Calibrated, multiband radiometric measurements of the optical radiation emitted by rocket-triggered lightning (RTL) have been made in the ultraviolet (UV, 200-360 nm), the visible and near infrared (VNIR, 400-1000 nm), and the long wave infrared (LWIR, 8-12 µm) spectral bands. Measurements were recorded from a distance of 198 m at the University of Florida International Center for Lightning Research and Testing (ICLRT) during the summers of 2011 and 2012. The ICLRT provided time-correlated measurements of the current at the base of the RTL channels. Following the onset of a return stroke, the dominant mechanism for the initial rise of the UV and VNIR waveforms was the geometrical growth of the channel in the field-of-view of the sensors. The UV emissions peaked about 0.7 µs after the current peak, with a peak spectral power emitted by the source per unit length of channel of 10 ± 7 kW/(nm-m) in the UV. The VNIR emissions peaked 0.9 µs after the current peak, with a spectral power of at 7 ± 4 kW/(nm-m). The LWIR emissions peaked 30-50 µs after the current peak, and the mean peak spectral power was 940 ± 380 mW/(nm-m), a value that is about 4 orders of magnitude lower than the other spectral band emissions. In some returns strokes the LWIR peak coincides with a secondary maximum in the VNIR band that occurs during a steady decrease in channel current. Examples of the optical waveforms in each spectral band are shown as a function of time and are discussed in the context of the current measured at the channel base. Source power estimates in the VNIR band have a mean and standard deviation of 2.5 ± 2.2 MW/m and are in excellent agreement with similar estimates of the emission from natural subsequent strokes that remain in a pre-existing channel which have a mean and standard deviation of 2.3 ± 3.4 MW/m. The peak optical power emitted by RTL in the UV and VNIR bands are observed to be proportional to the square of the peak current at the channel base. The same trend was found for natural lightning using peak currents estimates provided by the National Lightning Detection Network. Ratios of the optical power to the electromagnetic power emitted at the time of peak current suggest the radiative efficiency in the VNIR band is a few percent during the early onset of a return stroke. The majority of return strokes in RTL are found to emit most of their optical energy during the initial impulse phase.

Vattenfall Eldistribution AB distribuerar el till ca 900 000 kunder i Sverige. Det handlar om både privatkunder och företagskunder. Enheten Nätdrift vars driftcentral är placerad i Trollhättan har till uppgift att se till att elnätet är spänningssatt och att man skall minimera avbrottstiderna. Då dagens samhälle är allt mer beroende av störningsfri leverans av el är det viktigt att kartlägga faktorer som orsakar korta avbrott på nätet. Ett kort avbrott definieras som ett avbrott som varar allt från 100 millisekunder till 3 min. I myndigheternas föreskrifter finns inga krav angående hur frekvent korta avbrott får förekomma i elnätet, då dessa avbrott oftast är orsakade av åska och därmed omöjliga att förutse. Genom att åskan åstadkommer en nedbrytning av isolationshållfastheten i systemet kan en ljusbåge uppträda vilken drar med sig nätspänningen till jord. Ledningsskydden känner av förekommande felströmmar och löser ut. En konsekvens av detta är att ett kort avbrott av nätets driftspänning uppstår innan en återinkoppling kan ske och normal drift åter föreligger. Arbetet är avgränsat genom att det endast handlar om avbrott orsakade av åsköverspänningar samt endast spänningsnivåer över 1000V. Utifrån litteraturstudier som är gjorda på kurslitteratur, forskning samt Vattenfalls eget material i ämnet, har arbetet resulterat i ett antal olika återgärder som skulle kunna minska antalet korta avbrott i högspänningsnätet. Detta examensarbete förordar att arbetet med att identifiera och analysera bakomliggande orsaker och möjliga åtgärder för att kunna minska antalet återinkopplingar fortsätter. I en fortsatt fördjupad analys bör även ekonomiska aspekter vägas mot nyttan av åtgärderna för både kunder och nätbolag. / In Sweden Vattenfall Eldistribution AB provides electrical power to approximatly 900000 customers, both private customers and business customers. The grid is operated from Trollhättan and it is the division Nätdrift's main purpose to, beside keeping the grid operating with a minimum of disturbances, to plan, optimize, manage and develop the operating systems. The society today is increasingly depending of an uninterrupted transmission of electricity and therefore it is important to make a survey of the factors that causes short interruptions in the grid. A short interruption is defined as an interruption that has a duration between 100 ms and 3 min. The regulations provided by the authorities do not include any demands regarding how frequent these short interruptions may occure in the grid. This is due to the fact that they are mostly caused by overvoltage from lightning storms, and therefore hard to predict. When lightning strikes on an overhead line, a breakdown of the insulation will occur due to overcurrent and a shortcut will ignite an arc between the wire and earth. This will start the phase-fault protection system to react and activate the feeder circuit breakers involved. This protection of the grid will cause a short interruption of the power supply before the automatic reclosing repowers the overhead line back to normal operating voltage. This thesis has been based on short interruptions caused by lightning and there has been no considerations taken to short interruptions occurring in grids with a voltage level below 1000 V. In this thesis a study of literature has been conducted from course literature, research and Vattenfalls internal documents. The result has been that a number of possible actions can be taken in consideration for making short interruptions less frequent. This thesis is also recommending that the survey of actors which are causing short interruptions continues. When doing so, the economical aspects should also be taken in consideration regarding the customers as well as the network company.

