Low-voltage Equipment Research Articles

Green analytical methods

In 1995 an analytical journal published the first small issue on green analytical chemistry entitled “Environmentally conscientious analytical chemistry”, which was devoted to environmental deleterious side effects of analytical methods, thus indicating that, in spite of the great advances in automation, miniaturization, and alternative sample treatments (such as the use of microwave-assisted processes instead of convective ones), the environmental conscience of the analytical community was less interested in these advances than in the need to reduce the costs of determinations and to increase laboratory productivity. After that, the success of the green chemistry revolution led by Paul Anastas provided a good frame in which both the ethical concerns regarding the planet’s future and business opportunities could be conveniently integrated. The excellent reviews of Jacek Namiesnik and the first book on the subject of green analytical chemistry, published by Mihkel Koel and Mihkel Kaljurand in 2010, together with our own book and two additional ones edited with Salvador Garrigues, have created an important critical mass on the topic. Additional special issues in analytical journals devoted to this subject have been published since 2008 and have contained a number of important contributions, and so we can conclude that editors and authors are finally very concerned about the elimination of or, at least, reduction of the risks of analytical operations for both operators and the environment. However, there is still a lack of green analytical methods as alternatives to classical ones, and most of the interesting and highly cited publications in the field are review papers. The late 1970s provided many of the practical tools to move procedures from in-batch to mechanized and automatized methods, to reduce the amounts of reagents and samples consumed, to reduce drastically the power required, and to move from high-voltage equipment to low-voltage portable equipment. The last five years has provided a substantial revision of the opportunities offered by greening the methods. So, now it is time to move from the bench to the real world. Because of the aforementioned reasons, this special issue of Analytical and Bioanalytical Chemistry is an attempt to explore real alternatives: without sample handling or with highly reduced sample handling, alternative solvents and reagents that do not have persistent biocumulative and toxic effects, great reduction of the contact between samples and reagents and operators, and the online detoxification of wastes. In this sense, it is a new ambition to move from theory to practice, and upon analyzing the strengths and weakness of the methods proposed here and the opportunities they provide, the reader can identify that these methods will move analytical chemistry into the future and be well integrated in the ecological paradigm of chemistry. It is our aim that when reading the excellent contributions in this special issue of Analytical and Bioanalytical Chemistry, the reader can dream about the exciting suggestions that the proposed methods incorporate to solve real analytical problems, but also to create new green methods using similar tools for greening the reader's own work. Nowadays, it is clear that journal editors and writers of scientific editorials trust in green analytical chemistry. The next step is that teachers could incorporate the green principles, priorities, and strategies of green analytical chemistry in their university activities and also that authors, method users, and policy makers could integrate these practices in their everyday work. A change in public opinion about chemistry in general and analytical chemistry in particular, together with the health of our planet, will be the reward for all these efforts. M. de la Guardia (*) Department of Analytical Chemistry, University of Valencia, 46100 Valencia, Spain e-mail: miguel.delaguardia@uv.es

低圧配電線間における雷過電圧のフィールド観測

Recently, the number of home electric appliances, such as personal computers and telephones, is rapidly increased. Lightning damage to these home electric appliances has a great impact on highly sophisticated information society. There are some cases that lightning overvoltages on low-voltage distribution lines cause malfunction of them, though they equipped surge protective devices to protect against lightning overvoltages. Therefore, for lightning protection of low-voltage equipments including home electric appliances, it's important to understand the phenomenon of lightning overvoltages on low-voltage distribution lines. However, it's not so clear including the generation of them.The Tokyo Electric Power Company carries out the lightning observation on low-voltage distribution lines. The observation results provide the statistical distribution of lightning overvoltages on low-voltage distribution lines. The generation mechanism of lightning overvoltages on low-voltage distribution lines is assumed based on observed waveforms and facilities data.

