The relationship between lightning rod principle and capacitor

Lightning rod definition:

Lightning rods, also known as lightning rods, are devices used to protect buildings, tall trees, etc. from lightning strikes. Install a lightning receptor on the top of the protected object and connect it to the underground grounding net with a wire that meets the specifications. The lightning rod specifications must comply with the GB standard, and the lightning rod height specifications required for each lightning protection category are different.

It distorts the ground electric field when the thundercloud discharges close to the ground. At the top of the lightning rod, a space for local electric field concentration is formed to influence the development direction of the lightning pilot discharge, guide the lightning discharge to the lightning rod, and then introduce the lightning current into the earth through the grounding down conductor and the grounding device, thereby protecting the protected object from lightning strikes. .

Reasons for lightning strikes to destroy buildings:

If lightning rods are not installed on tall buildings, then in thunderstorms, charged clouds and tall buildings form a capacitor. To ionize the air, the electric field strength needs to reach a certain value. According to the distance between the charged cloud layer and the tall building, the potential difference between the two must be large enough. The roof surface of tall buildings is the facing area of the capacitor, which is much larger than that of the lightning rod. The capacitance of this capacitor is also very large. When it reaches a very large level, the potential difference between the cloud layer and the building can be achieved. To the extent that the capacitor can be discharged, the electric field between the cloud and the floor converges on the huge electric field energy, which is instantly converted into electrical energy, which can damage the building.

Lightning rod and capacitor contact:

For a charged conductor, after electrostatic equilibrium, the charge is distributed on the outer surface of the conductor, and the sharper the place, the denser the charge, the stronger the electric field around the tip, and thus the discharge is easy. The lightning rod is made by this principle, and the building is protected from lightning strikes by lightning discharge in thunderstorms.

Compared with tall buildings, the lightning rod has a small area facing the capacitor (that is, the needle tip is so large), so the capacitance of the capacitor is also small. According to the above principle, the accumulation of less charge on the lightning rod can make the cloud layer The potential difference between the lightning rod and the lightning rod reaches a level at which the air can be ionized. At this time, since the amount of electric charge is small, the electric field energy is also small, and the lightning rod is not damaged after being converted into electric energy during discharging. At the same time, since the lightning rods are directly connected to the ground through the thick wires, the current does not pass through the building when flowing, so the building is absolutely safe.

In thunderstorms, when there is a charged cloud over a tall building, the lightning rod and the top of the tall building are all sensitive to a large amount of charge. Because the lightning rod needle is pointed, the tip of the conductor always accumulates the most charge when it is electrostatically induced. In this way, the lightning rod collects most of the charge. The lightning rods in turn form a capacitor with these charged clouds. Because of its sharpness, the two plates of this capacitor have a small opposing area and a small capacitance, that is, it can hold a small amount of charge. And it accumulates most of the charge, so when there is more charge on the cloud, the air between the lightning rod and the cloud layer is easily broken down and becomes a conductor. In this way, the charged cloud layer forms a path with the lightning rod, and the lightning rod is grounded again. The lightning rod can push the charge on the cloud to the ground, making it dangerous to high-rise buildings and ensuring its safety.

When the lightning rod is intercepted by lightning, the lightning body is connected to the flash, and the lightning waveform processing device uses a gap of 3 mm between the outer casing and the grounding rod to form a coupling capacitor, and the outer casing is grounded through an inductor coil (center grounding rod). When the pilot approaches the lightning receptor, the inductor is in an open state due to the extremely high frequency, and the capacitor exhibits a short-circuit characteristic to the high frequency. Therefore, under the action of the coupling capacitor, the electric field strength of the surface of the lightning receptor increases rapidly until the avalanche process is triggered, so that in an instant The lightning current is discharged into the ground, so as to effectively achieve the purpose of lightning protection and safety.