The lightning is most dangerous when a person is caught in a large open area or a forest; this is a well-known fact. It is not really dangerous to be in a large modern city during a severe thunderstorm. Lightning arresters are installed everywhere and tall buildings "take" the force of nature. But it is not that easy, and, in fact, a modern metropolis is vulnerable to lightnings very much.
Pulse Noise
The modern equipment contains integrated control computers very often. Under the lightning exposure, the pulse noise appears, which usually penetrates the apartments through the power wires. It leads rarely to the control computer failure. A failure in the software occurs much more often. Then, the device may only be returned to the normal state by pressing the reset button, and if there is no such button, then power off for some time and then power on.
This is a very common lightning effect. Many of us have dealt with the situation when during the storm, the complex home equipment halts. This can happen not only to the Wi-Fi access point but also to, e.g., a washing machine. And this phenomenon is observed even when the lightning strikes somewhere far away, e.g. somewhere outside the city, but there is a path of distribution of the powerful pulse noise.
But temporary stop of washing machine is not as important as the halt of the computer operating an elevator. There may be phone communication, Internet access, or cable TV failures, since a personal visit of the servicing personnel to the object is often required to restart the respective equipment completely.
An example of the filter suppressing the interference in the mains
The above-mentioned problems are solved in two ways. First, in the power line, special filters inhibiting the pulse noise are installed. We have to distinguish the systems preventing the pulse overvoltage and the systems inhibiting the pulse noise; they are based on different operating principles. Second, control computers provide for the possibility of remote reset without the servicing personnel or automatic reset in case of failure.
Emergencies Resulting in the Equipment Failure
The pulse overvoltage may be associated with the lightning strike to the power cable, with the interference to the power wires from the metal elements of the building, into which the lightning got, as well as with switching in the power grids due to the protection triggering. If we continue parallels with the elevator, we can say that, in this case, there is a possibility of entire failure of the control computer instead of its halt. It means that not only the elevator attendant visit is required, but the entire house will live without the elevator for several days, since new operating equipment will have to be ordered, installed, and set up. Certainly, the modern electronic control devices contain the protection against the pulse overvoltage. But, first, it is often that when the manufacturer makes its choice, he effect a compromise to reduce the product price. And, second, the integrated protection systems are usually intended for the proper installation of the control device, and the lightning protection conforms to the accepted regulatory documents. But the practice may be different. High price of equipment and costs associated with its shutdown, make people think of the installation of additional protection means and proper arrangement of lightning protection and earthing.
The most dangerous accident is a null wire burning-off. It leads to the long-term exposure of high voltage (about 400 kV) on the equipment installed in the house. Moreover, the appearance of the dangerous voltage is possible in the metal parts of the equipment, connected to the earthed wire if the full earthing is replaced with the neutral wire earthing (such as, e.g., in the old houses). And all possible mains power filters as well as major part of the devices protecting against the pulse overvoltage cannot protect the equipment and people against the long-term exposure of high voltage in this situation. The null wire burning-off is a common reason of fire in residential houses.
One of the most common reasons for the null wire burning-off is an improper arrangement of earthing and lightning protection.
Power Failures
Surely, we can live for some time without electricity, but today, the power supply is being associated with increasingly more essential things. It is annoying when the power is shut down accidentally, which happens upon the lightning strike.
The discharger installed in the power line to protect against the lightning strikes
The most common instance of the power supply failure that is especially often in the private houses are false RCD or differential automatic breaker triggering. If the building does not have an earthing circuit or it is incorrectly installed, the current difference in the power wires may occur upon the lightning strike near the buildings. The protection system perceives such event as flowing of the dangerous current through the human body and, therefore, shuts down the power. One of the struggle means is installing an earthing circuit in the building according to all rules. You can read more, e.g. here.
Air power lines are often used in the cities. Surely, the lightning may strike them. Then, the fuses will trigger in the substation. But if we are talking about high voltage power lines, it is not that easy as in a household electrical box: you cannot restore the power supply using a protective automation device only. Specialists should evaluate the situation in the field, if it is possible to start the power supply and then activate a pretty large apparatus closing contacts through which the current flows to the consumers.
Direct Lightning Strike Consequences
In a large city, a person may get the direct lightning strike primarily in parks as well as in deserted wastelands. The presence of the deserted wastelands that are not fenced in any way in the city is not the issue of lightning protection but rather of the urban management quality. But in the park, during the storm, any city resident may be, even though he/she has no tendency for extreme adventures.
Measures to provide lightning protection are required for large amusement rides
Unfortunately, the Russian lightning protection standards for parks is not specified separately. But the qualified designer may organize the lightning protection for the park using effective standards, since the park may be classified as well as the other objects to be protected against lightnings. A very valuable experience of this design is provided here.
Moreover, a person getting into zone of the step voltage flowing from the improperly arranged earthing. One option is the installation of the earthing device in the location where people often walk. This is possible even in a large city. We can struggle with it through the compliance with the rules as well as with the use of the quality earthing systems with significant service lives, the parameters of which change weakly over time.
Note that deaths and injuries to people as a result of improper earthing or its absence are punished according to the Criminal Code of the Russian Federation, article "Tort of Negligence".
Conclusions
Modern urban economy is increasingly more saturated with the digital technologies. This fact makes it more susceptible to the pulse noise and failures in the equipment. Therefore, the proper earthing system provides safety not only as a means of protection against the power impact but as a means of protection against interference.
In the modern cities, increasingly more attention is being paid to the recreational zones, in particular, parks. But when you provide an European-type design and arrange fancy events in the parks, do not forget about the protection of people against the lightning strike.
And the regulatory base for the lightning protection in both directions is far behind the life. Surely, it does not mean that we have to refuse the effective standards. They contain the results of long-term research, and the lightning physics has not changed since then. But the use of the standards developed many years ago requires a particular experience now. Therefore, to design the lightning protection system in a large city, it is better to contact the organization that has accumulated a large amount of experience and employed qualified specialists, namely Zandz.com Technical Center.
Related Articles:
Lightning protection of residential and public buildings - answers to frequently asked questions in the design
Shopping center lightning protection project
The Evolution of Lightning Protection Regulations
Protecting Fire Alarm Systems against Direct and Indirect Lightning Exposure
Five Most Dangerous Effects of Lightning
