Electrotechnics: Basics


Potential of electric field of the Earth's atmosphere

Natural electric field of the Earth

Celestial body called Earth, has an electric charge, which creates a natural electric field of the Earth. One of the characteristics electric field - this potential, and the electric field of the Earth is also characterized potential. You can also say that in addition to the natural electric field has a natural and direct current (DC) of the planet Earth. The gradient of the potential land is distributed from the surface to the ionosphere. During good weather for static electric field of the atmosphere is about 150 volts per meter (V/m) near the Earth surface, but this value decreases exponentially with increase in height of up to 1 V/m or less (at a height of 30 km). The reason for reducing a gradient including the increase in the conductivity of the atmosphere.

Distribution of potential over the Earth

If you wear clothes from a good insulator, is an excellent dielectric, such as nylon clothing and shoes use only rubber, it does not have any clothes on the surface of metal objects, then between the ground and the top of the head is possible to measure the potential difference. Since each meter is 150 volts, then the growth of 170 cm on the top surface is relatively potential difference 1,7x150 = 255 volts. If the head put on a metal pan, then it will hold a surface charge. The reason for the charge collection in the clothes of nylon is a good insulator and rubber shoes. Grounding i.e. conductive contact with the ground is absent. In order not to accumulate on electric charges must be grounded. Likewise, objects, things, buildings and facilities, especially high-rise, are able to accumulate atmospheric electricity. This can lead to unpleasant consequences, since any accumulated charge can cause an electric current and spark breakdown in gas. Such electrostatic discharges can damage the electronics and cause fires, especially flammable substances.

In order not to save the charges of atmospheric electricity is sufficient to connect the upper point to the lower (land), an electrical conductor, and if the area is large, the grounding is performed in a cell circuit, but, in fact, use what is called "Faraday cage".

Characteristics of atmospheric electricity

The earth is negatively charged, and a charge equal to 500,000 Coulomb electric charge. Potential difference is the value of the 300,000 volt (300 kV), if we consider the voltage between the positively charged ionosphere and the Earth's surface. There is also a constant current of electricity, of the order of 1350 amperes (A), and the resistance of Earth's atmosphere is about 220 ohms. This gives an output power of about 400 megawatts (MW), which is regenerated by solar activity. This affects the capacity of the earth's ionosphere and to lower layers, which causes a thunderstorm. The electrical energy that is stored and is stored in the earth's atmosphere is about 150 gigajoules (GJ). The system of "Earth-ionosphere" acts as a giant capacitor whose capacitance is 1.8 Farad. Given the huge size of the surface area of the Earth, 1 square meter of surface accounts for only 1 nC electric charge.

Electrosphere of Earth

Electrosphere of Earth extends from sea level to an altitude of about 60 km. In the upper layers, where a lot of free ions and this part of the sphere is called the ionosphere, maximum conductivity, as there are free charge carriers. Potential of ionospheric substantially aligned, as this area is basically considered a conductor of electricity, there exist currents in gases and transfer current. The source of free ions are radioactive of the Sun. The flow of charged particles coming from the Sun and from space "knock" electrons from the gas molecules, which leads to ionization. The higher the sea surface, the lower the conductivity of the atmosphere. At the sea surface conductivity of the air is about 10-14 Siemens/m (S/m), but it is growing rapidly with increasing altitude, and at an altitude of 35 km is already 10-11 cm/m. At this altitude, the air density is only 1% from that of the surface of the sea. The higher the level of the sea more and more non-uniform conductivity of the atmosphere, because it affects Earth's magnetic field and the flow of photons from the Sun. This means that the conductivity Electrosphere than 35 km from the sea level is not uniform, depending on time of day (photon flux) and by geographical location (Earth's magnetic field).

Electrosphere of Earth

To electrical breakdown occurred between two plane parallel electrodes (spaced 1 meter), which are located at the sea surface, when dry air is required field intensity of 3000 kV/m. If these electrodes are raised to a height of 10 km above sea level, it would take only 3% of such intensity that is enough to 90 kV/m. If the electrodes pull together so that the distance therebetween is 1 mm, then the need to 1000 times less for the breakdown voltage, that is 3 kV (sea level) and 9 (at 10 km).

The natural value of the electric field of the Earth at its surface (sea level) is about 150 V/m, which is much less than the values required for the breakdown between the electrodes even in the range of 1 mm (requires 3 kV/m).

What generates the potential of the electric field of the Earth?

As already mentioned above, the Earth is a capacitor, one plate of which the surface of Earth and the other lining supercapacitor - a region of the ionosphere. On the Earth's surface charge is negative, and the ionosphere - a positive. Also, as the surface of of Earth, the ionosphere is also a conductor, and a layer of the atmosphere between them is a heterogeneous gaseous dielectric. The positive charge of the ionosphere is formed by cosmic radiation, but what charges the surface of of Earth negative charge?

For clarity, it is necessary to remember how charged the normal electrical capacitor. It includes an electrical circuit to a power supply, and it is charged to the maximum voltage across the plates. For such a of capacitor as the Earth, something like this happens. Likewise, should turn on a source, an electric current flows, and the plates are formed unlike charges. Remember the lightning, which are usually accompanied by thunderstorms. These lightning is precisely the electrical circuit, which charges the Earth.

That lightning, beating the surface of Earth are the source that charges the surface of of Earth negative charge. Lightning has a current of about 1800 amps, and the number of lightning per day more than 300. thundercloud has polarity. The upper part of a height of approximately 6-7 km at an air temperature of about -20°C is positively charged and the lower part at a height of 3-4 km at temperatures from 0° to -10°C is negative. Charge the lower part of thunderstorm cloud is enough to create a potential difference with the surface of Earth in the 20-100 million volts. Lightning bolt usually about 20-30 Coulomb of electricity. Lightning hit discharges between clouds and between the clouds and the Earth's surface. For each charge it takes about 5 seconds, so with such a precedence constraint can come lightning, but that does not mean that 5 seconds will happen discharge.

Lightnings

Atmospheric discharge in a lightning bolt has a rather complicated structure. In any case - the phenomenon of the electric current in the gases, which occurs when the conditions necessary for the breakdown of the gas, i.e. ionization of air molecules. The most curious thing that the Earth's atmosphere acts as a continuous dynamo that charges the surface of Earth is negative. Each lightning has provided the Earth's surface is devoid of negative charges, which provides the required potential difference for the discharge (gas ionization).

Lightnings

Once the lightning strikes the ground, the negative charge flows to the surface, but after that the lower part of the thundercloud is discharged and its potential changes, it becomes positive. Further, the reverse current and excess charge, got on the Earth's surface moves up, charging thundercloud again. The process can be repeated again, but with smaller values of voltage and current. This happens as long as the conditions exist for the ionization of gases required potential difference and an excess of negative electric charge.

Summing up it can be said that the lightning strikes in steps, thereby creating an electrical circuit through which current flows in gases, alternating in direction. Each recharge lightning lasts about 5 seconds and shoots only when the necessary conditions exist this (breakdown voltage and ionized gases). Voltage between the beginning and the end of the lightning may be about 100 million volts, and the average current of about 1,800 amperes. The current peak reaches more than 10,000 amperes and the charge is equal to 20-30 Coulomb electricity.

Date: 01.31.2016

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© Valentin Grigoryev


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