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Power flow, on both AC and DC overhead transmission lines, is limited to keep the conductor temperature below a maximum (TCMAX) specified to limit both conductor sag and the aging of conductors and splices over time. This power flow limit (line thermal rating) varies with weather conditions along the line corridor but, for simplicity, static line ratings (SLR) are normally calculated for “suitably conservative” annual or seasonal weather conditions. Dynamic line ratings (DLR) change with the real-time weather conditions along the line, are usually higher than SLR, and are more complex to use in system operation. Forecasting of DLR requires forecasting of line corridor weather conditions but makes DLR more useful to power system operations. This paper discusses DLR methods including forecast techniques and presents various field applications.

This chapter describes two of the most adopted software tools for the evaluation of the lightning performance of transmission and distribution lines, namely FLASH and LIOV-EMTP (Lightning Induced OverVoltage - ElectroMagnetic Transient Program), together with some application examples. The FLASH program has been developed by IEEE Working Groups. LIOV-EMTP is the result of the integration between the EMTP and the LIOV code, developed by Alma Mater Studiorum - University of Bologna (Italy), Ecole Polytechnique Federale de Lausanne - EPFL (Switzerland), with the support of University of Rome `La Sapienza' and of Centro Elettrotecnico Sperimentale Italiano `G. Motta' CESI S.p.A. (Italy).

The awareness of the potential safety risk is paramount in the safe operation of overhead transmission lines. The consequence of safety hazards from touch, step and transferred voltages due to Ground Potential Rise (GPR) cannot be ignored or under-estimated. A CIGRE Technical Brochure [1] has been developed to provide a brief overview of the source of the GPR problems related to ground current from ac line faults to the line grounding systems. The GPR issues are sensitive to the soil resistivity near the tower and to other factors. Any safety risk mitigation may require stringent measures at locations where public access is frequent and to a lesser degree when the access is extremely rare. The GPR mitigation should be designed to ensure any potential hazards be kept to acceptable levels.

This paper discusses the wide range of real-time line monitoring devices which can be used to determine the dynamic thermal rating of an overhead transmission line with the power system operating normally or during a system contingency. The most common types of real-time monitors are described including those that measure the line clearance, conductor temperature, and weather data in the line right of way. The strengths and weaknesses of the various monitoring methods are evaluated, concluding that some are more effective during system normal and others during system contingency conditions.

Recent reviews have shown that many methods can be used for estimating the dynamic thermal capacity of overhead transmission lines. A number of approaches are described and key features of each system are organized. Data from field trials provide a unique basis for assessing the variation in ten different parameters. Characteristics of distributed measurement systems are underscored and contrasted against point measurements systems.

In February and December 2012, SaskPower experienced two flashovers of "clean" Fiberglass-Reinforced Plastic (FRP) hot stick during cold weather live-line work under steady-state 230 kV ac system conditions. As for SaskPower, Manitoba Hydro had two separate live-line tool flashover events, in 1997 and 2002. Clean-fog tests and non-uniform wetting tests at Hydro-Quebec Research Institute (IREQ), and cold-fog tests at Kinectrics and UQAC were carried out to explain these flashovers. The laboratory tests demonstrated that inadvertent contamination of clean tools at a very light level () of Equivalent Salt Deposit Density (ESDD) likely reduced voltage withstand capability of FRP hot sticks, particularly under freezing conditions. The flashover mechanism was identified when surfaces become fully wetted by the environment or surrounding fog. However, the source of moisture in field flashovers well below 0°C, i.e. as low as -19°C, was not identified. This study is based on laboratory tests and on using available pollution flashover models to explain the results. In this paper, the main objective is to determine the potential and electric field distribution along a FRP hot stick under dry condition and non-uniform wetting. A commercial software, COMSOL MultiphysicsTM, based on the finite element method (FEM), was used for the three-dimensional modeling and simulations. The results obtained will be useful to improve knowledge on the determination of discharge initiation conditions based on electric field distributions along a FRP hot stick.