Natural lightning strikes induce impulsive overvoltages on transmission lines and its terminal equipment. These overvoltages may cause failures in insulation mechanisms of electrical devices in the power system. It is important to test the insulation strength of a device against these impulsive overvoltages. Usually, Marx generators are used to generate impulse waveforms for testing purposes. A novel approach is proposed to obtain resistor settings of a Marx generator for impulse testing of power transformers. This approach enables us to overcome most of the major challenges in the commonly used trial-and-error method, including excessive time consumption and potential damage to the transformer. The proposed approach uses the frequency response of the transformer to synthesize a circuit model. Then, a genetic algorithm based optimization-enabled electromagnetic transient simulation approach is used to obtain the resistor settings. The proposed approach is validated by a real impulse test conducted on a three phase power transformer.

The research work presented here is concerned with numerical simulations of two different electrical phenomena: Long gap electrical discharges under switching impulses and the lightning attachment process associated with positive upward leaders. The development of positive upward leaders and the progression of discharges in long gaps are attributable to two intertwined physical phenomena, namely, the leader channel and the streamer zone. The physical description and the proposed calculations of the above-mentioned phenomena are based on experimental tests conducted in long spark gaps. The methodology presented here proposes a new geometrical approximation for the representation of the streamer and the calculation of the accumulated electrical charge. Furthermore, two different approaches to representing the leader channel are applied and compared. Statistical delays before the inception of the first corona, and random distributions to represent the tortuous nature of the path taken by the leader channel were included based on the behavior observed in experimental tests, with the intention of ensuring the discharge behaved in a realistic manner. A reasonable agreement was found between the physical model and the experimental test results. A model is proposed to simulate the negative discharges produced by switching impulses using the methodology developed to simulate positive leader discharges and the physics underlying the negative leader phenomena. The validation of the method demonstrated that phenomena such as the pilot leader and negative leader currents are successfully represented. In addition, based on previous work conducted on the physics of lightning and the lightning attachment process, a new methodology is developed and tested. In this new approach, the background electric field and the ionized region, considered in conjunction with the advance of the leader segment, are computed using a novel method. The proposed methodology was employed to test two engineering methods that are accepted in international standards, the mesh method and the electro-geometrical method. The results demonstrated that the engineering approximations are consistent with the physical approach. In addition to the electrical phenomena mentioned above, one should remember that, to simplify the calculation, there are certain real effects arising from the lightning attachment process that have not been considered. In fact, when a structure is subjected to a strong electric field, it is possible to generate multiple upward leaders from that structure. This effect has not been taken into account in the numerical models available previously, and therefore the process of generating multiple upward leaders incepted over a structure is incorporated here. The results have shown that a slight advantage from the background electric field is enough for one upward connecting leader to take over, thereby forcing the others to abort the attachment process.

Remote measurement of electric field generated by lightning has played a major role in understanding the lightning phenomenon. Even though other measurements such as photographic and channel base current have contributed to this research field, due to practical reasons remote measurements of electric field is considered as the most useful tool in lightning research. This thesis discusses the remotely measured radiation field component of electric field generated by cloud flashes (ICs) and narrow bipolar pulses (NBPs). The associated HF radiation of these events at 3 MHz and 30 MHz are also discussed. To understand the initiation process of these discharges, a comparative study of the initial pulse of cloud flashes against the initial pulse of cloud to ground flashes was conducted. The result suggests that both discharges might have been initiated by similar physical processes inside the thunderclouds. Comparing the features of initial pulse of cloud and ground flashes with that of pulses that appeared in the later stages of cloud flashes suggests that the initiation process involved in both flashes are not very much different from the initiation of cloud flashes at the later stage. The average spectral amplitudes of electric field of full duration cloud flashes (180 ms) showed f  -1 frequency dependence within the interval of 10 kHz to approximately 10 MHz. This is in contrast to the standard f  -2 decrement (or even steeper ) at high frequency region for other lightning processes such as return strokes. It was suggested that small pulses which repeatedly appeared at the later stage of cloud flashes might have contributed to enhance the spectral amplitude at higher frequencies. Electric fields generated by Narrow Bipolar Pulses (NBPs), which are considered as one of the strongest sources of HF radiation, were measured in the tropics of Malaysia and Sri Lanka.  Their features were also studied and show a good agreement with previously published observations of NBPs from other geographical regions. Thorough analyses and observations of these pulses found previously unreported sharp, fine peaks embedded in the rising and decaying edge of the electric field change of NBPs. Therefore it was suggested that these fine peaks are mostly responsible for the intense HF radiation at 30 MHz.

