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Lightning rod

A lightning rod or lightning rod is a metal rod or metal object mounted on top of a building, electrically bonded using an electrical conductor to communicate with ground or “earth” through a electrode, designed to protect the building in the event of a lightning strike. Lightning will strike a building target and will hit a lightning rod and then be transmitted to the ground via conductors, rather than through a building, where it could start a fire or cause an electric shock. . This is a very useful tool for humans, which can help us reduce the risk from lightning.

Born, release

Lắp Đặt Cột Thu Lôi Chống Sét – Quang Hưng

Lightning poles were invented in 1752 by American scientist Benjamin Franklin. At that time, he did the very famous atmospheric electricity experiment. He tied a kite to a pole, where he also tied a key. Then the storm came, the rain began to pour down, wet the string of the kite. Lightning at that time was also very scary, hitting the kite. Due to being wet, the kite is able to conduct electricity. Franklin touched the key and felt the electric shock very scary. He then used a Leyden bottle (the original form of a capacitor) to charge it and built up a large amount of it. Benjamin Franklin performed this experiment with his son William Franklin. Luckily for Benjamin, a year later, German-Russian physicist Georg Wilhelm Richmann was struck by lightning while performing the same experiment.

Thanks to the above experiment, Benjamin Franklin boldly used the first lightning rod in Philadelphia. After several days of storms, his house, where the lightning rod was located, remained unaffected. Seeing this, the people of Philadelphia also followed suit. Gradually, lightning rods became popular

Benjamin Franklin later showed the usefulness of the lightning rod in The Poor Richard Almanach.

A lightning rod consists of a long metal rod that connects the top of a structure to the ground. At the top, the lightning rod has a pointed tip that can focus the lightning. Later, to increase the level of safety, people added a porcelain outer shell to prevent the possible effects of lightning on the structures.
Working principle

Lightning rods only work during a thunderstorm. At that time, the clouds were negatively charged and the ground was positively charged due to the electrostatic response. There is a huge electric potential difference between the clouds and the ground. Then, lightning is formed. High points in the ground like spikes are where the electric field is strongest (because the reactive charge is distributed mainly there). Once formed, the step or lead channel of lightning will move down from the cloud and open the way for the lightning to strike the ground. The step channel is attracted by high elevations, so lightning strikes those places the most (that’s why when there is intense thunder, we should not stand on high ground or take shelter under a tree, but should lie on the ground) . At that time, the point of the lightning rod will come into play. Due to its height and sharp point, the lightning rod will have a large electric field, so lightning will strike it. After being struck by lightning, it conducts that current to the ground. That current will be electrically neutral, because at this time the earth has a positive charge, and the current in the lightning rod carries a negative charge.

The protection scope of the lightning system is the space around the lightning system, which encloses and protects in terms of lightning protection for the building and the people inside, which is determined experimentally.

The protection coverage of the lightning rod depends on the height of the lightning rod (the height of the pinnacle). The higher the lightning rod, the greater the protection range.
System of two equal height lightning rods combined with protection

According to TCXD 46:1984, when two lightning rods are of equal height, spaced a sufficiently small distance from each other (smaller than the limit defined below), but may still be larger than the diameter of the circle in the plane of protection. At the base of the column (equal to 3H), in addition to the conical protection areas around each column (like an independent column), in the middle of about 2 columns the protection range is also expanded to form a combined protection area. is the space below a quadratic surface in the form of a saddle. The birth line on the vertical plane passes through the axis connecting the 2 columns, of this saddle curvature is taken as a circular arc whose center lies on the orthogonal of the distance between the two columns on the plan, and lies at the height of 4H (4 times the height of lightning rod). According to standard TCXD 46:1984, the birth line on the vertical plane passes through the axis connecting the 2 columns, of this hyperbolic paraboloid surface is taken as an arc of radius R, centered on the perpendicular bisector of the distance. two columns on the ground A, and located at 4H (4 times the height of the lightning rod). The lowest point of this birth line, located at the midpoint of the distance 2 columns on plane A, has the cough altitude determined as:

ho=4H – ((0.25A2+9H2)1/2)={\displaystyle 4H-{\sqrt {(0.25A^{2}+9H^{2})}}}{\displaystyle 4H-{ \sqrt {(0.25A^{2}+9H^{2})}}}

Where A is the distance between 2 columns on the plan. The larger the distance A, the smaller it is (when ho=0, the 2 columns return to the independent case and no longer form a combined system). Therefore, the condition for two equal columns to be protected is:


TCXDVN standard 46:2007 takes the upper birth line as a broken straight line, joined by a protection angle of 60o from the top of each column, about 2 columns inside. Therefore, tg60o=1,732=A/(2(Hc – ho)), the condition for two equal columns to combine protection according to 2007 standard, is:


(and if the height of the lightning rod is taken according to TCXDVN 46:2007 standard, one and a half times the height of the pole according to the 1984 standard, (Hc=1.5H), then: A≤5,196H=3,464Hc).

Although the scope of internal combined protection between two columns is limited by the quadratic face, in the lightning protection standards 1984 and 2007 all consider the approximate intersection of this curved surface with the column foot elevation as the line. symmetrically folded lines through the axis connecting the two columns and through the perpendicular bisector of this axis. These lines form the combined protection ground area at the base of the lightning rod, extending and connecting the two circular areas of the protection area at the foot of each column, in the space between the two columns. The equations of the boundary lines are defined as:
bx=1.5(H – 2(H – cough)x/A); With 0≤x≤A/2, bx is the radius (or width) of the combined protection range between the two columns at the base height on each side of the 2-column axis (bx at the base of the column is 1, 5H, and at the midpoint, the distance between the two legs of the column is 1.5ho).

The latest lightning protection standard is TCVN 9385-2012 which inherits TCXDVN 46:2007 and adds more stringent conditions for applying protection zones and protection angles to TCXDVN 46:2007 standard.
System of two different high lightning rods combined with protection

Each individual lightning rod has an independent protection range like a single pole, so the outer space is about 2 columns about each column, the protection range of the system is the same as the case of each independent standing pole.

Lightning wire and net system

Lightning rods are very effective in preventing and minimizing damage caused by lightning. However, because lightning is an electric current up to millions of volts, lightning rods cannot completely block the fear of lightning. Therefore, to be as safe as possible, we need to implement safety methods such as:

Unplug all the plugs when the storm comes.

Do not use laptop, phone or tablet when lightning comes

Avoid metal or damp objects that can be harmful to yourself and your loved ones, such as showerheads.


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