Controlled laboratory tests validated a hypothesis that extremely light (~2-3 μg/cm2) levels of Equivalent Salt Deposit Density (ESDD) with no Non-Soluble Deposit (NSDD) can reduce voltage withstand capability of Fiberglass-Reinforced Plastic (FRP) hot sticks under cold-fog conditions near the freezing point, where the tool surfaces are fully wetted by the environment or alternately surrounded by fog. However, the source of moisture in flashovers at temperatures below -13 °C was not established. The mechanism of tool surface wetting was explored through coupled Computational Fluid Dynamics (CFD) and Heat Transfer mathematical equations for a FRP hot stick modeled in Commercial software, COMSOL Multiphysics. The results show that the flow of partial discharge current could be sufficient to raise the temperature of an iced pollution layer just below freezing, where the cold-fog flashover mechanism prevails.

During the last 50 years a significant technical advance, namely in our understanding and control of switching-surge overvoltages, has had some unintended and adverse consequences when designers took full advantage of the possibility of reduced insulator dimensions. Glaze ice accretion can produce harmful effects, especially on closely spaced or large-diameter station post insulators and bushings. Partial or full bridging of the leakage distance occurs for moderate ice-accretion levels and reduces insulator reliability during melting in saturated conditions. Colocation of HV or EHV substations with roads or expressways on which deicing salt is spread has proved particularly problematic. The DEIS has played an important role as a forum for exploring icing flashover physics and as a sponsor of improved test methods and applications guidance.

CIGRE TB 549 (2013) is an update on previous CIGRE documents on the subject, published in Electra more than three decades ago. Lightning parameters needed in different engineering applications are reviewed. New experimental data, as well as the old data, are evaluated. Additional lightning parameters, previously not considered by CIGRE, are included. Possible geographical and seasonal variations in lightning parameters are examined. Specific applications are considered and recommendations are made.

This paper provides an overview of the electric field (E-field) distribution on transmission line composite insulators applied in alternating current applications. Factors that affect the E-field distribution are discussed as well as the influence of the E-field distribution on the short and long term performance. Modeling and measurement methods are reported and examples of calculated E-field magnitudes determined are presented together with corona ring application information. This paper was developed by the IEEE Task force on electric fields and composite insulators.

Two clean live-line tool flashovers in Manitoba at 500-kV line voltage and two recent ones in Saskatchewan at 230 kV during freezing conditions led to extensive laboratory tests to reproduce some of these flashover conditions in a controlled laboratory environment to understand the underlying mechanisms and to assess mitigation measures. This paper improves on the three-dimensional finite element method model developed in our previous study to compute the potential and electric field along and around a fiberglass-reinforced plastic hot-stick in a series of “true” cold fog tests at the UQAC. In the previous study, the simulations were carried out with a dry surface and non-uniform wetting. In simulating the non-uniform wetting conditions, since a non-continuous water film was considered to be on the hot-stick surface, there was no leakage current. However, in the flashover and cold fog tests at the UQAC, leakage current activities were observed between the HV and ground electrodes on the surface of the hot-stick. In the present study, the mathematical equations of the model were modified to allow for the presence of leakage current flowing through a continuous thin layer of ice on the surface of the hot-stick in freezing and cold conditions, as was the case for the flashover incidents experienced in Saskatchewan. The potential and electric field distribution along and around the hot-stick were calculated and compared with those in dry surface conditions.

Quantitative assessment of the imperfections in the shape of cooling towers is required to enable strength studies to be carried out. Terrestrial photogrammetric methods are described which provide the initial data by locating the position of surface cracks and depicting the surface by means of ring contours. These serve as a basis for further analysis. Resume Une description quantitative des defauts de construction des tours de refrigeration est necessaire pour mener a bien l'etude de leur resistance. On decrit des methodes de photogrammitrie terrestre permettant de localiser leurs fractures et de decrire leur surface au moyen de sections circulaires. Zusammenfassung Zur Analyse der Belastung von Kuhlturmen werden quantitative Angaben uber die Deformation des Baukorpers benotigt. Es werden Verfahren der terrestrischen Photogrammetrie beschrieben, womit die geforderten Daten durch Lokalisierung von Rissen an der Oberflache und Beschreibung der Oberflache mit Umrisslinien bereitgestellt werden. Diese Angaben dienen als Grundlage fur weitere Untersuchungen.

