Техническое чтение для энергетиков. Бухарова Г.П. - 82 стр.

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84
material, thus forming a cylindrical cage. It is built into an iron cylinder which is
mounted on the shaft, and forms the rotor, the rotating part of the machine. It is
exposed to a rotating magnetic field set up by the stator, the fixed part of the
machine, consisting of many interconnected electrical conductors called the winding.
The relative motion between the magnetic field and the rotor induces voltages and
currents which exert the driving force, turning the 'cage' round.
Although the induction motor has been improved a great deal and its power
increased many times over since its invention, there has never been any change of the
underlying principle. One of its drawbacks was that its speed was constant and
unchangeable. Only in 1959 did a research team at the University of Bristol succeed
in developing a squirrel-cage motor with two speeds – the most far-reaching
innovation since the invention of the induction motor. The speed-change is achieved
by modulating the pole-amplitude of the machine.
From the day when Edison's lamps began to glow in New York, all the world
asked for electricity. Already a year earlier, Werner von Siemens had succeeded in
coupling a steam-engine directly to a dynamo. But the engineers had their eyes on
another, cheaper source of mechanical power than the reciprocating steam-engine:
that of falling water. We do not know which of them suggested the idea of a hydro-
electric power station for the first time; it was probably very much 'in the air'. Back in
1827, a young Frenchman, had won the first prize in a competition for the most
effective water turbine in which the water would act on the wheel inside a casing
instead of from outside. It was one of the prototypes of the modern water turbine. In
the 1880's, an American engineer designed a turbine wheel with enormous bucket-
shaped blades along the rim, and a few American towns with waterfalls installed
these turbines coupled to Edison generators. This type proved especially efficient
where the fall of water was steep but its quantity limited; for a low fall of water the
turbine – with only four large blades proved better suited. However, the type which
appeals most
5
to the engineers is now the turbine for falls of water from 100 to 1,000
feet, with a great number of curved blades. The power station which convincingly
showed the enormous possibilities of hydro-generated electricity was the one at
Niagara Falls, begun in 1891, and put into operation a few years later with an output
of 5,000 h. p. – it is 8 millions h. p. today.
The early power stations generated direct current at low voltage, but they could
distribute it only within a radius of a few hundred yards. The Niagara station was one
of the first to use alternating current (although the sceptics prophesied that this would
never work
)
, generated at high voltage; this was transmitted by overhead cables to the
communities where it was to be used, and here 'stepped down' into lower voltages
(110 or 220) for domestic and industrial use by means of transformers. High-voltage
transmission is much more economical than low-voltage; all other circumstances
being equal, if the transmission voltage is increased tenfold the losses in electric
energy during transmission are reduced to one-hundredth. This means that alternating
current at tens or even hundreds of thousands of volts, as it is transmitted today, can
be sent over long distances without much loss.
These ideas must have had something frightening to the people at the end of the

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