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Conductors and Insulators
Conductors are materials having a low resistance so that current easily passes
through them. The lower the resistance of the material, the more current can pass
through it.
he most common conductors are metals. Silver and copper arc the best of
them. The advantage of copper is that it is much cheaper than silver. Thus copper is
widely used to produce wire conductors. One of the common functions of wire conductors
is to connect a voltage source to a load resistance. Since copper wire conductors
have a very low resistance a minimum voltage drop is produced in them. Thus,
all of the applied voltage can produce current in the load resistance.
It should be taken into consideration that most materials change the value of
resistance when their temperature changes.
Metals increase their resistance when the temperature increases while carbon
decreases its resistance when the temperature increases. Thus metals have a positive
temperature coefficient of resistance while carbon has a negative temperature coefficient.
The smaller is the temperature coefficient or the less the change of resistance
with the change of temperature, the more perfect is the resistance material.
Materials having a very high resistance are called insulators. Current passes
through insulators with great difficulty.
The most common insulators are air, paper, rubber, plastics.
Any insulator can conduct current when a high enough voltage is applied to it.
Currents of great value must be applied to insulators in order to make them conduct.
The higher the resistance of an insulator, the greater the applied voltage must be.
Atomic Power Plant
Atomic power plants are modem installations. They consist of several main
units and a great number of auxiliary ones.
In a nuclear reactor uranium is utilized as a fuel. During operation process
powerful heat and radioactive radiation are produced. The nuclear reactor is cooled
by water circulation. Cooling water circulates through a system of tubes, in which the
water is heated to a temperature of 250-300C. In order to prevent boiling of water, it
passes into the reactor at a pressure up to 150 atmospheres.
A steam generator includes a series of heat exchangers comprising tubes. The
water heated in the reactor is delivered into the heat exchanger tubes. The water to be
converted into steam flows outside these tubes. The steam produced is fed into the
turbogenerator.
Besides, an atomic power plant comprises a common turbogenerator, a steam
condenser with circulating water and a switchboard.
Atomic power plants have their advantages as well as disadvantages. The reactors
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and steam generators operate in them noiselessly; the atmosphere is not polluted
by dust and smoke. As to the fuel consumption, it is of no special importance and
there is no problem of fuel transportation.
The disadvantage of power plants utilizing nuclear fuel is their radiation. Radioactive
radiation produced in the reactors is dangerous for attending personnel.
Therefore, the reactors and steam generators are installed underground. They are also
shielded by thick (up to 1.5 m) concrete walls. All their controls are operated by
means of automatic devices. These measures serve to protect people from radioactive
radiation.