In contrast to the surveyor/photogrammetrist steeped in survey techniques and map use, the majority of people who commission and use air photographs and photogrammetric mapping have very different backgrounds and interests and have widely differing objectives. They come largely from the disciplines of economics, planning, engineering, geography, biological sciences and accountancy. They, too, have their own view of the value of air survey and the analysis here of the trends in demand and use for such material suggests that these sources of information play only a minor and occasional part in their everyday work

In selecting adequate insulators for substations at distribution and transmission voltage levels, special measures may be needed in locations exposed to freezing conditions. This first part of the paper describes the environmental and insulator parameters that influence the risk of flashover on station insulators exposed to freezing conditions.

The paper presents the statistical data of the significant parameters of lightning flash, collected by many researchers over many years around the world. The significant parameters of a lightning flash are: peak current, waveshape and velocity of the return stroke, the total flash charge and /spl int/I/sup 2/dt. Negative first strokes have traditionally been considered to produce the worst stress on the system insulation. The subsequent negative strokes have significantly lower peak current but shorter wavefronts. This may stress the system insulation more. The positive strokes have about the same median current value as the negative first strokes and longer fronts, thus producing less stress. However, their duration is longer than that of the negative strokes. Therefore, the system insulation may be damaged because of the lower volt-time characteristic for long-duration waves. The positive strokes may also cause more thermal damage because of their significantly higher charge and /spl int/I/sup 2/dt. The relationship between the return-stroke velocity and the current peak is a significant parameter in estimating lightning-induced voltages and also in estimating the peak current from the radiated electromagnetic fields of the lightning channel. For better accuracy, the current and the velocity should be measured simultaneously. Better methods to measure the stroke current need to be developed. Correlation coefficient between various lightning parameters is another important parameter which will affect the analysis significantly. Lightning characteristics should be classified according to geographical regions and seasons instead of assuming these characteristics to be globally uniform.

In locations exposed to freezing conditions over the station service life, additional measures for selecting adequate station insulators at distribution and transmission voltage levels should be taken. This second part of the paper describes the selection process and mitigation options, based on the environmental parameters, as discussed in Part I. These include insulator size, shape, surface material, surface quality, electric field improvement, and orientation.

A study of multipulse sequences that can be used for the detection of HMX (N4(CH2)4(NO2)4) has been undertaken. On the basis of this study, a general method for experimentally optimizing multipulse sequences for the efficient detection of substances is proposed. The relaxation parameters and signal intensities for the nitrogen-14 spectral lines of a polycrystalline HMX sample were measured and the lines that are the most important for practical purposes were chosen.

A number of methods for cancelling magnetoacoustic and piezoelectric ringing signals in the spectroscopy of the nuclear quadrupole resonance are presented. The suggested methods include using the sequence (ϕ0)ϕ-(τ-ϕx-2τ-ϕ y -2τ-ϕ−x -2τ-ϕ−y -τ) n and a multipulse analog of the two-pulse Hahn sequence with the first pulse replaced by a short steady-state sequence. Another method presented is the method of orthogonal effective fields for a fast saturation of the quadrupole spin system which can be used for subtracting the magnetoacoustic and piezoelectric components from the signal. The suggested methods can be used for the practical purposes of detecting explosive substances and narcotics.

Modification of the steady-state free precession (SSFP) multipulse technique for the effective detection of nuclear quadrupole resonance (NQR) signals was studied. This modification is based on the use of the preparatory pulse in the SSFP pulse sequences. It was shown that under certain conditions the total intensity of accumulated NQR signal can be increased. Experimental results of applying the proposed technique to nitrogen-14 NQR in the sample of sodium nitrite (NaNO2) are presented and convincingly demonstrate the technique’s effectiveness.