Electric power systems are a recent feature of community infrastructure, little more than a century having elapsed since the first public electricity supply was offered. The speed with which they have spread across the world, and the extent to which electricity has displaced other energy sources in commercial, industrial and domestic applications, has been quite remarkable. The widespread availability of a reliable supply of electricity has become one of the dominant factors in the lifestyle of the citizens of developed countries, and one of the differences between developed and developing countries. Yet not many histories of this remarkable industry have been written, and most of those have confined their attention to political and administrative matters, although technical issues have virtually dictated the pace of development of the industry. In the 1920s, when power systems began to spread beyond city centres, lightning became a major adverse factor in their capital costs, operating costs and reliability, and inadequate reliability reduced the rate of acceptance of electricity supply by the public, especially in rural areas. Although lightning has long inspired fear and wonder, its fundamental nature - the fact that it is an electrical discharge - was not known until less than three centuries ago, and the first measurements of lightning currents and voltages were not made until the middle 1920s, when instruments for measuring the electrical properties of lightning first became available. Intensive research programmes were undertaken in America, Britain, and some European countries from about 1925 onwards, but no research on the effects of lightning on power systems was undertaken in Australia until after 1950. This delay of almost three decades forced Australian power system engineers to base some very important aspects of power system design entirely upon data from other countries, which was of doubtful applicability in Australian conditions. During this period, the uncertainty over basic design data resulted in some power systems being over-insulated, with consequent waste of capital expenditure, while others were under-insulated, and had to be modified later to achieve adequate reliability. It is believed that this long delay in commencing lightning research in Australia was caused by a number of factors, including community attitudes to higher education and research (other than primary industry research), and the belief of many managers in the electricity supply industry that only the major manufacturers of electrical plant, located mainly in the United Kingdom and the United States of America, could successfully conduct power system research. In 1948 the Senate of the University of Queensland decided to replace the Chair of Engineering with four Chairs in separate branches of engineering. The founding Professor of Electrical Engineering, S.A. Prentice, was appointed in 1950 and soon decided to adopt lightning and its effects on power systems as the principal research thrust of the new Department. By the late 1950s, the University of Queensland had become the recognised centre of Australian research in lightning and high voltage insulation. With financial support from the electricity industry, the University completed a new high voltage laboratory in 1960, and soon began to be recognised overseas as a significant contributor to the world-wide search for knowledge in those areas. During the next fifteen years, the cooperative research programme of the University and the electricity industry developed fully, and valuable research was pursued in a number of areas, including the impulse strength and arc-quenching properties of Australian hardwoods used in poles and crossarms, the prediction of lightning outage rates of transmission lines, the causes of high lightning-failure rates in distribution systems, the performance of insulation under pollution conditions, and the validity of high voltage test procedures. The work frequently involved people from the electricity supply industry as well as people from the university, and attracted attention in overseas countries as well as in Australia. In 1974 Prentice reached retiring age, but the principal members of the staff he had recruited continued to produce research of high quality, and of considerable practical benefit to the electricity industry. By 1995, Prentice's principal staff members had reached or were approaching retirement, and the nature of lightning research had changed somewhat, with the principal interest turning to the details of the lightning stroke itself, and to protection of buildings and electronic equipment rather than power systems.

