Lightning safety psyche

How is lightning protection ranked in the field of safety science? What is the general perception of the public with regard to the risk of receiving a lightning strike to their building? How do business entities manipulate the psyche of the public in upsizing financial gains? What is the true risk of public adopting lightning protection techniques that have not been included in major international standards? Is the research presented so far in condemning the lightning protection systems rejected by the scientific community, well-conducted? Is tabooing of some lightning protection technologies a productive strategy in driving the public to adopt protection systems recommended by international (IEC) standards? This paper makes comprehensive attempts to answer these questions

Concerns of the application of lightning protection risk assesment for small structures

International Standards on lightning protection risk assessment (IEC 62305-2: 2010) are well accepted and applied in many parts of the world. During the last few years a large number of lightning related accidents, especially due to direct strikes, have been reported from Asia and Africa where the lightning struck objects are small structures. Information gathered from several investigations done on these cases have been used to determine the level of protection needed for these structures as per the standard risk assessment. In many cases the outcome was the none-requirement of any LPS for such structures or a risk factor for direct strike probability which is less than the critical value. As there are millions of similar structures in these regions, we propose the development of a separate risk assessment algorithm for such structures, especially in underdeveloped countries

Evaluation of lightning protection systems proposed for small structures by electromagnetic simulation

This paper validates the performance of low-cost lightning protection systems for small structures proposed by researchers in the past. Such structures have an acute demand in the countries with very high lightning ground flash density, yet the affordability of the mass public is quite limited due to the struggling economies of the countries. The protection systems for small housing structure, and a standalone protection structure for one or few people have been investigated by implementing the structures in HFSS/ANSYS software which employs finite element method. By applying current waveforms to represent first negative return stroke, subsequent negative return stroke and positive return stroke, the electric field and potential gradient of the entire space and the current density and the thermal profile of the protective structure have been computed. The objectives were to find whether the voltage distribution in the wake of a lightning strike could initiate side flashes, generate touch potential and step potentials that exceed dangerous levels, drive current densities due to which the structure collapse under thermal effects. It has been found that the proposed protective structures could suppress side flashes and harmful effects due to step potential while the structure will be able to withstand the heat generated. However, the touch potential could still be beyond the human injury thresholds, thus a minimum separation from the lightning current passage should be advised to the occupants

Frequency dependent permittivity of soil and bentonite: for lightning protection and high frequency earthing systems

This paper presents the frequency dependent permittivity of a selected type of soil, bentonite and four of their mixes by weight. The permittivity at a low frequencies, vary significantly with moisture content in the cases of both sand and bentonite. For dry sand, bentonite and all bentonite mixes, the permittivity shows a rapid drop with the increment of frequency from near 0 Hz to 0.6 kHz, followed by a moderate decrement up to about 10-20 kHz. All parameters have rather insignificant variation after about 50 kHz and level of around 1 MHz. These outcomes provide some key information to analyze the behavior of bentonite based backfill materials that are widely used in electrical earthing networks, especially in the case of high frequency earthing and lightning protection systems

Characteristics of fulgurite-like structures under HV conditions: effects on electrical earthing systems

Fulgurites are natural tubes of glass formed by the fusion of silica sand or rock from a lightning strike. The fulgurites have been produced artificially in HV conditions in the past. Recent studies have found that fulguritic structures can be formed in some other materials, such as bentonite and cement, as well. These fulgurites can change the overall physical and electrical properties of the original materials. Thus, formation of fulgurites can modify the performance of electrical earthing systems, both ordinary and those improvised with backfill materials. This study investigates the fulgurite formation under alternating, direct and impulse current application. Bentonite and sand were tested under high voltage conditions. The type of fulgurites and their effects on electrical earthing systems were studied by analyzing the resistivity and permittivity of original materials and fulgurites. It has been found that fulgurites formation has a severe effect on the earth resistance of grounding systems

Lightning damages in glass fiber-epoxy composite material used for aerospace applications

