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Cloud Electrification and Lightning Questions and Answers

101.

State whether the following is true or false.
Lightning can be initiated upward from very tall structures.

Answer: A

Correct answer: True

From structures above about 100 metres - tall masts, skyscrapers, wind turbines - the field enhancement at the tip is enough to launch an upward leader towards the cloud, and such upward flashes dominate the strike statistics of very tall objects. They differ from downward flashes in their current waveform, often carrying a long continuing current rather than a large peak, which matters for the protection design.

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102.

The proportion of upward initiated flashes rises with structure height because

Answer: B

A tall grounded conductor concentrates the ambient field enough to launch its own leader. Above about a hundred metres upward flashes become an appreciable fraction. Very tall structures are struck almost exclusively upward.

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103.

All of the following influence how often a structure is struck EXCEPT

Answer: C

Colour has no bearing on the electrical behaviour of the structure. The other three are the factors used in standard risk assessment. Geometry and regional climatology together set the risk. Cladding colour has no electrical significance.

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104.

Lightning risk assessment for a structure combines

Answer: D

The collection area grows with height and accounts for flashes that would otherwise have struck nearby. Multiplying by the regional flash density gives an expected strike frequency. The result feeds directly into protection design.

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105.

Consider the following statements about lightning protection standards.
1. Risk depends on local flash density and structure geometry.
2. A protection system provides a preferred path to earth.
3. A protection system stops lightning from occurring.

Answer: A

The first two are correct and underlie the standards. The third misstates the purpose, since no system prevents a discharge that the atmosphere has already initiated. Protection manages the current rather than the event.

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106.

Compared with the first return stroke, subsequent strokes typically have

Answer: B

The channel is already conditioned, so the dart leader and its stroke behave differently. The faster rise time makes subsequent strokes significant for electromagnetic coupling. Induced voltages depend on the rate of change of current.

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107.

Assertion (A): Subsequent return strokes matter for induced voltages despite their lower peak current.
Reason (R): Their faster current rise time produces a larger rate of change of the field.

Answer: C

Both are true and the reason gives the reason, and induced effects depend on the derivative rather than the peak. Surge protection design must account for both stroke types. First and subsequent strokes stress equipment differently.

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108.

Lightning induced surges on power lines arise chiefly from

Answer: D

Correct answer: electromagnetic coupling from a nearby strike

Direct strikes to a line are comparatively rare; most lightning-related surges are induced by the rapidly changing electromagnetic field of a stroke to ground nearby, which couples into the conductors and drives a travelling wave along them. Because induced surges are far more numerous than direct ones, distribution line protection is designed around them, with shield wires, arresters and good earthing.

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109.

State whether the following is true or false.
Most lightning damage to electrical equipment comes from nearby rather than direct strikes.

Answer: A

Induced surges from nearby flashes are far more frequent than direct hits. Surge protective devices are specified with this in mind. Coordination of protection levels matters more than raw rating. Most damage is induced rather than direct.

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110.

Three of the following are used to detect lightning. Which is the odd one out?

Answer: B

A rain gauge measures precipitation and has no electrical sensitivity. The other three are all established lightning detection techniques. Each senses a different signature of the discharge. A rain gauge senses none of them at all.

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