Electric Power Transmission

   Electric power transmission is one process in the delivery of electricity to consumers. It refers to the 'bulk' transfer of electrical power from place to place. Typically power transmission is between the power plant and a substation in the vicinity of a populated area. This is distinct from electricity distribution which is concerned with the delivery from the substation to the consumers. Due to the large amount of power involved, transmission normally takes place at high voltage (110 kV or above). Electricity is usually sent over long distance through overhead power transmission lines (such as those in the photo on the right). Power is transmitted underground in densely populated areas (such as large cities) but is typically avoided due to the high capacitive and resistive losses incurred.

   A power transmission system is sometimes referred to colloquially as a "grid". However, for reasons of economy, the network is rarely a grid (a fully connected network) in the mathematical sense. Redundant paths and lines are provided so that power can be routed from any power plant to any load center, through a variety of routes, based on the economics of the transmission path and the cost of power. Much analysis is done by transmission companies to determine the maximum reliable capacity of each line, which, due to system stability considerations, may be less than the physical limit of the line. Deregulation of electricity companies in many countries has lead to renewed interest in reliable economic design of transmission networks. The separation of transmission and generation functions is one of the factors that contributed to the 2003 North America blackout.

ВАРІАНТ III

Bulk Power Transmission

   A transmission grid is a network of power stations, transmission circuits, and substations. Energy is usually transmitted within the grid with 3-phase alternating current (AC).

   The capital cost of electric power stations is so high, and electric demand is so variable, that it is often cheaper to import some portion of the variable load than to generate it locally. Because nearby loads are often correlated (hot weather in the Southwest portion of the United States might cause many people there to turn on their air conditioners), imported electricity must often come from far away. Because of the irresistible economics of load balancing, transmission grids now span across countries and even large portions of continents. The web of interconnections between power producers and consumers ensures that power can flow even if one link is disabled.

  Long-distance transmission of electricity is almost always more expensive than the transportation of the fuels used to make that electricity. As a result, there is economic pressure to locate fuel-burning power plants near the population centers that they serve. The obvious exceptions are hydroelectric turbines ~ high-pressure water-filled pipes being more expensive than electric wires. The unvarying portion of the electric demand is known as the "base load", and is generally served best by facilities with low variable costs but high fixed costs, like nuclear or large coal-fired power plants.

ВАРІАНТ IV

Electricity Retailing

   Electricity retailing is the final process in the delivery of electricity from generation to the consumer. The other main processes are transmission and distribution.

   Electricity retailing began at the end of the 19th century when the bodies who generated electricity for their own use made supply available to third parties. In the beginning, electricity was primarily used for street lighting and trams. The provision of these services was generally the responsibility of municipal authorities who either set up their own departments or contracted the services from private entrepreneurs. Residential, commercial and industrial use of electricity was confined, initially, to lighting but this changed dramatically with the development of electric motors, heaters and communication devices.

   The basic principle of supply has not changed much over time. The amount of energy used by the domestic consumer, and thus the amount charged for, is measured through an electricity meter that is usually placed near the input of a home to provide easy access to the meter reader.

   Customers are usually charged a monthly service fee and additional charges based on the electrical energy (in kWh) consumed by the household or business during the month. Commercial and industrial consumers normally have more complex pricing schemes. These require meters that measure the energy usage in time intervals (such as a half hour) to impose charges based on both the amount of energy consumed and the maximum rate of consumption, i.e. the maximum demand, which is measured in kW.

ВАРІАНТ V

Generation

   The main source of electrical energy is generated by alternating current synchronous generators. The energy is converted from a primary form to the electrical form. Most of the energy sources come from: the conversion of chemical energy of fossil fuel nuclear power, and the hydropower. With the advent of technology development, there are some renewable sources of energy, such as solar power, wind power and other forms.

   In fossil fuel plants, the source of heat energy comes from the combustion of the fossil fuel. For example, the coal is fed to the plant where it undergoes combustion. The thermal energy produced heats water to produce the steam. The steam drives the turbine to convert the thermal energy into the rotational energy which is fed to the generators. In a hydropower plant, the potential energy of the water is stored by a dam. The water is imported into the turbines to produce the mechanical energy which is supplied to the generators. The output of the generator is directed to the transformer which steps up the voltage to the transmission subsystems.

Transmission

The electricity is transported to load locations from a power station to a transmission subsystem. There are two kinds of transmission lines, underground or overhead. Considering the economical issue, the overhead transmission lines are common. A overhead transmission line consists of conductors, insulators, and mechanical supports. And a underground line which is mainly used in urban areas consists of oil-filled cables placed in elaborate duct systems. Transformers are important static devices which transfer electrical energy from one circuit with another in the transmission subsystem. Transformers are used to step up the voltage on the transmission line to reduce the power loss which is dissipated on the way.

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ВАРІАНТ I

Energy and Its Sources

   The world is facing a serious problem of potential shortage of energy, which is extremely important to meeting all of man's physical needs—clothing, shelter, transportation, convenience, recreation, etc. The consumption of energy is expected to grow. The amount of energy consumed by a country is closely connected with its degree of technological development and industrialization, which are in turn related to the people's standard of living.

   Energy can be classified according to its sources. The principal materials now used for obtaining energy are of plant and animal origin, deposited in the earth over millions of years in the form of coal, oil, and natural gas. These so-called "fossil fuels" are extremely useful raw materials because of the conveniently stored chemical energy. But when they are burned for fuel, harmful pollution may result and there is a great waste of natural resources that will never be available again.