The behaviour of nuclear quadrupole resonance (NQR) signal was studied in the `observation windows' between RF pulses after applying a multi-pulse sequence to a nitrogen-14 spin-system with a non-symmetric electric field gradient tensor using a phase-cycling technique. The experiments revealed some peculiarities in the behaviour of the signals which are important for the understanding of the dynamic properties of the quadrupolar spin-system.

Lightning strikes to the Toronto Canadian National (CN) Tower have been observed since 1978. In this paper, a brief description of the lightning measurement systems is provided, with emphasis on the current measurement system. Current and field measurement systems with broad bandwidths and high resolutions have been operational since 1991. Typical current derivative and current waveforms of a CN Tower lightning return stroke are also presented. Extensive cumulative statistics of waveform parameters (maximum steepness, risetime to maximum steepness, wavefront peak, risetime to wavefront peak, and absolute peak) of lightning return-stroke current signals measured at the CN Tower during a 10-year period have been derived. The statistical analysis shows that in 50% of the current records: the current wavefront maximum steepness exceeds 18.8 kA/μs, the risetime to maximum steepness exceeds 138 ns, the current wavefront peak exceeds 5 kA, the risetime to wavefront peak exceeds 636 ns and the current absolute peak exceeds 7.2 kA. The statistical analysis also shows that first return strokes feature lower current steepness and higher current peak when compared with subsequent return strokes. Recommendations concerning instrumentation and techniques for the proper measurement of lightning return-stroke currents are discussed. The presented statistical results will be of assistance in the establishment of more sophisticated protective measures against lightning hazards, especially at elevated objects.

Welders are exposed to high concentrations of nanoparticles. Compared to larger particles, nanoparticles have been associated with more toxic effects at the cellular level, including the generation of more reactive oxygen species activity. Current methods for welding-fume aerosol exposures do not differentiate between the nano-fraction and the larger particles. The objectives of this work are to establish a method to estimate the respiratory deposition of the nano-fraction of selected metals in welding fumes and test this method in a laboratory setting. Manganese (Mn), Nickel (Ni), Chromium (Cr), and hexavalent chromium (Cr(VI)) are commonly found in welding fume aerosols and have been linked with severe adverse health outcomes. Inductively coupled plasma mass spectrometry (ICP-MS) and ion chromatography (IC) were evaluated as methods for analyzing the content of Mn, Ni, Cr, and Cr(VI) nanoparticles in welding fumes collected with nanoparticle respiratory deposition (NRD) samplers. NRD samplers collect nanoparticles at deposition efficiencies that closely resemble physiological deposition in the respiratory tract. The limits of detection (LODs) and quantitation (LOQs) for ICP-MS and IC were determined analytically. Mild and stainless steel welding fumes generated with a robotic welder were collected with NRD samplers inside a chamber. LODs (LOQs) for Mn, Ni, Cr, and Cr(VI) were 1.3 μg (4.43 μg), 0.4 μg (1.14 μg), 1.1 μg (3.33 μg), and 0.4 μg (1.42 μg), respectively. Recovery of spiked samples and certified welding fume reference material was greater than 95%. When testing the method, the average percentage of total mass concentrations collected by the NRD samplers was ∼30% for Mn, ∼50% for Cr, and ∼60% for Ni, indicating that a large fraction of the metals may lie in the nanoparticle fraction. This knowledge is critical to the development of toxicological studies aimed at finding links between exposure to welding fume nanoparticles and adverse health effects. Future work will involve the validation of the method in workplace settings.[Supplementary materials are available for this article. Go to the publisher's online edition of Journal of Occupational and Environmental Hygiene for the following free supplemental resource: Digestion, extraction, and analysis procedures for nylon mesh screens.]

A transient injection method was used to simultaneously measure the time variation of footing impedance and soil resistivity on a series of 345-kV steel pole towers. For each tower, the ratio of transient resistivity to impedance, giving an effective tower perimeter, reached an asymptote by 500 ns. The soil resistivity estimates were log-normally distributed with natural log standard deviation of 0.63 for this locale. These time-evolved resistivity values are compared with observations based on frequency domain modeling.