The evolutionary complexity of complex adaptive supply networks: A simulation and case study

A supply chain should be treated not just as a supply chain but also as a complex adaptive supply network (CASN). However, the literature on supply chain management has given little attention to the evolutionary complexity of the network structure and collaboration mechanism of CASNs. In this paper, we first model and simulate the evolution of CASNs based on complex adaptive system and fitness landscape theory. The simulation results indicate the evolutionary complexities such as emergence, quasi-equilibrium, chaos, and lock-in of CASNs. Then, a case study of the evolution of the LVEA (low voltage equipment apparatus) supply network in the emerging Chinese market has been explored to validate the findings from the simulation and develop a better understanding of the general principles influencing the emergence, adaptation and evolution of CASNs in the real world. Based on the simulation and the case study, we propose some propositions about the factors and principles influencing the evolutionary complexity of CASNs. The external environment factors and firm-internal mechanisms appear to be the dominant forces that shape the gradual evolution of CASNs. Factors in the external environment, such as government regulation, market demand and market structure appear to have a long-term impact on the evolution, while a firm's strategies, product structure, technology, and organization appear to be the internal factors that exert an immediate influence on the evolution of CASNs. Among these factors, cost and quality considerations appear to be the primary forces that influence the structure complexity, centralization and formalization of CASNs.

22.9 kV-Y 계통에서 지락고장이 인체 및 저압설비의 안전에 미치는 영향

This paper presents experimental results on the safety of persons and protection of low-voltage equipments of the sub-station due to a single-phase ground fault in 22.9 kV-Y distribution system. In order to evaluate the hazard voltages and the stress voltage of the low-voltage(LV) equipment due to faults between high-voltage systems and earth based on the newly prescribed KS C IEC 60364 standard series, the verification tests in a 22.9[kV] neutral multiple grounding system were carried out. From the experimental results, we introduce serious problems causing some discomfort when applying KS C IEC 60364 standard series to the existing domestic distribution system and the effective protective measures against temporary overvoltages due to a ground fault in the common grounding which is combined the 22.9 kV-Y grounding and the customer`s installation grounding are proposed. As a consequence, it was found that the equipotential bonding is an important prerequisite for the effectiveness of the protective measures for the safety of persons and LV equipment in the combined 22.9 kV-Y and low-voltage grounding system.

Three-Phase Machines and Drives—Equipment for a Laboratory-Based Course

The hazards associated with high-voltage three-phase inverters and high-powered large electrical machines have resulted in most of the engineering courses covering three-phase machines and drives theoretically. This paper describes a set of purpose-built, low-voltage, and low-cost teaching equipment that allows the hands-on instruction of three-phase inverters and rotating machines. The motivation for moving towards a system running at low voltages is that the students can safely experiment freely with the motors and inverter. The students can also access all of the current and voltage waveforms, which until now could only be studied in textbooks or observed as part of laboratory demonstrations. Both the motor and the inverter designs are for teaching purposes and require minimal effort and cost

A theoretical study on the consequence of a direct lightning strike to electrified railway system in Sweden

Direct lightning strike to a single-track electrified railway system in Sweden is modeled in this paper. Using this model, the induced voltages in each of the nine conductors at heights varying from 0.5 m (tracks) to 10 m above the ground are estimated. The effect of the finitely conducting ground is included using a time domain expression for the transient ground impedance that has better early time and late time behavior. The main interconnection between the conductors and the flashover strength of the supporting insulators is included in the simulations. A simple model for the arc channel during flashover of the insulators and the ionization of the soil around the pole foundations is also included in the model to assess the possible realistic surge voltage distribution in the system. It is shown in the paper that finite ground conductivity, interconnections between the conductors, arcing phenomena of insulation flashover and grounding of the poles decide the voltage/current distribution in the conductors. Simulations have been also carried out to determine the voltages on the lines and across the rails as function of distance from the point of strike as it could be a necessary data for deciding the possible future protection schemes. It was found that for a lightning stroke of 31 kA peak, large common mode and differential mode surges exist on the lines which could create excessive voltages between the line and neutral of the transformer and might pose a threat to the various low voltage equipments used for telecommunication, signaling and control.

Dielectric testing of solid insulation with respect to insulation coordination of low-voltage equipment

In real insulation systems with solid insulation, partial discharges usually occur far below the breakdown voltage. In the long run, these lead to the destruction of nearly all solid insulating materials. The question, How much time has passed until the partial discharges have destroyed the solid insulation?, is of little relevance in low-voltage equipment since the occurrence of partial discharge during normal use will, in general not allow a sufficient lifetime. Moreover, the results of such lifetime investigations are influenced by many parameters; therefore, statements with general validity cannot be made.

