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Part 18 - Electricity

The Leclanchè cell (the dry battery), invented in 1866, used rods of carbon and zinc immersed in a solution of ammonium chloride. It was superior to the original voltaic cells but still suffered the problem of a falling voltage as the rods and solution degraded. The growing telegraph industry's need for a more reliable cell with a constant output were met by a cell invented by J.F.Daniell in 1836 and improved by J.C.Fuller in 1853. This used copper and zinc plates (electrodes) each immersed in a different solution (electrolytes) of copper sulphate and zinc sulphate. This battery was used until the 1870's when it was replaced by the chromic acid battery.

R.L.G. Planté demonstrated his rechargeable storage battery in 1878. It used large lead plates immersed in sulphuric acid. When charged from a supply of electricity, the positive plates became coated with lead peroxide which was depleted as the battery was discharged.

The first commercial electric generator (invented by H.Pixii in France) was demonstrated in 1831. It used fixed coils of wire and a magnet rotated by hand. It was quickly superceded by a generator with fixed magnets and rotating coils. 

 A steam engine driven generator was demonstrated in England in 1857 and this was quickly adopted to supply power for the new carbon-arc lamps installed in light houses for coastal navigation. (As more of these were built, they each used an identifying signal such as one flash every second or one flash every 5 seconds which permitted navigators to identify the lighthouse on his marine chart and to measure the angle between two lights to locate his position. A single lighthouse could also be used by measuring the angle at a later time and with two lines of position (LOP) marked on the chart, with the ships speed and course, the ship's position could be established). 

The earliest generators produced an alternating current with a large fluctuation of the voltage (the flow of electricity was reversed with each revolution of the coils with a frequency depended on the speed of rotation which meant that the voltage varied from zero to maximum positive and zero to maximum negative each revolution). This problem was solved with Ampère's invention of a commutator. 

Since most researchers needed a steady direct current, designers used many coils (the armature) rotating around a fixed magnet to smooth out the voltage fluctuations. Then, instead of using permanent magnets, William Sturgeon used electro-magnets excited by batteries and by 1866, C.F.Varley, Werner Von Siemens and others realized that the electro-magnets could be excited with part of the generator's output. There was also enough residual magnetism remaining in the electro-magnets (when not in use) to restart the process. This principle of self-excitation was very important as it meant that a generator had only to be rotated to generate electricity.

Z.T.Gramme developed an improved ring armature in 1870 and these dynamos, driven by steam engines, were widely used to generate continuous power without over heating. During an industrial exposition in Vienna in 1873, Gramme's partner, Hippolyte Fontaine, accidentally connected the terminals of a Gramme generator to another which was producing electricity and discovered that the generator was acting as an electric motor. This was the first powerful electric motor and some aspects of the design are still used in modern DC (direct current) motors. 

In 1875 a Gramme generator was used to power arc lamps at the Gare du Nord (north railway station) in Paris. The demand for electric arc and filament bulb lighting increased the need for large generating stations which had to be located near the users to reduce the loss of energy caused by transmitting direct current over long distances. Engineers quickly realized that very high voltages (typically more than 33,000V (volts)) permitted long distance transmission with less loss of energy but low voltages (in the range 110V to 230V)were less dangerous for lighting and power uses. 

The solution was to generate a high voltage, alternating current and use transformers (which can only use alternating current) to reduce the voltage. In 1889 Ferranti's power station at Deptford, Britain, included four 10,000 hp steam engines driving 10,000 V (volt) AC (alternating current) generators (alternators). 

In 1887, in Britain, Charles Algernon Parsons built a steam turbine to drive an electrical generator and in 1899 he built a 4000V, 1 MW (megawatt) turbogenerator for the city of Elberfeld, Germany. Today, about 80% of the world's electrical supply is generated with steam turbines. Watts (W) = Amps (A) x Volts (V).

In 1887, Nicola Tesla developed an induction motor that ran on alternating current (AC), because of its advantages in high-voltage, long-distance transmission. The motor used polyphase current (two or three phases distributed on separate wires), which generated a rotating magnetic field to turn the motor. This innovation was a self-starting design that did not need a commutator, thus avoiding sparking and the high maintenance of constantly servicing and replacing mechanical brushes. George Westinghouse licensed the motor to complement his alternating current distribution system and hired Tesla as a consultant with a large fee. 

Tesla helped to create a power system for Pittsburgh's streetcars but used DC traction motors instead of his AC motors (which could run only at a speed fixed by the 60 Hz (cycle/second) frequency of the alternating current).

The competition between Westinghouse, Edison, and Thomson-Houston was extreme and Westinghouse did not have the cash to develop Tesla's motor and the related polyphase system right away. So Tesla released the company from royalty payments but later sold his patent to Westinghouse as part of an agreement with General Electric (formed by the merger of Edison and Thomson-Houston in 1892).

The invention of the three-phase alternating current by Russian engineer Mikhail Dolivo-Dobrovolsky in 1889 made transmission of electricity over long distances possible.

In 1889, Tesla learned that Heinrich Hertz had proved the existence of electromagnetic radiation, including radio waves, and began experimenting by powering a Ruhmkorff spark coil with a high speed alternator. He found that the high-frequency current melted the insulation and solved this problem with the 'Tesla coil.' This used an air gap (instead of insulating material) between the primary and secondary windings and a moveable iron core.

He also continued experiments with a wireless lighting system based on near-field inductive and capacitive coupling and conducted a series of public demonstrations where he lit Geissler tubes and even incandescent light bulbs from across a stage.

Westinghouse asked Tesla to participate in the 1893 World's Columbian Exposition in Chicago. Westinghouse Electric won the bid to light the Exposition and demonstrated the safety, reliability, and efficiency of a fully integrated alternating current system. Tesla demonstrated several electrical effects related to alternating current as well as his wireless lighting system including the use of high-voltage, high-frequency alternating current to light a wireless gas-discharge lamp.

In 1893, Edward Dean Adams, of the Niagara Falls Cataract Construction Company, asked Tesla what system would be best to transmit power generated at the falls. Tesla recommended a two-phased AC system and Westinghouse Electric won the contracts for the first hydro-electric station at Niagara Falls.