   Wood was already the main source a hundred years ago. The growth 'of coal usage in the early 1900s is associated with rapidly increasing industrial development. There followed a great expansion in the consumption of natural gas and fuel oil for heating, electrical generation and especially transportation.

   The reserves of such popular sources of energy as natural gas and oil are not expected to meet the long-term demands.

   Natural gas is a popular source of energy because of its convenience for use and cleanliness in burning. It is generally believed that gas will be the first fossil fuel to be in short supply, and the cost of oil extraction is high. To these sources we can add the energy obtained from water motion anal the sun.            

ВАРІАНТ II

   Hydroelectric power is available when a stream can be dammed to form a large reservoir, permitting falling water to turn a hydraulic turbine connected to an electric generator. It is generally agreed that this, source cannot meet the total need in power.

  Solar power is often mentioned as the logical alternative. And indeed, the amount of radiant energy that reaches the earth's surface is more than what is needed. For the generation of electricity, however, there are serious problems to be solved. To collect and concentrate the energy by reflectors and converters of present efficiency is the major difficulty. There remain many technological problems in this area.

   Man is consuming the remaining resources at such a rate that they may last only a few centuries. This may seem to be a long time in comparison with the life of a single generation, but in man's history it is only a short period. If the world is to solve the long-range energy problem, it must look for and make use of all available practical sources economically. Efforts to eliminate the extravagant waste of energy are needed at the same time. Several other conclusions can be made: that research and development work with a view to find new sources of energy and ways of increasing efficiency are urgently needed; that the new sources of other types of fuels must be fully developed and utilized wherever possible. And we must give a serious consideration, as a possible solution, to nuclear energy, i.e. the energy from nuclear reactions, the burning of nuclear fuel.

  ВАРІАНТ III

Nuclear Energy

   A very rapid growth of energy consumption has occurred in the twentieth century. A major problem is that much of the 'world's energy supply is based on fossil fuels. Fossil fuels are limited and their supply is running out. From this it follows that the future of our energy supply must be based on sources other than fossil fuels like coal, oil and natural gas.

   Hydroelectric, wind, tidal and solar power require much technological development. New and different sources of energy have to be found and brought into practical use. The problem consists in developing technology to extract energy from nature without causing air, water, thermal or radioactive pollution. The wise use of nuclear energy, based on an understanding of both dangers and benefits, will be required to meet this challenge to our existence.

   In the near future about half of electrical supply is expected to come from nuclear sources. There are many factors that will determine the accuracy of this prediction. It is noted that the cost of construction of a nuclear plant is high but the fuel cost is relatively low.

   Yet there is considerable confusion in the public mind when it comes to nuclear power plants. There are those who consider it to be a major solution to the world's energy needs. There are opponents with good reason to be critical. In either case we are faced with the rapidly increasing energy demands of the future.

   A nuclear power plant is very much like a conventional steam power plant. The only difference is that the heat used to run the electric generator is Kot obtained by burning coal, gas, or oil but from controlled nuclear reactions.

  A nuclear reactor is a device in which these reactions take place. There are various types of nuclear reactors. All of them operate more or less on the same principle. Yet we always face the fact that the use of nuclear energy requires safe transportation, processing, storage, and disposal of potentially dangerous materials. However the dream of limitless power will force mankind to find solutions to all these proems for the satisfaction of man's needs.

  ВАРІАНТ IV

Panel Heating

   Heating and ventilation are two branches of engineering which are very closely connected, they are therefore treated as a dual subject. Both are concerned with providing a required atmospheric environment within a space, the former with respect to heat supply to produce a desired temperature for maintaining comfort, health or efficiency of the occupants, the latter with regard to supply and removal of air frequently with emphasis on contamination of the air. Air conditioning is closely related to both heating and ventilation.

   It is for heating to prevent the too rapid loss of heat from the body. By heating the ambient air of walls, ceiling or floor the rate of heat loss from the body is controlled. Some old concepts of heating were gradually changed since engineers obtained more precise knowledge about how the body loses heat. Insufficient attention was paid formerly to loss by radiation, which is the transmission of energy in the form of waves from a body, to surrounding bodies at a temperature. The human being also loses heat by conduction (through his clothes) and convection. The determination of the capacity or size of the various components of the heating system is based on the fundamental concept that heat supplied to a space equals heat lost from the space. The most widely used system of heating is the central heating, where the fuel is burned in one place — the-basement or a specially designed room and from which steam, hot water or warm air is distributed to adjacent and remote spaces to be heated.

   There are two most common systems of heating—hot water and steam.Both systems are widely used nowadays. A hot-water system consists of the boilers and a system of pipes connected to radiators suitably located in rooms to be heated. The pipes, usually of steel or copper, feed hot water to radiators or convectors.

   As for steam systems, steam is generated usually, at less than 5 pounds per square inch in the boiler and the steam is led to the radiators through or by means of steel or copper pipes. The steam gives up its heat to the radiators and the radiators to the room and the cooling of the steam condenses it to water. The condensate is returned to the boiler either by gravity or by a pump. The air valve on each radiator is necessary for air to escape. Otherwise it would prevent steam from entering the radiator.

ВАРІАНТ V