304 stainless steel base metal was welded with the SAW process using a 308L solid wire and two kinds of fluxes and constant voltage power sources with two types of electrical outputs: direct current electrode positive and balanced square wave alternating current. The welded joints were analyzed by chemical composition, microstructure characterization, room temperature mechanical properties, and CVN impact test at -100 degrees C (-73 degrees F). Results showed that an increase of chromium and nickel content was observed in all weld beads compared to base metal. The chromium and nickel equivalents ratio for the weld beads were always higher for welding with square wave AC for the two types of fluxes than for direct current. The modification in the Cr(eq)/Ni(eq) ratio changes the delta ferrite morphology and, consequently, modifies the weld bead toughness at lower temperatures. The oxygen content can also affect the toughness in the weld bead. The highest absorbed energy in a CVN impact test was obtained for the welding condition with square wave AC electrical output and neutral flux, followed by DC(+) electrical output and neutral flux, and square wave AC electrical output and alloyed flux.

Chemical characterization of a high nitrogen stainless steel by optimized electron probe microanalysis

The distribution of Cr and N in a high-temperature gas-nitrided stainless steel was measured by using a scanning electron microscope-coupled wavelength-dispersive X-ray spectrometer and the results were related to the microhardness profile of the hardened case. The experimental spectrometric procedure was optimized to consistently measure N contents varying between 0.1 and 0.8 wt.% in martensite and between 18.3 and 21.6 wt.% in nitrides, as well as Cr contents ranging from 11.5 to 17.0 wt.%. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

High temperature flexural strength and fracture toughness of AlN with Y(2)O(3) ceramic

The effects of temperature on the fast fracture behavior of aluminum nitride with 5 wt% Y(2)O(3) ceramic were investigated. Four-point flexural strength and fracture toughness were measured in air at several temperatures (30-1,300 A degrees C). The flexural strength gradually decreased with the increase of temperature up to 1,000 A degrees C due to the change in the fracture mode from transgranular to intergranular, and then became almost constant up to 1,300 A degrees C. Two main flaw types as fracture origin were identified: small surface flaw and large pores. The volume fraction of the large pores was only 0.01%; however, they limited the strength on about 50% of the specimens. The fracture toughness decreased slightly up to 800 A degrees C controlled by the elastic modulus change, and then decreased significantly at 1,000 A degrees C due to the decrease in the grain-boundary toughness. Above 1,000 A degrees C, the fracture toughness increased significantly, and at 1,300 A degrees C, its value was close to that measured at room temperature.

Study on Iron Formation During the Carbothermic Reduction of Iron Ore in Carbon Composite Pellets in the Temperature Range 1423 K-1623 K

The aim of this work is to study the reaction rate and the morphology of the intermediary reaction products during reduction of iron ore, when iron ore and carbonaceous material are agglomerated together as a carbon composite iron ore pellet. The reaction was performed at high temperatures, and in order to avoid heat transfer constraints small size samples were used. The carbonaceous materials employed were coke breeze and pure graphite. Portland cement was employed as a binder, and the pellets diameter was 5.2 mm. The experimental technique involved the measurement of the pellets weight loss, as well as interruption of the reaction at different stages in order to submit the partially reduced pellet to scanning electron microscopy. It has been observed that above 1523 K there is the formation of liquid slag inside the pellets, which partially dissolves iron oxides. The apparent activation energies obtained were 255 kJ/mol for coke breeze containing pellets, and 230 kJ/mol for those pellets containing graphite. It was possible to avoid heat transfer control of the reaction rate up to 1523 K by employing small composite pellets.