North American codes and standards: a global challenge

In the rush toward the global harmonization of codes and standards, it is worthwhile, or perhaps necessary, to understand the cornerstones of safety in the present system. Examining the life of an electrical installation, one realizes that a typical installation lasts well over 25 years in many cases. It is interconnected with other similar systems through its life. Upgrades and expansions must be compatible over its life. The system need not be changed rapidly, but it must retain safety. This article examines some of the elements of the system, recognizes that they are already regionally in place across North America, and suggests that regional harmonization be strengthened on the way toward examining the feasibility of worldwide harmonization. This discussion relates primarily to low-voltage distribution equipment within an electrical installation. Products include busways, circuit breakers, fuses and switches, industrial control equipment, panelboards, and switchboards. The discussion is not limited to this equipment since wiring devices, utilization equipment, wiring and wiring methods, and other devices are essential to the system.

低圧配電機器のアーク続流による雷被害の発生メカニズムの検討

低圧配電機器のアーク続流による雷被害の発生メカニズムの検討

1 V FM demodulator circuit

The design of a 1 V narrowband FM demodulator is described which is intended for low-voltage portable consumer communication equipment. This FM demodulator circuit with a build-in band-gap reference circuit can be powered by a single 1.2 V battery. At 1 V supply, the FM demodulator consumes 0.9 mW of power with a conversion gain of 33 dB. In addition, a low-voltage four-quadrant analogue multiplier cell which can operate below 1 V DC supply is also presented.

The importance of knowing available fault currents when specifying interrupting ratings for low-voltage equipment

In a number of industrial plants, personnel responsible for the maintenance and design of the electrical power systems have done an excellent job at sizing equipment for connected loads; however, on more than one occasion, those same personnel appeared to be unaware of the interrupting rating for low voltage equipment. This sometimes resulted in electrical power systems that posed hazards to personnel and equipment due to the incorrect application of protective equipment. Several aspects of proper equipment selection based on interrupting ratings are addressed by the author.

Principles of stress-related insulation coordination in low voltage installations and equipment

A brief description of the principles of stress-related insulation coordination is given based on a very large field test of electrical insulations and several university investigations. This report is intended to give the basis for a physically founded revision of insulation coordination standards. Long-time and short-time voltage stresses are discussed. The microenvironmental conditions acting on the insulations are described. The insulating material and shape of the electrodes are discussed. The electric strength of clearances in air and the electric strength of creepage distances are detailed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Probability evaluation of low-voltage distribution equipment lightning failures due to AC arc

To construct low-voltage power distribution systems, it is important to have correct information on the probability of failures by lightning to meet the requirement for high reliability of these systems. The burn-out of low-voltage distribution equipment is triggered by flashover due to lightning overvoltage followed by the arc discharge current at the commercial frequency voltage. The arc characteristics were investigated by superimposing the lightning impulse voltage across terminals of the low-voltage distribution equipment connected to the commercial frequency power supply to reproduce these events on an experimental basis. As a result, it was found that the arc characteristics were affected by a number of factors. The probability of flashover occurrence on low-voltage distribution equipment is determined based on the frequency distribution data of lightning overvoltage occurrence obtained by monitoring the surge counters on actual distribution lines. Then the probability distribution of arc currents is established by application of the forementioned experimental equation on arc characteristics. Finally, the method for evaluating damages by lightning to low-voltage distribution equipment on actual lines was investigated with the frequency of lightning strokes and the configuration of low-voltage distribution systems taken into consideration.

Partial discharge. VI: PD testing of printed circuit boards

For pt.V see ibid., vol.7, no.2, p.28 et seq. (1991). The results of a research program concerned with applying partial-discharge (PD) testing to the nondestructive evaluation of the dielectric characteristics of coated printed circuit board (PCB) systems that must meet the high-voltage dielectric test requirements of low-voltage equipment are reported. To insure that the resulting data were applicable to typical PCBs a standardized test board layout was used, and the various coatings applied to the board were subjected to a range of conditioning treatments. The measurement and test specimens are described. The PD inception voltage and extinction voltage data for seven coatings and four conditioning regimes are presented, for either parallel conductor traces or pads adjacent to conductor traces, as measured from either the component or the solder side of the board. The data indicate that PD measurements, in combination with suitable conditioning, provide a good tool for determining the quality of coated PCBs. If applied correctly, the PD test is nondestructive. >