No abstract available

Electric power systems are a recent feature of community infrastructure, little more than a century having elapsed since the first public electricity supply was offered. The speed with which they have spread across the world, and the extent to which electricity has displaced other energy sources in commercial, industrial and domestic applications, has been quite remarkable. The widespread availability of a reliable supply of electricity has become one of the dominant factors in the lifestyle of the citizens of developed countries, and one of the differences between developed and developing countries. Yet not many histories of this remarkable industry have been written, and most of those have confined their attention to political and administrative matters, although technical issues have virtually dictated the pace of development of the industry. In the 1920s, when power systems began to spread beyond city centres, lightning became a major adverse factor in their capital costs, operating costs and reliability, and inadequate reliability reduced the rate of acceptance of electricity supply by the public, especially in rural areas. Although lightning has long inspired fear and wonder, its fundamental nature - the fact that it is an electrical discharge - was not known until less than three centuries ago, and the first measurements of lightning currents and voltages were not made until the middle 1920s, when instruments for measuring the electrical properties of lightning first became available. Intensive research programmes were undertaken in America, Britain, and some European countries from about 1925 onwards, but no research on the effects of lightning on power systems was undertaken in Australia until after 1950. This delay of almost three decades forced Australian power system engineers to base some very important aspects of power system design entirely upon data from other countries, which was of doubtful applicability in Australian conditions. During this period, the uncertainty over basic design data resulted in some power systems being over-insulated, with consequent waste of capital expenditure, while others were under-insulated, and had to be modified later to achieve adequate reliability. It is believed that this long delay in commencing lightning research in Australia was caused by a number of factors, including community attitudes to higher education and research (other than primary industry research), and the belief of many managers in the electricity supply industry that only the major manufacturers of electrical plant, located mainly in the United Kingdom and the United States of America, could successfully conduct power system research. In 1948 the Senate of the University of Queensland decided to replace the Chair of Engineering with four Chairs in separate branches of engineering. The founding Professor of Electrical Engineering, S.A. Prentice, was appointed in 1950 and soon decided to adopt lightning and its effects on power systems as the principal research thrust of the new Department. By the late 1950s, the University of Queensland had become the recognised centre of Australian research in lightning and high voltage insulation. With financial support from the electricity industry, the University completed a new high voltage laboratory in 1960, and soon began to be recognised overseas as a significant contributor to the world-wide search for knowledge in those areas. During the next fifteen years, the cooperative research programme of the University and the electricity industry developed fully, and valuable research was pursued in a number of areas, including the impulse strength and arc-quenching properties of Australian hardwoods used in poles and crossarms, the prediction of lightning outage rates of transmission lines, the causes of high lightning-failure rates in distribution systems, the performance of insulation under pollution conditions, and the validity of high voltage test procedures. The work frequently involved people from the electricity supply industry as well as people from the university, and attracted attention in overseas countries as well as in Australia. In 1974 Prentice reached retiring age, but the principal members of the staff he had recruited continued to produce research of high quality, and of considerable practical benefit to the electricity industry. By 1995, Prentice's principal staff members had reached or were approaching retirement, and the nature of lightning research had changed somewhat, with the principal interest turning to the details of the lightning stroke itself, and to protection of buildings and electronic equipment rather than power systems.

Electric power systems are a recent feature of community infrastructure, little more than a century having elapsed since the first public electricity supply was offered. The speed with which they have spread across the world, and the extent to which electricity has displaced other energy sources in commercial, industrial and domestic applications, has been quite remarkable. The widespread availability of a reliable supply of electricity has become one of the dominant factors in the lifestyle of the citizens of developed countries, and one of the differences between developed and developing countries. Yet not many histories of this remarkable industry have been written, and most of those have confined their attention to political and administrative matters, although technical issues have virtually dictated the pace of development of the industry. In the 1920s, when power systems began to spread beyond city centres, lightning became a major adverse factor in their capital costs, operating costs and reliability, and inadequate reliability reduced the rate of acceptance of electricity supply by the public, especially in rural areas. Although lightning has long inspired fear and wonder, its fundamental nature - the fact that it is an electrical discharge - was not known until less than three centuries ago, and the first measurements of lightning currents and voltages were not made until the middle 1920s, when instruments for measuring the electrical properties of lightning first became available. Intensive research programmes were undertaken in America, Britain, and some European countries from about 1925 onwards, but no research on the effects of lightning on power systems was undertaken in Australia until after 1950. This delay of almost three decades forced Australian power system engineers to base some very important aspects of power system design entirely upon data from other countries, which was of doubtful applicability in Australian conditions. During this period, the uncertainty over basic design data resulted in some power systems being over-insulated, with consequent waste of capital expenditure, while others were under-insulated, and had to be modified later to achieve adequate reliability. It is believed that this long delay in commencing lightning research in Australia was caused by a number of factors, including community attitudes to higher education and research (other than primary industry research), and the belief of many managers in the electricity supply industry that only the major manufacturers of electrical plant, located mainly in the United Kingdom and the United States of America, could successfully conduct power system research. In 1948 the Senate of the University of Queensland decided to replace the Chair of Engineering with four Chairs in separate branches of engineering. The founding Professor of Electrical Engineering, S.A. Prentice, was appointed in 1950 and soon decided to adopt lightning and its effects on power systems as the principal research thrust of the new Department. By the late 1950s, the University of Queensland had become the recognised centre of Australian research in lightning and high voltage insulation. With financial support from the electricity industry, the University completed a new high voltage laboratory in 1960, and soon began to be recognised overseas as a significant contributor to the world-wide search for knowledge in those areas. During the next fifteen years, the cooperative research programme of the University and the electricity industry developed fully, and valuable research was pursued in a number of areas, including the impulse strength and arc-quenching properties of Australian hardwoods used in poles and crossarms, the prediction of lightning outage rates of transmission lines, the causes of high lightning-failure rates in distribution systems, the performance of insulation under pollution conditions, and the validity of high voltage test procedures. The work frequently involved people from the electricity supply industry as well as people from the university, and attracted attention in overseas countries as well as in Australia. In 1974 Prentice reached retiring age, but the principal members of the staff he had recruited continued to produce research of high quality, and of considerable practical benefit to the electricity industry. By 1995, Prentice's principal staff members had reached or were approaching retirement, and the nature of lightning research had changed somewhat, with the principal interest turning to the details of the lightning stroke itself, and to protection of buildings and electronic equipment rather than power systems.

