Lightning strike protection

The incorporation of nanocarbons in hierarchical composites can also result in large improvements in their electrical conductivity, and to a lesser extent in their thermal conductivity. For ceramic fibers both in-plane and out-of-plane electrical conductivities are increased by several orders of magnitude [41], whereas for CF the improvement is significant only perpendicular to the fiber direction due to the already high conductivity of the fiber itself [46]. The out-of-plane electrical conductivity of CNT/CF/epoxy composites is approaching the requirements for lightning strike protection in aerospace composites, thought to be around 1 10 S/m. Yet further improvements are required, as well as the evaluation of other composite properties relevant for this application, such as maximum current density and thermal conductivity. 

M.N. Islam, M.R. Rahman, M.M. Haque, and M.M. Huque, Carbon nanofiber paper for lightning strike protection of composite materials. Compos. A 41,192-198 (2010). 

For aircraft, nonmetallic repairs must incorporate lightning strike protection. 

Gou, J., Tang, Y., Liang, F., Zhao, Z., Firsich, D., Fielding, J., 2010a. Carbon nanoliber paper for lightning strike protection of composite materials. Composites Part B Engineering 41, 192-198. 

The primary advantages of mechanical scales are that they are relatively inexpensive in smaller capacities they do not need electrical power, enhancing thein portabiUty and they do not need to be protected from power line transients or lightning strikes. 

When equipment is exposed to direct lightning strikes Equipment connected directly to an overhead line, or even through a transformer, will fall into this category. Select the highest value of BIL and even then a surge protection will become necessary for critical installations. 

When equipment is shielded This is when it is installed indoors, like a generator or motor. Now it may be subject to only attenuated surges. One may now select a lower value of BIL. In most cases surge protection may not be essential for direct lightning strikes. 

These are only basic guidelines. It is difficult to define exposed or shielded equipment accurately. Equipment installed indoors may never be subject to lightning strikes or their transferences, but may be exposed to severe switching surges and require surge protection as for an exposed installation. There is no readymade formula by... 

A fault current-limiter is a component which protects power transmission and distribution systems from surges caused by, for example, a lightning strike, fulfilling a function similar to that of a varistor (see Section 4.3.1). The limiter should be capable of reducing the fault current to a fraction of its peak value in less than a cycle. Because for this application the requirement is for low Jc, fault current limiters are already a commercial product. In the case of the lead shown in Fig. 4.58(b) the fault current is limited to a safe value within 5 ms of the arrival of the current spike . 

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