Test methods for evaluating flashover voltage of ceramic and nonceramic insulators under ice, snow, and cold-fog conditions are recommended. The paper describes the procedure to be followed at various stages of an evaluation test including preparation of the test object, insulator precontamination, ice, snow, and cold-fog deposits as well as voltage applications and flashover voltage evaluation. Some relevant parameters for ice accretion, flashover voltage evaluation, artificial pollution, and power source requirements are taken from IEC 60129, IEC 60507, and IEEE Std.-4-1995 on standard techniques for high-voltage testing.

Various parameters of lightning discharges will be reviewed. Both common negative and less frequent but potentially more destructive positive and bipolar flashes will be covered. Direct lightning current measurements on instrumented towers will be discussed. Properties of first and subsequent strokes will be compared. The average number of strokes per flash and multiple channel terminations on ground will be considered. Parameters of subsequent strokes in natural lightning will be compared to their counterparts in rocket-triggered lightning. New insights into the lightning processes gained from triggered-lightning experiments will be discussed.

This paper presents a novel method to improve simulation of the road salt deposit process on energized high voltage insulators under winter conditions. A pollution generator system prototype was especially designed to produce an external mixing of dry solid contaminants (kaolin powder) with supercooled atomized brine droplets. The formed pollutant particles are transported by air flow, which is produced by a speed variable fan, and then settle on the energized specimen insulator surface which is installed at a specific distance of the pollution generator nozzle. The pollution accumulation process took place inside a climate chamber at −5°C. At the end of each ten-minute exposure, specimen insulators were removed for ESDD measurement according to the IEC 60815 standard. No pre-treatment of the insulator surface is needed and contrary to most of the other contamination methods, it enables study of the rate of increase of ESDD with wind speed and insulator profile under winter conditions. The combined effect of wind speed and dielectrophoretic force was also investigated using a 45-kV ac variable voltage source.

This paper describes the observation and analysis of electromagnetic field radiation from lightning strokes to tall structures. Electromagnetic field waveforms and current waveforms of lightning strokes to the CN Tower have been simultaneously measured since 1991. A new calculation model of electromagnetic field radiation is proposed. The proposed model consists of the lightning current propagation and distribution model and the electromagnetic field radiation model. Electromagnetic fields calculated by the proposed model, based on the observed lightning current at the CN Tower, agree well with the observed fields at 2 km north of the tower.

We have made a preliminary study of cloud‐to‐ground lightning over southern Ontario and the adjoining Great Lakes region. The lightning data set, using magnetic direction finding, is sufficiently accurate to study lightning climatology. Cloud‐to‐ground flash totals have been found for the three warm seasons 1989–91. A large variation in flash total, lightning‐day frequency and number of high flash density storms occurs over the area, with the maximum in southwestern Ontario. The area of the maximum also has a strong diurnal cycle and relatively few positive flashes. Several physical causes may contribute to this. Lake areas usually have slightly fewer flashes than nearby land areas and warm water usually has more flashes than cold water. The Great Lakes do produce more lightning than ocean areas. Convergence lines of lake breezes and other lake circulations can, however, be sites for storms with intense lightning. High surface temperature and moisture leads to an increase in lightning generation....

