Overhead Transmission Lines |
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The first transmission of electrical impulses over an extended distance was demonstrated on July 14, 1729 by the physicist stephen Gay, in order to show that one can transfer electricity by that method. The demonstration used damp hemp cords suspended by silk threads.
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The electric power from the generating stations, which are held in regions where coal or water power is readily available, is supplied through long-distance transmission lines to every consumer. These are usually of the overhead type consisting of conductors suspended from lattice steel towers. Long-distance power transmission with direct current is in fact being tried out experimentally in various countries.
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Let us
consider simple example, a 220 kilowatt generator supplies
a current of 1000 A at 220V to the primary circuit of a high-tension
transformer which increases the voltage a thousandfold and
whose 220 kilowatt output is transmitted through a long-distance
power line as a current of 1A at 22,000V. Before the electric
power is supplied to the consumer, its voltage is transformed
down in the ratio of 1000 to 1, so that a current of 1000A
at 220V is again obtained. In actual practice the high tension
of 220,000 V is usually first transformed down to 20,000 or
6000V as an intermediate stage, which is used for local distribution
lines, the final step-down of the voltage to 220 V1 being
performed in a second transformation stage at or near the
consumer’s premises.
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Since
the resistance of a power line to alternating current is higher
than its resistance to direct current, the use of alternating
current involves additional losses. Such losses could be avoided
by using high-tension direct current, but this demands for
dependable high-duty rectifier equipment. The high-tension
power transmission lines of the various generating stations
are interconnected in a network known as the grip. A system
of this kind, of course, requires elaborate switchgear. High-tension
switchgear and transformer equipment is very often installed
in the open air. |
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Fig.3 we can understand how the distribution of electricity
by means of transmission lines and transformers from the power
stations to the individual consumers.
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