Nikola Tesla (1856-1943) is one of the biggest influences on technical development in the 20th century but he died in poverty and relative obscurity. He fully accorded with the image of the "mad scientist" and was a prolific inventor. He had a brilliant mind and progressively became more and more eccentric. Although he became obsessed with the transmission of power without wires, it was his earlier work on rejecting Direct Current electric systems in favour of Alternating Current Polyphase systems which transformed our world.
Nowadays, when the developed world is completely electrified, it's hard to think back to a time when electricity was a novelty (not quite so hard for me: in the 1950s I lived for a number of years in a house without electricity). Production and distribution systems for gas became widespread in urban areas during the 19th century but the generation and transmission of electricity was still in its infancy. Direct Current systems were universal, partly because an important use for electricity was to produce mechanical power using an electric motor. Electric motors of the time needed direct current to operate - the alternating current motor was invented by Tesla around 1883 and started to be introduced around 1888, together with his Alternating Current Polyphase transmission.
When I was young, some parts of the country still used direct current (d.c.) transmission. When it was necessary to change the voltage, a rotary converter was used where the supplied voltage would drive a d.c. motor coupled to a generator producing the required voltage. This was complex and introduced power losses. The brilliance of the alternating current (a.c.) system is that voltage can be readily changed using a transformer - a completely static device. Even a transformer will introduce some power loss as heat but this can be minimised by careful design and choice of materials. The lack of moving parts and relative simplicity makes a transformer very reliable.
Even today, high-power electricity generation relies on rotating machines. Alternators (a.c. generators)are generally spun by turbines powered by steam (obtained by burning fossil fuel or nuclear reaction) to achieve relatively high efficiencies. Alternately, gas-turbines can be used. In smaller generators, it's possible to use reciprocating engines to spin the electric generator. In hydro-electric plant, a water turbine is used to spin the generator. In the case of (highly over-sold) wind generators, a big fan spins the generator directly.
The power is moved from place to place over wires. Copper is an excellent material to use, as it has little resistance to the flow of electricity. The resistance produces heat so, to minimise power loss through heating, the wire must be as thick as possible. These days, aluminium is also used. Its performance is not as good as copper, but it's cheaper.
Here's the attraction of a.c. transmission. Heat losses due to wire resistance can be reduced by increasing the transmitted voltage. For a given power, increasing the voltage will reduce the current. Voltage can be changed quite easily, using a transformer, to a higher voltage for transmission then, using a second transformer, transformed back to a lower voltage near the point of use.
Multiple transmission lines in Germany
The developed world is now covered by a 'Grid' of transmission lines, often at high voltages of 132 thousand volts or, in the case of the 'Super Grid', 400 thousand volts. Whilst voltages up to a few thousand volts can be carried in multi-core cables where the individual conductors are insulated from one another by plastic materials, higher voltages are normally carried by bare conductors in air, since air is a pretty good insulator. The conductors are carried on pylons, suspended from ceramic or glass insulator strings.
Electricity pylon routes marching across the landscape may not be elegant but they have facilitated the high energy consumption lifestyle which many of us enjoy.
Tesla wrote a number of publications, some of which have been reprinted, such as 'Tesla's Experiments with Alternate Currents of High Potential and High Frequency'. This was originally published in 1904 by McGraw Publishing Co., New York and reprinted by Lindsay Publications in 1986 (ISBN 0-917914-39-2).
There's a small collection of pictures showing various transmission lines.