This paper examines the intentions, successes and failures of remarkable Romano-Libyan floodwater farmers who settled the arid Libyan pre-desert and used complexes of walls to manage the occasional floodwater as well as the desert's soils, sediments and biota. The paper presents and analyses a near ‘total’ data-set on the determinable locational properties of these ancient walls within one wadi — the 10 km long Wadi Umm el-Kharab. The organisation of these wall systems is shown to alter along the wadi according to changes in topographic, geomorphic and hydrological factors, as well as in relation to what are regarded in this paper as design and settlement factors. The organisation of the walls changes at confluences and distinctive topographic features. An analysis of the shape of enclosed areas indicates that the wadi can be divided into three broad sectors, each of which can be identified by differences in the shapes of the areas enclosed by walls. The enclosed shapes, as well as the general properties of the walls themselves do not vary in any simple linear manner along the wadi. Precise field mapping, as well as statistical displays of wall-related data, indicate the presence of similar ‘gaps’ in both the frequencies of settlement and of walls along the wadi. These gaps are, in part, explicable as the secondary consequences of hypothesised past flood-management problems associated with the confluences within the wadi system. They are also interpreted in this paper as some type of land use or other territorial ‘break’ created between the ancient community groups who occupied the wadi. This study has demonstrated the existence of distinct ‘preferences’ in the distances between walls, the areas enclosed between walls, and the thicknesses of walls. Overall, the types of organisation, and presumed functions of walls in this wadi are similar to those established from elsewhere in the Libyan pre-desert, but the balance is different in the Wadi Umm el-Kharab. The emphasis of wall-design in the Wadi Umm el-Kharab appeared to be upon the containment and management of floodwater, rather than the maximisation of the input of waters to the wadi floor, as deduced elsewhere. The long-term robustness and the environmental sophistication of these wall-systems are evident.

The electrical performance of outdoor insulation degrades severely during combinations of factors that include surface contamination, ice, fog and an ambient temperature that rises through 0/spl deg/C (T(0/spl deg/)). Failures at operating voltage on 115 kV, 230 kV and 500 kV power systems occur with increasing probability under those conditions. A new CFT(0/spl deg/) or "cold-fog" test method has been developed to reproduce the flashovers at all three voltage levels. Three options are identified for improving CFT(0/spl deg/) performance: use of semi-conductive glazes; substitution of silicone for porcelain; and use of silicone coatings on existing porcelain insulators.

This December 2014 issue of the IEEE Transactions on Dielectrics and Electrical Insulation is devoted to promoting new links between outdoor insulation knowledge and other domains of technology.

The authors describe how accurate estimates of low levels of insulator contamination, in the range of 200 mg/m/sup 2/ (0.02 mg/cm/sup 2/), can only be obtained if several minor errors in conventional surface contamination measurements are corrected. >

Although the impulse insulation level of a power apparatus is specified under the standard 1.2/spl times/50-/spl mu/s voltage wave, the apparatus seldom encounters such a voltage wave in the field. A wealth of knowledge exists on the behavior of air gaps under nonstandard lightning impulse voltages. The objective of the Task Force was to compile a bibliography on the nonstandard lightning impulse voltages and review the present state of research. This paper reviews the present status of research including the behaviour of air gaps under transient voltages, and the generation and measurement of fast-front impulse voltage waveforms. >

Because of the increasing importance of the effects of the nonstandard lightning voltage waves on power apparatus, the Task Force was formed to (1) compile a bibliography of the research on the nonstandard lightning voltages, and (2) review the previous research. The bibliography and the review dealt with: (1) behavior of air gaps under nonstandard lightning voltages, (2) generation of fast-front voltage waves, and (3) measurement of fast-front voltage waves. The bibliography is presented in this paper. The bibliography contains 207 publications, published by IEEE and by other societies, in English and in other languages. >