Electric power systems are a recent feature of community infrastructure, little more than a century having elapsed since the first public electricity supply was offered. The speed with which they have spread across the world, and the extent to which electricity has displaced other energy sources in commercial, industrial and domestic applications, has been quite remarkable. The widespread availability of a reliable supply of electricity has become one of the dominant factors in the lifestyle of the citizens of developed countries, and one of the differences between developed and developing countries. Yet not many histories of this remarkable industry have been written, and most of those have confined their attention to political and administrative matters, although technical issues have virtually dictated the pace of development of the industry. In the 1920s, when power systems began to spread beyond city centres, lightning became a major adverse factor in their capital costs, operating costs and reliability, and inadequate reliability reduced the rate of acceptance of electricity supply by the public, especially in rural areas. Although lightning has long inspired fear and wonder, its fundamental nature - the fact that it is an electrical discharge - was not known until less than three centuries ago, and the first measurements of lightning currents and voltages were not made until the middle 1920s, when instruments for measuring the electrical properties of lightning first became available. Intensive research programmes were undertaken in America, Britain, and some European countries from about 1925 onwards, but no research on the effects of lightning on power systems was undertaken in Australia until after 1950. This delay of almost three decades forced Australian power system engineers to base some very important aspects of power system design entirely upon data from other countries, which was of doubtful applicability in Australian conditions. During this period, the uncertainty over basic design data resulted in some power systems being over-insulated, with consequent waste of capital expenditure, while others were under-insulated, and had to be modified later to achieve adequate reliability. It is believed that this long delay in commencing lightning research in Australia was caused by a number of factors, including community attitudes to higher education and research (other than primary industry research), and the belief of many managers in the electricity supply industry that only the major manufacturers of electrical plant, located mainly in the United Kingdom and the United States of America, could successfully conduct power system research. In 1948 the Senate of the University of Queensland decided to replace the Chair of Engineering with four Chairs in separate branches of engineering. The founding Professor of Electrical Engineering, S.A. Prentice, was appointed in 1950 and soon decided to adopt lightning and its effects on power systems as the principal research thrust of the new Department. By the late 1950s, the University of Queensland had become the recognised centre of Australian research in lightning and high voltage insulation. With financial support from the electricity industry, the University completed a new high voltage laboratory in 1960, and soon began to be recognised overseas as a significant contributor to the world-wide search for knowledge in those areas. During the next fifteen years, the cooperative research programme of the University and the electricity industry developed fully, and valuable research was pursued in a number of areas, including the impulse strength and arc-quenching properties of Australian hardwoods used in poles and crossarms, the prediction of lightning outage rates of transmission lines, the causes of high lightning-failure rates in distribution systems, the performance of insulation under pollution conditions, and the validity of high voltage test procedures. The work frequently involved people from the electricity supply industry as well as people from the university, and attracted attention in overseas countries as well as in Australia. In 1974 Prentice reached retiring age, but the principal members of the staff he had recruited continued to produce research of high quality, and of considerable practical benefit to the electricity industry. By 1995, Prentice's principal staff members had reached or were approaching retirement, and the nature of lightning research had changed somewhat, with the principal interest turning to the details of the lightning stroke itself, and to protection of buildings and electronic equipment rather than power systems.