High-frequency voltage stress of insulation. Methods of testing

Traditionally high electrical stress of insulation occurs in HV equipment. Usually this stress is 50/60 Hz AC and rather seldom DC. Exceptional situations may occur in RF transmitters. This is very different in low voltage equipment. Due to the increased use of high-power semiconductors with high cutoff frequency, working voltages of rather high amplitudes and with frequencies >100 kHz occur frequently. Also, the distances through solid insulation may be rather low resulting in electrical fields in excess of those being typical for HV equipment. In combination with such HF working voltages, this means an extraordinary stress for the insulation. As there is a strong economical interest in further miniaturization, those problems have to be analyzed more precisely. The most important data about HF stress of insulation are summarized in this paper.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Partial-discharge testing of components for low-voltage equipment

The present test methods and requirements for solid insulation are discussed. It is demonstrated, that those tests and thickness requirements cannot guarantee safe performance of solid insulation throughout the whole equipment life. Moreover, such tests may cause severe damage is applied as a sampling or a routine test. As a replacement, the partial discharge test is proposed. Its applications for testing of transformers, optocouplers, coatings and similar arrangements is demonstrated. It is shown that this test method in combination with conditioning is appropriate for nondestructive testing of solid insulation. >

低圧配電機器の交流アークによる雷被害発生確率の推定

To construct low-voltage power distribution systems, it is important to have correct information on the probability of failures by lightning to meet the requirement for high reliability of these systems. The burn-out of low-voltage distribution equipment is triggered by flashover due to lightning overvoltage followed by the arc discharge current at the commercial frequency voltage. The arc characteristics were investigated by superimposing the lightning impulse voltage across terminals of the low-voltage distribution equipment connected to the commercial frequency power supply to reproduce these events on an experimental basis. As a result, it was found that the arc characteristics were affected by a number of factors. The probability of flashover occurrence on low-voltage distribution equipment is determined based on the frequency distribution data of lightning overvoltage occurrence obtained by monitoring the surge counters on actual distribution lines. Then the probability distribution of arc currents is established by application of the forementioned experimental equation on arc characteristics. Finally, the method for evaluating damages by lightning to low-voltage distribution equipment on actual lines was investigated with the frequency of lightning strokes and the configuration of low-voltage distribution systems taken into consideration.

Physical fundamentals of insulation design for low-voltage equipment

Insulation coordination for low-voltage equipment has been an important concern of several international committees. The reports 664 and 664A of the International Electrical Commission (IEC) gave the basis for thorough investigations in 1980 and 1981. About 30000 insulators have been observed for several years under various voltages. Insulation resistance and electrical strength were measured and have provided approximately=10/sup 6/ data points. These results were evaluating using statistical methods. In addition, a research program was carried out to quantify the influence of insulating materials, environmental conditions, and the design of the insulating systems on the long-term insulation behavior. The final results are intended to support the drafting of scientifically founded, revised standards on insulation coordination in the IEC.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The San Salvador Earthquake of October 10, 1986—Performance of Lifelines

Although the October 10, 1986 San Salvador earthquake was only a moderate event of magnitude 5.4 and the recorded ground motions had a relatively short duration, the high recorded peak accelerations caused substantial damage to lifelines. There was significant and widespread damage to buried lifelines. Long-distance telecommunications facilities were reportedly undamaged, but there was substantial loss of local phone service caused by damage to buildings, failures of equipment racks, and loss of emergency power (tilting of batteries). Power generating facilities (hydroelectric and geothermal) that supply electricity to San Salvador are located too far from the city to have been affected by the earthquake. Both 115-kV substations that serve San Salvador experienced a moderate level of damage, consisting mostly of ceramic column circuit breaker failures. As has been observed in past earthquakes, control and instrumentation systems and low-voltage power-supply equipment displayed an ability to withstand high ground accelerations.

Electric Strength of Small Insulating Distances

The capabilities of modern materials and new technologies allow significant size reductions to be achieved particularly in the field of low-voltage equipment. The limits encountered are often due not so much to technical or physical factors, but to widely varying safety requirements determined in many cases by earlier technological capabilities and the limits and specifications based thereon. This paper reports further results obtained from an extensive research project. Exposure of a large number of test specimens to various environmental conditions has proved conclusively that spacings on the surfaces of insulating materials are affected only if contamination is significant. Under heavy contamination these so-called creepage distances form tracks leading sooner or later to failure. Comparatively clean creepage distances however are not affected by tracking and should therefore only be dimensioned on the basis of their short-term electric strength. The results of this extensive series of tests are a statistically verified basis for the dimensioning of rather clean, small creepage distances (>10 mm). They can be incorporated directly into the relevant standards. Other results from the research project will be reported on conclusion of current investigations. However, it is expected that this work will not be completed before 1988.