Arcing effects, such as that due to lightning, on glass fiber reinforced epoxy composite laminate used in aerospace applications, have been studied. Lightning voltage impulses (1.2/50 micro seconds) were applied at breakdown voltage on the specimens and the arc points were inspected nondestructively using an Ultrasonic Propagation Imaging (UPI) system. The data acquired were processed using the Statistically Thresholded Anomaly Mapping (STAM) method. The outcomes depict that the size of lightning penetration damage is proportional to the breakdown voltage and significantly larger than the charring mark at the point of breakdown. Specimens subjected to surface flash-over reconfirms that whereas the arc leaves little or no visual sign on the specimen surface, there may be significant degradation of the material at microscopic scale. Inspection of 3-layer laminates reveals that the arc damage is characterized by larger charred region, exposed glass fibers due to vaporization of epoxy matrix, and delamination. The delamination could happen for the first ply, the third ply, or both at the same time. The size of the delaminations estimated from STAM image was smaller than those estimated using backlight illumination

Impulse flashover characteristics of oil palm trunk (OPT) veneer plywood

Oil palm is one of the largest crop industries in South East Asia, thus, it is of importance to use all parts of the Oil palm trees. Recently Oil Palm Trunks (OPT) have been used to make veneer, which can be processed to produce plywood. Even though OPT plywood doesn't have the same mechanical properties as timber, with proper treatment and adhesives during the processing of veneer to plywood, it can be made to compete with hardwood. OPT plywood has been used in various applications from wooden appliances to housing and roofing structures. These structures are at risk of surface flashovers through lightning and electrical breakdowns. However, no study has been conducted on the effects or characteristics of OPT plywood. In this paper, the effects of impulse surface flashover under different conditions on three-layered OPT plywood has been analyzed. Experiments were conducted to identify the characteristics of OPT under clean and dry, clean and wet, and contaminated surface conditions for both parallel and perpendicular fiber orientations. The 50% breakdown voltage was determined by the up and down method. Results identified the importance of the fibre orientation and the decrease in breakdown voltage under contaminants

Development of a portable type I to III lightning surge protective device for compact structures

Lightning Surge protection of large structures is done under zonal concept due to the requirement of a system with high current handling capacity and low voltage protection level. Induction of transient voltage in the wiring system within the building is another reason for such. However, in the case of compact structures such as base transmission stations (BTS) of tower sites, outside broadcast vehicles (OBV), various stages of railway systems etc. there are no sufficient lengths in the wiring network for implementing SPDs in such zonal-segment scenario. Also due to the remoteness of most BTSs and need for regular and/or continuous usage of OBVs and railway systems, the time-consuming replacement of out-of-order fixed SPDs is most often not warranted. In this backdrop, it was proposed to develop a portable/pluggable system of coordinated SPDs with high current handling capacity and low voltage protection level. A compact SPD system that is capable of handling high currents (50 kA) with low let through voltage (1 kV) was designed using PSCAD and a thorough market research was conducted to identify products that satisfied the requirements of the system designed in PSCAD. Type I and III SPDs capable of handling 50 kA and 2.5 kA respectively, were identified and used for the hardware implementation of the system. Elimination of the type II SPD made the design more compact and better suited for applications at space-restricted locations

Artificial neural networks in image processing for early detection of breast cancer

Medical imaging techniques have widely been in use in the diagnosis and detection of breast cancer. The drawback of applying these techniques is the large time consumption in the manual diagnosis of each image pattern by a professional radiologist. Automated classifiers could substantially upgrade the diagnosis process, in terms of both accuracy and time requirement by distinguishing benign and malignant patterns automatically. Neural network (NN) plays an important role in this respect, especially in the application of breast cancer detection. Despite the large number of publications that describe the utilization of NN in various medical techniques, only a few reviews are available that guide the development of these algorithms to enhance the detection techniques with respect to specificity and sensitivity. The purpose of this review is to analyze the contents of recently published literature with special attention to techniques and states of the art of NN in medical imaging. We discuss the usage of NN in four different medical imaging applications to show that NN is not restricted to few areas of medicine. Types of NN used, along with the various types of feeding data, have been reviewed. We also address hybrid NN adaptation in breast cancer detection

Bioluminescence

Microcosm describes a miniature representation of a living or non-living thing. For example, there are miniature buildings, cars, furniture, dolls, mushrooms, flowers and plants. Microcosm bioluminescent mushrooms are miniatures of real mushrooms that produce light which is visible in the dark as a result of a biochemical reaction