Lightning: Physics and Effects

Lightning Physics and Lightning Protection

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Human-Wildlife Interactions. Their transverse size ranges from a fraction of millimeters at ground pressure to tens of meters at sprite altitudes. They can propagate as fast as one fifth of the speed of light. Studying streamers experimentally is challenging because they are extremely transient. They however hold the key to understanding lightning initiation and propagation, radio emissions from electrical discharges, X-ray production by lightning, dynamics of jets and sprites, etc.

Lightning is dangerous, killing or injuring many people each year. However, we don't need to be afraid of lightning if we follow some common sense rules:. Skip to main content. Space Science Center. Enter your keywords. Lightning Physics. Who We Are.

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Current Projects. Mapping and imaging lightning using optical and radio instruments Lightning emits electromagnetic waves in a broad range of timescales nanoseconds to seconds and wavelengths nanometers to kilometers , giving it an electromagnetic spectrum that ranges from radio to visible light and up to x-rays and gamma rays, all of which can be observed using specialized instrumentation. Observing X-rays and Gamma-rays associated with thunderstorms and lightning Gamma-ray glows are emissions of gamma rays that last from seconds to minutes and are produced by runaway electrons in high-field regions of thunderclouds.

Theoretical and modeling studies of energetic radiation associated with thunderstorms and lightning Thunderstorms are fascinating places. Understanding the physical mechanisms of transient luminous events Transient luminous events are massive electrical discharges occurring above thunderstorms, including jets, gigantic jets, sprites, halos and elves. Modeling streamer discharges Streamer discharges are plasma filaments that appear in many electrical discharges in air such as laboratory sparks, lightning, sprites, and jets.

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Lightning Facts. Lightning strikes the Earth about 4 million times every day. The lightning capital of the world is Lake Maracaibo in northwestern Venezuela, where lighting strikes the lake about seven times per minute on average for active days per year. Every year lightning kills about people in the US, more than hurricanes or tornadoes. Lightning has been documented traveling over km about miles , or about the width of Oklahoma. The highest peak current in lightning is estimated to be about kA, whereas a typical lightning strike carries about 25 kA.

Even for typical lightning, that's the same current draw as 2, amp microwave ovens! Some lightning subprocesses are so energetic that they are confused with nuclear bombs detonations. The total energy released during a thunderstorm is about hundreds of trillions of Joule, which rivals the atomic bomb dropped on Hiroshima about one trillion Joule. About one thousand thunderstorms are active across the globe mainly in the tropics at any given time.

A typical thunderstorm has two opposing charge regions, which are continually charged by cloud processes and discharged by lightning. At any given time, the thunderstorm charge regions carry about C charge, while lightning discharges about 10 C at a time. Lightning Safety. Direct stroke overvoltage represents a hazardous rise of voltage when a lightning current impulse propagates across the construction elements. We shall analyse this very dangerous effect of lightning with reference to a power transmission line, because engineers first encountered the phenomenon of overvoltage in such lines.

Moreover, the problem of electric insulation for a transmission line can be stated most clearly. Above the wire, there may be a lightning conductor attached right to the tower.

Lightning hazards 15 Figure 1. Lightning current as an overvoltage source on a power transmission line during a stroke at the power wire a and a grounded tower b. A rigorous solution to this problem is given later in this book.

Here, we should only like to explain the nature of overvoltages phenomenologically. Suppose at first that the lightning conductor has proved unreliable, and a discharge has struck the wire figure 1.

The tower potential will practically remain unchanged and equal to zero, so the insulation overvoltage will be close to the calculated value of U,. This will be clear if we compare U , with the operating line voltage which does not exceed kV even in high power lines but normally is kV. In reality, the distance to the line ends I is as large as many dozens of kilometres.

This time is much longer than the strong current duration in the return stroke loops. For this reason, reflected waves, which become strongly attenuated, do not normally have enough time to interfere with the process so that the overvoltage acts as long as a lightning current impulse. Practically, any lightning stroke at a wire represents a real hazard: the insulation will be broken down to produce short-circuiting. The power line in that case must be disconnected. Suppose now that lightning has struck a tower. More often, this is actually not a tower but rather an overhead grounded wire connected to it.

Let us take point A at the height of the insulator string connection. As a result, the overvoltage U may prove to be the sum of the three terms in equation 1. For this reason, this component makes the principal contribution to the insulation flashover. The emergency situation just described is not as bad as a direct stroke at a power wire when the same lightning current can induce an order of magnitude higher voltage. The insulation of a ultrahigh voltage line can withstand short overvoltages up to kV and seldom suffers from lightning strokes at a tower or a lightning protection wire.

To produce a harmful effect, the lightning current must be times the average value.

Lightning Physics and Effects

Quite different is the effect of a direct stroke at a power network with an operating voltage of 35 kV and lower. The insulation system will suffer equally from a stroke at a power wire or a tower. It is no use protecting such a line with grounded wire. Insulation flashover due to the tower potential rise is referred to as reverse flashover.

This name does not imply the definite direction of the discharge development but only indicates the direction from which the potential rises, i. Lightning hazards 17 The above illustration of overvoltages on the line transmission insulation demonstrates, to some extent, a variety of mechanisms of direct lightning current effects. In actual reality, such mechanisms are much more diverse. It is important to remember that in modern technologies, overvoltages are not always measured in hundreds of kilovolts, as for high-voltage transmission lines.

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