This chapter discusses Benjamin Franklin's work on electricity and lightning.

The rocket-and-wire technique has been routinely used since the 1970s to artificially initiate (trigger) lightning from natural thunderclouds for purposes of research and testing. Leader/return stroke sequences in triggered lightning are similar in most (if not all) respects to subsequent leader/return-stroke sequences in natural downward lightning and to all such sequences in object-initiated lightning. The initial processes in triggered lightning are similar to those in object-initiated (upward) lightning and are distinctly different from the first leader/return-stroke sequence in natural downward lightning. The results of triggered-lightning experiments have provided considerable insight into natural lightning processes that would not have been possible from studies of natural lightning due to its random occurrence in space and time. Among such findings are the observation of an UCL in a dart leader/return-stroke sequence, identification of the M-component mode of charge transfer to ground, the observation of a lack of dependence of return-stroke current peak on grounding conditions, discovery of X-rays produced by lightning dart leaders, new insights into the mechanism of cutoff and reestablishment of current in the lightning channel, direct measurements of NO_x production by an isolated lightning channel section and the characterization of the electromagnetic environment within tens to hundreds of metres of the lightning channel. Triggered-lightning experiments have contributed significantly to testing the validity of various lightning models and to providing ground-truth data for the US National Lightning Detection Network (NLDN). Triggered lightning has proved to be a very useful tool to study the interaction of lightning with various objects and systems, particularly in view of the fact that simulation of the lightning channel in a high-voltage laboratory does not allow the reproduction of many lightning features important for lightning protection and it does not allow the testing of large distributed systems such as overhead power lines.

The term 'surge' denotes a state of electrical overstress that lasts less than a few milliseconds, a duration much less than that of a power frequency cycle. The brief nature of the surge is emphasized by adding the word 'transient' before it. To distinguish from other types of electrical overstresses, some authors prefer the term 'transient overvoltages. Sometimes transients may not exceed the normal operating voltage, but they may still be of concern because of their high-frequency content. The most common sources of transients in power and telecommunication systems are lightning and switching events. Current and voltage transients are part of what is known as conducted electromagnetic interference (EMI). Here, we consider only lightning transients. In this chapter we first give a brief overview of the characteristics of lightning and provide examples of the nature of lightning transients measured in low-voltage networks. This is followed by a discussion on transient protection methods and components.

In the modern world, industry, the economy and many other public activities are highly dependent on electronic data processing (EDP) systems containing sensitive electronic apparatus. As shown, surges caused by lightning and switching operations are responsible for a large number of occurrences of damage to electronic equipment in Germany. It can be seen that in nearly 24 percent of cases, lightning and other switching impulses are responsible for defects and breakdowns in electronic circuits. In general, overvoltages first damage the most sensitive section of an electronic system. In the case of a network, the most probable areas to experience damage are the network interface units of servers, workstations and PC stations. The immediate effect of such damage could be very severe. For example, a stop in the data flow in a network system could paralyse organizations such as banks, halt production lines in industry, or interrupt the customer services of a supermarket.

Grounding has an important role in lightning protection. This subject is considered in this book in three complementary chapters, with the present chapter providing an introduction. Through a simplified general approach the concept of grounding resistance is explained, together with its role in lightning protection practice. To support this conceptual approach, some experimental results related to the response of grounding electrodes to impulsive currents are presented, and there is a discussion of the relation between grounding resistance and this response. Finally, some relevant conclusive remarks related to lightning protection applications are presented.

In this chapter we have presented several soil ionization models created by scientists to evaluate the voltage-current relationship of buried conductors in the presence of soil ionization. Following through the models one can observe that some models are pure engineering constructions while others attempt to incorporate more physics in model development. The models should be judged according to the validity of the physics underlying them and their ability to make reasonable predictions. In this respect it is desirable to have a model the parameters of which do not change from one experimental configuration to another. This is so because a model with parameters that change from one configuration to another could not be used in making predictions. Because all the discussed models involved assumptions that may not be valid in real situations, caution should be applied in making use of the results of the models. Moreover, all the models assume that discharges takes place uniformly around the electrodes. In practice, the grounding may mediate through a few sparks, and in such cases all the models that assume uniform ionization break down. One parameter that all models require is the critical electric field necessary for ionization of the soil. More experimental data gathered under realistic conditions are necessary to evaluate this critical electric field.

The problem of lightning protection of medium-voltage (MV) networks has been seriously reconsidered in recent years due to the proliferation of sensitive loads and the increasing demand by customers for good quality in the power supply. Overvoltages originated by lightning are indeed a major cause of flashovers on overhead power lines. These flashovers may cause permanent or short interruptions, as well as voltage dips, on the above-mentioned distribution networks. Additionally, lightning-originated surges, depending on their amplitude and energy content, can also damage the power components connected to these networks as well as electronic devices. The objective of this chapter is to provide a survey of the basic concepts and general principles applicable to the protection of MV networks against lightning-originated overvoltages, taking into account the two aspects of the problem: protection of the components connected to the line (e.g. distribution transformers) against the disruptive effect of lightning-caused surges; insulation/protection coordination in order to minimize the number of flashovers (and also voltage interruptions or voltage dips) along the distribution lines.

A campaign of measurements on some of the RAΓs rebroadcasting stations of typical design has made it possible to determine the principal characteristics of the over voltages of atmospheric origin that affect stations, as well as the places where they assume dangerous values. It thus became practicable to determine which, in principle, are the optimum precautions to be taken at stations of that type, to reduce the over voltages to tolerable values. Individual tests are, however, necessary for those stations that are particularly endangered by lightning flashes, or that are exceptional on account of the importance of the service or of the complexity of the circuitry.

This chapter is devoted to the provision of guidance on the protection against lightning-related electric sparks to structures containing explosive or highly flammable materials that can generate an explosive atmosphere. These materials can take the form of solids, liquids, gases, vapours or dusts. In this chapter, 'structures' is the term used for vessels, tanks or other containers in which these materials are contained.

Previous chapters have dealt primarily with lightning protection of buildings, power systems and equipment, and principally from the point of view of minimizing or avoiding direct or induced damage from direct or nearby lightning strikes. In this chapter, we change the focus to discuss primarily lightning protection of people through providing advance notice of the threat of lightning. Although the primary focus of this chapter is on human safety in the presence of lightning, this material also has relevance in other areas of lightning protection and avoidance. For example, even though modern aircraft are capable of withstanding a triggered lightning discharge, other hazards posed by thunderstorms are a more serious threat. Examples are the severe thunderstorm downdrafts that may be encountered by aircraft upon take-off or landing and the icing and turbulence associated with the clouds aloft. In addition, the whole class of lightning protection methods known as 'active protection' is based on shutting down sensitive systems or processes in advance of the presence of lightning.

The international lightning standards are issued by the International Electrical Commission (IEC) and lain down in the IEC 62305 standard series developed by the Technical Committee TC 81 of IEC.

In this chapter we will describe and discuss several engineering models that can be utilized either to evaluate electromagnetic fields from lightning flashes or to study the direct effects of lightning attachment to various structures including tall towers. We will start by describing the basic concepts of engineering return stroke models. This discussion will be followed by a description of various return stroke models and the equations necessary for the evaluation of electromagnetic fields using these return stroke models.