[1] In this paper, simultaneous GPS time-stamped measurements of the electric and magnetic fields at three distances and of the return stroke current associated with lightning strikes to the Toronto CN Tower (553 m) during the summer of 2005 are presented. The lightning return stroke current was measured using a Rogowski coil installed at a height of 474 m above ground level (AGL). The vertical component of the electric field and the azimuthal component of the magnetic field were measured simultaneously at distances of 2.0 km, 16.8 km, and 50.9 km from the CN Tower. The propagation path from the CN Tower to the first two stations (2.0 and 16.8 km) was along the soil and through the Toronto city, whereas for the third location (50.9 km) the propagation path was nearly entirely across Lake Ontario. The waveforms of the electric and magnetic fields at 16.8 km and 50.9 km exhibit a first zero crossing about 5 μs after the onset of the return stroke. This early zero crossing is part of a narrow undershoot. For fields at 50.9 km the expected zero crossing at about 40 μs is also observed. Metallic beams and other conducting parts in buildings on which electric and magnetic field sensors were located cause an enhancement effect on the measured fields. Although an enhancement can be identified both on the electric and the magnetic fields, the degree of enhancement is actually more significant for the electric field than for the magnetic field. It is shown that the value of the wave impedance (E-field peak to H-field peak ratio) could give an estimate of the enhancement effect of the building on the electric field. Propagation effects (decrease of field amplitude and increase of its risetime) can also be observed in experimental records. It is shown that the fields at 50.9 km are less affected by such attenuation, compared to those at 16.8 km, presumably because the path of propagation is mostly across Lake Ontario. Measured waveforms are compared with theoretical predictions obtained using the five engineering return stroke models extended to include the presence of the strike object, namely, transmission line (TL), modified transmission line (MTLL and MTLE), Bruce-Golde (BG), and traveling current source (TCS) models. A reasonable agreement is found with all five engineering models for the magnetic field waveforms at the three considered distances, although the peak values of the computed fields are systematically about 25% lower than measured values. None of the models was able to reproduce the early zero crossing and the narrow undershoot. As far as the electric field is concerned, larger differences have been observed between simulations and measurements. This may be due to the fact that the enhancement effect of the building on the electric field is stronger than that on the magnetic field. The expression relating current and field peaks associated with strikes to tall structures is also tested versus obtained sets of experimental data. The overall agreement between the theoretically predicted and the experimentally observed field-to-current ratio is reasonable, although the formula of Bermudez et al. (2005) appears also to underestimate the experimentally measured ratio (by about 25%). This may be due, at least in part, to the enhancement effect of the buildings on which the field measurement antennae were installed.

This paper presents an analysis of lightning return strokes to tall structures. The interaction of lightning with a tall structure is modeled using the antenna theory. The finite ground conductivity as well as the buried grounding system of the tall structure are taken into account in the analysis. It is shown that the current waveform, in sections of the tower close to ground, is somewhat affected by a finite ground conductivity. However, for sections further up the tower, it is not significantly influenced. Furthermore, our simulations show that some fine structure associated with current waveforms measured on the Toronto CN tower can be attributed to the finite ground conductivity. It is also shown that the current path down the tower structure is notably subjected to the skin effect. The current distribution along the buried grounding structure of the tower is also presented, illustrating the dispersion effect as a function of the ground conductivity. Finally, the lightning return-stroke generated electric and magnetic fields computed at a distance of 2 km from the tower are presented. It is shown that some late-time subsidiary peaks are smoothed out by the effect of the propagation along a finitely-conducting ground.

Hollow-core composite 230-kV station post insulators have been tested with single-phase short-circuit currents, simulating levels up to 85 kA rms-symmetric current (worst-case offset for an outer phase) in a three- phase system. Acoustic emission measurements indicated that these non-ceramic insulators (NCI) were not damaged by the short-circuit tests. Finite-element modelling of the insulator-bus system provided a good description of the tests. The finite-element modelling was used to calibrate a simpler model for station design, similar to the models upon which the ANSI/IEEE Standard 605 [ANSI/IEEE, 1984] and the IEC Standard 865 [IEC Standard, 1986; The Mechanical Effects of Short-Circuit Currents, 1996] are based.

In this study, we present an experimental validation of the transmission line representation of an elevated object struck by lightning. The experimental results are obtained using a reduced-scale model and injected signals with narrow pulse widths (down to 500 ps). The validation is performed using a reduced scale structure representing the Toronto CN Tower in Canada. Two models consisting, respectively, of 1-section and 3-section uniform transmission lines were considered for the comparison. It is shown that the 3-section model is able to accurately reproduce the obtained experimental data. The overall agreement between the 1-section model and the experimental results is also satisfactory, at least for the early-time response.

Pure Nuclear Quadrupole Resonance (NQR) is a very promising method for the detection and identification of illicit materials such as explosives and narcotics. NQR based machines are able to test closed luggage for illicit materials not readily identifiable by other methods. The application of the pure NQR method for screening of airport luggage is discussed. An advanced NQR machine which is a mid-sized luggage scanner has been developed by QRSciences Limited for use primarily in airports. The basic design, performance and some characteristics of this machine are reported.

