Atmospheric electricity, power generation and overcoming the shortage
Electric current and electric shock: The flow of electrons through a conductor constitutes an electric current. One ampere of electric current is the flow of 6x1018 electrons per second. If a current of 100 milliampere i.e. 1/10th ampere flows through a human body for a period of 3 seconds, it is certainly going to be fatal. However, one can die for even a smaller dose. At 230V, 0.1A, the energy released through a body in 3 seconds is approximately 0.02 watt-hour.
Magnetism: The earth possesses a magnetic field, the strength of which varies with time and locality. The field is similar to that which would be produced by an enormously powerful magnet situated at the centre of earth and pointing approximately north and south.
For all latest news, follow The Daily Star's Google News channel. Ionosphere: In the earth's upper atmosphere free electrons arising from ionizing occur, mainly as a result of ultra-violet radiation and X-rays from the sun. The wave length of ultra-violet radiation is in the range of approximately 4x10-7 to 5x10-8 metres i.e. between visible light waves and X-rays.
Terrestrial atmospheric electricity: It is concerned with the sources of atmospheric electrification and the resulting electrical charges, fields and current in the vicinity of the earth. The earth and the ionosphere provide highly conducting boundaries to the global electrical circuit, which consists of thunderstorm and lightning, and the fair weather field.
Thunderstorm and lightning: A brilliant flash of lightning followed by a deafening roll of thunder is one of nature's most dramatic displays. It is no wonder that in ancient times people thought that thunder and lightning had super natural causes.
Today, we know that lightning is simply a series of huge electric sparks. When a large amount of static electricity builds up in a storm cloud, a giant spark appears. The lightning may jump from one storm cloud to another in the sky. The lightning we usually see jumps from the storm cloud to the earth.
Benjamin Franklin, the famous American inventor was the first person to prove in 1752 that lightning is electricity. A lightning heats the air along its path by many thousand of degrees. The heat causes the air along lightning flash to expand very quickly forming sound wave, which we hear as thunder.
How does a cloud become charged? Laboratory experiments have shown in a mixture of water and ice, that the water has a positive charge and the ice, a negative charge, when hailstones and other heavy ice particles in the cloud collide with tiny water droplets, the ice particles become negatively charged. Because of their weight they fall to the bottom of the cloud. The light particles -- the water droplets -- rise, giving the top of the cloud a strong positive charge.
Building up an electrical charge in a thunder cloud may last for more than an hour. When the top of the cloud is positively charged and the bottom of the cloud is negatively charged, there may be a voltage difference of 100,000,000 volts or 100,000 kv.
The lightning strike: When the charges in the cloud are strong enough, electrons flow from negatively charged bottom section to the positively charged top section. That is, a rapid discharge takes place, which is the lightning flash. Cloud-to-earth lightning is of prime interest.
When the first stroke nears the ground, a strong charge from the ground surges up the jagged path to cloud. It is this return stroke that we see as lightning flash. Secondary strokes move down the same path and more return strokes result. These occur within a fraction of second. The return strokes follow each other so quickly that there may be 3 to 30 or more return strokes what we see as a single flash of lightning.
Safeguards against lightning: At any one time, as many as 2000 thunder storms are occurring in various parts of the world. About 100 flashes of cloud-to-earth lightning are occurring every second. This enormous sparks of electricity can be very destructive. In the United States alone, between 100 and 200 people are killed each year by lightning. In Bangladesh we read in the newspapers every year of the deaths in villages due to lightning strike. However, there is no statistics of such deaths. Property damage is also caused by lightning strike. The principal protection for property against lightning is the lightning rod, which was invented by Banjamin Franklin. It is generally a sharp pointed rod of about 5 ft high placed on top of a house and connected using thick wires to a plate or a pipe placed 10-12 ft below the surface of earth.
Safety precaution during a thunderstorm can be, first, do not believe the old saying, "lightning never strikes twice in the same place". It can and it does. If you are out in the open, do not try to keep dry by standing under a lone tree. This can be a dangerous, because tall objects make good target for lightning strike. If you are in an open field in a village, walk back home as quickly as possible through low lands. Low places such as valleys between hills are safer than high places. During a thunderstorm walk back home following a path parallel to HT distribution lines, because these lines are protected with lightning arresters. Do not use telephone unless necessary. The safest place during a thunder storm is in the house or in a large building.
Lightning arresters: Apart from the lightning rod, three other widely used arresters are -- (i) Earth wire or ground wire on top of the transmission lines. (ii) The horn gap arresters are generally used on HT distribution lines. (iii) The thyrite arrester. The short duration high lightning voltage surges quickly discharge through this. Thyrite arresters are widely used in power stations for protection of unit transformers and generators. However, thyrite cannot stand sustained long duration over-voltages.
Fair weather field: The concept of the global electrical circuit of the earth is an electrical system powered by upward currents from thunder storms all over the earth (totaling 1500 A) reaching and flowing through the "ionosphere" about 60/70 km above the earth. The current of 1500 A returns to earth in fair-weather regions. The resistance between the ionosphere and the earth is about 200ohm, giving rise to an ionosphere potential of about 300 kv. The vertical electric field near the earth's surface is of the order of 100v/m, and the associated current density is typically several picoamperes/(metr) 2 - pico=10-12. This is the air-earth current flowing through human body all the time.
The electricity we have been considering so far is the naturally produced atmospheric electricity. The first human generated electricity or DC was obtained from the Volta's pile.
New era for electricity: In 1800 Alexandro Volta conducted his pile or battery to supply steady direct current. In 1808 Sir Humphry Davy connected a number of piles to produce strong DC. His device was called a battery, which he used to strike an arc between two carbon rods. These glowed brilliantly and thus an arc lamp supplied brilliant light. The electric generator is based on the discovery of electromagnetic induction by Michael Faradey in 1831. The electric incandescent light bulb was invented by Edison in October 1879. In 1882, Edison put into operation the first DC power station. The decade from 1880 to 1890 saw some important events unfold. Three were especially notable. The AC generator was developed by Westinghouse company. In 1885, the high voltage transformer was developed for transmission of power over long distance. In 1888 Nicola Tesla invented 3-phase induction motors and 3-phase synchronous motors.
In 1890's and afterwards many power stations were built around the world. These power stations were later interconnected to form power grids. In Bangladesh we have now have the East Grid and the West Grid, which are inter-connected by a 230 KV inter-connector.
The invention of fluorescent tubes etc. made available to people almost the daytime light at night. The introduction of rugged induction motors in factories has relieved the mankind of huge amount of manual labour. The development of high voltage transformers such as the 11/132kv, 3-phase, 50 hz, has made possible transmission of bulk power over a long distance at a minimum line loss.
Conclusion: Now, despite so much generation of electricity, we are still facing a power shortage. Because the demand for electricity is increasing day by day. The total power generation falls short of the total requirement. And in case of Bangladesh, it is by a wide margin. Therefore, we shall have to increase our conventional power generation as much as possible with our own resources as well as outside assistance.
At a time, when we are trying options like wind energy, solar energy, tidal energy as well as nuclear energy to meet our present as well as future requirement, can we not also explore possibility of exploiting atmospheric electricity with the advancement of science, to overcome the shortage?
Electric energy has improved the quality of life of mankind so much so that the per capita consumption of electricity is now considered as a measure of standard of living of a people. Electricity has become now perhaps, as essential as water for the mankind. There is enormous amount of electricity in the atmosphere. If we can exploit even a very small fraction of it, we shall be simply affluent in powers' understandably. But can we do it?