A parallel is drawn between the design of curricula for the university education of engineers and the engineering design of products and systems. This “engineering design analogy” is explored with the aim of producing a fresh perspective on how to make the initial education of engineers better suited to the rapidly changing world of the future, and to improve its overall quality. The analogy is pursued from its implications for institutional corporate strategy, then through the different phases of design and briefly considers curriculum design solutions.

Objective: To examine, in free-living adults eating self-selected diets, the effects on plasma cholesterol of substituting saturated fat rich foods with either n-6 polyunsaturated or monounsaturated fat rich foods while at the same time adhering to a total fat intake of 30–33% of dietary energy. Design: Two randomised crossover trials. Setting: General community. Subjects: Volunteer sample of healthy free-living nutrition students at the University of Otago. Trial I, n=29; and trial II, n=42. Interventions: In trials I and II participants were asked to follow for 2½ weeks a diet high in saturated fat yet with a total fat content that conformed to nutrition recommendations (30–33% energy). During the 2 1/2 week comparison diet, saturated fat rich foods were replaced with foods rich in n-6 polyunsaturated fats (trial I) whereas in trial II the replacement foods were rich in monounsaturated fats. Participants were asked to maintain a total fat intake of 30–33% of energy on all diets. Main outcome measures: Energy and nutrient intakes, plasma triglyceride fatty acids, and plasma cholesterol. Results: When replacing saturated fat with either n-6 polyunsaturated fat or monounsaturated fat, total fat intakes decreased by 2.9% energy and 5.1% energy, respectively. Replacing saturated fat with n-6 polyunsaturated fat (trial I) lowered plasma total cholesterol by 19% [from 4.87 (0.88) to 3.94 (0.92) mmol/l, mean (s.d.)], low density lipoprotein cholesterol by 22% [from 2.87 (0.75) to 2.24 (0.67) mmol/l], and high density lipoprotein cholesterol by 14% [from 1.39 (0.36) to 1.19 (0.34) mmol/l], whereas replacing saturated fat with monounsaturated fat (trial II) decreased total cholesterol by 12%, low density lipoprotein cholesterol by 15%, and high density lipoprotein cholesterol by 4%, respectively. The change in the ratio of total to high density lipoprotein cholesterol was similar during trial I and trial II. Conclusions: Young adults are very responsive to dietary-induced changes in plasma cholesterol even when an isocaloric replacement of saturated fat with n-6 polyunsaturated or monounsaturated fat is not achieved. Replacing saturated fat with either n-6 polyunsaturated or monounsaturated fat is equally efficacious at reducing the total to high density lipoprotein cholesterol ratio. Sponsorship: University of Otago, Meadow Lea Ltd. European Journal of Clinical Nutrition (2001) 55, 908–915

The 15 papers in this special issue focus on the subject of flashover of ice- and snow-covered insulators.

This is a position paper prepared by the IEEE Task Force on Insulator Icing Test Methods. Test methods for evaluating flashover voltage of ceramic and nonceramic insulators under ice, snow, and cold-fog conditions are recommended. The paper describes the procedure to be followed at various stages of an evaluation test including preparation of the test object, insulator precontamination, ice, snow, and cold-fog deposits, as well as voltage applications and flashover voltage evaluation. Some relevant parameters for ice accretion, flashover voltage evaluation, artificial pollution, and power source requirements are taken from IEC 60129, IEC 60507, and IEEE Standard 4-1995 on standard techniques for high-voltage testing.

The electrical performance of outdoor insulation degrades severely during combinations of factors that include surface contamination (C), ice (I), fog (F) and an ambient temperature that rises through 0 C (T{sub 0{degree}}). Failures at operating voltage on 115-kV, 230-kV and 500-kV systems occur with increasing probability under these conditions. A new CFT{sub 0{degree}} or cold-fog test method has been developed to reproduce the flashovers at all three voltage levels. Three options are identified for improving CFT{sub 0{degree}} performance: use of semi-conductive glazes, substitution of silicone for porcelain and use of silicone coatings on existing porcelain insulators.